2019 Vol. 39, No. 5
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2019, 39(5): 051101.
doi: 10.11883/bzycj-2018-0319
Abstract:
Parameter design of precise controlled blasting in urban tunnels is crucial, which needs the high-speed photography image acquisition and study on the dynamic failure process of rock on field. However, it has not been studied in-depth in the past due to restrict of many factors, the factors include protection of the camera and the bad environment. Based on the technical problems tests on field are solved in a tunnel in Chongqing, China. Original data that include the images of the complete blasting process in tunnel and the blasting vibration data are collected simultaneously, which is the basis for analyzing the phenomenon of rock burst during blasting. 15−18 ms after initiation, the rock masses begin to move and caves are expanded continuously while the rock masses are thrown at about 21 ms. The blast effects is much better if the millisecond delay time between two blast-holes sets 8−50 ms, which can balance the contradiction between two blasting effects, one is the blasting synergetic effect between a pair of cutting holes, and the other is vibration reduction effects of millisecond blasting. The second free face is formed at 54 ms by analyzing the characteristics of crack propagation curves combined with field-measured vibration data. The method is more accurate than the time determined by past methods. Based on this, the optimized on-field delay design of detonators was carried out and got good vibration reduction results. The results can serve as a reference for precise controlled blasting of tunnel in the future.
Parameter design of precise controlled blasting in urban tunnels is crucial, which needs the high-speed photography image acquisition and study on the dynamic failure process of rock on field. However, it has not been studied in-depth in the past due to restrict of many factors, the factors include protection of the camera and the bad environment. Based on the technical problems tests on field are solved in a tunnel in Chongqing, China. Original data that include the images of the complete blasting process in tunnel and the blasting vibration data are collected simultaneously, which is the basis for analyzing the phenomenon of rock burst during blasting. 15−18 ms after initiation, the rock masses begin to move and caves are expanded continuously while the rock masses are thrown at about 21 ms. The blast effects is much better if the millisecond delay time between two blast-holes sets 8−50 ms, which can balance the contradiction between two blasting effects, one is the blasting synergetic effect between a pair of cutting holes, and the other is vibration reduction effects of millisecond blasting. The second free face is formed at 54 ms by analyzing the characteristics of crack propagation curves combined with field-measured vibration data. The method is more accurate than the time determined by past methods. Based on this, the optimized on-field delay design of detonators was carried out and got good vibration reduction results. The results can serve as a reference for precise controlled blasting of tunnel in the future.
2019, 39(5): 052101.
doi: 10.11883/bzycj-2017-0370
Abstract:
In order to investigate the interaction of the shock wave on a reinforced concrete composite shell structure with the external protecting wall, the explosion experiments were carried out. There were two conditions in the experiments, the first condition was that the test structure was located on the ground, and the second one was that the test structure was surrounded by soil. The blast wave load distribution and the vibration characters of the structure were analyzed. The experimental results are as follows. Under external shock wave attack, the structure surface explosion load was mainly formed in the shock wave diffraction process. When determining the structure surface blast load, the shock wave pressure attenuation in the diffraction process should be considered. The structure component which first contacts with the shock wave first begins to vibrate, then the vibration frequency and amplitude decrease because the whole structure takes part in vibration gradually. In the experimental conditions, the soil surrounding the structure could reduce the vibration frequency of the protecting wall component which meeting shock wave, and reduce the vibration amplitudes of the protecting wall and the composite shell structure.
In order to investigate the interaction of the shock wave on a reinforced concrete composite shell structure with the external protecting wall, the explosion experiments were carried out. There were two conditions in the experiments, the first condition was that the test structure was located on the ground, and the second one was that the test structure was surrounded by soil. The blast wave load distribution and the vibration characters of the structure were analyzed. The experimental results are as follows. Under external shock wave attack, the structure surface explosion load was mainly formed in the shock wave diffraction process. When determining the structure surface blast load, the shock wave pressure attenuation in the diffraction process should be considered. The structure component which first contacts with the shock wave first begins to vibrate, then the vibration frequency and amplitude decrease because the whole structure takes part in vibration gradually. In the experimental conditions, the soil surrounding the structure could reduce the vibration frequency of the protecting wall component which meeting shock wave, and reduce the vibration amplitudes of the protecting wall and the composite shell structure.
