2023 Vol. 43, No. 11
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2023, 43(11): 112201.
doi: 10.11883/bzycj-2023-0080
Abstract:
To study the anti-blast performance of prestressed concrete (PC) frame structure, the dynamic response of a 3-story 2-span long-span bonded/unbonded PC frame structure under the action of external remote blast loads of different scaled distances was analyzed using the finite element software LS-DYNA. In the different blast conditions, the type of explosion was a surface detonation, the explosion distance was 100 m, and the scaled distances were 2−8 m/kg1/3. Explosive loads on the building surface were calculated according to unified facilities criteria 3-340-02. The different types of prestress in the numerical model were realized by controlling the direction of coupling of concrete and prestressing tendons. To validate the numerical model, the results of the numerical simulations were compared with the experimental results. The blast resistance mechanism, story drift ratios, structural damage mode, and damage assessment of PC frames were analyzed under blast loads at different scaled distances. The analysis results show that the ground floor of the large-span PC frame is easy to damage under the action of the external remote blast load, and the ground floor columns can be strengthened to improve the overall structural blast resistance. In the PC frame, columns relative to the frame beams are weaker and prone to damage. The PC frame structure with a low degree of redundancy is easy to collapse. The maximum story drift ratio of the prestressed concrete frame under the surface blast load is approximately linearly related to the peak reflected overpressure applied to the front wall. Compared with the unbonded prestressed concrete frame, the bonded prestressed concrete frame structure has a smaller story drift ratio, more uniform damage distribution, and better structural blast resistance. Based on the analysis results, the damage states at different scaled distances was given, which can realize the rapid assessment of the explosion damage state of prestressed concrete frame structures.
To study the anti-blast performance of prestressed concrete (PC) frame structure, the dynamic response of a 3-story 2-span long-span bonded/unbonded PC frame structure under the action of external remote blast loads of different scaled distances was analyzed using the finite element software LS-DYNA. In the different blast conditions, the type of explosion was a surface detonation, the explosion distance was 100 m, and the scaled distances were 2−8 m/kg1/3. Explosive loads on the building surface were calculated according to unified facilities criteria 3-340-02. The different types of prestress in the numerical model were realized by controlling the direction of coupling of concrete and prestressing tendons. To validate the numerical model, the results of the numerical simulations were compared with the experimental results. The blast resistance mechanism, story drift ratios, structural damage mode, and damage assessment of PC frames were analyzed under blast loads at different scaled distances. The analysis results show that the ground floor of the large-span PC frame is easy to damage under the action of the external remote blast load, and the ground floor columns can be strengthened to improve the overall structural blast resistance. In the PC frame, columns relative to the frame beams are weaker and prone to damage. The PC frame structure with a low degree of redundancy is easy to collapse. The maximum story drift ratio of the prestressed concrete frame under the surface blast load is approximately linearly related to the peak reflected overpressure applied to the front wall. Compared with the unbonded prestressed concrete frame, the bonded prestressed concrete frame structure has a smaller story drift ratio, more uniform damage distribution, and better structural blast resistance. Based on the analysis results, the damage states at different scaled distances was given, which can realize the rapid assessment of the explosion damage state of prestressed concrete frame structures.
2023, 43(11): 112202.
doi: 10.11883/bzycj-2022-0385
Abstract:
In order to improve the blast resistant performance of prefabricated highway bridges, a precast segmental concrete-filled double-skin steel tube (PS-CFDST) column was developed. A large equivalent field blast test on the PS-CFDST columns was conducted and a high-fidelity finite element model was established using LS-DYNA to simulate the dynamic response and failure mode of the PS-CFDST columns under blast loading. The experimental and numerical results demonstrated that the failure mode of the PS-CFDST columns under large equivalent surface explosion was fracture failure of prestressing tendons induced loss of column integrity. The PS-CFDST column exhibited large shear slippage at the column bottom segment-to-footing joint. The damage to core concrete was concentrated at the joints and contact areas between segment and prestressing tendons. The modeling approaches for prestressing tendons have a significant influence on the dynamic response of the PS-CFDST columns. Increasing axial loads can effectively mitigate the column lateral deflection and shear slippage at the column bottom and it is beneficial to improve the blast resistance of the PS-CFDST columns.
In order to improve the blast resistant performance of prefabricated highway bridges, a precast segmental concrete-filled double-skin steel tube (PS-CFDST) column was developed. A large equivalent field blast test on the PS-CFDST columns was conducted and a high-fidelity finite element model was established using LS-DYNA to simulate the dynamic response and failure mode of the PS-CFDST columns under blast loading. The experimental and numerical results demonstrated that the failure mode of the PS-CFDST columns under large equivalent surface explosion was fracture failure of prestressing tendons induced loss of column integrity. The PS-CFDST column exhibited large shear slippage at the column bottom segment-to-footing joint. The damage to core concrete was concentrated at the joints and contact areas between segment and prestressing tendons. The modeling approaches for prestressing tendons have a significant influence on the dynamic response of the PS-CFDST columns. Increasing axial loads can effectively mitigate the column lateral deflection and shear slippage at the column bottom and it is beneficial to improve the blast resistance of the PS-CFDST columns.
