2019 Vol. 39, No. 3
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2019, 39(3): 032101.
doi: 10.11883/bzycj-2017-0458
Abstract:
In this paper we investigated the influence of the pre-ignition turbulence intensity on the explosion parameters of n-pentane mists. By using 0.4, 0.6 and 0.8 MPa of pneumatic pressure spray, we obtained n-pentane mists with the Sauter mean diameter (SMD) of 21.21, 14.51 and 8.64 μm, and at the same time, the pre-ignition turbulence intensity under different pneumatic pressures. Then, in a 20 L mists explosion parameter measuring system for experimental research, we aquired the influence of the pre-ignition turbulence on the evaporation rate, the peak explosion overpressure, the explosion pressure rise rate and the ignition delay time of n-pentane mists. The results showed that, the average turbulence velocity of the enviromental fluid field was zero. The smaller the droplet size was, the more obvious was the increase of the evaporation rate of the mists with the increase of the turbulence intensity. At the same time, for the SMDs of 14.51 and 21.21 μm, the peak pressure and the maximum pressure rise rate increased more obviously with the SMD of 8.64 μm, and the explosion intensity was significantly strong, suggesting the existence of a transition range. For the SMDs in the range of 8−22 μm, the mean square turbulence velocity in 1.0−4.0 m/s was the low growth stage of the flame propagation delay time, whereas that in 4.0−6.2 m/s was the high growth stage. The turbulence intensity and the flame propagation delay time exhibited a linear growth in both stages.
In this paper we investigated the influence of the pre-ignition turbulence intensity on the explosion parameters of n-pentane mists. By using 0.4, 0.6 and 0.8 MPa of pneumatic pressure spray, we obtained n-pentane mists with the Sauter mean diameter (SMD) of 21.21, 14.51 and 8.64 μm, and at the same time, the pre-ignition turbulence intensity under different pneumatic pressures. Then, in a 20 L mists explosion parameter measuring system for experimental research, we aquired the influence of the pre-ignition turbulence on the evaporation rate, the peak explosion overpressure, the explosion pressure rise rate and the ignition delay time of n-pentane mists. The results showed that, the average turbulence velocity of the enviromental fluid field was zero. The smaller the droplet size was, the more obvious was the increase of the evaporation rate of the mists with the increase of the turbulence intensity. At the same time, for the SMDs of 14.51 and 21.21 μm, the peak pressure and the maximum pressure rise rate increased more obviously with the SMD of 8.64 μm, and the explosion intensity was significantly strong, suggesting the existence of a transition range. For the SMDs in the range of 8−22 μm, the mean square turbulence velocity in 1.0−4.0 m/s was the low growth stage of the flame propagation delay time, whereas that in 4.0−6.2 m/s was the high growth stage. The turbulence intensity and the flame propagation delay time exhibited a linear growth in both stages.
2019, 39(3): 032102.
doi: 10.11883/bzycj-2017-0248
Abstract:
In order to investigate the propagation mode of rotating detonation wave in rotating detonation engine (RDE) with different annular gap width, the experiment was conducted on non-premixed RDE. During the experiment, high-frequency pressure transducers, ion probes and high-speed photography were used simultaneously. Under the condition of the same inlet mass flow rate, the annular gap width of air inlet and detonation chamber were changed. As a result, the propagation mode including the single wave, double wave, four wave collision and mixed mode were obtained. By analyzing the experimental results, it was found that when the detonation chamber width was 6 mm, the detonation wave was changed from four wave collision to double wave, and finally to the single wave as the air inlet width was increased. When the detonation chamber width were 10 and 15 mm, the air inlet width had little influence on detonation wave propagation mode. In addition, under the four wave collision mode, both of the pressure peak and ion signal peak were lower than that of the single wave and double wave modes.
In order to investigate the propagation mode of rotating detonation wave in rotating detonation engine (RDE) with different annular gap width, the experiment was conducted on non-premixed RDE. During the experiment, high-frequency pressure transducers, ion probes and high-speed photography were used simultaneously. Under the condition of the same inlet mass flow rate, the annular gap width of air inlet and detonation chamber were changed. As a result, the propagation mode including the single wave, double wave, four wave collision and mixed mode were obtained. By analyzing the experimental results, it was found that when the detonation chamber width was 6 mm, the detonation wave was changed from four wave collision to double wave, and finally to the single wave as the air inlet width was increased. When the detonation chamber width were 10 and 15 mm, the air inlet width had little influence on detonation wave propagation mode. In addition, under the four wave collision mode, both of the pressure peak and ion signal peak were lower than that of the single wave and double wave modes.
