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, Available online , doi: 10.11883/bzycj-2023-0418
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Hydrogen is crucial in the global shift towards clean energy and is gaining significance in the energy industry, while its high flammability and explosive hazard make its safety a research hotspot. It is crucial to thoroughly investigate and assess the safety of hydrogen as it progresses toward commercialization in the energy sector. This article reviews the latest advancements in hydrogen explosion suppression conducted by researchers around the world, aiming at offering a scientific foundation and technical approach to efficiently manage and reduce the damaging impacts of hydrogen explosion incidents. The article focuses on the study of hydrogen explosion suppression materials and their suppression mechanisms, so as to provide scientific understanding and technical support for the safe application of hydrogen. Firstly, it systematically introduces the research progress in hydrogen explosion suppression by discussing four significant categories, i.e., gas, liquid, solid, and multiphase composite explosion suppression materials. By comparing and analyzing the effects, key performance parameters, and the variation rules of these materials, the current research status and effectiveness of various explosion suppression materials are sorted out, helping to deepen the understanding of the explosion suppression effects of these materials. Secondly, focusing on the suppression mechanism, the research delves into the vital role of explosion suppression materials in suppressing hydrogen explosions. Starting from three dimensions, i.e., physical suppression, chemical suppression, and physicochemical comprehensive suppression, it elucidates the mechanisms of action of explosion suppression materials in the suppression process, contributing to a deeper understanding of the role of explosion suppression materials in suppressing or mitigating hydrogen explosions. Finally, the article looks forward to the future development directions of hydrogen explosion suppression materials, especially emphasizing the importance of further studies on the high-efficiency explosion suppression materials and the challenges faced in practical applications. This review is aimed to provide scientific reference and inspiration for the research, development, and application of new hydrogen explosion suppression materials.
Hydrogen is crucial in the global shift towards clean energy and is gaining significance in the energy industry, while its high flammability and explosive hazard make its safety a research hotspot. It is crucial to thoroughly investigate and assess the safety of hydrogen as it progresses toward commercialization in the energy sector. This article reviews the latest advancements in hydrogen explosion suppression conducted by researchers around the world, aiming at offering a scientific foundation and technical approach to efficiently manage and reduce the damaging impacts of hydrogen explosion incidents. The article focuses on the study of hydrogen explosion suppression materials and their suppression mechanisms, so as to provide scientific understanding and technical support for the safe application of hydrogen. Firstly, it systematically introduces the research progress in hydrogen explosion suppression by discussing four significant categories, i.e., gas, liquid, solid, and multiphase composite explosion suppression materials. By comparing and analyzing the effects, key performance parameters, and the variation rules of these materials, the current research status and effectiveness of various explosion suppression materials are sorted out, helping to deepen the understanding of the explosion suppression effects of these materials. Secondly, focusing on the suppression mechanism, the research delves into the vital role of explosion suppression materials in suppressing hydrogen explosions. Starting from three dimensions, i.e., physical suppression, chemical suppression, and physicochemical comprehensive suppression, it elucidates the mechanisms of action of explosion suppression materials in the suppression process, contributing to a deeper understanding of the role of explosion suppression materials in suppressing or mitigating hydrogen explosions. Finally, the article looks forward to the future development directions of hydrogen explosion suppression materials, especially emphasizing the importance of further studies on the high-efficiency explosion suppression materials and the challenges faced in practical applications. This review is aimed to provide scientific reference and inspiration for the research, development, and application of new hydrogen explosion suppression materials.
, Available online , doi: 10.11883/bzycj-2024-0083
Abstract:
Reinforced concrete slabs, as the main load-bearing components in the structure of construction projects, are very likely to suffer serious damage in explosive accidents, while polyurea elastomers, with their better anti-blast and anti-impact properties, have been widely used in the field of protective engineering. It is well known that the mechanical properties and deformation mechanisms of thin slabs in the range from 100 mm to 250 mm and thick concrete slabs above 250 mm are not the same, and the thickness of reinforced concrete substrates studied so far is generally concentrated in the range from 100 mm to 250 mm, and there are relatively few studies on thick slabs of polyurea-coated reinforced concrete with a slab thickness of 250 mm or more. In order to study the anti-blast performance of the polyurea/reinforced concrete thick slab composite structure, firstly, the contact explosion tests were carried out on the polyurea/reinforced concrete thick slab composite structure with different charges, while the overall and local damage characteristics were analyzed. Secondly, numerical simulations were carried out using LS-DYNA finite element simulation software to verify the correctness of the numerical model by comparing with the experimental results. Based on LS-DYNA finite element simulations, the damage process of polyurea/reinforced concrete thick plate composite structure and the evolution of shock wave inside the polyurea/reinforced concrete thick plate were investigated, which revealed the anti-blast mechanism of the polyurea coating, and further analyzed the damage mode and damage characteristics of the polyurea/reinforced concrete thick plate composite structure. The test and finite element results showed that the polyurea/steel-reinforced concrete composite structure exhibited six damage modes under the contact explosion load (i.e., crate; spall; spall and bulge; threshold spall, bulging deformation of the polyurea coating; severe spall, serious bulging deformation of the polyurea coating; perforation). The investigation also demonstrated that the backside polyurea-coated reinforced concrete thick slabs effectively improved the anti-blast performance of the composite structure. The results of the study can provide a basis and reference for the design of blast resistance of polyurea/reinforced concrete thick slab composite structures.
Reinforced concrete slabs, as the main load-bearing components in the structure of construction projects, are very likely to suffer serious damage in explosive accidents, while polyurea elastomers, with their better anti-blast and anti-impact properties, have been widely used in the field of protective engineering. It is well known that the mechanical properties and deformation mechanisms of thin slabs in the range from 100 mm to 250 mm and thick concrete slabs above 250 mm are not the same, and the thickness of reinforced concrete substrates studied so far is generally concentrated in the range from 100 mm to 250 mm, and there are relatively few studies on thick slabs of polyurea-coated reinforced concrete with a slab thickness of 250 mm or more. In order to study the anti-blast performance of the polyurea/reinforced concrete thick slab composite structure, firstly, the contact explosion tests were carried out on the polyurea/reinforced concrete thick slab composite structure with different charges, while the overall and local damage characteristics were analyzed. Secondly, numerical simulations were carried out using LS-DYNA finite element simulation software to verify the correctness of the numerical model by comparing with the experimental results. Based on LS-DYNA finite element simulations, the damage process of polyurea/reinforced concrete thick plate composite structure and the evolution of shock wave inside the polyurea/reinforced concrete thick plate were investigated, which revealed the anti-blast mechanism of the polyurea coating, and further analyzed the damage mode and damage characteristics of the polyurea/reinforced concrete thick plate composite structure. The test and finite element results showed that the polyurea/steel-reinforced concrete composite structure exhibited six damage modes under the contact explosion load (i.e., crate; spall; spall and bulge; threshold spall, bulging deformation of the polyurea coating; severe spall, serious bulging deformation of the polyurea coating; perforation). The investigation also demonstrated that the backside polyurea-coated reinforced concrete thick slabs effectively improved the anti-blast performance of the composite structure. The results of the study can provide a basis and reference for the design of blast resistance of polyurea/reinforced concrete thick slab composite structures.
, Available online , doi: 10.11883/bzycj-2024-0053
Abstract:
Damage assessment of building structures plays an important role in military operations and engineering protection design. However, there is a lack of high-efficiency and validated damage assessment methods due to the complexity, variety, and large size of building structures. Therefore, a structural damage assessment method was proposed based on the high-precision numerical simulation analysis, in which the blast loadings, as well as the damage degrees of members, rooms, and building structures, were comprehensively considered. Firstly, the typical explosion tests and collapse accidents of reinforced concrete (RC) structures and masonry walls were numerically reproduced to verify the reliability of the numerical simulation approach for masonry-infilled RC frame structures. Subsequently, the blast-resistant analysis of a typical three-story masonry-infilled RC frame structure was conducted under internal explosions of different charge weights (25−200kg TNT), including the propagation of blast waves, structural damage, and scattering of infilled walls. Besides, the proposed high-efficiency assessment method exhibited four key characteristics: (1) the concept of mirror explosion source and the non-linear shock addition rules were combined to predict the internal blast loadings in central and adjacent rooms; (2) the damage degrees of structural and non-structural members, i.e., beams, slabs, columns, and infilled walls, were determined by the equivalent single degree of freedom method; (3) the importance factor of members was considered and weighted to evaluate the damage degree of the room; (4) the influence of usage and location of each room on the damage degree of the building structure was considered. Finally, the proposed assessment method was employed to predict the aforementioned explosion scenarios. It derives that the RC frame structures exhibit slight, moderate, and severe damage under the explosions of 25, 100, and 200 kg TNT, respectively. The predicted damage degrees are identical to the simulation results, while the calculation time is reduced by over 99%. Therefore, the proposed method possesses reliability and timeliness in damage assessment of building structures.
Damage assessment of building structures plays an important role in military operations and engineering protection design. However, there is a lack of high-efficiency and validated damage assessment methods due to the complexity, variety, and large size of building structures. Therefore, a structural damage assessment method was proposed based on the high-precision numerical simulation analysis, in which the blast loadings, as well as the damage degrees of members, rooms, and building structures, were comprehensively considered. Firstly, the typical explosion tests and collapse accidents of reinforced concrete (RC) structures and masonry walls were numerically reproduced to verify the reliability of the numerical simulation approach for masonry-infilled RC frame structures. Subsequently, the blast-resistant analysis of a typical three-story masonry-infilled RC frame structure was conducted under internal explosions of different charge weights (25−200kg TNT), including the propagation of blast waves, structural damage, and scattering of infilled walls. Besides, the proposed high-efficiency assessment method exhibited four key characteristics: (1) the concept of mirror explosion source and the non-linear shock addition rules were combined to predict the internal blast loadings in central and adjacent rooms; (2) the damage degrees of structural and non-structural members, i.e., beams, slabs, columns, and infilled walls, were determined by the equivalent single degree of freedom method; (3) the importance factor of members was considered and weighted to evaluate the damage degree of the room; (4) the influence of usage and location of each room on the damage degree of the building structure was considered. Finally, the proposed assessment method was employed to predict the aforementioned explosion scenarios. It derives that the RC frame structures exhibit slight, moderate, and severe damage under the explosions of 25, 100, and 200 kg TNT, respectively. The predicted damage degrees are identical to the simulation results, while the calculation time is reduced by over 99%. Therefore, the proposed method possesses reliability and timeliness in damage assessment of building structures.
, Available online , doi: 10.11883/bzycj-2024-0061
Abstract:
Due to the high compressive/tensile strengths and fracture toughness, ultra-high performance concrete (UHPC) has great application potential in protective structures against the attack of earth penetrating weapons. Accurately evaluating the damage and failure and establishing reliable design methods of UHPC shields against the combination of penetration and explosion of warheads can provide a helpful reference for protective structure design and resistance improvement. In this study, combined tests of 105 mm-caliber projectile penetration test and 5 kg TNT explosion test on semi-infinite UHPC target were conducted first. The detailed test data of the projectile and target under penetration and the combined effect of penetration and explosion were recorded. Then, a finite element model of UHPC under penetration and explosion was established. By conducting the numerical simulations of the above-conducted test and the existing prefabricated hole charge explosion test on the finite UHPC slab, as well as comprehensively comparing the destroy depth and cracking dimension of the target, the reliability of the established finite element model and the corresponding analysis approach in predicting the damage and failure of UHPC shield against the combination of penetration and explosion of warheads were validated. Finally, the perforation limit and scabbing limit of the UHPC shield under the combination of penetration and explosion of three typical prototype warheads, i.e., SDB, WDU-43/B, and BLU-109/B, were determined and compared with those of normal strength concrete shield. The results show that, the perforation limit and scabbing limit of the UHPC shield against the above three warheads are in ranges of 1.30−2.60 m and 1.70−5.00 m, respectively. The corresponding critical perforation and scabbing coefficients are in the ranges of 1.81−2.17 and 2.46−4.17, respectively. Compared with the normal strength concrete shield, the cracking diameter of the UHPC shield is reduced by 34.4%−42.4%. The perforation limit and scabbing limit are reduced by 7.1%−31.6% and 39.7%−52.8%, respectively. The present work can provide an analysis method and reference for the resistance evaluation and design of the UHPC shield.
Due to the high compressive/tensile strengths and fracture toughness, ultra-high performance concrete (UHPC) has great application potential in protective structures against the attack of earth penetrating weapons. Accurately evaluating the damage and failure and establishing reliable design methods of UHPC shields against the combination of penetration and explosion of warheads can provide a helpful reference for protective structure design and resistance improvement. In this study, combined tests of 105 mm-caliber projectile penetration test and 5 kg TNT explosion test on semi-infinite UHPC target were conducted first. The detailed test data of the projectile and target under penetration and the combined effect of penetration and explosion were recorded. Then, a finite element model of UHPC under penetration and explosion was established. By conducting the numerical simulations of the above-conducted test and the existing prefabricated hole charge explosion test on the finite UHPC slab, as well as comprehensively comparing the destroy depth and cracking dimension of the target, the reliability of the established finite element model and the corresponding analysis approach in predicting the damage and failure of UHPC shield against the combination of penetration and explosion of warheads were validated. Finally, the perforation limit and scabbing limit of the UHPC shield under the combination of penetration and explosion of three typical prototype warheads, i.e., SDB, WDU-43/B, and BLU-109/B, were determined and compared with those of normal strength concrete shield. The results show that, the perforation limit and scabbing limit of the UHPC shield against the above three warheads are in ranges of 1.30−2.60 m and 1.70−5.00 m, respectively. The corresponding critical perforation and scabbing coefficients are in the ranges of 1.81−2.17 and 2.46−4.17, respectively. Compared with the normal strength concrete shield, the cracking diameter of the UHPC shield is reduced by 34.4%−42.4%. The perforation limit and scabbing limit are reduced by 7.1%−31.6% and 39.7%−52.8%, respectively. The present work can provide an analysis method and reference for the resistance evaluation and design of the UHPC shield.
