2021 Vol. 41, No. 10
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2021, 41(10): 101101.
doi: 10.11883/bzycj-2021-0010
Abstract:
The cavity expansion theory is one of the main basic theories for the theoretical analysis of penetration problems. It is mainly used to analyze the failure response characteristics of typical target materials under impact load, and then to determine the penetration resistance of the target. It is widely used in the analysis of high-speed impact penetration and failure problems. Domestic and foreign scholars have made abundant research achievements on plastic and (quasi) brittle materials based on the theory of cylindrical and spherical cavity expansion. Starting from the theoretical system of the static/dynamic cavity expansion model, the results of the cavity expansion model in different directions are introduced, mainly involving the cavity expansion pressure theoretical calculation model and numerical simulation method under ideal penetration conditions, and the application of cavity expansion model to typical penetration problems and complex missile target conditions. The theoretical calculation model under ideal penetration conditions based on cavity expansion theory mainly discusses the influence aspects of target material, yield criterion and equation of state on target resistance and the applicability of the cavity expansion model. According to the different initial conditions in the numerical simulation, two numerical simulation methods of cavity surface constant velocity/constant pressure are introduced, and the reliability of the numerical simulation method is proved. The basic assumptions, application scope and engineering application characteristics of the cavity expansion model are summarized, and its applications in typical penetration problems and complex missile targets such as multilayer composite target plate, constrained target, projectile grooves and projectile body with special cross-section are listed. Based on the current status of the cavity expansion model, we summarized the current cavity expansion model application direction in the field of impact dynamics, and the problems existing in the application of the cavity expansion model, as well as the key development direction in the cavity expansion model.
The cavity expansion theory is one of the main basic theories for the theoretical analysis of penetration problems. It is mainly used to analyze the failure response characteristics of typical target materials under impact load, and then to determine the penetration resistance of the target. It is widely used in the analysis of high-speed impact penetration and failure problems. Domestic and foreign scholars have made abundant research achievements on plastic and (quasi) brittle materials based on the theory of cylindrical and spherical cavity expansion. Starting from the theoretical system of the static/dynamic cavity expansion model, the results of the cavity expansion model in different directions are introduced, mainly involving the cavity expansion pressure theoretical calculation model and numerical simulation method under ideal penetration conditions, and the application of cavity expansion model to typical penetration problems and complex missile target conditions. The theoretical calculation model under ideal penetration conditions based on cavity expansion theory mainly discusses the influence aspects of target material, yield criterion and equation of state on target resistance and the applicability of the cavity expansion model. According to the different initial conditions in the numerical simulation, two numerical simulation methods of cavity surface constant velocity/constant pressure are introduced, and the reliability of the numerical simulation method is proved. The basic assumptions, application scope and engineering application characteristics of the cavity expansion model are summarized, and its applications in typical penetration problems and complex missile targets such as multilayer composite target plate, constrained target, projectile grooves and projectile body with special cross-section are listed. Based on the current status of the cavity expansion model, we summarized the current cavity expansion model application direction in the field of impact dynamics, and the problems existing in the application of the cavity expansion model, as well as the key development direction in the cavity expansion model.
2021, 41(10): 101102.
doi: 10.11883/bzycj-2021-0017
Abstract:
The traditional fragmental warhead used in air defense and antimissile can not effectively destroy the incoming insensitive ammunition due to the weak fragmentations, which limits its development. After explosion of the circumferential multiple linear explosively-formed projectile (MLEFP) warhead, a number of folded linear explosively formed projectiles (LEFP) are produced in the circumferential direction with high speed, large mass and large length to diameter ratio. These projectiles can penetrate thick cases and ignite insensitive ammunitions, so the MLEFP warhead has a great application prospect in the medium-short range air defense and anti-missile system. Based on the development of linear projectile and the forming method of new LEFPs, the influences of charge and liner are focused on. Theories, merits and demerits of three initial velocity models are compared. The results of penetration tests using folded LEFPs in recent years are summarized. Finally, the future development direction of circumferential MLEFP warhead and linear projectile is analyzed.
