2023 Vol. 43, No. 10
Display Method:
PDF 
Cited by
Read OL
2023, 43(10): 102201.
doi: 10.11883/bzycj-2022-0397
Abstract:
Damage elements such as high-speed explosively-formed projectiles and strong discontinuous shock waves are generated during the process of the shaped charge associated with the underwater explosion. The theory on the action time sequence of the explosively-formed projectile and the shock wave should be refined because their action time is close. Therefore, it is of great significance to investigate the action time sequence of different loads and their damage on ship structures. First, the formulations of acceleration and velocity equations are deduced in the forming process of the explosively-formed projectile, based on the contact explosion theory and Newton’s second law. Subsequently, based on the Eulerian governing equations, numerical models of air and water explosions of shaped charges are established. The evolution of pressure at the interaction of the charge and the liner is obtained. The acceleration and velocity equations of the explosively-formed projectile are presented quantitatively in this paper as a result. Besides, the obtained theoretical formulation can be utilized to solve the problem of the action time sequence of the explosively-formed projectile and direct shock wave. In order to verify the reliability of this theoretical formulation, the case in which the air cavity length is five times of the charge radius is studied. The numerical results are in general agreement with those of the theoretical derivation. The results show that when the length of the air cavity is five times of the charge radius and the stand-off distance is greater than three times of the charge radius, the shock wave precedes the explosively-formed projectile. The basic form of theoretical formulas is presented for the acceleration and velocity of the explosively-formed projectile. Moreover, the idea of solving the action time sequence problem of these two loads provides a theoretical basis for analyzing the action time sequence of underwater explosions.
Damage elements such as high-speed explosively-formed projectiles and strong discontinuous shock waves are generated during the process of the shaped charge associated with the underwater explosion. The theory on the action time sequence of the explosively-formed projectile and the shock wave should be refined because their action time is close. Therefore, it is of great significance to investigate the action time sequence of different loads and their damage on ship structures. First, the formulations of acceleration and velocity equations are deduced in the forming process of the explosively-formed projectile, based on the contact explosion theory and Newton’s second law. Subsequently, based on the Eulerian governing equations, numerical models of air and water explosions of shaped charges are established. The evolution of pressure at the interaction of the charge and the liner is obtained. The acceleration and velocity equations of the explosively-formed projectile are presented quantitatively in this paper as a result. Besides, the obtained theoretical formulation can be utilized to solve the problem of the action time sequence of the explosively-formed projectile and direct shock wave. In order to verify the reliability of this theoretical formulation, the case in which the air cavity length is five times of the charge radius is studied. The numerical results are in general agreement with those of the theoretical derivation. The results show that when the length of the air cavity is five times of the charge radius and the stand-off distance is greater than three times of the charge radius, the shock wave precedes the explosively-formed projectile. The basic form of theoretical formulas is presented for the acceleration and velocity of the explosively-formed projectile. Moreover, the idea of solving the action time sequence problem of these two loads provides a theoretical basis for analyzing the action time sequence of underwater explosions.
2023, 43(10): 102202.
doi: 10.11883/bzycj-2022-0415
Abstract:
The evaluation of failure effect on concrete under explosion is of great significance to both engineering blasting construction and anti-explosion safety of engineering structures. The key is to obtain the characteristics of failure zones of the target. Firstly, main physical processes of underwater contact explosion were analyzed. Loading characteristics of underwater contact explosion were studied with the difference between underwater contact explosion and air contact explosion compared. Then, a calculation method for range of failure zones in underwater contact explosion considering the crushing effect on target from explosion shock wave and the quasi-static effect on target from detonation products was established. The quasi-static effect was further subdivided into quasi-static compression fracturing and quasi-static tensile fracturing. Finally, the proposed method was verified with finite element numerical simulation and experimental data in literatures. The results show that the expansion of detonation products is inhibited by water compared with air contact explosion. And then the duration of explosion load and the impulse acting on the surrounding medium are increased in underwater contact explosion. Circumferential compression criterion is suggested to calculate cracked zone of concrete subjected to underwater contact explosion. And fracture zone is suggested to divide into dynamic fracturing zone, quasi-static compression fracturing zone and quasi-static tension fracturing zone for calculation. Failure range of mass concrete subjected to underwater contact explosion is well predicted by proposed calculation method. With the same explosive type and water depth, the range of fracture zone is greatly influenced by the tensile strength and compressive strength ratio of concrete. This provides a basis for both blast resistance research of engineering structures and underwater engineering blasting construction.
The evaluation of failure effect on concrete under explosion is of great significance to both engineering blasting construction and anti-explosion safety of engineering structures. The key is to obtain the characteristics of failure zones of the target. Firstly, main physical processes of underwater contact explosion were analyzed. Loading characteristics of underwater contact explosion were studied with the difference between underwater contact explosion and air contact explosion compared. Then, a calculation method for range of failure zones in underwater contact explosion considering the crushing effect on target from explosion shock wave and the quasi-static effect on target from detonation products was established. The quasi-static effect was further subdivided into quasi-static compression fracturing and quasi-static tensile fracturing. Finally, the proposed method was verified with finite element numerical simulation and experimental data in literatures. The results show that the expansion of detonation products is inhibited by water compared with air contact explosion. And then the duration of explosion load and the impulse acting on the surrounding medium are increased in underwater contact explosion. Circumferential compression criterion is suggested to calculate cracked zone of concrete subjected to underwater contact explosion. And fracture zone is suggested to divide into dynamic fracturing zone, quasi-static compression fracturing zone and quasi-static tension fracturing zone for calculation. Failure range of mass concrete subjected to underwater contact explosion is well predicted by proposed calculation method. With the same explosive type and water depth, the range of fracture zone is greatly influenced by the tensile strength and compressive strength ratio of concrete. This provides a basis for both blast resistance research of engineering structures and underwater engineering blasting construction.