2023, 43(11): 112203.
doi: 10.11883/bzycj-2023-0039
Abstract:
By employing the mode approximation method for rigid-plastic structural dynamic behavior and numerical simulation, a dynamic response analysis was conducted on circular-section concrete-filled steel tubular (CFST) structures subjected to lateral impact loadings. The mechanical model of the CFST structure was equivalently represented as a rigid-plastic foundation beam model according to its plastic behavior. Under the linear velocity field assumption and the geometric similarity, the equivalently initial velocity for mode approximation of the structure was derived and compared with the existing experimental data. An analytical solution for the plastic lateral deformation at the mid-span of the CFST with two fixed ends by the rigid-plastic mode approximation method was provided, yielding non-dimensional geometric and physical parameters that influenced the ultimate lateral plastic deformation. A numerical model of the CFST structure under lateral impact was established using ABAQUS/Explicit. The theoretical and numerical predictions were both compared with existing experimental global deformations. Dimensional analysis and numerical modeling were combined to analyze the geometric and physical parameters, as well as the initial impact impulse, which influence the plastic deformation of the CFST structure. The results demonstrate a good agreement between the theoretical, numerical results, and experimental data, confirming that the plastic deformations of the structure align with the assumed distribution of plastic hinges. For geometric variables, the ratio of length to diameter and ratio of thickness to diameter exert a significant influence on the final lateral deformation. The relative width of the indenter can alter the deformation shape of the structure. The physical parameters of the steel tube and core concrete have less impact on the deflection at the mid-span compared with the geometric variables. The final lateral deformation of the CFST structure exhibits a quadratic correlation with the initial impact impulse. Finally, the applicable range of all the theoretical analysis variables is given according to the corresponding parameter analysis. The proposed mode solutions for rigid-plastic response provide a reliable prediction of the plastic deformation behavior of the CFST structures under lateral impact loadings.
By employing the mode approximation method for rigid-plastic structural dynamic behavior and numerical simulation, a dynamic response analysis was conducted on circular-section concrete-filled steel tubular (CFST) structures subjected to lateral impact loadings. The mechanical model of the CFST structure was equivalently represented as a rigid-plastic foundation beam model according to its plastic behavior. Under the linear velocity field assumption and the geometric similarity, the equivalently initial velocity for mode approximation of the structure was derived and compared with the existing experimental data. An analytical solution for the plastic lateral deformation at the mid-span of the CFST with two fixed ends by the rigid-plastic mode approximation method was provided, yielding non-dimensional geometric and physical parameters that influenced the ultimate lateral plastic deformation. A numerical model of the CFST structure under lateral impact was established using ABAQUS/Explicit. The theoretical and numerical predictions were both compared with existing experimental global deformations. Dimensional analysis and numerical modeling were combined to analyze the geometric and physical parameters, as well as the initial impact impulse, which influence the plastic deformation of the CFST structure. The results demonstrate a good agreement between the theoretical, numerical results, and experimental data, confirming that the plastic deformations of the structure align with the assumed distribution of plastic hinges. For geometric variables, the ratio of length to diameter and ratio of thickness to diameter exert a significant influence on the final lateral deformation. The relative width of the indenter can alter the deformation shape of the structure. The physical parameters of the steel tube and core concrete have less impact on the deflection at the mid-span compared with the geometric variables. The final lateral deformation of the CFST structure exhibits a quadratic correlation with the initial impact impulse. Finally, the applicable range of all the theoretical analysis variables is given according to the corresponding parameter analysis. The proposed mode solutions for rigid-plastic response provide a reliable prediction of the plastic deformation behavior of the CFST structures under lateral impact loadings.
2023, 43(11): 112204.
doi: 10.11883/bzycj-2023-0164
Abstract:
Near-field underwater explosion produces complex loading patterns, and complex boundary conditions make the damage patterns of structures under near-field underwater explosion more difficult to predict. Thus, the investigation on the evolution of underwater explosion bubbles and the damage effects on the clamped square plates with the coupling of multi-boundary (free surface, elastoplastic plates and sediment boundary) was conducted using the coupled Eulerian-Lagrangian (CEL) method. Firstly, to verify the accuracy of the finite element method, underwater explosion tests were performed 10 cm under the bottom of the clamped square plates in different dimensions (the side lengths of the plates were 0.46, 0.92 and 1.61 times the maximum bubble diameter) using 2.5 g TNT. Then, the damage mechanism of the clamped square plates was analyzed by combining the test and finite element results. Finally, a series of numerical simulations reveal that with increasing plate dimension and stand-off distance, bubbles show three different evolution modes: collapse, downward jet, and upward jet. With increasing plate dimension, the effects of stand-off distance on the final deformation of the plate center decreases. The sediment boundary can alleviate the bubble shrinkage, make the bubble firstly collapse from the middle to form jets in the opposite direction, and reduce the displacement and strain of the clamped square plates. The sediment boundary has no effects when the bubbles collapse in advance.
