2019 Vol. 39, No. 8
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2019, 39(8): 081101.
doi: 10.11883/bzycj-2019-0286
Abstract:
In recent years, as the developing of hyper-velocity weapons, the research emphasis of penetration effects is shifting from high-velocity penetration to hyper-velocity penetration. With the increasing of impact velocity of projectiles, the penetration mechanism changes, where effects as cratering and ground shock are induced. In this paper, progress in theoretical research of penetration into rock-like materials in a wide velocity range is reviewed, where velocity range is divided into zones, and theoretical models of penetration, cratering and ground shock are introduced. The existing problems concerned and research orientation in the future are also forecasted.
In recent years, as the developing of hyper-velocity weapons, the research emphasis of penetration effects is shifting from high-velocity penetration to hyper-velocity penetration. With the increasing of impact velocity of projectiles, the penetration mechanism changes, where effects as cratering and ground shock are induced. In this paper, progress in theoretical research of penetration into rock-like materials in a wide velocity range is reviewed, where velocity range is divided into zones, and theoretical models of penetration, cratering and ground shock are introduced. The existing problems concerned and research orientation in the future are also forecasted.
2019, 39(8): 081102.
doi: 10.11883/bzycj-2018-0480
Abstract:
In this paper we investigated the interaction mechanism between blast stress waves and cracks, and examined the variation of the dynamic characteristics of prefabricated horizontal static crack and horizontal motion crack produced by a split-tube holder charge under the normal incidence blast stress wave using the transmitted explosion dynamic caustics optical experiment system. The results showed that when the normal incident blast stress wave interacted with the stationary crack, the P wave causes the crack to close and then open, and the S wave formed a wavy speckle on the crack wall surface and the speckle alternately expands up and down along the stress wave propagation direction. The stress field surrounding the moving crack tip exerted a significant influence on the crack initiation and propagation of the static cracks. The blast stress wave generated by the post-explosion blasthole had an obvious impact on the dynamic characteristics of the horizontal directional motion crack produced by the first blasthole. When the direction of the propagation of the blast stress wave coincided with the direction of the propagation of the moving crack, the P wave causes the crack propagation velocity and the stress intensity factor\begin{document}${\rm{K}}_{\rm{I}}^{\rm{d}}$\end{document} ![]()
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In this paper we investigated the interaction mechanism between blast stress waves and cracks, and examined the variation of the dynamic characteristics of prefabricated horizontal static crack and horizontal motion crack produced by a split-tube holder charge under the normal incidence blast stress wave using the transmitted explosion dynamic caustics optical experiment system. The results showed that when the normal incident blast stress wave interacted with the stationary crack, the P wave causes the crack to close and then open, and the S wave formed a wavy speckle on the crack wall surface and the speckle alternately expands up and down along the stress wave propagation direction. The stress field surrounding the moving crack tip exerted a significant influence on the crack initiation and propagation of the static cracks. The blast stress wave generated by the post-explosion blasthole had an obvious impact on the dynamic characteristics of the horizontal directional motion crack produced by the first blasthole. When the direction of the propagation of the blast stress wave coincided with the direction of the propagation of the moving crack, the P wave causes the crack propagation velocity and the stress intensity factor
2019, 39(8): 081103.
doi: 10.11883/bzycj-2019-0191
Abstract:
As high elastic strain energy is stored in deep rock masses with high geo-stress, the initial equilibrium state in rock masses is broken as a result of excavation and explosion, thus forming the unbalanced force and energy field forms. The deformation and fracture of rock masses exhibit remarkable nonlinearity, such as zonal disintegration, large deformation, rockburst and artificial earthquake, under the combination of unbalanced force field and disturbance of dynamic loads, which leads to the special stress state for the deep rock masses. The classic continuum theory does not consider the natural discrete and energetic characteristics, and therefore cannot describe the nonlinear mechanical behavior of deep rock masses. Combining statistical physics, the characteristic energy factor provides a powerful theoretical proof for studying the deformation and fracture process of deep rock masses under the action of dynamic and static loading. In this paper, the characteristic energy factor is introduced briefly and its applications in engineering disasters such as zonal disintegration and irreversible deformation are reviewed.
As high elastic strain energy is stored in deep rock masses with high geo-stress, the initial equilibrium state in rock masses is broken as a result of excavation and explosion, thus forming the unbalanced force and energy field forms. The deformation and fracture of rock masses exhibit remarkable nonlinearity, such as zonal disintegration, large deformation, rockburst and artificial earthquake, under the combination of unbalanced force field and disturbance of dynamic loads, which leads to the special stress state for the deep rock masses. The classic continuum theory does not consider the natural discrete and energetic characteristics, and therefore cannot describe the nonlinear mechanical behavior of deep rock masses. Combining statistical physics, the characteristic energy factor provides a powerful theoretical proof for studying the deformation and fracture process of deep rock masses under the action of dynamic and static loading. In this paper, the characteristic energy factor is introduced briefly and its applications in engineering disasters such as zonal disintegration and irreversible deformation are reviewed.
