2016 Vol. 36, No. 6
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2016, 36(6): 745-751.
doi: 10.11883/1001-1455(2016)06-0745-07
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Abstract:
In order to study the explosive friction safety, a numerical simulation of high explosive friction sensitivity experiment was performed based on a melting friction model. The numerical results agree with the experiment results. The law of friction sensitivity was then analyzed based on the thermal decomposition rate. As the melting temperature is usually lower than the ignition temperature, a one-dimension numerical simulation of sensitivity experiment was conducted using a model that took account of melting, and the ignition times and melting results were obtained. The order of four explosives' ignition time including DATB, NQ, TATB and TNT meet agree with the experiment results, proving the applicability of the model. Furthermore, based on the order of the thermal decomposition rate, the numerical results have proved that, when the friction strength reaches certain degrees, the order of ignition time will change, which means that the sensitivity experiment cannot fully describe the order of the explosive sensitivity.
In order to study the explosive friction safety, a numerical simulation of high explosive friction sensitivity experiment was performed based on a melting friction model. The numerical results agree with the experiment results. The law of friction sensitivity was then analyzed based on the thermal decomposition rate. As the melting temperature is usually lower than the ignition temperature, a one-dimension numerical simulation of sensitivity experiment was conducted using a model that took account of melting, and the ignition times and melting results were obtained. The order of four explosives' ignition time including DATB, NQ, TATB and TNT meet agree with the experiment results, proving the applicability of the model. Furthermore, based on the order of the thermal decomposition rate, the numerical results have proved that, when the friction strength reaches certain degrees, the order of ignition time will change, which means that the sensitivity experiment cannot fully describe the order of the explosive sensitivity.
2016, 36(6): 752-758.
doi: 10.11883/1001-1455(2016)06-0752-07
Abstract:
This paper carried out high-speed penetration experiments using semi-infinite plain concrete targets with different projectile materials and aspect ratios to investigate the effects of striking velocity and material strength on projectile loss and penetration efficiency. Characterized with caliber-radius-head (CRH) 3.0 and 30-mm diameter, the ogive-nose projectiles were launched at high-speed striking velocities between 880-1 900 m/s to impact the concrete target. The measured experiment data indicates that the penetration efficiency is in parabolic relation with the striking velocity, i.e. the maximum penetration efficiency corresponds to an impact velocity of about 1 400 m/s. The main abrasion occurs around the projectile nose while only negligible erosion is observed at the projectile shank and end cap. When the speed exceeds the characteristic impact velocity, the projectile's mass loss is so serious that even bending deformation or disintegration occurs. When the projectile strength is nearly doubled, the mass loss is reduced by about 80%. Based on the experimental data, the relationship function of dimensionless penetration efficiency and impact velocity was achieved using dimensional analysis. The dimensionless model obtained in this paper is capable of predicting the corresponding impact speed for the maximum penetration efficiency, thereby providing theoretical guidance for high-speed simulated penetration experiments.
This paper carried out high-speed penetration experiments using semi-infinite plain concrete targets with different projectile materials and aspect ratios to investigate the effects of striking velocity and material strength on projectile loss and penetration efficiency. Characterized with caliber-radius-head (CRH) 3.0 and 30-mm diameter, the ogive-nose projectiles were launched at high-speed striking velocities between 880-1 900 m/s to impact the concrete target. The measured experiment data indicates that the penetration efficiency is in parabolic relation with the striking velocity, i.e. the maximum penetration efficiency corresponds to an impact velocity of about 1 400 m/s. The main abrasion occurs around the projectile nose while only negligible erosion is observed at the projectile shank and end cap. When the speed exceeds the characteristic impact velocity, the projectile's mass loss is so serious that even bending deformation or disintegration occurs. When the projectile strength is nearly doubled, the mass loss is reduced by about 80%. Based on the experimental data, the relationship function of dimensionless penetration efficiency and impact velocity was achieved using dimensional analysis. The dimensionless model obtained in this paper is capable of predicting the corresponding impact speed for the maximum penetration efficiency, thereby providing theoretical guidance for high-speed simulated penetration experiments.
2016, 36(6): 759-766.
doi: 10.11883/1001-1455(2016)06-0759-08
Abstract:
The coefficient of the ultimate elongation is one of significant parameters related with theoretical calculations of a shaped charge jet (SCJ). Based on the effect of a longitudinal magnetic field on the stress-strain of SCJ, and following the motion equation and the plastic instability condition, the formula of the coefficient of the ultimate elongation of a shaped charge inside the magnetic field was obtained and, using this formula, the ratio of the coefficient of the ultimate elongation was calculated respectively with and without the existence of a magnetic field. In addition, the theoretical model was verified through the experiments with two different standoffs. The results indicate that the electromagnetic force arising from the deformation of the SCJ due to the magnetic field that has penetrated into its material inhibits the development of the necking, and extends the stretching stage before the SCJ breaks up into particles, thus increasing the coefficient of the ultimate elongation. Predictions from the theoretical calculation are in good agreement with the data obtained from the experiments.