Numerical simulation on steel box damage under internal explosion by smoothed particle hydrodynamics
2019, 39(5): 052201.
doi: 10.11883/bzycj-2017-0439
Abstract:
With the strategic structure of the evolving terrorist attacks, ships and bridges which are supported by steel boxes gradually become important targets of terrorist attacks and enemy military strikes. We simulate the explosion process in a steel box by applying the smoothed particle hydrodynamics (SPH) method, analyze the deformation process of the steel box during the internal explosion, obtain the distributions of the pressure and the von Mises stress at different times, and achieve the trend of velocity and pressure at the center of the steel box plate. We find the feasibility and accuracy of the SPH method in simulating the internal steel box explosion through comparing with the experiment. We simulate the damage form and damage degree of the steel box structure subjected to internal blast at different positions. The results show that: when the explosive explodes at the corner and 60 mm from each box’s plate, there is the most serious damage; when the explosive explodes in the center, there is the least damage.
With the strategic structure of the evolving terrorist attacks, ships and bridges which are supported by steel boxes gradually become important targets of terrorist attacks and enemy military strikes. We simulate the explosion process in a steel box by applying the smoothed particle hydrodynamics (SPH) method, analyze the deformation process of the steel box during the internal explosion, obtain the distributions of the pressure and the von Mises stress at different times, and achieve the trend of velocity and pressure at the center of the steel box plate. We find the feasibility and accuracy of the SPH method in simulating the internal steel box explosion through comparing with the experiment. We simulate the damage form and damage degree of the steel box structure subjected to internal blast at different positions. The results show that: when the explosive explodes at the corner and 60 mm from each box’s plate, there is the most serious damage; when the explosive explodes in the center, there is the least damage.
2019, 39(5): 052202.
doi: 10.11883/bzycj-2018-0025
Abstract:
In order to study the vibration characteristics of the elastic zone of underground explosion, the key is to obtain the experimental parameters of the radiated elastic wave under the coupling of the site medium and the explosive energy. The rock-like sandy soil is not easily processed into large size model. To study the characteristics of the elastic wave radiated from the tamped explosion, a method was proposed by using 0.125 g TNT spherical charge as the explosive source and taking a\begin{document}$\varnothing $\end{document} ![]()
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In order to study the vibration characteristics of the elastic zone of underground explosion, the key is to obtain the experimental parameters of the radiated elastic wave under the coupling of the site medium and the explosive energy. The rock-like sandy soil is not easily processed into large size model. To study the characteristics of the elastic wave radiated from the tamped explosion, a method was proposed by using 0.125 g TNT spherical charge as the explosive source and taking a
2019, 39(5): 052203.
doi: 10.11883/bzycj-2018-0203
Abstract:
To improve the anti-detonation property of surrounding rock, the surrounding rock reninforced by crossing cable method was proposed, and the effects of the method were analyzed by anology experiments and numerical simulation. The d pressure and strain distributions under detonation, explosion cavity dimensions and reinforcing cable parameters on strengthening effects were investigated. The results indicate that the detonation pressure peak value near the detonation center, radial strain peak value and circumferential strain peak value are all negative exponential decay with the proportional distance, no matter the rock is strengthened or not. Under the focus point explosion, the pressure and peak strain rapidly decrease with the distance apart from the detonation point. Under the concentrated charging case, the explosion cavity displays as a vase with the thin head part and fat bottom part. The explosion cavity of the magmatic body without strengthening is comparatively large. The influences of reinforced crossing cable angle on medium compression radius is limited. With the increase of the density of the reinforced crossing cable, the peak value of the compression wave in the strengthened medium decreases about 20%-35% and the destruction radius decreases about 30%. The results of this paper can provide references to the underground protective engineering design and enclosing rock strengthening.