The traditional fragmental warhead used in air defense and antimissile can not effectively destroy the incoming insensitive ammunition due to the weak fragmentations, which limits its development. After explosion of the circumferential multiple linear explosively-formed projectile (MLEFP) warhead, a number of folded linear explosively formed projectiles (LEFP) are produced in the circumferential direction with high speed, large mass and large length to diameter ratio. These projectiles can penetrate thick cases and ignite insensitive ammunitions, so the MLEFP warhead has a great application prospect in the medium-short range air defense and anti-missile system. Based on the development of linear projectile and the forming method of new LEFPs, the influences of charge and liner are focused on. Theories, merits and demerits of three initial velocity models are compared. The results of penetration tests using folded LEFPs in recent years are summarized. Finally, the future development direction of circumferential MLEFP warhead and linear projectile is analyzed.
2021, 41(10): 102101.
doi: 10.11883/bzycj-2020-0432
Abstract:
The TNT equivalent coefficient is an important evidence to guide the blast-resistant design and safe-distance determination for dangerous goods. To find out the TNT equivalent coefficients of two new kinds of propellants (H1, H2), a series of free-field static detonation tests were performed for the two propellants (H1, H2) and flaky 2,4,6-trinitrotoluene (TNT). Five repeated tests were carried out for each explosive and the mass of the tested explosive was 10 kg in each test. And the existing method for calculating the TNT equivalent coefficients was modified. Base on the overpressure-time curves of the shock waves at different distances from the explosion centers, the TNT equivalent coefficients for overpressure and specific impulse at different scaling distances were analyzed by the modified calculation method. The results show that the propagations of shock waves induced by explosions of the propellants agree well with the similar law, and are similar with that induced by explosion of the TNT explosive. Meanwhile, the overpressures and specific impulses of shock waves induced by explosions of the two propellants are much higher than those of the TNT explosive. With the increase of scaling distance, the overpressure TNT equivalent coefficient of H1 first increases to 1.34 and then decreases, while that of H2 decrease monotonously, and the maximum value is 1.26. With the increase of the scaling distance, both the specific impulse TNT equivalent coefficients of H1 and H2 first increase and then decrease. The specific impulse TNT equivalent coefficient of H1 with the peak value 1.38 is greater than that of H2. The modified method can be used to accurately calculate the TNT equivalent coefficients of the tested samples, and the results can improve the safety design of blast-resistant structures.
The TNT equivalent coefficient is an important evidence to guide the blast-resistant design and safe-distance determination for dangerous goods. To find out the TNT equivalent coefficients of two new kinds of propellants (H1, H2), a series of free-field static detonation tests were performed for the two propellants (H1, H2) and flaky 2,4,6-trinitrotoluene (TNT). Five repeated tests were carried out for each explosive and the mass of the tested explosive was 10 kg in each test. And the existing method for calculating the TNT equivalent coefficients was modified. Base on the overpressure-time curves of the shock waves at different distances from the explosion centers, the TNT equivalent coefficients for overpressure and specific impulse at different scaling distances were analyzed by the modified calculation method. The results show that the propagations of shock waves induced by explosions of the propellants agree well with the similar law, and are similar with that induced by explosion of the TNT explosive. Meanwhile, the overpressures and specific impulses of shock waves induced by explosions of the two propellants are much higher than those of the TNT explosive. With the increase of scaling distance, the overpressure TNT equivalent coefficient of H1 first increases to 1.34 and then decreases, while that of H2 decrease monotonously, and the maximum value is 1.26. With the increase of the scaling distance, both the specific impulse TNT equivalent coefficients of H1 and H2 first increase and then decrease. The specific impulse TNT equivalent coefficient of H1 with the peak value 1.38 is greater than that of H2. The modified method can be used to accurately calculate the TNT equivalent coefficients of the tested samples, and the results can improve the safety design of blast-resistant structures.
2021, 41(10): 102102.
doi: 10.11883/bzycj-2020-0458
Abstract:
A variety of complex wave zones are formed during the impact and expansion of explosive gas products. When the adiabatic index γ of explosive gas is different, the attenuation characteristics of the wave zones are quite different. In order to understand the characteristics of the complex wave zone under the different γ conditions (γ＞3, γ=3, γ＜3), the intersection characteristics of different complex wave zones in a planar detonation were analyzed based on the characteristic line method. The flow field in the planar detonation was simulated by MATLAB to verify and analyze the parameter change characteristics of the flow fields in the different complex wave zones. Comparisons display that the differences in the attenuation characteristics of the wave zones are mainly reflected in the differences in the u-c plane characteristics related to the particle velocity and the gas sound velocity. Among them, in the complex wave zone where two rarefaction waves intersect, the difference is also reflected in that when γ≠3, the rarefaction wave no longer has the characteristic of central divergence. The analysis result on the characteristics of each wave zone in the explosion process provides a reference for comprehensively understanding the attenuation of each characteristic parameter.