The coefficient of the ultimate elongation is one of significant parameters related with theoretical calculations of a shaped charge jet (SCJ). Based on the effect of a longitudinal magnetic field on the stress-strain of SCJ, and following the motion equation and the plastic instability condition, the formula of the coefficient of the ultimate elongation of a shaped charge inside the magnetic field was obtained and, using this formula, the ratio of the coefficient of the ultimate elongation was calculated respectively with and without the existence of a magnetic field. In addition, the theoretical model was verified through the experiments with two different standoffs. The results indicate that the electromagnetic force arising from the deformation of the SCJ due to the magnetic field that has penetrated into its material inhibits the development of the necking, and extends the stretching stage before the SCJ breaks up into particles, thus increasing the coefficient of the ultimate elongation. Predictions from the theoretical calculation are in good agreement with the data obtained from the experiments.
2016, 36(6): 774-780.
doi: 10.11883/1001-1455(2016)06-0774-07
Abstract:
An experimental method in the confinement vessel for silver aerosol source-term investigation of metal under high explosive detonation was designed to simulate the plutonium aerosol source-term of nuclear devices under the circumstance of high explosive detonation. Seven silver source-term experiments under variable explosive pressure were conducted in the aerosol facility and the size distribution characteristics of the silver aerosol with an aerodynamic diameter less than 10 μm were examined and compared with the data from the field test. The results show that the silver aerosol source-term under specific conditions has good agreement with the plutonium aerosol source-term obtained by the U. S. government under test conditions simulating an open-air detonation accident of nuclear device. The amount of the silver aerosolized in the experiment is determined by the peak value of high explosive pressure that acted on the silver plate and exhibited a quadratic polynomial. The silver aerosol with an aerodynamic diameter ranging from 0.7 to 3.3 μm account for the major part of the silver aerosol induced by high explosive detonation. When the peak value exceeds a certain critical value, the total amount of aerosol reaches the maximum. Settlement and combination of aerosol were observed in the comparative analysis of the size-mass distribution of the samples collected at different times after the explosion.
An experimental method in the confinement vessel for silver aerosol source-term investigation of metal under high explosive detonation was designed to simulate the plutonium aerosol source-term of nuclear devices under the circumstance of high explosive detonation. Seven silver source-term experiments under variable explosive pressure were conducted in the aerosol facility and the size distribution characteristics of the silver aerosol with an aerodynamic diameter less than 10 μm were examined and compared with the data from the field test. The results show that the silver aerosol source-term under specific conditions has good agreement with the plutonium aerosol source-term obtained by the U. S. government under test conditions simulating an open-air detonation accident of nuclear device. The amount of the silver aerosolized in the experiment is determined by the peak value of high explosive pressure that acted on the silver plate and exhibited a quadratic polynomial. The silver aerosol with an aerodynamic diameter ranging from 0.7 to 3.3 μm account for the major part of the silver aerosol induced by high explosive detonation. When the peak value exceeds a certain critical value, the total amount of aerosol reaches the maximum. Settlement and combination of aerosol were observed in the comparative analysis of the size-mass distribution of the samples collected at different times after the explosion.
2016, 36(6): 781-788.
doi: 10.11883/1001-1455(2016)06-0781-08
Abstract:
The supercavitating projectile is a new underwater weapon with high speed and kinetic energy. Based on the theory of the ideal compressible potential flow, and taking into account of the gravity effect, an unified theoretical model and numerical calculation for the supercavitating flow caused by an underwater slender conical projectile were constructed, the integral-differential equations for computing the supercavity profiles at subsonic and supersonic speed were derived, and the numerical discrete scheme and a recursive solution were proposed using local fitting of quadratic polynomial, thus obtaining the supercavity profile. The theoretical model and numerical calculation were verified by comparing the asymptotic solutions with the numerical ones of the supercavity aspect ratio. The effects of gravity and compressibility on the supercavity scale, pressure distribution over the projectile and base drag coefficient were summarized through analysis of the supercavity profiles and hydrodynamic coefficients in different movement modes, depths and speeds for the slender conical projectile.
The supercavitating projectile is a new underwater weapon with high speed and kinetic energy. Based on the theory of the ideal compressible potential flow, and taking into account of the gravity effect, an unified theoretical model and numerical calculation for the supercavitating flow caused by an underwater slender conical projectile were constructed, the integral-differential equations for computing the supercavity profiles at subsonic and supersonic speed were derived, and the numerical discrete scheme and a recursive solution were proposed using local fitting of quadratic polynomial, thus obtaining the supercavity profile. The theoretical model and numerical calculation were verified by comparing the asymptotic solutions with the numerical ones of the supercavity aspect ratio. The effects of gravity and compressibility on the supercavity scale, pressure distribution over the projectile and base drag coefficient were summarized through analysis of the supercavity profiles and hydrodynamic coefficients in different movement modes, depths and speeds for the slender conical projectile.