To improve the anti-detonation property of surrounding rock, the surrounding rock reninforced by crossing cable method was proposed, and the effects of the method were analyzed by anology experiments and numerical simulation. The d pressure and strain distributions under detonation, explosion cavity dimensions and reinforcing cable parameters on strengthening effects were investigated. The results indicate that the detonation pressure peak value near the detonation center, radial strain peak value and circumferential strain peak value are all negative exponential decay with the proportional distance, no matter the rock is strengthened or not. Under the focus point explosion, the pressure and peak strain rapidly decrease with the distance apart from the detonation point. Under the concentrated charging case, the explosion cavity displays as a vase with the thin head part and fat bottom part. The explosion cavity of the magmatic body without strengthening is comparatively large. The influences of reinforced crossing cable angle on medium compression radius is limited. With the increase of the density of the reinforced crossing cable, the peak value of the compression wave in the strengthened medium decreases about 20%-35% and the destruction radius decreases about 30%. The results of this paper can provide references to the underground protective engineering design and enclosing rock strengthening.
2019, 39(5): 052301.
doi: 10.11883/bzycj-2017-0395
Abstract:
In order to obtain the Hugoniot relation of unreacted JB-9014 explosive, one-dimensional plane impact experiments of the JB-9014 explosive were completed on a gun by using the reverse-impact method. The JB-9014 explosive sample was mounted on the front surface of the sabot as a flyer. The LiF window was taken as a device target. The sabot was accelerated to a certain speed by the gun and then the explosive sample impacted the LiF window. The impact velocity of the flyer and the particle velocity at the sample/window interface were measured by a photonic Doppler velocimetry (PDV). The Hugoniot data was obtained according to the conservation of the shock. The Hugoniot relationship of the JB-9014 explosive sample within the pressure range of 3.1−8.2 GPa was established by using the least square method. The results show that reverse-impact method has the characteristics of high accuracy and fast response time (＜5 ns). In addition, the reverse-impact method can be used to detect the reaction degree of the JB-9014 explosive, which can be applied to judge whether the real Hugoniot data of the unreacted explosive is measured in the experiment.
In order to obtain the Hugoniot relation of unreacted JB-9014 explosive, one-dimensional plane impact experiments of the JB-9014 explosive were completed on a gun by using the reverse-impact method. The JB-9014 explosive sample was mounted on the front surface of the sabot as a flyer. The LiF window was taken as a device target. The sabot was accelerated to a certain speed by the gun and then the explosive sample impacted the LiF window. The impact velocity of the flyer and the particle velocity at the sample/window interface were measured by a photonic Doppler velocimetry (PDV). The Hugoniot data was obtained according to the conservation of the shock. The Hugoniot relationship of the JB-9014 explosive sample within the pressure range of 3.1−8.2 GPa was established by using the least square method. The results show that reverse-impact method has the characteristics of high accuracy and fast response time (＜5 ns). In addition, the reverse-impact method can be used to detect the reaction degree of the JB-9014 explosive, which can be applied to judge whether the real Hugoniot data of the unreacted explosive is measured in the experiment.
2019, 39(5): 053101.
doi: 10.11883/bzycj-2018-0076
Abstract:
Under the common action of high axial stress and confining pressure, the main types of energy were discussed in the study of frequent dynamic disturbance firstly. At the same time, the formula for calculating elastic energy, plastic energy are deduced before and after the impact disturbance. In order to conduct dynamic test, the horizontal stress, the vertical stress, the influence of blasting excavation disturbance of the deep rock mass were simulated by pre-confining pressure, pre-high axial stress, 0.5 MPa impact pressure, respectively. Based on the experimental results, the dynamic characteristics and energy evolution of the copper serpentine were analyzed. The results show that the cumulative disturbance impact times of copper snake-like rock decrease with the increase of axial pressure, while they increase with the increasing confining pressure, and the dynamic peak stress decreases with the increasing number of disturbances. As the number of disturbances increases, the elastic energy in the rock sample increases first and then decreases, the plastic energy shows a trend of increase, and the ratio of the reflection energy to the incident energy increases while the ratio of the transmission energy to incident energy decreases. The unit volume absorption (release) energy shows the trend of the lower convex curve with the number of disturbances increases. In addition, the averages of unit volume absorption (release) energy decreases first and then increases with the increasing confining pressure, but decreases with the increase of axial pressure.