, Available online , doi: 10.11883/bzycj-2024-0070
Abstract:
Silicone rubber has been widely used as a typical sandwich-structure or cushion-structure material in various high pressure loading environments. Under pressure loading of up to tens of GPa, silicone rubber may undergo shock decomposition reaction, and the decomposition products contain gas-solid mixture. Numerical simulation without the shock decomposition of silicone rubber can’t interpret some complex physical phenomena observed in detonation driven experiment. In order to illustrate the shock decomposition effect of silicone rubber, a simple shock decomposition model for silicone rubber is proposed based on the existing physical knowledge. By using the simple shock decomposition model for silicone rubber, the simulations of the experiment setup of detonation driven silicone rubber foam are carried out, and the simulated free surface velocities are compared with the experiments. The results show that the shock decomposition of silicone rubber can reasonably interpret the two grotesque phenomena observed in the experiment. During the shock decomposition process, the first incident pressure of silicone rubber would relax around the critical shock decomposition pressure for a period of time. As a result, the free surface velocity of steel plate exhibits a platform as observed in the experiment during the first take-off process. The compressibility of gas phase products of silicone rubber after shock decomposition is much higher than the solid/fluid materials, so more energy in the first incident wave is consumed to compress gas products to do work, leading to energy attenuation and peak pressure reduction when the first incident wave propagates to the outer surface of steel plate. Consequently, the peak value of the first take-off free surface velocity of steel plate decreases. Insight into the dynamic behavior of silicone rubber at high pressures is particularly valuable for predicting their response to extreme conditions, and it contributes to a deeper understanding of such experimental phenomena and to the proposal of a more refined shock decomposition model for silicone rubber.
Silicone rubber has been widely used as a typical sandwich-structure or cushion-structure material in various high pressure loading environments. Under pressure loading of up to tens of GPa, silicone rubber may undergo shock decomposition reaction, and the decomposition products contain gas-solid mixture. Numerical simulation without the shock decomposition of silicone rubber can’t interpret some complex physical phenomena observed in detonation driven experiment. In order to illustrate the shock decomposition effect of silicone rubber, a simple shock decomposition model for silicone rubber is proposed based on the existing physical knowledge. By using the simple shock decomposition model for silicone rubber, the simulations of the experiment setup of detonation driven silicone rubber foam are carried out, and the simulated free surface velocities are compared with the experiments. The results show that the shock decomposition of silicone rubber can reasonably interpret the two grotesque phenomena observed in the experiment. During the shock decomposition process, the first incident pressure of silicone rubber would relax around the critical shock decomposition pressure for a period of time. As a result, the free surface velocity of steel plate exhibits a platform as observed in the experiment during the first take-off process. The compressibility of gas phase products of silicone rubber after shock decomposition is much higher than the solid/fluid materials, so more energy in the first incident wave is consumed to compress gas products to do work, leading to energy attenuation and peak pressure reduction when the first incident wave propagates to the outer surface of steel plate. Consequently, the peak value of the first take-off free surface velocity of steel plate decreases. Insight into the dynamic behavior of silicone rubber at high pressures is particularly valuable for predicting their response to extreme conditions, and it contributes to a deeper understanding of such experimental phenomena and to the proposal of a more refined shock decomposition model for silicone rubber.
, Available online , doi: 10.11883/bzycj-2023-0452
Abstract:
To predict precisely the lower explosion limit of thermal runaway products of lithium iron phosphate batteries, thermal runaway tests of lithium iron phosphate batteries were carried out in a closed pressure vessel. The experiments were carried out at 25 ℃ and 0.1 MPa, and the method was used to analyze the thermal runaway gas production. The vent gas species composition of lithium iron phosphate batteries was analyzed by gas chromatography and mass spectrometry. Combined with the thermal runaway characteristics of the battery and gas chromatography-mass spectrometry (GC-MS) technology, the gas composition of thermal runaway products of lithium iron phosphate batteries was calculated. It was assumed that the thermal runway products released from the relief valve to the first injection were all dimethyl carbonate (DMC), and the secondary injection gas was the mixed gas generated by the internal chemical reaction, which is mainly composed of H2, CO2, CO, CH4, and C2H4. A prediction model of the lower explosion limit of thermal runaway products was established based on the energy conservation equation and adiabatic flame temperature. The prediction methods of lower explosion limit of multicomponent gases based on adiabatic flame temperature, Le Chatelier law method, and Jones method were verified, and the influence of electrolyte vapor on the lower explosion limit of thermal runaway production was also investigated. The results show that the smallest deviation of the lower explosion limit calculated by the Le Chatelier law method at normal temperature and pressure was 1.14%, and the largest deviation of the lower explosion limit calculated by the adiabatic flame temperature method was 10.02%. Within the range of 60%~100% SOC, the lower explosion limit of the discharge gas increases first and then decreases. When the electrolyte vapor is considered in the thermal runaway products, the lower explosion limit of thermal runaway products of lithium iron phosphate batteries with 60% SOC is only 3.93%, which is 22.49% lower than that of the thermal runaway gas without considering the electrolyte vapor. Actually, the electrolyte vapor is contained in the thermal runaway products of lithium iron phosphate batteries. These results indicate that the addition of electrolyte vapor increases the explosion risk of thermal runaway production of lithium iron phosphate batteries.
To predict precisely the lower explosion limit of thermal runaway products of lithium iron phosphate batteries, thermal runaway tests of lithium iron phosphate batteries were carried out in a closed pressure vessel. The experiments were carried out at 25 ℃ and 0.1 MPa, and the method was used to analyze the thermal runaway gas production. The vent gas species composition of lithium iron phosphate batteries was analyzed by gas chromatography and mass spectrometry. Combined with the thermal runaway characteristics of the battery and gas chromatography-mass spectrometry (GC-MS) technology, the gas composition of thermal runaway products of lithium iron phosphate batteries was calculated. It was assumed that the thermal runway products released from the relief valve to the first injection were all dimethyl carbonate (DMC), and the secondary injection gas was the mixed gas generated by the internal chemical reaction, which is mainly composed of H2, CO2, CO, CH4, and C2H4. A prediction model of the lower explosion limit of thermal runaway products was established based on the energy conservation equation and adiabatic flame temperature. The prediction methods of lower explosion limit of multicomponent gases based on adiabatic flame temperature, Le Chatelier law method, and Jones method were verified, and the influence of electrolyte vapor on the lower explosion limit of thermal runaway production was also investigated. The results show that the smallest deviation of the lower explosion limit calculated by the Le Chatelier law method at normal temperature and pressure was 1.14%, and the largest deviation of the lower explosion limit calculated by the adiabatic flame temperature method was 10.02%. Within the range of 60%~100% SOC, the lower explosion limit of the discharge gas increases first and then decreases. When the electrolyte vapor is considered in the thermal runaway products, the lower explosion limit of thermal runaway products of lithium iron phosphate batteries with 60% SOC is only 3.93%, which is 22.49% lower than that of the thermal runaway gas without considering the electrolyte vapor. Actually, the electrolyte vapor is contained in the thermal runaway products of lithium iron phosphate batteries. These results indicate that the addition of electrolyte vapor increases the explosion risk of thermal runaway production of lithium iron phosphate batteries.
, Available online , doi: 10.11883/bzycj-2024-0063
Abstract:
Reactive fragments are composed of multifunctional impact reactive structural materials. After reactive fragments penetrate the front target of warhead, the debris cloud generated by the sufficient reaction of reactive material will damage the medium behind the target in the form of kinetic energy-chemical energy coupling damage. Ballistic impact experiments and finite element simulations were conducted to investigate the impact damage effect of reactive fragments on cased charge. Based on the criteria for failure levels of cased charge characterized by equivalent fragments initial velocity and equivalent gurney velocity, the ratio of the equivalent gurney velocity under abnormal detonation conditions to gurney velocity or the ratio of the equivalent fragments initial velocity under abnormal detonation conditions to the fragments initial velocity is used to measure the reaction violence of the cased charge. Equivalent gurney velocity of cased charge under impact of inert fragments and reactive fragments, response duration of cased charge, the damage of the authentication target, and the peak pressure of explosive layer are compared. The influence of energy release characteristics of reactive fragments on the failure of cased charge is also analyzed. The results show that explosive detonate under the impact of inert fragments, while explosive deflagrate or explode under the impact of reactive fragments. The steel verification target only presents significant circular pit during explosive detonation. The explosive detonation process captured by high-speed photography is on the microsecond scale, while the explosive explosion or deflagration process is on the millisecond scale. Under the penetration of six reactive fragments, the corresponding ratio of equivalent gurney velocity to gurney velocity ranges from 0.014 to 0.233, which is far below the ratio of equivalent gurney velocity to gurney velocity under the condition of inert fragments penetrating cased charges. By using AUTODYN, the peak pressure at the observation point on the axis of the cased charge during detonation failure under the penetration of inert fragments ranges from 17.3 to 34.5 GPa, while the peak pressure of cased charge during deflagration failure under the penetration of reactive fragments ranges from 1.04 to 3.62 GPa, which is far below the critical detonation pressure. Based on the ratio of the equivalent gurney velocity to gurney velocity, the peak pressure of explosive and superimposed effect of kinetic energy and chemical energy of reactive fragments, the idea that it is difficult to detonate cased charge under the penetration of reactive fragments is proposed.
Reactive fragments are composed of multifunctional impact reactive structural materials. After reactive fragments penetrate the front target of warhead, the debris cloud generated by the sufficient reaction of reactive material will damage the medium behind the target in the form of kinetic energy-chemical energy coupling damage. Ballistic impact experiments and finite element simulations were conducted to investigate the impact damage effect of reactive fragments on cased charge. Based on the criteria for failure levels of cased charge characterized by equivalent fragments initial velocity and equivalent gurney velocity, the ratio of the equivalent gurney velocity under abnormal detonation conditions to gurney velocity or the ratio of the equivalent fragments initial velocity under abnormal detonation conditions to the fragments initial velocity is used to measure the reaction violence of the cased charge. Equivalent gurney velocity of cased charge under impact of inert fragments and reactive fragments, response duration of cased charge, the damage of the authentication target, and the peak pressure of explosive layer are compared. The influence of energy release characteristics of reactive fragments on the failure of cased charge is also analyzed. The results show that explosive detonate under the impact of inert fragments, while explosive deflagrate or explode under the impact of reactive fragments. The steel verification target only presents significant circular pit during explosive detonation. The explosive detonation process captured by high-speed photography is on the microsecond scale, while the explosive explosion or deflagration process is on the millisecond scale. Under the penetration of six reactive fragments, the corresponding ratio of equivalent gurney velocity to gurney velocity ranges from 0.014 to 0.233, which is far below the ratio of equivalent gurney velocity to gurney velocity under the condition of inert fragments penetrating cased charges. By using AUTODYN, the peak pressure at the observation point on the axis of the cased charge during detonation failure under the penetration of inert fragments ranges from 17.3 to 34.5 GPa, while the peak pressure of cased charge during deflagration failure under the penetration of reactive fragments ranges from 1.04 to 3.62 GPa, which is far below the critical detonation pressure. Based on the ratio of the equivalent gurney velocity to gurney velocity, the peak pressure of explosive and superimposed effect of kinetic energy and chemical energy of reactive fragments, the idea that it is difficult to detonate cased charge under the penetration of reactive fragments is proposed.
, Available online , doi: 10.11883/bzycj-2023-0199
Abstract:
As a typical characteristic of fireball phenomena, thermal radiation plays an important role in damage assessments. Up to now, many studies of thermal radiation using theoretical, numerical, and experimental methods have been carried out and empirical formulas in forms of yield or density are constructed to feature the extremal characteristic of fireball thermal radiation. However, due to the combined action of radiation free path (RFP) and fireball characteristic length (FCL) it is difficult to identify these formula’s application scope and further theoretical studies are needed to take the scale effect (SE) into account. By radiation heat conduction approximation model under optical thickness assumption, scale effect similarity parameter (SESP) is theoretically derived and its scope of application is further verified by high-precision numerical method. The numerical code is developed within a framework of Euler method and adaptive mesh refinement method is employed to improve the precision in the radiation front. The results of theoretical analysis show that SESP is consistent with existed conclusions regarding the thermal radiation of fireball at different altitudes, and it can be applied to the analysis of laboratory scale fireball. Meanwhile, numerical results also show that both scale effects at different altitudes and laboratory scale can be characterized by SESP.
