2018 Vol. 38, No. 4
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2018, 38(4): 707-715.
doi: 10.11883/bzycj-2016-0329
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Abstract:
In this study we fabricated four kinds of unpoled PZT95/5 ferroelectric ceramics in a range of different porosity levels by systematic additions of pore formers and investigated the high strain rate response of the unpoled PZT95/5 using the ultra-high speed camera and digital image correlation (DIC) technique to measure the full-field strain in a split Hopkinson pressure bar (SHPB) test. Based on the results of the full-field strain, we found that the strain distribution is uniform in the middle of the specimen and its average value as the strain of the specimen is more reasonable than the strain calculated from the traditional theory of SHPB. By using the pulse shaping technique to obtain an early constant strain rate, the effect of the lateral inertia confinement can be eliminated. The apparent dynamic compressive strength enhancement of the unpoled PZT95/5 in a SHPB test was observed to be strain-rate sensitive. Based on the variation of the axial strain and radial strain with axial stress, we attributed the nonlinear deformation mechanism of the unpoled PZT95/5 to the domain switching and phase transformation. The critical stresses for the domain switching and phase transformation increased with the strain rate. In addition, we discussed the influence of porosity in the high strain-rate response, and the results indicated that the dynamic compressive strength and the critical stresses for the domain switching and phase transformation of the unpoled PZT95/5 decreased with the increase of porosity.
In this study we fabricated four kinds of unpoled PZT95/5 ferroelectric ceramics in a range of different porosity levels by systematic additions of pore formers and investigated the high strain rate response of the unpoled PZT95/5 using the ultra-high speed camera and digital image correlation (DIC) technique to measure the full-field strain in a split Hopkinson pressure bar (SHPB) test. Based on the results of the full-field strain, we found that the strain distribution is uniform in the middle of the specimen and its average value as the strain of the specimen is more reasonable than the strain calculated from the traditional theory of SHPB. By using the pulse shaping technique to obtain an early constant strain rate, the effect of the lateral inertia confinement can be eliminated. The apparent dynamic compressive strength enhancement of the unpoled PZT95/5 in a SHPB test was observed to be strain-rate sensitive. Based on the variation of the axial strain and radial strain with axial stress, we attributed the nonlinear deformation mechanism of the unpoled PZT95/5 to the domain switching and phase transformation. The critical stresses for the domain switching and phase transformation increased with the strain rate. In addition, we discussed the influence of porosity in the high strain-rate response, and the results indicated that the dynamic compressive strength and the critical stresses for the domain switching and phase transformation of the unpoled PZT95/5 decreased with the increase of porosity.
2018, 38(4): 716-724.
doi: 10.11883/bzycj-2017-0383
Abstract:
The rockburst process was reproduced using a true-triaixal rockburst test system in laboratory. The sound signal in the rockburst process was recorded and preprocessed, and the feature indexes of the sound signals in three typical failures in the rockburst process, including rock particles ejection, rock splitting, and rock plate ejection, were investigated. The results show that the feature indexes in the three typical failures such as the waveform, the spectrum, the sound print and the short-term energy exhibit significant differences from each other. Finally, an indicator called total energy of local sound (TELS) was proposed as applicable to assessing the rockburst intensity.
The rockburst process was reproduced using a true-triaixal rockburst test system in laboratory. The sound signal in the rockburst process was recorded and preprocessed, and the feature indexes of the sound signals in three typical failures in the rockburst process, including rock particles ejection, rock splitting, and rock plate ejection, were investigated. The results show that the feature indexes in the three typical failures such as the waveform, the spectrum, the sound print and the short-term energy exhibit significant differences from each other. Finally, an indicator called total energy of local sound (TELS) was proposed as applicable to assessing the rockburst intensity.
2018, 38(4): 725-734.
doi: 10.11883/bzycj-2016-0283
Abstract:
The coupled smoothed particle hydrodynamics-finite element method (SPH-FEM) has been gradually introduced in some researches about the impact dynamics due to its combined advantages of the two algorithms, but the early research focused mostly on simple structures of single material and the results obtained were not applicable in actual engineering. Based on the work previously done, we developed a coupled SPH-FEM method using a damage model of the composite, built a three-dimensional numerical model for the composite skin aircraft structure and studied its impact dynamic characteristics under explosion loading. The comparison of the numerical with experimental results verified the model and algorithm both as valid and accurate, thereby realizing the actual engineering application of the coupled SPH-FEM method. Furthermore, we also analyzed and summarized the dynamic response mechanism of the composite skin aircraft structure under shock loading. Our study can serve as references for the structural design and protection of the aerospace craft.
The coupled smoothed particle hydrodynamics-finite element method (SPH-FEM) has been gradually introduced in some researches about the impact dynamics due to its combined advantages of the two algorithms, but the early research focused mostly on simple structures of single material and the results obtained were not applicable in actual engineering. Based on the work previously done, we developed a coupled SPH-FEM method using a damage model of the composite, built a three-dimensional numerical model for the composite skin aircraft structure and studied its impact dynamic characteristics under explosion loading. The comparison of the numerical with experimental results verified the model and algorithm both as valid and accurate, thereby realizing the actual engineering application of the coupled SPH-FEM method. Furthermore, we also analyzed and summarized the dynamic response mechanism of the composite skin aircraft structure under shock loading. Our study can serve as references for the structural design and protection of the aerospace craft.
2018, 38(4): 735-742.
doi: 10.11883/bzycj-2016-0340
Abstract:
In this study we firstly calculated the parameters of equation of state (EOS) for ideal gas considering temperature and relative humidity to obtain the calculation models for parameters of the blasting shock wave in ambient temperature and humidity. Then, we established the spherical charge model using the SPEED software to simulate the blasting processes in typical air conditions. The results show that the temperature and relative humidity have little influence on the shock wave overpressure, and that both the positive phase duration and the impulse, which are 21.8% and 18.4% smaller in high temperature and humidity than those in the cold and dry air, respectively, decrease linearly with the increase of the temperature and relative humidity. Furthermore, based on classical engineering calculation models, we established the calculation models for the shock wave parameters in spherical charge blasting considering ambient temperature and humidity by introducing correction factors such as temperature, relative humidity and scaled distance. From these models we obtained the blasting shock wave parameters with different doses of spherical TNT. The parameters were found quite consistent with those from numerical simulation, thereby suggesting that the calculation models can serve as reference for power assessment in real environments.
