2021 Vol. 41, No. 5
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2021, 41(5): 051101.
doi: 10.11883/bzycj-2020-0422
Abstract:
The traditional knowledge of plastic flow behavior of metal, dislocation activation theory, and thermoviscoplastic constitutive model of metal needs a further perfection due to the occurrence of third-type strain aging. Third-type strain aging leads to a bell-shaped flow stress-temperature curve, that is, the flow stress first increases as temperature increases, and after a peak value is reached, it decreases with further increase of temperature. Third-type strain aging occurs at both low and high strain rates. The bell-shaped segment induced by third-type strain aging on the flow stress-temperature curve shifts to higher temperature region as strain rate increases. In order to develop a systematic understanding of the third-type strain aging, firstly, macro characteristics of third-type stain aging effect that was distinguished from static strain aging effect and Portevin-Le Chatelier dynamic strain aging effect were introduced. Then, the micro mechanism of third-type strain aging and correlation of third-type strain aging, Portevin-Le Chatelier dynamic strain aging, blue brittleness phenomenon, and internal friction were systematically concluded. Third-type strain aging, Portevin-Le Chatelier dynamic strain aging, blue brittleness phenomenon, and mechanical spectroscopy are all resulted from the interaction of mobile dislocations with diffusion atoms. Third-type strain aging, Portevin-Le Chatelier dynamic strain aging, and blue brittleness phenomenon are different manifestations of dynamic strain aging. Third-type strain aging can be considered as another mode of mechanical spectroscopy. The common constitutive models are able to capture the plastic behavior of many metals under the coupling influence of strain rate and temperature in some cases. However, these thermoviscoplastic constitutive models do not take the effect of third-type strain aging into consideration, and they cannot describe the thermoviscoplastic behavior including the third-type strain aging effect. To accurately describe the plastic behavior of metals, some constitutive models including the effect of third type strain aging were proposed. The development of the thermoviscoplastic constitutive model of metal considering the effect of third type strain aging was finally introduced.
The traditional knowledge of plastic flow behavior of metal, dislocation activation theory, and thermoviscoplastic constitutive model of metal needs a further perfection due to the occurrence of third-type strain aging. Third-type strain aging leads to a bell-shaped flow stress-temperature curve, that is, the flow stress first increases as temperature increases, and after a peak value is reached, it decreases with further increase of temperature. Third-type strain aging occurs at both low and high strain rates. The bell-shaped segment induced by third-type strain aging on the flow stress-temperature curve shifts to higher temperature region as strain rate increases. In order to develop a systematic understanding of the third-type strain aging, firstly, macro characteristics of third-type stain aging effect that was distinguished from static strain aging effect and Portevin-Le Chatelier dynamic strain aging effect were introduced. Then, the micro mechanism of third-type strain aging and correlation of third-type strain aging, Portevin-Le Chatelier dynamic strain aging, blue brittleness phenomenon, and internal friction were systematically concluded. Third-type strain aging, Portevin-Le Chatelier dynamic strain aging, blue brittleness phenomenon, and mechanical spectroscopy are all resulted from the interaction of mobile dislocations with diffusion atoms. Third-type strain aging, Portevin-Le Chatelier dynamic strain aging, and blue brittleness phenomenon are different manifestations of dynamic strain aging. Third-type strain aging can be considered as another mode of mechanical spectroscopy. The common constitutive models are able to capture the plastic behavior of many metals under the coupling influence of strain rate and temperature in some cases. However, these thermoviscoplastic constitutive models do not take the effect of third-type strain aging into consideration, and they cannot describe the thermoviscoplastic behavior including the third-type strain aging effect. To accurately describe the plastic behavior of metals, some constitutive models including the effect of third type strain aging were proposed. The development of the thermoviscoplastic constitutive model of metal considering the effect of third type strain aging was finally introduced.
2021, 41(5): 052201.
doi: 10.11883/bzycj-2021-0075
Abstract:
Aiming at the process of uranium material forming radioactive aerosol under the action of explosion load, numerical simulation and experimental research were carried out based on the smoothed particle hydrodynamic method (SPH method). Through the combination of particle dynamics and SPH method, a numerical simulation model of explosive detonation acting on a uranium metal shell was established, which would be used to describe the formation process of uranium aerosol. The specific internal energy of uranium material was used as the aerosol conversion criterion, and the physical process of uranium material conversion into aerosol was obtained. We found two types of damage mode of the uranium under explosive load, one was overall damage when the uranium shell mass was close to the explosive mass, and the other one was crushing damage when the uranium shell mass was much less than the explosive mass. Under the same explosive equivalent, the aerosol conversion efficiencies of uranium materials with different mass were compared with the experimental results. The results show that uranium material can be considered to be completely converted into aerosol when its specific internal energy reaches 1.9 MJ/kg under explosive load. According to the explosive device structure in this paper, when the explosive mass is six times than the mass of uranium, the conversion ratio exceeds 90%. The experimental results have a good agreement with the numerical simulations, which shows that the method used in this paper can accurately describe the aerosol conversion process of uranium materials.