2023, 43(10): 102203.
doi: 10.11883/bzycj-2022-0556
Abstract:
With the further development of ocean engineering, the dynamic response of calcareous sand sites under strong dynamic loading has received broad attention. In order to investigate the crater characteristics of calcareous sand sites under explosion impact, filed experiments and numerical simulations were conducted. Firstly, a series of field explosion experiments were conducted on calcareous sand sites, with different equivalent sizes and burial depths. The longitudinal and transverse diameter, as well as the depth of craters were measured for each case. Secondly, a new numerical algorithm (FEM-SPH) was used to simulate the formation process of explosion craters, combining the finite element model (FEM) and the smoothed particle hydrodynamics (SPH). Furthermore, the simulated crater dimensions were compared with the experimental results to validate the accuracy of the FEM-SPH model. Thanks to the advantage of the FEM-SPH in simulating large deformations, the crater formation process of ground contact explosions and buried explosions agreed well with the experimental results. The experiment research showed the crater size resulting from buried explosions is larger in calcareous sand compared to siliceous sand. The phenomenon was mainly attributed to the higher porosity and lower interparticle bonding strength of calcareous sand. With the validated FEM-SPH model, parametric analyses, including soil parameters and shapes of charges, were detailed discussed. Under the same equivalent, the influence of soil parameters on the size of the crater was about 6%, while the change in the shape of the charge caused a significant influence on the shape and size of the craters. Finally, empirical formulas were derived to determine the carter diameter and depth under cubic charge explosion according to the FEM-SPH numerical results in calcareous sand sites. The formulas can predict the dimensions of ground contact explosions and buried explosions within different equivalent charge weight ranges (0–500 kg). The above research results provided a useful reference for the blast-resistant protection design and emergency reinforcement of calcareous sand foundations.
With the further development of ocean engineering, the dynamic response of calcareous sand sites under strong dynamic loading has received broad attention. In order to investigate the crater characteristics of calcareous sand sites under explosion impact, filed experiments and numerical simulations were conducted. Firstly, a series of field explosion experiments were conducted on calcareous sand sites, with different equivalent sizes and burial depths. The longitudinal and transverse diameter, as well as the depth of craters were measured for each case. Secondly, a new numerical algorithm (FEM-SPH) was used to simulate the formation process of explosion craters, combining the finite element model (FEM) and the smoothed particle hydrodynamics (SPH). Furthermore, the simulated crater dimensions were compared with the experimental results to validate the accuracy of the FEM-SPH model. Thanks to the advantage of the FEM-SPH in simulating large deformations, the crater formation process of ground contact explosions and buried explosions agreed well with the experimental results. The experiment research showed the crater size resulting from buried explosions is larger in calcareous sand compared to siliceous sand. The phenomenon was mainly attributed to the higher porosity and lower interparticle bonding strength of calcareous sand. With the validated FEM-SPH model, parametric analyses, including soil parameters and shapes of charges, were detailed discussed. Under the same equivalent, the influence of soil parameters on the size of the crater was about 6%, while the change in the shape of the charge caused a significant influence on the shape and size of the craters. Finally, empirical formulas were derived to determine the carter diameter and depth under cubic charge explosion according to the FEM-SPH numerical results in calcareous sand sites. The formulas can predict the dimensions of ground contact explosions and buried explosions within different equivalent charge weight ranges (0–500 kg). The above research results provided a useful reference for the blast-resistant protection design and emergency reinforcement of calcareous sand foundations.
2023, 43(10): 103101.
doi: 10.11883/bzycj-2022-0335
Abstract:
FRP-concrete-steel double skin tubular columns (FRP-DSTCs) consist of an outer FRP tube and an inner steel tube, with the space between them infilled by concrete. This type of members has been applied in bridge piers, and the impact resistance is an important index for its utilization. Therefore, based on the previous test, the finite element analysis (FEA) models considering the coupling of axial and impact loads are established using ABAQUS software and verified by comparing the simulation and test results. In the model, the static implicit and dynamic explicit analysis are coupled by using Restart and Import commands. In addition, the strain rate effect of the steel and concrete are considered. Firstly, the mechanism of impact resistance under coupling axial and impact loads is analyzed. Then, the influence of thickness and fiber orientations of FRP, axial-load ratio, impact velocity, hollow ratio, diameter-to-thickness ratio of the steel tube and material strengths on the impact resistance are investigated. Finally, the formula used to predict the dynamic increase factor of the plateau impact force under coupling axial and impact loads is suggested. Results indicate that the deformation pattern of FRP-DSTCs mainly presents flexural deformation, and the plastic deformation of concrete is the main energy dissipation mechanism of such members. The outer FRP can significantly improve the lateral impact resistance of the specimen, and increasing the number of FRP layers leads to enhanced impact resistance. In addition, the axial load has an obvious effect on the impact resistance, and the effect is negative when the axial load ratio exceeds 0.7. The diameter-to-thickness ratio of steel tube presents marginal effects on the impact resistance. The proposed formula that considers the hollow ratio, strengths of concrete and inner steel tube, thickness of FRP, axial load ratio and impact velocity can reasonably predict the impact bearing capacity of FRP-DSTCs.
