2020 Vol. 40, No. 7
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2020, 40(7): 071401.
doi: 10.11883/bzycj-2019-0403
Abstract:
Based on the generation method of layered density graded foam, new radial density graded foam models were designed by 3D-Voronoi technique, and their mechanical behavior under different impact loads was numerically simulated by finite element software. By analyzing the effects of impact velocity, density gradient and average relative density on the stress of impact end and support end, and energy absorption capacity of metal foams, it is found that the radial positive graded foam has smaller stress values at both ends than the layered positive and negative graded foams, which can simultaneously protect objects at any ends. The stress fluctuation of radial negative graded foam is small, which can ensure the stability of the force received by the object, and the energy absorption values of four metal foams vary alternately at different impact velocities. For the radial graded foam, energy absorption capacity is insensitive to density gradient, but sensitive to gradient direction. The energy absorption capacity of radial negative graded foam is always greater than radial positive graded foam. The larger the average relative density, the greater the stress at both ends, and the energy absorption effect is also enhanced.
Based on the generation method of layered density graded foam, new radial density graded foam models were designed by 3D-Voronoi technique, and their mechanical behavior under different impact loads was numerically simulated by finite element software. By analyzing the effects of impact velocity, density gradient and average relative density on the stress of impact end and support end, and energy absorption capacity of metal foams, it is found that the radial positive graded foam has smaller stress values at both ends than the layered positive and negative graded foams, which can simultaneously protect objects at any ends. The stress fluctuation of radial negative graded foam is small, which can ensure the stability of the force received by the object, and the energy absorption values of four metal foams vary alternately at different impact velocities. For the radial graded foam, energy absorption capacity is insensitive to density gradient, but sensitive to gradient direction. The energy absorption capacity of radial negative graded foam is always greater than radial positive graded foam. The larger the average relative density, the greater the stress at both ends, and the energy absorption effect is also enhanced.
2020, 40(7): 071402.
doi: 10.11883/bzycj-2019-0418
Abstract:
Dynamic response of sandwich tubes subjected to blast loading is investigated numerically. The 3D-Voronoi technology is introduced to establish three-dimensional mesoscopic finite element model of aluminum foam. The influences of the thickness of inner and outer tubes, the relative density of foam core and the core gradient on the blast resistance and energy absorption of the sandwich tubes are analyzed and compared with the double circular tubes with air core. The results show that the relative density of foam materials can be controlled by changing the size and wall thickness of cell, and the calculation results of the sandwich tube constructed by two methods are consistent. The increase of the inner tube thickness can effectively reduce the plastic deformation of outer tube and weaken the energy absorption of foam core. Foam filling is of benefit to reduce the plastic deformation of inner tube and the blast resistance of positive gradient is better than that of negative gradient and uniform core.
Dynamic response of sandwich tubes subjected to blast loading is investigated numerically. The 3D-Voronoi technology is introduced to establish three-dimensional mesoscopic finite element model of aluminum foam. The influences of the thickness of inner and outer tubes, the relative density of foam core and the core gradient on the blast resistance and energy absorption of the sandwich tubes are analyzed and compared with the double circular tubes with air core. The results show that the relative density of foam materials can be controlled by changing the size and wall thickness of cell, and the calculation results of the sandwich tube constructed by two methods are consistent. The increase of the inner tube thickness can effectively reduce the plastic deformation of outer tube and weaken the energy absorption of foam core. Foam filling is of benefit to reduce the plastic deformation of inner tube and the blast resistance of positive gradient is better than that of negative gradient and uniform core.
Impact resistance of thickness-graded arrow-shaped honeycomb pedestals with negative Poisson’s ratio
2020, 40(7): 071403.
doi: 10.11883/bzycj-2019-0414
Abstract:
An arrow-shaped honeycomb pedestal with negative Poisson’s ratio was designed. An analytical formula was derived for the mechanical properties of the cell structures, and the impact resistance of the thickness-graded arrow-shaped honeycomb materials with negative Poisson's ratio was numerically studied by the explicit dynamic finite element method. Based on the concept of functionally-graded materials, honeycomb layers with pathwise thickness gradient, inverse thickness gradient and uniform thickness were designed, by taking the thickness of the cell wall as the independent variable, the relevant model was established. The influence of thickness gradients on the impact resistance of the pedestal was discussed concretely under the premise of constant pedestal mass. The results show that, under the same gradient setting, the change of cell angle will cause the change of equivalent elastic modulus of the honeycomb structure, thus changing the impact resistance of the pedestal. When the honeycomb layer with a thinner cell wall is placed at the impact end, the stress level of the pedestal is significantly reduced. By placing a honeycomb layer with a thicker cell wall on the impact end, the output impact environment of the pedestal panel can be effectively controlled.