As a typical characteristic of fireball phenomena, thermal radiation plays an important role in damage assessments. Up to now, many studies of thermal radiation using theoretical, numerical, and experimental methods have been carried out and empirical formulas in forms of yield or density are constructed to feature the extremal characteristic of fireball thermal radiation. However, due to the combined action of radiation free path (RFP) and fireball characteristic length (FCL) it is difficult to identify these formula’s application scope and further theoretical studies are needed to take the scale effect (SE) into account. By radiation heat conduction approximation model under optical thickness assumption, scale effect similarity parameter (SESP) is theoretically derived and its scope of application is further verified by high-precision numerical method. The numerical code is developed within a framework of Euler method and adaptive mesh refinement method is employed to improve the precision in the radiation front. The results of theoretical analysis show that SESP is consistent with existed conclusions regarding the thermal radiation of fireball at different altitudes, and it can be applied to the analysis of laboratory scale fireball. Meanwhile, numerical results also show that both scale effects at different altitudes and laboratory scale can be characterized by SESP.
, Available online , doi: 10.11883/bzycj-2023-0208
Abstract:
In order to solve the problem of high-performance lightweight bulletproof inserts being protected by the penetration of light weapon killing element, this paper carried out penetration experiments on ultra-high molecular weight polyethylene (UHMWPE) laminated sheet, analysed the deformation and failure characteristics of the UHMWPE sheet after penetration and compared the damage morphology of light weapon killing element. A numerical model of UHMWPE laminate against the penetration of light weapon killers was established by using the finite element software LS-DYNA, and the validity of the numerical model was verified by the experimental results of the damage morphology of the target plate, the depth of the depression and the deformation of the warhead. On this basis, the failure mode of UHMWPE thin plate subjected to oblique penetration by the projectile is investigated by numerical methods, and the influence of the incidence angle on the ricochet phenomenon and the damage morphology of UHMWPE thin plate under the penetration of three kinds of light weapon killing elements is revealed. The results show that the ricochet angles of 7.62 mm×25 mm steel-core bullets and 7.62 mm×39 mm ordinary bullets (steel-core) obliquely penetrating UHMWPE plates are located in the range of 45°–50°; 7.62 mm×25 mm lead-core bullets can be completely ricocheted out when the angle of incidence is greater than 70°, and the rest of the bullets are in the form of broken shrapnel splinters, and the destruction of the bullet body has an effect on the ricochet condition; the oblique penetration bullets produce a large area and a large number of damage patterns at a smaller angle of incidence; the oblique penetration bullets produce a larger area and a larger number of damage patterns in the UHMWPE plates. When the angle of incidence is small, the oblique penetration bullet will produce a larger area and a certain depth of the crater, the next bullet will be easier to penetrate the crater weakness of the fibre plate, the oblique penetration effect on the thin plate by the secondary penetration of the negative impact, the angle of incidence is larger, the bullet will be more complete ricochet and has a high residual velocity, which will produce a secondary killing of personnel. The research results can be used for UHMWPE thin plate for lightweight military bulletproof insert design to provide reference.
In order to solve the problem of high-performance lightweight bulletproof inserts being protected by the penetration of light weapon killing element, this paper carried out penetration experiments on ultra-high molecular weight polyethylene (UHMWPE) laminated sheet, analysed the deformation and failure characteristics of the UHMWPE sheet after penetration and compared the damage morphology of light weapon killing element. A numerical model of UHMWPE laminate against the penetration of light weapon killers was established by using the finite element software LS-DYNA, and the validity of the numerical model was verified by the experimental results of the damage morphology of the target plate, the depth of the depression and the deformation of the warhead. On this basis, the failure mode of UHMWPE thin plate subjected to oblique penetration by the projectile is investigated by numerical methods, and the influence of the incidence angle on the ricochet phenomenon and the damage morphology of UHMWPE thin plate under the penetration of three kinds of light weapon killing elements is revealed. The results show that the ricochet angles of 7.62 mm×25 mm steel-core bullets and 7.62 mm×39 mm ordinary bullets (steel-core) obliquely penetrating UHMWPE plates are located in the range of 45°–50°; 7.62 mm×25 mm lead-core bullets can be completely ricocheted out when the angle of incidence is greater than 70°, and the rest of the bullets are in the form of broken shrapnel splinters, and the destruction of the bullet body has an effect on the ricochet condition; the oblique penetration bullets produce a large area and a large number of damage patterns at a smaller angle of incidence; the oblique penetration bullets produce a larger area and a larger number of damage patterns in the UHMWPE plates. When the angle of incidence is small, the oblique penetration bullet will produce a larger area and a certain depth of the crater, the next bullet will be easier to penetrate the crater weakness of the fibre plate, the oblique penetration effect on the thin plate by the secondary penetration of the negative impact, the angle of incidence is larger, the bullet will be more complete ricochet and has a high residual velocity, which will produce a secondary killing of personnel. The research results can be used for UHMWPE thin plate for lightweight military bulletproof insert design to provide reference.
, Available online , doi: 10.11883/bzycj-2024-0082
Abstract:
When X-rays generated by high-altitude nuclear detonation irradiates on the shell structure of missile, blow-off impulse (BOI) and thermal shock waves generated may produce dynamic response and damage on it. The existing three one-dimensional theoretical models, Whitener, BBAY, and MBBAY, can only provide approximate BOI values and accurate results of peak pressure and other information are inaccessible. Solving this problem requires numerical calculations based on real physical laws. The numerical simulation program TSHOCK3D for X-ray thermal excitation wave is used to calculate the BOI and peak pressure to make a comparative analysis. An aluminum plate with a length and width of 0.4 centimeters and a thickness of 0.1 centimeters is set as the target for X-ray radiation. The range of the working conditions is 0.1−3.0 keV for the Planck's blackbody temperatures and radiant energy flux are in the range of 220−400 J/cm2. The results indicate that the TSHOCK3D can give the results effectively and reliably. The simulation results are consistent with the theoretical models mentioned above. The BOI and peak pressure are approximately linear with the energy flux, while the maximum value exist for different blackbody temperatures.
When X-rays generated by high-altitude nuclear detonation irradiates on the shell structure of missile, blow-off impulse (BOI) and thermal shock waves generated may produce dynamic response and damage on it. The existing three one-dimensional theoretical models, Whitener, BBAY, and MBBAY, can only provide approximate BOI values and accurate results of peak pressure and other information are inaccessible. Solving this problem requires numerical calculations based on real physical laws. The numerical simulation program TSHOCK3D for X-ray thermal excitation wave is used to calculate the BOI and peak pressure to make a comparative analysis. An aluminum plate with a length and width of 0.4 centimeters and a thickness of 0.1 centimeters is set as the target for X-ray radiation. The range of the working conditions is 0.1−3.0 keV for the Planck's blackbody temperatures and radiant energy flux are in the range of 220−400 J/cm2. The results indicate that the TSHOCK3D can give the results effectively and reliably. The simulation results are consistent with the theoretical models mentioned above. The BOI and peak pressure are approximately linear with the energy flux, while the maximum value exist for different blackbody temperatures.
, Available online , doi: 10.11883/bzycj-2023-0368
Abstract:
Shape memory alloys undergo phase transformation under strong impact loads, and the phase transformation has a significant impact on the dynamic mechanical response of their structural components. Based on the phase transformation critical criterion considering both hydrostatic pressure and deviatoric stress effects, an incremental constitutive model of phase transformation is derived. The analytical expression of characteristic wave speed under complex stress state is obtained based on the generalized characteristic theory. The characteristic wave speed is not only related to the mechanical parameters of the material itself (such as the tension-compression asymmetry and the modulus of the mixed phase), but also related to the stress state of the material. For TiNi alloys with volume expansion due to phase transformation, the increase of tensile-compressive asymmetry coefficient will increase the wave speed of slow waves, while having almost no effect on fast waves. At the short axis of the phase transformation ellipse (α = 90°), the wave speed of slow waves is the lowest and decreases significantly with the increase of the dimensionless modulus of the mixed phase. When the dimensionless modulus of the mixed phase increases from 2 to 5, the wave speed decreases by 36.2%, while the wave speed of fast waves reaches the maximum value c0, which is independent of the modulus of the mixed phase; at the long axis of the phase transformation ellipse (α = 180°), the speed of slow waves reaches the maximum value, and the wave speed of fast waves reaches the minimum value c2.
Shape memory alloys undergo phase transformation under strong impact loads, and the phase transformation has a significant impact on the dynamic mechanical response of their structural components. Based on the phase transformation critical criterion considering both hydrostatic pressure and deviatoric stress effects, an incremental constitutive model of phase transformation is derived. The analytical expression of characteristic wave speed under complex stress state is obtained based on the generalized characteristic theory. The characteristic wave speed is not only related to the mechanical parameters of the material itself (such as the tension-compression asymmetry and the modulus of the mixed phase), but also related to the stress state of the material. For TiNi alloys with volume expansion due to phase transformation, the increase of tensile-compressive asymmetry coefficient will increase the wave speed of slow waves, while having almost no effect on fast waves. At the short axis of the phase transformation ellipse (α = 90°), the wave speed of slow waves is the lowest and decreases significantly with the increase of the dimensionless modulus of the mixed phase. When the dimensionless modulus of the mixed phase increases from 2 to 5, the wave speed decreases by 36.2%, while the wave speed of fast waves reaches the maximum value c0, which is independent of the modulus of the mixed phase; at the long axis of the phase transformation ellipse (α = 180°), the speed of slow waves reaches the maximum value, and the wave speed of fast waves reaches the minimum value c2.
, Available online , doi: 10.11883/bzycj-2024-0074
Abstract:
The annular shaped charges serve as the precursor of a tandem warhead, prized for its ability to create large diameter perforation in targets. In an effort to enhance the penetration capacity of the annular shaped charge jet and mitigate the impact of the inner casing on subsequent sections induced by a reversed penetrator, a novel approach was taken to implement the investigation. Four different combinations of inner and outer casing materials based on steel and aluminum alloy were explored. It was found that when the inner casing was made of aluminum alloy, the average penetration depth in the rear target was 36.13% lower than that when the inner casing was made of steel. Selecting an inner casing of aluminum alloy and an outer casing of steel, the effects of tip offset, liner thickness, and standoff distance on the formation and penetration characteristics of the annular jet were further investigated. The results show that the jet formed by the non-eccentric liner exhibits radial offset, negatively influencing its penetration capability. However, by offsetting the liner tip to the outer side by 0.05d (where d represents the radial thickness of the annular shaped charge), both the forming and penetration performances of the jet are significantly improved. In addition, as the liner thickness increases, the velocity of the jet tip gradually decreases. Notably, the annular jet formed by an eccentric conical liner with a thickness of 0.045d exhibits superior penetration performance. Furthermore, the standoff distance emerges as a critical factor influencing the penetration capability of the annular jet. Optimal performance is achieved at a standoff distance of 1.12d. Under the same scenario, jet penetration tests were implemented. The difference between the radius of the penetration tunnel from numerical and experimental study lies within 12%. Subsequently, the reliability of the numerical simulation model and the conclusions are verified.
The annular shaped charges serve as the precursor of a tandem warhead, prized for its ability to create large diameter perforation in targets. In an effort to enhance the penetration capacity of the annular shaped charge jet and mitigate the impact of the inner casing on subsequent sections induced by a reversed penetrator, a novel approach was taken to implement the investigation. Four different combinations of inner and outer casing materials based on steel and aluminum alloy were explored. It was found that when the inner casing was made of aluminum alloy, the average penetration depth in the rear target was 36.13% lower than that when the inner casing was made of steel. Selecting an inner casing of aluminum alloy and an outer casing of steel, the effects of tip offset, liner thickness, and standoff distance on the formation and penetration characteristics of the annular jet were further investigated. The results show that the jet formed by the non-eccentric liner exhibits radial offset, negatively influencing its penetration capability. However, by offsetting the liner tip to the outer side by 0.05d (where d represents the radial thickness of the annular shaped charge), both the forming and penetration performances of the jet are significantly improved. In addition, as the liner thickness increases, the velocity of the jet tip gradually decreases. Notably, the annular jet formed by an eccentric conical liner with a thickness of 0.045d exhibits superior penetration performance. Furthermore, the standoff distance emerges as a critical factor influencing the penetration capability of the annular jet. Optimal performance is achieved at a standoff distance of 1.12d. Under the same scenario, jet penetration tests were implemented. The difference between the radius of the penetration tunnel from numerical and experimental study lies within 12%. Subsequently, the reliability of the numerical simulation model and the conclusions are verified.
, Available online , doi: 10.11883/bzycj-2024-0007
Abstract:
The propagation characteristics of waves are the basis for studying the dynamic behavior of materials, and the theoretical study of waves in continuous media at the macro scale has been well developed. With the widespread application of materials and structures at the micro and nano scales, the study of wave propagation characteristics at the lattice scale is receiving increasing attention. In this article, the Tersoff potential interaction between lattices is applied to study the wave propagation characteristics in single-crystal and polycrystalline systems. Firstly, in the case of micro-vibration, the propagation of lattice waves in a single-crystal system is studied based on three potential energy functions between lattices: linear interaction, Tersoff potential, and Tersoff potential with defects. The dispersion relationship in the lattice and the expression of lattice wave velocity are obtained. Secondly, taking carbon lattice and silicon lattice as examples, the finite difference method is applied to study the wave propagation process in the single-crystal system under three potential energies. The differences in lattice motion under compressive and tensile impacts are compared, and the influence of incident velocity on the displacement peak and force peak is discussed, which reveals the difference in wave propagation between single-crystal systems and continuous media. Finally, taking diamond and silicon carbide as examples, molecular dynamics simulations are used to study the wave propagation characteristics in polycrystalline systems, and the differences in atomic motion at different spatial positions are discussed. The results indicate that the lattice structure in polycrystalline systems is more complex, and the wave propagation characteristics in polycrystalline systems are different from those in single-crystal systems. The existence of defects has a significant impact on the propagation law of waves, which is more prominent in polycrystalline systems. This study has good reference significance for the study of material dynamics performance at the micro and nano scales.
