2022 Vol. 42, No. 6
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2022, 42(6): 062101.
doi: 10.11883/bzycj-2021-0190
Abstract:
To expand the application field of environmental protection materials, a composite powder explosion inhibitor was developed to suppress the explosion disaster of aluminum powder. The KH2PO4/SiO2 composite powder explosion inhibitor, a new type of explosion inhibitors, was prepared by grinding KH2PO4 and SiO2 using a ball mill and used to study its inhibition effect on aluminum powder deflagration. The deflagration flame propagation inhibition experiments were carried out in a Hartmann tube experimental device. The results show that the propagation length and speed of the deflagration flame gradually decrease with the increase of the KH2PO4/SiO2 composite powder explosion inhibitor content. When a KH2PO4/SiO2 composite powder explosion inhibitor with the mass ratio of 10∶6 is added, the deflagration flame propagation inhibition of the aluminum powder can be realized. The pressure test experiments of the composite powder explosion inhibitor to inhibit the aluminum powder explosion were carried out in a 20-L spherical explosive device. The results show that the maximum explosion pressure (pmax) and maximum explosion pressure rise rate ((dp/dt)max) of the aluminum powder explosion gradually decrease with the content of the KH2PO4/SiO2 composite powder explosion inhibitor. When a KH2PO4/SiO2 composite powder explosion inhibitor with the mass ratio of 10∶9 is added, the complete inhibition of aluminum powder deflagration can be realized. By comparison with the KH2PO4 powder, SiO2 powder and composite powder explosion inhibitors, the inhibition effect of the composite powder explosion inhibitor on the flame propagation and explosion pressure of the aluminum powder is better than that of monomer powder explosion inhibitors. Through the thermogravimetric analysis of aluminum powder and KH2PO4, the inhibition mechanism of the KH2PO4/SiO2 composite powder explosion inhibitor on aluminum powder deflagration was analyzed from both chemical and physical aspects. The KH2PO4 attached to the surface of composite powder explosion inhibitor absorbs heat rapidly, and the volatile participates in the explosion and combustion reaction of aluminum powder, which significantly reduces the maximum volatile content (dp/dt)max. The SiO2 affects the heat transfer of aluminum powder explosion and combustion, resulting in incomplete combustion and pmax reduction.
To expand the application field of environmental protection materials, a composite powder explosion inhibitor was developed to suppress the explosion disaster of aluminum powder. The KH2PO4/SiO2 composite powder explosion inhibitor, a new type of explosion inhibitors, was prepared by grinding KH2PO4 and SiO2 using a ball mill and used to study its inhibition effect on aluminum powder deflagration. The deflagration flame propagation inhibition experiments were carried out in a Hartmann tube experimental device. The results show that the propagation length and speed of the deflagration flame gradually decrease with the increase of the KH2PO4/SiO2 composite powder explosion inhibitor content. When a KH2PO4/SiO2 composite powder explosion inhibitor with the mass ratio of 10∶6 is added, the deflagration flame propagation inhibition of the aluminum powder can be realized. The pressure test experiments of the composite powder explosion inhibitor to inhibit the aluminum powder explosion were carried out in a 20-L spherical explosive device. The results show that the maximum explosion pressure (pmax) and maximum explosion pressure rise rate ((dp/dt)max) of the aluminum powder explosion gradually decrease with the content of the KH2PO4/SiO2 composite powder explosion inhibitor. When a KH2PO4/SiO2 composite powder explosion inhibitor with the mass ratio of 10∶9 is added, the complete inhibition of aluminum powder deflagration can be realized. By comparison with the KH2PO4 powder, SiO2 powder and composite powder explosion inhibitors, the inhibition effect of the composite powder explosion inhibitor on the flame propagation and explosion pressure of the aluminum powder is better than that of monomer powder explosion inhibitors. Through the thermogravimetric analysis of aluminum powder and KH2PO4, the inhibition mechanism of the KH2PO4/SiO2 composite powder explosion inhibitor on aluminum powder deflagration was analyzed from both chemical and physical aspects. The KH2PO4 attached to the surface of composite powder explosion inhibitor absorbs heat rapidly, and the volatile participates in the explosion and combustion reaction of aluminum powder, which significantly reduces the maximum volatile content (dp/dt)max. The SiO2 affects the heat transfer of aluminum powder explosion and combustion, resulting in incomplete combustion and pmax reduction.
2022, 42(6): 062301.
doi: 10.11883/bzycj-2021-0217
Abstract:
In order to evaluate the reaction of the aluminum powder in detonation products of aluminized explosives, experimental measurements of the detonation wave profiles in RDX/Al and RDX/LiF explosives using photon Doppler velocimetry (PDV) were performed. Planar detonations were produced by impacting the explosives with sapphire flyers in a gas gun. LiF windows with very thin vapor deposited aluminum mirrors were used in the experiments. The original data obtained in the experiments were processed by the window Fourier transform method, then the pressure in the detonation reaction zone was calculated using the impedance matching formula. The initial reaction times were compared between the Al powders with the Al particle sizes of 2 and 10 μm by averaging the interface particle velocities at multiple locations measured in each experiment. Simultaneously, the isentropic equation of state of LiF was used as the reference line to construct the equation of state of the aluminized explosives and to analyze the reaction degrees of the Al powders. The results show that the detonation wave profiles in the aluminized explosives are different from those in ideal explosives. And measurements show no distinct end to the reaction zone indicating a CJ point. At the beginning, the interface particle velocity in the RDX/Al explosive is lower than that in the RDX/LiF explosive due to the temperature disequilibrium between the Al particles and gas detonation products. Subsequently, the interface particle velocity in the RDX/Al explosive is higher than that in the RDX/LiF explosive due to the energy released by the reaction of aluminum. Micron-sized Al particles hardly react before the CJ front. And for the Al particles with the sizes of 2 and 10 μm, the Al reaction delay time is less than 0.8 μs. At the end of the measurements, the evaluated Al reaction degree was about 16% to 31%.
