2021 Vol. 41, No. 6
Display Method:
Read OL
PDF 
Cited by
2021, 41(6): 062201.
doi: 10.11883/bzycj-2020-0381
Abstract:
Decoupled charge blasting can effectively reduce the peak pressure of hole wall and improve the blasting effect. Aiming at the issues associated with the explosive energy transferred into rock mass with different coupling medium, the deformation and failure characteristics of rock mass under explosion were analyzed theoretically with the consideration of strain rate effect of the rock mass, and the theoretical energy transfer efficiency of blasting with different coupling medium was obtained. Combined with the numerical simulations, the effects of rock mass properties, explosive categories and decoupled charge coefficient on the energy transfer efficiency of blasting with different coupling medium were studied. The results show that the energy transferred into rock mass from explosive of decoupling charge blasting is related to the coupling medium, the energy transfer efficiency of water coupling blasting is higher than that of air coupling blasting for the same charge structure and same blasting medium. When the charge structure and blasting rock mass are the same but the coupling medium is different, the energy transferred into the rock mass from explosive will be different, depending on blasting rock mass, explosive categories and decoupling charge coefficient. When blasting with the same decoupling charge coefficient but different coupling medium, the higher the rock mass strength, the greater the difference of energy transfer efficiency between different coupling medium. For blasting with the same rock mass properties and same charge structure, the difference of energy transfer efficiency between air coupling blasting and water coupling blasting increases with the increase of decoupling charge coefficient. For emulsion explosive exploding in siltstone, when the decoupling charge coefficient increases from 1.28 to 3.44, the energy transferred from water coupling blasting to surrounding rock mass increases from 1.45 to 6.52 times of air coupling blasting. The research results are of great reference significance for optimizing blasting design, improving explosion energy distribution and increasing the explosion energy utilization rate.
Decoupled charge blasting can effectively reduce the peak pressure of hole wall and improve the blasting effect. Aiming at the issues associated with the explosive energy transferred into rock mass with different coupling medium, the deformation and failure characteristics of rock mass under explosion were analyzed theoretically with the consideration of strain rate effect of the rock mass, and the theoretical energy transfer efficiency of blasting with different coupling medium was obtained. Combined with the numerical simulations, the effects of rock mass properties, explosive categories and decoupled charge coefficient on the energy transfer efficiency of blasting with different coupling medium were studied. The results show that the energy transferred into rock mass from explosive of decoupling charge blasting is related to the coupling medium, the energy transfer efficiency of water coupling blasting is higher than that of air coupling blasting for the same charge structure and same blasting medium. When the charge structure and blasting rock mass are the same but the coupling medium is different, the energy transferred into the rock mass from explosive will be different, depending on blasting rock mass, explosive categories and decoupling charge coefficient. When blasting with the same decoupling charge coefficient but different coupling medium, the higher the rock mass strength, the greater the difference of energy transfer efficiency between different coupling medium. For blasting with the same rock mass properties and same charge structure, the difference of energy transfer efficiency between air coupling blasting and water coupling blasting increases with the increase of decoupling charge coefficient. For emulsion explosive exploding in siltstone, when the decoupling charge coefficient increases from 1.28 to 3.44, the energy transferred from water coupling blasting to surrounding rock mass increases from 1.45 to 6.52 times of air coupling blasting. The research results are of great reference significance for optimizing blasting design, improving explosion energy distribution and increasing the explosion energy utilization rate.
2021, 41(6): 062301.
doi: 10.11883/bzycj-2020-0157
Abstract:
In order to reveal the mechanisms of gun breech-blow phenomenon caused by the fracture of propellant charge, it is urgent to carry out the simulation research on the compression and fracture of propellant charge under the corresponding charge structure. Through the analysis of the mechanical environment in the gun bore and the fracture progress of propellant charge, the discrete element method was employed to simulate the compression and fracture of propellant charge. The lace 19-hole propellant for the large caliber artillery was taken as the research object, a simulation system of compression and fracture of propellant charge was constructed using the EDEM software. And the Hertz-Mindlin contact model parameters were determined by using the drop hammer impact test of the single propellant at low temperature (–40 ℃). Then the compression andfracture simulation of the propellant charge was verified through the dynamic compression and fracture test of the propellant charge at low temperature (–40 ℃). Under the same impact load, the fracture of propellant charges and the compression stress-time curves of propellant charge were achieved by test and simulation, respectively. Using the obtained fracture propellant charge, the closed bomb simulation and test were carried out respectively. Among them, a combustion function based on the discrete element method was used to represent the gas generation law of the simulation fracture propellant charge. Finally, the initial dynamic vivacity ratio of the fracture propellant charge was processed according to the pressure-time curve. The researchresults show that the time histories of compression stress of propellant charge, the closed bomb pressure-time curves, and the initial dynamic vivacity ratios obtained by simulation and test are in good agreement with each other, indicating the designed simulation system is effective and reasonable. The research method has great engineering application value, which lays a foundation for the study of the impact fracture process of high-energy propellant charge and the launch safety of propellant charge.