2019, 39(3): 032103.
doi: 10.11883/bzycj-2017-0396
Abstract:
Cast HMX/TNT/AL compositions are an aluminized explosive. In the present investigation of the deflagration to detonation transition of the cast HMX/TNT/AL compositions with a metal shell at fast thermal ignition, we constructed an experimental platform of DDT of the explosives with a metal shell at fast thermal ignition, which was composed of an experimental equipment, a pressure testing system and a fiber probe system used in the velocity measure. The experimental equipment was composed of the fast heating equipment, the steel tube and the explosives. The peak temperatures were more than 1 100 °C, the temperature rise ranged from 85 °C/s to 95 °C/s when the steel plates 16 mm chick were heated up by the fast heating equipment. Experiments on DDT of the explosives were conducted in which the cast HMX/TNT/AL compositions in the steel tube was heated up using the fast heating equipment. The velocity of the chemical reaction front was measured by the fiber probe as less than 2 600 m/s. The pressure of the chemical reaction front was measured by the high pressure sensor as approximately 1 GPa. The track of the chemical reaction front was obtained using the fiber history. The vicinity and distance of the shock formation were obtained through the characteristics diagram, showing the distance as more than 850 mm. Comparison was made between the estimated fragment mass values of the models and the measured values, with the latter larger than the former. It was concluded that the state of the chemical reaction on the cast HMX/TNT/AL compositions was not detonation but deflagration. According to the Adams & Pack model and the CJ deflagration model, the distance of the shock formation and the pressure of combustion wave was semi-quantitatively evaluated. The results of the CJ deflagration model was found to be closer to the measured values than the Adams & Pack model.
Cast HMX/TNT/AL compositions are an aluminized explosive. In the present investigation of the deflagration to detonation transition of the cast HMX/TNT/AL compositions with a metal shell at fast thermal ignition, we constructed an experimental platform of DDT of the explosives with a metal shell at fast thermal ignition, which was composed of an experimental equipment, a pressure testing system and a fiber probe system used in the velocity measure. The experimental equipment was composed of the fast heating equipment, the steel tube and the explosives. The peak temperatures were more than 1 100 °C, the temperature rise ranged from 85 °C/s to 95 °C/s when the steel plates 16 mm chick were heated up by the fast heating equipment. Experiments on DDT of the explosives were conducted in which the cast HMX/TNT/AL compositions in the steel tube was heated up using the fast heating equipment. The velocity of the chemical reaction front was measured by the fiber probe as less than 2 600 m/s. The pressure of the chemical reaction front was measured by the high pressure sensor as approximately 1 GPa. The track of the chemical reaction front was obtained using the fiber history. The vicinity and distance of the shock formation were obtained through the characteristics diagram, showing the distance as more than 850 mm. Comparison was made between the estimated fragment mass values of the models and the measured values, with the latter larger than the former. It was concluded that the state of the chemical reaction on the cast HMX/TNT/AL compositions was not detonation but deflagration. According to the Adams & Pack model and the CJ deflagration model, the distance of the shock formation and the pressure of combustion wave was semi-quantitatively evaluated. The results of the CJ deflagration model was found to be closer to the measured values than the Adams & Pack model.
2019, 39(3): 032201.
doi: 10.11883/bzycj-2018-0048
Abstract:
Compared to linear attenuation load calculation model, exponential attenuation load with transition expression was given to build equivalent SDOF differential equations under air blast loading. The expressions, which had relationship to transition duration, overpressure peak, exponential load adjusting parameter, natural frequency and overpressure duration, were derived to solve equivalent static load dynamical coefficients. Changed with transition duration and load adjusting parameters, four typical calculation conditions results were calculated. The results show that the linear attenuation blast load’s application range is limited. When the ductility ratio β＜3.0, the dynamical coefficients from the linear attenuation blast load behaves greater value and safer characteristic. When the ductility ratio β≥3.0 and wt+＞1.4δ, it will be lower 17.4% than the value from exponential attenuation load with transition. For the much transition duration ratio, dynamical coefficients will be greater. In the range of 1%−2% for the transition duration ratio, the effect on dynamical coefficients is greater at 0.4−0.7% and can be ignored. Exponential load adjusting parameter has no effect on structural design with great flexibility while it would lead to increase or decrease the dynamical coefficients for the structure with the general flexibility.