Aiming at the process of uranium material forming radioactive aerosol under the action of explosion load, numerical simulation and experimental research were carried out based on the smoothed particle hydrodynamic method (SPH method). Through the combination of particle dynamics and SPH method, a numerical simulation model of explosive detonation acting on a uranium metal shell was established, which would be used to describe the formation process of uranium aerosol. The specific internal energy of uranium material was used as the aerosol conversion criterion, and the physical process of uranium material conversion into aerosol was obtained. We found two types of damage mode of the uranium under explosive load, one was overall damage when the uranium shell mass was close to the explosive mass, and the other one was crushing damage when the uranium shell mass was much less than the explosive mass. Under the same explosive equivalent, the aerosol conversion efficiencies of uranium materials with different mass were compared with the experimental results. The results show that uranium material can be considered to be completely converted into aerosol when its specific internal energy reaches 1.9 MJ/kg under explosive load. According to the explosive device structure in this paper, when the explosive mass is six times than the mass of uranium, the conversion ratio exceeds 90%. The experimental results have a good agreement with the numerical simulations, which shows that the method used in this paper can accurately describe the aerosol conversion process of uranium materials.
2021, 41(5): 053101.
doi: 10.11883/bzycj-2020-0071
Abstract:
The dynamics of HMX single crystals under ramp wave loading was studied experimentally and numerically. The ramp wave compression experiments of (010) and (011) crystal oriented HMX crystals within 15 GPa were carried out with the magnetic driven device CQ-4, which can provide a loading pressure with a rising time of 450−600 ns. The velocity curves of the interface between the HMX single crystal and the LiF single crystal were obtained with dual laser heterodyne velocimetry (DLHV). The experimental results show that there is an obvious elastic-plastic transition behavior in the loading section. The velocity waveforms have a downward trend in the elastic-plastic transition section, which is caused by the viscous effect of the HMX single crystal. The elastic limit of the HMX single crystal changes with the increase of the sample thickness. The Lagrange sound speed-particle velocity data and pressure-specific volume curves of (010) and (011) crystal oriented HMX crystals were obtained with the iterative Lagrange data processing method for dynamic impedance mismatch. The Lagrange sound speed-particle velocity relationships in the different crystal directions are different. The pressure-specific volume curve is close to isentropic experimental data by Sandia laboratory. The numerical simulation of the physical process of ramp wave compression of the HMX crystal was carried out with the viscoelastic plastic constitutive relation of Hobnemser-Prager and the third-order Birch-Murnaghan equation of state. The calculation results can well describe the physical process of the elastic-plastic transformation of HMX crystal.
The dynamics of HMX single crystals under ramp wave loading was studied experimentally and numerically. The ramp wave compression experiments of (010) and (011) crystal oriented HMX crystals within 15 GPa were carried out with the magnetic driven device CQ-4, which can provide a loading pressure with a rising time of 450−600 ns. The velocity curves of the interface between the HMX single crystal and the LiF single crystal were obtained with dual laser heterodyne velocimetry (DLHV). The experimental results show that there is an obvious elastic-plastic transition behavior in the loading section. The velocity waveforms have a downward trend in the elastic-plastic transition section, which is caused by the viscous effect of the HMX single crystal. The elastic limit of the HMX single crystal changes with the increase of the sample thickness. The Lagrange sound speed-particle velocity data and pressure-specific volume curves of (010) and (011) crystal oriented HMX crystals were obtained with the iterative Lagrange data processing method for dynamic impedance mismatch. The Lagrange sound speed-particle velocity relationships in the different crystal directions are different. The pressure-specific volume curve is close to isentropic experimental data by Sandia laboratory. The numerical simulation of the physical process of ramp wave compression of the HMX crystal was carried out with the viscoelastic plastic constitutive relation of Hobnemser-Prager and the third-order Birch-Murnaghan equation of state. The calculation results can well describe the physical process of the elastic-plastic transformation of HMX crystal.
2021, 41(5): 053102.
doi: 10.11883/bzycj-2020-0125
Abstract:
To deeply understanding dynamic fracture properties and preventing crack propagation of fractured rock mass under dynamic loads, impact experiments were conducted using TWSRC (tunnel with single radial crack) samples, and sandstone were selected as the raw material to manufacture fractured rock samples. The crack initiation, propagation and obstructing behavior were measured by using a drop hammer impact test device and crack propagation gauge measuring system. The mechanism of preventing crack propagation and failure behavior during dynamic fracturing process was focused, and then the corresponding numerical simulation was conducted by using the finite difference code, which can be used to accurately estimate the experiment result. The results indicate that the whole dynamic fracturing process of fractured rock under dynamic loads is composed of the cyclic process of crack initiation, high-speed crack propagation, slowly deceleration, preventing crack propagation. In addition, the period of crack obstruction was approximate the microsecond level. The ratio of transgranular (TG) fracture at the crack obstruction point of fractured rock was smaller than that of the crack initiation point, and the ratio of TG fracture of green sandstone during the dynamic fracturing process was larger than that of black sandstone. The fracture energy for crack initiation again after crack obstruction was much less than the fracture energy required for the initial initiation of pre-existing crack.