Under the common action of high axial stress and confining pressure, the main types of energy were discussed in the study of frequent dynamic disturbance firstly. At the same time, the formula for calculating elastic energy, plastic energy are deduced before and after the impact disturbance. In order to conduct dynamic test, the horizontal stress, the vertical stress, the influence of blasting excavation disturbance of the deep rock mass were simulated by pre-confining pressure, pre-high axial stress, 0.5 MPa impact pressure, respectively. Based on the experimental results, the dynamic characteristics and energy evolution of the copper serpentine were analyzed. The results show that the cumulative disturbance impact times of copper snake-like rock decrease with the increase of axial pressure, while they increase with the increasing confining pressure, and the dynamic peak stress decreases with the increasing number of disturbances. As the number of disturbances increases, the elastic energy in the rock sample increases first and then decreases, the plastic energy shows a trend of increase, and the ratio of the reflection energy to the incident energy increases while the ratio of the transmission energy to incident energy decreases. The unit volume absorption (release) energy shows the trend of the lower convex curve with the number of disturbances increases. In addition, the averages of unit volume absorption (release) energy decreases first and then increases with the increasing confining pressure, but decreases with the increase of axial pressure.
2019, 39(5): 054101.
doi: 10.11883/bzycj-2017-0394
Abstract:
The dynamic mechanical properties of soft materials have attracted great attention, and the separated Hopkinson pressure bar (SHPB) technique is the most important test method at present. However, the SHPB technique still needs some improvements when it is applied to extra-soft materials. So, a double-striker electromagnetic driving SHPB system was developed. In the developed system, the bars were made of polycarbonate, and the double-striker scheme was designed to precisely control the velocities of the strikers. Both the aluminum SHPB facility and the double-striker electromagnetic driving SHPB system were employed to carry out dynamic experiments on the silicone, and the agreement between the test results by these two systems indicated the reliability of the innovative system. And dynamic mechanical properties of PVA hydrogels were successfully tested by the double-striker electromagnetic driving SHPB system.
The dynamic mechanical properties of soft materials have attracted great attention, and the separated Hopkinson pressure bar (SHPB) technique is the most important test method at present. However, the SHPB technique still needs some improvements when it is applied to extra-soft materials. So, a double-striker electromagnetic driving SHPB system was developed. In the developed system, the bars were made of polycarbonate, and the double-striker scheme was designed to precisely control the velocities of the strikers. Both the aluminum SHPB facility and the double-striker electromagnetic driving SHPB system were employed to carry out dynamic experiments on the silicone, and the agreement between the test results by these two systems indicated the reliability of the innovative system. And dynamic mechanical properties of PVA hydrogels were successfully tested by the double-striker electromagnetic driving SHPB system.
2019, 39(5): 054201.
doi: 10.11883/bzycj-2017-0373
Abstract:
To study the surface particle vibration of vibration wave propagation on slope casting blast, we utilize dimensional analysis to construct the vibration peak velocity formula including the factor of elevation. On the basis of the above theory and slope casting blast model, we divide a blasthole charge into sumless micro-units for integral operation, and eventually obtain the formula of particle vibration peak velocity on slope casting blast. The results show that under the same condition of geographical environment and blasting technology, peak velocity primarily depends on explosive performance, charge depth, monitoring point, explosion source space and blasting acting index. We obtain a series of peak velocity on explosion site, and put the measured data at the slope surface and in the slope body into the Saudorsky formula, the average errors between the predicted peak velocity values by the formulas and the measured values at the slope surface are 32%, 34.25%, 29.58%, 39% and 7%, respectively. The average errors between the predicted peak velocity values by the formulas and the measured values in the slope body are 27.63%, 23.5%, 16.88%, 33.889% and 13.25%, respectively.
