2020 Vol. 40, No. 8
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2020, 40(8): 081101.
doi: 10.11883/bzycj-2020-0050
Abstract:
Dynamic mechanical behavior of metallic materials under complicated loading conditions has attracted much attention. However, it is hard to obtain the dynamic Bauschinger effect of metallic materials due to the limitation of loading equipment. In order to investigate the relationship between the Bauschinger effect and strain rate effect of metallic materials, this paper proposes an asynchronous loading technique based on electromagnetic split Hopkinson bar system, which could provide an effective way to study the Bauschinger effect of metallic materials under high strain rate loading. We first introduce the main characteristics of the asynchronous loading device, that is, the specimen can be loaded by one cycle of continuous dynamic tension-compression loading pulse in which the two separate stress waves are created by electromagnetic pulse generators and prove to maintain their consistency. The propagation of stress waves was analyzed to ensure the continuity of the loading process. Then the dynamic loading process and the methods of data processing and stress wave separation are presented. Stress equilibrium was also analyzed in order to demonstrate the reliability of the equipment. Finally, the Bauschinger effect of 6061 aluminum alloy at 5% pre-strain during the process of dynamic compression to dynamic tension loading was studied using this method, and the corresponding quasi-static tests were also conducted for comparison. It was found that the material shows less strain-rate sensitivity under axial compression loading, while its Bauschinger stress parameter increases from 0.07 in quasi-static loading to 0.17 in dynamic loading. The results indicate that the Bauschinger effect of 6061 aluminum alloys depends on the strain rate and can be significantly enhanced under dynamic loading. This conclusion presents a challenge to the traditional conception that aluminum alloys are insensitive to strain rate.
Dynamic mechanical behavior of metallic materials under complicated loading conditions has attracted much attention. However, it is hard to obtain the dynamic Bauschinger effect of metallic materials due to the limitation of loading equipment. In order to investigate the relationship between the Bauschinger effect and strain rate effect of metallic materials, this paper proposes an asynchronous loading technique based on electromagnetic split Hopkinson bar system, which could provide an effective way to study the Bauschinger effect of metallic materials under high strain rate loading. We first introduce the main characteristics of the asynchronous loading device, that is, the specimen can be loaded by one cycle of continuous dynamic tension-compression loading pulse in which the two separate stress waves are created by electromagnetic pulse generators and prove to maintain their consistency. The propagation of stress waves was analyzed to ensure the continuity of the loading process. Then the dynamic loading process and the methods of data processing and stress wave separation are presented. Stress equilibrium was also analyzed in order to demonstrate the reliability of the equipment. Finally, the Bauschinger effect of 6061 aluminum alloy at 5% pre-strain during the process of dynamic compression to dynamic tension loading was studied using this method, and the corresponding quasi-static tests were also conducted for comparison. It was found that the material shows less strain-rate sensitivity under axial compression loading, while its Bauschinger stress parameter increases from 0.07 in quasi-static loading to 0.17 in dynamic loading. The results indicate that the Bauschinger effect of 6061 aluminum alloys depends on the strain rate and can be significantly enhanced under dynamic loading. This conclusion presents a challenge to the traditional conception that aluminum alloys are insensitive to strain rate.
2020, 40(8): 082101.