2019, 39(8): 083101.
doi: 10.11883/bzycj-2019-0078
Abstract:
The dynamic microcrack growth has a great influence on the macroscopic dynamic mechanical properties of brittle rocks under dynamic compressive loadings. However, the relationships between dynamic microcrack growth and macroscopic dynamic mechanical properties are rarely studied. Based on the microcrack growth-induced stress-strain constitutive relationship, the relationship between quasi-static and dynamic fracture toughness, the relationship between crack velocity and strain rate, the relationship between strain rate and dynamic fracture toughness, a micromechanics-based stress-strain constitutive model is proposed. Furthermore, the relationship between crack velocity and strain rate is derived by the time derivative of equation describing the relationship between crack length and axial strain. The relationship between strain rate and dynamic fracture toughness is obtained by coupling the suggested relationship between crack velocity and strain rate, and the crack velocity and fracture toughness. Effects of strain rate on stress-strain relation and dynamic compressive strength are studied. The reasonability of the proposed dynamic constitutive model is verified by the experimental results. Sensitivities of initial damage, confining pressure, parameters m, ε0 and R on stress-strain relation, dynamic compressive strength and dynamic elastic modulus are discussed. These studies will provide a certain theoretical help for analyzing the stability of brittle surrounding rocks in deep undergrounding engineering.
The dynamic microcrack growth has a great influence on the macroscopic dynamic mechanical properties of brittle rocks under dynamic compressive loadings. However, the relationships between dynamic microcrack growth and macroscopic dynamic mechanical properties are rarely studied. Based on the microcrack growth-induced stress-strain constitutive relationship, the relationship between quasi-static and dynamic fracture toughness, the relationship between crack velocity and strain rate, the relationship between strain rate and dynamic fracture toughness, a micromechanics-based stress-strain constitutive model is proposed. Furthermore, the relationship between crack velocity and strain rate is derived by the time derivative of equation describing the relationship between crack length and axial strain. The relationship between strain rate and dynamic fracture toughness is obtained by coupling the suggested relationship between crack velocity and strain rate, and the crack velocity and fracture toughness. Effects of strain rate on stress-strain relation and dynamic compressive strength are studied. The reasonability of the proposed dynamic constitutive model is verified by the experimental results. Sensitivities of initial damage, confining pressure, parameters m, ε0 and R on stress-strain relation, dynamic compressive strength and dynamic elastic modulus are discussed. These studies will provide a certain theoretical help for analyzing the stability of brittle surrounding rocks in deep undergrounding engineering.
2019, 39(8): 083102.
doi: 10.11883/bzycj-2019-0164
Abstract:
The rock mass will bear the cyclic loading during the construction of underground engineering. Mechanical properties of the damaged rock mass under disturbance of cyclic loading are important for supporting capacity of the surrounding rock. Moreover, the disturbed rock mass is also potentially threatened by impact loads such as blasting. Therefore, it is necessary to investigate the re-bearing mechanical behavior of disturbing rock mass under cyclic loading. The cyclic loading experiments with four various maximum cyclic stress levels were carried out by using MTS 815 test system. The maximum cycling stresses are 80%, 85%, 90%, and 95% of uniaxial compressive strength respectively and the numbers of cycle are set to be 20, 40, 60 and 80 for each maximum cyclic stresses. The dynamic tests of the disturbed rock sample were conducted by using split Hopkinson pressure bar (SHPB). We analyzed the effects of maximum cyclic stress and the numbers of cycle on plastic strain and revealed the evolution law of dynamic strength and dynamic elastic modulus of marble with damage variable. The test results show that the plastic strain positively correlated with cycles, and the larger the maximum cycling stress, the more the cycles required to reach the stable plastic strain. The dynamic uniaxial compressive strength and dynamic elastic modulus decrease exponentially with the increase of the damage variable. The ratio of breakage energy divided into two stages and the critical point of damage variable is D=0.343. When D<0.343, the breakage energy ratio is stable at about 10%, and the value is about 13 J. When D>0.343, the ratio of breakage energy increases with the increase of damage variable. The findings of this research can provide guidelines for the selection of the mechanical parameters of the surrounding rock and the optimization of the support scheme.