In order to evaluate the reaction of the aluminum powder in detonation products of aluminized explosives, experimental measurements of the detonation wave profiles in RDX/Al and RDX/LiF explosives using photon Doppler velocimetry (PDV) were performed. Planar detonations were produced by impacting the explosives with sapphire flyers in a gas gun. LiF windows with very thin vapor deposited aluminum mirrors were used in the experiments. The original data obtained in the experiments were processed by the window Fourier transform method, then the pressure in the detonation reaction zone was calculated using the impedance matching formula. The initial reaction times were compared between the Al powders with the Al particle sizes of 2 and 10 μm by averaging the interface particle velocities at multiple locations measured in each experiment. Simultaneously, the isentropic equation of state of LiF was used as the reference line to construct the equation of state of the aluminized explosives and to analyze the reaction degrees of the Al powders. The results show that the detonation wave profiles in the aluminized explosives are different from those in ideal explosives. And measurements show no distinct end to the reaction zone indicating a CJ point. At the beginning, the interface particle velocity in the RDX/Al explosive is lower than that in the RDX/LiF explosive due to the temperature disequilibrium between the Al particles and gas detonation products. Subsequently, the interface particle velocity in the RDX/Al explosive is higher than that in the RDX/LiF explosive due to the energy released by the reaction of aluminum. Micron-sized Al particles hardly react before the CJ front. And for the Al particles with the sizes of 2 and 10 μm, the Al reaction delay time is less than 0.8 μs. At the end of the measurements, the evaluated Al reaction degree was about 16% to 31%.
2022, 42(6): 063101.
doi: 10.11883/bzycj-2021-0369
Abstract:
The damage and failure mechanism of two-dimensional triaxially braided composite (2DTBC) under low-velocity impact and compression after impact (CAI) was experimentally investigated through tests with various impact energies (5, 10, 20 and 30 J). The low-velocity impact specimens were prepared according to the ASTM D7136 standard and tested using the Instron drop tower 9250HV with a hemispherical punch, and CAI tests were carried out on an Aowei PLD-250 fatigue machine following the ASTM D7137 standard. An infrared thermal imaging camera was employed to monitor the temperature distribution of the specimens during the low-velocity impact and CAI tests. Delamination damage of impacted specimens was characterized by an ICS-Ⅱ ultrasonic C-scanner. The relationship between impact energy and residual compression strength of 2DTBC after impact load was compared and analyzed. The evolution of the temperature field and its sensitivity against impact energy were discussed based on the infrared image data. Regarding the CAI tests, the global strain field was measured using the digital image correlation (DIC). Combining the thermal and deformation fields, and the optical failure images, the compression failure behavior of 2DTBC after impact of different energies were systematically investigated, validating the feasibility of infrared thermal imaging technology on characterizing the damage and failure behavior of braided composites. The experimental results show that the temperature field contours in low-velocity impact and CAI tests of braided composites are significantly correlated with braided architecture. The magnitude of temperature rise during the low-velocity impact test increases rapidly with the increase of impact energy, while the magnitude of temperature rise during the CAI test decreases with the increase of impact energy. Moreover, the maximum temperature rise is about 56.2 ºC in the 30 J low-velocity impact test. The delamination area is found to increase with the increase of impact energy, and the residual compression strength after impact decreases with the increase of impact energy. The residual compression strengths ratios are 90.9%, 82.2%, 73.8% and 65.8% for specimens after 5, 10, 20 and 30 J impacts, respectively. Through this study, we demonstrate that infrared thermal imaging camera can clearly capture the temperature rise phenomenon of composite specimens, which is caused by the releasing of fracture energy at the failure instant. More notably, the temperature contour can better reflect the damage location and failure characteristics than the global strain field.
The damage and failure mechanism of two-dimensional triaxially braided composite (2DTBC) under low-velocity impact and compression after impact (CAI) was experimentally investigated through tests with various impact energies (5, 10, 20 and 30 J). The low-velocity impact specimens were prepared according to the ASTM D7136 standard and tested using the Instron drop tower 9250HV with a hemispherical punch, and CAI tests were carried out on an Aowei PLD-250 fatigue machine following the ASTM D7137 standard. An infrared thermal imaging camera was employed to monitor the temperature distribution of the specimens during the low-velocity impact and CAI tests. Delamination damage of impacted specimens was characterized by an ICS-Ⅱ ultrasonic C-scanner. The relationship between impact energy and residual compression strength of 2DTBC after impact load was compared and analyzed. The evolution of the temperature field and its sensitivity against impact energy were discussed based on the infrared image data. Regarding the CAI tests, the global strain field was measured using the digital image correlation (DIC). Combining the thermal and deformation fields, and the optical failure images, the compression failure behavior of 2DTBC after impact of different energies were systematically investigated, validating the feasibility of infrared thermal imaging technology on characterizing the damage and failure behavior of braided composites. The experimental results show that the temperature field contours in low-velocity impact and CAI tests of braided composites are significantly correlated with braided architecture. The magnitude of temperature rise during the low-velocity impact test increases rapidly with the increase of impact energy, while the magnitude of temperature rise during the CAI test decreases with the increase of impact energy. Moreover, the maximum temperature rise is about 56.2 ºC in the 30 J low-velocity impact test. The delamination area is found to increase with the increase of impact energy, and the residual compression strength after impact decreases with the increase of impact energy. The residual compression strengths ratios are 90.9%, 82.2%, 73.8% and 65.8% for specimens after 5, 10, 20 and 30 J impacts, respectively. Through this study, we demonstrate that infrared thermal imaging camera can clearly capture the temperature rise phenomenon of composite specimens, which is caused by the releasing of fracture energy at the failure instant. More notably, the temperature contour can better reflect the damage location and failure characteristics than the global strain field.