doi: 10.11883/bzycj-2019-0469
Abstract:
In order to study the impact of the metal jet formed by a shaped charge on a solid-rocket engine, the shaped-charge blasting experiment was carried out, and the jet impingement experiment was performed for the shaped jet impacting a certain-size engine without protection. A high-speed camera was used to record the response processes of the explosions. Air overpressures and fragment velocities were measured at different distances and in different directions. The jet forming process and the jet-impacting-motor process were numerically simulated by using the finite element software AUTODYN. And in the simulation, the problem of fluid-solid coupling grid leakage was avoided by adjusting the grid thickness. The experimental results show that when the rocket engine was impacted by the jet, it exploded violently and the propellant reacted completely. The steel equipment fixing the rocket engine after the explosion was almost destroyed completely. The velocity of fragments reached above 4 700 m/s. The air overpressure at 1 m away from the explosion center of the engine reached 19.78 MPa. Through the pictures collected by the high-speed camera, it could be judged that the temperature in the explosion center reached above 3 000 ℃. According to the peak of the air overpressure and the law of air similarity, the energy produced by this type of propellant explosion was slightly higher than those produced by explosives such as 8701 and TNT. The simulated results show that when the jet impinged on the engine shell at the head velocity of 7 000 m/s, the tip of the jet head was severely ablated, and the velocity of the jet head decreased to about 5 600 m/s; the propellant reacted violently while being penetrated 1−2 mm by the jet; the shock wave propagated along the propellant in a spherical shape, and the propellant on the other side underwent shock initiation twice with a retonation; there were three overpressure peaks at the Gauss point located in the center of the propellant. The first peak was generated by the shock wave from the left side; the second peak was due to the shock wave hitting the solid wall of the propellant and a certain wave surface reflection was generated, causing a pressure rise; the third peak was caused by a new shock wave generated by the retonation. The simulated average air overpressure peak is 18.75 MPa at the three Gauss points set at 1 m from the center of the engine, which is in good agreement with the experimental results.
In order to study the impact of the metal jet formed by a shaped charge on a solid-rocket engine, the shaped-charge blasting experiment was carried out, and the jet impingement experiment was performed for the shaped jet impacting a certain-size engine without protection. A high-speed camera was used to record the response processes of the explosions. Air overpressures and fragment velocities were measured at different distances and in different directions. The jet forming process and the jet-impacting-motor process were numerically simulated by using the finite element software AUTODYN. And in the simulation, the problem of fluid-solid coupling grid leakage was avoided by adjusting the grid thickness. The experimental results show that when the rocket engine was impacted by the jet, it exploded violently and the propellant reacted completely. The steel equipment fixing the rocket engine after the explosion was almost destroyed completely. The velocity of fragments reached above 4 700 m/s. The air overpressure at 1 m away from the explosion center of the engine reached 19.78 MPa. Through the pictures collected by the high-speed camera, it could be judged that the temperature in the explosion center reached above 3 000 ℃. According to the peak of the air overpressure and the law of air similarity, the energy produced by this type of propellant explosion was slightly higher than those produced by explosives such as 8701 and TNT. The simulated results show that when the jet impinged on the engine shell at the head velocity of 7 000 m/s, the tip of the jet head was severely ablated, and the velocity of the jet head decreased to about 5 600 m/s; the propellant reacted violently while being penetrated 1−2 mm by the jet; the shock wave propagated along the propellant in a spherical shape, and the propellant on the other side underwent shock initiation twice with a retonation; there were three overpressure peaks at the Gauss point located in the center of the propellant. The first peak was generated by the shock wave from the left side; the second peak was due to the shock wave hitting the solid wall of the propellant and a certain wave surface reflection was generated, causing a pressure rise; the third peak was caused by a new shock wave generated by the retonation. The simulated average air overpressure peak is 18.75 MPa at the three Gauss points set at 1 m from the center of the engine, which is in good agreement with the experimental results.
2020, 40(8): 082102.
doi: 10.11883/bzycj-2019-0436
Abstract:
The photomultiplier tube (PMT) is the core component of the neutrino detector. It is a thin shell structure made of glass material with a vacuum inside and arranged to work in deep water. Once the PMT is crushed, it generates a strong shock wave, which will cause a blast of the surrounding PMT. Aiming at the implosion of PMT, a simplified simulation model of PMT implosion was established, and the simulation results were compared with the experimental results to verify the rationality of the simplified model. On this basis, the PMT implosion calculation method was proposed based on the area reduction equivalent model, the influence of the breach area of the guard on the PMT implosion was analyzed by the equivalent model. The results show that with the decrease of the breach area of the guard, the moment of PMT implosion caused by the collision of water flow is correspondingly advanced, the pulse width of the shock wave generated by the implosion remains basically unchanged, and the peak value of the shock wave is significantly reduced. This study is helpful for finding an effective PMT implosion protection method.
