2020 Vol. 40, No. 12
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2020, 40(12): 121401.
doi: 10.11883/bzycj-2020-0002
Abstract:
To study the dynamic compression characteristics of concrete under high hydrostatic pressure and to determine the equation of state parameters of the HJC constitutive model, inverse flyer-impact tests and numerical simulation analysis were conducted with two kinds of concrete flyers of which the compressive strengths were 26.5 MPa and 42.1 MPa, respectively. The concrete flyers were launched by\begin{document}$\varnothing $\end{document} ![]()
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To study the dynamic compression characteristics of concrete under high hydrostatic pressure and to determine the equation of state parameters of the HJC constitutive model, inverse flyer-impact tests and numerical simulation analysis were conducted with two kinds of concrete flyers of which the compressive strengths were 26.5 MPa and 42.1 MPa, respectively. The concrete flyers were launched by
2020, 40(12): 121402.
doi: 10.11883/bzycj-2020-0180
Abstract:
In order to study the failure mode and anti-explosion performance of PODZ coated square reinforced concrete slabs under contact explosion, the PODZ coated square reinforced concrete slabs were tested under contact explosion conditions. In the test, the reinforced concrete slab commonly used in floor design in building structures was used as the research object. Through 11 independent explosion tests, the influence of different PODZ coating thickness on the anti-explosion performance was analyzed, and the reinforced concrete slab failure modes and damage characteristics were observed at different charges TNT mass and different PODZ coating thickness conditions. The results show that the main failure mode of the coated PODZ reinforced concrete slab is the crater of reinforced concrete slab on the front and the conical shape bulge of POZD coating on the back. The bulging of POZD coating is mainly due to the detachment of POZD coating from the base plate and large plastic deformation under explosion shock wave. When the shock wave load strength exceeds the ultimate tensile strength of POZD material, a small round hole shear failure is formed at the tip of coating cone, and the other areas of the coating remain intact, so that the reinforced concrete slab will not produce a large range of seismic collapse failure. Under the strong shock wave load, the POZD coating can still maintain large deformation and high plasticity, which can extend the action time and dissipation time of explosion load through its large deformation and absorb large shock wave energy, so as to restrain the concrete spall debris and improve the anti-explosion performance of steel-concrete concrete slabs. With the increase of the thickness of POZD coating, the stronger the anti-explosion ability of the plate under contact explosion, the more the critical collapse damage TNT mass. The research results can provide references for engineering application and damage assessment.
In order to study the failure mode and anti-explosion performance of PODZ coated square reinforced concrete slabs under contact explosion, the PODZ coated square reinforced concrete slabs were tested under contact explosion conditions. In the test, the reinforced concrete slab commonly used in floor design in building structures was used as the research object. Through 11 independent explosion tests, the influence of different PODZ coating thickness on the anti-explosion performance was analyzed, and the reinforced concrete slab failure modes and damage characteristics were observed at different charges TNT mass and different PODZ coating thickness conditions. The results show that the main failure mode of the coated PODZ reinforced concrete slab is the crater of reinforced concrete slab on the front and the conical shape bulge of POZD coating on the back. The bulging of POZD coating is mainly due to the detachment of POZD coating from the base plate and large plastic deformation under explosion shock wave. When the shock wave load strength exceeds the ultimate tensile strength of POZD material, a small round hole shear failure is formed at the tip of coating cone, and the other areas of the coating remain intact, so that the reinforced concrete slab will not produce a large range of seismic collapse failure. Under the strong shock wave load, the POZD coating can still maintain large deformation and high plasticity, which can extend the action time and dissipation time of explosion load through its large deformation and absorb large shock wave energy, so as to restrain the concrete spall debris and improve the anti-explosion performance of steel-concrete concrete slabs. With the increase of the thickness of POZD coating, the stronger the anti-explosion ability of the plate under contact explosion, the more the critical collapse damage TNT mass. The research results can provide references for engineering application and damage assessment.