The rock mass will bear the cyclic loading during the construction of underground engineering. Mechanical properties of the damaged rock mass under disturbance of cyclic loading are important for supporting capacity of the surrounding rock. Moreover, the disturbed rock mass is also potentially threatened by impact loads such as blasting. Therefore, it is necessary to investigate the re-bearing mechanical behavior of disturbing rock mass under cyclic loading. The cyclic loading experiments with four various maximum cyclic stress levels were carried out by using MTS 815 test system. The maximum cycling stresses are 80%, 85%, 90%, and 95% of uniaxial compressive strength respectively and the numbers of cycle are set to be 20, 40, 60 and 80 for each maximum cyclic stresses. The dynamic tests of the disturbed rock sample were conducted by using split Hopkinson pressure bar (SHPB). We analyzed the effects of maximum cyclic stress and the numbers of cycle on plastic strain and revealed the evolution law of dynamic strength and dynamic elastic modulus of marble with damage variable. The test results show that the plastic strain positively correlated with cycles, and the larger the maximum cycling stress, the more the cycles required to reach the stable plastic strain. The dynamic uniaxial compressive strength and dynamic elastic modulus decrease exponentially with the increase of the damage variable. The ratio of breakage energy divided into two stages and the critical point of damage variable is D=0.343. When D<0.343, the breakage energy ratio is stable at about 10%, and the value is about 13 J. When D>0.343, the ratio of breakage energy increases with the increase of damage variable. The findings of this research can provide guidelines for the selection of the mechanical parameters of the surrounding rock and the optimization of the support scheme.
2019, 39(8): 083103.
doi: 10.11883/bzycj-2019-0140
Abstract:
In order to use the measured particle velocities from spherical wave experiment to analyze the motion and deformation characteristics of medium under underground explosion, a new method for constructing the motion and deformation field for underground explosion was proposed based on the viscoelastic spherical wave theory and local viscoelastic equivalence hypothesis. Firstly, the velocity spectrums of the adjacent measuring points in granite were used to find out the corresponding spectrum ratio. Secondly, the equivalent spherical wave propagation coefficient in the region between adjacent measuring points was obtained by combining the theoretical spectrum ratio given by viscoelastic spherical wave theory. Thirdly, using the local viscoelastic equivalence hypothesis, the velocity spectrum of the particle at any point between adjacent measuring points was dramn out, and then the time domain waveform of the particle velocity was obtained by the inverse Fourier transform. Finally, the physical relationships between the motion field and the deformation field were used to construct the motion field and the deformation field in the whole analysis region. The results showed that the wave propagation coefficients obtained from the inversion of adjacent measuring points can construct the motion and deformation fields of the medium in the region between corresponding measuring points with high precision. Within the radius of 15-50 mm, the peak value of radial compressive strain decreased from 1.7×10−2 to 2.1×10−3, the peak value of tangential tensile strain decreased from 4.7×10−3 to 0.4×10−3, the peak value of radial compressive strain rate decreased from 5.1×104 s−1 to 2.5×103 s−1, and the peak value of tangential tensile strain rate decreases from 5.0×103 s−1 to 1.4×102 s−1, covering the whole process of loading and unloading from high strain (or strain rate) to intermediate and low strain (or strain rate).
In order to use the measured particle velocities from spherical wave experiment to analyze the motion and deformation characteristics of medium under underground explosion, a new method for constructing the motion and deformation field for underground explosion was proposed based on the viscoelastic spherical wave theory and local viscoelastic equivalence hypothesis. Firstly, the velocity spectrums of the adjacent measuring points in granite were used to find out the corresponding spectrum ratio. Secondly, the equivalent spherical wave propagation coefficient in the region between adjacent measuring points was obtained by combining the theoretical spectrum ratio given by viscoelastic spherical wave theory. Thirdly, using the local viscoelastic equivalence hypothesis, the velocity spectrum of the particle at any point between adjacent measuring points was dramn out, and then the time domain waveform of the particle velocity was obtained by the inverse Fourier transform. Finally, the physical relationships between the motion field and the deformation field were used to construct the motion field and the deformation field in the whole analysis region. The results showed that the wave propagation coefficients obtained from the inversion of adjacent measuring points can construct the motion and deformation fields of the medium in the region between corresponding measuring points with high precision. Within the radius of 15-50 mm, the peak value of radial compressive strain decreased from 1.7×10−2 to 2.1×10−3, the peak value of tangential tensile strain decreased from 4.7×10−3 to 0.4×10−3, the peak value of radial compressive strain rate decreased from 5.1×104 s−1 to 2.5×103 s−1, and the peak value of tangential tensile strain rate decreases from 5.0×103 s−1 to 1.4×102 s−1, covering the whole process of loading and unloading from high strain (or strain rate) to intermediate and low strain (or strain rate).