FRP-concrete-steel double skin tubular columns (FRP-DSTCs) consist of an outer FRP tube and an inner steel tube, with the space between them infilled by concrete. This type of members has been applied in bridge piers, and the impact resistance is an important index for its utilization. Therefore, based on the previous test, the finite element analysis (FEA) models considering the coupling of axial and impact loads are established using ABAQUS software and verified by comparing the simulation and test results. In the model, the static implicit and dynamic explicit analysis are coupled by using Restart and Import commands. In addition, the strain rate effect of the steel and concrete are considered. Firstly, the mechanism of impact resistance under coupling axial and impact loads is analyzed. Then, the influence of thickness and fiber orientations of FRP, axial-load ratio, impact velocity, hollow ratio, diameter-to-thickness ratio of the steel tube and material strengths on the impact resistance are investigated. Finally, the formula used to predict the dynamic increase factor of the plateau impact force under coupling axial and impact loads is suggested. Results indicate that the deformation pattern of FRP-DSTCs mainly presents flexural deformation, and the plastic deformation of concrete is the main energy dissipation mechanism of such members. The outer FRP can significantly improve the lateral impact resistance of the specimen, and increasing the number of FRP layers leads to enhanced impact resistance. In addition, the axial load has an obvious effect on the impact resistance, and the effect is negative when the axial load ratio exceeds 0.7. The diameter-to-thickness ratio of steel tube presents marginal effects on the impact resistance. The proposed formula that considers the hollow ratio, strengths of concrete and inner steel tube, thickness of FRP, axial load ratio and impact velocity can reasonably predict the impact bearing capacity of FRP-DSTCs.
2023, 43(10): 103102.
doi: 10.11883/bzycj-2023-0065
Abstract:
The identification of stress threshold for crack propagation of rock under compressive loading is an important issue for understanding the progressive damage process and analyzing the macroscopic damage mechanism of rocks. In order to accurately identify the stress threshold of brittle hard rock under quasi-static and dynamic compressive loads, uniaxial and dynamic compression tests were carried out for three kinds of rock specimens (including marble, coarse granite and fine granite) by using an INSTRON 1346 and a split Hopkinson pressure bar (SHPB) system. Two deformation parameters were introduced in the paper, including crack axial strain and crack radial area strain. According to the slope difference of the crack radial area strain curves at the failure point, the three kinds of rocks were classified into type Ⅰ (marble) and type Ⅱ (coarse granite and fine granite) rocks. The testing results indicate that the crack axial strain curves and crack axial strain stiffness curves can be used to accurately identify the crack stability propagation stress σsd, crack instability propagation stress σusd and the crack connectivity stress σct under quasi-static compressive loading for type Ⅰ and type Ⅱ rocks respectively. It is proved that the stress thresholds of type Ⅰ and type Ⅱ rocks can be identified only by using the axial strain data. The method based on crack axial strain is extended to identify the stress threshold of rock under dynamic impact loading. It solves the problem to identify the stress threshold of rock specimens under dynamic compressive loading. Different from the stress threshold of rock under quasi static loading, it is found that the ratio of the crack stability propagation stress to the peak strength of the rock decreases under dynamic loading. The crack instability propagation stress and the crack connectivity stress coincide with each other, and the ratio to the peak strength also decreases. When the specimen is failed under dynamic loading, it usually generates more penetrating cracks and more fragments than that under quasi-static loading.
The identification of stress threshold for crack propagation of rock under compressive loading is an important issue for understanding the progressive damage process and analyzing the macroscopic damage mechanism of rocks. In order to accurately identify the stress threshold of brittle hard rock under quasi-static and dynamic compressive loads, uniaxial and dynamic compression tests were carried out for three kinds of rock specimens (including marble, coarse granite and fine granite) by using an INSTRON 1346 and a split Hopkinson pressure bar (SHPB) system. Two deformation parameters were introduced in the paper, including crack axial strain and crack radial area strain. According to the slope difference of the crack radial area strain curves at the failure point, the three kinds of rocks were classified into type Ⅰ (marble) and type Ⅱ (coarse granite and fine granite) rocks. The testing results indicate that the crack axial strain curves and crack axial strain stiffness curves can be used to accurately identify the crack stability propagation stress σsd, crack instability propagation stress σusd and the crack connectivity stress σct under quasi-static compressive loading for type Ⅰ and type Ⅱ rocks respectively. It is proved that the stress thresholds of type Ⅰ and type Ⅱ rocks can be identified only by using the axial strain data. The method based on crack axial strain is extended to identify the stress threshold of rock under dynamic impact loading. It solves the problem to identify the stress threshold of rock specimens under dynamic compressive loading. Different from the stress threshold of rock under quasi static loading, it is found that the ratio of the crack stability propagation stress to the peak strength of the rock decreases under dynamic loading. The crack instability propagation stress and the crack connectivity stress coincide with each other, and the ratio to the peak strength also decreases. When the specimen is failed under dynamic loading, it usually generates more penetrating cracks and more fragments than that under quasi-static loading.
2023, 43(10): 103103.
doi: 10.11883/bzycj-2022-0199
Abstract:
Transparent sandwich structures can combine the advantages of various materials, thus avoiding secondary damage caused by brittle material fragments. Therefore, they are widely used in various impact protection fields. However, the impact resistance of the structure is influenced by different material thicknesses in a complex manner, and there is a lack of quick and convenient design guidance. Artificial neural network has good applicability to the nonlinear problems of multi-material structures, and provides a novel approach to structural design. In this study, a transparent sandwich structure consisting of sapphire (Al2O3) ceramic as the impact-absorbing layer, silica inorganic glass, polycarbonate plexiglass as the energy absorption layers, and polyurethane as the bonding material was selected as the research subject. Impact experiments were conducted on samples using a first-stage light-gas gun. Two failure modes were observed in the samples: ceramic layer bending failure and impact compression failure. The dynamic crack propagation process was meticulously captured using high-speed cameras. Subsequently, Abaqus finite element software was employed to simulate projectile impact on transparent sandwich structures with varying layers thickness ratios at 120, 150, and 180 m/s. For ceramic materials, a subroutine based on the JH-2 constitutive model was introduced. The numerical simulation of crack propagation and debris splashing process was performed using the element deletion method. The simulation results exhibited good agreement with the experimental results. Finally, the BP neural network algorithm was utilized to predict peak displacement behind the impact point. The average calculation time for single-layer and multi-layer neural network models was 1 minute and 3 minutes, respectively. Compared with the numerical simulation results of displacement peak, the average relative error of the predicted results of the two neural network models was 7.6% and 3.2%, respectively. The BP neural network model fulfills the requirement for calculation time and accuracy, saving a substantial amount of time compared to the traditional 5-hour finite element calculations. It can provide valuable guidance for the design and development of transparent sandwich structures.