The photomultiplier tube (PMT) is the core component of the neutrino detector. It is a thin shell structure made of glass material with a vacuum inside and arranged to work in deep water. Once the PMT is crushed, it generates a strong shock wave, which will cause a blast of the surrounding PMT. Aiming at the implosion of PMT, a simplified simulation model of PMT implosion was established, and the simulation results were compared with the experimental results to verify the rationality of the simplified model. On this basis, the PMT implosion calculation method was proposed based on the area reduction equivalent model, the influence of the breach area of the guard on the PMT implosion was analyzed by the equivalent model. The results show that with the decrease of the breach area of the guard, the moment of PMT implosion caused by the collision of water flow is correspondingly advanced, the pulse width of the shock wave generated by the implosion remains basically unchanged, and the peak value of the shock wave is significantly reduced. This study is helpful for finding an effective PMT implosion protection method.
2020, 40(8): 082103.
doi: 10.11883/bzycj-2019-0480
Abstract:
Taking methane as the representative gas, the effect of setting multi-hole obstacle in semi-enclosed pipe on the flame propagation of flammable gas explosion was studied, and the experiment was reproduced based on the large eddy simulation (LES), the shape, position and speed of flame propagation were compared in the experiment and simulation, the flow field and area change of the flame before and after the obstacle were analyze and then the method of measuring the refractory rate of the flame is proposed. The results show that the LES results are in good consistency with the experimental results. Flame propagation has gone through four stages in the duct, followed by the layer flow bubbles rapid expansion stage, the flame pulsation reflux stage, the turbulent flame rapid development stage, the flame deceleration stabilization stage, in which the speed of the flame fluctuates. After the flame has passed through the multi-hole obstacles, the propagation speed suddenly rises to a peak value, which is 58.7% higher than the maximum speed in front of the obstacle. The discharge vent and ignition are at the same end in the duct, when the flame is near the obstacle, which is effected by the top of pipe and obstacle significantly, and the speed would be negative and the flame will flow back. Obstacles are the direct cause of the broken layer flow bubbles and the increase of area fold rate, the maximum flame fold rate is 44.8% after flame passed the obstacle, which is increased by 36.72%.
Taking methane as the representative gas, the effect of setting multi-hole obstacle in semi-enclosed pipe on the flame propagation of flammable gas explosion was studied, and the experiment was reproduced based on the large eddy simulation (LES), the shape, position and speed of flame propagation were compared in the experiment and simulation, the flow field and area change of the flame before and after the obstacle were analyze and then the method of measuring the refractory rate of the flame is proposed. The results show that the LES results are in good consistency with the experimental results. Flame propagation has gone through four stages in the duct, followed by the layer flow bubbles rapid expansion stage, the flame pulsation reflux stage, the turbulent flame rapid development stage, the flame deceleration stabilization stage, in which the speed of the flame fluctuates. After the flame has passed through the multi-hole obstacles, the propagation speed suddenly rises to a peak value, which is 58.7% higher than the maximum speed in front of the obstacle. The discharge vent and ignition are at the same end in the duct, when the flame is near the obstacle, which is effected by the top of pipe and obstacle significantly, and the speed would be negative and the flame will flow back. Obstacles are the direct cause of the broken layer flow bubbles and the increase of area fold rate, the maximum flame fold rate is 44.8% after flame passed the obstacle, which is increased by 36.72%.