2019, 39(8): 083104.
doi: 10.11883/bzycj-2019-0169
Abstract:
The microscopic damage and dynamic mechanical properties of high-temperature granite after water cooling were studied through wave velocity test, nuclear magnetic resonance (NMR) test, split Hopkinson pressure bar (SHPB) impact test and scanning electron microscope（SEM）test. The variation of porosity and dynamic mechanical parameters of granite were analyzed. The results show that the wave velocity of high-temperature granite decreases nonlinearly after water cooling and the components of porosity with large pore increase with the increase of temperature. Moreover, water cooling leads to the more cracks and greater crack sizes than that of natural cooling. The dynamic parameters of high-temperature granite after water cooling show that the increase in temperature results in a decrease in the peak stress, an increase in the peak strain, and an increase at first then decrease in the elastic modulus. Additional thermal stress, resulted from sharply decrease in surface temperature of the high-temperature granite, leads to increased internal damage and decreased wave velocity and peak stress. Compared with natural cooling, the plasticity of high-temperature granite is reduced, because the cold hardening effect improves the hardness of surface granite. After water cooling, the granite specimens exhibit the brittle failure characteristics and their peak strain decreases but their elastic modulus increases. Cooling way has a minor effect on the cracks induced by shock before 400 ℃. As the temperature up to 800 ℃, the impact fracture surface of granite after natural cooling is characterized by honeycomb and irregular shape, in contrast, the impact fracture surface of granite after the water cooling is relatively flat.
The microscopic damage and dynamic mechanical properties of high-temperature granite after water cooling were studied through wave velocity test, nuclear magnetic resonance (NMR) test, split Hopkinson pressure bar (SHPB) impact test and scanning electron microscope（SEM）test. The variation of porosity and dynamic mechanical parameters of granite were analyzed. The results show that the wave velocity of high-temperature granite decreases nonlinearly after water cooling and the components of porosity with large pore increase with the increase of temperature. Moreover, water cooling leads to the more cracks and greater crack sizes than that of natural cooling. The dynamic parameters of high-temperature granite after water cooling show that the increase in temperature results in a decrease in the peak stress, an increase in the peak strain, and an increase at first then decrease in the elastic modulus. Additional thermal stress, resulted from sharply decrease in surface temperature of the high-temperature granite, leads to increased internal damage and decreased wave velocity and peak stress. Compared with natural cooling, the plasticity of high-temperature granite is reduced, because the cold hardening effect improves the hardness of surface granite. After water cooling, the granite specimens exhibit the brittle failure characteristics and their peak strain decreases but their elastic modulus increases. Cooling way has a minor effect on the cracks induced by shock before 400 ℃. As the temperature up to 800 ℃, the impact fracture surface of granite after natural cooling is characterized by honeycomb and irregular shape, in contrast, the impact fracture surface of granite after the water cooling is relatively flat.
2019, 39(8): 083105.
doi: 10.11883/bzycj-2019-0008
Abstract:
There are many cracks inside the rock mass. In this paper, taking a pair of parallel cracks as an example, we studied the effect of two parallel cracks on the main crack’s propagation behavior and investigated the relationship of the main crack’s extended length with the two parallel cracks’ spacing, using experiment and numerical simulation. In our experiments, we used a circular sandstone specimen including a center hole charged with a detonator and pre-existing cracks and a test system consisting of an oscilloscope, an ultra-dynamic strain amplifier and crack propagation gauges (CPGs), and monitored the propagation velocity and length of the main crack. In our simulation we used the AUTODYN code to investigate the propagation behavior of the main crack and the two parallel cracks. We described the state of the rock material using the linear equation of state and the maximum tensile stress failure criteria, and designed some target points between the two parallel cracks to record the stress history. The experiments and numerical simulation show that the compressive stress perpendicular to the direction of the main crack occurs between the two parallel cracks under explosive loading; that, as a result of just following the shock waves and encountering the parallel crack surfaces, the rarefactional waves change into compressive waves, thus leading to the confinement of the propagating cracks; and that this compressive stress is related to the spacing between the two parallel cracks, and leads to differences in the main crack’s confinement, propagation velocity, and eventual propagation length.
There are many cracks inside the rock mass. In this paper, taking a pair of parallel cracks as an example, we studied the effect of two parallel cracks on the main crack’s propagation behavior and investigated the relationship of the main crack’s extended length with the two parallel cracks’ spacing, using experiment and numerical simulation. In our experiments, we used a circular sandstone specimen including a center hole charged with a detonator and pre-existing cracks and a test system consisting of an oscilloscope, an ultra-dynamic strain amplifier and crack propagation gauges (CPGs), and monitored the propagation velocity and length of the main crack. In our simulation we used the AUTODYN code to investigate the propagation behavior of the main crack and the two parallel cracks. We described the state of the rock material using the linear equation of state and the maximum tensile stress failure criteria, and designed some target points between the two parallel cracks to record the stress history. The experiments and numerical simulation show that the compressive stress perpendicular to the direction of the main crack occurs between the two parallel cracks under explosive loading; that, as a result of just following the shock waves and encountering the parallel crack surfaces, the rarefactional waves change into compressive waves, thus leading to the confinement of the propagating cracks; and that this compressive stress is related to the spacing between the two parallel cracks, and leads to differences in the main crack’s confinement, propagation velocity, and eventual propagation length.