Transparent sandwich structures can combine the advantages of various materials, thus avoiding secondary damage caused by brittle material fragments. Therefore, they are widely used in various impact protection fields. However, the impact resistance of the structure is influenced by different material thicknesses in a complex manner, and there is a lack of quick and convenient design guidance. Artificial neural network has good applicability to the nonlinear problems of multi-material structures, and provides a novel approach to structural design. In this study, a transparent sandwich structure consisting of sapphire (Al2O3) ceramic as the impact-absorbing layer, silica inorganic glass, polycarbonate plexiglass as the energy absorption layers, and polyurethane as the bonding material was selected as the research subject. Impact experiments were conducted on samples using a first-stage light-gas gun. Two failure modes were observed in the samples: ceramic layer bending failure and impact compression failure. The dynamic crack propagation process was meticulously captured using high-speed cameras. Subsequently, Abaqus finite element software was employed to simulate projectile impact on transparent sandwich structures with varying layers thickness ratios at 120, 150, and 180 m/s. For ceramic materials, a subroutine based on the JH-2 constitutive model was introduced. The numerical simulation of crack propagation and debris splashing process was performed using the element deletion method. The simulation results exhibited good agreement with the experimental results. Finally, the BP neural network algorithm was utilized to predict peak displacement behind the impact point. The average calculation time for single-layer and multi-layer neural network models was 1 minute and 3 minutes, respectively. Compared with the numerical simulation results of displacement peak, the average relative error of the predicted results of the two neural network models was 7.6% and 3.2%, respectively. The BP neural network model fulfills the requirement for calculation time and accuracy, saving a substantial amount of time compared to the traditional 5-hour finite element calculations. It can provide valuable guidance for the design and development of transparent sandwich structures.
2023, 43(10): 103105.
doi: 10.11883/bzycj-2022-0486
Abstract:
Under irradiation conditions, a large number of micro-defects such as helium bubbles are produced in some materials, and the size and number density of helium bubbles increase with the increase of irradiation years. The variation of helium bubble distribution not only affects the physical and mechanical properties of the material itself, but also directly affects the distribution characteristics of fracture particle size in the later stage of spallation damage evolution. The evolution process of spallation damage in ductile materials generally includes nucleation, growth and confluence of pores. However, due to the inhibition of existing pores on new nucleation pores, when the initial number density of pores reaches a certain critical value, the calculation of spallation damage may not consider the influence of new nucleation. Based on the characteristics of early damage evolution, a formula for calculating this critical value is given, and based on this formula, the calculation method of spallation damage of plutonium materials irradiated by helium bubbles is further discussed. Then, in view of the difference between the initial damage parameters of the damage model and the real initial damage of the material, we propose a method to determine the damage parameters in the void growth (VG) model. Finally, this problem is analyzed qualitatively by using the experimental results of spallation of conventional aluminum materials containing helium bubbles. The analysis results show that for the calculation of spallation damage of irradiated materials containing helium bubbles, only when the helium bubble size changes little and the helium bubble concentration is lower than the critical helium bubble concentration given in this paper, it is necessary to consider the comprehensive influence of initial helium bubbles and new holes. otherwise, a simple spallation damage model can be adopted, and the nucleation of holes does not need to be calculated.
Under irradiation conditions, a large number of micro-defects such as helium bubbles are produced in some materials, and the size and number density of helium bubbles increase with the increase of irradiation years. The variation of helium bubble distribution not only affects the physical and mechanical properties of the material itself, but also directly affects the distribution characteristics of fracture particle size in the later stage of spallation damage evolution. The evolution process of spallation damage in ductile materials generally includes nucleation, growth and confluence of pores. However, due to the inhibition of existing pores on new nucleation pores, when the initial number density of pores reaches a certain critical value, the calculation of spallation damage may not consider the influence of new nucleation. Based on the characteristics of early damage evolution, a formula for calculating this critical value is given, and based on this formula, the calculation method of spallation damage of plutonium materials irradiated by helium bubbles is further discussed. Then, in view of the difference between the initial damage parameters of the damage model and the real initial damage of the material, we propose a method to determine the damage parameters in the void growth (VG) model. Finally, this problem is analyzed qualitatively by using the experimental results of spallation of conventional aluminum materials containing helium bubbles. The analysis results show that for the calculation of spallation damage of irradiated materials containing helium bubbles, only when the helium bubble size changes little and the helium bubble concentration is lower than the critical helium bubble concentration given in this paper, it is necessary to consider the comprehensive influence of initial helium bubbles and new holes. otherwise, a simple spallation damage model can be adopted, and the nucleation of holes does not need to be calculated.