2022, 42(6): 063102.
doi: 10.11883/bzycj-2021-0347
Abstract:
In order to study the energy absorption characteristics of open-section thin-walled composite structures, axial compression tests were carried out by using a high-speed hydraulic servo test system. The loading speed was set to 0.01, 0.1 and 1 m/s. A high-speed camera was used to record the deformation and failure of the test specimens. The effects of cross-section shape, section aspect ratio, trigger mechanism, and loading speed on the energy absorption characteristics of the composite structures are analyzed. The failure and energy absorption mechanism of the structure in the crushing process is revealed. The results show that the energy absorption is mainly attributed to material bending, delamination, shear failure and friction between crushing zones during the crushing process. The cross-section shape has a significant influence on its energy absorption capacity. The average crushing loads of the hat shaped and Ω- shaped specimens are 14.1% and 14.6% higher than that of the C-channel specimens, and their specific energy absorption (SEA) are 14.3% and 14.8% higher than that of C-channel specimens, respectively. The stress concentration of C-channel specimens leads to insufficient material damage, responsible to their lower energy absorption capacity. On the other hand, the section aspect ratio has less effect on the energy absorption capacity of composite thin-walled structures. The trigger mechanism mainly affects the initial crushing stage of the structures. For the C-channel specimens, 45° chamfer trigger is more effective in reducing the initial peak load; while for the hat shaped test piece, the 15° steeple trigger is better. When the loading speed was increased from 0.01 m/s to 1 m/s, the average crushing load of the C channel, hat shaped and Ω-shaped specimens were reduced by 6.1%, 10.9% and 6.1%, respectively; while the SAE were reduced by 6.2%, 11.0% and 6.2% respectively. The increase of loading speed leads to more debris flying out, which reduces the loading area and material utilization of the structure, and it reduces the friction energy absorption of the collapse zone, too.
In order to study the energy absorption characteristics of open-section thin-walled composite structures, axial compression tests were carried out by using a high-speed hydraulic servo test system. The loading speed was set to 0.01, 0.1 and 1 m/s. A high-speed camera was used to record the deformation and failure of the test specimens. The effects of cross-section shape, section aspect ratio, trigger mechanism, and loading speed on the energy absorption characteristics of the composite structures are analyzed. The failure and energy absorption mechanism of the structure in the crushing process is revealed. The results show that the energy absorption is mainly attributed to material bending, delamination, shear failure and friction between crushing zones during the crushing process. The cross-section shape has a significant influence on its energy absorption capacity. The average crushing loads of the hat shaped and Ω- shaped specimens are 14.1% and 14.6% higher than that of the C-channel specimens, and their specific energy absorption (SEA) are 14.3% and 14.8% higher than that of C-channel specimens, respectively. The stress concentration of C-channel specimens leads to insufficient material damage, responsible to their lower energy absorption capacity. On the other hand, the section aspect ratio has less effect on the energy absorption capacity of composite thin-walled structures. The trigger mechanism mainly affects the initial crushing stage of the structures. For the C-channel specimens, 45° chamfer trigger is more effective in reducing the initial peak load; while for the hat shaped test piece, the 15° steeple trigger is better. When the loading speed was increased from 0.01 m/s to 1 m/s, the average crushing load of the C channel, hat shaped and Ω-shaped specimens were reduced by 6.1%, 10.9% and 6.1%, respectively; while the SAE were reduced by 6.2%, 11.0% and 6.2% respectively. The increase of loading speed leads to more debris flying out, which reduces the loading area and material utilization of the structure, and it reduces the friction energy absorption of the collapse zone, too.
2022, 42(6): 063103.
doi: 10.11883/bzycj-2021-0397
Abstract:
To investigate the response characteristics of aluminum/polytetrafluoroethylene (Al/PTFE) reactive materials under shock loading, the Al powder with the diameter of 10 μm and the PTFE powder with the diameter of 15 μm were mixed. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis were performed to ensure the uniformity and reactivity of the Al/PTFE mixed powders. The Al/PTFE specimen was prepared by using a cold pressing technique. The density of the Al/PTFE materials was 1.92 g/cm3. The Lagrangian experiment was designed to understand the response characteristics of the Al/PTFE specimen under shock loading. PBX8701 was used to produce high pressure. The shock loading was attenuated after passing an aluminum partition and acted on the specimen. Four block specimens with the sizes of\begin{document}$\varnothing$\end{document} ![]()
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To investigate the response characteristics of aluminum/polytetrafluoroethylene (Al/PTFE) reactive materials under shock loading, the Al powder with the diameter of 10 μm and the PTFE powder with the diameter of 15 μm were mixed. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis were performed to ensure the uniformity and reactivity of the Al/PTFE mixed powders. The Al/PTFE specimen was prepared by using a cold pressing technique. The density of the Al/PTFE materials was 1.92 g/cm3. The Lagrangian experiment was designed to understand the response characteristics of the Al/PTFE specimen under shock loading. PBX8701 was used to produce high pressure. The shock loading was attenuated after passing an aluminum partition and acted on the specimen. Four block specimens with the sizes of
2022, 42(6): 063104.
doi: 10.11883/bzycj-2021-0283
Abstract:
The mixed cellular materials with soft matrix are a new type of cushioning and protective materials which have excellent energy absorption properties. In order to study the effect of strain rate on the mechanical behaviors of this kind of materials, uniaxial tensile and compression experiments were conducted on the artificial cartilage foam (ACF) material, at different velocities to obtain the stress-strain curves of the ACF material under different strain rate conditions. Based on the obtained stress-strain curves, the elastic moduli and material strengths of the ACF material were gained under different strain rate conditions. And the comparative tests of the ACF material and expanded polypropylene (EPP) material of the same size and thickness under multiple impacts were carried out by a drop-hammer impact test machine. By comparing the impact responses of the two materials under single and multiple impact loads, the energy absorption characteristics, and the stability of the energy absorption characteristics of the two materials were analyzed. The results reveal that the ACF material is a strain rate-sensitive material, and the stress-strain curves under different strain-rate conditions take on the same trend. The elastic modulus, tensile and compressive strengths of the material gradually increase with the increasing strain rate. Under the action of 50-J impact energy, the ACF material can absorb more than 96% of the impact energy, higher than the 70% of the impact energy absorbed by the EPP material. Moreover, the maximum displacement of the ACF material is only 40% of that of the EPP material. Therefore, the ACF material has more excellent energy absorption performance than the EPP material. The peak force, maximum displacement, and energy absorption ability of the ACF material were almost unchanged after five impacts. Compared with the EPP materials, the ACF material has more favorable recoverability and more stable repeated impact resistance. The research of the work can provide an experimental basis for the application of the mixed cellular materials with soft matrix in multiple impact protection.