To study the surface particle vibration of vibration wave propagation on slope casting blast, we utilize dimensional analysis to construct the vibration peak velocity formula including the factor of elevation. On the basis of the above theory and slope casting blast model, we divide a blasthole charge into sumless micro-units for integral operation, and eventually obtain the formula of particle vibration peak velocity on slope casting blast. The results show that under the same condition of geographical environment and blasting technology, peak velocity primarily depends on explosive performance, charge depth, monitoring point, explosion source space and blasting acting index. We obtain a series of peak velocity on explosion site, and put the measured data at the slope surface and in the slope body into the Saudorsky formula, the average errors between the predicted peak velocity values by the formulas and the measured values at the slope surface are 32%, 34.25%, 29.58%, 39% and 7%, respectively. The average errors between the predicted peak velocity values by the formulas and the measured values in the slope body are 27.63%, 23.5%, 16.88%, 33.889% and 13.25%, respectively.
2019, 39(5): 054202.
doi: 10.11883/bzycj-2017-0380
Abstract:
In order to solve the problem of temporal and spatial distribution of explosive clouds, three groups of TNT explosion cloud field experiments were designed and carried out under the premise of strictly restricting the explosion conditions. The experiments obtained the spatiotemporal distribution of cloud under different experimental conditions. The diffusion process of the explosive cloud was simulated by computational fluid dynamics (CFD). By analyzing the space-time distribution data from the cloud experiments and simulations, the evolution process of the cloud and the information of the buoyancy flow field were obtained, and the diffusion height distribution models of different clouds were determined under the conditions of thick cement floor and hard ground. The results show that the combination of experiment and simulation can be used to characterize the spatial and temporal distribution model of the cloud. The cloud height of the explosion increases by 1/2 power function with time. The cloud width increases linearly with time in a short time. The temperature of the cloud attenuates in inverse proportion to time. The ground conditions for the detonation, and the shell thickness of the explosive device can affect the diffusion height of the explosive cloud in different degrees.
In order to solve the problem of temporal and spatial distribution of explosive clouds, three groups of TNT explosion cloud field experiments were designed and carried out under the premise of strictly restricting the explosion conditions. The experiments obtained the spatiotemporal distribution of cloud under different experimental conditions. The diffusion process of the explosive cloud was simulated by computational fluid dynamics (CFD). By analyzing the space-time distribution data from the cloud experiments and simulations, the evolution process of the cloud and the information of the buoyancy flow field were obtained, and the diffusion height distribution models of different clouds were determined under the conditions of thick cement floor and hard ground. The results show that the combination of experiment and simulation can be used to characterize the spatial and temporal distribution model of the cloud. The cloud height of the explosion increases by 1/2 power function with time. The cloud width increases linearly with time in a short time. The temperature of the cloud attenuates in inverse proportion to time. The ground conditions for the detonation, and the shell thickness of the explosive device can affect the diffusion height of the explosive cloud in different degrees.
2019, 39(5): 054203.
doi: 10.11883/bzycj-2017-0399
Abstract:
By differentiating the explosion venting process in a confined space, the process in each step was assumed to develop in three independent sub-steps: combustion, venting and equilibrium, and a sub-step calculation model was obtained for gas explosion venting pressure. In order to verify the calculation model, the vented explosion experiments were carried out in a 2 m×1.2 m×0.6 m chamber, in which was mounted on two kinds of venting components with the same burst pressure and different venting areas. The results show that: in the case of large-size venting, only one peak overpressure was measured and the pressure curves recorded by the pressure transducers T1 and T2 were nearly overlapping. In this condition, the pressure values by the model agree well with the test data. In the case of small-size venting, double-peak pressure curves were recorded. The second peak measured by the pressure transducer T1 near the vent is larger than that measured by the pressure transducer T2 in the chamber as a result of pressure gradient, which is caused by the turbulent distortion due to the change of the flow cross section. The calculation model under turbulent velocity correction can well describe the pressure change near the vent.