In this study we firstly calculated the parameters of equation of state (EOS) for ideal gas considering temperature and relative humidity to obtain the calculation models for parameters of the blasting shock wave in ambient temperature and humidity. Then, we established the spherical charge model using the SPEED software to simulate the blasting processes in typical air conditions. The results show that the temperature and relative humidity have little influence on the shock wave overpressure, and that both the positive phase duration and the impulse, which are 21.8% and 18.4% smaller in high temperature and humidity than those in the cold and dry air, respectively, decrease linearly with the increase of the temperature and relative humidity. Furthermore, based on classical engineering calculation models, we established the calculation models for the shock wave parameters in spherical charge blasting considering ambient temperature and humidity by introducing correction factors such as temperature, relative humidity and scaled distance. From these models we obtained the blasting shock wave parameters with different doses of spherical TNT. The parameters were found quite consistent with those from numerical simulation, thereby suggesting that the calculation models can serve as reference for power assessment in real environments.
2018, 38(4): 743-748.
doi: 10.11883/bzycj-2016-0330
Abstract:
In this study we performed experiment on JBO-9021, a new kind of high insensitive explosive, in which the mass fractions of TATB, HMX and binder are 80%, 15% and 5%, respectively, under strong shock and achieved its particle velocity histories using laser interferometry and a high-speed scanning camera. We derived the initial shock pressures at different positions in the wedge-shaped test explosive from the particle velocity histories that were measured by laser interferometry and the Hugoniot curve of the unreacted JBO-9021 explosive. According to the run distance to detonation obtained by a streak camera and the locations of the pins, we investigated the Pop relationship of this high insensitive explosive as a function of the initial shock pressure and the run distance to detonation, and demonstrated that JBO-9021's shock initiation performance is superior to that of the TATB based explosive PBX9502 and the HMX based explosive PBX9501.
In this study we performed experiment on JBO-9021, a new kind of high insensitive explosive, in which the mass fractions of TATB, HMX and binder are 80%, 15% and 5%, respectively, under strong shock and achieved its particle velocity histories using laser interferometry and a high-speed scanning camera. We derived the initial shock pressures at different positions in the wedge-shaped test explosive from the particle velocity histories that were measured by laser interferometry and the Hugoniot curve of the unreacted JBO-9021 explosive. According to the run distance to detonation obtained by a streak camera and the locations of the pins, we investigated the Pop relationship of this high insensitive explosive as a function of the initial shock pressure and the run distance to detonation, and demonstrated that JBO-9021's shock initiation performance is superior to that of the TATB based explosive PBX9502 and the HMX based explosive PBX9501.
2018, 38(4): 749-758.
doi: 10.11883/bzycj-2016-0389
Abstract:
Dynamic expansion crack freezing recovery tests of 6061 aluminum alloy thin-walled cylindrical tubes with different roughnesses after surface processing were carried out with the split Hopkinson pressure bar experimental technique, and the crack initiation, propagation and final fracture mode of the thin-walled metal cylindrical tubes of dynamic expansion fracture process were studied. The results show that: under the same impact pressure, the greater the surface roughness of the thin-walled metal cylindrical tube, the more prone to the expansion of the material in the process of expanding fracture; the crack initiating on the surface of the outer wall is extended from the outside to the inside, and the crack propagation is mainly affected by the stress state at the crack; the fracture mode is dominated by the tensile and shear fracture mechanism, the fracture mode is a mixed type of tension and shear fracture.
Dynamic expansion crack freezing recovery tests of 6061 aluminum alloy thin-walled cylindrical tubes with different roughnesses after surface processing were carried out with the split Hopkinson pressure bar experimental technique, and the crack initiation, propagation and final fracture mode of the thin-walled metal cylindrical tubes of dynamic expansion fracture process were studied. The results show that: under the same impact pressure, the greater the surface roughness of the thin-walled metal cylindrical tube, the more prone to the expansion of the material in the process of expanding fracture; the crack initiating on the surface of the outer wall is extended from the outside to the inside, and the crack propagation is mainly affected by the stress state at the crack; the fracture mode is dominated by the tensile and shear fracture mechanism, the fracture mode is a mixed type of tension and shear fracture.
2018, 38(4): 759-767.
doi: 10.11883/bzycj-2016-0349
Abstract:
In this study, we set up a finite element model for a carbon fiber reinforced polymer (CFRP)-concrete-steel composite structure under low-velocity impact load using ABAQUS. The analytic results from our model were found to agree well with the test results, thus capable of being used to simulate the mechanical performance of the structure. Using this model, we analyzed all the stages of the dynamic response of the specimen under lateral impact load, and investigated the effects of seven factors, such as impact height and hollow ratio, on the peak value and the platform value of the impact force and the mid-span residual deflection, using orthogonal analysis. We found that the impact height (impact energy) is the main factor influencing the peak value of the impact force; the residual deflection is affected by the interaction of the main factors including the impact height, the hollow ratio, the number of CFRP layers and the direction of CFRP; the main factor of the platform value of the impact force is the hollow ratio, and the anti-impact performance of the specimen gradually increases with the increase of the hollow ratio ranging from 0.3 to 0.7.
In this study, we set up a finite element model for a carbon fiber reinforced polymer (CFRP)-concrete-steel composite structure under low-velocity impact load using ABAQUS. The analytic results from our model were found to agree well with the test results, thus capable of being used to simulate the mechanical performance of the structure. Using this model, we analyzed all the stages of the dynamic response of the specimen under lateral impact load, and investigated the effects of seven factors, such as impact height and hollow ratio, on the peak value and the platform value of the impact force and the mid-span residual deflection, using orthogonal analysis. We found that the impact height (impact energy) is the main factor influencing the peak value of the impact force; the residual deflection is affected by the interaction of the main factors including the impact height, the hollow ratio, the number of CFRP layers and the direction of CFRP; the main factor of the platform value of the impact force is the hollow ratio, and the anti-impact performance of the specimen gradually increases with the increase of the hollow ratio ranging from 0.3 to 0.7.
2018, 38(4): 768-776.
doi: 10.11883/bzycj-2016-0334
Abstract:
As a major technique for rock breakage, the drill and blast method brings about serious blasting vibration that poses hazards for the structural stability of the shaft wall. In this paper, we simulated the interactive process of the blasting seismic wave and the semi-ellipse-shaped shaft wall using the finite-element numerical software ANSYS/LS-DYNA3D and taking the peak particle velocity (PPV) and the effective tensile stress as the evaluation indexes of the dynamic response. The calculated results indicate that for the shaft walls with different excavation depths there exist similar patterns governing the dynamic response to different maximum charges, and both the peak effective tensile stress and PPV are located at the top arch, whose intensities decrease along with the decrease of the maximum charge. Based on the tensile strength principle and the linear relationship between the peak effective tensile stress and PPV, we established the critical blasting vibration safety criterion as 8 cm/s under the present engineering conditions for this project, and conducted on-site tests which verified the validity of the pre-set criterion.