To deeply understanding dynamic fracture properties and preventing crack propagation of fractured rock mass under dynamic loads, impact experiments were conducted using TWSRC (tunnel with single radial crack) samples, and sandstone were selected as the raw material to manufacture fractured rock samples. The crack initiation, propagation and obstructing behavior were measured by using a drop hammer impact test device and crack propagation gauge measuring system. The mechanism of preventing crack propagation and failure behavior during dynamic fracturing process was focused, and then the corresponding numerical simulation was conducted by using the finite difference code, which can be used to accurately estimate the experiment result. The results indicate that the whole dynamic fracturing process of fractured rock under dynamic loads is composed of the cyclic process of crack initiation, high-speed crack propagation, slowly deceleration, preventing crack propagation. In addition, the period of crack obstruction was approximate the microsecond level. The ratio of transgranular (TG) fracture at the crack obstruction point of fractured rock was smaller than that of the crack initiation point, and the ratio of TG fracture of green sandstone during the dynamic fracturing process was larger than that of black sandstone. The fracture energy for crack initiation again after crack obstruction was much less than the fracture energy required for the initial initiation of pre-existing crack.
2021, 41(5): 053103.
doi: 10.11883/bzycj-2020-0072
Abstract:
With the increasing demand for coal resources, safe and efficient coal mining has attracted the attention of all sectors of society. In order to study the dynamic failure characteristics and constitutive relation of coal rock under different strain rates, uniaxial impact compression tests of coal rock were carried out over a strain rate range from 20 s−1 to 100 s−1 under nine air pressures by using a split Hopkinson pressure bar (SHPB) with a diameter of 50 mm, and a high-speed camera was used to monitor the whole process of coal rock failure. Based on the dynamic mechanical properties and fracture fractal dimension characteristics of coal rock under different strain rates, the dynamic failure characteristics of coal rock were deeply analyzed, and a dynamic strength statistical damage constitutive model was established based on Weibull statistical distribution and Drucker-Prager failure criterion. The results show that the dynamic stress-strain curves of coal rock under different strain rates exhibit obvious nonlinear characteristics, which can be roughly divided into linear elastic stage, plastic yield stage, peak stress stage and post-peak softening stage. As strain rate increases, dynamic uniaxial compressive strength and elastic modulus both show a significant linear growth. The failure mode of coal rock changes from axial cleaving failure at low strain rate to crushing failure at high strain rate. Coal rock fragments after dynamic failure are sieved and found to have obvious fractal characteristics. At the strain rates of 20−100 s−1, average fragmentation of coal rock samples is concentrated in 30−40 mm, and fractal dimension ranges from 1.9 to 2.2. With the increase of strain rate, the degree of fragmentation increases and fractal dimension increases, indicating that the proportion of large-scale coal rock fragments to the total mass gradually decreases. Based on the relationship between the Weibull distribution parameters F0, m and strain rate, the dynamic constitutive model of coal rock is modified. Comparing the model results with test results, it is found that the model can fully reflect the relationship between stress, strain and strain rate, and the rationality of this model is also verified.
With the increasing demand for coal resources, safe and efficient coal mining has attracted the attention of all sectors of society. In order to study the dynamic failure characteristics and constitutive relation of coal rock under different strain rates, uniaxial impact compression tests of coal rock were carried out over a strain rate range from 20 s−1 to 100 s−1 under nine air pressures by using a split Hopkinson pressure bar (SHPB) with a diameter of 50 mm, and a high-speed camera was used to monitor the whole process of coal rock failure. Based on the dynamic mechanical properties and fracture fractal dimension characteristics of coal rock under different strain rates, the dynamic failure characteristics of coal rock were deeply analyzed, and a dynamic strength statistical damage constitutive model was established based on Weibull statistical distribution and Drucker-Prager failure criterion. The results show that the dynamic stress-strain curves of coal rock under different strain rates exhibit obvious nonlinear characteristics, which can be roughly divided into linear elastic stage, plastic yield stage, peak stress stage and post-peak softening stage. As strain rate increases, dynamic uniaxial compressive strength and elastic modulus both show a significant linear growth. The failure mode of coal rock changes from axial cleaving failure at low strain rate to crushing failure at high strain rate. Coal rock fragments after dynamic failure are sieved and found to have obvious fractal characteristics. At the strain rates of 20−100 s−1, average fragmentation of coal rock samples is concentrated in 30−40 mm, and fractal dimension ranges from 1.9 to 2.2. With the increase of strain rate, the degree of fragmentation increases and fractal dimension increases, indicating that the proportion of large-scale coal rock fragments to the total mass gradually decreases. Based on the relationship between the Weibull distribution parameters F0, m and strain rate, the dynamic constitutive model of coal rock is modified. Comparing the model results with test results, it is found that the model can fully reflect the relationship between stress, strain and strain rate, and the rationality of this model is also verified.