2020, 40(8): 082201.
doi: 10.11883/bzycj-2019-0456
Abstract:
In order to solve the safety problem caused by flammable gas explosion in pipeline transportation, an experimental system for premixed gas explosion and explosion suppression in multiple pipelines was self-built. And then a series of premixed methane-air explosion and explosion suppression experiments were carried out under the ultrafine water mists without or with three kinds of salts in the different working conditions including the different salt mass fractions and the different mist fluxes. In the experiments, the methane volume fraction in the premixed methane-air mixture was 9.5%, and three salts used as additives were NaCl, NaHCO3 and MgCl2. According to the theories of fire science and explosion science, the different changes in the explosion characteristics were explored involving the oscillation curves and the maximum peak values of explosion overpressure, the front positions and the average propagation velocities of the explosion flame, the evolution images of the flame structure in pipe B. The results show that with the increases of salt mass fractions and ultrafine water mist fluxes with salts (NaCl, NaHCO3 and MgCl2), the maximum peaks of explosion overpressure decreased by different amplitudes compared with those under the action of pure water mist, the oscillation curves of explosion overpressure increased slowly, and the average propagation velocities of explosion flame decreased significantly. The explosion flame fronts receded different times in the pipe B. And the times when the explosion flames reached the terminal end of the pipe B delayed obviously compared with those with or without the pure ultrafine water mist. Comparisons display that the ultrafine water mist containing NaCl is superior to the ones containing MgCl2 and NaHCO3, respectively, in weakening the explosion overpressure, delaying the advance of the flame front position, decreasing the average flame propagation velocity, and reducing the receding times of the explosion flame front. The primary reason is that the ability of the anion Cl−to destroy OH· and H· radicals in chain explosion reactions is stronger than that of the anion\begin{document}${\rm{HCO}}_3^- $\end{document} ![]()
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In order to solve the safety problem caused by flammable gas explosion in pipeline transportation, an experimental system for premixed gas explosion and explosion suppression in multiple pipelines was self-built. And then a series of premixed methane-air explosion and explosion suppression experiments were carried out under the ultrafine water mists without or with three kinds of salts in the different working conditions including the different salt mass fractions and the different mist fluxes. In the experiments, the methane volume fraction in the premixed methane-air mixture was 9.5%, and three salts used as additives were NaCl, NaHCO3 and MgCl2. According to the theories of fire science and explosion science, the different changes in the explosion characteristics were explored involving the oscillation curves and the maximum peak values of explosion overpressure, the front positions and the average propagation velocities of the explosion flame, the evolution images of the flame structure in pipe B. The results show that with the increases of salt mass fractions and ultrafine water mist fluxes with salts (NaCl, NaHCO3 and MgCl2), the maximum peaks of explosion overpressure decreased by different amplitudes compared with those under the action of pure water mist, the oscillation curves of explosion overpressure increased slowly, and the average propagation velocities of explosion flame decreased significantly. The explosion flame fronts receded different times in the pipe B. And the times when the explosion flames reached the terminal end of the pipe B delayed obviously compared with those with or without the pure ultrafine water mist. Comparisons display that the ultrafine water mist containing NaCl is superior to the ones containing MgCl2 and NaHCO3, respectively, in weakening the explosion overpressure, delaying the advance of the flame front position, decreasing the average flame propagation velocity, and reducing the receding times of the explosion flame front. The primary reason is that the ability of the anion Cl−to destroy OH· and H· radicals in chain explosion reactions is stronger than that of the anion
2020, 40(8): 083101.
doi: 10.11883/bzycj-2019-0254
Abstract:
In order to accurately and reliably test the dynamic shear characteristics of laser metal deposition GH4169 on a traditional split Hopkinson pressure bar, this study compared the three different dynamic shear sample forms and dimensions to the shear zone stress based on numerical simulation. The influence of the distribution shows that the shear stress of the shear zone of the double shear specimen after optimization is dominant, and the dynamic shear test of approximate pure shear can be realized. Using this specimen form, the shear stress-strain curves of LMD GH4169 specimens with different orientations (scanning direction, deposition direction) at different strain rates were systematically tested, and the specimens were analyzed by SEM. The results show that: (1) the specimen used in this paper has high shear purity and uniform thickness distribution along the shear zone width, which can better obtain the dynamic shear properties of the material; (2) the shear stress-shear strain curves obtained from the experiment were analyzed. It is found that the material shows unobvious anisotropy in the scanning path direction and deposition direction. With the increase of strain rate, it has obvious strain rate strengthening effect; the uniaxial compression and dynamic shear stress-strain curves were simultaneously converted into equivalent stress-strain curves; the comparison confirms that the specimen form in this manuscript can exactly reflect the shear properties of the material; (3) through the microscopic analysis of the shear deformation of LMD GH4169, the size and depth of the fracture dimple decrease as the strain rate increases, and the toughness decreases. The shear failure is easy under a smaller deformation. Initial microscopic defects are likely to cause dynamic shear failure of the material.