A variety of complex wave zones are formed during the impact and expansion of explosive gas products. When the adiabatic index γ of explosive gas is different, the attenuation characteristics of the wave zones are quite different. In order to understand the characteristics of the complex wave zone under the different γ conditions (γ＞3, γ=3, γ＜3), the intersection characteristics of different complex wave zones in a planar detonation were analyzed based on the characteristic line method. The flow field in the planar detonation was simulated by MATLAB to verify and analyze the parameter change characteristics of the flow fields in the different complex wave zones. Comparisons display that the differences in the attenuation characteristics of the wave zones are mainly reflected in the differences in the u-c plane characteristics related to the particle velocity and the gas sound velocity. Among them, in the complex wave zone where two rarefaction waves intersect, the difference is also reflected in that when γ≠3, the rarefaction wave no longer has the characteristic of central divergence. The analysis result on the characteristics of each wave zone in the explosion process provides a reference for comprehensively understanding the attenuation of each characteristic parameter.
2021, 41(10): 103101.
doi: 10.11883/bzycj-2021-0172
Abstract:
The expanding fracture of ductile alloy cylinder subject to the explosion includes multiple fracture modes, such as tensile, shear, and mixed tensile-shear fracture. The mechanism and the factors influencing the fracture processes are still enigmatic and far from understood. In this paper, the smoothed particle hydrodynamics (SPH) method is used to simulate the explosion experiment of 45 steel cylinders shell with different charges of JOB-9003 and RHT-901. The shear fracture, tension-shear mixed fracture modes and the evolution process of cylindrical shell with different charges are discussed. The simulation results are consistent with the experimental trend. The SPH results show that due to the propagation and reflection of shock wave between the inner and outer surfaces of cylinder during the loading stage of detonation wave, the distribution of equivalent plastic strain on wall-thickness of the cylinder is a convex shape, i.e. the strain in the middle of wall-thickness is larger than that of in the inner and outer walls; when loading by a higher explosive pressure (JOB-9003), the fracture cracks initiate from the middle of wall-thickness, and then develop to the inner and outer walls along the direction of maximum shear in loading stage, showingthe shear fracture mode. However, under the loading caused by charge RHT-901 with relatively low pressure, although the crack still starts from the middle of wall-thickness and propagates along the shear direction, the shear crack could not grow through the section of the wall completely in the loading stage; then the cylinder experiences the stage of free expansion, the stress state of unbroken zone changes into triaxial tensile stress state and the structural instability, similar to “necking” occurs in the unbroken zone. Consequently, the cracks turn from the shear direction to the necking zone along the radial direction, showing the mixed tensile-shear fracture mode. The proportion of tension and shear cracks is related to the occurrence time of structural instability. The results show that the explosion expanding-fracture process of a metal cylinders involves the interaction between shock wave and cylinder structure, and cannot be treated as that of a series of expansion rings.
The expanding fracture of ductile alloy cylinder subject to the explosion includes multiple fracture modes, such as tensile, shear, and mixed tensile-shear fracture. The mechanism and the factors influencing the fracture processes are still enigmatic and far from understood. In this paper, the smoothed particle hydrodynamics (SPH) method is used to simulate the explosion experiment of 45 steel cylinders shell with different charges of JOB-9003 and RHT-901. The shear fracture, tension-shear mixed fracture modes and the evolution process of cylindrical shell with different charges are discussed. The simulation results are consistent with the experimental trend. The SPH results show that due to the propagation and reflection of shock wave between the inner and outer surfaces of cylinder during the loading stage of detonation wave, the distribution of equivalent plastic strain on wall-thickness of the cylinder is a convex shape, i.e. the strain in the middle of wall-thickness is larger than that of in the inner and outer walls; when loading by a higher explosive pressure (JOB-9003), the fracture cracks initiate from the middle of wall-thickness, and then develop to the inner and outer walls along the direction of maximum shear in loading stage, showingthe shear fracture mode. However, under the loading caused by charge RHT-901 with relatively low pressure, although the crack still starts from the middle of wall-thickness and propagates along the shear direction, the shear crack could not grow through the section of the wall completely in the loading stage; then the cylinder experiences the stage of free expansion, the stress state of unbroken zone changes into triaxial tensile stress state and the structural instability, similar to “necking” occurs in the unbroken zone. Consequently, the cracks turn from the shear direction to the necking zone along the radial direction, showing the mixed tensile-shear fracture mode. The proportion of tension and shear cracks is related to the occurrence time of structural instability. The results show that the explosion expanding-fracture process of a metal cylinders involves the interaction between shock wave and cylinder structure, and cannot be treated as that of a series of expansion rings.