As a major technique for rock breakage, the drill and blast method brings about serious blasting vibration that poses hazards for the structural stability of the shaft wall. In this paper, we simulated the interactive process of the blasting seismic wave and the semi-ellipse-shaped shaft wall using the finite-element numerical software ANSYS/LS-DYNA3D and taking the peak particle velocity (PPV) and the effective tensile stress as the evaluation indexes of the dynamic response. The calculated results indicate that for the shaft walls with different excavation depths there exist similar patterns governing the dynamic response to different maximum charges, and both the peak effective tensile stress and PPV are located at the top arch, whose intensities decrease along with the decrease of the maximum charge. Based on the tensile strength principle and the linear relationship between the peak effective tensile stress and PPV, we established the critical blasting vibration safety criterion as 8 cm/s under the present engineering conditions for this project, and conducted on-site tests which verified the validity of the pre-set criterion.
2018, 38(4): 777-784.
doi: 10.11883/bzycj-2016-0395
Abstract:
For a better characterization of the correlation between the rotating detonation combustion chamber and the turbine, the characteristics of the rotating detonation outlet's flow field with equivalent hydrogen-air mixture were investigated numerically based on two-dimensional compressible Euler equations. The mean value of the outlet's total pressure pulse, distortion index and temperature distribution factor were analyzed in connection with different axial lengths and radiuses of the combustion. The results show that the value of the outlet's total pressure fluctuates periodically when the rotating detonation combustion remains in a steady state. The size of the combustor has significant influence on the homogeneity of the outlet's flow field. With the increase of the axial length or the decrease of the circumferential dimension of the combustion, the mean value of the outlet's total pressure pulsation, the distortion index and the outlet temperature distribution coefficient all decrease, whereas the homogeneity of the outlet's flow field increases. In addition, the height of the detonation wave gets bigger as does the circumferential size but the axial length has little effect on the height of the detonation wave.
For a better characterization of the correlation between the rotating detonation combustion chamber and the turbine, the characteristics of the rotating detonation outlet's flow field with equivalent hydrogen-air mixture were investigated numerically based on two-dimensional compressible Euler equations. The mean value of the outlet's total pressure pulse, distortion index and temperature distribution factor were analyzed in connection with different axial lengths and radiuses of the combustion. The results show that the value of the outlet's total pressure fluctuates periodically when the rotating detonation combustion remains in a steady state. The size of the combustor has significant influence on the homogeneity of the outlet's flow field. With the increase of the axial length or the decrease of the circumferential dimension of the combustion, the mean value of the outlet's total pressure pulsation, the distortion index and the outlet temperature distribution coefficient all decrease, whereas the homogeneity of the outlet's flow field increases. In addition, the height of the detonation wave gets bigger as does the circumferential size but the axial length has little effect on the height of the detonation wave.
2018, 38(4): 785-794.
doi: 10.11883/bzycj-2016-0383
Abstract:
In order to obtain the dynamic response of the pre-cracked tunnel under impact loads, we investigated the crack propagation characteristics in the tunnel using the green sandstone as the model material of the tunnel, and the self-developed adjustable speed-drop hammer impact tester that can realize low- and medium-impact loading speed as the loading device. We determined the crack's initiation time, propagation velocity and arrest time, using a measuring system consisting of a crack propagation gauge and a strain gauge, and successfully obtained the crack's initiation toughness, propagation toughness and arrest toughness using the finite element software AUTODYN and ABAQUS based on the test data. The results showed that crack arrest occurred in the process of crack propagation; and that the experimental-numerical method can be successfully used to calculate the crack initiation toughness, propagation toughness and arrest toughness. Further, we conducted a preliminary analysis of crack arrest, and examined the influence of internal stress reflection wave and transmission wave on crack arrest.
In order to obtain the dynamic response of the pre-cracked tunnel under impact loads, we investigated the crack propagation characteristics in the tunnel using the green sandstone as the model material of the tunnel, and the self-developed adjustable speed-drop hammer impact tester that can realize low- and medium-impact loading speed as the loading device. We determined the crack's initiation time, propagation velocity and arrest time, using a measuring system consisting of a crack propagation gauge and a strain gauge, and successfully obtained the crack's initiation toughness, propagation toughness and arrest toughness using the finite element software AUTODYN and ABAQUS based on the test data. The results showed that crack arrest occurred in the process of crack propagation; and that the experimental-numerical method can be successfully used to calculate the crack initiation toughness, propagation toughness and arrest toughness. Further, we conducted a preliminary analysis of crack arrest, and examined the influence of internal stress reflection wave and transmission wave on crack arrest.
2018, 38(4): 795-803.
doi: 10.11883/bzycj-2016-0359
Abstract:
To obtain the optimal pre-splitting hole spacing in a retained gob-side entry formed by roof cutting and pressure releasing, we investigated the directional pre-splitting of the roadway roof under bilateral cumulative tensile explosion using the LS-DYNA software and field test. The numerical results showed that the effective tension stress was generated after the stress wave superposition when the hole spacing was 400 mm; that when the hole spacing was 500 mm, the effective tension stress was also higher than the tensile strength of the hole wall rock, thus forming the cracks in the hole wall rock along the direction of cumulative energy and expanding the cracks between the adjacent holes; and that when the hole spacing was 600 mm, the cracks between the adjacent holes failed to form because the hole spacing was too large to generate the effective tension stress. The field tests showed that continuous cracks were formed from the hole bottom to porthole in the blasting-free holes when the hole spacing was 400 or 500 mm and the crack length reached 2.4 m, forming a continuous cutting surface and effectively restraining the displacement of roof and floor and the roof pressure along the roadway in the gob-side entry. Out study concluded that the interval blasting with a 500 mm hole spacing was the optimal design in the three tests under different hole-spacing conditions.
To obtain the optimal pre-splitting hole spacing in a retained gob-side entry formed by roof cutting and pressure releasing, we investigated the directional pre-splitting of the roadway roof under bilateral cumulative tensile explosion using the LS-DYNA software and field test. The numerical results showed that the effective tension stress was generated after the stress wave superposition when the hole spacing was 400 mm; that when the hole spacing was 500 mm, the effective tension stress was also higher than the tensile strength of the hole wall rock, thus forming the cracks in the hole wall rock along the direction of cumulative energy and expanding the cracks between the adjacent holes; and that when the hole spacing was 600 mm, the cracks between the adjacent holes failed to form because the hole spacing was too large to generate the effective tension stress. The field tests showed that continuous cracks were formed from the hole bottom to porthole in the blasting-free holes when the hole spacing was 400 or 500 mm and the crack length reached 2.4 m, forming a continuous cutting surface and effectively restraining the displacement of roof and floor and the roof pressure along the roadway in the gob-side entry. Out study concluded that the interval blasting with a 500 mm hole spacing was the optimal design in the three tests under different hole-spacing conditions.
2018, 38(4): 804-810.
doi: 10.11883/bzycj-2016-0333
Abstract:
In this paper, we studied the quasi-static performance and the dynamic compression and tensile properties of the Q235 steel at temperatures ranging from the room temperature to 900 ℃ using a universal testing machine and the split Hopkinson bar system. Based on the experimental results, we modified the thermal softening item in the Johnson-Cook (J-C) constitutive model and proposed a revised J-C constitutive model for Q235 steel, which we then validated using Taylor impact experiments and corresponding numerical simulations.