2023, 43(10): 103304.
doi: 10.11883/bzycj-2023-0143
Abstract:
Based on high-speed photography technology, an experiment study on water-entry of oblique projectile constrained by ice hole was conducted. Digital image processing technology was employed to extract the experimental data. The water-entry process of oblique projectile was analyzed under both ice-free and ice hole constraint environment, and the water-entry process is divided into three stages: cavity expansion stage, cavity closure stage and cavity collapse stage. Additionally, a series water-entry experiments were also conducted with different initial velocities of projectiles under the same ice hole constraint, allowing for the establishment of a relationship between initial velocity and ice hole constraint. Results show that during the cavity expansion stage, the free surface under the ice-hole constraint does not form a bulge, and the splashing on the water-away side of the projectile is suppressed by the ice hole and is more dispersed. The ice-hole constraint leads to the obstruction of cavity expansion and the appearance of bending on the left side of the cavity near the free surface, the maximum diameter of cavity decreases. In the cavity closure stage, the closure time of the cavity is advanced under the constraint of the ice hole. The reflected flow impacts the right side of cavity wall, which causes the pinch-off and local collapse of the cavity. During the cavity collapse stage, under the constraint of ice hole, the wake of cavity collapse consists of local impact collapse, pinch-off cavity collapse and normal cavity collapse, and the wake vortex generated by the collapse is small. As the initial velocity increases, the length and maximum diameter of the cavity significantly increase, and the width of local impact collapse also increases. Furthermore, the ice hole constraint makes the projectile velocity decay faster during the cavity expansion stage, advances the closure time of the cavity, and delays the collapse time of the cavity.
Based on high-speed photography technology, an experiment study on water-entry of oblique projectile constrained by ice hole was conducted. Digital image processing technology was employed to extract the experimental data. The water-entry process of oblique projectile was analyzed under both ice-free and ice hole constraint environment, and the water-entry process is divided into three stages: cavity expansion stage, cavity closure stage and cavity collapse stage. Additionally, a series water-entry experiments were also conducted with different initial velocities of projectiles under the same ice hole constraint, allowing for the establishment of a relationship between initial velocity and ice hole constraint. Results show that during the cavity expansion stage, the free surface under the ice-hole constraint does not form a bulge, and the splashing on the water-away side of the projectile is suppressed by the ice hole and is more dispersed. The ice-hole constraint leads to the obstruction of cavity expansion and the appearance of bending on the left side of the cavity near the free surface, the maximum diameter of cavity decreases. In the cavity closure stage, the closure time of the cavity is advanced under the constraint of the ice hole. The reflected flow impacts the right side of cavity wall, which causes the pinch-off and local collapse of the cavity. During the cavity collapse stage, under the constraint of ice hole, the wake of cavity collapse consists of local impact collapse, pinch-off cavity collapse and normal cavity collapse, and the wake vortex generated by the collapse is small. As the initial velocity increases, the length and maximum diameter of the cavity significantly increase, and the width of local impact collapse also increases. Furthermore, the ice hole constraint makes the projectile velocity decay faster during the cavity expansion stage, advances the closure time of the cavity, and delays the collapse time of the cavity.
2023, 43(10): 104201.
doi: 10.11883/bzycj-2023-0127
Abstract:
The research on generation and properties of materials under ultra-high pressure and density constitutes an important part of the extreme physics and hence a field of modern frontier science, especially the magnetically-driven high-energy-density physics herein is meaningful and in great need by core technologies. High pulsed power devices with tens-megampere output current and thousands-Tesla magnetic field were developed in past decades, e.g., the Z machine capable of 30 MA and 100 TW on load at the Sandia National Laboratories, USA; also a record intense magnetic field of 2800 T achieved with a cascade magneto-cumulative generator of MC-1 type at VNIIEF, Russia. It is available now to compress heavy metals up to 1 TPa or to launch thin Al flyer plates to super high speed over 45 km/s using isentropic compression experiments on the Z machine. Although these experiments take various forms, they have intrinsic unity in physics, which is based on the conservation laws of mechanics and the macroscopic electromagnetic theory. Therefore, it is feasible and necessary to establish a unified numerical simulation platform and determine the mechanical motion of the load configuration and its coupling with various physical fields under extreme experimental conditions by relying on the load current data (or the real data of the drive circuit). The magneto-hydrodynamics multi-physics codes have been successfully developed in USA, e.g., the excellent performance codes—ALEGRA series at the Sandia National Laboratories. This paper substantively extends the one-dimensional Lagrangian code SSS, which has been extensively validated by shock, detonation and laser radiation effect simulations, into a magneto-hydrodynamics multi-physics one and now it is renamed as SSS-MHD. The simulation results of various high-energy-density dynamic experiments with typical significance, such as planar quasi-isentropic ramp wave compression, ultra-high speed solid flyer launch, solid liner implosion, and explosively-driven magnetic flux compression, indicate that their relative deviations of the SSS-MHD simulations from the experimental data of America’s Z machine, China’s CQ and CJ series devices, and ALEGRA-1D/2D calculations are generally less than 5%. The SSS-MHD code turns into a powerful platform to simulate experiments of extreme material dynamics (including gases, liquids, metals and compounds) and its practice could be helpful to develop advanced multi-dimensional MHD multi-physics codes.
The research on generation and properties of materials under ultra-high pressure and density constitutes an important part of the extreme physics and hence a field of modern frontier science, especially the magnetically-driven high-energy-density physics herein is meaningful and in great need by core technologies. High pulsed power devices with tens-megampere output current and thousands-Tesla magnetic field were developed in past decades, e.g., the Z machine capable of 30 MA and 100 TW on load at the Sandia National Laboratories, USA; also a record intense magnetic field of 2800 T achieved with a cascade magneto-cumulative generator of MC-1 type at VNIIEF, Russia. It is available now to compress heavy metals up to 1 TPa or to launch thin Al flyer plates to super high speed over 45 km/s using isentropic compression experiments on the Z machine. Although these experiments take various forms, they have intrinsic unity in physics, which is based on the conservation laws of mechanics and the macroscopic electromagnetic theory. Therefore, it is feasible and necessary to establish a unified numerical simulation platform and determine the mechanical motion of the load configuration and its coupling with various physical fields under extreme experimental conditions by relying on the load current data (or the real data of the drive circuit). The magneto-hydrodynamics multi-physics codes have been successfully developed in USA, e.g., the excellent performance codes—ALEGRA series at the Sandia National Laboratories. This paper substantively extends the one-dimensional Lagrangian code SSS, which has been extensively validated by shock, detonation and laser radiation effect simulations, into a magneto-hydrodynamics multi-physics one and now it is renamed as SSS-MHD. The simulation results of various high-energy-density dynamic experiments with typical significance, such as planar quasi-isentropic ramp wave compression, ultra-high speed solid flyer launch, solid liner implosion, and explosively-driven magnetic flux compression, indicate that their relative deviations of the SSS-MHD simulations from the experimental data of America’s Z machine, China’s CQ and CJ series devices, and ALEGRA-1D/2D calculations are generally less than 5%. The SSS-MHD code turns into a powerful platform to simulate experiments of extreme material dynamics (including gases, liquids, metals and compounds) and its practice could be helpful to develop advanced multi-dimensional MHD multi-physics codes.