In order to reveal the mechanisms of gun breech-blow phenomenon caused by the fracture of propellant charge, it is urgent to carry out the simulation research on the compression and fracture of propellant charge under the corresponding charge structure. Through the analysis of the mechanical environment in the gun bore and the fracture progress of propellant charge, the discrete element method was employed to simulate the compression and fracture of propellant charge. The lace 19-hole propellant for the large caliber artillery was taken as the research object, a simulation system of compression and fracture of propellant charge was constructed using the EDEM software. And the Hertz-Mindlin contact model parameters were determined by using the drop hammer impact test of the single propellant at low temperature (–40 ℃). Then the compression andfracture simulation of the propellant charge was verified through the dynamic compression and fracture test of the propellant charge at low temperature (–40 ℃). Under the same impact load, the fracture of propellant charges and the compression stress-time curves of propellant charge were achieved by test and simulation, respectively. Using the obtained fracture propellant charge, the closed bomb simulation and test were carried out respectively. Among them, a combustion function based on the discrete element method was used to represent the gas generation law of the simulation fracture propellant charge. Finally, the initial dynamic vivacity ratio of the fracture propellant charge was processed according to the pressure-time curve. The researchresults show that the time histories of compression stress of propellant charge, the closed bomb pressure-time curves, and the initial dynamic vivacity ratios obtained by simulation and test are in good agreement with each other, indicating the designed simulation system is effective and reasonable. The research method has great engineering application value, which lays a foundation for the study of the impact fracture process of high-energy propellant charge and the launch safety of propellant charge.
2021, 41(6): 062901.
doi: 10.11883/bzycj-2020-0193
Abstract:
The blast loading from an explosion in a confined space is quite different from that in an open environment. The detonation products of TNT can be fully mixed with the surrounding air, and release additional energy through combustion effect, resulting in a significantly increase of the reflected shockwaves and quasi-static pressure in the confined space.In order to investigate the mitigation effect of different atmosphere on explosion load in confined space, the experimental tests of TNT with three different charge masses were performed in a fully confined chamber filled with air, water mist and nitrogen, respectively. The explosive load pressure, temperature and the response characteristics of blast-loaded steel plates in the confined space were analyzed by theoretical calculation and experiment. The results show that both the water mist and the nitrogen can effectively reduce the reflected shock wave, the quasi-static pressure and the temperature in the confined chamber. The average reduction rate of quasi-static pressure is 36.0% and 51.7%, and the average reduction rate of temperature is 42.6% and 40.3%, respectively. The ideal gas state equation was used to calculate the theoretical value of quasi-static pressure in the confined space filled with nitrogen. It is found that the theoretical value is slightly larger than the experimental value, which is due to the insufficient combustion of detonation products in the test. The dynamic response of blast-loaded steel plates in water mist and nitrogen atmosphere is significantly lower than that in the air condition, and the residual deformation of the steel plate at 160 g TNT in water mist and air conditions, the attenuating effect of nitrogen is better than that of water mist. It is revealed that the mechanism of the water mist and nitrogen in mitigating the confined blast load and the subsequent dynamic response of structure is restraining the energy release from the combustion of the detonation products. The conclusions can provide references for the design of anti-blast structure.
The blast loading from an explosion in a confined space is quite different from that in an open environment. The detonation products of TNT can be fully mixed with the surrounding air, and release additional energy through combustion effect, resulting in a significantly increase of the reflected shockwaves and quasi-static pressure in the confined space.In order to investigate the mitigation effect of different atmosphere on explosion load in confined space, the experimental tests of TNT with three different charge masses were performed in a fully confined chamber filled with air, water mist and nitrogen, respectively. The explosive load pressure, temperature and the response characteristics of blast-loaded steel plates in the confined space were analyzed by theoretical calculation and experiment. The results show that both the water mist and the nitrogen can effectively reduce the reflected shock wave, the quasi-static pressure and the temperature in the confined chamber. The average reduction rate of quasi-static pressure is 36.0% and 51.7%, and the average reduction rate of temperature is 42.6% and 40.3%, respectively. The ideal gas state equation was used to calculate the theoretical value of quasi-static pressure in the confined space filled with nitrogen. It is found that the theoretical value is slightly larger than the experimental value, which is due to the insufficient combustion of detonation products in the test. The dynamic response of blast-loaded steel plates in water mist and nitrogen atmosphere is significantly lower than that in the air condition, and the residual deformation of the steel plate at 160 g TNT in water mist and air conditions, the attenuating effect of nitrogen is better than that of water mist. It is revealed that the mechanism of the water mist and nitrogen in mitigating the confined blast load and the subsequent dynamic response of structure is restraining the energy release from the combustion of the detonation products. The conclusions can provide references for the design of anti-blast structure.