The propagation characteristics of waves are the basis for studying the dynamic behavior of materials, and the theoretical study of waves in continuous media at the macro scale has been well developed. With the widespread application of materials and structures at the micro and nano scales, the study of wave propagation characteristics at the lattice scale is receiving increasing attention. In this article, the Tersoff potential interaction between lattices is applied to study the wave propagation characteristics in single-crystal and polycrystalline systems. Firstly, in the case of micro-vibration, the propagation of lattice waves in a single-crystal system is studied based on three potential energy functions between lattices: linear interaction, Tersoff potential, and Tersoff potential with defects. The dispersion relationship in the lattice and the expression of lattice wave velocity are obtained. Secondly, taking carbon lattice and silicon lattice as examples, the finite difference method is applied to study the wave propagation process in the single-crystal system under three potential energies. The differences in lattice motion under compressive and tensile impacts are compared, and the influence of incident velocity on the displacement peak and force peak is discussed, which reveals the difference in wave propagation between single-crystal systems and continuous media. Finally, taking diamond and silicon carbide as examples, molecular dynamics simulations are used to study the wave propagation characteristics in polycrystalline systems, and the differences in atomic motion at different spatial positions are discussed. The results indicate that the lattice structure in polycrystalline systems is more complex, and the wave propagation characteristics in polycrystalline systems are different from those in single-crystal systems. The existence of defects has a significant impact on the propagation law of waves, which is more prominent in polycrystalline systems. This study has good reference significance for the study of material dynamics performance at the micro and nano scales.
, Available online , doi: 10.11883/bzycj-2023-0195
Abstract:
Based on the basic principles of electromagnetic induction, an impact device is proposed that generates high-amplitude and long-pulse acceleration loads driven by electromagnetic forces. The impact device goes to make up for the shortcomings of the current stage of ground impact test technology. The disadvantages of the current stage of ground impact test technology include mainly time-consuming, high cost, low repeatability and controllability, and it is difficult to continuously improve the pulse width of acceleration load. Acceleration impact tests were performed using an electromagnetic Hopkinson bar, and the working process of the device from the generation of electromagnetic force to its transformation into impact load was analyzed. In the acceleration impact test, the stress on the bar was obtained by strain gauges and the acceleration loads at the end of the bar were obtained by acceleration transducers. A plurality of test results without loss of repeatability. The classical one-dimensional stress wave theory for predicting the relationship between acceleration and stress in slender bars is developed. Comparative analysis against experimental data are presented to demonstrate the effectiveness of the present approach. The electromagnetic Hopkinson bar acceleration impact test was numerically simulated using COMSOL finite element software, and the simulation results showed good consistency with the experimental results, indicating that the numerical model could simulate this kind of impact test more accurately and verifying the accuracy of the numerical model. Based on this finite element model, an impact device that generates high-amplitude, long-pulse acceleration is proposed, and numerical simulations of the device are carried out at different voltages and capacitances. The simulation results show that the device is able to generate the required acceleration. The acceleration amplitude increases with increasing capacitance voltage and the acceleration pulse width increases with increasing capacitance value. By regulating the values of the circuit parameters, the device can generate acceleration loads with different amplitudes and pulse widths.
Based on the basic principles of electromagnetic induction, an impact device is proposed that generates high-amplitude and long-pulse acceleration loads driven by electromagnetic forces. The impact device goes to make up for the shortcomings of the current stage of ground impact test technology. The disadvantages of the current stage of ground impact test technology include mainly time-consuming, high cost, low repeatability and controllability, and it is difficult to continuously improve the pulse width of acceleration load. Acceleration impact tests were performed using an electromagnetic Hopkinson bar, and the working process of the device from the generation of electromagnetic force to its transformation into impact load was analyzed. In the acceleration impact test, the stress on the bar was obtained by strain gauges and the acceleration loads at the end of the bar were obtained by acceleration transducers. A plurality of test results without loss of repeatability. The classical one-dimensional stress wave theory for predicting the relationship between acceleration and stress in slender bars is developed. Comparative analysis against experimental data are presented to demonstrate the effectiveness of the present approach. The electromagnetic Hopkinson bar acceleration impact test was numerically simulated using COMSOL finite element software, and the simulation results showed good consistency with the experimental results, indicating that the numerical model could simulate this kind of impact test more accurately and verifying the accuracy of the numerical model. Based on this finite element model, an impact device that generates high-amplitude, long-pulse acceleration is proposed, and numerical simulations of the device are carried out at different voltages and capacitances. The simulation results show that the device is able to generate the required acceleration. The acceleration amplitude increases with increasing capacitance voltage and the acceleration pulse width increases with increasing capacitance value. By regulating the values of the circuit parameters, the device can generate acceleration loads with different amplitudes and pulse widths.
, Available online , doi: 10.11883/bzycj-2023-0455
Abstract:
Explosive welding production in a vacuum explosion containment vessel can not only restrict the shock wave and noise generated by explosive explosion in a certain space range, but also effectively improve the quality of explosive welding products. Meanwhile, it also alleviates the problems of unstable product quality and rainy season shutdown caused by the influence of weather and climate during explosive welding production, which is an invention that can promote the development of the explosive processing industry. In order to develop a super large vacuum explosion containment vessel for explosive welding, it is necessary to explore the internal blast load and dynamic response of vacuum explosion containment vessel with sand covered for explosive welding. In order to meet the requirements of the experiment, a 0.55 m3 small cylindrical vacuum explosion containment vessel with the cap covered by a certain thickness of sand was designed, and a series of vacuum explosion experiments were carried out in it. At the same time, using the AUTODYN finite element analysis program, the numerical simulation analysis of the corresponding experimental groups is carried out. The evolution of shock wave inside the container, the distribution of blast load, the dynamic response of the structure, and the mechanism of sand covering on the end of the container on the damping of the plate structure are explored in depth. By analyzing the results of experiment and numerical simulation, it is concluded that the peak value of the second impulse of the time-history curve of the blast load in the explosion containment vessel is obviously higher than that of the first impulse, and the superposition and reflection of the shock wave always occur in the inner wall of the cover. With the decrease of vacuum degree inside the container, the peak value of the blast load is weakened obviously. According to the time-history curves of blast load and dynamic strain calculated by the numerical simulation, the dynamic response of the container cover is divided into four development phases: step-up phase, impulse follower phase, inertial lag phase and static pressure stabilization phase. With the decrease of vacuum degree, the amplitude of dynamic response is weakened obviously. With the increase of the thickness of sand cover, the dynamic response of explosion vessel is gradually weakened. Ultimately, it is concluded that reducing the environmental pressure inside the vessel and increasing the thickness of the sand covered on the cap of the container can be used as an effective method to reduce the forced vibration of the explosion containment vessel. The conclusions of the study are useful for the structural design of super large vacuum explosion containment vessels.
Explosive welding production in a vacuum explosion containment vessel can not only restrict the shock wave and noise generated by explosive explosion in a certain space range, but also effectively improve the quality of explosive welding products. Meanwhile, it also alleviates the problems of unstable product quality and rainy season shutdown caused by the influence of weather and climate during explosive welding production, which is an invention that can promote the development of the explosive processing industry. In order to develop a super large vacuum explosion containment vessel for explosive welding, it is necessary to explore the internal blast load and dynamic response of vacuum explosion containment vessel with sand covered for explosive welding. In order to meet the requirements of the experiment, a 0.55 m3 small cylindrical vacuum explosion containment vessel with the cap covered by a certain thickness of sand was designed, and a series of vacuum explosion experiments were carried out in it. At the same time, using the AUTODYN finite element analysis program, the numerical simulation analysis of the corresponding experimental groups is carried out. The evolution of shock wave inside the container, the distribution of blast load, the dynamic response of the structure, and the mechanism of sand covering on the end of the container on the damping of the plate structure are explored in depth. By analyzing the results of experiment and numerical simulation, it is concluded that the peak value of the second impulse of the time-history curve of the blast load in the explosion containment vessel is obviously higher than that of the first impulse, and the superposition and reflection of the shock wave always occur in the inner wall of the cover. With the decrease of vacuum degree inside the container, the peak value of the blast load is weakened obviously. According to the time-history curves of blast load and dynamic strain calculated by the numerical simulation, the dynamic response of the container cover is divided into four development phases: step-up phase, impulse follower phase, inertial lag phase and static pressure stabilization phase. With the decrease of vacuum degree, the amplitude of dynamic response is weakened obviously. With the increase of the thickness of sand cover, the dynamic response of explosion vessel is gradually weakened. Ultimately, it is concluded that reducing the environmental pressure inside the vessel and increasing the thickness of the sand covered on the cap of the container can be used as an effective method to reduce the forced vibration of the explosion containment vessel. The conclusions of the study are useful for the structural design of super large vacuum explosion containment vessels.
, Available online , doi: 10.11883/bzycj-2023-0433
Abstract:
In order to deal with the difficulty of measuring the transmitted wave in the backfilling SHPB (split Hopkinson pressure bar) test, rock bars are used to instead of steel bar as the incident bar and transmitted bar for improving the pendulum hammer driven SHPB system. The wave impedance matching formula and viscoelastic wave propagation in SHPB test is proposed. Based on the study of stress wave propagation in rock bar systems, the viscosity attenuation coefficients of stress wave propagation in the incident and transmitted rock bars and the reflection and transmission attenuation coefficient of the rock bar-backfilling body are defined. Based on the Kelvin-Voigt model, the effects of rock bar density and wave velocity on the transmitted wave measured of the filling body in the SHPB tests were simulated and analyzed by using a one-dimensional wave propagation analysis procedure. The relationship between the wave impedance matching coefficient and the reflection and transmission attenuation coefficient of the rock bar-backfilling body were obtained. According to the characteristics of field backfilling, the wave impedance matching coefficient and the reflection and transmission attenuation coefficient, four long rock bars were selected to modify the pendulum hammer driven SHPB system. The viscosity coefficient of the rock bar was measured and stresses and strains on the interfaces of rock bar and backfilling body were calculated by using the one-dimensional wave propagation analysis procedure. The stress waveform characteristics and signal-to-noise ratio of the transmitted waves were analyzed. The matching degree of four kinds of rock bars and backfilling wave impedance from good to poor is obtained, which is green sandstone, granite, marble and basalt. The dynamic impacting experiment on the filling body was conducted and the stress balance in the sample was verified. The pendulum hammer driven SHPB system with green sandstone incident bar and transmission bar is established, which provides support for the dynamic mechanical characteristics of the backfilling.
In order to deal with the difficulty of measuring the transmitted wave in the backfilling SHPB (split Hopkinson pressure bar) test, rock bars are used to instead of steel bar as the incident bar and transmitted bar for improving the pendulum hammer driven SHPB system. The wave impedance matching formula and viscoelastic wave propagation in SHPB test is proposed. Based on the study of stress wave propagation in rock bar systems, the viscosity attenuation coefficients of stress wave propagation in the incident and transmitted rock bars and the reflection and transmission attenuation coefficient of the rock bar-backfilling body are defined. Based on the Kelvin-Voigt model, the effects of rock bar density and wave velocity on the transmitted wave measured of the filling body in the SHPB tests were simulated and analyzed by using a one-dimensional wave propagation analysis procedure. The relationship between the wave impedance matching coefficient and the reflection and transmission attenuation coefficient of the rock bar-backfilling body were obtained. According to the characteristics of field backfilling, the wave impedance matching coefficient and the reflection and transmission attenuation coefficient, four long rock bars were selected to modify the pendulum hammer driven SHPB system. The viscosity coefficient of the rock bar was measured and stresses and strains on the interfaces of rock bar and backfilling body were calculated by using the one-dimensional wave propagation analysis procedure. The stress waveform characteristics and signal-to-noise ratio of the transmitted waves were analyzed. The matching degree of four kinds of rock bars and backfilling wave impedance from good to poor is obtained, which is green sandstone, granite, marble and basalt. The dynamic impacting experiment on the filling body was conducted and the stress balance in the sample was verified. The pendulum hammer driven SHPB system with green sandstone incident bar and transmission bar is established, which provides support for the dynamic mechanical characteristics of the backfilling.
, Available online , doi: 10.11883/bzycj-2024-0077
Abstract:
In order to study the anti-explosion ability of reinforced masonry wall and the reinforcement performance of polyurea on the wall, LS-DYNA software was used to numerically simulate the dynamic response of unreinforced masonry wall, reinforced masonry wall, and masonry wall strengthened with polyurea respectively. The anti-gas explosion performance of different walls under gas explosion load with peak value of 5, 10, 20 and 30 kPa was obtained. The reinforcing effect of vertical reinforcement in ash joint and polyurea were compared and analyzed. The results show that: (1) The anti-gas explosion capability of the unreinforced wall is relatively weak, which generally causes irreparable damage under the load of 20 kPa and collapses under the load of 30 kPa. (2) The explosion resistance of the masonry wall can be enhanced by the vertical displacement of rebar in the ash joint and the spraying of polyurea on the wall surface. Under the load of 20 kPa, the peak displacement at mid-span of each reinforced wall is smaller than that of the unreinforced wall, and the damage is lighter, which is repairable. Among them, the anti-explosion effect of double-sided spraying polyurea on unreinforced wall surface is the best, and there is no collapse damage under the load of 30 kPa. The reinforcing effect of vertical reinforcement in ash joint and polyurea spraying on the back surface are the second. (3) The three groups of reinforced walls with polyurea can all withstand 30 kPa gas explosion load. Cracks occur in the middle of the wall strengthened by spraying on the explosive side, fragments splash, the mid-span peak displacement is the largest. Local damage occurs at both ends of the wall strengthened by back side and double-sided spraying, and the walls are basically complete, and the mid-span peak displacement of the wall strengthened by double-side spraying is the smallest. It is shown that spraying polyurea on both sides on the basis of vertical reinforcement in ash joint has the best explosion resistance effect, and can also bear greater gas explosion load. The research results can provide reference for the reinforcement of reinforced masonry wall against gas explosion.
