2020 Vol. 40, No. 6
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2020, 40(6): 063201.
doi: 10.11883/bzycj-2019-0379
Abstract:
Integrated with the relevant penetrating tests, the ballistic behavior of the tungsten fiber/metallic glass matrix (WF/MG) composite segmented rod is systematically investigated based on the meso-scale finite element method (FEM), and the comparative analysis on the penetrating performance is conducted between the composite segmented rod and the composite long rod. Related analysis shows that the composite long rod has the remarkable “self-sharpening” behavior as well as good penetrating performance, the “self-sharpening” in the composite segmented rod is less significant, and particularly, dispersal of the reinforced fibers is easily to occur in the structure. Correspondingly, the penetrating capability in the composite segmented rod is remarkably weakened compared with that in the long rod. In addition, the segmental number and the segmental interval have considerable effects on the ballistic behavior; however, the penetrating performance of the composite segmented rods with various structures is always lower than that of the composite long rod.
Integrated with the relevant penetrating tests, the ballistic behavior of the tungsten fiber/metallic glass matrix (WF/MG) composite segmented rod is systematically investigated based on the meso-scale finite element method (FEM), and the comparative analysis on the penetrating performance is conducted between the composite segmented rod and the composite long rod. Related analysis shows that the composite long rod has the remarkable “self-sharpening” behavior as well as good penetrating performance, the “self-sharpening” in the composite segmented rod is less significant, and particularly, dispersal of the reinforced fibers is easily to occur in the structure. Correspondingly, the penetrating capability in the composite segmented rod is remarkably weakened compared with that in the long rod. In addition, the segmental number and the segmental interval have considerable effects on the ballistic behavior; however, the penetrating performance of the composite segmented rods with various structures is always lower than that of the composite long rod.
2020, 40(6): 063101.
doi: 10.11883/bzycj-2019-0337
Abstract:
To investigate the mechanical properties of brittle hollow particles (BHPs) under impact loading, Quasi-static and dynamic compressive tests were conducted on fly ash cenospheres (CPs) with two different particle size graduations. The breakage rate and fracture mechanism of the cenospheres and their effects on the strain rate sensitivity of the cenospheres accumulation were discussed based on the single loading experiments, which were implemented by limiting the compression strain of the particles accumulation to 50%. The results are as follows. (1) The dynamic strength of cenosphere materials was significantly enhanced as compared to the quasi-static compression results. In the strain rate range of 0.001-150 s−1, the strength of the cenosphere accumulations with large and small average particle sizes (marked LGs and LTs) increased by 200% and 195%, respectively. The strength of LGs and LTs increased 39% and 51.5% with the strain rate increased from 150 s−1 to 300 s−1. However, when the strain rate increased to 800 s−1, no obvious change on the strength of both LGs and LTs were observed. (2) At the same loading rate, the strength and energy absorption of particle accumulation with smaller average size were35%～40% and 35%～48% higher than that containing larger particles. (3) According to the particle fragments size distribution analysis, the broken rate of the particle accumulation and the broken severity of single particle both increased with the loading rate. In addition, the broken rate of LGs was higher than that of LTs at the same loading rate. (4) Based on Hardin fracture potential analysis, it can be concluded that the relative breaking potential of particles decreases with the increase of impact velocity under unit input energy, and the energy utilization rate for particle breaking decreases under dynamic impact, which leads to higher energy dissipation and stress level of materials under the same compression amount, namely, the macroscopic strain rate effect.