Near-field underwater explosion produces complex loading patterns, and complex boundary conditions make the damage patterns of structures under near-field underwater explosion more difficult to predict. Thus, the investigation on the evolution of underwater explosion bubbles and the damage effects on the clamped square plates with the coupling of multi-boundary (free surface, elastoplastic plates and sediment boundary) was conducted using the coupled Eulerian-Lagrangian (CEL) method. Firstly, to verify the accuracy of the finite element method, underwater explosion tests were performed 10 cm under the bottom of the clamped square plates in different dimensions (the side lengths of the plates were 0.46, 0.92 and 1.61 times the maximum bubble diameter) using 2.5 g TNT. Then, the damage mechanism of the clamped square plates was analyzed by combining the test and finite element results. Finally, a series of numerical simulations reveal that with increasing plate dimension and stand-off distance, bubbles show three different evolution modes: collapse, downward jet, and upward jet. With increasing plate dimension, the effects of stand-off distance on the final deformation of the plate center decreases. The sediment boundary can alleviate the bubble shrinkage, make the bubble firstly collapse from the middle to form jets in the opposite direction, and reduce the displacement and strain of the clamped square plates. The sediment boundary has no effects when the bubbles collapse in advance.
2023, 43(11): 112301.
doi: 10.11883/bzycj-2023-0085
Abstract:
To investigate the releasing characteristics of detonation-driving energy in a laminated composite charge, a meticulously prepared composite charge of two distinct types of 3,4-dinitrofurazanfuroxan (DNTF) based explosives with uniform layer thickness was employed. These explosives demonstrated a noticeable detonation velocity difference of 1.85 km/s, one with exceptionally high detonation velocity while the other with exceedingly high detonation heat. The trajectory of the detonation wave at the bus bar of the composite charge was observed using the GSJ streak camera to analyze the velocity change process of the detonation wave as it crossed the two explosives. Subsequently, a\begin{document}$\varnothing $\end{document} ![]()
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To investigate the releasing characteristics of detonation-driving energy in a laminated composite charge, a meticulously prepared composite charge of two distinct types of 3,4-dinitrofurazanfuroxan (DNTF) based explosives with uniform layer thickness was employed. These explosives demonstrated a noticeable detonation velocity difference of 1.85 km/s, one with exceptionally high detonation velocity while the other with exceedingly high detonation heat. The trajectory of the detonation wave at the bus bar of the composite charge was observed using the GSJ streak camera to analyze the velocity change process of the detonation wave as it crossed the two explosives. Subsequently, a
2023, 43(11): 113101.
doi: 10.11883/bzycj-2023-0172
Abstract:
To in-depth understand the dynamic fracture behaviors of metal materials under complex loading, based on the finite element simulation, two types of Mach stem loading experiments were designed and carried out to investigate the dynamic fragmentation of oxygen-free high-conducting copper (OFHC Cu) under complex loading. In the experiments, a powder gun was used to impact the Mach lens, and a laser particle-velocity interferometer was applied to measure the free surface velocity. And dynamic loadings with the peak pressures of 95.75 and 32.38 GPa, respectively, were achieved. Stable Mach stem loading was successfully generated, and the Mach stem-related features were consistent with the simulated ones. At the same time, two different near-surface fracture behaviors in the OFHC Cu were observed, namely the micro-spallation under high pressure and the triangular-wave spallation under low pressure, with the cracked area distributed in a convex shape. These findings have a certain value for further understanding the dynamic fracture behaviors of metal materials and can provide new experimental methods for understanding material failure under various complex loading conditions.
To in-depth understand the dynamic fracture behaviors of metal materials under complex loading, based on the finite element simulation, two types of Mach stem loading experiments were designed and carried out to investigate the dynamic fragmentation of oxygen-free high-conducting copper (OFHC Cu) under complex loading. In the experiments, a powder gun was used to impact the Mach lens, and a laser particle-velocity interferometer was applied to measure the free surface velocity. And dynamic loadings with the peak pressures of 95.75 and 32.38 GPa, respectively, were achieved. Stable Mach stem loading was successfully generated, and the Mach stem-related features were consistent with the simulated ones. At the same time, two different near-surface fracture behaviors in the OFHC Cu were observed, namely the micro-spallation under high pressure and the triangular-wave spallation under low pressure, with the cracked area distributed in a convex shape. These findings have a certain value for further understanding the dynamic fracture behaviors of metal materials and can provide new experimental methods for understanding material failure under various complex loading conditions.
2023, 43(11): 113102.
doi: 10.11883/bzycj/2022-0520
Abstract:
High-porosity structures with negative Poisson’s ratio often experience severe stress fluctuations and significant peak stresses during energy absorption, which can easily cause local damage to the honeycomb structure and affect continuous energy absorption. In order to reduce the occurrence of local damage, an anti-symmetric arc-shaped cell element is designed based on the traditional negative Poisson’s ratio honeycomb cell element, and two new anti-symmetric negative Poisson’s ratio arc-shaped honeycomb structures are obtained through different array directions. Through 0.0025 m/s (quasi-static) compression test and 10 m/s (low velocity), 50 m/s (medium velocity) and 100 m/s (high velocity) finite element simulation, the effect of velocity gradient on the overall deformation pattern, horizontal strain distribution of different layers, deformation mechanism, and impact resistance of the new anti-symmetric arc-shaped honeycomb structure model are revealed. The research results show that unlike the large number of local densification areas that appear in traditional negative Poisson’s ratio honeycomb models, the local densification bands in the new anti-symmetric negative Poisson’s ratio arc-shaped honeycomb structure are significantly reduced. The deformation areas composed of multiple layers of cells in the structure participate in deformation at the same time, showing a very stable deformation pattern as a whole. This is closely related to the increase in maximum horizontal strain and the enhancement of impact resistance of the new honeycomb structure. Especially under the medium-speed loading, the impact resistance of the new anti-symmetric arc-shaped honeycomb model is significantly enhanced, and the impact load efficiency reaches 78%, which is much higher than the 43% impact load efficiency of the traditional honeycomb model; in addition, the anti-symmetric arc-shaped honeycomb structure cells also drive the cell walls between adjacent cells to bend upwards to resist bending moments, further increasing the maximum horizontal strain. Under low-speed loading, the maximum horizontal strain of the two types of new anti-symmetric arc-shaped honeycomb models increases by 100% and 36%, respectively. Under medium-speed loading, it increases by 39% for both types.