Compared to linear attenuation load calculation model, exponential attenuation load with transition expression was given to build equivalent SDOF differential equations under air blast loading. The expressions, which had relationship to transition duration, overpressure peak, exponential load adjusting parameter, natural frequency and overpressure duration, were derived to solve equivalent static load dynamical coefficients. Changed with transition duration and load adjusting parameters, four typical calculation conditions results were calculated. The results show that the linear attenuation blast load’s application range is limited. When the ductility ratio β＜3.0, the dynamical coefficients from the linear attenuation blast load behaves greater value and safer characteristic. When the ductility ratio β≥3.0 and wt+＞1.4δ, it will be lower 17.4% than the value from exponential attenuation load with transition. For the much transition duration ratio, dynamical coefficients will be greater. In the range of 1%−2% for the transition duration ratio, the effect on dynamical coefficients is greater at 0.4−0.7% and can be ignored. Exponential load adjusting parameter has no effect on structural design with great flexibility while it would lead to increase or decrease the dynamical coefficients for the structure with the general flexibility.
2019, 39(3): 033101.
doi: 10.11883/bzycj-2018-0015
Abstract:
The 100 mm split Hopkinson pressure bar was used to study the dynamic mechanical properties of the calcareous sand confined by confinement at strain rates ranging from 500 to 800 s−1 and pressures ranging from 0 to 200 MPa under different pre-pressures. The static mechanical properties of calcareous sand under the same conditions were investigated in the strain rate of 2×10−3 s−1 and the pressure range of 0−120 MPa by using HUT106D universal material testing machine. It is found that the pre-pressure value has little effect on the mechanical properties of calcareous sand when the load is more than a certain value; Tait equation of state can describe the relationship between hydrostatic pressure and volume strain of calcareous sand in static state and the dynamic state under high pressure; the volumetric compression process of calcareous sand shows a strain rate effect.
The 100 mm split Hopkinson pressure bar was used to study the dynamic mechanical properties of the calcareous sand confined by confinement at strain rates ranging from 500 to 800 s−1 and pressures ranging from 0 to 200 MPa under different pre-pressures. The static mechanical properties of calcareous sand under the same conditions were investigated in the strain rate of 2×10−3 s−1 and the pressure range of 0−120 MPa by using HUT106D universal material testing machine. It is found that the pre-pressure value has little effect on the mechanical properties of calcareous sand when the load is more than a certain value; Tait equation of state can describe the relationship between hydrostatic pressure and volume strain of calcareous sand in static state and the dynamic state under high pressure; the volumetric compression process of calcareous sand shows a strain rate effect.
2019, 39(3): 033102.
doi: 10.11883/bzycj-2017-0334
Abstract:
In order to solve the safety assessment of a buried pipeline nearby blasting operation location, a series of dynamic responses of the polyethylene (PE) pipe in high saturated clay under the action of the explosive wave were carried out. The experimental data of the dynamic strain and dynamic pressure were gotten, and the velocity data of the pipe and the ground were measured at the same time. The experimental results show that the peak strain of the PE pipe has a good power function attenuation relationship with scaled distance. In the scaled distance range of 6−11 m/kg1/3, the attenuation index of hoop strain (absolute value) is larger than the attenuation index of axial strain. The main vibration frequency of the dynamic response of the pipeline is slightly higher than the main vibration frequency of the soil, both in the same order. The pipeline synthesis velocity attenuation index is roughly the same as the axial strain attenuation index of the pipe. There is a strong correlation between the dynamic pressure signal measured by PZT and the strain rate signal of the same point. Due to the high water content in the high saturated soil, the PE pipe will be locally impacted and the greater circumferential strain will be produced, so this factor should be taken full account of the pipeline safety assessment. The hoop strain level is reduced, and the axial strain level relatively enhances when the scaled distance increases. Because of good and reliable dynamic performance of the PZT, the PZT is worthy of use and promotion as a mean for field detection of pipelines.