In order to accurately and reliably test the dynamic shear characteristics of laser metal deposition GH4169 on a traditional split Hopkinson pressure bar, this study compared the three different dynamic shear sample forms and dimensions to the shear zone stress based on numerical simulation. The influence of the distribution shows that the shear stress of the shear zone of the double shear specimen after optimization is dominant, and the dynamic shear test of approximate pure shear can be realized. Using this specimen form, the shear stress-strain curves of LMD GH4169 specimens with different orientations (scanning direction, deposition direction) at different strain rates were systematically tested, and the specimens were analyzed by SEM. The results show that: (1) the specimen used in this paper has high shear purity and uniform thickness distribution along the shear zone width, which can better obtain the dynamic shear properties of the material; (2) the shear stress-shear strain curves obtained from the experiment were analyzed. It is found that the material shows unobvious anisotropy in the scanning path direction and deposition direction. With the increase of strain rate, it has obvious strain rate strengthening effect; the uniaxial compression and dynamic shear stress-strain curves were simultaneously converted into equivalent stress-strain curves; the comparison confirms that the specimen form in this manuscript can exactly reflect the shear properties of the material; (3) through the microscopic analysis of the shear deformation of LMD GH4169, the size and depth of the fracture dimple decrease as the strain rate increases, and the toughness decreases. The shear failure is easy under a smaller deformation. Initial microscopic defects are likely to cause dynamic shear failure of the material.
2020, 40(8): 083102.
doi: 10.11883/bzycj-2019-0358
Abstract:
To explore the effects of the thickness of joint-filling material on the dynamic fracture properties of cracks under impact load, the gypsum was used as the material filled into the prefabricated cracks in polymethyl methacrylate (PMMA) specimens, three-point bending impact tests were conducted on the PMMA specimens with different joint filling thicknesses by using a novel digital laser dynamic caustics experimental system. The experimental results show that the vertical prefabricated cracks propagate vertically upward toward the free surface under the same impact load, which is a tytical mode-Ⅰ crack, and the thicker the filling, the easier the vertical crack initiation. When the vertical crack propagates to the horizontal prefabricated crack, the energy gathering times of the horizontal prefabricated cracks in the specimens with a filling thickness of 1, 3 and 5 mm are 433, 2 200 and 2 580 μs, respectively. And the stress intensity factors of crack initiation are 635.2, 742.4 and 906.8 kN/m3/2, respectively. It indicates that the thicker the filling, the more difficult the horizontal crack initiation. The horizontal prefabricated crack is a typical Ⅰ-Ⅱ composite crack. The thicker the joint filler, the more curved the propagation path of the horizontal prefabricated crack. When the distance between the crack and the upper boundary of the specimen is 3 mm, the horizontal crack propagates towards the upper boundary of the specimen, and the specimen finally breaks. It is found that the distances between the fracture points and the impact load points of the specimens with the filling thicknesses of 1, 3 and 5 mm are 16.5, 11.0 and 6.0 mm, respectively.