By differentiating the explosion venting process in a confined space, the process in each step was assumed to develop in three independent sub-steps: combustion, venting and equilibrium, and a sub-step calculation model was obtained for gas explosion venting pressure. In order to verify the calculation model, the vented explosion experiments were carried out in a 2 m×1.2 m×0.6 m chamber, in which was mounted on two kinds of venting components with the same burst pressure and different venting areas. The results show that: in the case of large-size venting, only one peak overpressure was measured and the pressure curves recorded by the pressure transducers T1 and T2 were nearly overlapping. In this condition, the pressure values by the model agree well with the test data. In the case of small-size venting, double-peak pressure curves were recorded. The second peak measured by the pressure transducer T1 near the vent is larger than that measured by the pressure transducer T2 in the chamber as a result of pressure gradient, which is caused by the turbulent distortion due to the change of the flow cross section. The calculation model under turbulent velocity correction can well describe the pressure change near the vent.
2019, 39(5): 054204.
doi: 10.11883/bzycj-2018-0075
Abstract:
The aim of the paper is to extend the Mie-Grüneisen mixture model to spherical coordinate. As the multi-component mixture model is applied to the Riemann problem under spherical coordinate, many problems need to be taken into account: weak equilibrium, singular point treatment, complex equations of states and so on. In the article, the research work starts from the Mie-Grüneisen mixture model, then extend to the revision and modification about many details, include: revision of the thermo dynamical parameters at interface, deduction of new transport equation by mass fraction, weighting evaluation of partial derivatives by mass fraction, definition of physical parameters by the adjacent grid for singular point and other so on. The seriously modified numerical model, can not only obtain non-oscillation solutions, but also catch the positions of shock wave and interface clearly. In addition, the modified mass fraction model, can get more accurate results than the original model with mass fraction.
The aim of the paper is to extend the Mie-Grüneisen mixture model to spherical coordinate. As the multi-component mixture model is applied to the Riemann problem under spherical coordinate, many problems need to be taken into account: weak equilibrium, singular point treatment, complex equations of states and so on. In the article, the research work starts from the Mie-Grüneisen mixture model, then extend to the revision and modification about many details, include: revision of the thermo dynamical parameters at interface, deduction of new transport equation by mass fraction, weighting evaluation of partial derivatives by mass fraction, definition of physical parameters by the adjacent grid for singular point and other so on. The seriously modified numerical model, can not only obtain non-oscillation solutions, but also catch the positions of shock wave and interface clearly. In addition, the modified mass fraction model, can get more accurate results than the original model with mass fraction.
2019, 39(5): 054205.
doi: 10.11883/bzycj-2018-0408
Abstract:
According to the mechanical properties and components of concrete from the mesoscale viewpoint, a simple and high-efficiency method based on 3D-Voronoi is proposed to construct realistic meso-structure model of concrete. In this paper, 3D mesoscale numerical simulation is conducted using damaged plasticity modeling under quasi-static and dynamic load. The simulation results resemble the corresponding experimental results both in strain-stress curves and failure modes. The current method can simulate static and dynamic mechanical properties well. In addition, the proved 3D model can provide an effective approach in elucidating fundamental mechanical behavior of concrete-like materials.
According to the mechanical properties and components of concrete from the mesoscale viewpoint, a simple and high-efficiency method based on 3D-Voronoi is proposed to construct realistic meso-structure model of concrete. In this paper, 3D mesoscale numerical simulation is conducted using damaged plasticity modeling under quasi-static and dynamic load. The simulation results resemble the corresponding experimental results both in strain-stress curves and failure modes. The current method can simulate static and dynamic mechanical properties well. In addition, the proved 3D model can provide an effective approach in elucidating fundamental mechanical behavior of concrete-like materials.