In order to solve the safety assessment of a buried pipeline nearby blasting operation location, a series of dynamic responses of the polyethylene (PE) pipe in high saturated clay under the action of the explosive wave were carried out. The experimental data of the dynamic strain and dynamic pressure were gotten, and the velocity data of the pipe and the ground were measured at the same time. The experimental results show that the peak strain of the PE pipe has a good power function attenuation relationship with scaled distance. In the scaled distance range of 6−11 m/kg1/3, the attenuation index of hoop strain (absolute value) is larger than the attenuation index of axial strain. The main vibration frequency of the dynamic response of the pipeline is slightly higher than the main vibration frequency of the soil, both in the same order. The pipeline synthesis velocity attenuation index is roughly the same as the axial strain attenuation index of the pipe. There is a strong correlation between the dynamic pressure signal measured by PZT and the strain rate signal of the same point. Due to the high water content in the high saturated soil, the PE pipe will be locally impacted and the greater circumferential strain will be produced, so this factor should be taken full account of the pipeline safety assessment. The hoop strain level is reduced, and the axial strain level relatively enhances when the scaled distance increases. Because of good and reliable dynamic performance of the PZT, the PZT is worthy of use and promotion as a mean for field detection of pipelines.
2019, 39(3): 033103.
doi: 10.11883/bzycj-2017-0405
Abstract:
Accurate measurement of the dynamic compressive performance of concrete and its strain rate enhancement effect is a key point in impact dynamics research. In this study, aiming at the dynamic compressive behavior test of concrete C110, we examined the stress uniformity, constant loading strain rate and interface contact in the large-size Split Hopkinson Pressure Bar test and found that the upper-limit strain rate in consideration of the stress uniformity hypothesis was less than 166 s−1 for the concrete specimens in this test and that, owing to the imperfect contact of the interface between the rod and the end surface of the specimen, the experimental young modulus and yield strength were obviously smaller than the actual value. Then we developed the five-step test method and prestress method, by which the approximate constant strain rate loading was realized using the combined pulse shaping technology. Using the above technologies the dynamic and static stress-strain curves the concrete C110 were presented. The results showed that the strain-rate effect of the young's modulus of the concrete C110 was not observed and the yield strengths of the uniaxial compression were linearly proportionate to the logarithmic strain rates, with the experimental strain-rate enhancement factor to be 0.10, and that the concrete-like pressure-sensitive material should be calibrated using the yield criteria. In this research, the strain-rate enhancement factor of the concrete material, respectively, were calibrated using the Tresca yield criterion and the K&C yield criterion, and then the strain-rate enhancement factor of the concrete material were found to be 0.015 and 0.038 respectively.
Accurate measurement of the dynamic compressive performance of concrete and its strain rate enhancement effect is a key point in impact dynamics research. In this study, aiming at the dynamic compressive behavior test of concrete C110, we examined the stress uniformity, constant loading strain rate and interface contact in the large-size Split Hopkinson Pressure Bar test and found that the upper-limit strain rate in consideration of the stress uniformity hypothesis was less than 166 s−1 for the concrete specimens in this test and that, owing to the imperfect contact of the interface between the rod and the end surface of the specimen, the experimental young modulus and yield strength were obviously smaller than the actual value. Then we developed the five-step test method and prestress method, by which the approximate constant strain rate loading was realized using the combined pulse shaping technology. Using the above technologies the dynamic and static stress-strain curves the concrete C110 were presented. The results showed that the strain-rate effect of the young's modulus of the concrete C110 was not observed and the yield strengths of the uniaxial compression were linearly proportionate to the logarithmic strain rates, with the experimental strain-rate enhancement factor to be 0.10, and that the concrete-like pressure-sensitive material should be calibrated using the yield criteria. In this research, the strain-rate enhancement factor of the concrete material, respectively, were calibrated using the Tresca yield criterion and the K&C yield criterion, and then the strain-rate enhancement factor of the concrete material were found to be 0.015 and 0.038 respectively.
2019, 39(3): 033201.
doi: 10.11883/bzycj-2017-0409
Abstract:
In order to investigate the effect of diaphragms thickness and combination on the maximum bearing pressure, the shock tube experiment was conducted on the PET diaphragms with different thicknesses. Two high-speed cameras were used to capture and record the whole deformation process of the PET diaphragms. The diaphragms displacement field at different moments were obtained by 3D-DIC. An unusual interesting phenomenon was observed that the diaphragms were recurved and then dramatically ruptured, and thus the diaphragm defamation was divided into two stages. The diaphragms deformation of any thickness in the first stage, and the shape characteristic of the diaphragm recurvation in the second stage as well as the thickness variation during the whole process were analyzed.