2016, 36(6): 789-796.
doi: 10.11883/1001-1455(2016)06-0789-08
Abstract:
In this paper, we investigated a novel method by carrying out a sclaed down underwater explosion experiment on a centrifuge apparatus and set up the similarity theory between the scaled down and actual underwater explosion experiment. Using numerical simulation, we also investigated the shock-wave load, the bubble load and bubble dynamic behaviors between original models, the novel scaled down experimental method and the conventional method. The results from our study indicate that the conventional scaled down model experiment is unable to accurately predict the bubble dynamics and the vertical near-field loading induced by the bubble collapse. When the deviation of the far-field bubble pulse is limited within 10%, the distance between the explosion source and the measuring point has to be larger than 9.5 times that of the maximum radius of the bubble. However, the novel experimental method can make a precise prediction for the original model. The experiment of a mini-charge underwater explosion almost reproduces the whole physical process of a mass-charge underwater explosion with the completely similar stages of the shock wave and the bubble. In addition, the depth of the water can also be scaled down, thereby overcoming the disadvantages of the conventional method. The present study aims at providing a novel way to perform underwater explosion model experiments.
In this paper, we investigated a novel method by carrying out a sclaed down underwater explosion experiment on a centrifuge apparatus and set up the similarity theory between the scaled down and actual underwater explosion experiment. Using numerical simulation, we also investigated the shock-wave load, the bubble load and bubble dynamic behaviors between original models, the novel scaled down experimental method and the conventional method. The results from our study indicate that the conventional scaled down model experiment is unable to accurately predict the bubble dynamics and the vertical near-field loading induced by the bubble collapse. When the deviation of the far-field bubble pulse is limited within 10%, the distance between the explosion source and the measuring point has to be larger than 9.5 times that of the maximum radius of the bubble. However, the novel experimental method can make a precise prediction for the original model. The experiment of a mini-charge underwater explosion almost reproduces the whole physical process of a mass-charge underwater explosion with the completely similar stages of the shock wave and the bubble. In addition, the depth of the water can also be scaled down, thereby overcoming the disadvantages of the conventional method. The present study aims at providing a novel way to perform underwater explosion model experiments.
2016, 36(6): 797-802.
doi: 10.11883/1001-1455(2016)06-0797-06
Abstract:
The critical ricochet angle of a penetrator impacting hard targets obliquely needs to be analyzed and estimated to ensure that no ricochet occur while the penetrator hits the targets. In this work the experiments on the ricochet performance of the penetrator with a big length-to-diameter ratio impacting reinforced concrete targets at a velocity of 250-430 m/s were conducted, the critical ricochet angles in which it impacts the reinforced concrete targets possessing a compressive strength of 30 MPa and 60 MPa respectively were analyzed and estimated, and the envelope curves of the critical ricochet angle were obtained. The results show that, when the intensity of the target is maintained the same, the projectile's critical ricochet angle increases with the increase of the penetration velocity. This increase gradually slows down. At the same penetration velocity, with the increase of the targets' strength, the projectile's critical ricochet angle decreases. The projectile's critical ricochet angles from the analysis of the empirical formula were lower than those from the experiments, but the deviation is less than 3°
The critical ricochet angle of a penetrator impacting hard targets obliquely needs to be analyzed and estimated to ensure that no ricochet occur while the penetrator hits the targets. In this work the experiments on the ricochet performance of the penetrator with a big length-to-diameter ratio impacting reinforced concrete targets at a velocity of 250-430 m/s were conducted, the critical ricochet angles in which it impacts the reinforced concrete targets possessing a compressive strength of 30 MPa and 60 MPa respectively were analyzed and estimated, and the envelope curves of the critical ricochet angle were obtained. The results show that, when the intensity of the target is maintained the same, the projectile's critical ricochet angle increases with the increase of the penetration velocity. This increase gradually slows down. At the same penetration velocity, with the increase of the targets' strength, the projectile's critical ricochet angle decreases. The projectile's critical ricochet angles from the analysis of the empirical formula were lower than those from the experiments, but the deviation is less than 3°
2016, 36(6): 825-831.
doi: 10.11883/1001-1455(2016)06-0825-07
Abstract:
The influences of the blast loading rate, the distance from the guide hole to the free boundary and the radius of the guide hole between the two charge holes, on the dynamic propagation of cracks in rock were studied using realistic failure process analysis (RFPA-dynamic). The results show that, as the loading rate decreases, the crushed zone around the charge hole is gradually reduced; the position of the crack initiation moves gradually from the crushed zone to the charge hole; and the number of small branch cracks gradually decreases while the length of the main crack increases. Due to the influence of the free boundary, the cracks that were previously downward now gradually bend in the horizontal direction, and this tendency becomes more observable as the distance from the charge hole to the free boundary gets shorter. As a result of the guidance of the guide hole, the cracks close to the guide hole gradually curve to the guide hole and, at the same time, a crack is formed at both ends of the guide hole wall that propagates to the charge hole. The radius of the guide hole has no obvious effect on the guiding role, but the nonuniformity of the material does have a significant effect on the way the cracks propagate.