In order to study the anti-explosion ability of reinforced masonry wall and the reinforcement performance of polyurea on the wall, LS-DYNA software was used to numerically simulate the dynamic response of unreinforced masonry wall, reinforced masonry wall, and masonry wall strengthened with polyurea respectively. The anti-gas explosion performance of different walls under gas explosion load with peak value of 5, 10, 20 and 30 kPa was obtained. The reinforcing effect of vertical reinforcement in ash joint and polyurea were compared and analyzed. The results show that: (1) The anti-gas explosion capability of the unreinforced wall is relatively weak, which generally causes irreparable damage under the load of 20 kPa and collapses under the load of 30 kPa. (2) The explosion resistance of the masonry wall can be enhanced by the vertical displacement of rebar in the ash joint and the spraying of polyurea on the wall surface. Under the load of 20 kPa, the peak displacement at mid-span of each reinforced wall is smaller than that of the unreinforced wall, and the damage is lighter, which is repairable. Among them, the anti-explosion effect of double-sided spraying polyurea on unreinforced wall surface is the best, and there is no collapse damage under the load of 30 kPa. The reinforcing effect of vertical reinforcement in ash joint and polyurea spraying on the back surface are the second. (3) The three groups of reinforced walls with polyurea can all withstand 30 kPa gas explosion load. Cracks occur in the middle of the wall strengthened by spraying on the explosive side, fragments splash, the mid-span peak displacement is the largest. Local damage occurs at both ends of the wall strengthened by back side and double-sided spraying, and the walls are basically complete, and the mid-span peak displacement of the wall strengthened by double-side spraying is the smallest. It is shown that spraying polyurea on both sides on the basis of vertical reinforcement in ash joint has the best explosion resistance effect, and can also bear greater gas explosion load. The research results can provide reference for the reinforcement of reinforced masonry wall against gas explosion.
, Available online , doi: 10.11883/bzycj-2024-0036
Abstract:
X-ray diffraction test was used to analyze the changes in the mineral composition of the granite before and after filling with water to study the effects of saturated water and initial damage degree on macroscopic and microscopic failure characteristics of granite under impact load. The Hopkinson device was used to carry out dynamic mechanical tests on the granite samples under different states to analyze the dynamic mechanical properties of the granite and the block size characteristics under different states. In addition, some of the granite fragments after impact were selected for electron microscope scanning test to analyze the fracture failure characteristics. The fractal dimension was used to analyze the fragmentation degree of the granite fragments after impact and the scanning images of the fracture under electron microscopy. The influence of the image magnification selected during electron microscope scanning on the fractal dimension is discussed. The micro-cracking mechanism of granite induced by saturated water under impact load is briefly analyzed. The results show that the mineral composition of the saturated granite changes compared with the natural granite. The proportions of hornblende, albite, microcline, and quartz in the saturated granite decrease, while the proportion of kaolinite increases significantly. With the increase of initial damage, the dynamic peak stress of granite gradually decreases while the fragmentation degree and the fractal dimension of the block increase gradually, and the influence of initial damage on the fractal dimension of the block is greater than that of saturated water. With the increase of initial damage, more micro-cracks and debris appear in the fracture image, and the fractal dimension of the fracture image increases gradually. In a certain range, the fractal dimension of electron microscope scanning images increases with the increase of image magnification, but when the image exceeds a certain multiple, the fractal dimension will decrease. The research results can provide some theoretical and engineering references for the failure and instability mechanism analysis of disturbed water-saturated granite with initial damage in geotechnical engineering.
X-ray diffraction test was used to analyze the changes in the mineral composition of the granite before and after filling with water to study the effects of saturated water and initial damage degree on macroscopic and microscopic failure characteristics of granite under impact load. The Hopkinson device was used to carry out dynamic mechanical tests on the granite samples under different states to analyze the dynamic mechanical properties of the granite and the block size characteristics under different states. In addition, some of the granite fragments after impact were selected for electron microscope scanning test to analyze the fracture failure characteristics. The fractal dimension was used to analyze the fragmentation degree of the granite fragments after impact and the scanning images of the fracture under electron microscopy. The influence of the image magnification selected during electron microscope scanning on the fractal dimension is discussed. The micro-cracking mechanism of granite induced by saturated water under impact load is briefly analyzed. The results show that the mineral composition of the saturated granite changes compared with the natural granite. The proportions of hornblende, albite, microcline, and quartz in the saturated granite decrease, while the proportion of kaolinite increases significantly. With the increase of initial damage, the dynamic peak stress of granite gradually decreases while the fragmentation degree and the fractal dimension of the block increase gradually, and the influence of initial damage on the fractal dimension of the block is greater than that of saturated water. With the increase of initial damage, more micro-cracks and debris appear in the fracture image, and the fractal dimension of the fracture image increases gradually. In a certain range, the fractal dimension of electron microscope scanning images increases with the increase of image magnification, but when the image exceeds a certain multiple, the fractal dimension will decrease. The research results can provide some theoretical and engineering references for the failure and instability mechanism analysis of disturbed water-saturated granite with initial damage in geotechnical engineering.
, Available online , doi: 10.11883/bzycj-2023-0472
Abstract:
It is of great scientific significance and application value to study the anti-penetration performance of continuous fiber-reinforced high-porosity composites. First, the ballistic penetration experiments of 20 mm thick continuous fiber-reinforced high-porosity composites were carried out by using two-stage light gas gun firing Q235 steel projectiles of diameter 4.5 mm. Based on the analysis of the initial and final velocities of bullet penetration, the ballistic limit of the material is obtained. By observing the damage patterns of the target plate, these patterns are divided into three types from low to high according to the initial velocity of the projectiles: back-crack type, back-burst type and penetrated type. The anti-penetration performance of this composite material is compared with other materials by specific energy absorption, showing that the anti-penetration performance of the composite against low-speed penetration up to 600 m/s is better than those of steel, aluminum, Kevlar and glass fiber composite. Then, an orthogonal anisotropic continuum damage constitutive model is proposed for the continuous fiber-reinforced high-porosity composites. This constitutive model is written as a subroutine and embedded in the finite element software by secondary development. On this basis, the finite element simulations of ballistic penetrations of continuous fiber reinforced high-porosity composites are conducted. The validity of the constitutive and finite element models is verified by comparing the final velocity, ballistic limit and damage range of the back surface obtained from experiment and simulation. Furthermore, the damage mechanism of the penetration process is analyzed by observing the shape of the bullet hole, stress distribution and damage distribution obtained from the finite element simulation. The results show that the formation of the bullet hole during the penetration of spherical projectile is caused by shear damage, the debonding of fiber and matrix is caused by the combined action of compression and shear, the delamination damage of the target plate is caused by the tension wave created by the reflection of compression wave, and the fiber breakage belongs to tension damage. Besides, the kinetic energy, internal energy and their proportion to the kinetic energy change of the bullet are compared with the initial velocity. It is pointed out that most of the kinetic energy of the projectile is transformed into the kinetic energy of the fragment of target plates and the plastic deformation energy of the projectile. The research results provide a reference for the multifunctional integration of these composite materials in heat protection, penetration protection and load bearing.
It is of great scientific significance and application value to study the anti-penetration performance of continuous fiber-reinforced high-porosity composites. First, the ballistic penetration experiments of 20 mm thick continuous fiber-reinforced high-porosity composites were carried out by using two-stage light gas gun firing Q235 steel projectiles of diameter 4.5 mm. Based on the analysis of the initial and final velocities of bullet penetration, the ballistic limit of the material is obtained. By observing the damage patterns of the target plate, these patterns are divided into three types from low to high according to the initial velocity of the projectiles: back-crack type, back-burst type and penetrated type. The anti-penetration performance of this composite material is compared with other materials by specific energy absorption, showing that the anti-penetration performance of the composite against low-speed penetration up to 600 m/s is better than those of steel, aluminum, Kevlar and glass fiber composite. Then, an orthogonal anisotropic continuum damage constitutive model is proposed for the continuous fiber-reinforced high-porosity composites. This constitutive model is written as a subroutine and embedded in the finite element software by secondary development. On this basis, the finite element simulations of ballistic penetrations of continuous fiber reinforced high-porosity composites are conducted. The validity of the constitutive and finite element models is verified by comparing the final velocity, ballistic limit and damage range of the back surface obtained from experiment and simulation. Furthermore, the damage mechanism of the penetration process is analyzed by observing the shape of the bullet hole, stress distribution and damage distribution obtained from the finite element simulation. The results show that the formation of the bullet hole during the penetration of spherical projectile is caused by shear damage, the debonding of fiber and matrix is caused by the combined action of compression and shear, the delamination damage of the target plate is caused by the tension wave created by the reflection of compression wave, and the fiber breakage belongs to tension damage. Besides, the kinetic energy, internal energy and their proportion to the kinetic energy change of the bullet are compared with the initial velocity. It is pointed out that most of the kinetic energy of the projectile is transformed into the kinetic energy of the fragment of target plates and the plastic deformation energy of the projectile. The research results provide a reference for the multifunctional integration of these composite materials in heat protection, penetration protection and load bearing.
, Available online , doi: 10.11883/bzycj-2024-0045
Abstract:
Cellular projectiles are widely used in the impact tests of protective structures, but the actual loads of cellular projectiles acting on the tested sandwich structures are still unclear. To explore the coupling response process between the uniform/graded cellular projectile and the foam sandwich beam and the loading effect of cellular projectiles, theoretical analysis, numerical simulations, and impact tests were carried out. The foam sandwich beam was equivalent to a monolithic beam to simplify the analysis. Based on the shock wave model of the cellular projectile and the equivalent response model of the foam sandwich beam, a coupling analysis model of the cellular projectile impacting the foam sandwich beam was developed, and its governing equations were presented and solved numerically by Runge-Kutta method. Meso-finite element simulations of a uniform/graded cellular projectile impacting a foam sandwich beam were carried out based on the 3D Voronoi technique. Impact tests were performed on the test platform of cellular projectiles, and the velocity response of the cellular projectiles and the foam sandwich beams was obtained by using a high-speed camera and a digital image processing technique. It is found that the coupling analysis model can accurately predict the velocity history curves of the cellular projectile and the foam sandwich beam and the impact pressure of the cellular projectile. Subjected to cellular projectiles with the same initial momentum but different density distribution or initial velocity, foam sandwich beams with the same configuration present different mechanical response processes, which demonstrates that the impact of cellular projectiles cannot be simply equivalent to impulse loading, and the coupling effect between the projectile and the sandwich beam cannot be ignored. Compared with uniform cellular projectiles, the impact pressure waveform of the graded cellular projectile is sharper and shows stronger nonlinearity during its attenuation. This study clarifies the loading effect of cellular projectiles on foam sandwich beams and lays a theoretical foundation for the optimal design of cellular projectiles simulating blast loads.
Cellular projectiles are widely used in the impact tests of protective structures, but the actual loads of cellular projectiles acting on the tested sandwich structures are still unclear. To explore the coupling response process between the uniform/graded cellular projectile and the foam sandwich beam and the loading effect of cellular projectiles, theoretical analysis, numerical simulations, and impact tests were carried out. The foam sandwich beam was equivalent to a monolithic beam to simplify the analysis. Based on the shock wave model of the cellular projectile and the equivalent response model of the foam sandwich beam, a coupling analysis model of the cellular projectile impacting the foam sandwich beam was developed, and its governing equations were presented and solved numerically by Runge-Kutta method. Meso-finite element simulations of a uniform/graded cellular projectile impacting a foam sandwich beam were carried out based on the 3D Voronoi technique. Impact tests were performed on the test platform of cellular projectiles, and the velocity response of the cellular projectiles and the foam sandwich beams was obtained by using a high-speed camera and a digital image processing technique. It is found that the coupling analysis model can accurately predict the velocity history curves of the cellular projectile and the foam sandwich beam and the impact pressure of the cellular projectile. Subjected to cellular projectiles with the same initial momentum but different density distribution or initial velocity, foam sandwich beams with the same configuration present different mechanical response processes, which demonstrates that the impact of cellular projectiles cannot be simply equivalent to impulse loading, and the coupling effect between the projectile and the sandwich beam cannot be ignored. Compared with uniform cellular projectiles, the impact pressure waveform of the graded cellular projectile is sharper and shows stronger nonlinearity during its attenuation. This study clarifies the loading effect of cellular projectiles on foam sandwich beams and lays a theoretical foundation for the optimal design of cellular projectiles simulating blast loads.