In order to investigate the effect of diaphragms thickness and combination on the maximum bearing pressure, the shock tube experiment was conducted on the PET diaphragms with different thicknesses. Two high-speed cameras were used to capture and record the whole deformation process of the PET diaphragms. The diaphragms displacement field at different moments were obtained by 3D-DIC. An unusual interesting phenomenon was observed that the diaphragms were recurved and then dramatically ruptured, and thus the diaphragm defamation was divided into two stages. The diaphragms deformation of any thickness in the first stage, and the shape characteristic of the diaphragm recurvation in the second stage as well as the thickness variation during the whole process were analyzed.
2019, 39(3): 033301.
doi: 10.11883/bzycj-2017-0047
Abstract:
In this paper, based on the projectile load analysis using the cavity expansion theory, we simplified the movement and deformation mode of the grooved-tapered projectile in the early stage of its oblique penetration into the concrete as the response behavior of a free beam under transversal and axial transient load at the end, and calculated the shear force, the moment and the yield function of each section of the projectile. In addition, we found out about how the projectile’s bending was affected by the projectile body’s thickness, yield strength, initial velocity and oblique angle.
In this paper, based on the projectile load analysis using the cavity expansion theory, we simplified the movement and deformation mode of the grooved-tapered projectile in the early stage of its oblique penetration into the concrete as the response behavior of a free beam under transversal and axial transient load at the end, and calculated the shear force, the moment and the yield function of each section of the projectile. In addition, we found out about how the projectile’s bending was affected by the projectile body’s thickness, yield strength, initial velocity and oblique angle.
2019, 39(3): 034101.
doi: 10.11883/bzycj-2017-0416
Abstract:
A new wavelength-time mapping linear chirped fiber Bragg grating (LCFBG) sensor is proposed, to resolve the problems in which the LCFBG needs to be entirely destroyed and be damaged accordingly to the reflective position for the longer wavelength prior to the shorter wavelength in the intensive LCFBG sensor. In this sensor, the reflective spectrum of the LCFBG destroyed by the detonation and the shock wave is transferred into the same temporal pulse by the high-repetition rate mode-locked laser and the dispersive fiber, which is then used to obtain the length of the LCFBG. The time-resolution and the relative uncertainty of the wave-front position in this sensor are analyzed and their values are found to be 10 ns and 1.7%, respectively. For the data analysis, the experimental data is transformed to 2D image and the wave-front position of the detonation and the shock wave is calculated from this 2D image. The detonation speed of the JB-9014 explosive is linearly fitted to be 7.58 km/s from the wave-front position of the detonation, which is coincidental with the electrical pin’s result of 7.63 km/s (relative error less than 1%).
A new wavelength-time mapping linear chirped fiber Bragg grating (LCFBG) sensor is proposed, to resolve the problems in which the LCFBG needs to be entirely destroyed and be damaged accordingly to the reflective position for the longer wavelength prior to the shorter wavelength in the intensive LCFBG sensor. In this sensor, the reflective spectrum of the LCFBG destroyed by the detonation and the shock wave is transferred into the same temporal pulse by the high-repetition rate mode-locked laser and the dispersive fiber, which is then used to obtain the length of the LCFBG. The time-resolution and the relative uncertainty of the wave-front position in this sensor are analyzed and their values are found to be 10 ns and 1.7%, respectively. For the data analysis, the experimental data is transformed to 2D image and the wave-front position of the detonation and the shock wave is calculated from this 2D image. The detonation speed of the JB-9014 explosive is linearly fitted to be 7.58 km/s from the wave-front position of the detonation, which is coincidental with the electrical pin’s result of 7.63 km/s (relative error less than 1%).
2019, 39(3): 034102.
doi: 10.11883/bzycj-2018-0058
Abstract:
In this paper, the strain growth of the flange bolts was observed in the experimental study of the dynamic response of the end cap and the bolts on the spherical explosive vessel. Numerical simulation based on the experiment was then carried out to detect the cause of this phenomenon. The results showed that the intensity of the pressure loading applied on the end cap and the bolts was much higher than that of the spherical vessel shell due to the strengthing effect of the opening’s structure. The resonance between the strengthened pressure loading and the periodical dynamic response of the end cap and bolts was the dominating cause for the bolt strain growth, which could be avoided by modulating the closure mass and the bolt preload.