The influences of the blast loading rate, the distance from the guide hole to the free boundary and the radius of the guide hole between the two charge holes, on the dynamic propagation of cracks in rock were studied using realistic failure process analysis (RFPA-dynamic). The results show that, as the loading rate decreases, the crushed zone around the charge hole is gradually reduced; the position of the crack initiation moves gradually from the crushed zone to the charge hole; and the number of small branch cracks gradually decreases while the length of the main crack increases. Due to the influence of the free boundary, the cracks that were previously downward now gradually bend in the horizontal direction, and this tendency becomes more observable as the distance from the charge hole to the free boundary gets shorter. As a result of the guidance of the guide hole, the cracks close to the guide hole gradually curve to the guide hole and, at the same time, a crack is formed at both ends of the guide hole wall that propagates to the charge hole. The radius of the guide hole has no obvious effect on the guiding role, but the nonuniformity of the material does have a significant effect on the way the cracks propagate.
2016, 36(6): 832-838.
doi: 10.11883/1001-1455(2016)06-0832-07
Abstract:
In order to investigate the flame characteristics of gasoline-air mixture deflagration in a confined space, visualized experiments were performed at different equivalence ratios. Three flame patterns of gasoline-air deflagration were proposed: smooth spherical flame, fold spherical flame and curling flocculent flame. Based on the chemical kinetics and flame spectroscopy, the forming mechanism of each flame pattern was examined. Then, the critical equivalence ratio, here used to distinguish the flame patterns, was obtained by theoretical analysis and experimental measurement. Combined with the collected key parameters in the experiments, the differences in key parameters of each flame pattern were summarized, such as reaction products, rate of pressure rise, flame intensity, duration of flame and maximum pressure.
In order to investigate the flame characteristics of gasoline-air mixture deflagration in a confined space, visualized experiments were performed at different equivalence ratios. Three flame patterns of gasoline-air deflagration were proposed: smooth spherical flame, fold spherical flame and curling flocculent flame. Based on the chemical kinetics and flame spectroscopy, the forming mechanism of each flame pattern was examined. Then, the critical equivalence ratio, here used to distinguish the flame patterns, was obtained by theoretical analysis and experimental measurement. Combined with the collected key parameters in the experiments, the differences in key parameters of each flame pattern were summarized, such as reaction products, rate of pressure rise, flame intensity, duration of flame and maximum pressure.
2016, 36(6): 839-846.
doi: 10.11883/1001-1455(2016)06-0839-08
Abstract:
In order to improve the blasting vibration and boost the efficiency of blasting energy, this paper mainly focuses on the delay time control research through transmission law. We performed an experiment with a delayed-detonation scheme in different period, which selects common detonator and Orica high precision detonator. The measured vibration of the earthquake wave is based on seismic wave function optimization theory foundation. The measured data and wavy figure were acquired through it, then we found out the variation characteristics of the rules of earthquake wave propagation, peak velocity, domain frequency, band energy and the total energy in different delayed period. At the same time, according to the characteristics to find velocity map which Synthesized by triaxialvibration wave and displacement map which assembled by speed Calculus correspond to the maximum in same time. On the basis of peak velocity-vibration displacement distribution characteristics, fitting method for Gaussian multi-peak is applied for measured vibration wave, to give the band energy maximize time points about t=60 ms, blasting vibration around the minimum time for t=25 ms.
In order to improve the blasting vibration and boost the efficiency of blasting energy, this paper mainly focuses on the delay time control research through transmission law. We performed an experiment with a delayed-detonation scheme in different period, which selects common detonator and Orica high precision detonator. The measured vibration of the earthquake wave is based on seismic wave function optimization theory foundation. The measured data and wavy figure were acquired through it, then we found out the variation characteristics of the rules of earthquake wave propagation, peak velocity, domain frequency, band energy and the total energy in different delayed period. At the same time, according to the characteristics to find velocity map which Synthesized by triaxialvibration wave and displacement map which assembled by speed Calculus correspond to the maximum in same time. On the basis of peak velocity-vibration displacement distribution characteristics, fitting method for Gaussian multi-peak is applied for measured vibration wave, to give the band energy maximize time points about t=60 ms, blasting vibration around the minimum time for t=25 ms.