High-porosity structures with negative Poisson’s ratio often experience severe stress fluctuations and significant peak stresses during energy absorption, which can easily cause local damage to the honeycomb structure and affect continuous energy absorption. In order to reduce the occurrence of local damage, an anti-symmetric arc-shaped cell element is designed based on the traditional negative Poisson’s ratio honeycomb cell element, and two new anti-symmetric negative Poisson’s ratio arc-shaped honeycomb structures are obtained through different array directions. Through 0.0025 m/s (quasi-static) compression test and 10 m/s (low velocity), 50 m/s (medium velocity) and 100 m/s (high velocity) finite element simulation, the effect of velocity gradient on the overall deformation pattern, horizontal strain distribution of different layers, deformation mechanism, and impact resistance of the new anti-symmetric arc-shaped honeycomb structure model are revealed. The research results show that unlike the large number of local densification areas that appear in traditional negative Poisson’s ratio honeycomb models, the local densification bands in the new anti-symmetric negative Poisson’s ratio arc-shaped honeycomb structure are significantly reduced. The deformation areas composed of multiple layers of cells in the structure participate in deformation at the same time, showing a very stable deformation pattern as a whole. This is closely related to the increase in maximum horizontal strain and the enhancement of impact resistance of the new honeycomb structure. Especially under the medium-speed loading, the impact resistance of the new anti-symmetric arc-shaped honeycomb model is significantly enhanced, and the impact load efficiency reaches 78%, which is much higher than the 43% impact load efficiency of the traditional honeycomb model; in addition, the anti-symmetric arc-shaped honeycomb structure cells also drive the cell walls between adjacent cells to bend upwards to resist bending moments, further increasing the maximum horizontal strain. Under low-speed loading, the maximum horizontal strain of the two types of new anti-symmetric arc-shaped honeycomb models increases by 100% and 36%, respectively. Under medium-speed loading, it increases by 39% for both types.
2023, 43(11): 113103.
doi: 10.11883/bzycj-2023-0061
Abstract:
In this experiment, finite size red sandstone containing pre-existing single crack was taken as the research object. The ratio of length to width of the samples was set about 0.65. The inclination angle of the pre-crack includes 0°, 30°, 45°, 60° and 90°. A split Hopkinson pressure bar was used for impact test, and a high-speed camera was used to record the crack propagation. The dynamic loads were applied along the width of the samples. Velocities of striker in impact tests were set as 6, 8 and 10 m/s by adjusting the pressure of the air gun. Acquisition frequency of the high-speed camera was set as 75000 s−1. The characteristics of crack propagation, dynamic compressive strength and dynamic elastic modulus of the samples were obtained. The fractal theory was used to describe the fragmentation characteristics of the samples. The relationship between dynamic mechanical properties, fragmentation characteristics and crack propagation under medium strain rate was discussed. The findings show that when the strain rate is high, more far-field cracks and separation cracks appear in the sample. In the range of medium strain rate, the failure mode and the number of cracks change differently with strain rate compared with the experimental results of low strain rate. The strain rate and the angle of pre-existing crack have a great influence on the crack propagation and failure mode of the samples. The crack propagation of the samples with different pre-existing crack is different. With the increase of strain rate, the failure mode of the sample becomes more complex, gradually evolving from critical failure with a tensile crack to complex failure mainly with X-shaped shear crack. When the angle of the pre-existing crack is fixed, the dynamic compressive strength and dynamic elastic modulus of the samples show obvious strain rate effect, and the pre-existing crack with different angles have significant influence on the strain rate sensitivity of the samples. With the increase of pre-existing crack angle, the variation of dynamic compressive strength, dynamic elastic modulus and fractal dimension of the samples show a certain similarity. In all types of samples, the dynamic compressive strength, dynamic elastic modulus and fractal dimension of the sample containing cracks with the inclination angle at 45° are the smallest. With the increase of strain rate, distribution of fragments becomes more dispersed. The higher the strain rate, the more significant the effect of the pre-existing crack on the fracture degree and fractal dimension of the samples.