In this paper, the strain growth of the flange bolts was observed in the experimental study of the dynamic response of the end cap and the bolts on the spherical explosive vessel. Numerical simulation based on the experiment was then carried out to detect the cause of this phenomenon. The results showed that the intensity of the pressure loading applied on the end cap and the bolts was much higher than that of the spherical vessel shell due to the strengthing effect of the opening’s structure. The resonance between the strengthened pressure loading and the periodical dynamic response of the end cap and bolts was the dominating cause for the bolt strain growth, which could be avoided by modulating the closure mass and the bolt preload.
2019, 39(3): 034201.
doi: 10.11883/bzycj-2017-0231
Abstract:
In this study we dealt with the robust non-fragile H∞ controller for the combustion process in liquid propellant rocket motor chambers. In developing a less conservative H∞ performance analysis criterion, we introduced a Lyapunov-Krasovskii functional comprising quadruple-integral term. Then, based on a new delay-partitioning method, the reciprocally convex combination technique and the integral inequality approach (IIA), we formulated the bounded real criterion in terms of linear matrix inequalities (LMIs). Furthermore, based on this bounded real criterion, we translated the nonlinear matrix inequality into the linear matrix inequality by using the matrix congruent transformation and the variable substitution technique, and obtained the parameter expression of non-fragile H∞ controller by solving the feasible linear matrix inequality. The numerical examples we provided showed the effectiveness of the proposed theoretical results.
In this study we dealt with the robust non-fragile H∞ controller for the combustion process in liquid propellant rocket motor chambers. In developing a less conservative H∞ performance analysis criterion, we introduced a Lyapunov-Krasovskii functional comprising quadruple-integral term. Then, based on a new delay-partitioning method, the reciprocally convex combination technique and the integral inequality approach (IIA), we formulated the bounded real criterion in terms of linear matrix inequalities (LMIs). Furthermore, based on this bounded real criterion, we translated the nonlinear matrix inequality into the linear matrix inequality by using the matrix congruent transformation and the variable substitution technique, and obtained the parameter expression of non-fragile H∞ controller by solving the feasible linear matrix inequality. The numerical examples we provided showed the effectiveness of the proposed theoretical results.
2019, 39(3): 035101.
doi: 10.11883/bzycj-2018-0053
Abstract:
In this study we established a simplified theoretical model of the distributed energy absorption system of trains with the influence of the propagation of elastic waves in the train carriage taken into account. Based on the one-dimensional stress wave theory, the responses of energy absorbers in the collision process were analyzed and the governing equations were obtained and solved. The typical stage and platform response of the velocities on the interfaces of each energy absorber was observed and the mechanism was revealed. The analysis about how to set up and arrange the energy absorbing devices was also carried out. The results show that the crushing strength of the front one should be higher than that of the rear one for the adjacent energy absorbers; otherwise the energy absorber at the rear end cannot work at the same time. The plateau stress and its arrangement of each absorber determine the performance of the energy absorption system, which can thereby determine the duration of the energy absorption and the total energy absorption of each energy absorber. The influence of the plateau stress distribution of the adjacent energy absorbers on the energy absorption performance of the system was analyzed in detail, and the optimal design parameter that maximizes the total energy consumption was obtained. Our study can serve as theoretical guidance for the train’s optimization design of the distributed energy absorption system.
In this study we established a simplified theoretical model of the distributed energy absorption system of trains with the influence of the propagation of elastic waves in the train carriage taken into account. Based on the one-dimensional stress wave theory, the responses of energy absorbers in the collision process were analyzed and the governing equations were obtained and solved. The typical stage and platform response of the velocities on the interfaces of each energy absorber was observed and the mechanism was revealed. The analysis about how to set up and arrange the energy absorbing devices was also carried out. The results show that the crushing strength of the front one should be higher than that of the rear one for the adjacent energy absorbers; otherwise the energy absorber at the rear end cannot work at the same time. The plateau stress and its arrangement of each absorber determine the performance of the energy absorption system, which can thereby determine the duration of the energy absorption and the total energy absorption of each energy absorber. The influence of the plateau stress distribution of the adjacent energy absorbers on the energy absorption performance of the system was analyzed in detail, and the optimal design parameter that maximizes the total energy consumption was obtained. Our study can serve as theoretical guidance for the train’s optimization design of the distributed energy absorption system.