2016, 36(6): 847-852.
doi: 10.11883/1001-1455(2016)06-0847-06
Abstract:
In this work experiments were carried out to investigate the effect of ignition locations and vent burst pressures on the pressure profile and the flame propagation during explosion venting of hydrogen-air mixtures. The results indicate that, in all the cases, the central ignition leads to the largest flame areas, the highest flame propagation velocities and peak pressures peak pressures; compared with that of the central ignition, the effect of the rear ignition on the flame propagation velocity, the flame areas and the peak pressures is reduced, while the front ignition results in the smallest flame areas, the lowest flame propagation velocity and peak pressures. For the front ignition, the pressure profile exhibits three peak pressures which correspond to the following three successive stages, but for the central and rear ignition, only the first and the third peak pressure can be found. Furthermore, both the peak pressures and the flame areas increase with the bursting pressure. Overpressure measurements made inside the chamber show clearly that the acoustic oscillation occurs and the internal pressures were influenced by the external explosion.
In this work experiments were carried out to investigate the effect of ignition locations and vent burst pressures on the pressure profile and the flame propagation during explosion venting of hydrogen-air mixtures. The results indicate that, in all the cases, the central ignition leads to the largest flame areas, the highest flame propagation velocities and peak pressures peak pressures; compared with that of the central ignition, the effect of the rear ignition on the flame propagation velocity, the flame areas and the peak pressures is reduced, while the front ignition results in the smallest flame areas, the lowest flame propagation velocity and peak pressures. For the front ignition, the pressure profile exhibits three peak pressures which correspond to the following three successive stages, but for the central and rear ignition, only the first and the third peak pressure can be found. Furthermore, both the peak pressures and the flame areas increase with the bursting pressure. Overpressure measurements made inside the chamber show clearly that the acoustic oscillation occurs and the internal pressures were influenced by the external explosion.
2016, 36(6): 853-860.
doi: 10.11883/1001-1455(2016)06-0853-08
Abstract:
In this work, based on the similarity theory, we conducted a model experiment to study the vibration effect and damage evolution of rocks surrounding a tunnel in push-type cyclic blasting excavation. The model was constructed with a ratio of 1: 15. By simulating the tunnel excavation of push-type cyclic blasting, we explored the influence of the change of blasting parameters on the vibration effect. The degree of the damage of the surrounding rock was evaluated by the change of the acoustic velocity at the same measuring point after blasting. The relationship between the damage evolution of the surrounding rock and the times of blasting was established. We arrived at the following results: (1) When the maximum section dose was about the same, the influence of the initiation section number on the dielectric coefficient (K) of Sodev formula was very small, but it was great on the attenuation coefficient of Sodev formula; (2) In push-type cyclic blasting excavation, there was a great difference in the decrease rates of the acoustic velocity among the measuring points with the same distance to the blasting region at the same depth, and the blasting damage ranges of the surrounding rock were typically an isotropic in terms of both depth and width; (3) When the blasting parameters were basically the same, the growth trend of the cumulative acoustic velocity's decrease rate at the measuring point was nonlinear in different cyclic blasting excavation; (4) There were nonlinear evolution characteristics between the blasting cumulative damage (D) of the surrounding rock and the times of blasting (n) under push-type cyclic blasting loading, and different measuring points had different blasting cumulative damage propagation models. The closer the measuring point was to the explosion source, the faster the cumulative damage extension. Blasting cumulative damage effect of the surrounding rock had typically nonlinear evolution properties and anisotropic characteristics.
In this work, based on the similarity theory, we conducted a model experiment to study the vibration effect and damage evolution of rocks surrounding a tunnel in push-type cyclic blasting excavation. The model was constructed with a ratio of 1: 15. By simulating the tunnel excavation of push-type cyclic blasting, we explored the influence of the change of blasting parameters on the vibration effect. The degree of the damage of the surrounding rock was evaluated by the change of the acoustic velocity at the same measuring point after blasting. The relationship between the damage evolution of the surrounding rock and the times of blasting was established. We arrived at the following results: (1) When the maximum section dose was about the same, the influence of the initiation section number on the dielectric coefficient (K) of Sodev formula was very small, but it was great on the attenuation coefficient of Sodev formula; (2) In push-type cyclic blasting excavation, there was a great difference in the decrease rates of the acoustic velocity among the measuring points with the same distance to the blasting region at the same depth, and the blasting damage ranges of the surrounding rock were typically an isotropic in terms of both depth and width; (3) When the blasting parameters were basically the same, the growth trend of the cumulative acoustic velocity's decrease rate at the measuring point was nonlinear in different cyclic blasting excavation; (4) There were nonlinear evolution characteristics between the blasting cumulative damage (D) of the surrounding rock and the times of blasting (n) under push-type cyclic blasting loading, and different measuring points had different blasting cumulative damage propagation models. The closer the measuring point was to the explosion source, the faster the cumulative damage extension. Blasting cumulative damage effect of the surrounding rock had typically nonlinear evolution properties and anisotropic characteristics.