2023, 43(10): 104202.
doi: 10.11883/bzycj-2023-0030
Abstract:
The Chapman-Jouguet theory is a powerful tool to predict the states of physical quantities at the rear of the shock front. However, uncertain factors and their influences on the system response quantities are neglected in the model of previous studies. Actually, the reliability and predictability of numerical simulation will be greatly affected by these uncertainties. To begin with, uncertainties of modeling and simulation of detonation process is discussed based on the detonation mechanism. Initial density and detonation velocity of PBX-9502 are assumed to satisfy the logarithmic normal distribution. The probability density functions (PDFs) of initial density and detonation velocity are derived from Anderson-Darling hypothesis test and parameter estimation combined with real experimental data. Beta distribution is utilized to cope with empirical parameters which have no physical meaning at all, with shaping parameters and supporting set are given according to the engineer’s experience. Rosenblatt transformation is used to transform the dependent and non-Gaussian random variables into independent standard Gaussian random variables. Furthermore, nonintrusive polynomial chaos (PC) method is used to study high dimensional uncertainty propagation of detonation waves. In particular, as for one variable PC, orthogonal polynomials are derived through Gram-Schmidt algorithm in Gauss-Hilbert space, Gauss integral formula with six quadrature points is used to compute coefficients of PC. Full tensor product of quadratures and weights is applied in PC of multivariate. PDF and corresponding Gaussian statistics such as expectation, standard deviation and confidence interval of quantity of interest (QoI) are obtained from the multivariate polynomial chaos. The result shows that the variation of detonation pressure is larger and the range of confidential interval is wider. It coincides with Professor Chengwei Sun’s conclusion that “The discreteness of detonation pressure is larger in experimental measurement”. The experimental data falls into the confidential interval of QoIs, then the reliability and robustness of the modeling is enhanced. And the methodology can be extended to the detonation system with much more complex equation of state.
The Chapman-Jouguet theory is a powerful tool to predict the states of physical quantities at the rear of the shock front. However, uncertain factors and their influences on the system response quantities are neglected in the model of previous studies. Actually, the reliability and predictability of numerical simulation will be greatly affected by these uncertainties. To begin with, uncertainties of modeling and simulation of detonation process is discussed based on the detonation mechanism. Initial density and detonation velocity of PBX-9502 are assumed to satisfy the logarithmic normal distribution. The probability density functions (PDFs) of initial density and detonation velocity are derived from Anderson-Darling hypothesis test and parameter estimation combined with real experimental data. Beta distribution is utilized to cope with empirical parameters which have no physical meaning at all, with shaping parameters and supporting set are given according to the engineer’s experience. Rosenblatt transformation is used to transform the dependent and non-Gaussian random variables into independent standard Gaussian random variables. Furthermore, nonintrusive polynomial chaos (PC) method is used to study high dimensional uncertainty propagation of detonation waves. In particular, as for one variable PC, orthogonal polynomials are derived through Gram-Schmidt algorithm in Gauss-Hilbert space, Gauss integral formula with six quadrature points is used to compute coefficients of PC. Full tensor product of quadratures and weights is applied in PC of multivariate. PDF and corresponding Gaussian statistics such as expectation, standard deviation and confidence interval of quantity of interest (QoI) are obtained from the multivariate polynomial chaos. The result shows that the variation of detonation pressure is larger and the range of confidential interval is wider. It coincides with Professor Chengwei Sun’s conclusion that “The discreteness of detonation pressure is larger in experimental measurement”. The experimental data falls into the confidential interval of QoIs, then the reliability and robustness of the modeling is enhanced. And the methodology can be extended to the detonation system with much more complex equation of state.
2023, 43(10): 105101.
doi: 10.11883/bzycj-2022-0375
Abstract:
In view of the hot problem of reducing the harm of explosive terrorist attacks in public security field, the research on explosion-proof structures is urgent. Polyurethane foam has the advantages of being lightweight, has excellent mechanical properties, and can avoid secondary debris damage. It has a good application prospect in the new explosive disposal equipment. Based on the research background of explosion hazard reduction, the mechanism and effectiveness of shock wave weakening of polyurethane foam and polyurethane-based composite barriers need to be investigated. The microstructure and mechanical properties of porous polyurethane were tested firstly. It was to obtain the basic parameters and contribute to construct the simulation model of the samples with different densities (100-300 kg/m3). A directional flow field device was set up to impact the polyurethane plate and the feasibility of the corresponding numerical model was analyzed to study its protective performance against the plane shock wave. On this basis, the weakening effect of the polyurethane-water annular composite barrier under internal explosive loading was analyzed numerically by using the verified numerical model. The design premise was that the total volume of barriers was equal, and the shockwave weakening performances of PU/water, pure water and water/PU barriers were compared. The influence of polyurethane density on shock wave weakening performance was analyzed. The results show that the existence of a barrier forces the shock wave to reflect, diffract, transmit and interact with each other. Compared with a pure water barrier, the PU/water barrier can effectively reduce shock wave peak (up to 13.3%) when the total mass decreases by 32%. This is mainly because of the lower impedance of the inner polyurethane foam, which can reduce the strength of the shock wave reflected back from the barrier wall. Under current simulation conditions, it is more effective for the protection of corresponding barrier when the density of PU is 200 kg/m3 in the PU/water barrier.