2021, 41(6): 062902.
doi: 10.11883/bzycj-2020-0200
Abstract:
In order to explore the flow characteristics and propagation law of combustion gas from the central ignition tube in the initial stage of internal ballistic, a visual experimental platform was designed to carry out ignition experiments with the substituted particle bed in the chamber. A high-speed camera system was used to capture the gas flow and flame propagation in the chamber, and a dynamic data acquisition and analysis system with pressure sensors was applied to record the pressure data at characteristic positions in the chamber. A two-dimensional, axisymmetrical, two-phase flow model of internal ballistics was constructed to simulate the flow process of the gas in the substituted particle bed based on a weighted essentially non-oscillatory (WENO) scheme, and the time term was determined by the third-order TVD Runge-Kuta method. The calculated results are in good agreement with the visual experimental results, and the global pressure average error is 5.35%. It indicates that the numerical simulation can accurately describe the gas flow characteristics and present the development process of the gas from the ignition tube in the substituted particle bed. The radial effect of the chamber pressure is obvious, and the gas moves rapidly along the radial direction, and the substituted particle basically does not move in the initial stage of ignition. Moreover, with the gradual propagation of the gas in the chamber, the chamber pressure is characterized by a radial uniformity and an axial gradient distribution. Under the action of the pressure gradient, the axial velocity of the gas phase begins to dominate, and furthermore, the radial velocity decreases to zero in the bottom and the middle region of the chamber, while the solid phase velocity varies with the gas phase velocity. In addition, before the gas reaches the bottom of the right end, the inverse velocity fluctuation appears in advance due to the solid particle congestion.
In order to explore the flow characteristics and propagation law of combustion gas from the central ignition tube in the initial stage of internal ballistic, a visual experimental platform was designed to carry out ignition experiments with the substituted particle bed in the chamber. A high-speed camera system was used to capture the gas flow and flame propagation in the chamber, and a dynamic data acquisition and analysis system with pressure sensors was applied to record the pressure data at characteristic positions in the chamber. A two-dimensional, axisymmetrical, two-phase flow model of internal ballistics was constructed to simulate the flow process of the gas in the substituted particle bed based on a weighted essentially non-oscillatory (WENO) scheme, and the time term was determined by the third-order TVD Runge-Kuta method. The calculated results are in good agreement with the visual experimental results, and the global pressure average error is 5.35%. It indicates that the numerical simulation can accurately describe the gas flow characteristics and present the development process of the gas from the ignition tube in the substituted particle bed. The radial effect of the chamber pressure is obvious, and the gas moves rapidly along the radial direction, and the substituted particle basically does not move in the initial stage of ignition. Moreover, with the gradual propagation of the gas in the chamber, the chamber pressure is characterized by a radial uniformity and an axial gradient distribution. Under the action of the pressure gradient, the axial velocity of the gas phase begins to dominate, and furthermore, the radial velocity decreases to zero in the bottom and the middle region of the chamber, while the solid phase velocity varies with the gas phase velocity. In addition, before the gas reaches the bottom of the right end, the inverse velocity fluctuation appears in advance due to the solid particle congestion.
2021, 41(6): 063101.
doi: 10.11883/bzycj-2020-0269
Abstract:
The elastic dynamic response of an infinite-length cylindrical shell (equivalent plane strain ring) was analyzed by using the single degree of freedom (SDOF) model under blast loading with triangular pulse load and quasi-static pressure load. The analytical solutions of radial displacement response and amplitude of elastic response under quasi-hydrostatic load were obtained. Based on the analytical solution, the influence of load pressure and the moment of the load boundary point (i.e. the time instant at which the triangular pulse load ends and the quasi-static pressure load begins) on the maximum radial displacement and the amplitude of elastic response in quasi-static pressure stage was analyzed by the control variable method, and the influence of explosion load on the structural response was further studied. The influence of blast loading on the elastic dynamic response of the infinite-length cylindrical shell was studied through the ratio of quasi-static pressure amplitude to triangular pulse peak value and the moment of the load boundary point, combined with the breathing vibration frequency of the structure. It is found that there is a critical time, when the moment of the load boundary point is earlier than the critical moment, the maximum value of radial displacement appears in the quasi-static pressure stage; when the moment of the load boundary point is later than the critical moment, the maximum value of radial displacement can be conveniently determined according to the obtained partition diagram of load stage. Based on the analysis of the above analytical solution, the monotonic zonal diagram of the amplitude variation in quasi-hydrostatic stage caused by the triangular pulse load peak value and quasi-hydrostatic load peak value has obtained, which is convenient to distinguish the increasing and decreasing trend of the amplitude in quasi-hydrostatic stage caused by the load pressure variation. By obtaining the influence of explosion pressure load on the structural response, the current study may provide some guidance for the design of explosion vessels and the basic research of structural protection.
The elastic dynamic response of an infinite-length cylindrical shell (equivalent plane strain ring) was analyzed by using the single degree of freedom (SDOF) model under blast loading with triangular pulse load and quasi-static pressure load. The analytical solutions of radial displacement response and amplitude of elastic response under quasi-hydrostatic load were obtained. Based on the analytical solution, the influence of load pressure and the moment of the load boundary point (i.e. the time instant at which the triangular pulse load ends and the quasi-static pressure load begins) on the maximum radial displacement and the amplitude of elastic response in quasi-static pressure stage was analyzed by the control variable method, and the influence of explosion load on the structural response was further studied. The influence of blast loading on the elastic dynamic response of the infinite-length cylindrical shell was studied through the ratio of quasi-static pressure amplitude to triangular pulse peak value and the moment of the load boundary point, combined with the breathing vibration frequency of the structure. It is found that there is a critical time, when the moment of the load boundary point is earlier than the critical moment, the maximum value of radial displacement appears in the quasi-static pressure stage; when the moment of the load boundary point is later than the critical moment, the maximum value of radial displacement can be conveniently determined according to the obtained partition diagram of load stage. Based on the analysis of the above analytical solution, the monotonic zonal diagram of the amplitude variation in quasi-hydrostatic stage caused by the triangular pulse load peak value and quasi-hydrostatic load peak value has obtained, which is convenient to distinguish the increasing and decreasing trend of the amplitude in quasi-hydrostatic stage caused by the load pressure variation. By obtaining the influence of explosion pressure load on the structural response, the current study may provide some guidance for the design of explosion vessels and the basic research of structural protection.