2016, 36(6): 861-868.
doi: 10.11883/1001-1455(2016)06-0861-08
Abstract:
In this work, the standard genetic algorithm (SGA) was parallel processed using multiple parallel structures. Based on the structures, a multiple-population genetic algorithm (MPGA) was established by introducing the immigration operator and quintessence population. Self-adaptive operators of crossover probability and mutation probability were designed to improve the convergence speed of the MPGA. Combining ABAQUS with the improved multiple-population genetic optimized algorithm, a parameter identification method of constitutive model was built. Using the proposed method, a simulation example of parameter identification for PBX viscoelastic damage constitutive model was carried out. Comparison was made between methods based on SGA and MPGA. The results show that the MPGA method can effectively overcome the difficulty of the premature convergence and the identification result is more robust. The method is suitable for the optimization of complex nonlinear systems due to its superiority in the convergence speed and searching ability, and it can be applied to the parameter identification of other models.
In this work, the standard genetic algorithm (SGA) was parallel processed using multiple parallel structures. Based on the structures, a multiple-population genetic algorithm (MPGA) was established by introducing the immigration operator and quintessence population. Self-adaptive operators of crossover probability and mutation probability were designed to improve the convergence speed of the MPGA. Combining ABAQUS with the improved multiple-population genetic optimized algorithm, a parameter identification method of constitutive model was built. Using the proposed method, a simulation example of parameter identification for PBX viscoelastic damage constitutive model was carried out. Comparison was made between methods based on SGA and MPGA. The results show that the MPGA method can effectively overcome the difficulty of the premature convergence and the identification result is more robust. The method is suitable for the optimization of complex nonlinear systems due to its superiority in the convergence speed and searching ability, and it can be applied to the parameter identification of other models.
2016, 36(6): 869-875.
doi: 10.11883/1001-1455(2016)06-0869-07
Abstract:
During high strain rate and large strain deformation of crystalline metals, there exist phenomena of continuous refinement of microstructural characteristic length, like the size of dislocation cells, which occurs intensively and would have significant influence on the work hardening and macroscopic flow stress. In this work, based on the inverse relation between macroscopic flow stress and and the cell size, a new type of BCJ constitutive model was proposed. The flow rule and evolution equations for internal state variables in BCJ model were modified by involving the cell size parameter; the evolution equation for the cell size considering the dependence of the strain rate and the temperature was introduced into the model; and an internal state variable viscoplastic constitutive model that considers the evolution of microstructural characteristic length, accumulation and annihilation of dislocations was then established. The new constitutive model was illustrated by predicting the experimental stress-strain data of OFHC Cu over a wide range of strain rates (10-4 -103 s-1), temperatures (298-542 K) and strains (0-1). The results show that the predicted data agree very well with the experimental data. Compared with the BCJ model, the predictive accuracies of the proposed model in various loading conditions are obviously improved, the maximum average relative error is reduced from 9.939% to 5.525%.
During high strain rate and large strain deformation of crystalline metals, there exist phenomena of continuous refinement of microstructural characteristic length, like the size of dislocation cells, which occurs intensively and would have significant influence on the work hardening and macroscopic flow stress. In this work, based on the inverse relation between macroscopic flow stress and and the cell size, a new type of BCJ constitutive model was proposed. The flow rule and evolution equations for internal state variables in BCJ model were modified by involving the cell size parameter; the evolution equation for the cell size considering the dependence of the strain rate and the temperature was introduced into the model; and an internal state variable viscoplastic constitutive model that considers the evolution of microstructural characteristic length, accumulation and annihilation of dislocations was then established. The new constitutive model was illustrated by predicting the experimental stress-strain data of OFHC Cu over a wide range of strain rates (10-4 -103 s-1), temperatures (298-542 K) and strains (0-1). The results show that the predicted data agree very well with the experimental data. Compared with the BCJ model, the predictive accuracies of the proposed model in various loading conditions are obviously improved, the maximum average relative error is reduced from 9.939% to 5.525%.
2016, 36(6): 876-882.
doi: 10.11883/1001-1455(2016)06-0876-07
Abstract:
To understand the energy evolution mechanism in the rock failure process, this paper firstly obtained the meso-mechanical parameters of granite using uniaxial compression experiments and particle flow codes, then tested the granite under different confining pressures and finally analyzed its energy evolution mechanism in the failure process and deduced its energy yield criterion. The main results are as follows: The internal damage of granite in the failure process occurs earlier under lower confining pressures while later under higher confining pressures, which shows that the internal damage under lower confining pressures is a progressive development process but under higher confining pressures the internal damage rapidly develops into failure once it occurs. The granite's elastic strain energy remains constant in a certain strain range before the peak under higher confining pressures, and the overall energy absorbed transforms into dissipation energy, which shows that the granite internal damage under higher confining pressures is more severe. The elastic strain energy increases and reaches the elastic strain energy limit and then decreases. There exists a linear relationship between the elastic strain energy limit and the confining pressure, therefore rock excavation under high confining pressures is likely to induce a rapid release of a large amount of elastic strain energy which causes the surrounding rock to become unstable and even to burst. The energy ratio at the granite's peak failure is a definite value and independent of the confining pressure. The energy yield criterion is derived based on the principle of energy. It includes lithology parameters and all principal stresses and can reflect the comprehensive factors influencing the rock failure.