To investigate the mechanical properties of brittle hollow particles (BHPs) under impact loading, Quasi-static and dynamic compressive tests were conducted on fly ash cenospheres (CPs) with two different particle size graduations. The breakage rate and fracture mechanism of the cenospheres and their effects on the strain rate sensitivity of the cenospheres accumulation were discussed based on the single loading experiments, which were implemented by limiting the compression strain of the particles accumulation to 50%. The results are as follows. (1) The dynamic strength of cenosphere materials was significantly enhanced as compared to the quasi-static compression results. In the strain rate range of 0.001-150 s−1, the strength of the cenosphere accumulations with large and small average particle sizes (marked LGs and LTs) increased by 200% and 195%, respectively. The strength of LGs and LTs increased 39% and 51.5% with the strain rate increased from 150 s−1 to 300 s−1. However, when the strain rate increased to 800 s−1, no obvious change on the strength of both LGs and LTs were observed. (2) At the same loading rate, the strength and energy absorption of particle accumulation with smaller average size were35%～40% and 35%～48% higher than that containing larger particles. (3) According to the particle fragments size distribution analysis, the broken rate of the particle accumulation and the broken severity of single particle both increased with the loading rate. In addition, the broken rate of LGs was higher than that of LTs at the same loading rate. (4) Based on Hardin fracture potential analysis, it can be concluded that the relative breaking potential of particles decreases with the increase of impact velocity under unit input energy, and the energy utilization rate for particle breaking decreases under dynamic impact, which leads to higher energy dissipation and stress level of materials under the same compression amount, namely, the macroscopic strain rate effect.
2020, 40(6): 063102.
doi: 10.11883/bzycj-2019-0341
Abstract:
This paper investigated comparatively the effect of structural parameters (tube direction, tube cross-section shape, tube length ratio) and impact parameters (impact mass, impact energy) on the cushioning energy absorption characteristics (specific energy absorption, stroke efficiency, crush force efficiency, specific total efficiency) of the polyethylene closed-foam single-filling paper corrugation tubes by axial drop impact tests. The results show that the single-filled X-direction tubes hold better dynamic cushioning energy absorption than the single-filled Y-direction tubes, but weaker static cushioning energy absorption than the single-filled Y-direction tubes. The regular quadrilateral single-filled tubes have superior dynamic cushioning energy absorption to the regular pentagonal and hexagonal single-filled tubes, e.g. the regular quadrilateral single-filled X-direction tubes can respectively increase the specific energy absorption by 114.4% and 182.3% for those with tube cross-section shape of regular pentagon and hexagon. During the drop impact process the specific energy absorption, stroke efficiency and specific total efficiency of the single-filled tubes decrease with the increase of tube length ratio, e.g. the single-filled X-direction tube with the tube length ratio of 1.4 can respectively increase the specific energy absorption by 45.8% and 117.9% for those with tube length ratio of 2.2 and 3.0, moreover the crush force efficiency increases as the tube length ratio increases. The characteristics of dynamic cushioning energy absorption increase with the increase of drop impact mass or impact energy, and the single-filled X-direction tube is greatly controlled by the mass of impact block, while the single-filled Y-direction tube is obviously affected by the velocity of drop impact.
This paper investigated comparatively the effect of structural parameters (tube direction, tube cross-section shape, tube length ratio) and impact parameters (impact mass, impact energy) on the cushioning energy absorption characteristics (specific energy absorption, stroke efficiency, crush force efficiency, specific total efficiency) of the polyethylene closed-foam single-filling paper corrugation tubes by axial drop impact tests. The results show that the single-filled X-direction tubes hold better dynamic cushioning energy absorption than the single-filled Y-direction tubes, but weaker static cushioning energy absorption than the single-filled Y-direction tubes. The regular quadrilateral single-filled tubes have superior dynamic cushioning energy absorption to the regular pentagonal and hexagonal single-filled tubes, e.g. the regular quadrilateral single-filled X-direction tubes can respectively increase the specific energy absorption by 114.4% and 182.3% for those with tube cross-section shape of regular pentagon and hexagon. During the drop impact process the specific energy absorption, stroke efficiency and specific total efficiency of the single-filled tubes decrease with the increase of tube length ratio, e.g. the single-filled X-direction tube with the tube length ratio of 1.4 can respectively increase the specific energy absorption by 45.8% and 117.9% for those with tube length ratio of 2.2 and 3.0, moreover the crush force efficiency increases as the tube length ratio increases. The characteristics of dynamic cushioning energy absorption increase with the increase of drop impact mass or impact energy, and the single-filled X-direction tube is greatly controlled by the mass of impact block, while the single-filled Y-direction tube is obviously affected by the velocity of drop impact.