2020, 40(12): 121403.
doi: 10.11883/bzycj-2020-0058
Abstract:
As a lateral resisting component, the single-side steel plate shear wall (SPSW) has a favorable capacity of energy dissipation and impact resistance, it has been gradually applied into the anti-seismic design of building and the anti-explosion design of protective structures. In this paper, three specimens of reinforced concrete slab (RCS), side steel plate shear wall slab (SSPSWS) and center steel plate shear wall slab (CSPWS) were designed and casted, the contact explosion experiment of SPSW were carried out in the field, and the nonlinear program LS-DYNA was used to establish finite model of SPSWS specimens, the dynamic response, failure models and anti-blast capacity of SPSWs subjected to contact explosion loads were compared and analyzed. The experimental results and numerical analysis show that there are three types of failure models occurred in the SPSWs, The midspan concrete of RCS occurrs penetration failure, and the reinforcement bar of RCS had larger bending deformation; while the concrete and steel plate of SSPSWS separate with the state of shear studs pulling out, losting its integrity and resistance capacity. The specimen of CSPWS is failure under upper concrete crushing, but the CSPWS specimen is still integrity and bearing capacity with strong connection performance. The midspan deflection of concrete slab and the splashing distance of concrete fragments are small. In addition, the capacity of bonding performance between concrete and steel plate of SSPSWS and CSPWS can be enhanced through equipping with reinforcing fabric, it can effectively reduce the cracking and peeling of the upper and lower layers of concrete and improve the integrity and anti-explosion capacity either .
As a lateral resisting component, the single-side steel plate shear wall (SPSW) has a favorable capacity of energy dissipation and impact resistance, it has been gradually applied into the anti-seismic design of building and the anti-explosion design of protective structures. In this paper, three specimens of reinforced concrete slab (RCS), side steel plate shear wall slab (SSPSWS) and center steel plate shear wall slab (CSPWS) were designed and casted, the contact explosion experiment of SPSW were carried out in the field, and the nonlinear program LS-DYNA was used to establish finite model of SPSWS specimens, the dynamic response, failure models and anti-blast capacity of SPSWs subjected to contact explosion loads were compared and analyzed. The experimental results and numerical analysis show that there are three types of failure models occurred in the SPSWs, The midspan concrete of RCS occurrs penetration failure, and the reinforcement bar of RCS had larger bending deformation; while the concrete and steel plate of SSPSWS separate with the state of shear studs pulling out, losting its integrity and resistance capacity. The specimen of CSPWS is failure under upper concrete crushing, but the CSPWS specimen is still integrity and bearing capacity with strong connection performance. The midspan deflection of concrete slab and the splashing distance of concrete fragments are small. In addition, the capacity of bonding performance between concrete and steel plate of SSPSWS and CSPWS can be enhanced through equipping with reinforcing fabric, it can effectively reduce the cracking and peeling of the upper and lower layers of concrete and improve the integrity and anti-explosion capacity either .
2020, 40(12): 121404.
doi: 10.11883/bzycj-2020-0171
Abstract:
In order to investigate the local failure modes and damage effects of reinforced concrete (RC) beams under contact explosion, the experimental studies of RC beams with the same size under different TNT charge masses were conducted. In the tests, the typical engineering scale RC prototype beams designed for frame structures were used as research objects. Through four independent explosion tests, the failure modes and damage characteristics of the RC beams were observed at different TNT charge masses, and the influence of different TNT charge masses on the local damage was analyzed. The results show that RC beams undergo four types of local failure modes such as front crater, side breakdown, back collapse and section punching under contact detonations. The depth of crater, thickness of the spallation, surface damaged area, and the deformation of the steel bars exhibited a linear increase with the cubic root of TNT charge masses. Based on the experimental data, the local damage degree could be divided into four grades: slight, moderate, serious and severe, that could be evaluated by the proportional charge criterion. The research results can provide a theoretical basis for designing the anti-blast structures and assessing the damage of components subjected to explosive loading.
In order to investigate the local failure modes and damage effects of reinforced concrete (RC) beams under contact explosion, the experimental studies of RC beams with the same size under different TNT charge masses were conducted. In the tests, the typical engineering scale RC prototype beams designed for frame structures were used as research objects. Through four independent explosion tests, the failure modes and damage characteristics of the RC beams were observed at different TNT charge masses, and the influence of different TNT charge masses on the local damage was analyzed. The results show that RC beams undergo four types of local failure modes such as front crater, side breakdown, back collapse and section punching under contact detonations. The depth of crater, thickness of the spallation, surface damaged area, and the deformation of the steel bars exhibited a linear increase with the cubic root of TNT charge masses. Based on the experimental data, the local damage degree could be divided into four grades: slight, moderate, serious and severe, that could be evaluated by the proportional charge criterion. The research results can provide a theoretical basis for designing the anti-blast structures and assessing the damage of components subjected to explosive loading.