To explore the effects of the thickness of joint-filling material on the dynamic fracture properties of cracks under impact load, the gypsum was used as the material filled into the prefabricated cracks in polymethyl methacrylate (PMMA) specimens, three-point bending impact tests were conducted on the PMMA specimens with different joint filling thicknesses by using a novel digital laser dynamic caustics experimental system. The experimental results show that the vertical prefabricated cracks propagate vertically upward toward the free surface under the same impact load, which is a tytical mode-Ⅰ crack, and the thicker the filling, the easier the vertical crack initiation. When the vertical crack propagates to the horizontal prefabricated crack, the energy gathering times of the horizontal prefabricated cracks in the specimens with a filling thickness of 1, 3 and 5 mm are 433, 2 200 and 2 580 μs, respectively. And the stress intensity factors of crack initiation are 635.2, 742.4 and 906.8 kN/m3/2, respectively. It indicates that the thicker the filling, the more difficult the horizontal crack initiation. The horizontal prefabricated crack is a typical Ⅰ-Ⅱ composite crack. The thicker the joint filler, the more curved the propagation path of the horizontal prefabricated crack. When the distance between the crack and the upper boundary of the specimen is 3 mm, the horizontal crack propagates towards the upper boundary of the specimen, and the specimen finally breaks. It is found that the distances between the fracture points and the impact load points of the specimens with the filling thicknesses of 1, 3 and 5 mm are 16.5, 11.0 and 6.0 mm, respectively.
2020, 40(8): 083201.
doi: 10.11883/bzycj-2019-0389
Abstract:
A series of large-scale explosion model tests were carried out in dense unsaturated calcareous sand using spherical TNT explosives. The propagation laws of the blast wave in dense calcareous sand were studied under various conditions, such as explosive mass, buried depth and water content of sand sample, based on analyzing the changes of major parameters of blast wave. The results show that the blast wave propagates mainly in the form of elastic-plastic wave in dense calcareous sand. Moreover, the plastic longitudinal wave velocity increases with the increase of initial density in the dry sand sample. For the wet sand sample, the plastic longitudinal wave velocity increase with the decrease of the water content. More specifically, the corresponding longitudinal wave velocity ranges from 250 to 282 m/s in the dry sand and ranges from 302 to 339 m/s in the wet sand. In the case of concentrated charge, the critical scaled buried depth of closed explosion in unsaturated calcareous sand is about 2.25 m/kg1/3. In the test range, the attenuations of peak normal stress and specific normal impulse of the blast wave in dense calcareous sand obey the explosion similarity law. The stress attenuation coefficient of blast wave in dry calcareous sand is 2.94 or 1.37 respectively at the measured points whose scaled distances are greater than or less than 0.75 m/kg1/3. The stress attenuation coefficient of explosion wave in wet calcareous sand increases with the increase of water content and ranges from 1.39 to 1.79. The attenuation coefficient of the specific normal impulse decreases with the increase of the sample water content, and the range is 0.97 to 1.18.
A series of large-scale explosion model tests were carried out in dense unsaturated calcareous sand using spherical TNT explosives. The propagation laws of the blast wave in dense calcareous sand were studied under various conditions, such as explosive mass, buried depth and water content of sand sample, based on analyzing the changes of major parameters of blast wave. The results show that the blast wave propagates mainly in the form of elastic-plastic wave in dense calcareous sand. Moreover, the plastic longitudinal wave velocity increases with the increase of initial density in the dry sand sample. For the wet sand sample, the plastic longitudinal wave velocity increase with the decrease of the water content. More specifically, the corresponding longitudinal wave velocity ranges from 250 to 282 m/s in the dry sand and ranges from 302 to 339 m/s in the wet sand. In the case of concentrated charge, the critical scaled buried depth of closed explosion in unsaturated calcareous sand is about 2.25 m/kg1/3. In the test range, the attenuations of peak normal stress and specific normal impulse of the blast wave in dense calcareous sand obey the explosion similarity law. The stress attenuation coefficient of blast wave in dry calcareous sand is 2.94 or 1.37 respectively at the measured points whose scaled distances are greater than or less than 0.75 m/kg1/3. The stress attenuation coefficient of explosion wave in wet calcareous sand increases with the increase of water content and ranges from 1.39 to 1.79. The attenuation coefficient of the specific normal impulse decreases with the increase of the sample water content, and the range is 0.97 to 1.18.