2020, 40(6): 063301.
doi: 10.11883/bzycj-2019-0252
Abstract:
Based on the research ideas of metamaterials, a novel concrete with wave-absorbing features was designed by introducing local resonant aggregates into plain concrete. First, the effective mass of the designed metaconcrete was calculated by means of structural dynamics. Simplified models for the start and cutoff frequencies of the band gap in the metaconcrete were established, and the theoretical expressions for the band gap start and cutoff frequencies were proposed. The effects of the following parameters on the band gap features of the metaconcrete were analyzed by the proposed theoretical models, including the coating elastic modulus, core density, matrix density, aggregate volume ratio, and ratio of core length to soft thickness. Finally, the numerical simulations were carried out to compare the attenuation effects of shock waves in the metaconcrete to those in the plain concrete. The research results reveal that the flexible coating results in a low-frequency attenuation domain, but the width of the attenuation domain is narrow; while the high elastic modulus coating can form a wider attenuation domain, but the attenuation domain has a higher start frequency. A low frequency and wide band gap can be obtained by selecting large-density core material and small-density matrix material. A wide band gap can be achieved by increasing the proportion of aggregate volume and the ratio of core length to soft thickness. Compared with the plain concrete, the metaconcrete has a better attenuation effect on shock wave.
Based on the research ideas of metamaterials, a novel concrete with wave-absorbing features was designed by introducing local resonant aggregates into plain concrete. First, the effective mass of the designed metaconcrete was calculated by means of structural dynamics. Simplified models for the start and cutoff frequencies of the band gap in the metaconcrete were established, and the theoretical expressions for the band gap start and cutoff frequencies were proposed. The effects of the following parameters on the band gap features of the metaconcrete were analyzed by the proposed theoretical models, including the coating elastic modulus, core density, matrix density, aggregate volume ratio, and ratio of core length to soft thickness. Finally, the numerical simulations were carried out to compare the attenuation effects of shock waves in the metaconcrete to those in the plain concrete. The research results reveal that the flexible coating results in a low-frequency attenuation domain, but the width of the attenuation domain is narrow; while the high elastic modulus coating can form a wider attenuation domain, but the attenuation domain has a higher start frequency. A low frequency and wide band gap can be obtained by selecting large-density core material and small-density matrix material. A wide band gap can be achieved by increasing the proportion of aggregate volume and the ratio of core length to soft thickness. Compared with the plain concrete, the metaconcrete has a better attenuation effect on shock wave.
2020, 40(6): 061101.
doi: 10.11883/bzycj-2019-0443
Abstract:
Based on cavity expansion theories, the very essences of static target resistance, i.e. Rt of plastic and brittle materials are discussed by comparing the difference of dynamic behaviors in near region of penetration, and some suggestions about applications of brittle materials for penetration are given. The summary of discussion is shown as follows. Firstly, Rt is the mean and time-averaged stress on the cross section of the projectile, which is the resistance of target materials in solid state against local cavity expanding. The specific value of Rt varies withphysical and mechanical properties of materials, penetration models, impact velocity and other factors, and thus is not an intrinsic property of material. Secondly, for the non-deformable projectile penetrating plastic materials, static cavity expansion theory is proper to predict Rt. For semi-hydrodynamic penetration cases, the results of static cavity expansion theory should be modified. Thirdly, Rt of brittle materials mainly depends on fractured materials, while it is weakly related to intact materials and not completely positively related to uniaxial compressive strength of intact materials. If penetration velocity is relatively low, the strengthening effect of Rt of brittle materials by penetration velocity increasing should be considered in terms of internal-friction. If penetration velocity is high enough, the intrinsic and constant resistance of brittle materials is realized, which is named as dynamic hardness. Fourthly, the key measures to increase Rt of brittle materials are to reduce the amplitude of hoop tensile stress following the peak compressive stress, to lower the crack velocity of materials and to restrain the fragmentation degree of materials. These can be solved by increasing external confining pressure and intensifying the tensile strength and fracture toughness of materials. Furthermore, it is suggested that the dynamic properties of fractured materials should be emphasized to increase the precision of numerical calculations of brittle materials under penetration.