2020, 40(12): 121405.
doi: 10.11883/bzycj-2020-0012
Abstract:
To study the failure law of reinforced concrete bent structures under large equivalent explosions, the damage grades of the bent structures against blast were numerically calculated based on the explosion test with the maximum equivalent of 3 t TNT. The load parameters and structural dimensions of the 1/2 scaled model were obtained through dimensional analysis. Based on the Abaqus finite element software, the CONWEP method was used to achieve the blast loading. The failure modes of the structures, under the explosion loads with TNT equivalent 0.5 t and blast distance 33 m as well as TNT equivalent 3 t and blast distance 33 m, were calculated, respectively, and compared with the test results. Further, the failure patterns of the scale model under different overpressures and impulses were calculated by controlling the TNT equivalent and blast distance. The research results show that the middle column of the bent structure is prone to damage in the form of overall overturning under a lateral blast load; the calculated failure morphologies are in good agreement with the experimental ones, and the maximum relative errors of the characteristic displacements and characteristic corners are 5.6% and 4.6%, respectively. The overturning angle of the load-bearing column was used as the basis for the damage-grade division, and the calculated results were divided into three damage levels. The fitted overpressure-impulse and equivalent-distance curves can be used in the design of safety distance and warehouse capacity and the estimation of the damage degree of accidental explosion.
To study the failure law of reinforced concrete bent structures under large equivalent explosions, the damage grades of the bent structures against blast were numerically calculated based on the explosion test with the maximum equivalent of 3 t TNT. The load parameters and structural dimensions of the 1/2 scaled model were obtained through dimensional analysis. Based on the Abaqus finite element software, the CONWEP method was used to achieve the blast loading. The failure modes of the structures, under the explosion loads with TNT equivalent 0.5 t and blast distance 33 m as well as TNT equivalent 3 t and blast distance 33 m, were calculated, respectively, and compared with the test results. Further, the failure patterns of the scale model under different overpressures and impulses were calculated by controlling the TNT equivalent and blast distance. The research results show that the middle column of the bent structure is prone to damage in the form of overall overturning under a lateral blast load; the calculated failure morphologies are in good agreement with the experimental ones, and the maximum relative errors of the characteristic displacements and characteristic corners are 5.6% and 4.6%, respectively. The overturning angle of the load-bearing column was used as the basis for the damage-grade division, and the calculated results were divided into three damage levels. The fitted overpressure-impulse and equivalent-distance curves can be used in the design of safety distance and warehouse capacity and the estimation of the damage degree of accidental explosion.
2020, 40(12): 122301.
doi: 10.11883/bzycj-2020-0046
Abstract:
Ti-6Al-4V is a kind of important alternative material for light-weight design of warhead whose impact-initiated reaction could enhance the damage power of the weapon. However, there is not enough research on the condition and mechanism of its impact-initiated reaction. Through experimental and theoretical analyses, the influences of fracture modes of Ti-6Al-4V structure on impact initiated reaction were studied in the present paper, in order to obtain the condition and mechanism of impact-initiated reaction of Ti-6Al-4V material. Two types of projectiles were designed to normally penetrate the unreinforced concrete target, i.e., the titanium projectile with ogival nose and the composite projectile with C/C nose and hollow titanium cylinder. The impact velocity followed between 222 m/s and 1008 m/s. Two projectiles exhibit different fracture modes. In the studied velocity range, there is an impact-initiated reaction during penetration for the titanium projectile, but no reaction is observed during the impact of the composite projectile. The fracture modes of the two projectiles were analyzed in the macroscopic and microscopic views. After penetration, the structure of the titanium projectile is almost intact. Only abrasion is observed on the outer-surface of the projectile. The main failure mode for abrasion is the shear deformation of its microstructure, which induces fragments with lengths in micrometers or hundreds of micrometers. The number of fragments could be up to 3 millions. For the hollow titanium cylinder in the composite projectile, it is teared up into large fragments, whose dimensions are in millimeters. The tearing surface develops along the shear band. The largest number of fragments is almost 120. Further analyses indicate that the efficiency of oxygen and heat supply is reverse proportional to the size of the fragment. Under certain oxygen and heat supply, the necessary condition to initiate the impact reaction of Ti-6Al-4V is that the size of fragments should be small enough. This must be the essential reason for the impact reaction in an ogival titanium projectile and no reaction in a composite projectile during penetration. With the necessary condition to initiate the impact reaction, the greater the number of fragments, the higher the impact reaction intensity is.