2021, 41(10): 103201.
doi: 10.11883/bzycj-2020-0316
Abstract:
A conical shock tube is a kind of underwater explosive devices which uses small conical explosive charge to form high intensity shock pressure. Theoretically, the shock wave pressure in the conical shock tube is the same as that generated by a virtual spherical explosive charge in free field water. However, considering the effect of practical factors, the characteristics of shock wave in the actual device and the theoretical device are different to some extent. In order to investigate the shock wave characteristics in the conical water explosion shock tube under a cylindrical charge condition, and to obtain the variation rules of the peak pressure value, the specific impulse and the energy flux density, a series of numerical calculations with different cone angles and different quality of cylindrical charges were conducted. The reliability of the simulation methods was verified by comparing with the published experimental data. Through the analysis of the pressure data obtained by the validated simulation method, it is found that the shock wave in the tube follows the same scaling law as it is in the free field underwater explosion. The constants k and n of the empirical expressions for peak pressure, the impulse and the energy flux density for the shock wave in shock tube are obtained by data fitting. Furthermore, the relationships among the coefficient k, index n and cone angle α were deduced, and the result shows that the coefficients k have well linear relationship with constructed angle coefficient β, and the indexes n can be quantitatively expressed by cone angle α. Regarding the free field as a special case with a cone angle of 360°, it’s constants k and n also conform to the obtained relationships. It is also found that the secondary pulsation pressure period shows an anomalous change rule with explosive mass, which can be well explained by the significant increasement of the equivalent hydrostatic pressure depth. The ratio between the secondary impulse pressure peak and initial pressure peak is bigger than that in free field while the ratio between the secondary impulse pressure’s impulse to the initial pressure impulse is almost the same. These results can provide support for the application of conical shock tubes.
A conical shock tube is a kind of underwater explosive devices which uses small conical explosive charge to form high intensity shock pressure. Theoretically, the shock wave pressure in the conical shock tube is the same as that generated by a virtual spherical explosive charge in free field water. However, considering the effect of practical factors, the characteristics of shock wave in the actual device and the theoretical device are different to some extent. In order to investigate the shock wave characteristics in the conical water explosion shock tube under a cylindrical charge condition, and to obtain the variation rules of the peak pressure value, the specific impulse and the energy flux density, a series of numerical calculations with different cone angles and different quality of cylindrical charges were conducted. The reliability of the simulation methods was verified by comparing with the published experimental data. Through the analysis of the pressure data obtained by the validated simulation method, it is found that the shock wave in the tube follows the same scaling law as it is in the free field underwater explosion. The constants k and n of the empirical expressions for peak pressure, the impulse and the energy flux density for the shock wave in shock tube are obtained by data fitting. Furthermore, the relationships among the coefficient k, index n and cone angle α were deduced, and the result shows that the coefficients k have well linear relationship with constructed angle coefficient β, and the indexes n can be quantitatively expressed by cone angle α. Regarding the free field as a special case with a cone angle of 360°, it’s constants k and n also conform to the obtained relationships. It is also found that the secondary pulsation pressure period shows an anomalous change rule with explosive mass, which can be well explained by the significant increasement of the equivalent hydrostatic pressure depth. The ratio between the secondary impulse pressure peak and initial pressure peak is bigger than that in free field while the ratio between the secondary impulse pressure’s impulse to the initial pressure impulse is almost the same. These results can provide support for the application of conical shock tubes.