An arrow-shaped honeycomb pedestal with negative Poisson’s ratio was designed. An analytical formula was derived for the mechanical properties of the cell structures, and the impact resistance of the thickness-graded arrow-shaped honeycomb materials with negative Poisson's ratio was numerically studied by the explicit dynamic finite element method. Based on the concept of functionally-graded materials, honeycomb layers with pathwise thickness gradient, inverse thickness gradient and uniform thickness were designed, by taking the thickness of the cell wall as the independent variable, the relevant model was established. The influence of thickness gradients on the impact resistance of the pedestal was discussed concretely under the premise of constant pedestal mass. The results show that, under the same gradient setting, the change of cell angle will cause the change of equivalent elastic modulus of the honeycomb structure, thus changing the impact resistance of the pedestal. When the honeycomb layer with a thinner cell wall is placed at the impact end, the stress level of the pedestal is significantly reduced. By placing a honeycomb layer with a thicker cell wall on the impact end, the output impact environment of the pedestal panel can be effectively controlled.
2020, 40(7): 071404.
doi: 10.11883/bzycj-2019-0423
Abstract:
With the characteristics of light weight and high specific energy absorption, multi-cell thin-wall structures have been widely used in automobile, ship, aerospace and other fields. Previous studies have shown that the crashworthiness of a structure is closely related to its topology and cell number. In order to study the influence of the structural shape and topology optimization on energy absorption, based on regular polygon structures, two kinds of new multi-cell thin-wall structures were designed by embedding polygons in the basic structures given and circumscribing circular tubes to them, respectively. Meanwhile, quasi-static compression and drop-hammer impact tests were carried out on the two kinds of multi-cell thin-wall structures. The deformation modes of the structures were captured by high-speed cameras, and their energy absorption characteristics were studied quantitatively. The experimental results show that local instability occurred in the structures obtained by second-order embedding quadrangles into the basic regular triangle tubes in the later stage of the quasi-static loading test; the other structures were compressed vertically in the quasi-static compression and drop hammer impact tests, and their corresponding deformation modes and energy absorption capacities were excellent. By comparing the experimental results of two kinds of structures, following conclusions are drawn: the energy absorption of the polygon-embedded structures is obviously higher than that of the structures by externally circumscribing a circular tube under quasi-static loading and drop hammer impact tests; the energy absorption performance of the quadrangle-embedded structure is obviously better than that of the triangle-embedded structure with the same mass.
With the characteristics of light weight and high specific energy absorption, multi-cell thin-wall structures have been widely used in automobile, ship, aerospace and other fields. Previous studies have shown that the crashworthiness of a structure is closely related to its topology and cell number. In order to study the influence of the structural shape and topology optimization on energy absorption, based on regular polygon structures, two kinds of new multi-cell thin-wall structures were designed by embedding polygons in the basic structures given and circumscribing circular tubes to them, respectively. Meanwhile, quasi-static compression and drop-hammer impact tests were carried out on the two kinds of multi-cell thin-wall structures. The deformation modes of the structures were captured by high-speed cameras, and their energy absorption characteristics were studied quantitatively. The experimental results show that local instability occurred in the structures obtained by second-order embedding quadrangles into the basic regular triangle tubes in the later stage of the quasi-static loading test; the other structures were compressed vertically in the quasi-static compression and drop hammer impact tests, and their corresponding deformation modes and energy absorption capacities were excellent. By comparing the experimental results of two kinds of structures, following conclusions are drawn: the energy absorption of the polygon-embedded structures is obviously higher than that of the structures by externally circumscribing a circular tube under quasi-static loading and drop hammer impact tests; the energy absorption performance of the quadrangle-embedded structure is obviously better than that of the triangle-embedded structure with the same mass.