2021, 41(5): 053301.
doi: 10.11883/bzycj-2020-0063
Abstract:
Zr-based metallic glass reinforced porous W matrix composite was prepared into fragments and loaded with grenade to study on penetration ability and aftereffect of fragments by explosion experiment. The results show that the Zr-based metallic glass reinforced porous W matrix composite has high density and strength, and the explosive integrity and penetration ability can meet the requirements of the shrapnel preformed fragments; the deformation of the Zr-based metallic glass reinforced porous W matrix composite fragments during the penetration process is one of the main reasons affecting the penetration ability of the metallic glass composite fragments; if the penetration ratio is high enough, the detonation effect of the preformed fragments can ignite the quilt and oil tank behind the target.
Zr-based metallic glass reinforced porous W matrix composite was prepared into fragments and loaded with grenade to study on penetration ability and aftereffect of fragments by explosion experiment. The results show that the Zr-based metallic glass reinforced porous W matrix composite has high density and strength, and the explosive integrity and penetration ability can meet the requirements of the shrapnel preformed fragments; the deformation of the Zr-based metallic glass reinforced porous W matrix composite fragments during the penetration process is one of the main reasons affecting the penetration ability of the metallic glass composite fragments; if the penetration ratio is high enough, the detonation effect of the preformed fragments can ignite the quilt and oil tank behind the target.
2021, 41(5): 053302.
doi: 10.11883/bzycj-2020-0129
Abstract:
Crater characteristics formed by the impact of the 5 cm thick Al 6061 targets with magnesium projectiles with length-diameter ratio l/dp=1/2 and diameter dp=0.8 cm at velocity of 10 km/s were investigated. The implosion-driven launcher designed by McGill University was manufactured by China Aerodynamics Research and Development Center. Eight experiments were carried out and the obtained maximal projectile velocities were in the range of 9.36−11.43 km/s. The profiles and flight attitude of projectile were snapped by use of the sequence laser shadowgraph imaging instrument. The results show that the projectiles deform obviously during the launching period in some experiments, but more than half projectiles could hold the initial shape well. Craters on targets were recovered and analyzed. A shallow damage area appeared around the semi-spherical crater. Such crater feature was compared with those craters impacted at velocity lower than 8 km/s in literatures and from other experiments with different projectile materials and aluminum types of targets. Typical dimensions of craters were measured. The crater depths Pc/dp was 1.5−2.0, crater diameters dc/dp was 3.0−3.5, crater-shape coefficient Pc/dc was about 0.50 and cratering efficiency E/Vc was about 3.74 kJ/cm3. Finally, the influences of l/dp, impact velocity and energy of projectiles on crater dimensions were analyzed along with the experimental data from literatures. An effective diameter of cylindrical projectile was proposed to reduce the effect of l/dp on the crater depth. And a crater depth formula of aluminum targets impacted by projectiles with different materials and velocities were fitted. Results show that the typical impact crater should not only be the central semi-sphere crater, but also contain shallow damage area formed by surface spallation. The type of target material influences the carter feature significantly. However, the projectile material and flight attitude have little influence on the crater feature. As for projectiles with l/dp≤1, the crater depth normalized by effective diameter would not vary with l/dp, but correlate with the impact velocity in form of 2/3 power law.
Crater characteristics formed by the impact of the 5 cm thick Al 6061 targets with magnesium projectiles with length-diameter ratio l/dp=1/2 and diameter dp=0.8 cm at velocity of 10 km/s were investigated. The implosion-driven launcher designed by McGill University was manufactured by China Aerodynamics Research and Development Center. Eight experiments were carried out and the obtained maximal projectile velocities were in the range of 9.36−11.43 km/s. The profiles and flight attitude of projectile were snapped by use of the sequence laser shadowgraph imaging instrument. The results show that the projectiles deform obviously during the launching period in some experiments, but more than half projectiles could hold the initial shape well. Craters on targets were recovered and analyzed. A shallow damage area appeared around the semi-spherical crater. Such crater feature was compared with those craters impacted at velocity lower than 8 km/s in literatures and from other experiments with different projectile materials and aluminum types of targets. Typical dimensions of craters were measured. The crater depths Pc/dp was 1.5−2.0, crater diameters dc/dp was 3.0−3.5, crater-shape coefficient Pc/dc was about 0.50 and cratering efficiency E/Vc was about 3.74 kJ/cm3. Finally, the influences of l/dp, impact velocity and energy of projectiles on crater dimensions were analyzed along with the experimental data from literatures. An effective diameter of cylindrical projectile was proposed to reduce the effect of l/dp on the crater depth. And a crater depth formula of aluminum targets impacted by projectiles with different materials and velocities were fitted. Results show that the typical impact crater should not only be the central semi-sphere crater, but also contain shallow damage area formed by surface spallation. The type of target material influences the carter feature significantly. However, the projectile material and flight attitude have little influence on the crater feature. As for projectiles with l/dp≤1, the crater depth normalized by effective diameter would not vary with l/dp, but correlate with the impact velocity in form of 2/3 power law.