In this experiment, finite size red sandstone containing pre-existing single crack was taken as the research object. The ratio of length to width of the samples was set about 0.65. The inclination angle of the pre-crack includes 0°, 30°, 45°, 60° and 90°. A split Hopkinson pressure bar was used for impact test, and a high-speed camera was used to record the crack propagation. The dynamic loads were applied along the width of the samples. Velocities of striker in impact tests were set as 6, 8 and 10 m/s by adjusting the pressure of the air gun. Acquisition frequency of the high-speed camera was set as 75000 s−1. The characteristics of crack propagation, dynamic compressive strength and dynamic elastic modulus of the samples were obtained. The fractal theory was used to describe the fragmentation characteristics of the samples. The relationship between dynamic mechanical properties, fragmentation characteristics and crack propagation under medium strain rate was discussed. The findings show that when the strain rate is high, more far-field cracks and separation cracks appear in the sample. In the range of medium strain rate, the failure mode and the number of cracks change differently with strain rate compared with the experimental results of low strain rate. The strain rate and the angle of pre-existing crack have a great influence on the crack propagation and failure mode of the samples. The crack propagation of the samples with different pre-existing crack is different. With the increase of strain rate, the failure mode of the sample becomes more complex, gradually evolving from critical failure with a tensile crack to complex failure mainly with X-shaped shear crack. When the angle of the pre-existing crack is fixed, the dynamic compressive strength and dynamic elastic modulus of the samples show obvious strain rate effect, and the pre-existing crack with different angles have significant influence on the strain rate sensitivity of the samples. With the increase of pre-existing crack angle, the variation of dynamic compressive strength, dynamic elastic modulus and fractal dimension of the samples show a certain similarity. In all types of samples, the dynamic compressive strength, dynamic elastic modulus and fractal dimension of the sample containing cracks with the inclination angle at 45° are the smallest. With the increase of strain rate, distribution of fragments becomes more dispersed. The higher the strain rate, the more significant the effect of the pre-existing crack on the fracture degree and fractal dimension of the samples.
2023, 43(11): 113301.
doi: 10.11883/bzycj-2022-0509
Abstract:
To study the cavity development and motion characteristics of the trans-media vehicle with tail-skirt during the process of oblique water entry at high velocity, a high-speed water-entry experiment at platform was built, and an experimental model with inertial measurement unit system was designed. The experimental study was carried out on the trans-media vehicle model with tail-skirt when the water-entry angle was 20° and the water-entry velocity ranged from 30 m/s to 130 m/s. A high-velocity camera was used to record the cavity during water entry, and the inertial measurement unit was used to measure the motion parameters of the vehicle and the pressure inside the cavity. The cavity development characteristics, the motion characteristics and the changing law of the pressure inside the cavity during the high-velocity oblique water entry were obtained. The experimental results show that the planning motion characteristics was formed during the water-entry process of the trans-media vehicle with tail-skirt, and the bending deformation of the cavity occurred. With the increase of the water entry velocity, the upward deflection trend of the water-entry trajectory became more obvious. The peak axial load of the vehicle entering water lasted for a long interval, so load reduction should be considered in the process of crossing media. The peak normal load gradually dropped to about zero after entering the water 1.5 times the length of the vehicle. During the high-velocity water-entry process, the upper surface of the trans-media vehicle was always wrapped in the cavity. The pressure inside the cavity decreased first and then increased with the formation and development of the cavity. The minimum pressure changed linearly with the water entry velocity, while the formation time was basically the same.
To study the cavity development and motion characteristics of the trans-media vehicle with tail-skirt during the process of oblique water entry at high velocity, a high-speed water-entry experiment at platform was built, and an experimental model with inertial measurement unit system was designed. The experimental study was carried out on the trans-media vehicle model with tail-skirt when the water-entry angle was 20° and the water-entry velocity ranged from 30 m/s to 130 m/s. A high-velocity camera was used to record the cavity during water entry, and the inertial measurement unit was used to measure the motion parameters of the vehicle and the pressure inside the cavity. The cavity development characteristics, the motion characteristics and the changing law of the pressure inside the cavity during the high-velocity oblique water entry were obtained. The experimental results show that the planning motion characteristics was formed during the water-entry process of the trans-media vehicle with tail-skirt, and the bending deformation of the cavity occurred. With the increase of the water entry velocity, the upward deflection trend of the water-entry trajectory became more obvious. The peak axial load of the vehicle entering water lasted for a long interval, so load reduction should be considered in the process of crossing media. The peak normal load gradually dropped to about zero after entering the water 1.5 times the length of the vehicle. During the high-velocity water-entry process, the upper surface of the trans-media vehicle was always wrapped in the cavity. The pressure inside the cavity decreased first and then increased with the formation and development of the cavity. The minimum pressure changed linearly with the water entry velocity, while the formation time was basically the same.
2023, 43(11): 114201.
doi: 10.11883/bzycj-2023-0047
Abstract:
In order to study the design thickness of the foam concrete distribution layer under blast load, the numerical model of one-dimensional blast wave propagation in foam concrete was established based on the LS-DYNA software, which was verified by comparing it with the corresponding experimental data, and then the propagation and attenuation of the blast wave in the foam concrete bars with semi-infinite and finite thicknesses were analyzed in detail based on the simplified stress-strain curve of foam concrete. The numerical results demonstrate that the triangular-shaped blast load will be attenuated into a trapezoidal-shaped load with the same amplitude as the yield strength of foam concrete when its thickness is enough, while the so-called load enhancement effect will occur at the fixed end due to the action of the stronger reflected wave when its thickness is small. Based on the compaction of foam concrete, the foam concrete with sufficient length can be divided into five regions, i.e., the compaction zone 1, the plateau zone 1, the elastic zone, the plateau zone 2, and the compaction zone 2, where the range of the elastic zone is gradually shortened as the pole length decreases. To avoid the load enhancement effect and minimize the load on the protected structures, the minimum thickness of the distribution layer of foam concrete was defined corresponding to that when the elastic area and two plateau areas disappeared. The sensitivity analysis of blast load and density of foam concrete on the minimum thickness of foam concrete shows that for the blast load concerned, the minimum thickness increases with the peak and duration time of blast load, but is less affected by the rise time of blast load. Furthermore, the minimum thickness of low-density foam concrete is larger than that of high-density foam concrete under the same blast load. Based on the numerical results, a formula for minimum thickness was proposed.
