2015 Vol. 35, No. 6
Display Method:
2015, 35(6): 769-776.
doi: 10.11883/1001-1455(2015)06-0769-08
Read OL
PDF 
Cited by
Abstract:
To investigate dynamic mechanical performances of YB-2 aeronautical polymer used as the aircraft windshield in extreme mechanical environments, we performed uniaxial compression tests on cylindrical samples, using an Instron servo hydraulic axial testing machine and the compression Hopkinson bar at strain rates ranging from 10-3 s-1 to 3 000 s-1 and at initial temperatures ranging from 218 K to 373 K, and obtained the true strain stress curves. Our results indicate that the Young's modulus and flow stress decrease as the temperature increases, while the fracture strain tends to increase as the temperature increases. At the same temperature, it was found the flow stress increases with the rising strain rate, and the strain softening effect was also observed to be more acute with the increasing strain rates. Based on the ZWT model, the parameters of a prediction model that takes temperature into consideration has been gained. The predictions are in good agreement with experimental results in the strain range of 8%.
To investigate dynamic mechanical performances of YB-2 aeronautical polymer used as the aircraft windshield in extreme mechanical environments, we performed uniaxial compression tests on cylindrical samples, using an Instron servo hydraulic axial testing machine and the compression Hopkinson bar at strain rates ranging from 10-3 s-1 to 3 000 s-1 and at initial temperatures ranging from 218 K to 373 K, and obtained the true strain stress curves. Our results indicate that the Young's modulus and flow stress decrease as the temperature increases, while the fracture strain tends to increase as the temperature increases. At the same temperature, it was found the flow stress increases with the rising strain rate, and the strain softening effect was also observed to be more acute with the increasing strain rates. Based on the ZWT model, the parameters of a prediction model that takes temperature into consideration has been gained. The predictions are in good agreement with experimental results in the strain range of 8%.
2015, 35(6): 777-784.
doi: 10.11883/1001-1455(2015)06-0777-08
Abstract:
By focusing our concern on the effect of chemical reactions with detonation products, we have done research on the calculation of the quasi-static temperature of confined explosion. On the basis of the energy conservation, considering the chemical kinetic reaction process of the detonation products, the formula and calculating method of quasi-static temperature were proposed. A computation program was designed using C++ language, which was used to calculate the quasi-static temperature of the TNT confined explosion. Calculation results show that chemical reactions of the detonation products play a very important role in the calculation of the quasi-static temperature in confined explosions, and obviously the temperature varies with the charge volume ratios. Ours is an efficient technique to obtain a more accurate quasi-static temperature and calculate some other parameters of confined explosions.
By focusing our concern on the effect of chemical reactions with detonation products, we have done research on the calculation of the quasi-static temperature of confined explosion. On the basis of the energy conservation, considering the chemical kinetic reaction process of the detonation products, the formula and calculating method of quasi-static temperature were proposed. A computation program was designed using C++ language, which was used to calculate the quasi-static temperature of the TNT confined explosion. Calculation results show that chemical reactions of the detonation products play a very important role in the calculation of the quasi-static temperature in confined explosions, and obviously the temperature varies with the charge volume ratios. Ours is an efficient technique to obtain a more accurate quasi-static temperature and calculate some other parameters of confined explosions.
2015, 35(6): 785-791.
doi: 10.11883/1001-1455(2015)06-0785-07
Abstract:
Based on the theory of relaxation approximation, the nonlinear governing equations of detonation in condensed explosives are transformed into linear relaxation systems, which can easily adopt simple and effective high resolution scheme. A fifth-order WENO reconstruction scheme in spatial discretization and a fifth-order IMEX scheme of linear multistep methods with monotonicity and TVB in time discrtiezation are utilized, where it can leave out solving Riemann problem and computing the Jacobian matrix of the nonlinear flux, and make it unnecessary to split the stiff source term resulting from the chemical reaction. The developed method is applied to simulating the steady structure of one-dimensional planar detonation wave and unsteady initiation and propagation of one-dimensional spherically convergent and divergent detonation wave in condensed explosives PBX9404, with the results demonstrating the excellent performance of the present method.
Based on the theory of relaxation approximation, the nonlinear governing equations of detonation in condensed explosives are transformed into linear relaxation systems, which can easily adopt simple and effective high resolution scheme. A fifth-order WENO reconstruction scheme in spatial discretization and a fifth-order IMEX scheme of linear multistep methods with monotonicity and TVB in time discrtiezation are utilized, where it can leave out solving Riemann problem and computing the Jacobian matrix of the nonlinear flux, and make it unnecessary to split the stiff source term resulting from the chemical reaction. The developed method is applied to simulating the steady structure of one-dimensional planar detonation wave and unsteady initiation and propagation of one-dimensional spherically convergent and divergent detonation wave in condensed explosives PBX9404, with the results demonstrating the excellent performance of the present method.