2019, 39(8): 083106.
doi: 10.11883/bzycj-2019-0187
Abstract:
The dynamic compressive strength characteristics and macroscopic failure modes of layered phyllite are carried out by the Split Hopkinson Pressure Bar. The micromorphology of fracture surface was obtained by 3D laser instrument, and the fractal geometry was introduced to quantitatively describe the roughness of fracture surface. Based on the fracture mechanism observed by SEM, the dynamic failure mechanism of layered rock with different bedding angles is analyzed. The results indicate that the weak bedding plane has a great influence on the dynamic compressive strength of layered rock. The fractal dimension of layered phyllite changes in U-shape with the increase of bedding angle. The influence of bedding plane on the failure characteristics of layered rocks is examined according to strength and crack propagation. For specimens with bedding angle of 0°, the failure strength is controlled by rock matrix, but the weak bedding plane still has a large impact on the distribution and trend of cracks in rock failure. For specimens with bedding angle of 22.5°, strength and direction of cracks are controlled by both the rock matrix and weak bedding plane. For specimens with bedding dip angle ranging from 45° to 67.5°, strength and direction of cracks are controlled by weak bedding plane. For the bedding angle of 90°, the dynamic compressive strength of the specimen is affected by the rock matrix, and longitudinal macro-cracks are formed early on the weak plane of the bedding, which results in that the cracks are greatly affected by the bedding plane.
The dynamic compressive strength characteristics and macroscopic failure modes of layered phyllite are carried out by the Split Hopkinson Pressure Bar. The micromorphology of fracture surface was obtained by 3D laser instrument, and the fractal geometry was introduced to quantitatively describe the roughness of fracture surface. Based on the fracture mechanism observed by SEM, the dynamic failure mechanism of layered rock with different bedding angles is analyzed. The results indicate that the weak bedding plane has a great influence on the dynamic compressive strength of layered rock. The fractal dimension of layered phyllite changes in U-shape with the increase of bedding angle. The influence of bedding plane on the failure characteristics of layered rocks is examined according to strength and crack propagation. For specimens with bedding angle of 0°, the failure strength is controlled by rock matrix, but the weak bedding plane still has a large impact on the distribution and trend of cracks in rock failure. For specimens with bedding angle of 22.5°, strength and direction of cracks are controlled by both the rock matrix and weak bedding plane. For specimens with bedding dip angle ranging from 45° to 67.5°, strength and direction of cracks are controlled by weak bedding plane. For the bedding angle of 90°, the dynamic compressive strength of the specimen is affected by the rock matrix, and longitudinal macro-cracks are formed early on the weak plane of the bedding, which results in that the cracks are greatly affected by the bedding plane.
2019, 39(8): 083107.
doi: 10.11883/bzycj-2018-0391
Abstract:
The non-penetrating fractured rock mass is the main form of rock mass in nature, and the geometric features of its fractures play a remarkable role in its strength and deformation. Its strain rate also has a significant rate dependence on its damage evolution and viscous effects. Firstly, using the model element method, we treated the dynamic failure process of non-penetrating fractured rock mass as a heterogeneous point with composite damage, static elastic properties and dynamic viscous properties, and improved the Maxwell body that responds to viscoelasticity. Then we combined the meso-damaged body and the macroscopic damage body of fracture damage evolutions into a macro-microscopic composite damage body following the equivalent strain hypothesis and constructed a dynamic damage model considering the macroscopic and microscopic defects of the rock mass. Furthermore, based on the fracture mechanics and strain energy theory, we analyzed the energy mechanism of the macroscopic fracture dynamic expansion of rock mass and obtained the calculation formula of the macroscopic dynamic damage variable of the fractured rock mass, with the initial fracture strain energy, the strain energy of the crack dynamic damage evolution process and the fracture closed strain energy, taken into consideration. Finally, we compared the results from the model calculation with those from experiment and found them in good agreement, thereby proving the rationality of the model. At the same time, we also discussed the influence of fracture inclination, strain rate and rock properties on rock mass deformation characteristics using the model.
The non-penetrating fractured rock mass is the main form of rock mass in nature, and the geometric features of its fractures play a remarkable role in its strength and deformation. Its strain rate also has a significant rate dependence on its damage evolution and viscous effects. Firstly, using the model element method, we treated the dynamic failure process of non-penetrating fractured rock mass as a heterogeneous point with composite damage, static elastic properties and dynamic viscous properties, and improved the Maxwell body that responds to viscoelasticity. Then we combined the meso-damaged body and the macroscopic damage body of fracture damage evolutions into a macro-microscopic composite damage body following the equivalent strain hypothesis and constructed a dynamic damage model considering the macroscopic and microscopic defects of the rock mass. Furthermore, based on the fracture mechanics and strain energy theory, we analyzed the energy mechanism of the macroscopic fracture dynamic expansion of rock mass and obtained the calculation formula of the macroscopic dynamic damage variable of the fractured rock mass, with the initial fracture strain energy, the strain energy of the crack dynamic damage evolution process and the fracture closed strain energy, taken into consideration. Finally, we compared the results from the model calculation with those from experiment and found them in good agreement, thereby proving the rationality of the model. At the same time, we also discussed the influence of fracture inclination, strain rate and rock properties on rock mass deformation characteristics using the model.