2021, 41(5): 053303.
doi: 10.11883/bzycj-2020-0473
Abstract:
To improve the ballistic performance of metal targets, a metallic structure composed of a series of crescent-shaped cavity cells, whose spatial distribution is similar to a honeycomb, was proposed. Each cavity cell is formed by two balls with an identical diameter offset by a certain distance and its shape looks like a crescent moon. The deflection performance of crescent-shaped cavity structures impacted by 12.7 mm armor-piercing incendiary projectile cores at an initial velocity of 818 m/s was studied numerically. Based on 3D voxel models, numerical simulation was carried out by using the finite element code ABAQUS/Explicit. The deflection angle of the projectile related to the initial impact direction was measured in the process of penetration simulation. By comparing with the experimental results in the literature, a virtual test was carried out to verify the validity of the finite element model. The influences of crescent shape, hitting position and space arrangement of cavity cells on the deflection performance were analyzed. The results show that the crescent shape has a significant effect on the overall deflection performance of the target. The deflection angle of the projectile increases with the increase of the cavity diameter, but the protection performance of the structure with larger cavity diameter becomes weaker. A cavity diameter of 18 mm with the offset distance of 5.4 mm may be appropriate when considering a high deflection performance without significant drop of the protection performance of the target plate. The target impacted by the projectile at different hitting positions shows different deflection performances. The deflection angle of the projectile is much large at those positions where the material distribution has a high asymmetry. The asymmetric treatment of the space arrangement of cavity cells can improve the deflection effect of the cavity structure. The deflection mechanism of the cavity structure is that when the projectile penetrates the interface between the material and cavity inside the target plate, the projectile is subjected to an asymmetric force distribution, which affects the subsequent penetration process.
To improve the ballistic performance of metal targets, a metallic structure composed of a series of crescent-shaped cavity cells, whose spatial distribution is similar to a honeycomb, was proposed. Each cavity cell is formed by two balls with an identical diameter offset by a certain distance and its shape looks like a crescent moon. The deflection performance of crescent-shaped cavity structures impacted by 12.7 mm armor-piercing incendiary projectile cores at an initial velocity of 818 m/s was studied numerically. Based on 3D voxel models, numerical simulation was carried out by using the finite element code ABAQUS/Explicit. The deflection angle of the projectile related to the initial impact direction was measured in the process of penetration simulation. By comparing with the experimental results in the literature, a virtual test was carried out to verify the validity of the finite element model. The influences of crescent shape, hitting position and space arrangement of cavity cells on the deflection performance were analyzed. The results show that the crescent shape has a significant effect on the overall deflection performance of the target. The deflection angle of the projectile increases with the increase of the cavity diameter, but the protection performance of the structure with larger cavity diameter becomes weaker. A cavity diameter of 18 mm with the offset distance of 5.4 mm may be appropriate when considering a high deflection performance without significant drop of the protection performance of the target plate. The target impacted by the projectile at different hitting positions shows different deflection performances. The deflection angle of the projectile is much large at those positions where the material distribution has a high asymmetry. The asymmetric treatment of the space arrangement of cavity cells can improve the deflection effect of the cavity structure. The deflection mechanism of the cavity structure is that when the projectile penetrates the interface between the material and cavity inside the target plate, the projectile is subjected to an asymmetric force distribution, which affects the subsequent penetration process.
2021, 41(5): 053304.
doi: 10.11883/bzycj-2020-0148
Abstract:
In order to explore the ballistic characteristics of a 9 mm pistol bullet penetrating wooden target board, a ballistic penetration experiment was carried out by choosing medium density fiberboard (MDF) as the research object. Key information such as the residual velocity and depth of penetration to the bullet at different velocities and impact angles was obtained by reducing the charge and adjusting the angle adjustable target frame. The experiment results were analyzed by the Poncelet resistance model, and the relationship between depth of penetration and penetration velocity was obtained. The numerical calculation model of the pistol bullet penetrating the MDF was established. The model studied the deflection behavior of bullet with different velocity and different impact angles, and the functional relationship between the critical ricochet angle and the target velocity was obtained. The results show that when the bullet penetrates the MDF with the thickness of 25 mm, the energy loss is linearly related to the incident velocity; when the bullet penetrates the MDF, it will deflect in the negative direction, and the reduction of the bullet velocity or the reduction of the impact angle will increase the deflection angle in the negative direction. When the bullet penetrates the MDF at a low velocity or the impact angle is less than 45°, the bullet shows a large deflection angle. When the bullet shoots out of the MDF, the trajectory turns positive.
In order to explore the ballistic characteristics of a 9 mm pistol bullet penetrating wooden target board, a ballistic penetration experiment was carried out by choosing medium density fiberboard (MDF) as the research object. Key information such as the residual velocity and depth of penetration to the bullet at different velocities and impact angles was obtained by reducing the charge and adjusting the angle adjustable target frame. The experiment results were analyzed by the Poncelet resistance model, and the relationship between depth of penetration and penetration velocity was obtained. The numerical calculation model of the pistol bullet penetrating the MDF was established. The model studied the deflection behavior of bullet with different velocity and different impact angles, and the functional relationship between the critical ricochet angle and the target velocity was obtained. The results show that when the bullet penetrates the MDF with the thickness of 25 mm, the energy loss is linearly related to the incident velocity; when the bullet penetrates the MDF, it will deflect in the negative direction, and the reduction of the bullet velocity or the reduction of the impact angle will increase the deflection angle in the negative direction. When the bullet penetrates the MDF at a low velocity or the impact angle is less than 45°, the bullet shows a large deflection angle. When the bullet shoots out of the MDF, the trajectory turns positive.