2021, 41(6): 063102.
doi: 10.11883/bzycj-2020-0121
Abstract:
Under impact loads, the crack resistance of reinforcement in concrete is the focus of impact dynamics research. In this study, the three-point bending tests of lightly reinforce concrete beams with notch were conducted with a drop hammer testing machine. The high speed camera and digital image correlation (DIC) technology were applied to catch the fracture process and analyse the displacement field. The shape and geometry of the specimen followed the RILEM recommendation, i.e., 150 mm × 150 mm in cross section, 800 mm in length, notch-depth ratio was around 1/3 and span was kept constant 600 mm. And the impact force, mid-span deflection, steel strain beneath the loading point and concrete strain at the notch tip were measured over four loading rates. The experiment results showed that the crack initiation strain rate increased linearly with the loading rate, and the growth trend weakened when loading rate was 1.771 m/s. Based on the test results, the empirical formula of crack initiation strain rate with respect to loading rate was given, which was meaningful to simulate the crack initiation in concrete under dynamic loading. In addition, with the increase of loading rate, the steel yielded gradually, which resulted in the response time difference between impact force and steel strain decreased. With the recovery of elastic deformation of steel bars, the crack started to close and the macro crack became visible clearly. Meanwhile, the crack mouth opening displacement (CMOD) declined to a constant value after reaching the maximum value. Then, the crack mouth opening displacement rate was obtained from the fitting curve, and a linear growth relationship between CMOD rate and loading rate was founded. The failure process of the lightly reinforced beams was analyzed based on the CMOD rate, which provided an idea for comparing the fracture process of the beam under dynamic and static loads.
Under impact loads, the crack resistance of reinforcement in concrete is the focus of impact dynamics research. In this study, the three-point bending tests of lightly reinforce concrete beams with notch were conducted with a drop hammer testing machine. The high speed camera and digital image correlation (DIC) technology were applied to catch the fracture process and analyse the displacement field. The shape and geometry of the specimen followed the RILEM recommendation, i.e., 150 mm × 150 mm in cross section, 800 mm in length, notch-depth ratio was around 1/3 and span was kept constant 600 mm. And the impact force, mid-span deflection, steel strain beneath the loading point and concrete strain at the notch tip were measured over four loading rates. The experiment results showed that the crack initiation strain rate increased linearly with the loading rate, and the growth trend weakened when loading rate was 1.771 m/s. Based on the test results, the empirical formula of crack initiation strain rate with respect to loading rate was given, which was meaningful to simulate the crack initiation in concrete under dynamic loading. In addition, with the increase of loading rate, the steel yielded gradually, which resulted in the response time difference between impact force and steel strain decreased. With the recovery of elastic deformation of steel bars, the crack started to close and the macro crack became visible clearly. Meanwhile, the crack mouth opening displacement (CMOD) declined to a constant value after reaching the maximum value. Then, the crack mouth opening displacement rate was obtained from the fitting curve, and a linear growth relationship between CMOD rate and loading rate was founded. The failure process of the lightly reinforced beams was analyzed based on the CMOD rate, which provided an idea for comparing the fracture process of the beam under dynamic and static loads.
2021, 41(6): 063301.
doi: 10.11883/bzycj-2020-0165
Abstract:
Reactive powder concrete (RPC) has ultra-high strength and excellent crack resistance. To study the damage law of the RPC subjected to multiple impact loads, a 25 mm caliber smoothbore gun was used to penetrate the RPC cylindrical target with the diameter of 600 mm and the height of 600 mm. In addition, the experimental data of the target after each penetration was obtained, and the correlation coefficient in the Forrestal empirical formula was determined. Based on the K&C constitutive model and the existing experimental data of the RPC, the model parameters for the RPC were determined systematically by modifying the strength and surface parameters, damage parameters, equation-of-state parameters, damage evolution model, the strain rate effect. The restart function in the LS-DYNA software was used to simulate the damage results of the projectile repeatedly penetrating the RPC target. The simulation results are basically consistent with the experimental results, and the effectiveness of the simulation method is verified. Finally, the numerical prediction of the penetration resistance experiment of the RPC target with the length of 2 200 mm, the width of 2 200 mm, and the height of 1 260 mm was carried out. The relationship between the penetration depth and the projectile velocity, the minimum velocity of the projectile passing through the target and the peak acceleration during projectile penetration were obtained.