In order to study the design thickness of the foam concrete distribution layer under blast load, the numerical model of one-dimensional blast wave propagation in foam concrete was established based on the LS-DYNA software, which was verified by comparing it with the corresponding experimental data, and then the propagation and attenuation of the blast wave in the foam concrete bars with semi-infinite and finite thicknesses were analyzed in detail based on the simplified stress-strain curve of foam concrete. The numerical results demonstrate that the triangular-shaped blast load will be attenuated into a trapezoidal-shaped load with the same amplitude as the yield strength of foam concrete when its thickness is enough, while the so-called load enhancement effect will occur at the fixed end due to the action of the stronger reflected wave when its thickness is small. Based on the compaction of foam concrete, the foam concrete with sufficient length can be divided into five regions, i.e., the compaction zone 1, the plateau zone 1, the elastic zone, the plateau zone 2, and the compaction zone 2, where the range of the elastic zone is gradually shortened as the pole length decreases. To avoid the load enhancement effect and minimize the load on the protected structures, the minimum thickness of the distribution layer of foam concrete was defined corresponding to that when the elastic area and two plateau areas disappeared. The sensitivity analysis of blast load and density of foam concrete on the minimum thickness of foam concrete shows that for the blast load concerned, the minimum thickness increases with the peak and duration time of blast load, but is less affected by the rise time of blast load. Furthermore, the minimum thickness of low-density foam concrete is larger than that of high-density foam concrete under the same blast load. Based on the numerical results, a formula for minimum thickness was proposed.
2023, 43(11): 114202.
doi: 10.11883/bzycj-2023-0004
Abstract:
In order to establish an empirical formula to describe the pressure, density and particle velocity of the blast wave at any time and distance in free field, and to support the theoretical calculation of shock wave loading in complex scenarios, the pressure, density and particle velocity histories at different scaled distances were obtained by one-dimensional numerical simulation. The empirical formula of the relationship between shock wave parameters and specific distance was obtained by using the curve fitting method, and the relationship of shock wave pressure, density and particle velocity with time were established by the improved modified Friedlander equation. Based on the two typical scenarios of ground reflection and rear diffraction of explosive shock wave, the application of the proposed model was explained. And the accuracy of the proposed model and related theoretical methods are verified by comparison with the experimental and numerical simulation results. The results show that, within the range from 0.1 to 10 m/kg1/3, the relation of scaled distance and shock wave parameters obtained by curve fitting method are highly consistent with the numerical simulation results, which R2 values are higher than 0.999. The developed basic shock wave parameters time-history curves can ensure the peak value and the maximum impulse is equal to the numerical simulation results in near-field. And in the middle and far-field, the developed time-history curves are in good agreement with the numerical simulation results. Under two typical conditions: ground reflection of explosive shock wave and rear diffraction shock wave around building, the theoretical results are in good agreement with the contour diagram of numerical simulation results. Under the same hardware condition, the time-consuming of theoretical calculation is only about 5% in the numerical simulation of 10 million-level grid, which shows that the method has obvious superiority in calculating speed.
In order to establish an empirical formula to describe the pressure, density and particle velocity of the blast wave at any time and distance in free field, and to support the theoretical calculation of shock wave loading in complex scenarios, the pressure, density and particle velocity histories at different scaled distances were obtained by one-dimensional numerical simulation. The empirical formula of the relationship between shock wave parameters and specific distance was obtained by using the curve fitting method, and the relationship of shock wave pressure, density and particle velocity with time were established by the improved modified Friedlander equation. Based on the two typical scenarios of ground reflection and rear diffraction of explosive shock wave, the application of the proposed model was explained. And the accuracy of the proposed model and related theoretical methods are verified by comparison with the experimental and numerical simulation results. The results show that, within the range from 0.1 to 10 m/kg1/3, the relation of scaled distance and shock wave parameters obtained by curve fitting method are highly consistent with the numerical simulation results, which R2 values are higher than 0.999. The developed basic shock wave parameters time-history curves can ensure the peak value and the maximum impulse is equal to the numerical simulation results in near-field. And in the middle and far-field, the developed time-history curves are in good agreement with the numerical simulation results. Under two typical conditions: ground reflection of explosive shock wave and rear diffraction shock wave around building, the theoretical results are in good agreement with the contour diagram of numerical simulation results. Under the same hardware condition, the time-consuming of theoretical calculation is only about 5% in the numerical simulation of 10 million-level grid, which shows that the method has obvious superiority in calculating speed.