To understand the energy evolution mechanism in the rock failure process, this paper firstly obtained the meso-mechanical parameters of granite using uniaxial compression experiments and particle flow codes, then tested the granite under different confining pressures and finally analyzed its energy evolution mechanism in the failure process and deduced its energy yield criterion. The main results are as follows: The internal damage of granite in the failure process occurs earlier under lower confining pressures while later under higher confining pressures, which shows that the internal damage under lower confining pressures is a progressive development process but under higher confining pressures the internal damage rapidly develops into failure once it occurs. The granite's elastic strain energy remains constant in a certain strain range before the peak under higher confining pressures, and the overall energy absorbed transforms into dissipation energy, which shows that the granite internal damage under higher confining pressures is more severe. The elastic strain energy increases and reaches the elastic strain energy limit and then decreases. There exists a linear relationship between the elastic strain energy limit and the confining pressure, therefore rock excavation under high confining pressures is likely to induce a rapid release of a large amount of elastic strain energy which causes the surrounding rock to become unstable and even to burst. The energy ratio at the granite's peak failure is a definite value and independent of the confining pressure. The energy yield criterion is derived based on the principle of energy. It includes lithology parameters and all principal stresses and can reflect the comprehensive factors influencing the rock failure.
2016, 36(6): 739-744.
doi: 10.11883/1001-1455(2016)06-0739-06
Abstract:
In this work the instability of the metal shell in the cylindrical implosion was studied numerically using a multi-component elastic-plastic hydrodynamic Eulerian code. Agreeing with those of the experiments, the numerical results show that the material strength restrains the growth of the interfacial perturbation with an effect not to be overlooked. The material yield strength has an obvious restraining effect on the higher mode of perturbation, while that of the shear module is similar but less sensitive. There exists a most instable mode number, which decreases as the yield strength increases and is approximately linear with the logarithm of the yield strength, and the perturbation grows faster as the shell grows thinner.
In this work the instability of the metal shell in the cylindrical implosion was studied numerically using a multi-component elastic-plastic hydrodynamic Eulerian code. Agreeing with those of the experiments, the numerical results show that the material strength restrains the growth of the interfacial perturbation with an effect not to be overlooked. The material yield strength has an obvious restraining effect on the higher mode of perturbation, while that of the shear module is similar but less sensitive. There exists a most instable mode number, which decreases as the yield strength increases and is approximately linear with the logarithm of the yield strength, and the perturbation grows faster as the shell grows thinner.
2016, 36(6): 767-773.
doi: 10.11883/1001-1455(2016)06-0767-07
Abstract:
Spall experiments of pure aluminum were performed on the light-gas gun equipment and SG Ⅱ high energy laser facility. An improved target configuration was applied to address the problem that the residual vibration was often lost in laser-loading spall experiments. By virtue of distinguishing the obvious difference in the strain rate between the two experiments, the material and rate-dependent issues related with the nucleation, growth and coalescence of micro-damage were examined using numerical simulations, which is important for developing predictive theoretical models. Results show that for our previously proposed model the average diameter, the critical pressure, and the nucleation rate parameter for micro-void nucleation can be regarded as material constants and the same is true with the critical pressure for micro-void growth, whereas the specific effective surface energy for micro-void growth and the critical damage for coalescence are typical rate-dependent. Furthermore, our simulations indicate that at the local spall position, although the spall strength has an apparent strain rate effect, the critical behavior of the transformation of the sample from continuous stretch to compression is determined by a critical damage, whose value is very small and is probably a material constant.
Spall experiments of pure aluminum were performed on the light-gas gun equipment and SG Ⅱ high energy laser facility. An improved target configuration was applied to address the problem that the residual vibration was often lost in laser-loading spall experiments. By virtue of distinguishing the obvious difference in the strain rate between the two experiments, the material and rate-dependent issues related with the nucleation, growth and coalescence of micro-damage were examined using numerical simulations, which is important for developing predictive theoretical models. Results show that for our previously proposed model the average diameter, the critical pressure, and the nucleation rate parameter for micro-void nucleation can be regarded as material constants and the same is true with the critical pressure for micro-void growth, whereas the specific effective surface energy for micro-void growth and the critical damage for coalescence are typical rate-dependent. Furthermore, our simulations indicate that at the local spall position, although the spall strength has an apparent strain rate effect, the critical behavior of the transformation of the sample from continuous stretch to compression is determined by a critical damage, whose value is very small and is probably a material constant.