Based on cavity expansion theories, the very essences of static target resistance, i.e. Rt of plastic and brittle materials are discussed by comparing the difference of dynamic behaviors in near region of penetration, and some suggestions about applications of brittle materials for penetration are given. The summary of discussion is shown as follows. Firstly, Rt is the mean and time-averaged stress on the cross section of the projectile, which is the resistance of target materials in solid state against local cavity expanding. The specific value of Rt varies withphysical and mechanical properties of materials, penetration models, impact velocity and other factors, and thus is not an intrinsic property of material. Secondly, for the non-deformable projectile penetrating plastic materials, static cavity expansion theory is proper to predict Rt. For semi-hydrodynamic penetration cases, the results of static cavity expansion theory should be modified. Thirdly, Rt of brittle materials mainly depends on fractured materials, while it is weakly related to intact materials and not completely positively related to uniaxial compressive strength of intact materials. If penetration velocity is relatively low, the strengthening effect of Rt of brittle materials by penetration velocity increasing should be considered in terms of internal-friction. If penetration velocity is high enough, the intrinsic and constant resistance of brittle materials is realized, which is named as dynamic hardness. Fourthly, the key measures to increase Rt of brittle materials are to reduce the amplitude of hoop tensile stress following the peak compressive stress, to lower the crack velocity of materials and to restrain the fragmentation degree of materials. These can be solved by increasing external confining pressure and intensifying the tensile strength and fracture toughness of materials. Furthermore, it is suggested that the dynamic properties of fractured materials should be emphasized to increase the precision of numerical calculations of brittle materials under penetration.
2020, 40(6): 062101.
doi: 10.11883/bzycj-2019-0402
Abstract:
Ignition delay of ethylene (C2H4) are measured under different temperatures in a rectangle shock tube to recognize the effects from diluent gases (nitrogen or argon) and criteria which is identified by pressure, bulk and radical chemiluminescences of OH and CH at specified wavelengths. Pressures were recorded by piezoelectric sensors (PCBs), and bulk chemiluminescence was detected by a photomultiplier (PMT) and an optical fiber. The chemiluminescences of OH and CH radicals were grated by spectrometer first, and then recorded by the PMT. The ignition delay is determined from the pressure and intensity histories of bulk and radical chemiluminescences at the points which share the same distances from the close end. Ignition delay database was built for mixture of C2H4/O2/N2 and C2H4/O2/Ar. Measurement and methodology are verified by the repeated experimental data under the same conditions. In the case of stoichimetric equivalence and pressure at 0.2 MPa, ignition delays were obtained and fitted with temperature as Arrhenius formula for mixtures of C2H4/O2/N2 and C2H4/O2/Ar at temperature ranging from 905 K to 1 489 K. Results show that the relative error of ignition delays is about 15%. Based on pressure, bulk and radical chemiluminescences, the relationships between the ignition delay and temperature remain the same although the ignition delay from single measurement is a bit different. Basically, the ignition delay of C2H4/O2/N2 is greater than that of C2H4/O2/Ar. The fitting relationship between ignition delay and temperature of C2H4/O2 /Ar in high temperature zone and low temperature zone is different, and the turning temperature is about 1 121 K.