2020, 40(7): 071405.
doi: 10.11883/bzycj-2019-0355
Abstract:
By chosing PolyMaxTM PLA as the sample material, thin-walled tube structures with arc-shaped origami patterns were prepared by a three-dimensional printing technology. Based on quasi-static axial compression experiments, their axial quasi-static crushing and impact compression deformation modes and energy absorption were simulated by using the ABAQUS software to investigate the influences of the prefolding angle and the number of in-plane arrays on the crushing mode and energy absorption of the structures. The results by the finite element calculation are in agreement with the experimental ones. The deformation of the tubes can be divided into four stages including initial crushing stage, prefolding-angle plastic rotation stage, web plastic buckling stage, and complete crushing and densification stage. The arc-shaped corrugations demonstrate some obvious advantages at reducing the initial peak force and the fluctuation range of the impact force. The square tube was compared with the arc-shaped origami patterns with the same height and approximately the same mass. For the single-cell models, the specific energy absorption of the model with only 70° crease inclination is higher than that of the square tube under the quasi-static crushing. For the multiple-array tube structures, the specific energy absorption of the single-cell square tube is higher than those of the arc-shaped tubes. When considering the crush force efficiency and specific total efficiency, the arc-shaped tubes have an advantage over the square tubes, the model with a crease inclination of 50° is the best. Under the impact crushing loading condition, the specific energy absorptions of the multiple-array tubes are higher than those of the arc-shaped tubes. The crush force efficiency and specific total efficiency of the arc-shaped tubes are higher than those of the square tubes under the impact velocity of 10 m/s, the model with a crease inclination of 50° is the highest. The crush force efficiency and specific total efficiency of the model with only 50° crease inclination are higher than those of the square tube under the impact velocity of 20 m/s.
By chosing PolyMaxTM PLA as the sample material, thin-walled tube structures with arc-shaped origami patterns were prepared by a three-dimensional printing technology. Based on quasi-static axial compression experiments, their axial quasi-static crushing and impact compression deformation modes and energy absorption were simulated by using the ABAQUS software to investigate the influences of the prefolding angle and the number of in-plane arrays on the crushing mode and energy absorption of the structures. The results by the finite element calculation are in agreement with the experimental ones. The deformation of the tubes can be divided into four stages including initial crushing stage, prefolding-angle plastic rotation stage, web plastic buckling stage, and complete crushing and densification stage. The arc-shaped corrugations demonstrate some obvious advantages at reducing the initial peak force and the fluctuation range of the impact force. The square tube was compared with the arc-shaped origami patterns with the same height and approximately the same mass. For the single-cell models, the specific energy absorption of the model with only 70° crease inclination is higher than that of the square tube under the quasi-static crushing. For the multiple-array tube structures, the specific energy absorption of the single-cell square tube is higher than those of the arc-shaped tubes. When considering the crush force efficiency and specific total efficiency, the arc-shaped tubes have an advantage over the square tubes, the model with a crease inclination of 50° is the best. Under the impact crushing loading condition, the specific energy absorptions of the multiple-array tubes are higher than those of the arc-shaped tubes. The crush force efficiency and specific total efficiency of the arc-shaped tubes are higher than those of the square tubes under the impact velocity of 10 m/s, the model with a crease inclination of 50° is the highest. The crush force efficiency and specific total efficiency of the model with only 50° crease inclination are higher than those of the square tube under the impact velocity of 20 m/s.
2020, 40(7): 071406.
doi: 10.11883/bzycj-2019-0339
Abstract:
In order to improve the anti-explosion ability of steel cylinders subjected to internal blast loading, the effect of aluminum foam lining on the deformation of the steel cylinders was explored. First of all, contrast experiments displayed that under the experimental conditions in this paper, the steel cylinders deformed more greatly due to foam aluminum lining, and some were even seriously damaged. Then the finite element models were established to study the change mechanism and law of the deformation of the steel cylinders with the equivalent of explosion and the thickness of aluminum foam lining. The results show that the aluminum foam lining with enough thickness will reduce the deformation of the steel cylinders, however, if the thickness of the aluminum foam lining is insufficient, there may be an opposite effect. For the aluminum-foam lined steel cylinder with a fixed size, the effect of aluminum foam lining on the plastic deformation of the steel cylinder mainly includes three modes as the explosive equivalent increases. In mode 1, the aluminum foam will absorb explosive loading through plastic deformation, thus reducing the deformation of the steel cylinder. In mode 2, the steel cylinder endures higher load and suffers larger plastic deformation due to adding the foam aluminum lining. For mode 3, the effect of the aluminum foam on the explosive loading can be ignored, and the aluminum foam decreases the plastic deformation of the steel cylinder by increasing the total mass of the structure.