2023, 43(11): 114203.
doi: 10.11883/bzycj-2023-0086
Abstract:
The calculation method of double-skin steel-concrete shield based on the energy method is discussed. Under the premise of a rigid projectile, the main structures that affect the energy dissipation of projectile penetration are front and rear steel plates, internal concrete, tied bars and distribution layer. In this paper, the energy consumption of steel plate in elastic state, plastic state and plastic membrane state is analyzed. Based on the principle of minimum energy consumption and dimensionless analysis, the energy consumption states of the rear steel plate of different materials and structural dimensions are inversely deduced. Combined with the strength limit condition of concrete, the formula for calculating the comprehensive energy consumption of the rear steel plate considering the plastic deformation and the penetration failure mode is proposed, and the analytical expression for the minimum critical thickness of the rear steel plate is given. The calculation results indicate that the comprehensive energy consumption of the sheet steel plate can reach 4−5 times that of merely considering the penetration effect. In view of the restraint effect of steel plates on both sides of concrete, the current relatively mature formula of concrete penetration energy consumption is modified. Based on the principle of energy conservation, a six-step method for designing double-skin steel-concrete shield is proposed, and the formula for calculating the critical penetration velocity of the projectile is given. The theoretical results are then compared with the existing test data. It indicates that the calculation formulas proposed in this paper are in good agreement with the test results and can provide a scientific guideline for the design of double-skin steel-concrete shield. The main principle of the six-step method is to take a full account of the plastic deformation energy consumption of the rear steel plate and the anti-penetration energy consumption of the front steel plate. This method is beneficial to reduce the thickness of the double-skin steel-concrete shield and improve the protection effect.
The calculation method of double-skin steel-concrete shield based on the energy method is discussed. Under the premise of a rigid projectile, the main structures that affect the energy dissipation of projectile penetration are front and rear steel plates, internal concrete, tied bars and distribution layer. In this paper, the energy consumption of steel plate in elastic state, plastic state and plastic membrane state is analyzed. Based on the principle of minimum energy consumption and dimensionless analysis, the energy consumption states of the rear steel plate of different materials and structural dimensions are inversely deduced. Combined with the strength limit condition of concrete, the formula for calculating the comprehensive energy consumption of the rear steel plate considering the plastic deformation and the penetration failure mode is proposed, and the analytical expression for the minimum critical thickness of the rear steel plate is given. The calculation results indicate that the comprehensive energy consumption of the sheet steel plate can reach 4−5 times that of merely considering the penetration effect. In view of the restraint effect of steel plates on both sides of concrete, the current relatively mature formula of concrete penetration energy consumption is modified. Based on the principle of energy conservation, a six-step method for designing double-skin steel-concrete shield is proposed, and the formula for calculating the critical penetration velocity of the projectile is given. The theoretical results are then compared with the existing test data. It indicates that the calculation formulas proposed in this paper are in good agreement with the test results and can provide a scientific guideline for the design of double-skin steel-concrete shield. The main principle of the six-step method is to take a full account of the plastic deformation energy consumption of the rear steel plate and the anti-penetration energy consumption of the front steel plate. This method is beneficial to reduce the thickness of the double-skin steel-concrete shield and improve the protection effect.
2023, 43(11): 115401.
doi: 10.11883/bzycj-2023-0084
Abstract:
To further explore the energy absorption characteristics of the foamed metal with the explosion-facing surface structure different from that of its base subjected to a gas explosion, based on the previous experiments carried on the energy absorption characteristics of serrated structural materials, mixed methane-air explosion energy absorption tests were conducted by using the self-built gas explosion pipe network experimental platform. Three kinds of different corrugated foamed metals were chosen as the explosion-proof materials, and their explosion-facing surfaces took on full convex, full concave, and continuous concave/convex, respectively. The variations of the corresponding typical physical quantities with time and space were measured and analyzed, including explosion shock wave overpressure, flame propagation velocity, and flame temperature. Results are shown as follows. (1) The foamed metals with corrugated structures can reduce explosion overpressure more effectively than the ones with the serrated structure and plane structure, and the foamed metals with fully convex and continuous concave-convex corrugated structures can decrease the explosion shock wave overpressure faster than the ones with serrated and full-concave structures. Additionally, the foamed metals with serrated structures can slow the flame propagation velocity down slightly faster than the ones with the corrugated and plane structures. And the foamed metals with the corrugated structures can weaken the flame temperature more strongly than the ones with the serrated and plane structures. (2) The quenching parameters of the corrugated foam metals whose explosion-facing surfaces taking on full convex, full concave and continuous concave/convex are 5.338, 4.340 and 6.090 MPa·°C, respectively, which are lower than that of the one with the serrated explosion-facing surface 17.680 MPa·°C, and far lower than the safety value 390 MPa·°C, indicating that the foamed metals with the corrugated explosion-facing surface have better explosion-proof capabilities. (3) The energy absorption performances of the foamed metals with the corrugated explosion-facing surfaces are stronger than those of the ones with the serrated explosion-facing surfaces, and are obviously stronger than that of the one with the plane explosion-facing surface. In addition, the foamed metals with the corrugated explosion-facing surfaces can still keep intact after the experiments, displaying that their material strengths are higher than those of the ones with the serrated structures.