2015, 35(6): 792-798.
doi: 10.11883/1001-1455(2015)06-0792-07
Abstract:
In order to carry out the complex loading research with the strain rates varying from 105 s-1 to 106 s-1 on the light gas gun, we numerically simulated the complex loading on the steel target by the graded ensity impactor (GDI) of Al-Cu-W system using our own developed Lagrangian code MLEP (multi-material Lagrangian elastic-plastic). In our simulation, the effects of the thickness of the GDI and the power exponent of denstiy distribution on the pressure, velocity, and peak strain rate of the target were investigated. The results indicate that the loading time decreases as the power exponent of density distribution increases, and the profiles of pressure, velocity and peak strain rate at the later stage of the loading are steeper than those with smaller power exponents. Moreover, the effect of the thickness of the GDI is considered in our computational design to prevent the confluence of the rarefaction waves emanating from the back of the GDI and the interface between the target and LiF window on the impact interface. Finally, a dynamic test was conducted for the GDI based on the design, and the results show the good agreement between the design and the experiment, which paves the way for the strength measurement of materials in the future.
In order to carry out the complex loading research with the strain rates varying from 105 s-1 to 106 s-1 on the light gas gun, we numerically simulated the complex loading on the steel target by the graded ensity impactor (GDI) of Al-Cu-W system using our own developed Lagrangian code MLEP (multi-material Lagrangian elastic-plastic). In our simulation, the effects of the thickness of the GDI and the power exponent of denstiy distribution on the pressure, velocity, and peak strain rate of the target were investigated. The results indicate that the loading time decreases as the power exponent of density distribution increases, and the profiles of pressure, velocity and peak strain rate at the later stage of the loading are steeper than those with smaller power exponents. Moreover, the effect of the thickness of the GDI is considered in our computational design to prevent the confluence of the rarefaction waves emanating from the back of the GDI and the interface between the target and LiF window on the impact interface. Finally, a dynamic test was conducted for the GDI based on the design, and the results show the good agreement between the design and the experiment, which paves the way for the strength measurement of materials in the future.
2015, 35(6): 799-806.
doi: 10.11883/1001-1455(2015)06-0799-08
Abstract:
To find out the effect of the velocity pulse of near-fault ground motions on the structural shock resistance, we simulated the seismic responses using three dimensional finite element model for high temperature gas-cooled reactor nuclear power plant, in which four strong motion records with the velocity pulse and the corresponding synthetic time histories with same response spectra and without velocity pulse were used as ground motion inputs. Our test results show that the seismic responses of the high temperature gas cooled reactor nuclear power plant to ground motions with velocity pulse are greater than those without velocity pulse, and the ground motions with velocity pulse can have strong unfavorable effect on seismic displacement responses of the high temperature gas-cooled reactor nuclear power plant. If the installed equipment is sensitive to the displacement response, the designers should focus great concern on the effect of the velocity pulse on seismic displacement responses of the high temperature gas cooled reactor nuclear power plant.
To find out the effect of the velocity pulse of near-fault ground motions on the structural shock resistance, we simulated the seismic responses using three dimensional finite element model for high temperature gas-cooled reactor nuclear power plant, in which four strong motion records with the velocity pulse and the corresponding synthetic time histories with same response spectra and without velocity pulse were used as ground motion inputs. Our test results show that the seismic responses of the high temperature gas cooled reactor nuclear power plant to ground motions with velocity pulse are greater than those without velocity pulse, and the ground motions with velocity pulse can have strong unfavorable effect on seismic displacement responses of the high temperature gas-cooled reactor nuclear power plant. If the installed equipment is sensitive to the displacement response, the designers should focus great concern on the effect of the velocity pulse on seismic displacement responses of the high temperature gas cooled reactor nuclear power plant.
2015, 35(6): 807-811.
doi: 10.11883/1001-1455(2015)06-0807-05
Abstract:
A hot-spot ignition model based on friction generated heat on microcrack face was established. In this model, the heat conduction equation including chemical reaction and friction was solved by implicit finite element method. Furthermore, the latent heat resulting from particle melting was also taken into account in this model. The effects of such key parameters hot-spot size, strain rate, and interface pressure on explosive ignition were detected and analyzed in detail. It is found that the temperature of the hot-spot rises more quickly and the response occurs earlier in time with the increase of the hot-spot size. The accumulation of heat is faster and the explosive is more likely to be ignited where the strain rate is larger or the pressure is higher.