Ignition delay of ethylene (C2H4) are measured under different temperatures in a rectangle shock tube to recognize the effects from diluent gases (nitrogen or argon) and criteria which is identified by pressure, bulk and radical chemiluminescences of OH and CH at specified wavelengths. Pressures were recorded by piezoelectric sensors (PCBs), and bulk chemiluminescence was detected by a photomultiplier (PMT) and an optical fiber. The chemiluminescences of OH and CH radicals were grated by spectrometer first, and then recorded by the PMT. The ignition delay is determined from the pressure and intensity histories of bulk and radical chemiluminescences at the points which share the same distances from the close end. Ignition delay database was built for mixture of C2H4/O2/N2 and C2H4/O2/Ar. Measurement and methodology are verified by the repeated experimental data under the same conditions. In the case of stoichimetric equivalence and pressure at 0.2 MPa, ignition delays were obtained and fitted with temperature as Arrhenius formula for mixtures of C2H4/O2/N2 and C2H4/O2/Ar at temperature ranging from 905 K to 1 489 K. Results show that the relative error of ignition delays is about 15%. Based on pressure, bulk and radical chemiluminescences, the relationships between the ignition delay and temperature remain the same although the ignition delay from single measurement is a bit different. Basically, the ignition delay of C2H4/O2/N2 is greater than that of C2H4/O2/Ar. The fitting relationship between ignition delay and temperature of C2H4/O2 /Ar in high temperature zone and low temperature zone is different, and the turning temperature is about 1 121 K.
2020, 40(6): 062301.
doi: 10.11883/bzycj-2019-0391
Abstract:
In order to investigate the shock initiation of missile warhead (cylindrical covered charge) by multiple tungsten spherical fragment impacts under actual combat circumstance, based on the analysis of single fragment impact, the numerical simulations were carried out by using AUTODYN-3D software. The influence on the shock initiation characteristics of different number, distance separation (impact angle θ and axial spherical center distance l), time separation were analyzed, and the critical initiation velocity of covered Comp B was obtained by the up-down method. The obtained simulation results show that, the critical initiation velocity decreases with the tungsten fragments number increase and the distance separation decrease. The critical initiation velocity of cylindrical covered charge impacted by six fragments synchronously is about 50% compare to the single fragment. The cylindrical covered charge is more difficult than plane covered charge to detonate by double fragments when the impact velocity below the critical velocity of a single fragment. The critical initiation velocity decreases initially and then increases with the increase of time separation when fragments impacting asynchronously on the cylindrical covered charge. The minimum critical initiation velocity of cylindrical covered charge impacted by double fragments synchronously is about 95% comparinge with that of impacted by double fragments asynchronously. For |θ2|＜|θ1| (θ1 is the impact angle of the first fragment, θ2 is the impact angle of the second fragment), the cylindrical covered charge is easy to detonate by double fragments asynchronously. The results provide the reference for cumulative damage assessment of cylindrical covered charge by multiple fragment impacts.
In order to investigate the shock initiation of missile warhead (cylindrical covered charge) by multiple tungsten spherical fragment impacts under actual combat circumstance, based on the analysis of single fragment impact, the numerical simulations were carried out by using AUTODYN-3D software. The influence on the shock initiation characteristics of different number, distance separation (impact angle θ and axial spherical center distance l), time separation were analyzed, and the critical initiation velocity of covered Comp B was obtained by the up-down method. The obtained simulation results show that, the critical initiation velocity decreases with the tungsten fragments number increase and the distance separation decrease. The critical initiation velocity of cylindrical covered charge impacted by six fragments synchronously is about 50% compare to the single fragment. The cylindrical covered charge is more difficult than plane covered charge to detonate by double fragments when the impact velocity below the critical velocity of a single fragment. The critical initiation velocity decreases initially and then increases with the increase of time separation when fragments impacting asynchronously on the cylindrical covered charge. The minimum critical initiation velocity of cylindrical covered charge impacted by double fragments synchronously is about 95% comparinge with that of impacted by double fragments asynchronously. For |θ2|＜|θ1| (θ1 is the impact angle of the first fragment, θ2 is the impact angle of the second fragment), the cylindrical covered charge is easy to detonate by double fragments asynchronously. The results provide the reference for cumulative damage assessment of cylindrical covered charge by multiple fragment impacts.