The mixed cellular materials with soft matrix are a new type of cushioning and protective materials which have excellent energy absorption properties. In order to study the effect of strain rate on the mechanical behaviors of this kind of materials, uniaxial tensile and compression experiments were conducted on the artificial cartilage foam (ACF) material, at different velocities to obtain the stress-strain curves of the ACF material under different strain rate conditions. Based on the obtained stress-strain curves, the elastic moduli and material strengths of the ACF material were gained under different strain rate conditions. And the comparative tests of the ACF material and expanded polypropylene (EPP) material of the same size and thickness under multiple impacts were carried out by a drop-hammer impact test machine. By comparing the impact responses of the two materials under single and multiple impact loads, the energy absorption characteristics, and the stability of the energy absorption characteristics of the two materials were analyzed. The results reveal that the ACF material is a strain rate-sensitive material, and the stress-strain curves under different strain-rate conditions take on the same trend. The elastic modulus, tensile and compressive strengths of the material gradually increase with the increasing strain rate. Under the action of 50-J impact energy, the ACF material can absorb more than 96% of the impact energy, higher than the 70% of the impact energy absorbed by the EPP material. Moreover, the maximum displacement of the ACF material is only 40% of that of the EPP material. Therefore, the ACF material has more excellent energy absorption performance than the EPP material. The peak force, maximum displacement, and energy absorption ability of the ACF material were almost unchanged after five impacts. Compared with the EPP materials, the ACF material has more favorable recoverability and more stable repeated impact resistance. The research of the work can provide an experimental basis for the application of the mixed cellular materials with soft matrix in multiple impact protection.
Structural optimization design and structural response of elliptical-section penetration projectiles
2022, 42(6): 063301.
doi: 10.11883/bzycj-2021-0436
Abstract:
According to the engineering application requirements of special-shaped section penetrating projectiles, the structural response and optimal design of elliptical-section penetration projectiles were studied. From this point of view, an improved general design method of elliptical-section projectiles was developed by introducing a dimensionless cartridge thickness coefficient of the elliptical projectile. In order to improve the inertia moment and static moment to the short axis of the cross-section, a bending optimization design method of the elliptical-section projectile was proposed by reducing the cartridge thickness of the projectile to a certain extent and redistributing the reduced materials. Based on a 152-mm-diameter light gas gun test device, the reverse tests of three kinds of elliptical-section hollow projectiles with the long axis of 1.8 cm and the short axis of 1.2 cm penetrating a 2024-O aluminum target were carried out, and the responses of the projectiles in the penetration process were obtained. The projectiles after tests were collected by the soft recovery method, and the deformation of the central axes of the projectile was obtained by the gray processing method. Numerical simulations of the tests were carried out by LS-DYNA. The stress, strain, and penetration load of the projectiles during the penetration process were obtained, and the equivalence of the normal ballistic test and reverse ballistic test was verified. Based on the free-free beam theory, a bending response calculation model of the elliptical-section projectile was established. Through the optimized design, the inertia moment to the short axis of the elliptical section increases by 16.44%, and the static moment increases by 15.95%. Under the test conditions, the bending deflection of the projectile decreases by 25.25%. The structural response model was used to calculate the projectile deformation under the test conditions. The calculation results of the theoretical model are in good agreement with the test results, which shows that the calculation method of the model has a certain accuracy and can provide a reference for engineering design.
According to the engineering application requirements of special-shaped section penetrating projectiles, the structural response and optimal design of elliptical-section penetration projectiles were studied. From this point of view, an improved general design method of elliptical-section projectiles was developed by introducing a dimensionless cartridge thickness coefficient of the elliptical projectile. In order to improve the inertia moment and static moment to the short axis of the cross-section, a bending optimization design method of the elliptical-section projectile was proposed by reducing the cartridge thickness of the projectile to a certain extent and redistributing the reduced materials. Based on a 152-mm-diameter light gas gun test device, the reverse tests of three kinds of elliptical-section hollow projectiles with the long axis of 1.8 cm and the short axis of 1.2 cm penetrating a 2024-O aluminum target were carried out, and the responses of the projectiles in the penetration process were obtained. The projectiles after tests were collected by the soft recovery method, and the deformation of the central axes of the projectile was obtained by the gray processing method. Numerical simulations of the tests were carried out by LS-DYNA. The stress, strain, and penetration load of the projectiles during the penetration process were obtained, and the equivalence of the normal ballistic test and reverse ballistic test was verified. Based on the free-free beam theory, a bending response calculation model of the elliptical-section projectile was established. Through the optimized design, the inertia moment to the short axis of the elliptical section increases by 16.44%, and the static moment increases by 15.95%. Under the test conditions, the bending deflection of the projectile decreases by 25.25%. The structural response model was used to calculate the projectile deformation under the test conditions. The calculation results of the theoretical model are in good agreement with the test results, which shows that the calculation method of the model has a certain accuracy and can provide a reference for engineering design.