Ti-6Al-4V is a kind of important alternative material for light-weight design of warhead whose impact-initiated reaction could enhance the damage power of the weapon. However, there is not enough research on the condition and mechanism of its impact-initiated reaction. Through experimental and theoretical analyses, the influences of fracture modes of Ti-6Al-4V structure on impact initiated reaction were studied in the present paper, in order to obtain the condition and mechanism of impact-initiated reaction of Ti-6Al-4V material. Two types of projectiles were designed to normally penetrate the unreinforced concrete target, i.e., the titanium projectile with ogival nose and the composite projectile with C/C nose and hollow titanium cylinder. The impact velocity followed between 222 m/s and 1008 m/s. Two projectiles exhibit different fracture modes. In the studied velocity range, there is an impact-initiated reaction during penetration for the titanium projectile, but no reaction is observed during the impact of the composite projectile. The fracture modes of the two projectiles were analyzed in the macroscopic and microscopic views. After penetration, the structure of the titanium projectile is almost intact. Only abrasion is observed on the outer-surface of the projectile. The main failure mode for abrasion is the shear deformation of its microstructure, which induces fragments with lengths in micrometers or hundreds of micrometers. The number of fragments could be up to 3 millions. For the hollow titanium cylinder in the composite projectile, it is teared up into large fragments, whose dimensions are in millimeters. The tearing surface develops along the shear band. The largest number of fragments is almost 120. Further analyses indicate that the efficiency of oxygen and heat supply is reverse proportional to the size of the fragment. Under certain oxygen and heat supply, the necessary condition to initiate the impact reaction of Ti-6Al-4V is that the size of fragments should be small enough. This must be the essential reason for the impact reaction in an ogival titanium projectile and no reaction in a composite projectile during penetration. With the necessary condition to initiate the impact reaction, the greater the number of fragments, the higher the impact reaction intensity is.
Influences of the heating rate and rheological properties on slow cook-off response of composition B
2020, 40(12): 122302.
doi: 10.11883/bzycj-2019-0431
Abstract:
In order to investigate the difference of internal temperature distribution and the location of response in slow cook off of Comp B with consideration about the rheology and its size-effect when under different heating rates, 2 types of cooking off bombs with diameters of 76 mm and 130 mm were designed. The temperature curves of the internal monitoring points in the bombs at the heating rates of 1 ℃/min and 3.3 ℃/h were obtained by the slow cook off test, and the characteristics of temperature field under various conditions were further analyzed in simulation. The results show that: at the heating rate of 1 ℃/min, the internal explosives of the 2 sizes of bombs have already responded before they have completely melted, affected by the convection, the explosive of the top melted significantly quicker than that of the bottom, size effect on the rheology was not obvious; When the heating rate is 3.3 ℃/h, after the phase changing is completely done, the intensity of internal flow field is low, and the temperature field of the smaller bomb changed very slowly. However, the internal temperature field in the larger bomb changed quickly to a typical liquid temperature field because of an intenser flow, size effect on the rheology was more palpable. Moreover, in any conditions, the highest temperature location, self-heating and response areas are all near the top of the explosive.
In order to investigate the difference of internal temperature distribution and the location of response in slow cook off of Comp B with consideration about the rheology and its size-effect when under different heating rates, 2 types of cooking off bombs with diameters of 76 mm and 130 mm were designed. The temperature curves of the internal monitoring points in the bombs at the heating rates of 1 ℃/min and 3.3 ℃/h were obtained by the slow cook off test, and the characteristics of temperature field under various conditions were further analyzed in simulation. The results show that: at the heating rate of 1 ℃/min, the internal explosives of the 2 sizes of bombs have already responded before they have completely melted, affected by the convection, the explosive of the top melted significantly quicker than that of the bottom, size effect on the rheology was not obvious; When the heating rate is 3.3 ℃/h, after the phase changing is completely done, the intensity of internal flow field is low, and the temperature field of the smaller bomb changed very slowly. However, the internal temperature field in the larger bomb changed quickly to a typical liquid temperature field because of an intenser flow, size effect on the rheology was more palpable. Moreover, in any conditions, the highest temperature location, self-heating and response areas are all near the top of the explosive.