2019, 39(3): 035103.
doi: 10.11883/bzycj-2018-0013
Abstract:
The property of continuous thickness or weight distributions plays an important even decisive role on the lightweight and performance design of an automotive body. The main study of safe design for continuous thickness components is to investigate on their crashworthiness in the crash process of automotive structures. We studied on a new energy-absorbed thin-walled structure with the thickness distributed according to the power exponent function. The analytical relationships of the relative parameters among the new structure, uniform thickness tubes, tailor welded tubes and taped tubes were obtained. And the crashworthiness design criteria was also carried out. The parametrical study shows that the crashworthiness of the new tube is superior to those of other cross-sectional tubes. Then, the crashworthiness design method of the new tube was performed. The graded exponent was given at two design regions and was sampled to construct reasonable approximate model. The compared results demonstrates that the optimal results of the higher model are not necessarily to be best. In addition, the crashworthiness of thethin-walled structures could be enhanced by reasonably designing the tube thickness.
The property of continuous thickness or weight distributions plays an important even decisive role on the lightweight and performance design of an automotive body. The main study of safe design for continuous thickness components is to investigate on their crashworthiness in the crash process of automotive structures. We studied on a new energy-absorbed thin-walled structure with the thickness distributed according to the power exponent function. The analytical relationships of the relative parameters among the new structure, uniform thickness tubes, tailor welded tubes and taped tubes were obtained. And the crashworthiness design criteria was also carried out. The parametrical study shows that the crashworthiness of the new tube is superior to those of other cross-sectional tubes. Then, the crashworthiness design method of the new tube was performed. The graded exponent was given at two design regions and was sampled to construct reasonable approximate model. The compared results demonstrates that the optimal results of the higher model are not necessarily to be best. In addition, the crashworthiness of thethin-walled structures could be enhanced by reasonably designing the tube thickness.
2019, 39(3): 035104.
doi: 10.11883/bzycj-2017-0429
Abstract:
In order to study the dynamic response and damage of the precast segmental pier under the impact of explosion, the three-dimensional separate models of the circular-section precast segmental bridge piers under explosion are established based on ANSYS/LS-DYNA. The reliability of the simulation method is verified by comparing with the previous experimental results. The influence of slender ratio of segments, initial post-tensioning level and pier system type on the dynamic response and damage of the circular-section precast segmental pier under blast are investigated based on the verified model. The results show that the decrease of segment slender ratio makes the precast piers gradually change from shear damage to inter-segment displacement and it can reduce the lateral displacement of the pier; the increase of the initial post-tensioning can improve the anti-blast performance of the piers to some extent; the piers with the hybrid system under blast have both the failure characteristics of the segmental and monolithic piers.
In order to study the dynamic response and damage of the precast segmental pier under the impact of explosion, the three-dimensional separate models of the circular-section precast segmental bridge piers under explosion are established based on ANSYS/LS-DYNA. The reliability of the simulation method is verified by comparing with the previous experimental results. The influence of slender ratio of segments, initial post-tensioning level and pier system type on the dynamic response and damage of the circular-section precast segmental pier under blast are investigated based on the verified model. The results show that the decrease of segment slender ratio makes the precast piers gradually change from shear damage to inter-segment displacement and it can reduce the lateral displacement of the pier; the increase of the initial post-tensioning can improve the anti-blast performance of the piers to some extent; the piers with the hybrid system under blast have both the failure characteristics of the segmental and monolithic piers.
2019, 39(3): 035401.