A hot-spot ignition model based on friction generated heat on microcrack face was established. In this model, the heat conduction equation including chemical reaction and friction was solved by implicit finite element method. Furthermore, the latent heat resulting from particle melting was also taken into account in this model. The effects of such key parameters hot-spot size, strain rate, and interface pressure on explosive ignition were detected and analyzed in detail. It is found that the temperature of the hot-spot rises more quickly and the response occurs earlier in time with the increase of the hot-spot size. The accumulation of heat is faster and the explosive is more likely to be ignited where the strain rate is larger or the pressure is higher.
2015, 35(6): 812-819.
doi: 10.11883/1001-1455(2015)06-0812-08
Abstract:
To improve the steel target penetrating capability of the rod-like jet, we designed an eccentric semispherical liner. The liner's collapsing velocity was deduced by detonation wave collision theory, and the rod-like jet formation model was established by combining the improved PER theory. The laws determining how the liner configuration parameters affect the detonation wave collision pressure were drawn out, and the jet mass and velocity distribution laws were obtained by changing the thickness of the equal mass liner. Our test results show that the Mach collision pressure increased with the increase of the eccentric distance, and decreased with the increase of the ectotheca curvature radius. Moreover, the variation law of the regular oblique reflection pressure was reverse with the Mach collision, which was greatly affected by the liner configuration. By comparing different schemes, we find that the jet mass of the liner, which was thick at the top and the bottom but thin in the middle, increased by 29.5%, and the tip velocity increased by 21.3%, while, with the maximum velocity gradient and the same condition of standoff distance, the penetration depth almost doubled the charge caliber. The simulation and experiment were carried out aiming at the optimal configuration, and the formation and penetration performance of the rod-like jet was improved remarkably through the optimum matching of the detonation wave form with the liner configuration.
To improve the steel target penetrating capability of the rod-like jet, we designed an eccentric semispherical liner. The liner's collapsing velocity was deduced by detonation wave collision theory, and the rod-like jet formation model was established by combining the improved PER theory. The laws determining how the liner configuration parameters affect the detonation wave collision pressure were drawn out, and the jet mass and velocity distribution laws were obtained by changing the thickness of the equal mass liner. Our test results show that the Mach collision pressure increased with the increase of the eccentric distance, and decreased with the increase of the ectotheca curvature radius. Moreover, the variation law of the regular oblique reflection pressure was reverse with the Mach collision, which was greatly affected by the liner configuration. By comparing different schemes, we find that the jet mass of the liner, which was thick at the top and the bottom but thin in the middle, increased by 29.5%, and the tip velocity increased by 21.3%, while, with the maximum velocity gradient and the same condition of standoff distance, the penetration depth almost doubled the charge caliber. The simulation and experiment were carried out aiming at the optimal configuration, and the formation and penetration performance of the rod-like jet was improved remarkably through the optimum matching of the detonation wave form with the liner configuration.
2015, 35(6): 820-824.
doi: 10.11883/1001-1455(2015)06-0820-05
Abstract:
In order to evaluate the protective effect and analyze the dynamic response of multi-layer steel cylinder under internal blast loading, we have conducted four experiments, with three different charge mass, ranging from 8.90 to 18.18 kg. The multi-layer steel cylinder we used is composed of 4 layers made of Q345 steel. The 4 layers altogether are 50 mm in thickness, with the 3 inner ones as 10 mm and the outer one as 20 mm respectively. The diameter of the innermost layer is 800 mm and the distance between layers is 5 mm. At the section of charge center and 20 cm axial distance from the charge, the hoop strain and axial strain are measured by eight strain gauges set on the outside of steel shell. Under the blast loading, the plastic deformation occurred locally at the charge center, and the largest deformation appeared at the innermost layer. However, even in the circumstance of the largest charge mass, there is no failure. It is concluded that the thickness of the steel cylinder could be predicted accurately with the energy absorbing design method applied to the unit section of the charge center of the multi-layer steel cylinder. With a proper change in charge mass, the peak hoop strain can reduce to about 1/2 of the section at the charge center, when the axial distance is beyond the 1/4 diameter of the inner layer.
In order to evaluate the protective effect and analyze the dynamic response of multi-layer steel cylinder under internal blast loading, we have conducted four experiments, with three different charge mass, ranging from 8.90 to 18.18 kg. The multi-layer steel cylinder we used is composed of 4 layers made of Q345 steel. The 4 layers altogether are 50 mm in thickness, with the 3 inner ones as 10 mm and the outer one as 20 mm respectively. The diameter of the innermost layer is 800 mm and the distance between layers is 5 mm. At the section of charge center and 20 cm axial distance from the charge, the hoop strain and axial strain are measured by eight strain gauges set on the outside of steel shell. Under the blast loading, the plastic deformation occurred locally at the charge center, and the largest deformation appeared at the innermost layer. However, even in the circumstance of the largest charge mass, there is no failure. It is concluded that the thickness of the steel cylinder could be predicted accurately with the energy absorbing design method applied to the unit section of the charge center of the multi-layer steel cylinder. With a proper change in charge mass, the peak hoop strain can reduce to about 1/2 of the section at the charge center, when the axial distance is beyond the 1/4 diameter of the inner layer.