2021, 41(10): 103301.
doi: 10.11883/bzycj-2020-0134
Abstract:
In this paper, the numerical simulation of 921A steel target under the impact of truncated-ogive projectile is studied. The numerical results agrees well with the experimental results. Under three different conditions, the residual velocity is in good agreement with the experimental results, and the error is less than 5%. With the change of the impact point position, the failure modes of the stiffened plate target plate is described in detail. First, the stiffener tears and the failure by symmetrical petalling occurs in target plate on the both left and right side. With the change of the impact point position, the tearing degree of stiffener decreases gradually, and the stiffener deforms plastically only. The petals on target plate are no longer symmetrical, and the dynamic response of the left target plate transforms from petalling failure to small break, and only plastic deformation remains at last. The right target plate always produced petalling failure mode, but the number and form of petals always change. The results show that material point method can be applied well, and it can provide some reference data for the future research of ship penetration.
In this paper, the numerical simulation of 921A steel target under the impact of truncated-ogive projectile is studied. The numerical results agrees well with the experimental results. Under three different conditions, the residual velocity is in good agreement with the experimental results, and the error is less than 5%. With the change of the impact point position, the failure modes of the stiffened plate target plate is described in detail. First, the stiffener tears and the failure by symmetrical petalling occurs in target plate on the both left and right side. With the change of the impact point position, the tearing degree of stiffener decreases gradually, and the stiffener deforms plastically only. The petals on target plate are no longer symmetrical, and the dynamic response of the left target plate transforms from petalling failure to small break, and only plastic deformation remains at last. The right target plate always produced petalling failure mode, but the number and form of petals always change. The results show that material point method can be applied well, and it can provide some reference data for the future research of ship penetration.
2021, 41(10): 103901.
doi: 10.11883/bzycj-2021-0056
Abstract:
To study the muzzle flow field created by a sealed launch of an underwater gun and the distribution characteristics of the muzzle flow field in different media, a two-dimensional axisymmetric numerical model for the muzzle multiphase flow created by an underwater sealed launch is established. The volume of fluid numerical model, standard k-\begin{document}$\varepsilon $\end{document} ![]()
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To study the muzzle flow field created by a sealed launch of an underwater gun and the distribution characteristics of the muzzle flow field in different media, a two-dimensional axisymmetric numerical model for the muzzle multiphase flow created by an underwater sealed launch is established. The volume of fluid numerical model, standard k-
2021, 41(10): 104201.
doi: 10.11883/bzycj-2020-0461
Abstract:
Aiming at the problem of load shedding in high-speed water entry of a vehicle, a composite structural buffer has been designed. Meanwhile, an accurate numerical model with the fluid-solid coupling is established to analyze the crushing process based on the arbitrary Lagrangian-Eulerian (ALE) algorithm and evaluate the effects of different schemes. The results show that the designed buffer can absorb the impact energy, leading to the damage and separation from the vehicle properly. The layered design of cushion foam changes the damage mode of the nose cap and causes it to be failure in advance. When the buffer is in contact with water, stress concentration occurs at the top of nose cap and preset groove. The groove effectively guides the destruction mode of the cap, such that the layered foam will not be too easy to be completely destroyed and the phenomenon of secondary cushion can occur. The velocity curve of the vehicle with the buffer changes more smoothly, the displacement is greater in the same time, and the load reduction rate of the layered foam scheme can reach 73.2% which is better than the single-layer foam scheme.
Aiming at the problem of load shedding in high-speed water entry of a vehicle, a composite structural buffer has been designed. Meanwhile, an accurate numerical model with the fluid-solid coupling is established to analyze the crushing process based on the arbitrary Lagrangian-Eulerian (ALE) algorithm and evaluate the effects of different schemes. The results show that the designed buffer can absorb the impact energy, leading to the damage and separation from the vehicle properly. The layered design of cushion foam changes the damage mode of the nose cap and causes it to be failure in advance. When the buffer is in contact with water, stress concentration occurs at the top of nose cap and preset groove. The groove effectively guides the destruction mode of the cap, such that the layered foam will not be too easy to be completely destroyed and the phenomenon of secondary cushion can occur. The velocity curve of the vehicle with the buffer changes more smoothly, the displacement is greater in the same time, and the load reduction rate of the layered foam scheme can reach 73.2% which is better than the single-layer foam scheme.