2020, 40(6): 064201.
doi: 10.11883/bzycj-2019-0340
Abstract:
The strain growth, caused by vibration superposition, has been anatomized by the membrane strain and the bending strain in existing studies, and the bending wave and deformation spatial periodic distribution of a spherical shell under explosive loading have been found. By referring to the theoretical method for Timoshenko beam bending, based on a plane-section assumption and a small-deformation limit, the relation between the velocity and the wavelength of bending wave was deduced, and the velocities of the shortest bending wave and the bending wave with a frequency similar to that of the membrane vibration were calculated. By combining the relation between the deformation spatial distribution period and the bending wave velocity presented in existing studies, the deformation spatial distribution period was calculated. The main conclusions are as follows: (1) The theoretical results are in good agreement with the numerical results, in which the difference between the numerical and theoretical results of bending wave velocity is within 15%, and the difference between the numerical and theoretical results of the deformation spatial distribution period is within 12%. (2) The shorter the wavelength, the higher the wave velocity, when the wavelength is infinite short, the bending wave velocity tends to the limit value, about 0.574 times the speed of sound. The theoretical method presented in this paper provides a certain theoretical support for anatomizing strain growth.
The strain growth, caused by vibration superposition, has been anatomized by the membrane strain and the bending strain in existing studies, and the bending wave and deformation spatial periodic distribution of a spherical shell under explosive loading have been found. By referring to the theoretical method for Timoshenko beam bending, based on a plane-section assumption and a small-deformation limit, the relation between the velocity and the wavelength of bending wave was deduced, and the velocities of the shortest bending wave and the bending wave with a frequency similar to that of the membrane vibration were calculated. By combining the relation between the deformation spatial distribution period and the bending wave velocity presented in existing studies, the deformation spatial distribution period was calculated. The main conclusions are as follows: (1) The theoretical results are in good agreement with the numerical results, in which the difference between the numerical and theoretical results of bending wave velocity is within 15%, and the difference between the numerical and theoretical results of the deformation spatial distribution period is within 12%. (2) The shorter the wavelength, the higher the wave velocity, when the wavelength is infinite short, the bending wave velocity tends to the limit value, about 0.574 times the speed of sound. The theoretical method presented in this paper provides a certain theoretical support for anatomizing strain growth.
2020, 40(6): 064202.
doi: 10.11883/bzycj-2019-0408
Abstract:
In order to study the gasoline/air mixture explosion characteristics in semi-confined spaces with branched structures, a large eddy simulation model based on WALE turbulence model and the Zimont premixed flame model was established. The explosion characteristics of semi-confined space with bilateral branches ware studied through the simulation. The applicability of the established model for the calculation of gasoline/air mixture explosion in semi-confined spaces with bilateral branches is verified by comparing of flame shape, flame propagation velocity and dynamic overpressure. The flow field, flame behavior and overpressure variation during the explosion process were analyzed through the numerical simulation results and the reasons for the formation of “splash-like” flame were pointed out, and the following results were obtained. (1) Before the flame propagates into the branch pipes, two symmetric vortex structure with opposite rotation directions are generated at the junctions of the main pipe and two branch pipes, and develop toward the inside of the branch pipes as the flame propagates continuously. (2) When the flame propagates into branch pipes, the flow field established in the early stage determines the shape of the flame. The flame front forms a “splash-like” flame under the action of the vortex structure. After that, the flame and the flow field interact with each other turning to the turbulent flow and distorted flame front. (3) The growing process of the overpressure can be divided into four stages, which are influenced by the flame front area and the branch pipe pressure unload, indicating that the explosion flow field, flame behavior and dynamic overpressure have significant coupling effects.