2015, 35(6): 825-831.
doi: 10.11883/1001-1455(2015)06-0825-07
Abstract:
Several typical additives were selected and added to ammonium nitrate (AN), and UN gap test was conducted to study the effects of the added amount and mixing method on the anti-explosion performance of AN. Experimental results obtained indicate improvement of certain anti-explosion performance on AN for potassium chlorate (KCl), sodium chloride (NaCl) and monoammonium phosphate (NH4H2PO4) added. When the added amount of KCl is 20% by mechanical mixing or 15% by solution mixing, that of NaCl is 35% or 15%, and that of NH4H2PO4 is 25% or 30%, AN ceases to propagate detonation. As to the chloride additives, solution mixing can mix AN and additives more evenly, thus obtaining better anti-explosion performance. In addition, as the acidity of NH4H2PO4 added to AN by solution mixing could accelerate thermal decomposition, better anti-explosion performance for that is also achieved by mechanical mixing.
Several typical additives were selected and added to ammonium nitrate (AN), and UN gap test was conducted to study the effects of the added amount and mixing method on the anti-explosion performance of AN. Experimental results obtained indicate improvement of certain anti-explosion performance on AN for potassium chlorate (KCl), sodium chloride (NaCl) and monoammonium phosphate (NH4H2PO4) added. When the added amount of KCl is 20% by mechanical mixing or 15% by solution mixing, that of NaCl is 35% or 15%, and that of NH4H2PO4 is 25% or 30%, AN ceases to propagate detonation. As to the chloride additives, solution mixing can mix AN and additives more evenly, thus obtaining better anti-explosion performance. In addition, as the acidity of NH4H2PO4 added to AN by solution mixing could accelerate thermal decomposition, better anti-explosion performance for that is also achieved by mechanical mixing.
2015, 35(6): 832-838.
doi: 10.11883/1001-1455(2015)06-0832-07
Abstract:
For the study of the mechanism of shipboard equipment on floating shock platform with installation of deck simulator fixture, the numerical simulation and theoretical analysis were carried out through building the finite element model and the mechanical model of the entire system. According to the vertical lowpass filtering characteristics of the deck structure from the hull, the function of the deck simulator fixture which can reduce the impact of high-frequency percussion and meet the requirements of equipment mounting frequency was put forward. The examining system of ship board equipment under test on floating shock platform was simplified to a damping forced vibration model of the three-axis system. The response of the shipboard equipment in different shock environments was calculated by Laplace transform. The results show that the numerical simulation is consistent with the theoretical calculation. The response of the equipment under test increases rapidly to maximum and then decays with time, and the vibration frequency transforms from high to low frequency. The damping effect should be considered when analyzing the long-term response of the examining system of the equipment under test on floating shock platform.
For the study of the mechanism of shipboard equipment on floating shock platform with installation of deck simulator fixture, the numerical simulation and theoretical analysis were carried out through building the finite element model and the mechanical model of the entire system. According to the vertical lowpass filtering characteristics of the deck structure from the hull, the function of the deck simulator fixture which can reduce the impact of high-frequency percussion and meet the requirements of equipment mounting frequency was put forward. The examining system of ship board equipment under test on floating shock platform was simplified to a damping forced vibration model of the three-axis system. The response of the shipboard equipment in different shock environments was calculated by Laplace transform. The results show that the numerical simulation is consistent with the theoretical calculation. The response of the equipment under test increases rapidly to maximum and then decays with time, and the vibration frequency transforms from high to low frequency. The damping effect should be considered when analyzing the long-term response of the examining system of the equipment under test on floating shock platform.
2015, 35(6): 839-845.
doi: 10.11883/1001-1455(2015)06-0839-07
Abstract:
The phenomenon of shock wave interacting with a flame involves a series of complicated physical and chemical processes, in which the generation and evolution of vorticity play an important role in controlling flame development. To systematically analyze the vorticity characteristics in the course of shock-flame interaction, a numerical study of a planar incident shock wave and its reflected wave interaction with a spherical flame was carried out by using the two-dimensional Navier-Stokes equations coupled with chemical reaction, and the requirement of high-resolution grid was met via the parallel computation. It is found that the baroclinic term plays a dominant role in the generation of vorticity within the flame zone, and the compression and dissipation terms restrain the generation of vorticity in the flame expanding stages. Besides, in the compression stages, the evolution of flame is mainly affected by the physical-rather than chemical-process.