In order to improve the anti-explosion ability of steel cylinders subjected to internal blast loading, the effect of aluminum foam lining on the deformation of the steel cylinders was explored. First of all, contrast experiments displayed that under the experimental conditions in this paper, the steel cylinders deformed more greatly due to foam aluminum lining, and some were even seriously damaged. Then the finite element models were established to study the change mechanism and law of the deformation of the steel cylinders with the equivalent of explosion and the thickness of aluminum foam lining. The results show that the aluminum foam lining with enough thickness will reduce the deformation of the steel cylinders, however, if the thickness of the aluminum foam lining is insufficient, there may be an opposite effect. For the aluminum-foam lined steel cylinder with a fixed size, the effect of aluminum foam lining on the plastic deformation of the steel cylinder mainly includes three modes as the explosive equivalent increases. In mode 1, the aluminum foam will absorb explosive loading through plastic deformation, thus reducing the deformation of the steel cylinder. In mode 2, the steel cylinder endures higher load and suffers larger plastic deformation due to adding the foam aluminum lining. For mode 3, the effect of the aluminum foam on the explosive loading can be ignored, and the aluminum foam decreases the plastic deformation of the steel cylinder by increasing the total mass of the structure.
2020, 40(7): 073101.
doi: 10.11883/bzycj-2019-0377
Abstract:
Zr-based bulk metallic glass is a type of glass alloy with many excellent properties, such as high strength and high hardness. With the increasing application of Zr-based bulk metallic glass alloys in military field, it is urgent to construct the mechanical models for these materials, including equations of state and constitutive relations. The Johnson-Holmquist constitutive model (JH-2 model) is the most widely used constitutive model to describe the response of brittle materials subjected to high pressures, large strains, and high strain rates. The parameters of the JH-2 model for the Zr62.5Nb3Cu14.5Ni14Al6 bulk metallic glass alloy were determined by experimental and theoretical methods, as well as “back out” approaches from simulation data. The Hydrostatic pressure-volume strain relationship was developed by theoretical derivation from the results of plate-impact experiments. The results of axial compression tests were used to propose the relationship between the intact strength and strain, strain rate of the material. The relationship between the damage parameters and fracture strength of the material was determined by the plate-impact experiments. The plate-impact data were used to “back out” the fracture strength parameters as well. Numerical simulation results including plate impact and fragment penetration were provided to validate the accuracy and applicability of the developed model. The results show that the particle velocity curve of the freedom surface agrees well with the numerical simulation. The penetration depth and cavity radius obtained in the tests are in good agreement with the numerical simulation results, and the developed model can describe the dynamic properties of the material accurately.
Zr-based bulk metallic glass is a type of glass alloy with many excellent properties, such as high strength and high hardness. With the increasing application of Zr-based bulk metallic glass alloys in military field, it is urgent to construct the mechanical models for these materials, including equations of state and constitutive relations. The Johnson-Holmquist constitutive model (JH-2 model) is the most widely used constitutive model to describe the response of brittle materials subjected to high pressures, large strains, and high strain rates. The parameters of the JH-2 model for the Zr62.5Nb3Cu14.5Ni14Al6 bulk metallic glass alloy were determined by experimental and theoretical methods, as well as “back out” approaches from simulation data. The Hydrostatic pressure-volume strain relationship was developed by theoretical derivation from the results of plate-impact experiments. The results of axial compression tests were used to propose the relationship between the intact strength and strain, strain rate of the material. The relationship between the damage parameters and fracture strength of the material was determined by the plate-impact experiments. The plate-impact data were used to “back out” the fracture strength parameters as well. Numerical simulation results including plate impact and fragment penetration were provided to validate the accuracy and applicability of the developed model. The results show that the particle velocity curve of the freedom surface agrees well with the numerical simulation. The penetration depth and cavity radius obtained in the tests are in good agreement with the numerical simulation results, and the developed model can describe the dynamic properties of the material accurately.