In view of the hot problem of reducing the harm of explosive terrorist attacks in public security field, the research on explosion-proof structures is urgent. Polyurethane foam has the advantages of being lightweight, has excellent mechanical properties, and can avoid secondary debris damage. It has a good application prospect in the new explosive disposal equipment. Based on the research background of explosion hazard reduction, the mechanism and effectiveness of shock wave weakening of polyurethane foam and polyurethane-based composite barriers need to be investigated. The microstructure and mechanical properties of porous polyurethane were tested firstly. It was to obtain the basic parameters and contribute to construct the simulation model of the samples with different densities (100-300 kg/m3). A directional flow field device was set up to impact the polyurethane plate and the feasibility of the corresponding numerical model was analyzed to study its protective performance against the plane shock wave. On this basis, the weakening effect of the polyurethane-water annular composite barrier under internal explosive loading was analyzed numerically by using the verified numerical model. The design premise was that the total volume of barriers was equal, and the shockwave weakening performances of PU/water, pure water and water/PU barriers were compared. The influence of polyurethane density on shock wave weakening performance was analyzed. The results show that the existence of a barrier forces the shock wave to reflect, diffract, transmit and interact with each other. Compared with a pure water barrier, the PU/water barrier can effectively reduce shock wave peak (up to 13.3%) when the total mass decreases by 32%. This is mainly because of the lower impedance of the inner polyurethane foam, which can reduce the strength of the shock wave reflected back from the barrier wall. Under current simulation conditions, it is more effective for the protection of corresponding barrier when the density of PU is 200 kg/m3 in the PU/water barrier.
2023, 43(10): 105201.
doi: 10.11883/bzycj-2023-0151
Abstract:
The technique of drilling and blasting is widely applied in rock excavation, and its working efficiency mainly relies on the rock mass structure and geological conditions. The initial stress plays a crucial role in the blast-induced cracking behavior and failure characteristics, and troubles such as over/underbreak and insufficient fragmentation may be arisen in deep rock masses, leading to other issues related to the waste of mineral resources and production costs. In this paper, the damage features and fracture mechanism of rock blasting under various initial stresses were studied using combined theoretical analysis and numerical simulation. Considering the effect of initial stress on the mechanical response of rock blasting, a theoretical model for single-hole blasting was developed based on elastic mechanics, and then the features of static stress distribution and dynamic pressure evolution were analyzed separately, revealing the fracture mechanism of rock blast-induced damage under initial stress. In addition, the Riedel-Hiermaier-Thoma (RHT) model parameters of rock were determined and adjusted based on a series of empirical formulas as well as dynamic mechanical tests. After calibrating the numerical model against the blasting crack pattern and attenuation of peak pressure by combining test and theoretical results, the single-hole geometric model was created and meshed in the commercial software ANSYS to study the dynamic tangential stress evolution as well as cracking behavior, and the fractal features of rock blasting cracks under different initial stresses were also discussed. The results show that the rationality of the theoretical model can be proved by the numerical simulation: the tangential tensile stress is a critical factor affecting the blasting crack propagation and the rock fragmentation can be improved by adjusting the distribution of hoop stress reasonably when the initial stress is large. In practical engineering, the stress distribution can be changed by controlling the field of geo-stress with presplitting technology.
The technique of drilling and blasting is widely applied in rock excavation, and its working efficiency mainly relies on the rock mass structure and geological conditions. The initial stress plays a crucial role in the blast-induced cracking behavior and failure characteristics, and troubles such as over/underbreak and insufficient fragmentation may be arisen in deep rock masses, leading to other issues related to the waste of mineral resources and production costs. In this paper, the damage features and fracture mechanism of rock blasting under various initial stresses were studied using combined theoretical analysis and numerical simulation. Considering the effect of initial stress on the mechanical response of rock blasting, a theoretical model for single-hole blasting was developed based on elastic mechanics, and then the features of static stress distribution and dynamic pressure evolution were analyzed separately, revealing the fracture mechanism of rock blast-induced damage under initial stress. In addition, the Riedel-Hiermaier-Thoma (RHT) model parameters of rock were determined and adjusted based on a series of empirical formulas as well as dynamic mechanical tests. After calibrating the numerical model against the blasting crack pattern and attenuation of peak pressure by combining test and theoretical results, the single-hole geometric model was created and meshed in the commercial software ANSYS to study the dynamic tangential stress evolution as well as cracking behavior, and the fractal features of rock blasting cracks under different initial stresses were also discussed. The results show that the rationality of the theoretical model can be proved by the numerical simulation: the tangential tensile stress is a critical factor affecting the blasting crack propagation and the rock fragmentation can be improved by adjusting the distribution of hoop stress reasonably when the initial stress is large. In practical engineering, the stress distribution can be changed by controlling the field of geo-stress with presplitting technology.