In this paper, we studied the quasi-static performance and the dynamic compression and tensile properties of the Q235 steel at temperatures ranging from the room temperature to 900 ℃ using a universal testing machine and the split Hopkinson bar system. Based on the experimental results, we modified the thermal softening item in the Johnson-Cook (J-C) constitutive model and proposed a revised J-C constitutive model for Q235 steel, which we then validated using Taylor impact experiments and corresponding numerical simulations.
2018, 38(4): 811-819.
doi: 10.11883/bzycj-2016-0337
Abstract:
To investigate the calculation method and the characteristics of the impact load for a large commercial aircraft impacting a nuclear power plant, we developed an integral test measurement system using the experiments of aircraft models impacting a movable steel-reinforced concrete target via a rocket sled loading test platform, and carried out two impact tests on two aircraft models of different sizes. In the two tests, the flying attitude and velocity of the aircraft models and the whole impact process were recorded using a high-speed photography system, and the acceleration and velocity time histories of the target were obtained using an acceleration measurement system and a displacement interferometer system for any reflector (DISAR), respectively. The computed results of the impact loads calculated by the measured acceleration and velocity data, respectively, were found to agree well, verifying the reliability of the measurement system. Moreover, we obtained the acceleration time histories of the aircraft models using the onboard overload storage, and calculated the crushing load of the aircraft model based on the measured data. On the other hand, we also calculated the impact load time histories using the modified Riera equation. Compared the impact load history calculated from the measured acceleration data of the aircraft model with that calculated from the measured acceleration data of the target, the modified Riera model was verified and the coefficient α was determined.
To investigate the calculation method and the characteristics of the impact load for a large commercial aircraft impacting a nuclear power plant, we developed an integral test measurement system using the experiments of aircraft models impacting a movable steel-reinforced concrete target via a rocket sled loading test platform, and carried out two impact tests on two aircraft models of different sizes. In the two tests, the flying attitude and velocity of the aircraft models and the whole impact process were recorded using a high-speed photography system, and the acceleration and velocity time histories of the target were obtained using an acceleration measurement system and a displacement interferometer system for any reflector (DISAR), respectively. The computed results of the impact loads calculated by the measured acceleration and velocity data, respectively, were found to agree well, verifying the reliability of the measurement system. Moreover, we obtained the acceleration time histories of the aircraft models using the onboard overload storage, and calculated the crushing load of the aircraft model based on the measured data. On the other hand, we also calculated the impact load time histories using the modified Riera equation. Compared the impact load history calculated from the measured acceleration data of the aircraft model with that calculated from the measured acceleration data of the target, the modified Riera model was verified and the coefficient α was determined.
2018, 38(4): 820-826.
doi: 10.11883/bzycj-2016-0354
Abstract:
The thin-wall obstruction block structure plays a significant role in energy absorbing guardrail systems. Research on the methods to improve the guardrail protection capability and minimize the passenger injury becomes increasingly more important. In this paper, using the commercial finite element software ABAQUS, we investigated the response of the single-span multi-grid obstruction block guardrail systems with three different wall thicknesses crashed by a mass block. The simulation results prove that the two-grid obstruction block with a gauge of 2 mm exhibits the best final internal energy mass ratio and energy absorbing density. In addition, the resultant acceleration peak of the 2 mm two-grid model is about 47.6% smaller than that of the 3 mm one-grid model, indicating a better passenger safety performance. According to the Wayne state tolerance curve (WSTC), the deceleration of a human's head is within the safety range for simulation cases. This study provides design guidelines for enhancing a guardrail system's impact resistant ability and safety grade.
The thin-wall obstruction block structure plays a significant role in energy absorbing guardrail systems. Research on the methods to improve the guardrail protection capability and minimize the passenger injury becomes increasingly more important. In this paper, using the commercial finite element software ABAQUS, we investigated the response of the single-span multi-grid obstruction block guardrail systems with three different wall thicknesses crashed by a mass block. The simulation results prove that the two-grid obstruction block with a gauge of 2 mm exhibits the best final internal energy mass ratio and energy absorbing density. In addition, the resultant acceleration peak of the 2 mm two-grid model is about 47.6% smaller than that of the 3 mm one-grid model, indicating a better passenger safety performance. According to the Wayne state tolerance curve (WSTC), the deceleration of a human's head is within the safety range for simulation cases. This study provides design guidelines for enhancing a guardrail system's impact resistant ability and safety grade.
2018, 38(4): 827-833.
doi: 10.11883/bzycj-2017-0173
Abstract:
In this study, using a split Hopkinson pressure bar (SHPB) system, we conducted the impact tests of sandstone at different impact velocities to collect the characteristics of the strain rate effect and obtained the typical dynamic constitutive curve of sandstone. The curve can be divided into an approximately linear elastic stage, a plastic stage, a plastic enhancement stage and a forward unloading stage. We constructed the dynamic damage constitutive model of sandstone adopting the combination model, and utilized the user subroutine UMAT interface of LS-DYNA to achieve the secondary development of the constitutive model, which was then used to simulate the SHPB dynamic impact compression tests of sandstone at four impact rates of 7.5, 9.5, 11.5 and 13.5 m/s. The calculation results showed that the as-constructed model gave a good description of the effect of the strain rate and the elastic stage of the stress-strain curve of sandstone. Moreover, the dynamic peak strength and maximum strain were in good agreement with the test results, and the relative errors of the strain rate, peak strength, maximum strain were less than 10%, thus indicating that the as-constructed dynamic constitutive model can accurately describe the dynamic mechanical properties of sandstone under impact.
In this study, using a split Hopkinson pressure bar (SHPB) system, we conducted the impact tests of sandstone at different impact velocities to collect the characteristics of the strain rate effect and obtained the typical dynamic constitutive curve of sandstone. The curve can be divided into an approximately linear elastic stage, a plastic stage, a plastic enhancement stage and a forward unloading stage. We constructed the dynamic damage constitutive model of sandstone adopting the combination model, and utilized the user subroutine UMAT interface of LS-DYNA to achieve the secondary development of the constitutive model, which was then used to simulate the SHPB dynamic impact compression tests of sandstone at four impact rates of 7.5, 9.5, 11.5 and 13.5 m/s. The calculation results showed that the as-constructed model gave a good description of the effect of the strain rate and the elastic stage of the stress-strain curve of sandstone. Moreover, the dynamic peak strength and maximum strain were in good agreement with the test results, and the relative errors of the strain rate, peak strength, maximum strain were less than 10%, thus indicating that the as-constructed dynamic constitutive model can accurately describe the dynamic mechanical properties of sandstone under impact.