2020, 40(7): 073102.
doi: 10.11883/bzycj-2019-0430
Abstract:
The deformation behavior of 8 mm and 12 mm WELDOX 700E steel, at stand-off distance 250 mm, subjected to air-blast loading by 6 kg and 10 kg spherical TNT, was investigated. The simulation model of WELDOX 700E steel subjected to air-blast loading is established using ABAQUS. The results indicate that strength is one of key factors affecting the deformation behavior of WELDOX 700E steel. High strength WELDOX 700E steel presents uniform arch deformation under spherical TNT air blast loading. The maximum dynamic displacement, permanent deflection and rebound of 8 mm WELDOX 700E steel midpoint subjected to 6 kg TNT are 144 mm, 124 mm and 21 mm, respectively. The maximum dynamic displacement, permanent deflection and rebound of 12 mm WELDOX 700E steel midpoint subjected to 10 kg TNT are 166 mm, 143 mm and 23 mm, respectively. Without considering the overall deviation of experimental setup, the simulation results can accurately reflect the deformation behavior of WELDOX 700E steel subjected to spherical TNT air blast loading. Under air-blast loading, the thickness of WELDOX 700E steel decreases significantly, accompanied by strain hardening behavior. Strain hardening behavior is the dislocation growth in martensite of WELDOX 700E steel. Compared with the edge, the dislocation density in the center of 8 mm and 12 mm WELDOX 700E steel plate increases by 80.31% and 151.76%, respectively.
The deformation behavior of 8 mm and 12 mm WELDOX 700E steel, at stand-off distance 250 mm, subjected to air-blast loading by 6 kg and 10 kg spherical TNT, was investigated. The simulation model of WELDOX 700E steel subjected to air-blast loading is established using ABAQUS. The results indicate that strength is one of key factors affecting the deformation behavior of WELDOX 700E steel. High strength WELDOX 700E steel presents uniform arch deformation under spherical TNT air blast loading. The maximum dynamic displacement, permanent deflection and rebound of 8 mm WELDOX 700E steel midpoint subjected to 6 kg TNT are 144 mm, 124 mm and 21 mm, respectively. The maximum dynamic displacement, permanent deflection and rebound of 12 mm WELDOX 700E steel midpoint subjected to 10 kg TNT are 166 mm, 143 mm and 23 mm, respectively. Without considering the overall deviation of experimental setup, the simulation results can accurately reflect the deformation behavior of WELDOX 700E steel subjected to spherical TNT air blast loading. Under air-blast loading, the thickness of WELDOX 700E steel decreases significantly, accompanied by strain hardening behavior. Strain hardening behavior is the dislocation growth in martensite of WELDOX 700E steel. Compared with the edge, the dislocation density in the center of 8 mm and 12 mm WELDOX 700E steel plate increases by 80.31% and 151.76%, respectively.
2020, 40(7): 073201.
doi: 10.11883/bzycj-2019-0401
Abstract:
To explore the interaction between dynamic and static cracks in brittle materials under impact load, polymethyl methacrylate (PMMA) was chosen as the experiment material, considering that the PMMA has good optical properties and its fracture behavior is similar to rock under dynamic load. The size of the specimens was 220 mm×50 mm×5 mm with a prefabricated crack of 5 mm in length and a static crack of 10 mm in length. The prefabricated crack was located at the center of the bottom edge of the specimen, and the center of the static crack was located at the horizontal axis of the specimen. Three-point bending experiments of different defects in PMMA had been explored by setting the static crack offset distance as the single variable with the digital laser dynamic caustic test system and the fractal law of dynamic crack at different bias distances was studied by combining with the geometric fractal theory. Researches show that when the offset distance is at a critical condition between prefabricated crack and static crack (6 mm in this experiment), the fractal dimension corresponding to the crack track is the largest, the regularity degree of the crack track is the lowest and the failure mode of the crack is the most complicated. When the offset distance is between 0 to 6 mm, crack Ⅰ propagates vertically and intersects with a distant static crack, then produces a secondary crack which penetrates the specimen after a period of stagnation, the linear function relationship between the offset distance and the vertical distance of the intersection point is then obtained. The existence of the offset distance does not affect the crack time and the stress intensity factor of crack Ⅰ, but it can significantly reduce the dynamic stress intensity factor of crack Ⅱ, the length of stagnation decreases with the increase of offset distance. When the offset distance is larger than the critical offset distance, the dynamic crack no longer intersects with the static crack, but extends to the upper edge of the specimen in an arch shape until it penetrates the specimen, and there is also a significant hysteresis in the cracking time and the position of the crack.