2019, 39(8): 083108.
doi: 10.11883/bzycj-2019-0044
Abstract:
Based on the theory of elastoplastic mechanics, the rock elastoplastic constitutive model considering hardening/softening behavior and strain rate effect is established with the uniform strength criterion as the yield criterion. Fortran language was used to program the elastoplastic constitutive model through the user-defined material interface (Umat) of LS-DYNA. The elastoplastic constitutive model is verified by uniaxial compression test and SHPB test of rock, and the results show that the elastoplastic constitutive model can reflect the mechanical behavior of rock under quasi-static and dynamic conditions.
Based on the theory of elastoplastic mechanics, the rock elastoplastic constitutive model considering hardening/softening behavior and strain rate effect is established with the uniform strength criterion as the yield criterion. Fortran language was used to program the elastoplastic constitutive model through the user-defined material interface (Umat) of LS-DYNA. The elastoplastic constitutive model is verified by uniaxial compression test and SHPB test of rock, and the results show that the elastoplastic constitutive model can reflect the mechanical behavior of rock under quasi-static and dynamic conditions.
2019, 39(8): 083301.
doi: 10.11883/bzycj-2019-0141
Abstract:
In this paper we carried out experiments using two-stage light gas gun with Gram-grade cylindrical tungsten alloy projectiles, impacting concrete targets at velocity from 1.82 km/s to 3.66 km/s ton investigate the cratering mechanism of concrete targets in hypervelocity impact conditions. We obtained the penetration depth and residual length of the projectiles using computerized tomography (CT) and used the numerical simulation results conducted by Euler algorithm to further examine the mechanism of hypervelocity impact, and achieved the following results: (1) The craters were structured by spalling areas and bullet holes; (2) The penetration depth increases at first and then decreases with the increase of the impact velocities, and the maximum penetration depth was 8.5 times that of the projectile length, which showed no significant advantage over low velocity penetration; (3) According to the pressure of the interface of the projectiles and targets, the penetration processes were divided into four stages, of which the quasi-steady stage and the third stage were crucial in determining the total penetration depth; (4) When the projectiles were completely eroded with the increase of the impact velocities, the penetration depth of the quasi-steady stages almost remained the same and the penetration depth of the third stage decreased so that the total penetration depth was observed to increase at first and then decrease.
In this paper we carried out experiments using two-stage light gas gun with Gram-grade cylindrical tungsten alloy projectiles, impacting concrete targets at velocity from 1.82 km/s to 3.66 km/s ton investigate the cratering mechanism of concrete targets in hypervelocity impact conditions. We obtained the penetration depth and residual length of the projectiles using computerized tomography (CT) and used the numerical simulation results conducted by Euler algorithm to further examine the mechanism of hypervelocity impact, and achieved the following results: (1) The craters were structured by spalling areas and bullet holes; (2) The penetration depth increases at first and then decreases with the increase of the impact velocities, and the maximum penetration depth was 8.5 times that of the projectile length, which showed no significant advantage over low velocity penetration; (3) According to the pressure of the interface of the projectiles and targets, the penetration processes were divided into four stages, of which the quasi-steady stage and the third stage were crucial in determining the total penetration depth; (4) When the projectiles were completely eroded with the increase of the impact velocities, the penetration depth of the quasi-steady stages almost remained the same and the penetration depth of the third stage decreased so that the total penetration depth was observed to increase at first and then decrease.
2019, 39(8): 084201.
doi: 10.11883/bzycj-2019-0154
Abstract:
To reduce the deviation of vibration signals effectively and improve the reliability of the data, the method of combining the ensemble empirical mode decomposition (EEMD) and the processing of high and low frequency is first applied to correct the acceleration zero-drift signals collected in the blasting test of granite. Then, according to the shock response spectrum of vibration signals, a correction index is proposed to characterize the average deviation amplitude of the frequency domain between the original and the corrected signals. Finally, the correction effects of signals in different white noise coefficients are discussed based on the frequency domain and the time domain. The analysis shows that the EEMD method can effectively eliminate the zero-drift phenomenon of the acceleration signal, but the improvement of zero-drift trend of the velocity signal after integration is limited. With the increase of the white noise coefficient, the correction indices in different frequency bands increase to varied extents, and the power exponent relationship is presented between them. According to the modified exponential analysis in different frequency bands, the optimal white noise coefficient range corresponding to different acceleration zero-drift signals can be determined. The correction index proposed in this study can provide a reference for the reasonable selection of white noise coefficient when EEMD method is used to process the zero-drift signal of acceleration.