The phenomenon of shock wave interacting with a flame involves a series of complicated physical and chemical processes, in which the generation and evolution of vorticity play an important role in controlling flame development. To systematically analyze the vorticity characteristics in the course of shock-flame interaction, a numerical study of a planar incident shock wave and its reflected wave interaction with a spherical flame was carried out by using the two-dimensional Navier-Stokes equations coupled with chemical reaction, and the requirement of high-resolution grid was met via the parallel computation. It is found that the baroclinic term plays a dominant role in the generation of vorticity within the flame zone, and the compression and dissipation terms restrain the generation of vorticity in the flame expanding stages. Besides, in the compression stages, the evolution of flame is mainly affected by the physical-rather than chemical-process.
2015, 35(6): 846-851.
doi: 10.11883/1001-1455(2015)06-0846-06
Abstract:
It is generally impossible to obtain valid constitutive data of casting explosive by conventional SHPB tests, due to its low impedance and soft texture and to its inability to attain uniformity required. A modified SHPB method is therefore proposed to get reliable dynamic response data of casting explosive. The piezoelectricity quartz gauges have been used to directly measure dynamic stress processing of specimen. This modified data processing method has been adopted, which can eliminate the effect caused by stress non-uniformity. By using the modified data processing, the signal failure problem caused by long pulse incident can also be resolved. With the modified SHPB method, satisfactory results have been obtained in processing casting explosive.
It is generally impossible to obtain valid constitutive data of casting explosive by conventional SHPB tests, due to its low impedance and soft texture and to its inability to attain uniformity required. A modified SHPB method is therefore proposed to get reliable dynamic response data of casting explosive. The piezoelectricity quartz gauges have been used to directly measure dynamic stress processing of specimen. This modified data processing method has been adopted, which can eliminate the effect caused by stress non-uniformity. By using the modified data processing, the signal failure problem caused by long pulse incident can also be resolved. With the modified SHPB method, satisfactory results have been obtained in processing casting explosive.
2015, 35(6): 852-857.
doi: 10.11883/1001-1455(2015)06-0852-06
Abstract:
The effect of pre-stress on elastic precursor of disk-shaped LY12 aluminum samples was studied, and the radial pre-stress (or pre-strain) state was achieved by using an excessively-conjugated heat assembly device. In the experiment, the LY12 samples were impacted by flyer plates driven by a one-stage light-gas gun, and elastic precursor signals of the samples in several pre-strain states were measured by VISAR. The experimental results show that the elastic precursors are 87.56, 95.24 and 121.03 m/s respectively corresponding to the pre-strains of 0, 964.5×10-6 and 1 886.0×10-6 when the samples are impacted by the flyer plates with almost the same velocity. This clearly indicates that the pre-stress (pre-strain) increases the elastic precursor of LY12 aluminum. According to these experiments, we discussed how to apply static loading on the sample in the radial direction. The result shows that the loading with rising edge time 100 μs can produce the same stress distribution as that of static loading. Using this technology, the simulation results show that by increasing pre-stress we can enhance the elastic precursor velocity on the free surface of the samples. The simulated results are in good agreement with those from the experiments.
The effect of pre-stress on elastic precursor of disk-shaped LY12 aluminum samples was studied, and the radial pre-stress (or pre-strain) state was achieved by using an excessively-conjugated heat assembly device. In the experiment, the LY12 samples were impacted by flyer plates driven by a one-stage light-gas gun, and elastic precursor signals of the samples in several pre-strain states were measured by VISAR. The experimental results show that the elastic precursors are 87.56, 95.24 and 121.03 m/s respectively corresponding to the pre-strains of 0, 964.5×10-6 and 1 886.0×10-6 when the samples are impacted by the flyer plates with almost the same velocity. This clearly indicates that the pre-stress (pre-strain) increases the elastic precursor of LY12 aluminum. According to these experiments, we discussed how to apply static loading on the sample in the radial direction. The result shows that the loading with rising edge time 100 μs can produce the same stress distribution as that of static loading. Using this technology, the simulation results show that by increasing pre-stress we can enhance the elastic precursor velocity on the free surface of the samples. The simulated results are in good agreement with those from the experiments.