2021, 41(10): 105101.
doi: 10.11883/bzycj-2020-0399
Abstract:
With frequent blast accidents of hundreds of tons equivalent explosion, increasing attention has been paid to the damage assessment and anti-explosion safety of building structures. Some evaluation methods give procedures to obtain the pressure-impulse diagrams on the structural components. However, to the best knowledge of authors, how to evaluate the damage degree of building structures as a whole still remains open. In this paper, a weighted component damage method is proposed to evaluate the damage of structures subjected to long duration blast loading. The method, as its name suggests, is to define a damage degree of the whole structure by adding the damage degrees of all components in a weighted manner. The weight of a component, which represents its contribution to the anti-explosion safety, is defined by a strain energy based method. In order to verify the effectiveness of the proposed method, a high-resolution numerical simulation has been performed on a two-story masonry structure subjected to blast loading with a positive phase duration of 100 ms using a self-developed parallel finite element program for shock wave structure destruction simulation. A support rotation criterion based on the flexural deformation model of components is adopted to determine the damage degree of load-bearing components such as brick walls, columns and floors. The damage degree of the whole structure is then obtained using the proposed weighted component damage method. Upon the overpressure-damage curve is obtained, interpolations was carried out to obtain the threshold values of the overpressure corresponding to the six predefined damage levels. The numerical predicted overpressure values were compared with those from literature data. It was shown that the relative error of the overpressure is between −16.9% and 26.2%, and the effectiveness of the proposed method was verified. The proposed assessment approach can be used to obtain the pressure-impulse diagrams of masonry structures and provide effective measures in protecting structures against blast loads.
With frequent blast accidents of hundreds of tons equivalent explosion, increasing attention has been paid to the damage assessment and anti-explosion safety of building structures. Some evaluation methods give procedures to obtain the pressure-impulse diagrams on the structural components. However, to the best knowledge of authors, how to evaluate the damage degree of building structures as a whole still remains open. In this paper, a weighted component damage method is proposed to evaluate the damage of structures subjected to long duration blast loading. The method, as its name suggests, is to define a damage degree of the whole structure by adding the damage degrees of all components in a weighted manner. The weight of a component, which represents its contribution to the anti-explosion safety, is defined by a strain energy based method. In order to verify the effectiveness of the proposed method, a high-resolution numerical simulation has been performed on a two-story masonry structure subjected to blast loading with a positive phase duration of 100 ms using a self-developed parallel finite element program for shock wave structure destruction simulation. A support rotation criterion based on the flexural deformation model of components is adopted to determine the damage degree of load-bearing components such as brick walls, columns and floors. The damage degree of the whole structure is then obtained using the proposed weighted component damage method. Upon the overpressure-damage curve is obtained, interpolations was carried out to obtain the threshold values of the overpressure corresponding to the six predefined damage levels. The numerical predicted overpressure values were compared with those from literature data. It was shown that the relative error of the overpressure is between −16.9% and 26.2%, and the effectiveness of the proposed method was verified. The proposed assessment approach can be used to obtain the pressure-impulse diagrams of masonry structures and provide effective measures in protecting structures against blast loads.
2021, 41(10): 105201.
doi: 10.11883/bzycj-2020-0352
Abstract:
In rock drilling and blasting, the in-hole initiation position determines the propagation direction of the explosive detonation wave, and thereby affects the distribution of blast vibration field (BVF). In this study, the acting mechanism of the initiation position was investigated via the comprehensive analysis of the distribution of the detonation products, the explosion energy as well as BVF of the cylindrical charge. Then, the distribution law of BVF under different initiation positions was analyzed using the Heelan’s short-column-solution based superposition model of an extended charge. At last, the acting effect of the initiation position on the distribution of BVF was demonstrated by the onsite blasting experiment. Results indicate that the acting mechanism of the initiation position lies in the axial non-uniform distribution of the explosive energy and the phase delay effect of the superposition of BVF. The in-hole initiation position has the adjustment effect on the distribution of BVF, due to which, the blast vibration amplitude is strengthened at the forward direction of the detonation wave. It needs to be pointed that the non-uniformity of the distribution of BVF is under some control of the explosive length and the explosive velocity of detonation. For the common initiation modes, the field test results indicate that the ground peak particle velocities under the bottom are larger than those under the top and mid-point initiations, and the top initiation is the smallest. Besides, the blast vibration differences becomes more obvious as the blast-hole depth increases, but the vibration difference gradually vanishes with distance.