2020, 40(8): 083301.
doi: 10.11883/bzycj-2019-0372
Abstract:
In order to study the projectile-proof performance and impact damage mechanism of yttrium aluminum garnet (YAG) transparent ceramic and glass, the residual penetration depths of 12.7 mm armor-piercing projectiles penetrating into YAG transparent ceramic/glass were experimentally studied. A theoretical model was established based on the mechanism of deformation penetration and rigid penetration to analyze the processes of the projectiles impacting the YAG transparent ceramic and glass, and the cavity penetration model was used to determine the residual penetration depth of the projectile into the 2024T351 aluminum. The experimental results show that the YAG transparent ceramic has a strong crushing effect on projectiles, and its projectile-proof ability is significantly better than that of the silicate glass. The mass of the residual projectile and the penetration depth calculated by the theoretical model agree well with the experimental results. So the established model can be used to evaluate the projectile-proof performances of different panel materials.
In order to study the projectile-proof performance and impact damage mechanism of yttrium aluminum garnet (YAG) transparent ceramic and glass, the residual penetration depths of 12.7 mm armor-piercing projectiles penetrating into YAG transparent ceramic/glass were experimentally studied. A theoretical model was established based on the mechanism of deformation penetration and rigid penetration to analyze the processes of the projectiles impacting the YAG transparent ceramic and glass, and the cavity penetration model was used to determine the residual penetration depth of the projectile into the 2024T351 aluminum. The experimental results show that the YAG transparent ceramic has a strong crushing effect on projectiles, and its projectile-proof ability is significantly better than that of the silicate glass. The mass of the residual projectile and the penetration depth calculated by the theoretical model agree well with the experimental results. So the established model can be used to evaluate the projectile-proof performances of different panel materials.
2020, 40(8): 083302.
doi: 10.11883/bzycj-2019-0457
Abstract:
At the initial velocity range of 380~680 m/s, positive impact on GH4169 spacer plates by 8 mm diameter tungsten spheres was performed, measuring the initial velocity, residual velocity and deflection. It is obvious that the first plate is mainly subjected to shear damage and ejected cup-shaped plug, the third plate is mainly subjected to tensile failure, and the deflection of the third plate is significantly greater than the first plate. The calculation formula for the consumption work of the spacer plates is established, the consumption work of each plates impacted by projectiles is calculated by combining the shear plugging model and the plug velocity model. The results show that the unit area density consumption work of the second and third plates is much higher than that of the first plate, which is closely related to the deformation and failure modes of the plates. Consumption work can be used to quantitatively describe the ballistic resistance of each plate.
At the initial velocity range of 380~680 m/s, positive impact on GH4169 spacer plates by 8 mm diameter tungsten spheres was performed, measuring the initial velocity, residual velocity and deflection. It is obvious that the first plate is mainly subjected to shear damage and ejected cup-shaped plug, the third plate is mainly subjected to tensile failure, and the deflection of the third plate is significantly greater than the first plate. The calculation formula for the consumption work of the spacer plates is established, the consumption work of each plates impacted by projectiles is calculated by combining the shear plugging model and the plug velocity model. The results show that the unit area density consumption work of the second and third plates is much higher than that of the first plate, which is closely related to the deformation and failure modes of the plates. Consumption work can be used to quantitatively describe the ballistic resistance of each plate.