2015, 35(6): 858-863.
doi: 10.11883/1001-1455(2015)06-0858-06
Abstract:
In order to obtain mechanical properties of phenolic cotton fabric material at different strain rates, we performed experiments of the uniaxial compression tests of phenolic cotton fabric material at the strain rate ranging from 10-3 to 103 s-1, using the universal testing machine and the split Hopkinson pressure bar (SHPB), obtained the stress-strain curve at different strain rates, and discussed compression failure mechanism under quasi-static and dynamic loads. The results from our experiments show that the dynamic compression fail strength of phenolic cotton fabric material has strong strain rate sensitivity and it increases along with the strain rate. Compared with the stress under the quasi-static loading, the peak stress under the dynamic loading increases by approximately 10 times, while the failure strain is reduced to about half. The differences in the mechanical properties under quasi-static and dynamic loading conditions is due to the strain rate effect of the fiber matrix interface characteristics on the one hand, and to the differences in failure modes at different strain rates on the other. Zhu-Wang-Tang (ZWT) constitutive was adopted to describe the mechanical behavior of the phenolic cotton fabric material.
In order to obtain mechanical properties of phenolic cotton fabric material at different strain rates, we performed experiments of the uniaxial compression tests of phenolic cotton fabric material at the strain rate ranging from 10-3 to 103 s-1, using the universal testing machine and the split Hopkinson pressure bar (SHPB), obtained the stress-strain curve at different strain rates, and discussed compression failure mechanism under quasi-static and dynamic loads. The results from our experiments show that the dynamic compression fail strength of phenolic cotton fabric material has strong strain rate sensitivity and it increases along with the strain rate. Compared with the stress under the quasi-static loading, the peak stress under the dynamic loading increases by approximately 10 times, while the failure strain is reduced to about half. The differences in the mechanical properties under quasi-static and dynamic loading conditions is due to the strain rate effect of the fiber matrix interface characteristics on the one hand, and to the differences in failure modes at different strain rates on the other. Zhu-Wang-Tang (ZWT) constitutive was adopted to describe the mechanical behavior of the phenolic cotton fabric material.
2015, 35(6): 864-870.
doi: 10.11883/1001-1455(2015)06-0864-07
Abstract:
We carried out SHPB tests on dry and saturated concretes using split Hopkinson and they were compared with quasi-static mechanical tests. The results show that the dry and saturated concretes produce an obvious strain rate effect: the ascending part of the stress-strain curve at moderate strain rate is steeper than that of the quasi-static curve; the increasing amplitude of dynamic strength of the saturated concrete, which has a stronger sensitivity to the strain rate, is nearly twice as that of the dry concrete; and there is a threshold of the strain rate, i.e., it is only when the strain rate exceeds this threshold that the dynamic strength of the saturated concrete becomes stronger than that of the dry concrete. Based on the experimental results, the equation showing the relationship between the concrete strength and the strain rate at different saturations is established and given.
We carried out SHPB tests on dry and saturated concretes using split Hopkinson and they were compared with quasi-static mechanical tests. The results show that the dry and saturated concretes produce an obvious strain rate effect: the ascending part of the stress-strain curve at moderate strain rate is steeper than that of the quasi-static curve; the increasing amplitude of dynamic strength of the saturated concrete, which has a stronger sensitivity to the strain rate, is nearly twice as that of the dry concrete; and there is a threshold of the strain rate, i.e., it is only when the strain rate exceeds this threshold that the dynamic strength of the saturated concrete becomes stronger than that of the dry concrete. Based on the experimental results, the equation showing the relationship between the concrete strength and the strain rate at different saturations is established and given.
2015, 35(6): 871-875.
doi: 10.11883/1001-1455(2015)06-0871-05
Abstract:
First, the pressure transducer is calibrated using the shock tube. Second, the mathematical model of the pressure transducer is established through the system identification with Generalized Least Square Iterative Method with Special Whitening Filter. According to the model the dynamic characteristics can be obtained. Finally, the dynamic characteristics compensation method based on the zero pole cancellation method is proposed and applied to data processing. Practical application shows that data processing method based on dynamic compensation can improve the dynamic characteristics of the sensor and the accuracy of the test data.
First, the pressure transducer is calibrated using the shock tube. Second, the mathematical model of the pressure transducer is established through the system identification with Generalized Least Square Iterative Method with Special Whitening Filter. According to the model the dynamic characteristics can be obtained. Finally, the dynamic characteristics compensation method based on the zero pole cancellation method is proposed and applied to data processing. Practical application shows that data processing method based on dynamic compensation can improve the dynamic characteristics of the sensor and the accuracy of the test data.