Reactive powder concrete (RPC) has ultra-high strength and excellent crack resistance. To study the damage law of the RPC subjected to multiple impact loads, a 25 mm caliber smoothbore gun was used to penetrate the RPC cylindrical target with the diameter of 600 mm and the height of 600 mm. In addition, the experimental data of the target after each penetration was obtained, and the correlation coefficient in the Forrestal empirical formula was determined. Based on the K&C constitutive model and the existing experimental data of the RPC, the model parameters for the RPC were determined systematically by modifying the strength and surface parameters, damage parameters, equation-of-state parameters, damage evolution model, the strain rate effect. The restart function in the LS-DYNA software was used to simulate the damage results of the projectile repeatedly penetrating the RPC target. The simulation results are basically consistent with the experimental results, and the effectiveness of the simulation method is verified. Finally, the numerical prediction of the penetration resistance experiment of the RPC target with the length of 2 200 mm, the width of 2 200 mm, and the height of 1 260 mm was carried out. The relationship between the penetration depth and the projectile velocity, the minimum velocity of the projectile passing through the target and the peak acceleration during projectile penetration were obtained.
2021, 41(6): 063302.
doi: 10.11883/bzycj-2020-0309
Abstract:
It is one of the future development directions to use small tungsten alloy spherical fragments in individual warhead. In order to investigation the penetration performance of small tungsten spheres against human simulation target covered with body armor, taking a 25 mm thick pine target of common international standards as the human simulation target, the experiment of small tungsten spheres penetrating into 25 mm thick pine target covered with third level body armor was carried out by a 12.7 mm ballistic gun. On this basis, the experiment was simulated by LS-DYNA3D software where the penetration process and failure mechanism were analyzed, and the influence of the mass change of tungsten spheres on energy absorption of target and ballistic limit were studied. According to dimensional analysis, energy formula of tungsten spheres penetrating into pine target covered with body armor was established, and the ballistic limit formula of tungsten spheres was deduced. The investigation results show that the ballistic limits of small tungsten spheres with the mass of 0.17, 0.21 and 0.44 g penetrating into the pine target covered with body armor are 742.3, 692.9 and 570.1 m/s, respectively. In the process of penetration, matrix crack, fiber breakage and tensile delamination are the main failure modes of body armor, and the damage similar to the "cross" shape appears on the fiber layer. However, the failure modes of pine target are mainly shear and plug spalling. The ballistic limit of tungsten sphere tends to decrease in the form of power function and energy absorption efficiency of target decreases gradually when the mass of tungsten sphere is increased. The calculated values of energy formula and ballistic limit formula of tungsten spheres penetrating into target are in good agreement with the experimental values, which can be used to calculate the energy of penetrating into target at different initial velocities and the ballistic limit of tungsten spheres with different mass.
It is one of the future development directions to use small tungsten alloy spherical fragments in individual warhead. In order to investigation the penetration performance of small tungsten spheres against human simulation target covered with body armor, taking a 25 mm thick pine target of common international standards as the human simulation target, the experiment of small tungsten spheres penetrating into 25 mm thick pine target covered with third level body armor was carried out by a 12.7 mm ballistic gun. On this basis, the experiment was simulated by LS-DYNA3D software where the penetration process and failure mechanism were analyzed, and the influence of the mass change of tungsten spheres on energy absorption of target and ballistic limit were studied. According to dimensional analysis, energy formula of tungsten spheres penetrating into pine target covered with body armor was established, and the ballistic limit formula of tungsten spheres was deduced. The investigation results show that the ballistic limits of small tungsten spheres with the mass of 0.17, 0.21 and 0.44 g penetrating into the pine target covered with body armor are 742.3, 692.9 and 570.1 m/s, respectively. In the process of penetration, matrix crack, fiber breakage and tensile delamination are the main failure modes of body armor, and the damage similar to the "cross" shape appears on the fiber layer. However, the failure modes of pine target are mainly shear and plug spalling. The ballistic limit of tungsten sphere tends to decrease in the form of power function and energy absorption efficiency of target decreases gradually when the mass of tungsten sphere is increased. The calculated values of energy formula and ballistic limit formula of tungsten spheres penetrating into target are in good agreement with the experimental values, which can be used to calculate the energy of penetrating into target at different initial velocities and the ballistic limit of tungsten spheres with different mass.
2021, 41(6): 064101.
doi: 10.11883/bzycj-2020-0138
Abstract:
Based on the Zwick HTM-5020 hydraulic servo high-speed loading system, a planar biaxial tensile test technique was developed. The biaxial tensile loading device is mainly composed of a cross-shaped cone hammer head, a loading force arm, a cross guide slide rail, and a sample clamping guide rod. The driving force in the vertical direction of the loading hammer is transformed into the horizontal driving force by using the cone contact method, so as to realize the plane biaxial loading of the cruciform specimen. The contact angle of the cone surface and the cruciform specimen geometry was optimized using an Abaqus FEM code. The simulation results show that: (1) when the contact cone angle is 45 °, the horizontal driving conversion efficiency is better and the contact force is smaller than those of others, so that the components loaded by the horizontal driving within the elastic deformation range can be used repeatedly; (2) the key parameters of the cruciform specimen, such as the number of the slits in the loading arm, the length of the slit edge and thinning area, and the thickness of the gauge section, are obtained, so as to realize the uniform deformation of the cruciform specimen in the gauge section. A guide rod integrated measuring force-clamping specimen and a noncontact digital image correlation technique for the measurement of strain were employed in the planar biaxial tensile test device. By using the planar biaxial tensile loading device, the uniaxial tensile test and laser detection synchronicity verification experiment of aluminum alloy plate were carried out to verify the feasibility of the device design. The biaxial tensile tests of the aluminum alloy plates under different strain rates were performed, and the stress-strain curves of the 2024-T351 aluminum alloy sheet under biaxial loading were obtained, which were compared with the results under uniaxial tensile loading.