2020, 40(12): 123101.
doi: 10.11883/bzycj-2020-0055
Abstract:
In order to improve the energy absorption capacity of thin-walled structures, a new type of thin-walled tube (SHT) with hierarchical characteristic was proposed based on the Sierpinski fractal structure. The deformation mode and energy absorption characteristics of SHTs under axial impact load were simulated using the nonlinear finite element method, and compared with those of ordinary triangular thin-walled tubes. The results show that the deformation mode of the new SHT is an axisymmetric progressive buckling mode. With the introduction of the Sierpinski hierarchical characteristics, the half-folded wavelength of the cell wall bending process is reduced, hence more plastic folding elements are formed and more energy is absorbed. Furthermore, theoretical expressions of the axial compression stress were obtained based on the energy conservation theory and plastic hinge theory. The correctness of the theoretical formula was verified by comparing with the finite element simulation. The results display that under the same relative density, the dynamic compressive stresses of the first-, second- and third-order SHTs are 85.8%, 138.2% and 183.8%, respectively, higher than that of the ordinary triangular thin-walled tubes. The introduction of the Sierpinski hierarchical characteristics into the design of the thin-walled tubes can effectively improve the crashworthiness of the thin-walled tubes, and it can provide a reference for the research and design of new energy absorbers.
2020, 40(12): 123201.
doi: 10.11883/bzycj-2020-0051
Abstract:
To explore the effect of droplet viscosity on the deformation process, and have a deep understanding of the mechanism of the droplet deformation and breakup process.Droplet deformation behaviors of three viscous silicone oils were experimentally captured by the high-speed shadowgraphic technique on a horizontal shock tube, the Weber number (We) ranged between 1 100～4 400. Results show that with the increasing of droplet viscosity: new deformation characteristics appear, and the duration that the droplet evolves into the special shape increases; The growth rates of characteristic space and displacement parameters all decrease, while the duration of the deformation process, the maximum of the droplet deformation extent/displacement all increase. This is because the enlarged viscous force has slowed down the deformation rate, consumed more inertia, and extended the deformation process;The most unstable wave of Kelvin-Helmholtz instability develops toward a larger scale and a slower growth rate tendency, thus the delaying effect caused by the viscosity on the deformation process is achieved.With the increasing of the maximum of deformation displacement, the maximum of droplet deformation extent firstly shows a linear growth trend then a slower growth rate.
To explore the effect of droplet viscosity on the deformation process, and have a deep understanding of the mechanism of the droplet deformation and breakup process.Droplet deformation behaviors of three viscous silicone oils were experimentally captured by the high-speed shadowgraphic technique on a horizontal shock tube, the Weber number (We) ranged between 1 100～4 400. Results show that with the increasing of droplet viscosity: new deformation characteristics appear, and the duration that the droplet evolves into the special shape increases; The growth rates of characteristic space and displacement parameters all decrease, while the duration of the deformation process, the maximum of the droplet deformation extent/displacement all increase. This is because the enlarged viscous force has slowed down the deformation rate, consumed more inertia, and extended the deformation process;The most unstable wave of Kelvin-Helmholtz instability develops toward a larger scale and a slower growth rate tendency, thus the delaying effect caused by the viscosity on the deformation process is achieved.With the increasing of the maximum of deformation displacement, the maximum of droplet deformation extent firstly shows a linear growth trend then a slower growth rate.
2020, 40(12): 123301.