In rock drilling and blasting, the in-hole initiation position determines the propagation direction of the explosive detonation wave, and thereby affects the distribution of blast vibration field (BVF). In this study, the acting mechanism of the initiation position was investigated via the comprehensive analysis of the distribution of the detonation products, the explosion energy as well as BVF of the cylindrical charge. Then, the distribution law of BVF under different initiation positions was analyzed using the Heelan’s short-column-solution based superposition model of an extended charge. At last, the acting effect of the initiation position on the distribution of BVF was demonstrated by the onsite blasting experiment. Results indicate that the acting mechanism of the initiation position lies in the axial non-uniform distribution of the explosive energy and the phase delay effect of the superposition of BVF. The in-hole initiation position has the adjustment effect on the distribution of BVF, due to which, the blast vibration amplitude is strengthened at the forward direction of the detonation wave. It needs to be pointed that the non-uniformity of the distribution of BVF is under some control of the explosive length and the explosive velocity of detonation. For the common initiation modes, the field test results indicate that the ground peak particle velocities under the bottom are larger than those under the top and mid-point initiations, and the top initiation is the smallest. Besides, the blast vibration differences becomes more obvious as the blast-hole depth increases, but the vibration difference gradually vanishes with distance.
2021, 41(10): 105202.
doi: 10.11883/bzycj-2020-0428
Abstract:
The technical potential of an electronic detonator has not yet been fully utilized in tunnel engineering. An important reason is that there is no calculation method of blasting parameters supported by rigorous theory. The pivotal blasting parameters such as charge and delay time, etc. are mostly designed following ordinary mining methods. And it can not solve the problem of calculation accuracy of blasting parameters after the formation of the second free surface. Taking Guanyinqiao Tunnel in Chongqing as the research background, based on the Anderson principle and the delay characteristics of the electronic detonator, a new method for designing the blasting parameters of electronic detonators was proposed under the different free surface conditions changing in the process of tunnel blasting, from single free surface to dual free surface. Firstly, based on the single-hole and single free surface blasting vibration curves of different charges acquired on site, the superimposed vibration of multiple blast-holes under each delay time was calculated one by one. After comparing the superimposed vibration curves of different charges and delays, it was determined the blasting parameters of single free surface, including the maximum single-hole charge and the optimal inter-hole delay. Secondly, according to the characteristics of the electronic detonator, the short-delay cut blasting field test was designed. By comparing the calculated waveform without considering the influence of the second free surface with the measured waveform affected by the vibration reduction effect of the second free surface, it was found that the second free surface had formed at 48 ms after initiation. Based on this, a single-hole blasting test was designed after the formation of the second free surface. By calculating the superimposed vibration velocity based on the single-hole waveforms before and after the formation of the second free surface, it was determined the blasting parameters under the dual free surfaces condition, including single-hole charge, inter-hole delay time, and delay between different types of holes. Finally, the calculation method of blasting parameters in the whole blasting process was formed. After the comprehensive analysis of the calculated results, the single-hole charge of the main cutting holes is 1.2 kg, and it is 1.4 kg of the auxiliary cutting holes, then the delay time between holes is 5 ms on site; the minimum delay time between the main cut holes and the auxiliary cut holes is 35 ms. The field test was carried out with the optimized parameters mentioned above, and it got high-efficiency footage as well as a low vibration velocity.
The technical potential of an electronic detonator has not yet been fully utilized in tunnel engineering. An important reason is that there is no calculation method of blasting parameters supported by rigorous theory. The pivotal blasting parameters such as charge and delay time, etc. are mostly designed following ordinary mining methods. And it can not solve the problem of calculation accuracy of blasting parameters after the formation of the second free surface. Taking Guanyinqiao Tunnel in Chongqing as the research background, based on the Anderson principle and the delay characteristics of the electronic detonator, a new method for designing the blasting parameters of electronic detonators was proposed under the different free surface conditions changing in the process of tunnel blasting, from single free surface to dual free surface. Firstly, based on the single-hole and single free surface blasting vibration curves of different charges acquired on site, the superimposed vibration of multiple blast-holes under each delay time was calculated one by one. After comparing the superimposed vibration curves of different charges and delays, it was determined the blasting parameters of single free surface, including the maximum single-hole charge and the optimal inter-hole delay. Secondly, according to the characteristics of the electronic detonator, the short-delay cut blasting field test was designed. By comparing the calculated waveform without considering the influence of the second free surface with the measured waveform affected by the vibration reduction effect of the second free surface, it was found that the second free surface had formed at 48 ms after initiation. Based on this, a single-hole blasting test was designed after the formation of the second free surface. By calculating the superimposed vibration velocity based on the single-hole waveforms before and after the formation of the second free surface, it was determined the blasting parameters under the dual free surfaces condition, including single-hole charge, inter-hole delay time, and delay between different types of holes. Finally, the calculation method of blasting parameters in the whole blasting process was formed. After the comprehensive analysis of the calculated results, the single-hole charge of the main cutting holes is 1.2 kg, and it is 1.4 kg of the auxiliary cutting holes, then the delay time between holes is 5 ms on site; the minimum delay time between the main cut holes and the auxiliary cut holes is 35 ms. The field test was carried out with the optimized parameters mentioned above, and it got high-efficiency footage as well as a low vibration velocity.