In order to study the gasoline/air mixture explosion characteristics in semi-confined spaces with branched structures, a large eddy simulation model based on WALE turbulence model and the Zimont premixed flame model was established. The explosion characteristics of semi-confined space with bilateral branches ware studied through the simulation. The applicability of the established model for the calculation of gasoline/air mixture explosion in semi-confined spaces with bilateral branches is verified by comparing of flame shape, flame propagation velocity and dynamic overpressure. The flow field, flame behavior and overpressure variation during the explosion process were analyzed through the numerical simulation results and the reasons for the formation of “splash-like” flame were pointed out, and the following results were obtained. (1) Before the flame propagates into the branch pipes, two symmetric vortex structure with opposite rotation directions are generated at the junctions of the main pipe and two branch pipes, and develop toward the inside of the branch pipes as the flame propagates continuously. (2) When the flame propagates into branch pipes, the flow field established in the early stage determines the shape of the flame. The flame front forms a “splash-like” flame under the action of the vortex structure. After that, the flame and the flow field interact with each other turning to the turbulent flow and distorted flame front. (3) The growing process of the overpressure can be divided into four stages, which are influenced by the flame front area and the branch pipe pressure unload, indicating that the explosion flow field, flame behavior and dynamic overpressure have significant coupling effects.
2020, 40(6): 065201.
doi: 10.11883/bzycj-2019-0396
Abstract:
In order to investigate the influence of different explosives type on the blasting effects, three kinds of explosives with the same quality were used to carry out blasting test on iron ore samples. The fractal dimension of surface crack and fragment size distribution of specimens were comparatively studied, and then the damage degree and blasting effects of specimens were quantitatively compared and evaluated. At the same time, the differences of blasting effects are analyzed theoretically from the angle of explosion stress wave superposition, energy release and energy transfer. The results are as follows. (1) Both loose charge and mixed charge will cause the uniformity of the explosion stress field distribution to deteriorate. (2) The greater the explosion heat, the greater the energy released after explosion; the higher the wave impedance matching, the higher the energy transfer efficiency after explosive explosion. (3) In the selection of explosives in blasting engineering, three parameters of explosive including density, explosion heat and detonation velocity should be considered; Explosives with a high degree of wave impedance matching and appropriate explosion heat should be selected so that the bulk and small pieces generated after blasting are less.
In order to investigate the influence of different explosives type on the blasting effects, three kinds of explosives with the same quality were used to carry out blasting test on iron ore samples. The fractal dimension of surface crack and fragment size distribution of specimens were comparatively studied, and then the damage degree and blasting effects of specimens were quantitatively compared and evaluated. At the same time, the differences of blasting effects are analyzed theoretically from the angle of explosion stress wave superposition, energy release and energy transfer. The results are as follows. (1) Both loose charge and mixed charge will cause the uniformity of the explosion stress field distribution to deteriorate. (2) The greater the explosion heat, the greater the energy released after explosion; the higher the wave impedance matching, the higher the energy transfer efficiency after explosive explosion. (3) In the selection of explosives in blasting engineering, three parameters of explosive including density, explosion heat and detonation velocity should be considered; Explosives with a high degree of wave impedance matching and appropriate explosion heat should be selected so that the bulk and small pieces generated after blasting are less.
2020, 40(6): 065202.
doi: 10.11883/bzycj-2019-0333
Abstract:
Studies on the attenuating characteristic of blasting seismic waves in propagating process are important in prediction and control of blasting vibration effects by engineering blasting. Field blasting tests of single-hole were conducted to study the quality factor of rock mass. The wave propagation velocities and the pulse rise times can be obtained by using the first arrival of P wave and S wave. Finally, based on the rise time method, the P wave quality factor of rock mass can be calculated. By analyzing the measured blasting vibration signals in Fengning hydropower station and Zhoushan large petrochemical industry, the average P wave quality factors in the above two regions are found to be 19.02 and 14.07, respectively. The experimental results show that the values derived by measuring blasting vibrations are far less than the values predicted by the empirical formulas and measured by the original rock mass. This results indicate that the soft covering layer has great influence on the seismic waves propagation induced by blasting.