To explore the interaction between dynamic and static cracks in brittle materials under impact load, polymethyl methacrylate (PMMA) was chosen as the experiment material, considering that the PMMA has good optical properties and its fracture behavior is similar to rock under dynamic load. The size of the specimens was 220 mm×50 mm×5 mm with a prefabricated crack of 5 mm in length and a static crack of 10 mm in length. The prefabricated crack was located at the center of the bottom edge of the specimen, and the center of the static crack was located at the horizontal axis of the specimen. Three-point bending experiments of different defects in PMMA had been explored by setting the static crack offset distance as the single variable with the digital laser dynamic caustic test system and the fractal law of dynamic crack at different bias distances was studied by combining with the geometric fractal theory. Researches show that when the offset distance is at a critical condition between prefabricated crack and static crack (6 mm in this experiment), the fractal dimension corresponding to the crack track is the largest, the regularity degree of the crack track is the lowest and the failure mode of the crack is the most complicated. When the offset distance is between 0 to 6 mm, crack Ⅰ propagates vertically and intersects with a distant static crack, then produces a secondary crack which penetrates the specimen after a period of stagnation, the linear function relationship between the offset distance and the vertical distance of the intersection point is then obtained. The existence of the offset distance does not affect the crack time and the stress intensity factor of crack Ⅰ, but it can significantly reduce the dynamic stress intensity factor of crack Ⅱ, the length of stagnation decreases with the increase of offset distance. When the offset distance is larger than the critical offset distance, the dynamic crack no longer intersects with the static crack, but extends to the upper edge of the specimen in an arch shape until it penetrates the specimen, and there is also a significant hysteresis in the cracking time and the position of the crack.
2020, 40(7): 074201.
doi: 10.11883/bzycj-2019-0241
Abstract:
The Whipple shield is often used for protecting spacecraftfrom the impact of space debris. There are a lot of defects in the general numerical simulation methods for hypervelocity impact problems, thus this paper used OTM (optimal transportation meshfree)method to simulate the impacting process. OTM is a Lagrangian meshless method which ischaracterized by applying optimal transportation theory to discretize time, using a set of nodal-points with position information and a set of material-points with material information to discretize space,utilizing LME (local maximum entropy) approximation schemes to get interpolation functions, and simulating the failure of materials by material-point failure method related toenergy release rate. In this paper, OTM method was firstly used to simulate the impact of an aluminum ball on a single aluminum plate. The applicability of OTM method in hypervelocity impact was verified by comparing with the test results and the calculation results of other SPH methods. Then we used OTM method to simulate the hypervelocity impact of Whipple shield. The damage of the outer bumper and the spacecraft wall predicted by the OTM method was compared with the experimental results. It could be seen that the OTM method could not only predict the diameter of the bullet hole of the outer bumper, but also accurately simulate the spalling and penetration of the spacecraft wall, and the shape of the debris cloud.
The Whipple shield is often used for protecting spacecraftfrom the impact of space debris. There are a lot of defects in the general numerical simulation methods for hypervelocity impact problems, thus this paper used OTM (optimal transportation meshfree)method to simulate the impacting process. OTM is a Lagrangian meshless method which ischaracterized by applying optimal transportation theory to discretize time, using a set of nodal-points with position information and a set of material-points with material information to discretize space,utilizing LME (local maximum entropy) approximation schemes to get interpolation functions, and simulating the failure of materials by material-point failure method related toenergy release rate. In this paper, OTM method was firstly used to simulate the impact of an aluminum ball on a single aluminum plate. The applicability of OTM method in hypervelocity impact was verified by comparing with the test results and the calculation results of other SPH methods. Then we used OTM method to simulate the hypervelocity impact of Whipple shield. The damage of the outer bumper and the spacecraft wall predicted by the OTM method was compared with the experimental results. It could be seen that the OTM method could not only predict the diameter of the bullet hole of the outer bumper, but also accurately simulate the spalling and penetration of the spacecraft wall, and the shape of the debris cloud.