To further explore the energy absorption characteristics of the foamed metal with the explosion-facing surface structure different from that of its base subjected to a gas explosion, based on the previous experiments carried on the energy absorption characteristics of serrated structural materials, mixed methane-air explosion energy absorption tests were conducted by using the self-built gas explosion pipe network experimental platform. Three kinds of different corrugated foamed metals were chosen as the explosion-proof materials, and their explosion-facing surfaces took on full convex, full concave, and continuous concave/convex, respectively. The variations of the corresponding typical physical quantities with time and space were measured and analyzed, including explosion shock wave overpressure, flame propagation velocity, and flame temperature. Results are shown as follows. (1) The foamed metals with corrugated structures can reduce explosion overpressure more effectively than the ones with the serrated structure and plane structure, and the foamed metals with fully convex and continuous concave-convex corrugated structures can decrease the explosion shock wave overpressure faster than the ones with serrated and full-concave structures. Additionally, the foamed metals with serrated structures can slow the flame propagation velocity down slightly faster than the ones with the corrugated and plane structures. And the foamed metals with the corrugated structures can weaken the flame temperature more strongly than the ones with the serrated and plane structures. (2) The quenching parameters of the corrugated foam metals whose explosion-facing surfaces taking on full convex, full concave and continuous concave/convex are 5.338, 4.340 and 6.090 MPa·°C, respectively, which are lower than that of the one with the serrated explosion-facing surface 17.680 MPa·°C, and far lower than the safety value 390 MPa·°C, indicating that the foamed metals with the corrugated explosion-facing surface have better explosion-proof capabilities. (3) The energy absorption performances of the foamed metals with the corrugated explosion-facing surfaces are stronger than those of the ones with the serrated explosion-facing surfaces, and are obviously stronger than that of the one with the plane explosion-facing surface. In addition, the foamed metals with the corrugated explosion-facing surfaces can still keep intact after the experiments, displaying that their material strengths are higher than those of the ones with the serrated structures.
2023, 43(11): 115402.
doi: 10.11883/bzycj-2023-0098
Abstract:
Natural gas is an important energy material for national development, but its hazardous properties lead to frequent explosion accidents. In order to pre-evaluate the maximum overpressure of natural gas explosion under the condition with external turbulence, it is proposed to reveal the mechanism of accelerated propagation of turbulent flame, and to establish a prediction model of natural gas explosion overpressure coupled with external turbulence. To this end, an experimental platform for natural gas explosion under external turbulence was firstly established, and the particle image velocimetry system was used to obtain the intensity of external turbulence. Then, the effects of external turbulence with different turbulent intensities on the flame evolution, flame front velocity and explosion overpressure of natural gas explosion were obtained for the methane-air premixed gas with stoichiometric ratio. Finally, through introducing the folding factors of flame instability-induced folds, flame turbulence-induced folds and external turbulence-induced folds, a theoretical model of predicting maximum explosion overpressure of natural gas explosion by considering external turbulence is established. The results indicated that compared with the condition without external turbulence, the external turbulence can exacerbate the degree of flame surface folds. Without external turbulence, the flame radius increases linearly with time; in the presence of external turbulence, the flame is characterized by self-accelerating propagation. The flame acceleration can be triggered by external turbulence, with the increasing intensity of external turbulence, the flame front velocity increases gradually. Additionally, with the increasing intensity of external turbulence, maximum explosion overpressure and maximum rate of pressure rise continue to increase. With the increasing distance between pressure monitoring point and ignition position, maximum explosion overpressure and maximum rate of pressure rise totally decrease. The flame acceleration must be considered to predict natural gas explosion overpressure under external turbulence. Maximum explosion overpressure measured in the experiments is between the value calculated using laminar flame model and turbulent flame model.
Natural gas is an important energy material for national development, but its hazardous properties lead to frequent explosion accidents. In order to pre-evaluate the maximum overpressure of natural gas explosion under the condition with external turbulence, it is proposed to reveal the mechanism of accelerated propagation of turbulent flame, and to establish a prediction model of natural gas explosion overpressure coupled with external turbulence. To this end, an experimental platform for natural gas explosion under external turbulence was firstly established, and the particle image velocimetry system was used to obtain the intensity of external turbulence. Then, the effects of external turbulence with different turbulent intensities on the flame evolution, flame front velocity and explosion overpressure of natural gas explosion were obtained for the methane-air premixed gas with stoichiometric ratio. Finally, through introducing the folding factors of flame instability-induced folds, flame turbulence-induced folds and external turbulence-induced folds, a theoretical model of predicting maximum explosion overpressure of natural gas explosion by considering external turbulence is established. The results indicated that compared with the condition without external turbulence, the external turbulence can exacerbate the degree of flame surface folds. Without external turbulence, the flame radius increases linearly with time; in the presence of external turbulence, the flame is characterized by self-accelerating propagation. The flame acceleration can be triggered by external turbulence, with the increasing intensity of external turbulence, the flame front velocity increases gradually. Additionally, with the increasing intensity of external turbulence, maximum explosion overpressure and maximum rate of pressure rise continue to increase. With the increasing distance between pressure monitoring point and ignition position, maximum explosion overpressure and maximum rate of pressure rise totally decrease. The flame acceleration must be considered to predict natural gas explosion overpressure under external turbulence. Maximum explosion overpressure measured in the experiments is between the value calculated using laminar flame model and turbulent flame model.