2019, 39(5): 055201.
doi: 10.11883/bzycj-2017-0366
Abstract:
The spectral characteristics of blasting vibration is of great significance to the safety construction of the tunnel. By using the dynamic finite element method, the blasting vibration frequency characteristics of surrounding rocks under different ground stress levels are analyzed. And by combining with the time-domain and frequency-domain analysis of the measured vibration signals, the vibration energy distributions at different frequency bands are studied. The results show that the dominant frequency of blasting vibration and the superior frequency bands of vibration energy decrease with the increase of stress level. This phenomenon results mainly from the dynamic effect of the in-situ stress transient unloading in the rock blasting process. The higher the in-situ stress level, the greater the proportion of low-frequency vibration energy of ＞20−100 Hz in blasting vibration signals. When the stress of the blasting area is 20 MPa, the vibration energy of ＞20−100 Hz band can reach about 35% of the total vibration energy; when the stress of the blasting area is 30−50 MPa, the vibration energy of ＞20−100 Hz band can reach more than 50% of the total vibration energy. In addition to the stress level, the stress unloading rate and the mechanical properties of rock mass also have a significant influence on the main frequency of blasting vibration. The higher the unloading rate is, the greater the proportion of low-frequency vibration energy. The unloading rate depends on the cutting blasting mode, and the straight hole cutting leads to the highest release rate of rock strain energy. The greater the elastic modulus of rock mass is, the higher the dominant frequency of blasting vibration.
The spectral characteristics of blasting vibration is of great significance to the safety construction of the tunnel. By using the dynamic finite element method, the blasting vibration frequency characteristics of surrounding rocks under different ground stress levels are analyzed. And by combining with the time-domain and frequency-domain analysis of the measured vibration signals, the vibration energy distributions at different frequency bands are studied. The results show that the dominant frequency of blasting vibration and the superior frequency bands of vibration energy decrease with the increase of stress level. This phenomenon results mainly from the dynamic effect of the in-situ stress transient unloading in the rock blasting process. The higher the in-situ stress level, the greater the proportion of low-frequency vibration energy of ＞20−100 Hz in blasting vibration signals. When the stress of the blasting area is 20 MPa, the vibration energy of ＞20−100 Hz band can reach about 35% of the total vibration energy; when the stress of the blasting area is 30−50 MPa, the vibration energy of ＞20−100 Hz band can reach more than 50% of the total vibration energy. In addition to the stress level, the stress unloading rate and the mechanical properties of rock mass also have a significant influence on the main frequency of blasting vibration. The higher the unloading rate is, the greater the proportion of low-frequency vibration energy. The unloading rate depends on the cutting blasting mode, and the straight hole cutting leads to the highest release rate of rock strain energy. The greater the elastic modulus of rock mass is, the higher the dominant frequency of blasting vibration.
2019, 39(5): 055301.
doi: 10.11883/bzycj-2017-0451
Abstract:
Al/Ni multi-layered composites were manufactured by cold rolling with different passes. The influence of cold rolling passes on the mechanical properties and shock-induced chemical reaction (SICR) behaviors of Al/Ni multi-layered composites was investigated by quasi-static compression tests and impact initiation experiments. A scanning electron microscopy (SEM) was used to obtain the microstructures of the Al/Ni multi-layered composites, and the microstructures from the scanning electron microscopy images were used to explain the experimental results. The results show that the cold-rolled Al/Ni multi-layered composites behave more plastically than the powder-compacted Al/Ni composites do. The compression strength of the Al/Ni multi-layered composites increases with the growth of rolling passes. On the other hand, more rolling passes result in decaying energy release capacity of the Al/Ni multi-layered composites under impact velocity from 800 m/s to 1 500 m/s.