, Available online , doi: 10.11883/bzycj-2023-0404
Abstract:
To study the explosion process of carbon-iron nanomaterials synthesized by gaseous detonation, the effects of different molar ratios of hydrogen-oxygen (2∶1, 3∶1, 4∶1) on the peak value time-history curve of detonation parameters (detonation velocity, detonation temperature, and detonation pressure) and the morphology of carbon-iron nanomaterials were studied by combination of hydrogen-oxygen experiments and numerical simulations. The explosion experiments used hydrogen and oxygen with a purity of 99.999% in a closed detonation tube. The precursor was ferrocene with a purity of 99%. A high-speed camera was used to observe in the middle of the tube. After the experiments, the samples were collected and characterized by transmission electron microscopy. The numerical simulation used ICEM software for modeling and meshing and then used FLUENT software to verify the rationality of the mesh size, and then performed simulation calculations after confirming the optimal mesh size. The results indicate that hydrogen-oxygen explosion inside a detonation tube involves two processes: the propagation of detonation waves and the attenuation of combustion waves, and the hydrogen-oxygen molar ratio has a significant impact on the peak time history curves of detonation velocity, detonation temperature, and detonation pressure. With the increase of the molar ratio of hydrogen to oxygen, the detonation velocity, detonation temperature, detonation pressure, and attenuation rate of the detonation wave all decrease. The molar ratio of hydrogen to oxygen affects the morphology growth of carbon-iron nanomaterials by influencing the propagation and attenuation of detonation waves. At zero oxygen balance, the sample consists of carbon-coated iron nanoparticles. As the hydrogen-oxygen molar ratio increases, the number of carbon nanotubes in the sample gradually increases. Adjusting the molar ratio of hydrogen to oxygen can achieve control over the propagation and attenuation process of detonation waves, and also achieve the goal of controlling the preparation of carbon iron nanomaterials with specific morphologies through gaseous detonation.
To study the explosion process of carbon-iron nanomaterials synthesized by gaseous detonation, the effects of different molar ratios of hydrogen-oxygen (2∶1, 3∶1, 4∶1) on the peak value time-history curve of detonation parameters (detonation velocity, detonation temperature, and detonation pressure) and the morphology of carbon-iron nanomaterials were studied by combination of hydrogen-oxygen experiments and numerical simulations. The explosion experiments used hydrogen and oxygen with a purity of 99.999% in a closed detonation tube. The precursor was ferrocene with a purity of 99%. A high-speed camera was used to observe in the middle of the tube. After the experiments, the samples were collected and characterized by transmission electron microscopy. The numerical simulation used ICEM software for modeling and meshing and then used FLUENT software to verify the rationality of the mesh size, and then performed simulation calculations after confirming the optimal mesh size. The results indicate that hydrogen-oxygen explosion inside a detonation tube involves two processes: the propagation of detonation waves and the attenuation of combustion waves, and the hydrogen-oxygen molar ratio has a significant impact on the peak time history curves of detonation velocity, detonation temperature, and detonation pressure. With the increase of the molar ratio of hydrogen to oxygen, the detonation velocity, detonation temperature, detonation pressure, and attenuation rate of the detonation wave all decrease. The molar ratio of hydrogen to oxygen affects the morphology growth of carbon-iron nanomaterials by influencing the propagation and attenuation of detonation waves. At zero oxygen balance, the sample consists of carbon-coated iron nanoparticles. As the hydrogen-oxygen molar ratio increases, the number of carbon nanotubes in the sample gradually increases. Adjusting the molar ratio of hydrogen to oxygen can achieve control over the propagation and attenuation process of detonation waves, and also achieve the goal of controlling the preparation of carbon iron nanomaterials with specific morphologies through gaseous detonation.
, Available online , doi: 10.11883/bzycj-2-23-0466
Abstract:
Coral concrete is a material with severely asymmetric tensile and compressive strengths. Therefore, studying the dynamic tensile mechanical properties of coral concrete is of great significance for island reef protective engineering. To investigate the dynamic tensile mechanical properties of carbon fiber (CF) and stainless steel fiber (SSF) reinforced coral sand cement mortar under impact loading, dynamic splitting tests were conducted using a 100 mm diameter split Hopkinson pressure bar (SHPB) device. Comparative analysis was carried out on the dynamic tensile strength and energy dissipation patterns of coral sand cement mortars with different fiber contents at various strain rates. In the SHPB tests, cement mortar specimens with different fiber contents were prepared: no fiber, 1.5% CF, 1.5% CF with 0.5% SSF, 1.5% CF with 1.0% SSF, and 1.5% CF with 1.5% SSF. The specimens were subjected to four impact speeds: 3.45, 4.86, 6.54, and 7.34 m/s. This allowed for impact-splitting tests conducted at different strain-rate ranges. In addition, SEM (Scanning Electron Microscope) tests were performed to reveal the action mechanism of the hybrid fibers. The results indicate that the static and dynamic tensile strengths of CF and SSF-reinforced coral sand cement mortar samples are significantly improved, with a maximum dynamic tensile strength increase rate of 66.03%. At the same strain rate, the dynamic tensile strength of the samples positively correlates with the fiber content, while the fragmentation degree negatively correlates with the fiber content. The fiber bridging effect effectively suppresses the development of cracks in the samples. Under the same fiber content, the dynamic increase factor increases significantly with the increase of strain rate, with a maximum increase factor of 2.44, demonstrating a clear tensile strain rate effect. The fragmentation degree and dissipated energy of coral sand cement mortar samples positively correlate with the strain rate, and samples with higher fiber dosages require more energy to dissipate during failure.
Coral concrete is a material with severely asymmetric tensile and compressive strengths. Therefore, studying the dynamic tensile mechanical properties of coral concrete is of great significance for island reef protective engineering. To investigate the dynamic tensile mechanical properties of carbon fiber (CF) and stainless steel fiber (SSF) reinforced coral sand cement mortar under impact loading, dynamic splitting tests were conducted using a 100 mm diameter split Hopkinson pressure bar (SHPB) device. Comparative analysis was carried out on the dynamic tensile strength and energy dissipation patterns of coral sand cement mortars with different fiber contents at various strain rates. In the SHPB tests, cement mortar specimens with different fiber contents were prepared: no fiber, 1.5% CF, 1.5% CF with 0.5% SSF, 1.5% CF with 1.0% SSF, and 1.5% CF with 1.5% SSF. The specimens were subjected to four impact speeds: 3.45, 4.86, 6.54, and 7.34 m/s. This allowed for impact-splitting tests conducted at different strain-rate ranges. In addition, SEM (Scanning Electron Microscope) tests were performed to reveal the action mechanism of the hybrid fibers. The results indicate that the static and dynamic tensile strengths of CF and SSF-reinforced coral sand cement mortar samples are significantly improved, with a maximum dynamic tensile strength increase rate of 66.03%. At the same strain rate, the dynamic tensile strength of the samples positively correlates with the fiber content, while the fragmentation degree negatively correlates with the fiber content. The fiber bridging effect effectively suppresses the development of cracks in the samples. Under the same fiber content, the dynamic increase factor increases significantly with the increase of strain rate, with a maximum increase factor of 2.44, demonstrating a clear tensile strain rate effect. The fragmentation degree and dissipated energy of coral sand cement mortar samples positively correlate with the strain rate, and samples with higher fiber dosages require more energy to dissipate during failure.
, Available online , doi: 10.11883/bzycj-2023-0459
Abstract:
The layered protective structure composed of bursting layer, distribution layer and structure layer is usually used to resist the penetration and blast waves induced by advanced earth penetrating weapons (EPWs). The defect of traditional layered protective structure with medium/coarse sand as the distribution layer is that it is difficult to reliably control the load on the structure layer. To solve this issue, an alternative approach is presented by replacing the material of distribution layer from the frequently-used medium/coarse sand to foam concrete. To investigate the blast resistance of layered protective structure sandwiched by foam concrete (named composite protective structure), the blast test on the layered composite target composed of CF120 concrete (a fiber reinforced high-strength concrete) bursting layer, C5 foam concrete distribution layer and C40 reinforced concrete structure layer was firstly conducted in the present study, in which the damage and failure in the layered composite target and blast waves at specific locations were the major concern and were accurately recorded. Then based on the concrete material model established by Kong and Fang and the Smoothed Particle Galerkin (SPG) algorithm available in the LS-DYNA, a corresponding numerical model was developed and validated against test data. Using the validated numerical model, the propagation and attenuation of blast waves and damage and failure in the composite protective structure induced by cylindrical charge explosion are discussed in detail. It is found that the blast resistance mechanism of the composite protective structure is attributed to the extreme wave impedance mismatch between the bursting layer and the foam concrete layer, which greatly reduces the propagation of blast waves into the foam concrete layer, leading to a transformation of more blast energy to the bursting layer, so that the blast load and energy on the structure layer can be greatly reduced. The research results can provide important reference for the design of protective structure against EPWs.
The layered protective structure composed of bursting layer, distribution layer and structure layer is usually used to resist the penetration and blast waves induced by advanced earth penetrating weapons (EPWs). The defect of traditional layered protective structure with medium/coarse sand as the distribution layer is that it is difficult to reliably control the load on the structure layer. To solve this issue, an alternative approach is presented by replacing the material of distribution layer from the frequently-used medium/coarse sand to foam concrete. To investigate the blast resistance of layered protective structure sandwiched by foam concrete (named composite protective structure), the blast test on the layered composite target composed of CF120 concrete (a fiber reinforced high-strength concrete) bursting layer, C5 foam concrete distribution layer and C40 reinforced concrete structure layer was firstly conducted in the present study, in which the damage and failure in the layered composite target and blast waves at specific locations were the major concern and were accurately recorded. Then based on the concrete material model established by Kong and Fang and the Smoothed Particle Galerkin (SPG) algorithm available in the LS-DYNA, a corresponding numerical model was developed and validated against test data. Using the validated numerical model, the propagation and attenuation of blast waves and damage and failure in the composite protective structure induced by cylindrical charge explosion are discussed in detail. It is found that the blast resistance mechanism of the composite protective structure is attributed to the extreme wave impedance mismatch between the bursting layer and the foam concrete layer, which greatly reduces the propagation of blast waves into the foam concrete layer, leading to a transformation of more blast energy to the bursting layer, so that the blast load and energy on the structure layer can be greatly reduced. The research results can provide important reference for the design of protective structure against EPWs.
, Available online , doi: 10.11883/bzycj-2024-0041
Abstract:
To investigate the velocity distribution characteristics of elliptical section warhead (ECSW) fragments under different initiation modes, a numerical simulation model was established for five ECSWs with different shape ratios. Numerical simulations were conducted to investigate the velocity distribution and energy output characteristics of fragments from ECSW under five different initiation modes: central single-point initiation, dual-point initiation at the midpoint of the minor (or major) axis, four-point initiation at the midpoint of the major and minor axes, as well as surface-initiated detonation. The research findings suggest that the maximum radial velocity of fragments follows a consistent logarithmic growth pattern in the radial direction across various initiation modes, increasing from the major axis to the minor axis direction. With an increase in the shape ratio, the difference in fragment velocities between the major and minor axis directions gradually decreases. However, the maximum velocity profiles of fragments from elliptical section warheads exhibit noticeable differences in average velocities under different initiation modes. Surface-initiated detonation produces the highest average radial velocity, whereas single-point initiation leads to the lowest. As the number of initiation points increases, the overall average fragment velocity on the maximum velocity profile gradually rises. In the axial direction, the influence of rarefaction waves leads to the maximum fragment velocities occurring near the 1/4 position from the non-initiating end at different azimuthal angles. Initiation points along the minor axis enhance the fragment velocity in the major axis direction near the initiating end compared to initiating points along the major axis. However, there are no significant variations in the axial velocity distribution of fragments in the minor axis direction. The different initiation modes have negligible effects on the energy output characteristics of elliptical section charges. Approximately 27% of the charge energy is converted into shell kinetic energy, while 50% is dissipated through casing fracture deformation and air shock wave propagation.
To investigate the velocity distribution characteristics of elliptical section warhead (ECSW) fragments under different initiation modes, a numerical simulation model was established for five ECSWs with different shape ratios. Numerical simulations were conducted to investigate the velocity distribution and energy output characteristics of fragments from ECSW under five different initiation modes: central single-point initiation, dual-point initiation at the midpoint of the minor (or major) axis, four-point initiation at the midpoint of the major and minor axes, as well as surface-initiated detonation. The research findings suggest that the maximum radial velocity of fragments follows a consistent logarithmic growth pattern in the radial direction across various initiation modes, increasing from the major axis to the minor axis direction. With an increase in the shape ratio, the difference in fragment velocities between the major and minor axis directions gradually decreases. However, the maximum velocity profiles of fragments from elliptical section warheads exhibit noticeable differences in average velocities under different initiation modes. Surface-initiated detonation produces the highest average radial velocity, whereas single-point initiation leads to the lowest. As the number of initiation points increases, the overall average fragment velocity on the maximum velocity profile gradually rises. In the axial direction, the influence of rarefaction waves leads to the maximum fragment velocities occurring near the 1/4 position from the non-initiating end at different azimuthal angles. Initiation points along the minor axis enhance the fragment velocity in the major axis direction near the initiating end compared to initiating points along the major axis. However, there are no significant variations in the axial velocity distribution of fragments in the minor axis direction. The different initiation modes have negligible effects on the energy output characteristics of elliptical section charges. Approximately 27% of the charge energy is converted into shell kinetic energy, while 50% is dissipated through casing fracture deformation and air shock wave propagation.