2022, 42(6): 063302.
doi: 10.11883/bzycj-2021-0373
Abstract:
Accurately evaluating the penetration depth of precision-guided weapons can provide an important reference for the design of protective engineering. The existing work mainly focuses on small or medium caliber projectiles and normal strength concrete targets. Besides, the applicability of existing calculation methods to predict the penetration depth of typical large-caliber earth-penetrating projectiles is worthy of discussion due to the scaling effect. Firstly, by analyzing the existing penetration test data, the main cause of the size effect of penetration depth is that the particle size of the coarse aggregate is not scaled with the projectile size accordingly. Then, five tests were carried out with 100.0-mm and 203.0-mm caliber scaled earth-penetrating projectiles penetrating into C40 and C100 concrete targets. The corresponding two-dimensional axisymmetric finite element model was established. By adjusting the predefined value of the eroding plastic strain to make the numerical penetration depth close to the test data, the constitutive model parameters, as well as the matched mesh size and the erosion criterion, were determined. Thus, a practical finite element analyses method for the penetration depth of large-caliber projectiles into concrete was proposed and verified. Furthermore, for the above two concrete strength grades, the penetration depths of the five typical earth-penetrating projectiles of the U.S. military into concrete at different impact velocities (100－600 m/s) were determined, and the applicability of the existing seven empirical or semi-empirical formulas was evaluated. The comparison results show that the ACE formula can obtain a better prediction of the penetration depth. Finally, the attenuation law of the penetration depth with the compressive strength of concrete was confirmed by fitting the existing penetration test data. The corresponding penetration depths of the five typical earth-penetrating projectiles into the C40－C200 concrete targets at the velocity of 340 m/s were determined. The present work and conclusions can be directly used in the protective engineering design.
Accurately evaluating the penetration depth of precision-guided weapons can provide an important reference for the design of protective engineering. The existing work mainly focuses on small or medium caliber projectiles and normal strength concrete targets. Besides, the applicability of existing calculation methods to predict the penetration depth of typical large-caliber earth-penetrating projectiles is worthy of discussion due to the scaling effect. Firstly, by analyzing the existing penetration test data, the main cause of the size effect of penetration depth is that the particle size of the coarse aggregate is not scaled with the projectile size accordingly. Then, five tests were carried out with 100.0-mm and 203.0-mm caliber scaled earth-penetrating projectiles penetrating into C40 and C100 concrete targets. The corresponding two-dimensional axisymmetric finite element model was established. By adjusting the predefined value of the eroding plastic strain to make the numerical penetration depth close to the test data, the constitutive model parameters, as well as the matched mesh size and the erosion criterion, were determined. Thus, a practical finite element analyses method for the penetration depth of large-caliber projectiles into concrete was proposed and verified. Furthermore, for the above two concrete strength grades, the penetration depths of the five typical earth-penetrating projectiles of the U.S. military into concrete at different impact velocities (100－600 m/s) were determined, and the applicability of the existing seven empirical or semi-empirical formulas was evaluated. The comparison results show that the ACE formula can obtain a better prediction of the penetration depth. Finally, the attenuation law of the penetration depth with the compressive strength of concrete was confirmed by fitting the existing penetration test data. The corresponding penetration depths of the five typical earth-penetrating projectiles into the C40－C200 concrete targets at the velocity of 340 m/s were determined. The present work and conclusions can be directly used in the protective engineering design.
2022, 42(6): 063303.
doi: 10.11883/bzycj-2021-0512
Abstract:
Based on the bi-directional evolutionary structural optimization method (BESO), the nested loop structure of the traditional dynamic load optimization method was introduced into the ABAQUS-MATLAB platform integrated optimization to improve the dynamic load topology optimization process. Topological optimization design and dynamic response analysis of sandwich arch structure under the impact of projectile with initial velocity of 100 m/s were carried out. After optimization, the deformation mode of the core for sandwich arch can be divided into three symmetrical part: the compression dominated deformation occurs in the middle and the upper part of the mid-span region, which like the triangular lattice truss structure; the tensile and compression dominated deformation occurs in the upper and the lower part of the boundary region respectively, which presents the C-shaped structure; and the transition region, which presents the Y-shaped structure, between the mid-span and the boundary is dominated by the combination of tension and bending deformation. The dynamic response of the optimization results under the impact load was analyzed. The deflections of top and bottom sheets and energy absorption of core of two comparison models with equal mass (Voronoi aluminum foam sandwich arch and solid arch) and optimization arch structure under the impact load with the initial velocity of 100 m/s were compared. The deflection and specific energy absorption of the cores of the three models under the impact of the projectiles with the initial velocities of 100, 80, 50 and 20 m/s were compared. The results show that: under the same impact velocity, the optimization structure has the minimum deflection and the maximum specific energy absorption capability; while with the low impact velocity, the impact-resistance advantage of the optimization structure is not obvious. Furthermore, in the range of the impact velocity which has been studied, the optimization structure shows the better impact-resistance performance with the higher velocity. The dynamic responses of the two optimization structures with symmetric load and asymmetric load (the offset of impact point is 100%) under different load conditions were compared. The deflection of top and bottom sheets and the specific energy absorption of core of four models (symmetric optimization result, asymmetric optimization result, Voronoi aluminum foam sandwich arch and solid arch) were compared. The results show that: under different load conditions, the final optimization results are slightly different, and the different of structural responses under the same load is relatively small. The optimization results obtained under each working condition show slightly better mechanical properties under the corresponding condition, but optimization structures are significantly better than the traditional structures. Therefore, the structure optimized by symmetrical impact load has a certain universality.