doi: 10.11883/bzycj-2020-0014
Abstract:
The high-speed water-entry process of a revolution body involves fluid and structure interaction, which is a complex nonlinear and unsteady process. The revolution body with high speed is subjected to extreme impact load at the moment of hitting water surface which would cause great deformation or even damage to the structure. In order to investigate the physical understanding of the structural strength of revolution bodies and the mechanism of the cavity dynamics during high-speed water-entry process, a fluid-structure interaction (FSI) model based on a co-simulation progress between STAR-CCM+ and ABAQUS was adopted. The model performed a two-way interaction analysis which can consider the influence of the deformation of structure to fluid into. In the form of CFD analysis, a three-dimensional simulation with a six-degree-of-freedom model was carried out, in which the Shear Stress Transfer (SST) turbulence model and the volume of fluid (VOF) technique were used for turbulence computation and air-liquid interface tracking, respectively. In the part of FEM research, the shell mesh form with a whole Johnson-Cook material model was implemented to give a full consideration of deformation process and the accuracy of structure computation, which can effectively reflect the plastic deformation of structure. Firstly, a comparison between FSI result and experimental result of the high-speed water-entry process was conducted. The results show that the velocity attenuation, displacement and the cavity features are in good agreement with the experimental result, which proves two-way FSI method can be effectively applied into the research of high-speed water-entry problem. Then a numerical simulation of revolution body oblique water-entry with different velocity was carried out. The results show that the stress initially focuses on the edge of the bottom side of the revolution body, then it transports to the central area, remaining steady in the end. Compared with the results of rigid body, the peak value of impact load of the flexible body appears smaller due to the repeated deformation for buffer, which also causes the fluctuation of the load curve. After the initial water impacting, the cavity presents an asymmetric shape. As water-entry time increases, the asymmetry of cavity becomes weaker. In the process of 60 m/s oblique water-entry, surface closure of the cavity occurs. With the increase of water-entry velocity, the time of cavity surface closure takes longer. The peak value of the impact load whose period is quite short appears immediately at very beginning of water-entry process. After entering the water surface, the impact load of the revolution body decreases dramatically and rapidly and fluctuates slightly. The peak value of the impact load is related to water-entry velocity. The higher the velocity is, the earlier peak value of the impact load occurs and more obviously it fluctuates. As water-entry velocity exceeds 100 m/s, plastic deformation appears in the central area of bottom of revolution body.
The high-speed water-entry process of a revolution body involves fluid and structure interaction, which is a complex nonlinear and unsteady process. The revolution body with high speed is subjected to extreme impact load at the moment of hitting water surface which would cause great deformation or even damage to the structure. In order to investigate the physical understanding of the structural strength of revolution bodies and the mechanism of the cavity dynamics during high-speed water-entry process, a fluid-structure interaction (FSI) model based on a co-simulation progress between STAR-CCM+ and ABAQUS was adopted. The model performed a two-way interaction analysis which can consider the influence of the deformation of structure to fluid into. In the form of CFD analysis, a three-dimensional simulation with a six-degree-of-freedom model was carried out, in which the Shear Stress Transfer (SST) turbulence model and the volume of fluid (VOF) technique were used for turbulence computation and air-liquid interface tracking, respectively. In the part of FEM research, the shell mesh form with a whole Johnson-Cook material model was implemented to give a full consideration of deformation process and the accuracy of structure computation, which can effectively reflect the plastic deformation of structure. Firstly, a comparison between FSI result and experimental result of the high-speed water-entry process was conducted. The results show that the velocity attenuation, displacement and the cavity features are in good agreement with the experimental result, which proves two-way FSI method can be effectively applied into the research of high-speed water-entry problem. Then a numerical simulation of revolution body oblique water-entry with different velocity was carried out. The results show that the stress initially focuses on the edge of the bottom side of the revolution body, then it transports to the central area, remaining steady in the end. Compared with the results of rigid body, the peak value of impact load of the flexible body appears smaller due to the repeated deformation for buffer, which also causes the fluctuation of the load curve. After the initial water impacting, the cavity presents an asymmetric shape. As water-entry time increases, the asymmetry of cavity becomes weaker. In the process of 60 m/s oblique water-entry, surface closure of the cavity occurs. With the increase of water-entry velocity, the time of cavity surface closure takes longer. The peak value of the impact load whose period is quite short appears immediately at very beginning of water-entry process. After entering the water surface, the impact load of the revolution body decreases dramatically and rapidly and fluctuates slightly. The peak value of the impact load is related to water-entry velocity. The higher the velocity is, the earlier peak value of the impact load occurs and more obviously it fluctuates. As water-entry velocity exceeds 100 m/s, plastic deformation appears in the central area of bottom of revolution body.
2020, 40(12): 124201.
doi: 10.11883/bzycj-2019-0411
Abstract:
Aiming to overcome the disadvantages and demerits in the stress calculation in the passive confinement pressure SHPB tests of granular materials, a numerical modified approach is proposed in the present paper. The modified approach is also verified by finite element numerical simulation and experimental results. The results show that when the length of specimen is much shorter than the length of thick-walled hollow cylinder, the edge effects will lead to a non-uniform distribution of deformation along the length of hollow cylinder. Therefore, the configuration of thick-walled cannot be simplified as a plain stress problem when calculating the stress and deformation state of granular material. Due to the fact that the thick-walled hollow cylinder is elastic, the real radial stress in the hollow cylinder is proportional to the theoretical predictions. The proportionality coefficient has a quadratic function relation with the length of specimen.