, Available online , doi: 10.11883/bzycj-2023-0465
Abstract:
To investigate the influence of typical metal powders on the shock wave effect and thermal damage performance of fuel air explosive (FAE), the explosion characteristics, flame structure and temperature distribution characteristics of epoxypropane (PO) with different types and contents of metal powders were experimentally studied using a 20 L spherical liquid explosion test system. The temperature field of explosion flame was reconstructed by the colorimetric temperature measurement method with a high-speed camera, which is based on the gray-body radiation theory and a self-written python code. The tungsten lamp was used to calibrate the measuring accuracy of the temperature mapping system, and the fitting relationship between the temperatures and the gray values of the high-speed images is derived to obtain the conversion coefficient. The experimental results show that the optimal mass concentration of pure PO was 780 g/m3, both the explosion overpressure (∆pmax) and the explosion pressure rise rate ((dp/dt)max) reached the maximum, ∆pmax=0.799 MPa and (dp/dt)max=52.438 MPa/s, respectively. The maximum explosion overpressure, maximum explosion pressure rise rate and maximum average temperature of PO added with Al, Ti and Mg powders all increase with the increase of mass ratios (I), while the trend of maximum pressure rise time is opposite. The variation rules of the maximum explosion overpressure and maximum average temperature are consistent, the order of their values is: Al/PO, Mg/PO, Ti/PO. When I=40%, the maximum explosion overpressure value of the three solid-liquid mixed fuels increases by 12.00%, 8.41% and 11.54%, respectively, compared with pure PO. In addition, the variation rules of the maximum explosion pressure rise rate and the combustion rate are consistent, the order of their values is: Al/PO, Mg/PO, Ti/PO. When I=40%, the maximum explosion pressure rise rate value of the three solid-liquid mixed fuels increases by 41.91%, 39.60% and 45.29%, respectively, compared with the pure PO. The results indicate that different high-energy metal powders have varied advantages in improving the explosion performance of PO, so metal powders should be appropriately selected as energetic additives according to the damage performance index in the formulation design of FAE.
To investigate the influence of typical metal powders on the shock wave effect and thermal damage performance of fuel air explosive (FAE), the explosion characteristics, flame structure and temperature distribution characteristics of epoxypropane (PO) with different types and contents of metal powders were experimentally studied using a 20 L spherical liquid explosion test system. The temperature field of explosion flame was reconstructed by the colorimetric temperature measurement method with a high-speed camera, which is based on the gray-body radiation theory and a self-written python code. The tungsten lamp was used to calibrate the measuring accuracy of the temperature mapping system, and the fitting relationship between the temperatures and the gray values of the high-speed images is derived to obtain the conversion coefficient. The experimental results show that the optimal mass concentration of pure PO was 780 g/m3, both the explosion overpressure (∆pmax) and the explosion pressure rise rate ((dp/dt)max) reached the maximum, ∆pmax=0.799 MPa and (dp/dt)max=52.438 MPa/s, respectively. The maximum explosion overpressure, maximum explosion pressure rise rate and maximum average temperature of PO added with Al, Ti and Mg powders all increase with the increase of mass ratios (I), while the trend of maximum pressure rise time is opposite. The variation rules of the maximum explosion overpressure and maximum average temperature are consistent, the order of their values is: Al/PO, Mg/PO, Ti/PO. When I=40%, the maximum explosion overpressure value of the three solid-liquid mixed fuels increases by 12.00%, 8.41% and 11.54%, respectively, compared with pure PO. In addition, the variation rules of the maximum explosion pressure rise rate and the combustion rate are consistent, the order of their values is: Al/PO, Mg/PO, Ti/PO. When I=40%, the maximum explosion pressure rise rate value of the three solid-liquid mixed fuels increases by 41.91%, 39.60% and 45.29%, respectively, compared with the pure PO. The results indicate that different high-energy metal powders have varied advantages in improving the explosion performance of PO, so metal powders should be appropriately selected as energetic additives according to the damage performance index in the formulation design of FAE.
, Available online , doi: 10.11883/bzycj-2023-0438
Abstract:
Heterogeneous media is very common in nature. Due to the complex internal structure, the heterogeneous compressive shear coupled stress field is inside heterogeneous media, which leads to the mutual influence of compression waves and shear waves. The study of wave mechanics behavior and description of heterogeneity in heterogeneous media is of great significance and full of challenges. This article established a general constitutive relationship that reflected the compression shear coupling characteristics of heterogeneous materials, proposed coupling coefficients to describe material heterogeneity, combined momentum conservation law to establish a generalized wave equation, and provided a general method for solving the generalized wave equation. As an example, expressions for the three characteristic wave velocities of compression shear coupling under the first-order compression shear coupling constitutive relationship were provided, and the finite difference method was employed to obtain the propagation process of coupled compression waves and shear waves. The effects of four heterogeneous coupling coefficients on stress state, coupled wave velocity, and wave propagation process were studied. The positive and negative values, as well as the combination of coupling parameters, reflected the structural characteristics of heterogeneous media and also determined the properties of compression shear coupling waves. For heterogeneous media with high-pressure effects, shear dilation effects, and shear weakening effects, the coupled compression wave velocity was lower than the elastic compression wave velocity corresponding to uniform media, and the coupled shear wave velocity was higher than the elastic shear wave velocity. The effect of shear on compression delayed the propagation of compressive stress, while compression promoted the propagation of shear. Coupled compression wave velocity was the result of the competition between the coupling effect of shear on compression and the volume compaction effect. Coupled shear wave velocity was the competition between the coupling effect of compression on shear and the shear weakening effect caused by continuous distortion of the medium. These mechanisms could be achieved through different combinations of compression shear coupling parameters. The true triaxial experimental testing system was used to measure the longitudinal wave velocity of granite, model materials made of mortar, and materials made of cement mortar with coarse aggregates under different compressive and shear stresses. The results indicated that for heterogeneous media, the longitudinal wave velocity decreased with the increase of static water pressure and equivalent shear stress, and the shear expansion effect and shear weakening effect dominated. The experimental results and theoretical results had the same trend. The conclusion of this study was expected to provide a physical mechanism explanation for the phenomenon of the variation of wave velocity with stress state in heterogeneous materials.
Heterogeneous media is very common in nature. Due to the complex internal structure, the heterogeneous compressive shear coupled stress field is inside heterogeneous media, which leads to the mutual influence of compression waves and shear waves. The study of wave mechanics behavior and description of heterogeneity in heterogeneous media is of great significance and full of challenges. This article established a general constitutive relationship that reflected the compression shear coupling characteristics of heterogeneous materials, proposed coupling coefficients to describe material heterogeneity, combined momentum conservation law to establish a generalized wave equation, and provided a general method for solving the generalized wave equation. As an example, expressions for the three characteristic wave velocities of compression shear coupling under the first-order compression shear coupling constitutive relationship were provided, and the finite difference method was employed to obtain the propagation process of coupled compression waves and shear waves. The effects of four heterogeneous coupling coefficients on stress state, coupled wave velocity, and wave propagation process were studied. The positive and negative values, as well as the combination of coupling parameters, reflected the structural characteristics of heterogeneous media and also determined the properties of compression shear coupling waves. For heterogeneous media with high-pressure effects, shear dilation effects, and shear weakening effects, the coupled compression wave velocity was lower than the elastic compression wave velocity corresponding to uniform media, and the coupled shear wave velocity was higher than the elastic shear wave velocity. The effect of shear on compression delayed the propagation of compressive stress, while compression promoted the propagation of shear. Coupled compression wave velocity was the result of the competition between the coupling effect of shear on compression and the volume compaction effect. Coupled shear wave velocity was the competition between the coupling effect of compression on shear and the shear weakening effect caused by continuous distortion of the medium. These mechanisms could be achieved through different combinations of compression shear coupling parameters. The true triaxial experimental testing system was used to measure the longitudinal wave velocity of granite, model materials made of mortar, and materials made of cement mortar with coarse aggregates under different compressive and shear stresses. The results indicated that for heterogeneous media, the longitudinal wave velocity decreased with the increase of static water pressure and equivalent shear stress, and the shear expansion effect and shear weakening effect dominated. The experimental results and theoretical results had the same trend. The conclusion of this study was expected to provide a physical mechanism explanation for the phenomenon of the variation of wave velocity with stress state in heterogeneous materials.
, Available online , doi: 10.11883/bzycj-2023-0252
Abstract:
A numerical simulation study is carried out on the overall battle damage circumstances of structures and the residual behavior of fragments after the typical parts of aircraft are attacked by high-speed fragments. An adaptive FEM-SPH coupling simulation method is established by using LS-DYNA software and combining the advantages of Finite Element Method (FEM) and Smoothed Particle Hydrodynamics (SPH). Using this coupling simulation method, the computational model of two typical parts of the aircraft is set up, and the accurate simulation of the core position is realized by a local refinement method of hexahedral FEM grids. Experiments were carried out to verify the numerical model. A series of high-velocity impact (HVI) battle damage simulations are carried out. The debris cloud and crater appearance formed after fragment impacting on structure at high speed under different working conditions are compared, while the residual velocity and mass of the fragment are analyzed. The critical ricochet angles of the fragment on the skin are also determined. The major conclusions are given below. The calculation results of the adaptive FEM-SPH coupling algorithm are in good agreement with the experimental results, and it can simulate fragment HVI damage effectively and precisely. The distribution shape of debris cloud becomes narrow and long with the increase of fragment incident velocity, and the incidence angle can change the shape orientation of debris cloud and crater on the structure. The variation trends of height and spread velocity of debris cloud with incident velocity or angle are basically consistent and linear. The velocity reduction of the fragment does not change with the incident velocity, and the mass reduction is positively correlated with it, both of which are negatively correlated with the incidence angle. The critical ricochet angle of fragment varies almost linearly with the incident velocity. The research results can provide a reference for the damage prediction and rapid maintenance of aircraft after air combat.
A numerical simulation study is carried out on the overall battle damage circumstances of structures and the residual behavior of fragments after the typical parts of aircraft are attacked by high-speed fragments. An adaptive FEM-SPH coupling simulation method is established by using LS-DYNA software and combining the advantages of Finite Element Method (FEM) and Smoothed Particle Hydrodynamics (SPH). Using this coupling simulation method, the computational model of two typical parts of the aircraft is set up, and the accurate simulation of the core position is realized by a local refinement method of hexahedral FEM grids. Experiments were carried out to verify the numerical model. A series of high-velocity impact (HVI) battle damage simulations are carried out. The debris cloud and crater appearance formed after fragment impacting on structure at high speed under different working conditions are compared, while the residual velocity and mass of the fragment are analyzed. The critical ricochet angles of the fragment on the skin are also determined. The major conclusions are given below. The calculation results of the adaptive FEM-SPH coupling algorithm are in good agreement with the experimental results, and it can simulate fragment HVI damage effectively and precisely. The distribution shape of debris cloud becomes narrow and long with the increase of fragment incident velocity, and the incidence angle can change the shape orientation of debris cloud and crater on the structure. The variation trends of height and spread velocity of debris cloud with incident velocity or angle are basically consistent and linear. The velocity reduction of the fragment does not change with the incident velocity, and the mass reduction is positively correlated with it, both of which are negatively correlated with the incidence angle. The critical ricochet angle of fragment varies almost linearly with the incident velocity. The research results can provide a reference for the damage prediction and rapid maintenance of aircraft after air combat.
, Available online , doi: 10.11883/bzycj-2023-0440
Abstract:
There is a lack of reliable calculation theory for the transmission and reflection pressures of shock waves at the water-soil interface. Using the mass conservation equation, momentum conservation equation, and the equations of state of water and soil, the Hugoniot relationship and p-u curve of the propagation of shock waves in water and soil medium are derived, and then the transmission and reflection pressures of the shock wave at the water-soil interface can be analyzed theoretically. Two-dimensional numerical models of the free field in water and water-soil layered medium field are established, in which the water and soil parameters are consistent with those in the three-phase medium saturated soil model used in the theoretical derivation. The calculation results show that the theoretical and numerical solutions of the water-soil interface transmission and reflection pressures are highly consistent. When using 80 g TNT explosives and exploding at 0.1–0.9 m from the water-soil interface (proportional burst distance of 0.232–2.089 m/kg1/3), the error of the theoretical and numerical solutions for transmission and reflection pressures is less than 7%, and the coefficient of the reflection pressure is in the range of 1.6–1.8 according to the analytical solution of the reflection pressure and the ratio of the incident pressure in the water. When exploding at 0.5 m from the water-soil interface and the gas content of the saturated soil varies in the range of 0–10%, the transmission and reflection pressures are 63.8–70.0 MPa, and the reflection pressure coefficients are in the range of 1.55–1.70 at this time. The calculation method for the shock wave transmission and reflection pressure at the water-soil interface has a clear physical meaning and high precision and can provide a theoretical basis for the soil damage assessment of engineering structures in submerged soil caused by underwater explosions.