2021, 41(5): 054101.
doi: 10.11883/bzycj-2020-0302
Abstract:
In testing explosion flame temperature with radiation thermometry, there is relatively great deviation of empirical value of flame emissivity from flame combustion mechanism. Meanwhile, the distance of measure point from the flame and ambient temperature and humidity also cause attenuation of thermal radiation to different extent, affecting the accuracy of measurement of explosion flame’s temperature. With focuses on foregoing two problems and based on atmospheric radiation theory and the law of optics propagation, a model of radiation path attenuation compensation was deduced in accordance with the functional relation among explosion flame’s radiance, digital output value of thermal imager and explosion flame’s temperature, followed by obtainment of relevant parameters i.e. system responsivity in the model from radiometric calibration of thermal imager; then, the applicability of the gray body hypothesis of TNT explosion flame was confirmed by analyzing the composition of the products of TNT explosion flame. Therefore, a function model of explosion flame’s dynamic average emissivity was deduced concerning onsite atmospheric transmittance, digital output value of thermal imager and explosion flame’s temperature measured by the colorimetric thermometer in accordance with the expression of explosion flame’s radiance; finally, based on the receiver function of thermal imager’s effective radiation, a joint temperature compensation evaluation method, which combines radiation path compensation and dynamic emissivity, was proposed for joint inversion of explosion flame’s temperature at the explosion site and the range of temperature error of inversion was obtained through comparison of measured result with explosion flame’s surface temperature measured by colorimetric thermometer. The test result suggests the error of explosion flame’s temperature measured with the proposed compensation model is reduced to 11.292%−59.077% from previous 55.699%−89.847% before compensation, thus effectively improving the accuracy of measurement of transient flame temperature of explosion at external field and providing a means for accurate infrared thermography-based evaluation of thermal effect in explosion field.
In testing explosion flame temperature with radiation thermometry, there is relatively great deviation of empirical value of flame emissivity from flame combustion mechanism. Meanwhile, the distance of measure point from the flame and ambient temperature and humidity also cause attenuation of thermal radiation to different extent, affecting the accuracy of measurement of explosion flame’s temperature. With focuses on foregoing two problems and based on atmospheric radiation theory and the law of optics propagation, a model of radiation path attenuation compensation was deduced in accordance with the functional relation among explosion flame’s radiance, digital output value of thermal imager and explosion flame’s temperature, followed by obtainment of relevant parameters i.e. system responsivity in the model from radiometric calibration of thermal imager; then, the applicability of the gray body hypothesis of TNT explosion flame was confirmed by analyzing the composition of the products of TNT explosion flame. Therefore, a function model of explosion flame’s dynamic average emissivity was deduced concerning onsite atmospheric transmittance, digital output value of thermal imager and explosion flame’s temperature measured by the colorimetric thermometer in accordance with the expression of explosion flame’s radiance; finally, based on the receiver function of thermal imager’s effective radiation, a joint temperature compensation evaluation method, which combines radiation path compensation and dynamic emissivity, was proposed for joint inversion of explosion flame’s temperature at the explosion site and the range of temperature error of inversion was obtained through comparison of measured result with explosion flame’s surface temperature measured by colorimetric thermometer. The test result suggests the error of explosion flame’s temperature measured with the proposed compensation model is reduced to 11.292%−59.077% from previous 55.699%−89.847% before compensation, thus effectively improving the accuracy of measurement of transient flame temperature of explosion at external field and providing a means for accurate infrared thermography-based evaluation of thermal effect in explosion field.
2021, 41(5): 054102.
doi: 10.11883/bzycj-2020-0151
Abstract:
The attitude measurement of a flyer plate is the basis for explosive welding mechanism study. Besides, the key parameters affecting the quality of explosive welding products in the actual explosive processing, including the collision point velocity, the dynamic angle of collision and the impact velocity of the flyer plate, must be determined on the premise by measuring the deformation curve of the flyer plate. Despite the readily available device and convenient operation, the measuring process of the traditional electrical method is easily disturbed by external uncertain factors, and susceptible to bending waves generated by the resistance wire itself. In view of the above shortcomings, a velocity probe-based method was innovatively developed for determining the flyer plate motion of explosive welding in the field. First of all, a velocity probe-based test device, which can effectively suppress the generation and influence of electromagnetic radiation, metal jet and bending wave, was designed and the geometric relationship between the probe data and the flyer plate motion curve was established. After that, three types of trapezoidal velocity probes with different structures were developed, whose conducting pressure and response time were analyzed by the finite element program. Based on the analysis results, two sets of explosive welding experiments were carried out for the three types of probes. The experimental results show that the test performance of the first type (without conducting medium) and the second type (threaded wire type) are not ideal, and there are a lot of data oscillation in the test curves, while the third type of probes (metal mesh type) overcomes the shortcomings of the above two types of probes, whose test curves are smooth without oscillation. The motion attitude curve of the flyer plate was then obtained based on the results of the metal mesh probe, which was in good agreement with the calculation results by Richter's simplified model. The present test method makes it possible to determine detonation velocity and flyer plate attitude continuously, reliably and rapidly, which provides a supplement for the study of the driving problem of sliding detonation and the equation of state of detonation products.