Based on the Zwick HTM-5020 hydraulic servo high-speed loading system, a planar biaxial tensile test technique was developed. The biaxial tensile loading device is mainly composed of a cross-shaped cone hammer head, a loading force arm, a cross guide slide rail, and a sample clamping guide rod. The driving force in the vertical direction of the loading hammer is transformed into the horizontal driving force by using the cone contact method, so as to realize the plane biaxial loading of the cruciform specimen. The contact angle of the cone surface and the cruciform specimen geometry was optimized using an Abaqus FEM code. The simulation results show that: (1) when the contact cone angle is 45 °, the horizontal driving conversion efficiency is better and the contact force is smaller than those of others, so that the components loaded by the horizontal driving within the elastic deformation range can be used repeatedly; (2) the key parameters of the cruciform specimen, such as the number of the slits in the loading arm, the length of the slit edge and thinning area, and the thickness of the gauge section, are obtained, so as to realize the uniform deformation of the cruciform specimen in the gauge section. A guide rod integrated measuring force-clamping specimen and a noncontact digital image correlation technique for the measurement of strain were employed in the planar biaxial tensile test device. By using the planar biaxial tensile loading device, the uniaxial tensile test and laser detection synchronicity verification experiment of aluminum alloy plate were carried out to verify the feasibility of the device design. The biaxial tensile tests of the aluminum alloy plates under different strain rates were performed, and the stress-strain curves of the 2024-T351 aluminum alloy sheet under biaxial loading were obtained, which were compared with the results under uniaxial tensile loading.
2021, 41(6): 064201.
doi: 10.11883/bzycj-2020-0156
Abstract:
It is very important to simulate and analyze the evolution of the electromagnetic field on the armature/rail in the electromagnetic emission process for optimizing and improving the design of the rail and armature, which is the main basis for controlling the temperature rise of the rail, armature and armature transition. Series enhanced trajectory design is an effective way to improve projectile initial velocity and launch efficiency under the condition of inherent energy storage. In this design, the magnetic field strength on the armature is increased through the series current of the circuit, thus improving the emission ability. A mathematical and physical model is established for the series enhanced orbit. The main control equations of the Railgun3D program are briefly introduced in this paper. The moving window FE/BE Hybrid simulation method is adopted to simulate the series reinforced railgun. This method can make more efficient use of computer resources and focus the simulation on the vicinity of the rail/armature interface. The evolution process of the electromagnetic field of a complex rail/armature under trapezoidal driving current is analyzed in detail. Due to the existence of the enhanced orbit, the driving current produces a large magnetic field on the enhanced orbit. Due to electromagnetic induction, the corresponding induced current will be generated on the inner orbit, that is, there are significant magnetic field and current distribution on the orbit at one end of the muzzle. The magnitude of the induced current depends on the change rate of the driving current. The distribution of current direction near the armature at several times is given, and the evolution process of the current vortex structure is observed. In the current drop section, the results of current reversal on the surface behind the armature are given. It is pointed out that this effect may be an important factor leading to insufficient contact stress between the armature and the track, and even the occurrence of armature transition. Through the current density nephogram on the central symmetry plane, the simulation results show the competition mechanism between magnetic diffusion and velocity skin effect in the whole process.
It is very important to simulate and analyze the evolution of the electromagnetic field on the armature/rail in the electromagnetic emission process for optimizing and improving the design of the rail and armature, which is the main basis for controlling the temperature rise of the rail, armature and armature transition. Series enhanced trajectory design is an effective way to improve projectile initial velocity and launch efficiency under the condition of inherent energy storage. In this design, the magnetic field strength on the armature is increased through the series current of the circuit, thus improving the emission ability. A mathematical and physical model is established for the series enhanced orbit. The main control equations of the Railgun3D program are briefly introduced in this paper. The moving window FE/BE Hybrid simulation method is adopted to simulate the series reinforced railgun. This method can make more efficient use of computer resources and focus the simulation on the vicinity of the rail/armature interface. The evolution process of the electromagnetic field of a complex rail/armature under trapezoidal driving current is analyzed in detail. Due to the existence of the enhanced orbit, the driving current produces a large magnetic field on the enhanced orbit. Due to electromagnetic induction, the corresponding induced current will be generated on the inner orbit, that is, there are significant magnetic field and current distribution on the orbit at one end of the muzzle. The magnitude of the induced current depends on the change rate of the driving current. The distribution of current direction near the armature at several times is given, and the evolution process of the current vortex structure is observed. In the current drop section, the results of current reversal on the surface behind the armature are given. It is pointed out that this effect may be an important factor leading to insufficient contact stress between the armature and the track, and even the occurrence of armature transition. Through the current density nephogram on the central symmetry plane, the simulation results show the competition mechanism between magnetic diffusion and velocity skin effect in the whole process.