2021, 41(10): 105401.
doi: 10.11883/bzycj-2020-0306
Abstract:
In order to study the inhibitory property and mechanism of inert powder on dust explosion flame in oil shale, five common inert powder and two types of oil shale were selected for the explosion flame inhibition experiment by using the dust explosion flame propagation test system. First, a high-speed camera was used to record the flame image during the inhibition of oil shale dust explosion by inert powder, and the differences in explosion flame length, minimum inerting ratio and flame morphology and structure were analyzed in detail. Then, the thermal decomposition and endothermic characteristics of the inert powder were tested by Thermogravimetric-Differential Scanning Calorimetry (TG-DSC), and the TG-DTG-DSC thermal characteristic curve of the inert powder was analyzed. Combined with the analysis of the inhibition effect of the inert powder in the preheating zone and the combustion flame zone, the inhibitory property and the mechanism of the inert powder on the oil shale dust explosion flame were systematically studied. The research results show that the inhibitory performance of inert powder to the explosion flame of two kinds of oil shale dust is ranked as: ABC dry powder ＞Al(OH)3＞Mg(OH)2＞NaHCO3＞rock powder, and their explosion inhibition performance against Huadian oil shale (HDOS) is better than that of Longkou oil shale (LKOS). In this paper, the physical model of the inhibition mechanism of inert powder on the explosion flame of oil shale dust is established and the inhibition mechanism is analyzed. Through the mechanism analysis, it is shown that the high-efficiency explosive inhibition powder should have good thermal stability (decomposition temperature around 200−400 ℃), high heat absorption, and the decomposition of intermediate products can combine with the combustion reactive radical to play a chemical inhibition effect. The research results can provide theoretical basis and basis for the design of explosion inhibition of oil shale dust and the development of explosive inhibition powder.
In order to study the inhibitory property and mechanism of inert powder on dust explosion flame in oil shale, five common inert powder and two types of oil shale were selected for the explosion flame inhibition experiment by using the dust explosion flame propagation test system. First, a high-speed camera was used to record the flame image during the inhibition of oil shale dust explosion by inert powder, and the differences in explosion flame length, minimum inerting ratio and flame morphology and structure were analyzed in detail. Then, the thermal decomposition and endothermic characteristics of the inert powder were tested by Thermogravimetric-Differential Scanning Calorimetry (TG-DSC), and the TG-DTG-DSC thermal characteristic curve of the inert powder was analyzed. Combined with the analysis of the inhibition effect of the inert powder in the preheating zone and the combustion flame zone, the inhibitory property and the mechanism of the inert powder on the oil shale dust explosion flame were systematically studied. The research results show that the inhibitory performance of inert powder to the explosion flame of two kinds of oil shale dust is ranked as: ABC dry powder ＞Al(OH)3＞Mg(OH)2＞NaHCO3＞rock powder, and their explosion inhibition performance against Huadian oil shale (HDOS) is better than that of Longkou oil shale (LKOS). In this paper, the physical model of the inhibition mechanism of inert powder on the explosion flame of oil shale dust is established and the inhibition mechanism is analyzed. Through the mechanism analysis, it is shown that the high-efficiency explosive inhibition powder should have good thermal stability (decomposition temperature around 200−400 ℃), high heat absorption, and the decomposition of intermediate products can combine with the combustion reactive radical to play a chemical inhibition effect. The research results can provide theoretical basis and basis for the design of explosion inhibition of oil shale dust and the development of explosive inhibition powder.