Based on the bi-directional evolutionary structural optimization method (BESO), the nested loop structure of the traditional dynamic load optimization method was introduced into the ABAQUS-MATLAB platform integrated optimization to improve the dynamic load topology optimization process. Topological optimization design and dynamic response analysis of sandwich arch structure under the impact of projectile with initial velocity of 100 m/s were carried out. After optimization, the deformation mode of the core for sandwich arch can be divided into three symmetrical part: the compression dominated deformation occurs in the middle and the upper part of the mid-span region, which like the triangular lattice truss structure; the tensile and compression dominated deformation occurs in the upper and the lower part of the boundary region respectively, which presents the C-shaped structure; and the transition region, which presents the Y-shaped structure, between the mid-span and the boundary is dominated by the combination of tension and bending deformation. The dynamic response of the optimization results under the impact load was analyzed. The deflections of top and bottom sheets and energy absorption of core of two comparison models with equal mass (Voronoi aluminum foam sandwich arch and solid arch) and optimization arch structure under the impact load with the initial velocity of 100 m/s were compared. The deflection and specific energy absorption of the cores of the three models under the impact of the projectiles with the initial velocities of 100, 80, 50 and 20 m/s were compared. The results show that: under the same impact velocity, the optimization structure has the minimum deflection and the maximum specific energy absorption capability; while with the low impact velocity, the impact-resistance advantage of the optimization structure is not obvious. Furthermore, in the range of the impact velocity which has been studied, the optimization structure shows the better impact-resistance performance with the higher velocity. The dynamic responses of the two optimization structures with symmetric load and asymmetric load (the offset of impact point is 100%) under different load conditions were compared. The deflection of top and bottom sheets and the specific energy absorption of core of four models (symmetric optimization result, asymmetric optimization result, Voronoi aluminum foam sandwich arch and solid arch) were compared. The results show that: under different load conditions, the final optimization results are slightly different, and the different of structural responses under the same load is relatively small. The optimization results obtained under each working condition show slightly better mechanical properties under the corresponding condition, but optimization structures are significantly better than the traditional structures. Therefore, the structure optimized by symmetrical impact load has a certain universality.
2022, 42(6): 064901.
doi: 10.11883/bzycj-2021-0357
Abstract:
The passive confined pressure SHPB (split Hopkinson pressure bar) test provides an efficient way to study the mechanical behaviors of granular materials at high strain rates (102 − 104 s−1) under the action of explosion and shock wave. In this study, aiming to overcome the disadvantages and demerits of design and calculations in the original passive confined pressure SHPB tests provided in previous works, which has been widely used to investigate the dynamical behaviors of granular materials, a rigid steel sleeve used to restrict the granular specimen is simplified as a circular cylindrical shell, instead of a thick-walled cylinder, subjected to band inner pressure. By using classical shell theory, the theoretical expressions are formulated for radial displacement and hoop strain of the steel sleeve, which contain the mechanical and geometrical parameters of inner pressure and rigid steel sleeve. The distributions of radial displacement and hoop strain along with the steel sleeve are also obtained, while the effects of dimensionless parameters (such as length, thickness, radius of steel sleeve and the width of inner pressure) on the calculation results are studied. Compared with the thick-walled cylinder theory, a modified coefficient k is proposed for estimating the stress states in granular specimens more accurately. To check the feasibility and validate the proposed modified theoretical method, the results derived from shell theory and hollow cylinder theory are compared with experimental and numerical results. It is noted that the shell theory gives better approximations than hollow cylinder theory, especially when d/L is much smaller than one; when the value of d/L approaches to one, the accuracy of two theories is both high, which could be accepted in engineering practices. Therefore, it is concluded that the modified theoretical method proposed in this study for estimating the stress state of specimen can serve as a reference in the passive confined pressure SHPB tests for granular materials.
The passive confined pressure SHPB (split Hopkinson pressure bar) test provides an efficient way to study the mechanical behaviors of granular materials at high strain rates (102 − 104 s−1) under the action of explosion and shock wave. In this study, aiming to overcome the disadvantages and demerits of design and calculations in the original passive confined pressure SHPB tests provided in previous works, which has been widely used to investigate the dynamical behaviors of granular materials, a rigid steel sleeve used to restrict the granular specimen is simplified as a circular cylindrical shell, instead of a thick-walled cylinder, subjected to band inner pressure. By using classical shell theory, the theoretical expressions are formulated for radial displacement and hoop strain of the steel sleeve, which contain the mechanical and geometrical parameters of inner pressure and rigid steel sleeve. The distributions of radial displacement and hoop strain along with the steel sleeve are also obtained, while the effects of dimensionless parameters (such as length, thickness, radius of steel sleeve and the width of inner pressure) on the calculation results are studied. Compared with the thick-walled cylinder theory, a modified coefficient k is proposed for estimating the stress states in granular specimens more accurately. To check the feasibility and validate the proposed modified theoretical method, the results derived from shell theory and hollow cylinder theory are compared with experimental and numerical results. It is noted that the shell theory gives better approximations than hollow cylinder theory, especially when d/L is much smaller than one; when the value of d/L approaches to one, the accuracy of two theories is both high, which could be accepted in engineering practices. Therefore, it is concluded that the modified theoretical method proposed in this study for estimating the stress state of specimen can serve as a reference in the passive confined pressure SHPB tests for granular materials.
2022, 42(6): 065101.
doi: 10.11883/bzycj-2021-0200
Abstract:
To develop the impact resistance technology of warship structures as well as to improve underwater weapon’s attack effectiveness, it is necessary to establish a method to rapidly judge and confirm the overall damage modes of the ship structure subjected to middle or near field underwater non-contact explosions. A numerical method was established using commercial software to analyze the overall damage characteristics of warship structures subjected to underwater explosion shock waves and bubble pulsation. An experiment was set up to verify the effectiveness of the method from both the overall damage mode and the deformation perspectives. By using this numerical method, the effects of the main structural strength parameters of the warship and the underwater explosion intensity on the overall damage modes of the warship were investigated. Based on the analysis of extensive experiments and numerical calculations, a factor C4, which reflects the combined effect of a middle/near field underwater non-contact explosion shock wave and a bubble pulsation load, and a factor S, which contains the main structural parameters representing the overall strength of the ship structure, were proposed. The overall damage mode distribution map of ships was established using factor C4 as the x-axis and factor S as the y-axis. The results show that the numerical analysis method can predict the overall damage mode and the deformation of ship structure with an error of less than 10%. The proposed two factors can reasonably characterize the underwater explosion intensity and the overall structural strength of the ship, respectively. The damage mode distribution map can distinguish the overall damage modes (the hogging damage, the sagging damage and the whipping response) of ships with different structural overall strengths subjected to different middle/near field underwater non-contact explosion intensities. The map can realize the rapid judgment on the overall damage modes of the ship subjected to underwater explosions.