Studies on the attenuating characteristic of blasting seismic waves in propagating process are important in prediction and control of blasting vibration effects by engineering blasting. Field blasting tests of single-hole were conducted to study the quality factor of rock mass. The wave propagation velocities and the pulse rise times can be obtained by using the first arrival of P wave and S wave. Finally, based on the rise time method, the P wave quality factor of rock mass can be calculated. By analyzing the measured blasting vibration signals in Fengning hydropower station and Zhoushan large petrochemical industry, the average P wave quality factors in the above two regions are found to be 19.02 and 14.07, respectively. The experimental results show that the values derived by measuring blasting vibrations are far less than the values predicted by the empirical formulas and measured by the original rock mass. This results indicate that the soft covering layer has great influence on the seismic waves propagation induced by blasting.
2020, 40(6): 065401.
doi: 10.11883/bzycj-2019-0412
Abstract:
Hydrogen is recognized as one of the most promising energies in the 21st century due to the nature of no pollution and high efficiency, unfortunately, it is likely to suffer from explosion in the process of usage. As one of the important ways of disaster, venting can effectively improve the safety and reliability of the structure under hydrogen explosion. In order to study the dynamical characteristics of the structure under vented hydrogen explosion, experimental and numerical studies were conducted in this paper. On the one hand, a number of scenarios were carried out for vented hydrogen explosion in a large-scale ISO container of 12 m×2.5 m×2.5 m to investigate the effects of hydrogen volume fraction, the position of ignition as well as the arrangement of obstacles on the structural dynamics. The characteristics of internal overpressure load and the evolution mechanism of dynamic response were analyzed. Results indicate that the structural displacements are dominated by the first overpressure peak. The trend of displacement agrees well with that of the overpressure, and there is a linear relationship between their peaks. The acceleration is dominated by high-frequency oscillations of the overpressure caused by unstable combustion. Furthermore, the peak of the displacement is significantly affected by hydrogen volume fraction and increases with the increase of hydrogen volume fraction. The peak acceleration is also affected by the ignition position, and the peak acceleration of central ignition is larger than that of back ignition. Additionally, the effects of the number of obstacles on structural dynamic response are not monotonic. On the other hand, a baseline finite element model of the structure is established based on the ambient vibration testing. The numerical simulation results agree well with those of the experimental results. Therefore, the model can be used to predict structural dynamic responses under vented hydrogen explosion.
Hydrogen is recognized as one of the most promising energies in the 21st century due to the nature of no pollution and high efficiency, unfortunately, it is likely to suffer from explosion in the process of usage. As one of the important ways of disaster, venting can effectively improve the safety and reliability of the structure under hydrogen explosion. In order to study the dynamical characteristics of the structure under vented hydrogen explosion, experimental and numerical studies were conducted in this paper. On the one hand, a number of scenarios were carried out for vented hydrogen explosion in a large-scale ISO container of 12 m×2.5 m×2.5 m to investigate the effects of hydrogen volume fraction, the position of ignition as well as the arrangement of obstacles on the structural dynamics. The characteristics of internal overpressure load and the evolution mechanism of dynamic response were analyzed. Results indicate that the structural displacements are dominated by the first overpressure peak. The trend of displacement agrees well with that of the overpressure, and there is a linear relationship between their peaks. The acceleration is dominated by high-frequency oscillations of the overpressure caused by unstable combustion. Furthermore, the peak of the displacement is significantly affected by hydrogen volume fraction and increases with the increase of hydrogen volume fraction. The peak acceleration is also affected by the ignition position, and the peak acceleration of central ignition is larger than that of back ignition. Additionally, the effects of the number of obstacles on structural dynamic response are not monotonic. On the other hand, a baseline finite element model of the structure is established based on the ambient vibration testing. The numerical simulation results agree well with those of the experimental results. Therefore, the model can be used to predict structural dynamic responses under vented hydrogen explosion.