2021, 41(6): 064901.
doi: 10.11883/bzcyj-2020-0185
Abstract:
The peak pressure on a borehole wall is an important parameter for the analysis of rock blasting rupture and the non-fluid solid coupling explosion impact dynamic response. Based on the relevant research of calculation methods for the peak pressure on the borehole wall for contour blasting, the interaction between the air shock waves and the borehole wall during low decoupling coefficient charge blasting was theoretically analyzed, and the influencing factors of pressure increase ratio were obtained by fully considering the process of air shock wave propagation and detonation product expansion. The parameters of detonation products were used instead of those of shock wave products in theoretical derivation. The single-hole finite element blasting model with radial decoupling charge for air medium was established, and the peak pressure of the borehole wall after single-point detonation of explosives was studied under the combination conditions of multiple low decoupling coefficient charge structure commonly used in engineering blasting. Moreover, the pressure increase ratio which was the ratio of the peak pressure on the borehole wall to the quasi-static isentropic expansion pressure of explosion gas was obtained under the corresponding conditions. The results show that in the process of explosive blasting with a low decoupling coefficient, there is no separation of air shock waves and detonation products, the parameters of the detonation products have a significant effect on the parameters after air shock waves, which in turn affects the interaction between the air shock waves and the borehole wall. It reveals the essential difference between the calculation methods for the peak pressure on the borehole wall in low decoupling coefficient charge blasting and contour blasting. In addition, the propagation of the axial detonation wave in the cylindrical charge structure causes a superposition effect when the air shock wave impacts the borehole wall, and the peak pressure increases accordingly. Through statistical analysis of the relationship between the pressure increase ratio and the decoupling coefficient under different explosive types and different rock types, it is found that the pressure increase ratio increases approximately linearly with the increase of the decoupling coefficient. Based on the the results of theoretical derivation and the commonly used calculation methods for the peak pressure on the borehole wall, a method for calculating the peak pressure on the borehole wall was proposed for low decoupling coefficient charge blasting by considering the effects of explosive characteristics, medium conditions of the borehole wall, and decoupling coefficient on the pressure increase ratio after the air shock wave colliding with the borehole wall.
The peak pressure on a borehole wall is an important parameter for the analysis of rock blasting rupture and the non-fluid solid coupling explosion impact dynamic response. Based on the relevant research of calculation methods for the peak pressure on the borehole wall for contour blasting, the interaction between the air shock waves and the borehole wall during low decoupling coefficient charge blasting was theoretically analyzed, and the influencing factors of pressure increase ratio were obtained by fully considering the process of air shock wave propagation and detonation product expansion. The parameters of detonation products were used instead of those of shock wave products in theoretical derivation. The single-hole finite element blasting model with radial decoupling charge for air medium was established, and the peak pressure of the borehole wall after single-point detonation of explosives was studied under the combination conditions of multiple low decoupling coefficient charge structure commonly used in engineering blasting. Moreover, the pressure increase ratio which was the ratio of the peak pressure on the borehole wall to the quasi-static isentropic expansion pressure of explosion gas was obtained under the corresponding conditions. The results show that in the process of explosive blasting with a low decoupling coefficient, there is no separation of air shock waves and detonation products, the parameters of the detonation products have a significant effect on the parameters after air shock waves, which in turn affects the interaction between the air shock waves and the borehole wall. It reveals the essential difference between the calculation methods for the peak pressure on the borehole wall in low decoupling coefficient charge blasting and contour blasting. In addition, the propagation of the axial detonation wave in the cylindrical charge structure causes a superposition effect when the air shock wave impacts the borehole wall, and the peak pressure increases accordingly. Through statistical analysis of the relationship between the pressure increase ratio and the decoupling coefficient under different explosive types and different rock types, it is found that the pressure increase ratio increases approximately linearly with the increase of the decoupling coefficient. Based on the the results of theoretical derivation and the commonly used calculation methods for the peak pressure on the borehole wall, a method for calculating the peak pressure on the borehole wall was proposed for low decoupling coefficient charge blasting by considering the effects of explosive characteristics, medium conditions of the borehole wall, and decoupling coefficient on the pressure increase ratio after the air shock wave colliding with the borehole wall.
2021, 41(6): 064902.
doi: 10.11883/bzycj-2020-0194
Abstract:
How to accurately define “close-in explosion” has always been a hotspot in the field of protection engineering research. In this paper, based on the fully validated 2D axisymmetric fine finite element model, the characteristics and laws of the propagation of air shock waves and high-speed expansion of detonation products generated by TNT spherical charge were studied. It is found that there is a significant influence of the detonation products on the blast load on rigid wall when the range of the scaled distance less than 0.8 m/kg1/3. It is recommended to use the scaled distance range from 0.30 m/kg1/3 to 0.80 m/kg1/3 as the definition criterion of close-in explosion for spherical TNT charge explosion. It was found that: due to the inhomogeneity and randomness of the detonation product rapid expansion, the peak value of the rigid-wall reflected overpressure experienced a sharp drop within a range of incident angle of 0°～5° in the case of close-in explosion defined in the paper. In addition, there were two peaks on the reflected overpressure curve in close-in explosion cases, and the first peak overpressure was caused by the interaction between the shock wave and rigid wall while the second peak overpressure was generated by the interaction between the detonation products and rigid wall. Based on curve fitting, the formulas for calculating the two peak values were proposed, respectively, and a simplified load model suitable for calculation of engineering structure response was put forward; The distribution law of the reflected overpressure on the rigid wall under close-in explosion was revealed.