2015, 35(6): 876-880.
doi: 10.11883/1001-1455(2015)06-0876-05
Abstract:
A novel experimental technique to study the reaction threshold of explosives is developed. The flyer is accelerated to an expected velocity to gain a low amplitude loading by the gas gun. The interface particle velocity between JOB-9003 and PMMA under different stresses is measured with electromagnetic particle velocity gauges. The interface velocities of unreacting and reacting explosive are achieved based on the curve of the explosive interface particle velocity. The relationship ofup-p is achieved according to interface velocity of unreacting and reacting explosives. The chemical reaction threshold and the ignition threshold of JOB-9003 are 1.65 GPa and 2.62 GPa under the low amplitude loading.
A novel experimental technique to study the reaction threshold of explosives is developed. The flyer is accelerated to an expected velocity to gain a low amplitude loading by the gas gun. The interface particle velocity between JOB-9003 and PMMA under different stresses is measured with electromagnetic particle velocity gauges. The interface velocities of unreacting and reacting explosive are achieved based on the curve of the explosive interface particle velocity. The relationship ofup-p is achieved according to interface velocity of unreacting and reacting explosives. The chemical reaction threshold and the ignition threshold of JOB-9003 are 1.65 GPa and 2.62 GPa under the low amplitude loading.
2015, 35(6): 881-887.
doi: 10.11883/1001-1455(2015)06-0881-07
Abstract:
New findings in the research of pulse shaping technique are widely used in dynamic compressive test. Dynamic tension, Brazilian disc test and dynamic bending fracture test are introduced in detail. Furthermore, the problems found in the application of the pulse shaping technique are summarized, and the directions for further research in this area are put forward.
New findings in the research of pulse shaping technique are widely used in dynamic compressive test. Dynamic tension, Brazilian disc test and dynamic bending fracture test are introduced in detail. Furthermore, the problems found in the application of the pulse shaping technique are summarized, and the directions for further research in this area are put forward.
2015, 35(6): 888-894.
doi: 10.11883/1001-1455(2015)06-0888-07
Abstract:
To investigate the shock resistance of multi-layered pyramidal lattice panels impacted by a ball hammer, we carried out an experiment of 4-layered pyramidal lattices under the impact of a ball hammer, analyzed the collapse deformation process and mode, and put forward the energy absorption mechanism. Our results show that, when subjected to a medium impact of a ball hammer, the final deformation of the multilayered pyramidal lattice panels can be composed of three parts where deformation occurs: head-on, interlayer, and backside, thus forming a "sandwich"-like deformation mode.
To investigate the shock resistance of multi-layered pyramidal lattice panels impacted by a ball hammer, we carried out an experiment of 4-layered pyramidal lattices under the impact of a ball hammer, analyzed the collapse deformation process and mode, and put forward the energy absorption mechanism. Our results show that, when subjected to a medium impact of a ball hammer, the final deformation of the multilayered pyramidal lattice panels can be composed of three parts where deformation occurs: head-on, interlayer, and backside, thus forming a "sandwich"-like deformation mode.
2015, 35(6): 895-900.
doi: 10.11883/1001-1455(2015)06-0895-06
Abstract:
Relying on the explosively driven setting of one-end detonator initiation and using the Doppler velocimetry and high-speed framing camera, we diagnosed the expansion and fracture process of the cylindrical shell. The results obtained from our experiment provide the velocity-time history of the shell surface and its dynamic snapshots referring to expansion deformation, crack initiation and propagation, and explosion product leakage. The results from the SPH simulation are in reasonably good agreement with the experimental findings. Systemic analysis of experiments and simulations determine incident angle of shock wave for cylindrical shell, releasing angle of explosion wave, velocity and pressure profile of internal wall and deformed strain, fracture process of cylindrical shell.
Relying on the explosively driven setting of one-end detonator initiation and using the Doppler velocimetry and high-speed framing camera, we diagnosed the expansion and fracture process of the cylindrical shell. The results obtained from our experiment provide the velocity-time history of the shell surface and its dynamic snapshots referring to expansion deformation, crack initiation and propagation, and explosion product leakage. The results from the SPH simulation are in reasonably good agreement with the experimental findings. Systemic analysis of experiments and simulations determine incident angle of shock wave for cylindrical shell, releasing angle of explosion wave, velocity and pressure profile of internal wall and deformed strain, fracture process of cylindrical shell.
2015, 35(6): 901-906.
doi: 10.11883/1001-1455(2015)06-0901-06
Abstract:
The methane has a high risk of gas explosion because its concentration has come into the explosion limit range in the liquefaction process of low-concentration oxygen-bed methane. This gas explosion process was simulated on a flow field platform at low temperature in an air tight container. According to the simulation results, when the reaction system volume and environmental pressure are invariable, the lower the ambient temperature, the greater the maximum explosion pressure, and the longer the time it takes the methane gas to reach the maximum explosion pressure; the explosion flow field set up the positive and negative flow areas with chemical reaction zone as the front, and continually approaching the wall; the flame propagation process as affected by the chemical reaction is a positive feedback mechanism, and four phases-flame ignition, accelerated propagation, attenuated propagation and quenching-are found occurring in the airtight container; with the falling down of the ambient temperature, flame propagation speed decreased markedly, and the flame duration extended. The resulting conclusions provide an important basis for understanding methane explosion mechanism and preventing explosion accidents in the liquefaction process of low-concentration oxygen-bed methane under low-temperature conditions.