2018, 38(4): 834-840.
doi: 10.11883/bzycj-2016-0387
Abstract:
Mechanical tests of high-nitrogen austenitic stainless steel (HNS) were performed at strain rates of 102-103 s-1 generated by a split Hopkinson bar apparatus and under different temperatures from 293 K to 873 K. The influences of strain rate and temperature on the plastic flow stress of HNS were analyzed by comparing the dynamic tests with quasi-static tests. The results show that the dynamic mechanical behavior of HNS is significantly sensitive to strain rate and temperature; the flow stress increases rapidly when strain rate exceeds 400 s-1; and at the same strain rate, the flow stress increases as temperature decreases. The coupling effect of strain rate and temperature on the plastic deformation behavior of HNS was investigated. The results indicate that the thermal softening effect plays a key role in the dynamic plastic deformation process of HNS. Based on the classical Johnson-Cook constitutive model, a modified Johnson-Cook constitutive model was given which can describe the dynamic mechanical behavior of HNS properly.
Mechanical tests of high-nitrogen austenitic stainless steel (HNS) were performed at strain rates of 102-103 s-1 generated by a split Hopkinson bar apparatus and under different temperatures from 293 K to 873 K. The influences of strain rate and temperature on the plastic flow stress of HNS were analyzed by comparing the dynamic tests with quasi-static tests. The results show that the dynamic mechanical behavior of HNS is significantly sensitive to strain rate and temperature; the flow stress increases rapidly when strain rate exceeds 400 s-1; and at the same strain rate, the flow stress increases as temperature decreases. The coupling effect of strain rate and temperature on the plastic deformation behavior of HNS was investigated. The results indicate that the thermal softening effect plays a key role in the dynamic plastic deformation process of HNS. Based on the classical Johnson-Cook constitutive model, a modified Johnson-Cook constitutive model was given which can describe the dynamic mechanical behavior of HNS properly.
2018, 38(4): 841-846.
doi: 10.11883/bzycj-2016-0335
Abstract:
In our study, we established a finite element model using Abaqus, a commercially available software, to simulate the dynamic response of a cold-formed thin-wall steel lipped channel under axial compact, and verified its reliability by the highly consistent data and residual deformation obtained both from the finite element simulation and a drop hammer test. Based on the finite element model, we analyzed the axial displacement histories of the web, the flange and the lip, and the changing process of the web's lateral deflection under different impact energies. The results indicate that the axial displacement and the speed of the lip are significantly greater than those of the web and the flange during the loading process of higher impact energy, while the flange exerts an obvious constraint on the lip under lower impact energy. The dynamic critical load of the cold-formed steel channel under axial impact increases as the impact velocity goes up.
In our study, we established a finite element model using Abaqus, a commercially available software, to simulate the dynamic response of a cold-formed thin-wall steel lipped channel under axial compact, and verified its reliability by the highly consistent data and residual deformation obtained both from the finite element simulation and a drop hammer test. Based on the finite element model, we analyzed the axial displacement histories of the web, the flange and the lip, and the changing process of the web's lateral deflection under different impact energies. The results indicate that the axial displacement and the speed of the lip are significantly greater than those of the web and the flange during the loading process of higher impact energy, while the flange exerts an obvious constraint on the lip under lower impact energy. The dynamic critical load of the cold-formed steel channel under axial impact increases as the impact velocity goes up.
2018, 38(4): 847-854.
doi: 10.11883/bzycj-2016-0314
Abstract:
In the present paper, we proposed a two-dimensional finite difference method (FDM) of characteristic lines to address problems of the non-isentropic steady flow of cylindrical explosive underwater explosion. This method describes the non-isentropic effect by adding an entropy-related variable along the flow line to the pressure-related equation along the Mach line, so that both the isentropic flow and the non-isentropic flow can be described in the same equations of the characteristics. Based on the features of the near-field shock wave we firstly modeled the underwater explosion with an infinitely long cylindrical explosive, then discretized those equations using this finite difference method and constructed an appropriate grid to ensure the numerical convergence, and finally calculated the underwater near-field shock wave for several explosives by programming. The numerical examples showed that the results of this method are consistent with those of the commercial finite element software AUTODYN and those of experiments, suggesting that the FDM of characteristics can capture the shock wave front with relatively high accuracy, and confirming that this method is applicable to solving problems in cylindrical explosive underwater explosion.
In the present paper, we proposed a two-dimensional finite difference method (FDM) of characteristic lines to address problems of the non-isentropic steady flow of cylindrical explosive underwater explosion. This method describes the non-isentropic effect by adding an entropy-related variable along the flow line to the pressure-related equation along the Mach line, so that both the isentropic flow and the non-isentropic flow can be described in the same equations of the characteristics. Based on the features of the near-field shock wave we firstly modeled the underwater explosion with an infinitely long cylindrical explosive, then discretized those equations using this finite difference method and constructed an appropriate grid to ensure the numerical convergence, and finally calculated the underwater near-field shock wave for several explosives by programming. The numerical examples showed that the results of this method are consistent with those of the commercial finite element software AUTODYN and those of experiments, suggesting that the FDM of characteristics can capture the shock wave front with relatively high accuracy, and confirming that this method is applicable to solving problems in cylindrical explosive underwater explosion.
2018, 38(4): 855-862.
doi: 10.11883/bzycj-2017-0093
Abstract:
In this study, we investigated the effect of underwater explosion of CL-20-based explosive and CL-20-based aluminized explosive, by examining the dynamics of the bubble pulses generated by CL-20-based explosives charge underwater explosions in a 2 m×2 m×2 m water tank, with the pressure history of the shock wave measured. The process of the generation, expansion and contraction of the air bubble was observed clearly using the high-speed photo technology. The variation of the bubble radius, its expanding and contracting velocities, and its expanding and contracting accelerations with time was achieved in the bubble pulse process under the given experimental conditions. The bubble pulsation of the CL-20-based explosive and CL-20-based aluminized explosive were analyzed and compared. For the first time, secondary reaction process of the aluminum for the CL-20-based aluminized explosive underwater explosion was captured by the high-speed photo technology under the experimental conditions. The results show that the bubble radius and bubble periods of CL-20-based aluminized explosive went through an obvious increase, the bubble radius going up by 13.7% and the bubble period by 6.9%, respectively. The peak pressure of the shock wave exhibited a slight decrease. The technology of underwater explosion test and high-speed photography can be used to study the secondary reaction of aluminized explosive effectively.