Aiming to overcome the disadvantages and demerits in the stress calculation in the passive confinement pressure SHPB tests of granular materials, a numerical modified approach is proposed in the present paper. The modified approach is also verified by finite element numerical simulation and experimental results. The results show that when the length of specimen is much shorter than the length of thick-walled hollow cylinder, the edge effects will lead to a non-uniform distribution of deformation along the length of hollow cylinder. Therefore, the configuration of thick-walled cannot be simplified as a plain stress problem when calculating the stress and deformation state of granular material. Due to the fact that the thick-walled hollow cylinder is elastic, the real radial stress in the hollow cylinder is proportional to the theoretical predictions. The proportionality coefficient has a quadratic function relation with the length of specimen.
2020, 40(12): 125401.
doi: 10.11883/bzycj-2020-0202
Abstract:
Storage tanks may leak due to corrosion or human error, resulting in released gas dispersion and vapor cloud explosion accidents. The computational fluid dynamics software FLACS was employed to reveal the development processes of explosion accidents and estimate their influences on the environment, focusing on the effect of the leakage and environmental wind as two dominant factors on the ethylene gas dispersion and gas explosion. The results show that gas cloud dispersion distance and gas cloud volume increase with the increasing leak rate. When the leak rate is less than 6 kg/s, the gas cloud dispersion distance and gas cloud volume are similar in different leak directions. When the leak rate is greater than 6 kg/s, the dispersion of released gas and formation of gas cloud are influenced by the obstacles. The gas cloud dispersion distance decreases and the gas cloud volume increases as the blockage rate of the geometric obstacles increases. When the leak direction is perpendicular to the central axis of the storage tank group and the leak rate is 18 kg/s, the gas cloud attains its maximum dispersion distance of 81.5 m. When the leak direction is parallel to the central axis of the storage tank group and the leak rate is 24 kg/s, the gas cloud reaches its maximum volume of 9 604 m3. The impact pressure of the explosion wave increases with the increase in the leak rate. Under the influence of the environmental wind, the dilution of combustible gas is prominently accelerated and the combustible gas cloud volume is substantially lessened. Meanwhile, the probability of ignition of gas clouds and the intensity of the vapor cloud explosion are effectively reduced. Moreover, the time corresponding to achieve the peak explosion pressure is earlier and the decrease of the temperature is quicker than their counterparts under the condition without the environmental wind. When the leak rate is 24 kg/s, the explosion overpressure around the leakage location on the surface of the tank is only 6.88 kPa, but the temperature is 2 384 K. Therefore, when the explosion accident occurs, cooling the storage tanks is crucial in rescue in order to avoid the secondary disaster.
Storage tanks may leak due to corrosion or human error, resulting in released gas dispersion and vapor cloud explosion accidents. The computational fluid dynamics software FLACS was employed to reveal the development processes of explosion accidents and estimate their influences on the environment, focusing on the effect of the leakage and environmental wind as two dominant factors on the ethylene gas dispersion and gas explosion. The results show that gas cloud dispersion distance and gas cloud volume increase with the increasing leak rate. When the leak rate is less than 6 kg/s, the gas cloud dispersion distance and gas cloud volume are similar in different leak directions. When the leak rate is greater than 6 kg/s, the dispersion of released gas and formation of gas cloud are influenced by the obstacles. The gas cloud dispersion distance decreases and the gas cloud volume increases as the blockage rate of the geometric obstacles increases. When the leak direction is perpendicular to the central axis of the storage tank group and the leak rate is 18 kg/s, the gas cloud attains its maximum dispersion distance of 81.5 m. When the leak direction is parallel to the central axis of the storage tank group and the leak rate is 24 kg/s, the gas cloud reaches its maximum volume of 9 604 m3. The impact pressure of the explosion wave increases with the increase in the leak rate. Under the influence of the environmental wind, the dilution of combustible gas is prominently accelerated and the combustible gas cloud volume is substantially lessened. Meanwhile, the probability of ignition of gas clouds and the intensity of the vapor cloud explosion are effectively reduced. Moreover, the time corresponding to achieve the peak explosion pressure is earlier and the decrease of the temperature is quicker than their counterparts under the condition without the environmental wind. When the leak rate is 24 kg/s, the explosion overpressure around the leakage location on the surface of the tank is only 6.88 kPa, but the temperature is 2 384 K. Therefore, when the explosion accident occurs, cooling the storage tanks is crucial in rescue in order to avoid the secondary disaster.