The methane has a high risk of gas explosion because its concentration has come into the explosion limit range in the liquefaction process of low-concentration oxygen-bed methane. This gas explosion process was simulated on a flow field platform at low temperature in an air tight container. According to the simulation results, when the reaction system volume and environmental pressure are invariable, the lower the ambient temperature, the greater the maximum explosion pressure, and the longer the time it takes the methane gas to reach the maximum explosion pressure; the explosion flow field set up the positive and negative flow areas with chemical reaction zone as the front, and continually approaching the wall; the flame propagation process as affected by the chemical reaction is a positive feedback mechanism, and four phases-flame ignition, accelerated propagation, attenuated propagation and quenching-are found occurring in the airtight container; with the falling down of the ambient temperature, flame propagation speed decreased markedly, and the flame duration extended. The resulting conclusions provide an important basis for understanding methane explosion mechanism and preventing explosion accidents in the liquefaction process of low-concentration oxygen-bed methane under low-temperature conditions.
2015, 35(6): 907-912.
doi: 10.11883/1001-1455(2015)06-0907-06
Abstract:
As polyurethane foam has a good cushioning and energy absorption performance, the sandwich structure with polyurethane foam as core and the steel as the shell plate has been widely used in engineering application. In this paper, in order to study the anti-explosion performance of the sandwich structure, the numerical simulation by Ansys/Autodyn nonlinear finite element code is adopted to analyze the energy absorption properties of the sandwich structure under blast loading and compared with that of the steel plate that has the same area density. The results show that, with the polyurethane foam as core body, the energy sandwich structure absorbed is 1.49 times that of the steel plate with the same area density, and the anti-explosion performance of the overall structure is greatly improved.
As polyurethane foam has a good cushioning and energy absorption performance, the sandwich structure with polyurethane foam as core and the steel as the shell plate has been widely used in engineering application. In this paper, in order to study the anti-explosion performance of the sandwich structure, the numerical simulation by Ansys/Autodyn nonlinear finite element code is adopted to analyze the energy absorption properties of the sandwich structure under blast loading and compared with that of the steel plate that has the same area density. The results show that, with the polyurethane foam as core body, the energy sandwich structure absorbed is 1.49 times that of the steel plate with the same area density, and the anti-explosion performance of the overall structure is greatly improved.
2015, 35(6): 913-918.
doi: 10.11883/1001-1455(2015)06-0913-06
Abstract:
The micromorphological characteristics of rock failure surface by rockburst are analyzed and studied with the scanning electron microscope to explore the rockburst mechanism. The relation between rock failure surface morphology with stress and rock constituent is studied with rock samples from the rockburst site of the 12th Pingdingshan Mine. The results show the rock failure surface of surrounding rock of roadway presents a step-like shape, and the split surface is parallel to the orientation of the maximum principal stress of in-situ stress; the rock failure surface belongs to a draw-stretch fracture, where the crack is brittle. The rock failure surface morphology with rockburst casting is very complicated, and the broken face is parallel to or intersected with the direction of the shear stress (maximum principal stress). The microcrack on different planes form steps with those among rockburst cracks or under tearing effect, with uneven surfaces, which can be defined as stretch-draw or shearing fracture. Rock micro-components have a greater effect on rockburst, and the rockburst occurs more likely for the compact and brittle rock with a high crystalline degree.
The micromorphological characteristics of rock failure surface by rockburst are analyzed and studied with the scanning electron microscope to explore the rockburst mechanism. The relation between rock failure surface morphology with stress and rock constituent is studied with rock samples from the rockburst site of the 12th Pingdingshan Mine. The results show the rock failure surface of surrounding rock of roadway presents a step-like shape, and the split surface is parallel to the orientation of the maximum principal stress of in-situ stress; the rock failure surface belongs to a draw-stretch fracture, where the crack is brittle. The rock failure surface morphology with rockburst casting is very complicated, and the broken face is parallel to or intersected with the direction of the shear stress (maximum principal stress). The microcrack on different planes form steps with those among rockburst cracks or under tearing effect, with uneven surfaces, which can be defined as stretch-draw or shearing fracture. Rock micro-components have a greater effect on rockburst, and the rockburst occurs more likely for the compact and brittle rock with a high crystalline degree.