To develop the impact resistance technology of warship structures as well as to improve underwater weapon’s attack effectiveness, it is necessary to establish a method to rapidly judge and confirm the overall damage modes of the ship structure subjected to middle or near field underwater non-contact explosions. A numerical method was established using commercial software to analyze the overall damage characteristics of warship structures subjected to underwater explosion shock waves and bubble pulsation. An experiment was set up to verify the effectiveness of the method from both the overall damage mode and the deformation perspectives. By using this numerical method, the effects of the main structural strength parameters of the warship and the underwater explosion intensity on the overall damage modes of the warship were investigated. Based on the analysis of extensive experiments and numerical calculations, a factor C4, which reflects the combined effect of a middle/near field underwater non-contact explosion shock wave and a bubble pulsation load, and a factor S, which contains the main structural parameters representing the overall strength of the ship structure, were proposed. The overall damage mode distribution map of ships was established using factor C4 as the x-axis and factor S as the y-axis. The results show that the numerical analysis method can predict the overall damage mode and the deformation of ship structure with an error of less than 10%. The proposed two factors can reasonably characterize the underwater explosion intensity and the overall structural strength of the ship, respectively. The damage mode distribution map can distinguish the overall damage modes (the hogging damage, the sagging damage and the whipping response) of ships with different structural overall strengths subjected to different middle/near field underwater non-contact explosion intensities. The map can realize the rapid judgment on the overall damage modes of the ship subjected to underwater explosions.
2022, 42(6): 065102.
doi: 10.11883/bzycj-2021-0286
Abstract:
The interaction between rebar and concrete must always be considered to well describe and predict the mechanical behavior of reinforced concrete (RC) structures. A common way to model RC structures is by discrete reinforcements in finite element models where the discrete reinforcements imply that bond conditions between rebar and concrete are perfect. In order to take into account the bond-slip phenomenon, a modified discrete numerical model for RC structures is presented in this paper. The model is formulated within the framework of the mixture theory, considering two phases corresponding to the matrix concrete and the reinforcement bars and incorporating bond-slip effects to the stress-strain relation of the latter by considering the bond-slip model recommended by CEB-FIB. A nonlinear equivalent stress-strain relation for discrete steel bars is generated by incorporating the bond-slip strain to the strain of bars. Based on this model, a comprehensive parametric study is accomplished to obtain the influence of the parameters, including the strengths of the concrete and steel bars as well as the diameter of bars on the modified stress-strain relation of the discrete steel bars. In comparison to the traditional discrete numerical model where interface elements are generated via connecting the degrees of freedom of the bars and concrete meshing, the new model allows for the slipping of the steel bars without explicit discretization of the steel bars and the steel/concrete interfaces. This fact makes it attractive for numerical simulation of concrete structures at the macrostructural level. Using a code JUST-PANDA that is developed in-house, the model is verified by the explosion experiments at the component level and the structural level respectively. The comparisons with experimental results show that the new model can provide a more reliable prediction of the concrete structural behavior due to the consideration of the bond-slip effects in the stress-strain relation of the discrete steel bars by means of a simple procedure.
The interaction between rebar and concrete must always be considered to well describe and predict the mechanical behavior of reinforced concrete (RC) structures. A common way to model RC structures is by discrete reinforcements in finite element models where the discrete reinforcements imply that bond conditions between rebar and concrete are perfect. In order to take into account the bond-slip phenomenon, a modified discrete numerical model for RC structures is presented in this paper. The model is formulated within the framework of the mixture theory, considering two phases corresponding to the matrix concrete and the reinforcement bars and incorporating bond-slip effects to the stress-strain relation of the latter by considering the bond-slip model recommended by CEB-FIB. A nonlinear equivalent stress-strain relation for discrete steel bars is generated by incorporating the bond-slip strain to the strain of bars. Based on this model, a comprehensive parametric study is accomplished to obtain the influence of the parameters, including the strengths of the concrete and steel bars as well as the diameter of bars on the modified stress-strain relation of the discrete steel bars. In comparison to the traditional discrete numerical model where interface elements are generated via connecting the degrees of freedom of the bars and concrete meshing, the new model allows for the slipping of the steel bars without explicit discretization of the steel bars and the steel/concrete interfaces. This fact makes it attractive for numerical simulation of concrete structures at the macrostructural level. Using a code JUST-PANDA that is developed in-house, the model is verified by the explosion experiments at the component level and the structural level respectively. The comparisons with experimental results show that the new model can provide a more reliable prediction of the concrete structural behavior due to the consideration of the bond-slip effects in the stress-strain relation of the discrete steel bars by means of a simple procedure.
2022, 42(6): 065401.
doi: 10.11883/bzycj-2021-0322
Abstract:
In order to study the inhibitory effect of Al(OH)3 powder explosion suppressant on polyacrylonitrile (PAN) powder explosion, a transparent pipeline explosion propagation test system was used to study the influence of mass fractions of Al(OH)3 on the flame propagation shape, temperature and other parameters of PAN powder explosion. The scanning electron microscope, thermogravimetric analyzer and Fourier infrared spectrometer were used to study the microscopic characteristics of Al(OH)3 inhibiting PAN powder explosion, and the mechanism of Al(OH)3 inhibiting PAN powder explosion was summarized. The results show that the maximum flame propagation distance and the velocity of PAN powder deflagration gradually decrease with the increase of the mass fraction of Al(OH)3. At the same time, pressure monitoring and temperature monitoring showed that with the increase of the mass fraction of Al(OH)3, the maximum explosion pressure and maximum temperature of PAN powder gradually decrease. Thus, the inhibition effect of Al(OH)3 on PAN powder explosion was verified, and the inhibition effect of Al(OH)3 at mass ratio of 60% was the best. Through the study of characterization and thermal analysis of PAN powder explosion solid products, the inhibition mechanism of PAN powder flame by Al(OH)3 was analyzed from both physical and chemical aspects. Physical suppression includes coating, endothermic cooling, and gas inerting. Chemical suppression is mainly by reducing the exothermic reaction between free radicals •H, •OH and •O through consuming the key free radicals O• and OH• that maintain the chain reaction of combustion and explosion.