2020, 40(7): 075201.
doi: 10.11883/bzycj-2019-0255
Abstract:
In order to solve the safety problem in the construction of slope and underpass adjacent tunnel by cooperative blasting, based on the expansion project of a domestic petroleum reserve base, the formula of peak vibration velocity considering elevation effect was established, and the vibration energy attenuation mechanism of tunnel blasting along the slope surface was systematically studied by using method combining dimension derivation, field test and signal analysis. The results show that the peak value of particle velocity at the edge of the same step is larger than that at the foot of the inner slope, and there is an elevation amplification effect of vibration velocity on the local slope surface. The blasting vibration formula with relative slope H/D has high accuracy in predicting the particle vibration velocity on the slope, and can reflect the influence of slope angle on the elevation amplification effect of vibration velocity. The vibration velocity and energy decay faster in the near region and slower in the far region with the increase of propagation distance. The energy of tunnel blasting vibration is concentrated in several Sub-vibration frequency bands in the range of 0-300 Hz, and the high frequency energy decays faster along slope surface. The median of dominant frequency band decays exponentially, and the energy concentrates in the low frequency band eventually.
In order to solve the safety problem in the construction of slope and underpass adjacent tunnel by cooperative blasting, based on the expansion project of a domestic petroleum reserve base, the formula of peak vibration velocity considering elevation effect was established, and the vibration energy attenuation mechanism of tunnel blasting along the slope surface was systematically studied by using method combining dimension derivation, field test and signal analysis. The results show that the peak value of particle velocity at the edge of the same step is larger than that at the foot of the inner slope, and there is an elevation amplification effect of vibration velocity on the local slope surface. The blasting vibration formula with relative slope H/D has high accuracy in predicting the particle vibration velocity on the slope, and can reflect the influence of slope angle on the elevation amplification effect of vibration velocity. The vibration velocity and energy decay faster in the near region and slower in the far region with the increase of propagation distance. The energy of tunnel blasting vibration is concentrated in several Sub-vibration frequency bands in the range of 0-300 Hz, and the high frequency energy decays faster along slope surface. The median of dominant frequency band decays exponentially, and the energy concentrates in the low frequency band eventually.
2020, 40(7): 075202.
doi: 10.11883/bzycj-2019-0427
Abstract:
During blasting in deep rock masses, the rock fragmentation is contributed to the combined effects of blast loading and high in-situ stress. An analysis model based on simplifying assumptions was developed for double-hole blasting in highly-stressed rock masses, and the crack propagation and dynamic stress evolution surrounding the blastholes were studied by using the coupled SPH (smoothed particle hydrodynamics）-FEM（finite element method) method. The results show that the blast-induced rock cracking is mainly caused by the dynamic circumferential tensile stress generated from blast loading. However, in the rock masses subjected to in-situ stress, the dynamic circumferential tensile stress is reduced in magnitude and duration due to the compressive effect of the in-situ stress. Therefore, the in-situ stress plays a role in inhibiting the rock fragmentation caused by blasting. For the case of multi-hole blasting in a hydrostatic in-situ stress field, the crack propagation perpendicular to the connecting line between the adjacent holes is more easily inhibited by the in-situ stress. The length of blast-induced crack growth decreases with an increase in the in-situ stress level. With regard to a non-hydrostatic in-situ stress field, the crack propagation along the direction of the minimum principal in-situ stress is most severely suppressed, and thus the cracks grow preferentially along the maximum principal stress direction. Therefore, arranging the blastholes along the maximum principal stress direction and shortening the spacing between the blastholes will facilitate the crack connections and the formation of excavation surfaces.
During blasting in deep rock masses, the rock fragmentation is contributed to the combined effects of blast loading and high in-situ stress. An analysis model based on simplifying assumptions was developed for double-hole blasting in highly-stressed rock masses, and the crack propagation and dynamic stress evolution surrounding the blastholes were studied by using the coupled SPH (smoothed particle hydrodynamics）-FEM（finite element method) method. The results show that the blast-induced rock cracking is mainly caused by the dynamic circumferential tensile stress generated from blast loading. However, in the rock masses subjected to in-situ stress, the dynamic circumferential tensile stress is reduced in magnitude and duration due to the compressive effect of the in-situ stress. Therefore, the in-situ stress plays a role in inhibiting the rock fragmentation caused by blasting. For the case of multi-hole blasting in a hydrostatic in-situ stress field, the crack propagation perpendicular to the connecting line between the adjacent holes is more easily inhibited by the in-situ stress. The length of blast-induced crack growth decreases with an increase in the in-situ stress level. With regard to a non-hydrostatic in-situ stress field, the crack propagation along the direction of the minimum principal in-situ stress is most severely suppressed, and thus the cracks grow preferentially along the maximum principal stress direction. Therefore, arranging the blastholes along the maximum principal stress direction and shortening the spacing between the blastholes will facilitate the crack connections and the formation of excavation surfaces.