To reduce the deviation of vibration signals effectively and improve the reliability of the data, the method of combining the ensemble empirical mode decomposition (EEMD) and the processing of high and low frequency is first applied to correct the acceleration zero-drift signals collected in the blasting test of granite. Then, according to the shock response spectrum of vibration signals, a correction index is proposed to characterize the average deviation amplitude of the frequency domain between the original and the corrected signals. Finally, the correction effects of signals in different white noise coefficients are discussed based on the frequency domain and the time domain. The analysis shows that the EEMD method can effectively eliminate the zero-drift phenomenon of the acceleration signal, but the improvement of zero-drift trend of the velocity signal after integration is limited. With the increase of the white noise coefficient, the correction indices in different frequency bands increase to varied extents, and the power exponent relationship is presented between them. According to the modified exponential analysis in different frequency bands, the optimal white noise coefficient range corresponding to different acceleration zero-drift signals can be determined. The correction index proposed in this study can provide a reference for the reasonable selection of white noise coefficient when EEMD method is used to process the zero-drift signal of acceleration.
2019, 39(8): 084202.
doi: 10.11883/bzycj-2019-0167
Abstract:
It is very important to monitor and evaluate the clandestine nuclear tests using the surface displacements such as subsidence craters induced by the underground nuclear explosion. Based on the similarity theory of the process of subsidence crater formation considering the influence of gravity, we conducted an explosive model test in a vacuum chamber, using our own independently developed explosive simulation apparatus and determined the subsidence zones of the surface displacements associated with the 3 September 2017 North Korean’s largest underground nuclear test. The results show that the radius of the surface subsidence zone is about 257 m, and the radius of collapse crater is about 154 m, which is equivalent to the estimated results according to the empirical formula and the monitored data of remote sensing with Synthetic Apeture Radar (SAR) by the TS-InSar satellite. Our results demonstrate that the explosive model test in a vacuum chamber can help characterize the irreversible zone of the surface displacements associated with the underground nuclear explosion, which has become an effective supplement of the seismological and satellite imagery methods to monitor the underground nuclear test.
It is very important to monitor and evaluate the clandestine nuclear tests using the surface displacements such as subsidence craters induced by the underground nuclear explosion. Based on the similarity theory of the process of subsidence crater formation considering the influence of gravity, we conducted an explosive model test in a vacuum chamber, using our own independently developed explosive simulation apparatus and determined the subsidence zones of the surface displacements associated with the 3 September 2017 North Korean’s largest underground nuclear test. The results show that the radius of the surface subsidence zone is about 257 m, and the radius of collapse crater is about 154 m, which is equivalent to the estimated results according to the empirical formula and the monitored data of remote sensing with Synthetic Apeture Radar (SAR) by the TS-InSar satellite. Our results demonstrate that the explosive model test in a vacuum chamber can help characterize the irreversible zone of the surface displacements associated with the underground nuclear explosion, which has become an effective supplement of the seismological and satellite imagery methods to monitor the underground nuclear test.
2019, 39(8): 085201.
doi: 10.11883/bzycj-2018-0280
Abstract:
In this paper, using polarization analysis, we characterized the seismic waves induced by the horizontal smooth blasting in a group of onsite blasting experiments, presenting interpretation of wave components and offering comparison of attenuation characteristics and evaluation of the influences of different waves. We also examined the inherent mechanical mechanism of the horizontal smooth blasting under some simplifications. The results show that the proportion of different waves and the dominant wave type both vary with the relative location of interest, and the dominant motion direction at a specific position closely correlates with the wave components. The pattern of the blasting source and the different attenuation characteristics jointly determine the wave components and their evolutions. For the horizontal smooth blasting, only S and R waves are included on the same plane of smooth blastholes, while the P wave component is negligible. The horizontal vibration is mainly caused by the R wave, while the S wave mainly vibrates in the vertical direction and its vertical velocity in the near field is much higher than that of the R wave. However, the R wave still dominates the vertical vibration if the scaled distance exceeds 22.5 m/kg1/2 (58−67 m), due to the different attenuation speeds of S and R waves. As for the seismic waves outside the same plane of smooth blastholes, the influence of the P wave cannot be ignored and it might become the dominant wave type somewhere. This study can help to enhance the understanding of blast-induced seismic waves.