2023, 43(10): 105401.
doi: 10.11883/bzycj-2023-0108
Abstract:
To examine the mitigation characterisitics of blast wave in water mist, a comprehensive series of blast experiments were carried out utilizing a blast-driven shock tube with a 4 m length and 180 mm square inner cross-section. The blast wave was generated by detonating trinitrotoluene charges with masses of 7, 10 and 13 g within the shock tube. Five pressure gauges were installed to measure blast wave pressure within the spray region. In order to create varying water mist properties, a spray system was employed, which covered a distance of 3 m within the experimental setup. Droplet size and distribution were measured using a laser light scattering analyzer. The mitigation effect of water mist with two distinct properties on blast overpressure and impulse was evaluated. Results indicated that the pressure in the spray region raised in two stages. The first stage corresponded to the pressure associated with the transmitted shock wave, while the second stage was attributed to the secondary atomization and relaxation processes of the droplets. The longer the spray region traversed by the blast wave, the greater the mitigation effect on peak overpressure and impulse. Increased shock wave intensity diminished the mitigation effect of water mist on blast loads. Specifically, when water mist with a Sauter mean diameter of 136.04 μm and a volume fraction of 1.72×10−3 was employed, peak pressure values experienced a reduction ranging from 34.2% to 60.9%, while impulse values were reduced by 9% to 54%. On the other hand, when water mist with a Sauter mean diameter of 255.34 μm and a volume fraction of 3.43×10−3 was used, peak pressure values witnessed a reduction ranging from 48.4% to 78.6%, and impulse values were reduced by 14% to 66%. The mitigation coefficient of peak overpressure decreased linearly with increased scaled exchange surface area between blast wave and droplets.
To examine the mitigation characterisitics of blast wave in water mist, a comprehensive series of blast experiments were carried out utilizing a blast-driven shock tube with a 4 m length and 180 mm square inner cross-section. The blast wave was generated by detonating trinitrotoluene charges with masses of 7, 10 and 13 g within the shock tube. Five pressure gauges were installed to measure blast wave pressure within the spray region. In order to create varying water mist properties, a spray system was employed, which covered a distance of 3 m within the experimental setup. Droplet size and distribution were measured using a laser light scattering analyzer. The mitigation effect of water mist with two distinct properties on blast overpressure and impulse was evaluated. Results indicated that the pressure in the spray region raised in two stages. The first stage corresponded to the pressure associated with the transmitted shock wave, while the second stage was attributed to the secondary atomization and relaxation processes of the droplets. The longer the spray region traversed by the blast wave, the greater the mitigation effect on peak overpressure and impulse. Increased shock wave intensity diminished the mitigation effect of water mist on blast loads. Specifically, when water mist with a Sauter mean diameter of 136.04 μm and a volume fraction of 1.72×10−3 was employed, peak pressure values experienced a reduction ranging from 34.2% to 60.9%, while impulse values were reduced by 9% to 54%. On the other hand, when water mist with a Sauter mean diameter of 255.34 μm and a volume fraction of 3.43×10−3 was used, peak pressure values witnessed a reduction ranging from 48.4% to 78.6%, and impulse values were reduced by 14% to 66%. The mitigation coefficient of peak overpressure decreased linearly with increased scaled exchange surface area between blast wave and droplets.
2023, 43(10): 105402.
doi: 10.11883/bzycj-2022-0562
Abstract:
To investigate the synergistic effect of N2 and combined porous media to suppress gas explosion, the experiments were carried out in an independently designed explosion pipe. The nitrogen curtain was 0.9 m away from the ignition location. The combined porous media used in the experiments consist of a combination of iron-nickel foam with pore densities of 10, 20, 30 and 40 ppi, as well as a combination of iron-nickel foam with 10 ppi and copper foam with 20 and 40 ppi. The results show that nitrogen curtains cause intact flames to propagate forward in a fragmented manner, diluting the concentration of combustible gases upstream of the porous medium and slowing down the flame propagation speed. The porous medium, on the other hand, effectively absorbs the precursor shock wave and disrupts the positive feedback mechanism, leading to further weakening of the flame propagation speed towards the porous medium and enhancing the quenching performance of the medium. The porous media with high pore density as the second layer of the combined porous media, can block the nitrogen from escaping upstream of the porous media, significantly reducing the concentration of combustible gases upstream, the flame propagation speed then decreases rapidly, and the slowed down flame is more easily quenched by the combined porous media. When the pore density of the second layer increases, the first overpressure peak remains largely unchanged, while the second overpressure peak rises sharply, which increases the risk of explosion. The combination of iron-nickel foam in the first layer and copper foam in the second layer significantly reduces the intensity of the flame when it reaches the porous media and lowers the overpressure peak, while the high strength of iron-nickel foam in front of the copper foam prevents the low strength copper foam from deforming and causing quenching failure. The combination with the best explosion suppression effect is the pore density 10 ppi of iron-nickel foam metal and 40 ppi of copper foam to form a combination of porous media.
To investigate the synergistic effect of N2 and combined porous media to suppress gas explosion, the experiments were carried out in an independently designed explosion pipe. The nitrogen curtain was 0.9 m away from the ignition location. The combined porous media used in the experiments consist of a combination of iron-nickel foam with pore densities of 10, 20, 30 and 40 ppi, as well as a combination of iron-nickel foam with 10 ppi and copper foam with 20 and 40 ppi. The results show that nitrogen curtains cause intact flames to propagate forward in a fragmented manner, diluting the concentration of combustible gases upstream of the porous medium and slowing down the flame propagation speed. The porous medium, on the other hand, effectively absorbs the precursor shock wave and disrupts the positive feedback mechanism, leading to further weakening of the flame propagation speed towards the porous medium and enhancing the quenching performance of the medium. The porous media with high pore density as the second layer of the combined porous media, can block the nitrogen from escaping upstream of the porous media, significantly reducing the concentration of combustible gases upstream, the flame propagation speed then decreases rapidly, and the slowed down flame is more easily quenched by the combined porous media. When the pore density of the second layer increases, the first overpressure peak remains largely unchanged, while the second overpressure peak rises sharply, which increases the risk of explosion. The combination of iron-nickel foam in the first layer and copper foam in the second layer significantly reduces the intensity of the flame when it reaches the porous media and lowers the overpressure peak, while the high strength of iron-nickel foam in front of the copper foam prevents the low strength copper foam from deforming and causing quenching failure. The combination with the best explosion suppression effect is the pore density 10 ppi of iron-nickel foam metal and 40 ppi of copper foam to form a combination of porous media.