Al/Ni multi-layered composites were manufactured by cold rolling with different passes. The influence of cold rolling passes on the mechanical properties and shock-induced chemical reaction (SICR) behaviors of Al/Ni multi-layered composites was investigated by quasi-static compression tests and impact initiation experiments. A scanning electron microscopy (SEM) was used to obtain the microstructures of the Al/Ni multi-layered composites, and the microstructures from the scanning electron microscopy images were used to explain the experimental results. The results show that the cold-rolled Al/Ni multi-layered composites behave more plastically than the powder-compacted Al/Ni composites do. The compression strength of the Al/Ni multi-layered composites increases with the growth of rolling passes. On the other hand, more rolling passes result in decaying energy release capacity of the Al/Ni multi-layered composites under impact velocity from 800 m/s to 1 500 m/s.
2019, 39(5): 055302.
doi: 10.11883/bzycj-2018-0400
Abstract:
This work studies the effect of base plate initial tensile strength on interface morphology and welding quality in explosive welding. The plates with different initial tensile strength were fabricated via explosive welding method under the same parameters. The microstructure of the interface for the explosive welding sample was analyzed, and the results showed that the interface of the explosive welding sample was greatly influenced by the strength of the material, the interface was formed of over-melted, periodic ripples and finally flattening with the increasing strength of the material. Combined with the numerical simulation results, it is found that the interface melting zone is large and can be considered as an incompressible fluid for analysis when the specific pressure of explosive welding is high. When the specific pressure is low, the local temperature rising speed of the welded sample will be higher and the adiabatic shear zone will be formed under the action of plastic strain, although the interface will still melt. The strength of the material cannot be neglected for the explosive welding.
This work studies the effect of base plate initial tensile strength on interface morphology and welding quality in explosive welding. The plates with different initial tensile strength were fabricated via explosive welding method under the same parameters. The microstructure of the interface for the explosive welding sample was analyzed, and the results showed that the interface of the explosive welding sample was greatly influenced by the strength of the material, the interface was formed of over-melted, periodic ripples and finally flattening with the increasing strength of the material. Combined with the numerical simulation results, it is found that the interface melting zone is large and can be considered as an incompressible fluid for analysis when the specific pressure of explosive welding is high. When the specific pressure is low, the local temperature rising speed of the welded sample will be higher and the adiabatic shear zone will be formed under the action of plastic strain, although the interface will still melt. The strength of the material cannot be neglected for the explosive welding.
2019, 39(5): 055401.
doi: 10.11883/bzycj-2017-0388
Abstract:
In order to evaluate the explosion sensitivity of corn starch dust cloud accurately, to carry out the dust explosion-proof work effectively, and to ensure safe production of grain industry, a series of experiments were performed by using a standard Godbert-Greenwald constant temperature oven device to explore the influence laws of the following factors on the minimum ignition temperature of corn starch dust cloud. These influencing factors include dust concentration, diffusing pressure, the mass fraction of CaCO3, and their interactions. The sensitivities of the minimum ignition temperature of corn starch dust cloud to these influencing factors were investigated on the basis of the interactive orthogonal design method. And the results are close through both the range analysis and the analysis of variance. The mass fraction of CaCO3 and the dust concentration have highly significant effects on the minimum ignition temperature of maize starch cloud. The interaction between the spraying pressure and the dust concentration has significant effects on the minimum ignition temperature of maize starch cloud.
In order to evaluate the explosion sensitivity of corn starch dust cloud accurately, to carry out the dust explosion-proof work effectively, and to ensure safe production of grain industry, a series of experiments were performed by using a standard Godbert-Greenwald constant temperature oven device to explore the influence laws of the following factors on the minimum ignition temperature of corn starch dust cloud. These influencing factors include dust concentration, diffusing pressure, the mass fraction of CaCO3, and their interactions. The sensitivities of the minimum ignition temperature of corn starch dust cloud to these influencing factors were investigated on the basis of the interactive orthogonal design method. And the results are close through both the range analysis and the analysis of variance. The mass fraction of CaCO3 and the dust concentration have highly significant effects on the minimum ignition temperature of maize starch cloud. The interaction between the spraying pressure and the dust concentration has significant effects on the minimum ignition temperature of maize starch cloud.