In this paper, using polarization analysis, we characterized the seismic waves induced by the horizontal smooth blasting in a group of onsite blasting experiments, presenting interpretation of wave components and offering comparison of attenuation characteristics and evaluation of the influences of different waves. We also examined the inherent mechanical mechanism of the horizontal smooth blasting under some simplifications. The results show that the proportion of different waves and the dominant wave type both vary with the relative location of interest, and the dominant motion direction at a specific position closely correlates with the wave components. The pattern of the blasting source and the different attenuation characteristics jointly determine the wave components and their evolutions. For the horizontal smooth blasting, only S and R waves are included on the same plane of smooth blastholes, while the P wave component is negligible. The horizontal vibration is mainly caused by the R wave, while the S wave mainly vibrates in the vertical direction and its vertical velocity in the near field is much higher than that of the R wave. However, the R wave still dominates the vertical vibration if the scaled distance exceeds 22.5 m/kg1/2 (58−67 m), due to the different attenuation speeds of S and R waves. As for the seismic waves outside the same plane of smooth blastholes, the influence of the P wave cannot be ignored and it might become the dominant wave type somewhere. This study can help to enhance the understanding of blast-induced seismic waves.
2019, 39(8): 085202.
doi: 10.11883/bzycj-2018-0337
Abstract:
In the present study we found out about the optimum millisecond time for reducing vibration in hole-by-hole blasting, on the basis of an actual slope detonation work. At first we constructed a two-dimensional static model using ANSYS and determined the potential sliding surface and the static safety factor in the natural state using finite element reduction. Then we rebuilt the three-dimensional dynamic model of millisecond hole-by-hole blasting and carried out the dynamic analysis using LS-DYAN. In the whole process, we set up three holes in the same row using millisecond detonating by five differential millisecond time control of 0, 17, 25, 42 and 65 ms. At the end of the construction site, we conducted small-scale vibration tests of four millisecond time control in row holes (25 ms, 17 ms), (25 ms, 25 ms), (25 ms, 42 ms), (25 ms, 65 ms), with the stress value of the sliding surface unit during the simultaneous detonation of three holes in the simulated results taken into the formula of limit equilibrium, and drew out the time history curve of slope stability coefficient under impact loading. Analyzing the time history curve, we found that the optimum millisecond time for vibration reduction was 48 ms. Moreover, the results of three-dimensional numerical simulation and vibration test showed that the effect of vibration reduction was better when the millisecond time between holes was 42 ms. The result shows that the millisecond time, given by the slope stability coefficient, is consistent with the simulated and experimental results, which provides a reference for related research on vibration reduction of millisecond hole-by-hole blasting.
In the present study we found out about the optimum millisecond time for reducing vibration in hole-by-hole blasting, on the basis of an actual slope detonation work. At first we constructed a two-dimensional static model using ANSYS and determined the potential sliding surface and the static safety factor in the natural state using finite element reduction. Then we rebuilt the three-dimensional dynamic model of millisecond hole-by-hole blasting and carried out the dynamic analysis using LS-DYAN. In the whole process, we set up three holes in the same row using millisecond detonating by five differential millisecond time control of 0, 17, 25, 42 and 65 ms. At the end of the construction site, we conducted small-scale vibration tests of four millisecond time control in row holes (25 ms, 17 ms), (25 ms, 25 ms), (25 ms, 42 ms), (25 ms, 65 ms), with the stress value of the sliding surface unit during the simultaneous detonation of three holes in the simulated results taken into the formula of limit equilibrium, and drew out the time history curve of slope stability coefficient under impact loading. Analyzing the time history curve, we found that the optimum millisecond time for vibration reduction was 48 ms. Moreover, the results of three-dimensional numerical simulation and vibration test showed that the effect of vibration reduction was better when the millisecond time between holes was 42 ms. The result shows that the millisecond time, given by the slope stability coefficient, is consistent with the simulated and experimental results, which provides a reference for related research on vibration reduction of millisecond hole-by-hole blasting.
2019, 39(8): 085203.
doi: 10.11883/bzycj-2019-0142
Abstract:
It is helpful to blasting parameter design and blasting vibration safety evaluation to make clear the dependence of blasting vibration response on frequency and duration. The relationship between single-delay blasting vibration, multi-delay blasting vibration and single-degree-of-freedom system response is derived from the frequency domain. The influence of blasting vibration frequency and duration on the vibration response of structure is analyzed by taking the delay time and the number of blasting stages as the link. Finally, a set of measured test data is used to verify. The results show that under the delay time ∆τ, the multi-delay blasting vibration has a frequency band phenomenon of 1/∆τ. The frequency component is concentrated to the dominant frequency\begin{document}${f_{\rm{i}}} = n/\Delta \tau \left( {n \in {Z^ + }} \right)$\end{document} ![]()
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It is helpful to blasting parameter design and blasting vibration safety evaluation to make clear the dependence of blasting vibration response on frequency and duration. The relationship between single-delay blasting vibration, multi-delay blasting vibration and single-degree-of-freedom system response is derived from the frequency domain. The influence of blasting vibration frequency and duration on the vibration response of structure is analyzed by taking the delay time and the number of blasting stages as the link. Finally, a set of measured test data is used to verify. The results show that under the delay time ∆τ, the multi-delay blasting vibration has a frequency band phenomenon of 1/∆τ. The frequency component is concentrated to the dominant frequency