How to accurately define “close-in explosion” has always been a hotspot in the field of protection engineering research. In this paper, based on the fully validated 2D axisymmetric fine finite element model, the characteristics and laws of the propagation of air shock waves and high-speed expansion of detonation products generated by TNT spherical charge were studied. It is found that there is a significant influence of the detonation products on the blast load on rigid wall when the range of the scaled distance less than 0.8 m/kg1/3. It is recommended to use the scaled distance range from 0.30 m/kg1/3 to 0.80 m/kg1/3 as the definition criterion of close-in explosion for spherical TNT charge explosion. It was found that: due to the inhomogeneity and randomness of the detonation product rapid expansion, the peak value of the rigid-wall reflected overpressure experienced a sharp drop within a range of incident angle of 0°～5° in the case of close-in explosion defined in the paper. In addition, there were two peaks on the reflected overpressure curve in close-in explosion cases, and the first peak overpressure was caused by the interaction between the shock wave and rigid wall while the second peak overpressure was generated by the interaction between the detonation products and rigid wall. Based on curve fitting, the formulas for calculating the two peak values were proposed, respectively, and a simplified load model suitable for calculation of engineering structure response was put forward; The distribution law of the reflected overpressure on the rigid wall under close-in explosion was revealed.
2021, 41(6): 065101.
doi: 10.11883/bzycj-2020-0168
Abstract:
In this work, in order to reduce hull structural damage caused by ice impact, a new type of square groove longitudinal anti-ice structure is used in the shoulder structure of a hull in ice belt. Using a falling weight impact test system, the structural dynamic responses of anti-ice and prototype stiffened plates under the same ice impact case were tested and the impacting processes were simulated by the MSC.Dytran software. The results show that under the same impact conditions, the impact force produced by the anti-ice structure is slightly higher than that by the prototype one, and the maximum depression depth is smaller than that of the prototype one. According to the structural damage degree of the hull shell plates and their protection function to the hull internal components and equipment, the new structure has a certain anti-ice effect compared with the prototype structure. The results of the present study can provide a reference for the design of the anti-ice structures of ice-going ships or icebreakers.
In this work, in order to reduce hull structural damage caused by ice impact, a new type of square groove longitudinal anti-ice structure is used in the shoulder structure of a hull in ice belt. Using a falling weight impact test system, the structural dynamic responses of anti-ice and prototype stiffened plates under the same ice impact case were tested and the impacting processes were simulated by the MSC.Dytran software. The results show that under the same impact conditions, the impact force produced by the anti-ice structure is slightly higher than that by the prototype one, and the maximum depression depth is smaller than that of the prototype one. According to the structural damage degree of the hull shell plates and their protection function to the hull internal components and equipment, the new structure has a certain anti-ice effect compared with the prototype structure. The results of the present study can provide a reference for the design of the anti-ice structures of ice-going ships or icebreakers.
2021, 41(6): 065102.
doi: 10.11883/bzycj-2020-0170
Abstract:
In order to study the dynamic characteristics of electric transmission lines undergone blasting de-icing and the corresponding de-icing effects, model experiments on the isolated transmission lines with a span of 50 m were carried out. The artificial icing was performed out and the detonating cords preset at the lower sides of the transmission lines were detonated to remove partial ice covers of the transmission lines. The displacements and dynamic tensions of three kinds of transmission lines were measured during blasting de-icing. The blasting load was simplified as a triangular wave load, and the experimental conditions were simulated and verified by the finite element software ABAQUS. Furthermore, the effects of the de-icing positions on the jumping height and dynamic tension were explored when the ice was removed by twenty percent. The results show that for glaze ice, the blasting action can only cause the ice to fall off in the blasting area of the transmission lines. The amplitudes of the jumping and dynamic tension induced by blasting de-icing are greater than those by natural de-icing at the same locations, and their changing trends with de-icing location are similar to those by natural de-icing. Compared with the conductor, the jump amplitudes of the ground wire and the optical cable are more significantly affected by blasting.
In order to study the dynamic characteristics of electric transmission lines undergone blasting de-icing and the corresponding de-icing effects, model experiments on the isolated transmission lines with a span of 50 m were carried out. The artificial icing was performed out and the detonating cords preset at the lower sides of the transmission lines were detonated to remove partial ice covers of the transmission lines. The displacements and dynamic tensions of three kinds of transmission lines were measured during blasting de-icing. The blasting load was simplified as a triangular wave load, and the experimental conditions were simulated and verified by the finite element software ABAQUS. Furthermore, the effects of the de-icing positions on the jumping height and dynamic tension were explored when the ice was removed by twenty percent. The results show that for glaze ice, the blasting action can only cause the ice to fall off in the blasting area of the transmission lines. The amplitudes of the jumping and dynamic tension induced by blasting de-icing are greater than those by natural de-icing at the same locations, and their changing trends with de-icing location are similar to those by natural de-icing. Compared with the conductor, the jump amplitudes of the ground wire and the optical cable are more significantly affected by blasting.