In this study, we investigated the effect of underwater explosion of CL-20-based explosive and CL-20-based aluminized explosive, by examining the dynamics of the bubble pulses generated by CL-20-based explosives charge underwater explosions in a 2 m×2 m×2 m water tank, with the pressure history of the shock wave measured. The process of the generation, expansion and contraction of the air bubble was observed clearly using the high-speed photo technology. The variation of the bubble radius, its expanding and contracting velocities, and its expanding and contracting accelerations with time was achieved in the bubble pulse process under the given experimental conditions. The bubble pulsation of the CL-20-based explosive and CL-20-based aluminized explosive were analyzed and compared. For the first time, secondary reaction process of the aluminum for the CL-20-based aluminized explosive underwater explosion was captured by the high-speed photo technology under the experimental conditions. The results show that the bubble radius and bubble periods of CL-20-based aluminized explosive went through an obvious increase, the bubble radius going up by 13.7% and the bubble period by 6.9%, respectively. The peak pressure of the shock wave exhibited a slight decrease. The technology of underwater explosion test and high-speed photography can be used to study the secondary reaction of aluminized explosive effectively.
2018, 38(4): 863-868.
doi: 10.11883/bzycj-2016-0394
Abstract:
In order to understand the effect of axial pulse magnetic field on the shaped charge jet (SCJ), we designed an experiment system and carried out related experiments based on the mechanism of a high-explosive anti-tank (HEAT) penetrating a target and the interaction between the magnetic field and SCJ, and came up with the key technology to match the time sequence between the formation of SCJ and the pulsed current generation of the coils, which was a major breakthrough. The experiment results show that the increment of the penetration depth for SCJ penetrating the target is largest when the voltage is 5 kV, the capacitor is 1 200 μF and the length of coil is 50 mm. The influence factors of the penetration depth are respectively the charging voltage of the capacitor, the capacitance and the coil length, each in a descending order. These results provide an important theoretical foundation and technical support for the feasibility demonstration, principle test and related physical design of the coil of the enhanced HEAT by the electromagnetic method.
In order to understand the effect of axial pulse magnetic field on the shaped charge jet (SCJ), we designed an experiment system and carried out related experiments based on the mechanism of a high-explosive anti-tank (HEAT) penetrating a target and the interaction between the magnetic field and SCJ, and came up with the key technology to match the time sequence between the formation of SCJ and the pulsed current generation of the coils, which was a major breakthrough. The experiment results show that the increment of the penetration depth for SCJ penetrating the target is largest when the voltage is 5 kV, the capacitor is 1 200 μF and the length of coil is 50 mm. The influence factors of the penetration depth are respectively the charging voltage of the capacitor, the capacitance and the coil length, each in a descending order. These results provide an important theoretical foundation and technical support for the feasibility demonstration, principle test and related physical design of the coil of the enhanced HEAT by the electromagnetic method.
2018, 38(4): 869-875.
doi: 10.11883/bzycj-2016-0376
Abstract:
In this work, to realize explosive directed loading metal particles of low collateral damage ammunition, we developed a launching device and used it to carry out the dispersing of tungsten particles of different sizes and charging ratios. We captured the dispersion attitude and velocity of tungsten particles using high speed photography and high speed infrared photography, and demonstrated the three dimensional spatial distribution of tungsten particles inside the soap target using computerized tomography and three dimensional reconstruction. The results revealed the three phases of detonation-driven particles, i.e. acceleration, deceleration, and scattering. For particles of different sizes, the average velocity ranged from 689.84 m/s to 889.14 m/s, and the maximum penetrating depth ranged from 65.23 mm to 167.35 mm. The launching device was observed to perform well at directed loading metal particles with a rate of over 30% in hitting the target. We adjusted the mass ratio of the charge to the particles to meet various experimental requirements and improved the analysis accuracy of terminal ballistics parameters using the CT image reconstruction technique. Our study here can serve as a useful technique for further investigation of the damage effects, wounding mechanism, injury evaluation and treatment of low collateral damage ammunition.
In this work, to realize explosive directed loading metal particles of low collateral damage ammunition, we developed a launching device and used it to carry out the dispersing of tungsten particles of different sizes and charging ratios. We captured the dispersion attitude and velocity of tungsten particles using high speed photography and high speed infrared photography, and demonstrated the three dimensional spatial distribution of tungsten particles inside the soap target using computerized tomography and three dimensional reconstruction. The results revealed the three phases of detonation-driven particles, i.e. acceleration, deceleration, and scattering. For particles of different sizes, the average velocity ranged from 689.84 m/s to 889.14 m/s, and the maximum penetrating depth ranged from 65.23 mm to 167.35 mm. The launching device was observed to perform well at directed loading metal particles with a rate of over 30% in hitting the target. We adjusted the mass ratio of the charge to the particles to meet various experimental requirements and improved the analysis accuracy of terminal ballistics parameters using the CT image reconstruction technique. Our study here can serve as a useful technique for further investigation of the damage effects, wounding mechanism, injury evaluation and treatment of low collateral damage ammunition.
2018, 38(4): 876-882.
doi: 10.11883/bzycj-2016-0342
Abstract:
The lethality of the circumferential direction fragment field of the warhead has improved greatly due to the premade fragment technique, but the axial fragments are still too few to block the battle space completely. Aiming to improve the distribution of the axial fragment field of the warhead and explore the factors influencing the velocity and scattering angle of the axial premade fragments, we designed an axial forward enhanced warhead by changing the shape and curvature of its head, and displacing the premade fragment to the head of the warhead to improve its lethality in the axial direction. We simulated the whole explosive driven process using LS-DYNA, the influence of the warhead structure on the velocity, and obtained the scattering angle of the axial premade fragments by setting different initial conditions. The results show that the velocity and the scattering angle of the axial premade fragments were closely related with the warhead structure. In addition, when the arc-shaped head warhead was adopted, the velocity, scattering angle, blocking area, and the lethality of the premade fragments were all significantly ameliorated.
The lethality of the circumferential direction fragment field of the warhead has improved greatly due to the premade fragment technique, but the axial fragments are still too few to block the battle space completely. Aiming to improve the distribution of the axial fragment field of the warhead and explore the factors influencing the velocity and scattering angle of the axial premade fragments, we designed an axial forward enhanced warhead by changing the shape and curvature of its head, and displacing the premade fragment to the head of the warhead to improve its lethality in the axial direction. We simulated the whole explosive driven process using LS-DYNA, the influence of the warhead structure on the velocity, and obtained the scattering angle of the axial premade fragments by setting different initial conditions. The results show that the velocity and the scattering angle of the axial premade fragments were closely related with the warhead structure. In addition, when the arc-shaped head warhead was adopted, the velocity, scattering angle, blocking area, and the lethality of the premade fragments were all significantly ameliorated.