doi: 10.11883/bzycj-2017-0457
Abstract:
To find out about the explosion suppression performance and mechanism of a new micro-emulsified diesel fuel, we carried out experiments on the dispersal and cloud explosion of −10# diesel fuel, ordinary micro-emulsified diesel fuel and new micro-emulsified diesel fuel. We calculated the average temperature at the maximum surface temperature, the high temperature duration (longer than 1 273.15 K), the maximum cross-sectional area and the radiant emittance of the cloud explosion fireballs of diesel fuel samples and evaluated them using the grey correlation analysis method and studied the dispersal atomization phenomena and explosion suppression mechanisms of the diesel fuel samples under the shock wave and high-speed airflow using the liquid fuel dispersal and imaging system. The results showed that the cloud radial expansion radius and the characteristic parameters of the explosion fireball of the new micro-emulsified diesel fuel were obviously lower than those of −10# diesel fuel and ordinary micro-emulsified diesel fuel. For example, the maximum surface mean temperatures of the fireballs of the new micro-emulsified diesel fuel samples made up by mixing 0.2% or 0.4% high polymer antifogging agents into the fuel containing 5% water were 296.90 and 336.90 K lower than those of −10# diesel fuel. Their high temperature duration is shorter by 94 and 234 ms respectively. The maximum cross-sectional areas of their fireballs were only 60.10% and 53.53% that of −10# diesel fuel respectively. The explosion power of the new micro-emulsified diesel fuel was the lowest and the explosion suppression performance was the best, followed by ordinary micro-emulsified diesel fuel and −10# diesel fuel. When the water mass fraction of the micro-emulsified diesel fuel was less than 15%, the explosion suppression effect of the micro-emulsified diesel fuel with an addition of 10% water was equivalent to that with an addition of 0.2% antifogging agents. The key for this better explosion suppression performance was that the viscosity and elasticity of the droplets increased due to the addition of antifogging agents to the diesel fuel, and that the droplets were not apt to be broken and atomized under the shearing action of high-speed airflow, and the dispersion of the droplets was not effective.
To find out about the explosion suppression performance and mechanism of a new micro-emulsified diesel fuel, we carried out experiments on the dispersal and cloud explosion of −10# diesel fuel, ordinary micro-emulsified diesel fuel and new micro-emulsified diesel fuel. We calculated the average temperature at the maximum surface temperature, the high temperature duration (longer than 1 273.15 K), the maximum cross-sectional area and the radiant emittance of the cloud explosion fireballs of diesel fuel samples and evaluated them using the grey correlation analysis method and studied the dispersal atomization phenomena and explosion suppression mechanisms of the diesel fuel samples under the shock wave and high-speed airflow using the liquid fuel dispersal and imaging system. The results showed that the cloud radial expansion radius and the characteristic parameters of the explosion fireball of the new micro-emulsified diesel fuel were obviously lower than those of −10# diesel fuel and ordinary micro-emulsified diesel fuel. For example, the maximum surface mean temperatures of the fireballs of the new micro-emulsified diesel fuel samples made up by mixing 0.2% or 0.4% high polymer antifogging agents into the fuel containing 5% water were 296.90 and 336.90 K lower than those of −10# diesel fuel. Their high temperature duration is shorter by 94 and 234 ms respectively. The maximum cross-sectional areas of their fireballs were only 60.10% and 53.53% that of −10# diesel fuel respectively. The explosion power of the new micro-emulsified diesel fuel was the lowest and the explosion suppression performance was the best, followed by ordinary micro-emulsified diesel fuel and −10# diesel fuel. When the water mass fraction of the micro-emulsified diesel fuel was less than 15%, the explosion suppression effect of the micro-emulsified diesel fuel with an addition of 10% water was equivalent to that with an addition of 0.2% antifogging agents. The key for this better explosion suppression performance was that the viscosity and elasticity of the droplets increased due to the addition of antifogging agents to the diesel fuel, and that the droplets were not apt to be broken and atomized under the shearing action of high-speed airflow, and the dispersion of the droplets was not effective.
2019, 39(3): 035102.
doi: 10.11883/bzycj-2018-0181
Abstract:
To improve the blast resistance of reinforced concrete (RC) beam, an efficient design method was proposed that bending the longitudinal bar as a wave at an appropriate location in the beam. Combing the experimental results and calculation of finite element model, the damage process of the RC beam with local kinked rebar was found, and the mechanism of blast resistance was revealed. Analytical results indicated that the kinked rebar can increase the allowable deformation of the RC beam under blast loads, effectively absorbing the explosive energy and greatly improving the blast-resistant performance. A theoretical method was developed to calculate the blast resistance of the RC beam with local kinked rebar under blast loads, on base of the energy method. Explicit formulae of the dynamic resistance coefficient were derived. The influences of three key design parameters, e.g. the bearing capacity ratio of platform period to yielding period, the deformation ratio of platform period to elastic period and the deformation ratio of yielding period to elastic period, on the blast resistance of RC beam with local kinked rebar were discussed. It provides a theoretical basis for further engineering application.