2016, 36(6): 803-810.
doi: 10.11883/1001-1455(2016)06-0803-08
Abstract:
In this study, experimental investigations on the liquid's explosive dispersal under different shell constraints were carried out, effects of shell constraints on the early characteristics of the flow field were discussed, and the mechanism for liquid state transition and breakup was analyzed and compared with the numerical simulation. The results show that cavitation occurs in the liquid when the rarefaction waves reflects on the shell. The stronger the shell constraint, the greater the delay of the cavitation that emerges and the closer to the center where the cavitation is located, and the earlier the explosive product mixes with the liquid on the nearby interfaces.
In this study, experimental investigations on the liquid's explosive dispersal under different shell constraints were carried out, effects of shell constraints on the early characteristics of the flow field were discussed, and the mechanism for liquid state transition and breakup was analyzed and compared with the numerical simulation. The results show that cavitation occurs in the liquid when the rarefaction waves reflects on the shell. The stronger the shell constraint, the greater the delay of the cavitation that emerges and the closer to the center where the cavitation is located, and the earlier the explosive product mixes with the liquid on the nearby interfaces.
2016, 36(6): 811-818.
doi: 10.11883/1001-1455(2016)06-0811-08
Abstract:
The limit hinge is one of key technologies in the design of evolvable warheads, and its damage efficiency is determined by keeping its integrity in the deploying process of the warhead. In this paper, a novel hinge with energy absorption properties was designed based on dynamic principles and theoretical models of evolvable warheads, and the evolving process of the evolvable warhead with charges of varying sizes was numerically simulated, and the different performances of the ordinary hinge and the energy absorption hinge compared and examined, with a particular focus on the status of force and energy absorption undergone by the warhead when the limit angel was reached. The results show that the energy absorption hinge can reduce the impact force and improve energy absorption. The results of the experiment carried out on the evolvable warhead structure equipped with the two kinds of hinges show that the traditional hinge suffers damage in varying degrees, while our novel hinge with energy absorption keeps the structural integrity, proving that the energy absorption hinge will ensure the integrity of the warhead and the hinge when reaching the limit angel, and verifying the rationality of the energy absorption hinge design plan and the reliability of the numerical simulation.
The limit hinge is one of key technologies in the design of evolvable warheads, and its damage efficiency is determined by keeping its integrity in the deploying process of the warhead. In this paper, a novel hinge with energy absorption properties was designed based on dynamic principles and theoretical models of evolvable warheads, and the evolving process of the evolvable warhead with charges of varying sizes was numerically simulated, and the different performances of the ordinary hinge and the energy absorption hinge compared and examined, with a particular focus on the status of force and energy absorption undergone by the warhead when the limit angel was reached. The results show that the energy absorption hinge can reduce the impact force and improve energy absorption. The results of the experiment carried out on the evolvable warhead structure equipped with the two kinds of hinges show that the traditional hinge suffers damage in varying degrees, while our novel hinge with energy absorption keeps the structural integrity, proving that the energy absorption hinge will ensure the integrity of the warhead and the hinge when reaching the limit angel, and verifying the rationality of the energy absorption hinge design plan and the reliability of the numerical simulation.
2016, 36(6): 819-824.
doi: 10.11883/1001-1455(2016)06-0819-06
Abstract:
Electromagnetic driving expanding ring experiment and explosive expanding ring experiment are two important means for obtaining dynamic tensile mechanical properties of materials. In this study, they were carried out to investigate the dynamic behaviors of oxygen-free copper (TU1) expanding rings. The results show that, during the loading stage, samples driven by electromagnetic force satisfy the assumption of the uniform deformation due to the body force whereas it is not the case with the explosive expanding ring because the sample is impacted by the surface force. With respect to this difference, a new method considering the deformation inhomogeneity was established, where the axial plastic strain and radial plastic strain during impact stage was included in the calculation of the equivalent plastic strain. Through the revised method a more accurate stress-strain relationship of TU1 was obtained.
Electromagnetic driving expanding ring experiment and explosive expanding ring experiment are two important means for obtaining dynamic tensile mechanical properties of materials. In this study, they were carried out to investigate the dynamic behaviors of oxygen-free copper (TU1) expanding rings. The results show that, during the loading stage, samples driven by electromagnetic force satisfy the assumption of the uniform deformation due to the body force whereas it is not the case with the explosive expanding ring because the sample is impacted by the surface force. With respect to this difference, a new method considering the deformation inhomogeneity was established, where the axial plastic strain and radial plastic strain during impact stage was included in the calculation of the equivalent plastic strain. Through the revised method a more accurate stress-strain relationship of TU1 was obtained.