2018, 38(4): 883-890.
doi: 10.11883/bzycj-2016-0356
Abstract:
In order to further improve the damage capacity of the multiple explosively formed penetrator (MEFP) warhead, we designed a rod-shaped and explosively formed penetrator warhead. We firstly investigated the formation process and scattering effect of the penetrator were investigated using numerical simulation, and presented a design of rod-shaped warhead penetrators based on the analysis of the influence of the warhead's outer linings on the penetrator's formation process. Then we fabricated two principal prototypes of the penetrator warhead, one with and the other without outer linings, and performed the static explosion experiments to find out about their damage effects. The results show that the average penetration depth on the 40 mm-thick-45 steel, 3 m apart from the detonation center by the warhead penetrators without outer linings, is 27 mm., while those with outer linings can completely penetrate the target. Moreover, the penetration results of the experiment and the simulation are consistent with each other, thereby concluding that our design can significantly improve the formation quality and the penetration power of the rod-shaped penetrators.
In order to further improve the damage capacity of the multiple explosively formed penetrator (MEFP) warhead, we designed a rod-shaped and explosively formed penetrator warhead. We firstly investigated the formation process and scattering effect of the penetrator were investigated using numerical simulation, and presented a design of rod-shaped warhead penetrators based on the analysis of the influence of the warhead's outer linings on the penetrator's formation process. Then we fabricated two principal prototypes of the penetrator warhead, one with and the other without outer linings, and performed the static explosion experiments to find out about their damage effects. The results show that the average penetration depth on the 40 mm-thick-45 steel, 3 m apart from the detonation center by the warhead penetrators without outer linings, is 27 mm., while those with outer linings can completely penetrate the target. Moreover, the penetration results of the experiment and the simulation are consistent with each other, thereby concluding that our design can significantly improve the formation quality and the penetration power of the rod-shaped penetrators.
2018, 38(4): 891-897.
doi: 10.11883/bzycj-2016-0323
Abstract:
It is known that low-temperature is apt to cause skin frost bite and material embrittlement, and that the propagation law of gas explosion is the foundation of explosion evolution and accident analysis. In this paper, we investigated the process of extensive gas leakage, gas mixing with air and explosion of the liquefied natural gas (LNG) in open space using numerical simulation. The results show that, as the diffusion distance increases, the lowest possible fluctuating temperature (i.e. temperature valley) of LNG increases, and this tendency gradually slows down; that the temperature is below 273 K in the area within 110 m away from the leakage center; that the temperature valley decreases almost linearly as the wind velocity increases. As the leakage time gets longer, the temperature valley decreases, and so does its decreasing tendency. With the distance from the leakage center getting longer, the peak overpressure increases at first and then decreases. In the area within 200 m away from the leakage center, the high temperature produced by the explosion may pose a hazard to human casualties.
It is known that low-temperature is apt to cause skin frost bite and material embrittlement, and that the propagation law of gas explosion is the foundation of explosion evolution and accident analysis. In this paper, we investigated the process of extensive gas leakage, gas mixing with air and explosion of the liquefied natural gas (LNG) in open space using numerical simulation. The results show that, as the diffusion distance increases, the lowest possible fluctuating temperature (i.e. temperature valley) of LNG increases, and this tendency gradually slows down; that the temperature is below 273 K in the area within 110 m away from the leakage center; that the temperature valley decreases almost linearly as the wind velocity increases. As the leakage time gets longer, the temperature valley decreases, and so does its decreasing tendency. With the distance from the leakage center getting longer, the peak overpressure increases at first and then decreases. In the area within 200 m away from the leakage center, the high temperature produced by the explosion may pose a hazard to human casualties.
2018, 38(4): 898-904.
doi: 10.11883/bzycj-2016-0344
Abstract:
Vented explosion tests were carried out in a 12 m3 concrete chamber filled with premixed methane-air mixture with the methane volume fraction of 9.5%, and the influence of the ignition position on the development of overpressure and the evolution of flame was investigated. The results show that this influence on the rising rate of Δp1 was nearly negligible but the peak value of Δp2 increased with the increase of the distance between the ignition position and the vent, and the peak value of Δp4 was correlated with different ignition positions, i.e. central ignition, rear ignition, front ignition, in an order of descending influence. Moreover, when the venting pressure got bigger, Δp1 had the same increment at all the ignition positions, whereas Δp2 vanished in front and central ignitions, and Δp4 increased with the increase of venting pressure only in center ignition. Besides, the evolution of the external frame was observed to fall into two stages: the fireball formation and the jet frame. The size of the fireball and the maximum length of the external jet flame in rear and central ignitions were larger than those in front ignition.
Vented explosion tests were carried out in a 12 m3 concrete chamber filled with premixed methane-air mixture with the methane volume fraction of 9.5%, and the influence of the ignition position on the development of overpressure and the evolution of flame was investigated. The results show that this influence on the rising rate of Δp1 was nearly negligible but the peak value of Δp2 increased with the increase of the distance between the ignition position and the vent, and the peak value of Δp4 was correlated with different ignition positions, i.e. central ignition, rear ignition, front ignition, in an order of descending influence. Moreover, when the venting pressure got bigger, Δp1 had the same increment at all the ignition positions, whereas Δp2 vanished in front and central ignitions, and Δp4 increased with the increase of venting pressure only in center ignition. Besides, the evolution of the external frame was observed to fall into two stages: the fireball formation and the jet frame. The size of the fireball and the maximum length of the external jet flame in rear and central ignitions were larger than those in front ignition.
2018, 38(4): 905-912.
doi: 10.11883/bzycj-2017-0064
Abstract:
The combinations which were structured from three categories of porous materials including six sub-categories, were tested for studying the suppression effects of the porous materials on the explosion of the combustible gas. The combustible gas was the methane-air mixture. The porous materials were fixed in a closed container piping system by using a self-made thin iron hoop, then the explosion suppression effects of a thin iron hoop, single-layer porous materials, double-layer combination porous materials and three-layer combination porous materials were compared. The results show that the thin iron hoop could enhance the gas explosive intensity and the maximum explosion pressure was achieved behind the iron hoop. The explosion suppression effects of the porous materials were obvious, and the explosion suppression effects of the double-layer combination porous materials were more stable compared to those of the single-type porous materials and the three-layer combination porous materials. The optimized combination of the porous materials for explosion suppression turned out to be Al2O3 10 mm/30 PPI+SiC 20 mm/20 PPI, and the optimized combination of the porous materials for explosion pressure suppression turned out to be Al2O3 10 mm/30 PPI+Fe-Ni 10 mm/90 PPI+SiC 20 mm/10 PPI.
The combinations which were structured from three categories of porous materials including six sub-categories, were tested for studying the suppression effects of the porous materials on the explosion of the combustible gas. The combustible gas was the methane-air mixture. The porous materials were fixed in a closed container piping system by using a self-made thin iron hoop, then the explosion suppression effects of a thin iron hoop, single-layer porous materials, double-layer combination porous materials and three-layer combination porous materials were compared. The results show that the thin iron hoop could enhance the gas explosive intensity and the maximum explosion pressure was achieved behind the iron hoop. The explosion suppression effects of the porous materials were obvious, and the explosion suppression effects of the double-layer combination porous materials were more stable compared to those of the single-type porous materials and the three-layer combination porous materials. The optimized combination of the porous materials for explosion suppression turned out to be Al2O3 10 mm/30 PPI+SiC 20 mm/20 PPI, and the optimized combination of the porous materials for explosion pressure suppression turned out to be Al2O3 10 mm/30 PPI+Fe-Ni 10 mm/90 PPI+SiC 20 mm/10 PPI.