There is a lack of reliable calculation theory for the transmission and reflection pressures of shock waves at the water-soil interface. Using the mass conservation equation, momentum conservation equation, and the equations of state of water and soil, the Hugoniot relationship and p-u curve of the propagation of shock waves in water and soil medium are derived, and then the transmission and reflection pressures of the shock wave at the water-soil interface can be analyzed theoretically. Two-dimensional numerical models of the free field in water and water-soil layered medium field are established, in which the water and soil parameters are consistent with those in the three-phase medium saturated soil model used in the theoretical derivation. The calculation results show that the theoretical and numerical solutions of the water-soil interface transmission and reflection pressures are highly consistent. When using 80 g TNT explosives and exploding at 0.1–0.9 m from the water-soil interface (proportional burst distance of 0.232–2.089 m/kg1/3), the error of the theoretical and numerical solutions for transmission and reflection pressures is less than 7%, and the coefficient of the reflection pressure is in the range of 1.6–1.8 according to the analytical solution of the reflection pressure and the ratio of the incident pressure in the water. When exploding at 0.5 m from the water-soil interface and the gas content of the saturated soil varies in the range of 0–10%, the transmission and reflection pressures are 63.8–70.0 MPa, and the reflection pressure coefficients are in the range of 1.55–1.70 at this time. The calculation method for the shock wave transmission and reflection pressure at the water-soil interface has a clear physical meaning and high precision and can provide a theoretical basis for the soil damage assessment of engineering structures in submerged soil caused by underwater explosions.
, Available online , doi: 10.11883/bzycj-2023-0424
Abstract:
In order to investigate the dynamic compression behavior of carbon nanotubes reinforced concrete under impact loading, the impact compression tests were carried out by using a split Hopkinson pressure bar (SHPB) test device with a diameter of 100 mm. The impact velocities in the SHPB tests were about 6.8, 7.8, 8.8, 9.8 and 10.8 m/s, respectively. The contents of carbon nanotubes in concrete (as a percentage of cement mass) were 0% (i.e. ordinary concrete, as a baseline of comparison), 0.10%, 0.20%, 0.30% and 0.40%, respectively. Then, based on the test results, the evolution laws of dynamic compressive strength, compression deformation, and energy dissipation characteristics of concrete under different impact velocities and carbon nanotubes contents were compared and analyzed. The experimental results show that the dynamic strength characteristics of carbon nanotubes reinforced concrete have significant loading rate sensitivity. The dynamic compressive strength and dynamic enhancement factor show linear positive correlations with impact velocity. When the loading level remains the same, the dynamic compressive strength increases first and then decreases slightly with the increase of carbon nanotubes content, and the growth rate can reach 23.7% compared to ordinary concrete. The variation characteristics of ultimate strain and impact toughness of carbon nanotubes reinforced concrete are similar, which gradually increase with the increase of impact velocity, and have a certain impact velocity strengthening effect, but there is no obvious linear relationship with the impact velocity. Toughness is a comprehensive reflection of material strength and deformation. Therefore, at the same loading level, when the content of carbon nanotubes was 0.30%, the impact toughness of concrete achieved a relative maximum, being about 10% higher than that of ordinary concrete. The appropriate addition of carbon nanotubes can effectively enhance the integrity and compactness of the internal structure of concrete, thereby improving its dynamic mechanical properties and energy dissipation performance.
In order to investigate the dynamic compression behavior of carbon nanotubes reinforced concrete under impact loading, the impact compression tests were carried out by using a split Hopkinson pressure bar (SHPB) test device with a diameter of 100 mm. The impact velocities in the SHPB tests were about 6.8, 7.8, 8.8, 9.8 and 10.8 m/s, respectively. The contents of carbon nanotubes in concrete (as a percentage of cement mass) were 0% (i.e. ordinary concrete, as a baseline of comparison), 0.10%, 0.20%, 0.30% and 0.40%, respectively. Then, based on the test results, the evolution laws of dynamic compressive strength, compression deformation, and energy dissipation characteristics of concrete under different impact velocities and carbon nanotubes contents were compared and analyzed. The experimental results show that the dynamic strength characteristics of carbon nanotubes reinforced concrete have significant loading rate sensitivity. The dynamic compressive strength and dynamic enhancement factor show linear positive correlations with impact velocity. When the loading level remains the same, the dynamic compressive strength increases first and then decreases slightly with the increase of carbon nanotubes content, and the growth rate can reach 23.7% compared to ordinary concrete. The variation characteristics of ultimate strain and impact toughness of carbon nanotubes reinforced concrete are similar, which gradually increase with the increase of impact velocity, and have a certain impact velocity strengthening effect, but there is no obvious linear relationship with the impact velocity. Toughness is a comprehensive reflection of material strength and deformation. Therefore, at the same loading level, when the content of carbon nanotubes was 0.30%, the impact toughness of concrete achieved a relative maximum, being about 10% higher than that of ordinary concrete. The appropriate addition of carbon nanotubes can effectively enhance the integrity and compactness of the internal structure of concrete, thereby improving its dynamic mechanical properties and energy dissipation performance.
, Available online , doi: 10.11883/bzycj-2023-0380
Abstract:
The stress-strain data obtained from split Hopkinson pressure bar (SHPB) tests include both strain rate effects and structural effects, where the structural effects result in non-uniform stress in the elastic phase of the stress-strain curve. The elastic phase is a critical focus of study for materials like concrete with low sound velocity or certain metals under high strain rate loading conditions. In this paper, we focus on one-dimensional rod systems and employ one-dimensional elastic incremental wave theory to derive analytical expressions for stress-strain curves and Young’s modulus under one-dimensional stress wave conditions with linear incident waves. We investigate the effects and mechanisms of stress difference and velocity difference at both ends of the specimen on the accuracy of stress-strain curves and Young’s modulus. Furthermore, we provide a method for determining stress-strain curves and tangent Young’s modulus during the elastic phase for arbitrary incident waveforms. We analyze the influence of the incident wave slope and shape characteristics on the stress uniformity in specimens and stress-strain curves. We establish the inherent relationship between stress uniformity and experimental stress-strain curves, and clarify the relative accuracy and applicability conditions of tangent modulus and secant modulus. The results indicate that stress uniformity is a key factor affecting the accuracy of stress-strain curves and Young’s modulus. However, the accuracy of Young’s modulus is not solely dependent on the change in stress difference at both ends of the specimen; it is also related to the factors such as the incident wave slope, shape characteristics, and the elastic segment range of the specimen. An increase in the linear wave slope leads to a greater difference between the tangent modulus and the secant modulus from the actual values. For larger slopes, the accuracy of the secant modulus is higher than that of the tangent modulus. When the incident wave shape is considered as a reference, curves with low initial slopes, such as sine waves, have higher accuracy for the tangent modulus compared to the secant modulus, whereas curves with high initial slopes show the opposite trend. For concrete specimens, we verify the influence of incident wave slope on Young’s modulus and evaluate the maximum incident wave slopes for concrete specimens to reach accurate values, which are 0.128 MPa/μs for the tangent modulus and 0.319 MPa/μs for the secant modulus.
The stress-strain data obtained from split Hopkinson pressure bar (SHPB) tests include both strain rate effects and structural effects, where the structural effects result in non-uniform stress in the elastic phase of the stress-strain curve. The elastic phase is a critical focus of study for materials like concrete with low sound velocity or certain metals under high strain rate loading conditions. In this paper, we focus on one-dimensional rod systems and employ one-dimensional elastic incremental wave theory to derive analytical expressions for stress-strain curves and Young’s modulus under one-dimensional stress wave conditions with linear incident waves. We investigate the effects and mechanisms of stress difference and velocity difference at both ends of the specimen on the accuracy of stress-strain curves and Young’s modulus. Furthermore, we provide a method for determining stress-strain curves and tangent Young’s modulus during the elastic phase for arbitrary incident waveforms. We analyze the influence of the incident wave slope and shape characteristics on the stress uniformity in specimens and stress-strain curves. We establish the inherent relationship between stress uniformity and experimental stress-strain curves, and clarify the relative accuracy and applicability conditions of tangent modulus and secant modulus. The results indicate that stress uniformity is a key factor affecting the accuracy of stress-strain curves and Young’s modulus. However, the accuracy of Young’s modulus is not solely dependent on the change in stress difference at both ends of the specimen; it is also related to the factors such as the incident wave slope, shape characteristics, and the elastic segment range of the specimen. An increase in the linear wave slope leads to a greater difference between the tangent modulus and the secant modulus from the actual values. For larger slopes, the accuracy of the secant modulus is higher than that of the tangent modulus. When the incident wave shape is considered as a reference, curves with low initial slopes, such as sine waves, have higher accuracy for the tangent modulus compared to the secant modulus, whereas curves with high initial slopes show the opposite trend. For concrete specimens, we verify the influence of incident wave slope on Young’s modulus and evaluate the maximum incident wave slopes for concrete specimens to reach accurate values, which are 0.128 MPa/μs for the tangent modulus and 0.319 MPa/μs for the secant modulus.
, Available online , doi: 10.11883/bzycj-2023-0365
Abstract:
Solid mediums, like rocks, concretes, shells and porous materials, etc., has the characteristics of microscopic discontinuity and macroscopic continuity. It is of great significance for material design, safety protection and other fields to reveal the influence of the meso-discontinuity on the dynamic response of the material. In this paper, based on the generalized Taylor’s formula under fractional definition, the governing equation of 1-D wave propagation in discontinuous medium is derived. Equivalent fractional order is introduced and the simplified form of the governing equation is presented for easily calculating. By using the finite difference method, the numerical solution of the governing equation is obtained. The influence of equivalent fractional order on wave propagation are analyzed. By the time domain analysis, the smaller the equivalent fractional order, the greater the degree of attenuation of the calculated waveform. By the frequency domain analysis, both high frequency wave and low frequency wave exhibit attenuation, and the attenuation of high frequency wave is higher than that of low frequency wave, which makes the pulse duration of the wave being larger. It is obvious that the equivalent fractional order has a certain relationship with the spatial structure of discontinuous medium. Based on the structural characteristics of some meso-discontinuous medium, e.g., porous materials and rocks, a randomly distributed pores model is established by using ABAQUS to verify the reliability of the governing equation and study the wave propagation of meso-discontinuous medium. The effects of porosity, material properties and input waves on wave propagation are analyzed. The degree of wave attenuation is positively related to the porosity of the medium, and negatively related to the wave velocity and the pulse duration of input wave. However, the equivalent fractional order is only related to the porosity and pore distribution of the discontinuous medium. When the spatial structure of the discontinuous medium remains unchanged, the corresponding equivalent fractional order does not change with the material property and the pulse duration of the input wave. By the randomly distributed pores model with various porosities, it is found that the equivalent fractional order decreases with the increase of porosity. Under the same porosity, the heterogeneity of pore distribution will result in different waveforms, while with the increase of porosity, this difference becomes more obvious, but the corresponding equivalent fractional order only has little difference. The statistical relation between equivalent fractional order and porosity is approximately linear when the pore distribution is almost the same. Compared with the randomly distributed pores medium, the statistical relation between equivalent fractional order and porosity of discontinuous medium with uniform distribution of different porosity shifts upward, indicating that the attenuation effect of random structure on wave is higher than that of uniform structure. This paper provides a new approach to investigate wave propagation in meso-discontinuous medium such as porous materials, rocks, shells, etc. It can be used as a basis to evaluate the dynamic response of discontinuous medium.
Solid mediums, like rocks, concretes, shells and porous materials, etc., has the characteristics of microscopic discontinuity and macroscopic continuity. It is of great significance for material design, safety protection and other fields to reveal the influence of the meso-discontinuity on the dynamic response of the material. In this paper, based on the generalized Taylor’s formula under fractional definition, the governing equation of 1-D wave propagation in discontinuous medium is derived. Equivalent fractional order is introduced and the simplified form of the governing equation is presented for easily calculating. By using the finite difference method, the numerical solution of the governing equation is obtained. The influence of equivalent fractional order on wave propagation are analyzed. By the time domain analysis, the smaller the equivalent fractional order, the greater the degree of attenuation of the calculated waveform. By the frequency domain analysis, both high frequency wave and low frequency wave exhibit attenuation, and the attenuation of high frequency wave is higher than that of low frequency wave, which makes the pulse duration of the wave being larger. It is obvious that the equivalent fractional order has a certain relationship with the spatial structure of discontinuous medium. Based on the structural characteristics of some meso-discontinuous medium, e.g., porous materials and rocks, a randomly distributed pores model is established by using ABAQUS to verify the reliability of the governing equation and study the wave propagation of meso-discontinuous medium. The effects of porosity, material properties and input waves on wave propagation are analyzed. The degree of wave attenuation is positively related to the porosity of the medium, and negatively related to the wave velocity and the pulse duration of input wave. However, the equivalent fractional order is only related to the porosity and pore distribution of the discontinuous medium. When the spatial structure of the discontinuous medium remains unchanged, the corresponding equivalent fractional order does not change with the material property and the pulse duration of the input wave. By the randomly distributed pores model with various porosities, it is found that the equivalent fractional order decreases with the increase of porosity. Under the same porosity, the heterogeneity of pore distribution will result in different waveforms, while with the increase of porosity, this difference becomes more obvious, but the corresponding equivalent fractional order only has little difference. The statistical relation between equivalent fractional order and porosity is approximately linear when the pore distribution is almost the same. Compared with the randomly distributed pores medium, the statistical relation between equivalent fractional order and porosity of discontinuous medium with uniform distribution of different porosity shifts upward, indicating that the attenuation effect of random structure on wave is higher than that of uniform structure. This paper provides a new approach to investigate wave propagation in meso-discontinuous medium such as porous materials, rocks, shells, etc. It can be used as a basis to evaluate the dynamic response of discontinuous medium.