2020, 40(8): 084101.
doi: 10.11883/bzycj-2019-0433
Abstract:
The M-shaped specimen can be used in dynamic tensile testing only by using the conventional split Hopkinson pressure bar, which do not need the connection between specimen and bars. But the feasibility of this method has not been further verified widely. In this paper, the dynamic tensile testing of M-shaped specimen were analyzed and improved by the finite element and experimental method. The results show that: (1) the improved closed M-shaped specimen was proposed, which can enhance the total stiffness of the specimen, effectively reduce the distortion deformation of the specimen and the influence of additional bending moment in the tensile gage section, and easily realize dynamic tensile through Hopkinson pressure bar; (2) the influence of the elastic deformation of the M-specimen on the tensile displacement could be corrected by the stiffness coefficient of specimen, the plastic strain of the tensile section of the specimen can be analyzed accurately; (3) under higher loading rate, it is suggested to adopt loading through the pulse shaper of Hopkinson bar, which can significantly improve the wave oscillation and stress balance at both ends of the specimen, obtain an accurate dynamic stress-strain curve, and realize the dynamic tensile test up to 5 900 s−1 or even higher strain rate. The study provides an important reference for the design and application of tensile test of M-shaped specimen.
The M-shaped specimen can be used in dynamic tensile testing only by using the conventional split Hopkinson pressure bar, which do not need the connection between specimen and bars. But the feasibility of this method has not been further verified widely. In this paper, the dynamic tensile testing of M-shaped specimen were analyzed and improved by the finite element and experimental method. The results show that: (1) the improved closed M-shaped specimen was proposed, which can enhance the total stiffness of the specimen, effectively reduce the distortion deformation of the specimen and the influence of additional bending moment in the tensile gage section, and easily realize dynamic tensile through Hopkinson pressure bar; (2) the influence of the elastic deformation of the M-specimen on the tensile displacement could be corrected by the stiffness coefficient of specimen, the plastic strain of the tensile section of the specimen can be analyzed accurately; (3) under higher loading rate, it is suggested to adopt loading through the pulse shaper of Hopkinson bar, which can significantly improve the wave oscillation and stress balance at both ends of the specimen, obtain an accurate dynamic stress-strain curve, and realize the dynamic tensile test up to 5 900 s−1 or even higher strain rate. The study provides an important reference for the design and application of tensile test of M-shaped specimen.
2020, 40(8): 085101.
doi: 10.11883/bzyjc-2019-0438
Abstract:
This paper simulated damage effect of the large size multi-cabin structure under internal blast. Cabins were divided into: explosion cabin, coplanar cabin, common boundary cabin and common point cabin, and the damage grade was presented to reflect the destructiveness. This paper studied the regulation of deformation and failure of bulkhead under internal blast by the dimensional analysis, in which a dimensionless damage number was deduced. Furthermore, the number can reflect the characteristics of internal explosive load, material properties and structure. Finally, a rapid damage prediction method was given. The analysis result shows: (1) the characteristics of damage include large deflection deformation, punching failure in the center of plate, tearing along the boundary; (2) the ratio of deflection to thickness (δ/H) has clear linear relationship with the ratio of the quantity to the volume of the cabin (m/V), and so is the ratio of length to thickness of tearing (l/H); (3) the dimensionless damage number and method of rapid damage assessment can reflect the destructiveness, which means the result and analysis method of this paper can provide valuable reference for the research of ship damage.
This paper simulated damage effect of the large size multi-cabin structure under internal blast. Cabins were divided into: explosion cabin, coplanar cabin, common boundary cabin and common point cabin, and the damage grade was presented to reflect the destructiveness. This paper studied the regulation of deformation and failure of bulkhead under internal blast by the dimensional analysis, in which a dimensionless damage number was deduced. Furthermore, the number can reflect the characteristics of internal explosive load, material properties and structure. Finally, a rapid damage prediction method was given. The analysis result shows: (1) the characteristics of damage include large deflection deformation, punching failure in the center of plate, tearing along the boundary; (2) the ratio of deflection to thickness (δ/H) has clear linear relationship with the ratio of the quantity to the volume of the cabin (m/V), and so is the ratio of length to thickness of tearing (l/H); (3) the dimensionless damage number and method of rapid damage assessment can reflect the destructiveness, which means the result and analysis method of this paper can provide valuable reference for the research of ship damage.