The attitude measurement of a flyer plate is the basis for explosive welding mechanism study. Besides, the key parameters affecting the quality of explosive welding products in the actual explosive processing, including the collision point velocity, the dynamic angle of collision and the impact velocity of the flyer plate, must be determined on the premise by measuring the deformation curve of the flyer plate. Despite the readily available device and convenient operation, the measuring process of the traditional electrical method is easily disturbed by external uncertain factors, and susceptible to bending waves generated by the resistance wire itself. In view of the above shortcomings, a velocity probe-based method was innovatively developed for determining the flyer plate motion of explosive welding in the field. First of all, a velocity probe-based test device, which can effectively suppress the generation and influence of electromagnetic radiation, metal jet and bending wave, was designed and the geometric relationship between the probe data and the flyer plate motion curve was established. After that, three types of trapezoidal velocity probes with different structures were developed, whose conducting pressure and response time were analyzed by the finite element program. Based on the analysis results, two sets of explosive welding experiments were carried out for the three types of probes. The experimental results show that the test performance of the first type (without conducting medium) and the second type (threaded wire type) are not ideal, and there are a lot of data oscillation in the test curves, while the third type of probes (metal mesh type) overcomes the shortcomings of the above two types of probes, whose test curves are smooth without oscillation. The motion attitude curve of the flyer plate was then obtained based on the results of the metal mesh probe, which was in good agreement with the calculation results by Richter's simplified model. The present test method makes it possible to determine detonation velocity and flyer plate attitude continuously, reliably and rapidly, which provides a supplement for the study of the driving problem of sliding detonation and the equation of state of detonation products.
2021, 41(5): 055201.
doi: 10.11883/bzycj-2020-0004
Abstract:
The peak pressure of borehole wall in decoupling charge blasting is an important parameter to control the quality of rock mass profile forming and to carry out numerical simulation analysis of blasting vibration response of non-fluid-solid coupling. In this paper, the peak pressure of borehole wall in decoupling charge blasting was studied from an experimental perspective. Based on the characteristics that the difference between the two higher wave impedance media, steel pipe and rock, has little effect on the peak pressure of borehole wall, the seamless thin-walled steel pipe made of 20# steel was used to simulate the borehole in decoupling blasting with high-sensitivity-high-precision strain gauge as sensor, four strain gauges arranged along the circumferential direction of a certain section of each steel pipe. Ultrahigh dynamic strainometer was used to collect the circumferential strain of steel pipe during the explosion process of built-in columnar explosive cartridge; the method of calculating the dynamic response of thin-walled cylinder under dynamic load is used to calculate the collected circumferential strain; the elastic dynamic formula of the thin-walled cylinder was used to deduce the collected circumferential strain; and the peak pressure on the borehole wall by the air shock wave has been measured indirectly. The peak pressure on the borehole wall under six working conditions was obtained, and calculated the ratio of the experimental values to the quasi-static gas-pressure under the corresponding working conditions to obtain increase multiples. The decoupling coefficient was taken as the abscissa and the pressure increase multiple as the ordinate for the fitting, the fitting results indicate that the pressure increase multiples increase approximately linearly with the increase of the decoupling coefficients, and the fitting correlation coefficient is as high as 0.99 or more.At the same time, the reasons why the experimental results under some working conditions are unsatisfactory have been analyzed, which can be referred to the measurement and calculation of the peak pressure of borehole wall in contour blasting.
The peak pressure of borehole wall in decoupling charge blasting is an important parameter to control the quality of rock mass profile forming and to carry out numerical simulation analysis of blasting vibration response of non-fluid-solid coupling. In this paper, the peak pressure of borehole wall in decoupling charge blasting was studied from an experimental perspective. Based on the characteristics that the difference between the two higher wave impedance media, steel pipe and rock, has little effect on the peak pressure of borehole wall, the seamless thin-walled steel pipe made of 20# steel was used to simulate the borehole in decoupling blasting with high-sensitivity-high-precision strain gauge as sensor, four strain gauges arranged along the circumferential direction of a certain section of each steel pipe. Ultrahigh dynamic strainometer was used to collect the circumferential strain of steel pipe during the explosion process of built-in columnar explosive cartridge; the method of calculating the dynamic response of thin-walled cylinder under dynamic load is used to calculate the collected circumferential strain; the elastic dynamic formula of the thin-walled cylinder was used to deduce the collected circumferential strain; and the peak pressure on the borehole wall by the air shock wave has been measured indirectly. The peak pressure on the borehole wall under six working conditions was obtained, and calculated the ratio of the experimental values to the quasi-static gas-pressure under the corresponding working conditions to obtain increase multiples. The decoupling coefficient was taken as the abscissa and the pressure increase multiple as the ordinate for the fitting, the fitting results indicate that the pressure increase multiples increase approximately linearly with the increase of the decoupling coefficients, and the fitting correlation coefficient is as high as 0.99 or more.At the same time, the reasons why the experimental results under some working conditions are unsatisfactory have been analyzed, which can be referred to the measurement and calculation of the peak pressure of borehole wall in contour blasting.