In order to study the inhibitory effect of Al(OH)3 powder explosion suppressant on polyacrylonitrile (PAN) powder explosion, a transparent pipeline explosion propagation test system was used to study the influence of mass fractions of Al(OH)3 on the flame propagation shape, temperature and other parameters of PAN powder explosion. The scanning electron microscope, thermogravimetric analyzer and Fourier infrared spectrometer were used to study the microscopic characteristics of Al(OH)3 inhibiting PAN powder explosion, and the mechanism of Al(OH)3 inhibiting PAN powder explosion was summarized. The results show that the maximum flame propagation distance and the velocity of PAN powder deflagration gradually decrease with the increase of the mass fraction of Al(OH)3. At the same time, pressure monitoring and temperature monitoring showed that with the increase of the mass fraction of Al(OH)3, the maximum explosion pressure and maximum temperature of PAN powder gradually decrease. Thus, the inhibition effect of Al(OH)3 on PAN powder explosion was verified, and the inhibition effect of Al(OH)3 at mass ratio of 60% was the best. Through the study of characterization and thermal analysis of PAN powder explosion solid products, the inhibition mechanism of PAN powder flame by Al(OH)3 was analyzed from both physical and chemical aspects. Physical suppression includes coating, endothermic cooling, and gas inerting. Chemical suppression is mainly by reducing the exothermic reaction between free radicals •H, •OH and •O through consuming the key free radicals O• and OH• that maintain the chain reaction of combustion and explosion.
2022, 42(6): 065402.
doi: 10.11883/bzycj-2021-0386
Abstract:
To explore the inhibitory effect of the combined use of trifluoroiodomethane and carbon dioxide on methane explosion, a 20-L spherical explosion experimental system was used to carry out explosion experiments under different methane volume fractions when the two were used alone and in combination. The variation law of methane explosion pressure characteristics under different working conditions was studied. The results show that after adding trifluoroiodomethane and carbon dioxide, the explosion limit of methane is gradually reduced, and the effect of trifluoroiodomethane on the explosion limit of methane is more obvious. When the volume fractions of trifluoroiodomethane and carbon dioxide reached 5.5% and 32.0%, respectively, the upper and lower explosion limits of methane coincided, and at this moment the corresponding critical oxygen volume fractions were 17.85% and 12.50%, respectively. The affection mechanism of trifluoroiodomethane on the explosion limit of methane is different from that of carbon dioxide, and it does not exert an inhibitory effect mainly by reducing oxygen. The inhibition effect of trifluoroiodomethane on methane explosion is significantly better than that of carbon dioxide. Compared with the decrease ratio of the maximum explosion pressure and the maximum explosion pressure rise rate of 9.5% methane, the suppression explosion effects of 5% trifluoroiodomethane are about 6 times and 5 times as strong as those of the same amount of carbon dioxide. After carbon dioxide is mixed with a small amount of trifluoroiodomethane, the suppression explosion effect is greatly improved. Furthermore, the higher ratio of adding trifluoroiodomethane, the more obvious the effect. When the volume fraction of trifluoroiodomethane is greater than or equal to 1.0%, the magnitude of the drop in the maximum explosion pressure of methane has increased due to the increment of carbon dioxide units. It is indicated that the addition of trifluoroiodomethane has the dual effect of improving the explosion suppression effect and enhancing the explosion suppression efficiency when carbon dioxide is used to suppress methane explosion.
To explore the inhibitory effect of the combined use of trifluoroiodomethane and carbon dioxide on methane explosion, a 20-L spherical explosion experimental system was used to carry out explosion experiments under different methane volume fractions when the two were used alone and in combination. The variation law of methane explosion pressure characteristics under different working conditions was studied. The results show that after adding trifluoroiodomethane and carbon dioxide, the explosion limit of methane is gradually reduced, and the effect of trifluoroiodomethane on the explosion limit of methane is more obvious. When the volume fractions of trifluoroiodomethane and carbon dioxide reached 5.5% and 32.0%, respectively, the upper and lower explosion limits of methane coincided, and at this moment the corresponding critical oxygen volume fractions were 17.85% and 12.50%, respectively. The affection mechanism of trifluoroiodomethane on the explosion limit of methane is different from that of carbon dioxide, and it does not exert an inhibitory effect mainly by reducing oxygen. The inhibition effect of trifluoroiodomethane on methane explosion is significantly better than that of carbon dioxide. Compared with the decrease ratio of the maximum explosion pressure and the maximum explosion pressure rise rate of 9.5% methane, the suppression explosion effects of 5% trifluoroiodomethane are about 6 times and 5 times as strong as those of the same amount of carbon dioxide. After carbon dioxide is mixed with a small amount of trifluoroiodomethane, the suppression explosion effect is greatly improved. Furthermore, the higher ratio of adding trifluoroiodomethane, the more obvious the effect. When the volume fraction of trifluoroiodomethane is greater than or equal to 1.0%, the magnitude of the drop in the maximum explosion pressure of methane has increased due to the increment of carbon dioxide units. It is indicated that the addition of trifluoroiodomethane has the dual effect of improving the explosion suppression effect and enhancing the explosion suppression efficiency when carbon dioxide is used to suppress methane explosion.