2018, 38(4): 913-917.
doi: 10.11883/bzycj-2016-0331
Abstract:
The present work was carried for the prevention of increasingly ever prevalent gas explosion accidents that had occurred in the coexistence of gas and coal dust in recent years. Using a 20 L explosion test system, we studied experimentally the explosive characteristics of the coexisting gas and coal dust and obtained the lower limit of gas explosion under different ignition energies, static and turbulent conditions and the lower limit concentration of coal dust explosion under different conditions. The results show that with the increase of gas concentration, the minimum explosive concentration of coal dust cloud decreases exponentially and that there is a critical gas concentration, in higher than which gas plays a leading role in the process of explosion, shown as the so-called "strong gas". Otherwise, coal dust plays the leading role, which is characterized by the "strong coal dust". The conclusions can serve as an important theoretical basis for preventing the coal mine gas and coal dust explosion.
The present work was carried for the prevention of increasingly ever prevalent gas explosion accidents that had occurred in the coexistence of gas and coal dust in recent years. Using a 20 L explosion test system, we studied experimentally the explosive characteristics of the coexisting gas and coal dust and obtained the lower limit of gas explosion under different ignition energies, static and turbulent conditions and the lower limit concentration of coal dust explosion under different conditions. The results show that with the increase of gas concentration, the minimum explosive concentration of coal dust cloud decreases exponentially and that there is a critical gas concentration, in higher than which gas plays a leading role in the process of explosion, shown as the so-called "strong gas". Otherwise, coal dust plays the leading role, which is characterized by the "strong coal dust". The conclusions can serve as an important theoretical basis for preventing the coal mine gas and coal dust explosion.
2018, 38(4): 918-924.
doi: 10.11883/bzycj-2016-0260
Abstract:
In the present work, the vibration velocities of the ground, roof and top of the 40 kg TNT equivalent blast containment chamber resulting respectively from 15, 20, 25 and 40 kg TNT explosion were monitored using velocity sensors and geophones. The measured results showed that all of the ground velocity peaks were less than 5 cm/s, the vibration frequency was almost higher than 10 Hz and the vibration duration reached 5 to 10 s, and the vertical vibration peak of the roof was obviously enlarged by 6 to 7 times that of the horizontal ones. The wavelet packet analysis of the velocities' signal showed that the vertical vibration energy of the ground was 2.5 to 4.0 times that of the horizontal vibration energy, more than 95% of the vibration energy mostly concentrated in the range of 0-160 Hz, while more than 90% of the vertical vibration energy was limited in the range of 10-40 Hz. The results reveal that the attenuation effect of the vibration-isolating trench at a depth of 6 m on the blast seismic waves is imperfect, the independent base and seismic isolation bearing should be adopted if we hope to obtain an ideal attenuation effect especially when the explosive weight exceeds 5 kg TNT equivalent.
In the present work, the vibration velocities of the ground, roof and top of the 40 kg TNT equivalent blast containment chamber resulting respectively from 15, 20, 25 and 40 kg TNT explosion were monitored using velocity sensors and geophones. The measured results showed that all of the ground velocity peaks were less than 5 cm/s, the vibration frequency was almost higher than 10 Hz and the vibration duration reached 5 to 10 s, and the vertical vibration peak of the roof was obviously enlarged by 6 to 7 times that of the horizontal ones. The wavelet packet analysis of the velocities' signal showed that the vertical vibration energy of the ground was 2.5 to 4.0 times that of the horizontal vibration energy, more than 95% of the vibration energy mostly concentrated in the range of 0-160 Hz, while more than 90% of the vertical vibration energy was limited in the range of 10-40 Hz. The results reveal that the attenuation effect of the vibration-isolating trench at a depth of 6 m on the blast seismic waves is imperfect, the independent base and seismic isolation bearing should be adopted if we hope to obtain an ideal attenuation effect especially when the explosive weight exceeds 5 kg TNT equivalent.
2018, 38(4): 925-930.
doi: 10.11883/bzycj-2016-0377
Abstract:
Based on the fractal damage evolution law of high strength concrete (HSC) specimen by the SHPB impact test, we deduced the patterns of the fractal damage variables of HSC, and calibrated the fractal dimension range of the HSC cracks. Then following the ZWT model, and in combination with the strain rate dependence, dynamic damage characteristic and quasi-constant strain rate, we obtained the HSC dynamic damage constitutive equation with the fractal damage evolution taken into account Finall. Our study verified the effectiveness of the constitutive equation by C60 and C80 stress-strain curves at four different strain ratios, and the theoretical curves matched well with the experimental ones.
Based on the fractal damage evolution law of high strength concrete (HSC) specimen by the SHPB impact test, we deduced the patterns of the fractal damage variables of HSC, and calibrated the fractal dimension range of the HSC cracks. Then following the ZWT model, and in combination with the strain rate dependence, dynamic damage characteristic and quasi-constant strain rate, we obtained the HSC dynamic damage constitutive equation with the fractal damage evolution taken into account Finall. Our study verified the effectiveness of the constitutive equation by C60 and C80 stress-strain curves at four different strain ratios, and the theoretical curves matched well with the experimental ones.
2018, 38(4): 931-936.
doi: 10.11883/bzycj-2016-0378
Abstract:
We simulated the launching progress of SSAGIT using the computational fluid dynamics (CFD) and the velocity of the impact car obtained from calculation are consistent with the experiment results. Based on this, we investigated the flow field, the pressure in the front and back of the car, and the pressure of the gasholder. The results showed that the launch field was filled with the leakage gas before the arrival of the impact car, causing the development of an initial flow field, and the alternatively positive and negative variations of the pressure in the front of the car, but its influence on the acceleration process was negligible because of its small value. In addition, the acceleration was maintained due to the effect of the jet after the impacted car entered the decompression part, and the increment was about 2 m/s.
We simulated the launching progress of SSAGIT using the computational fluid dynamics (CFD) and the velocity of the impact car obtained from calculation are consistent with the experiment results. Based on this, we investigated the flow field, the pressure in the front and back of the car, and the pressure of the gasholder. The results showed that the launch field was filled with the leakage gas before the arrival of the impact car, causing the development of an initial flow field, and the alternatively positive and negative variations of the pressure in the front of the car, but its influence on the acceleration process was negligible because of its small value. In addition, the acceleration was maintained due to the effect of the jet after the impacted car entered the decompression part, and the increment was about 2 m/s.