2021, 41(5): 055202.
doi: 10.11883/bzycj-2020-0123
Abstract:
Aiming at the measured vibration signals collected during tunnel blasting construction, a noise reduction method based on the overall average empirical mode decomposition method (CEEMDAN decomposition) combined with wavelet packet analysis was in troduced. First, a series of multiple intrinsic modal components were obtained by CEEMDAN decomposition, and the modal components containing noise were selected using correlation coefficients, checked by the spectrogram and the variance contribution rate of the modal components. Then, the wavelet packet threshold noise reduction method was used to process the modal components containing noise. Finally, the unprocessed modal components and the de-noised components were reconstructed to obtain the final pure blasting vibration signal. At the same time, the feasibility of this noise reduction method has been verified by wavelet packet energy spectrum analysis. This method combines the advantages of CEEMDAN decomposition and wavelet packet analysis. Compared with existing methods, the de-noising effect is better, and it can be applied to the de-noising processing of similar tunnel blasting signals.
Aiming at the measured vibration signals collected during tunnel blasting construction, a noise reduction method based on the overall average empirical mode decomposition method (CEEMDAN decomposition) combined with wavelet packet analysis was in troduced. First, a series of multiple intrinsic modal components were obtained by CEEMDAN decomposition, and the modal components containing noise were selected using correlation coefficients, checked by the spectrogram and the variance contribution rate of the modal components. Then, the wavelet packet threshold noise reduction method was used to process the modal components containing noise. Finally, the unprocessed modal components and the de-noised components were reconstructed to obtain the final pure blasting vibration signal. At the same time, the feasibility of this noise reduction method has been verified by wavelet packet energy spectrum analysis. This method combines the advantages of CEEMDAN decomposition and wavelet packet analysis. Compared with existing methods, the de-noising effect is better, and it can be applied to the de-noising processing of similar tunnel blasting signals.
2021, 41(5): 055401.
doi: 10.11883/bzycj-2020-0131
Abstract:
In this study, the explosion hazard and suppression technology were investigated in a concentrated ventilation tube filled with diesel fuel under room temperature and environmental pressure. A high-speed camera (model: nac HX-3) and pressure sensors (model: CY-YD-205) were used to record the flame picture and explosion overpressure. New explosion suppression balls and an ordinary corrugated flame arrester were employed as explosion suppression apparatuses. The results indicate that the explosion flame can propagate into the adjacent fuel tank through the ventilation tube under room temperature and environmental pressure, causing the second explosion. In addition, the ordinary corrugated flame arrester fails to suppress explosion, and the new explosion suppression balls have better anti-explosion effect. Compared to the case of a smooth ventilation tube, the maximum explosion overpressure can be significantly decreased from about 552.5 kPa to 35.0 kPa in the ignited chamber after the new explosion suppression balls are introduced into the tube. The superior explosion suppression effect of the explosion suppression balls can be due to the hollow porous structures. The porous structures not only can significantly increase the specific surface area and heat loss, but also can effectively segment and weaken the reaction surface.
In this study, the explosion hazard and suppression technology were investigated in a concentrated ventilation tube filled with diesel fuel under room temperature and environmental pressure. A high-speed camera (model: nac HX-3) and pressure sensors (model: CY-YD-205) were used to record the flame picture and explosion overpressure. New explosion suppression balls and an ordinary corrugated flame arrester were employed as explosion suppression apparatuses. The results indicate that the explosion flame can propagate into the adjacent fuel tank through the ventilation tube under room temperature and environmental pressure, causing the second explosion. In addition, the ordinary corrugated flame arrester fails to suppress explosion, and the new explosion suppression balls have better anti-explosion effect. Compared to the case of a smooth ventilation tube, the maximum explosion overpressure can be significantly decreased from about 552.5 kPa to 35.0 kPa in the ignited chamber after the new explosion suppression balls are introduced into the tube. The superior explosion suppression effect of the explosion suppression balls can be due to the hollow porous structures. The porous structures not only can significantly increase the specific surface area and heat loss, but also can effectively segment and weaken the reaction surface.
2021, 41(5): 055402.
doi: 10.11883/bzycj-2020-0144
Abstract:
In order to study the incentive effect of flexible obstacles on methane-air explosion waves, a biaxially oriented polypropylene ( BOPP) film was used as a flexible obstacle to separate the methane-air premixed gas from the air in the pipeline, the difference of the flame and shock wave before and after they propagated through the obstacle was compared, and the mechanism of the incentive effect of the flexible membrane obstacle was analyzed. The experimental results show that the incentive effect of this flexible obstacle with certain pressure-bearing capacity on the methane explosion wave cannot be ignored. Multiple reflections of shock wave before the rupture of the flexible membrane can result in the formation of turbulent flame, and thus greatly increase the explosion pressure. After the rupture of the flexible membrane, the velocity of the flame increases suddenly under the action of the concomitant flow and approaches the shock wave, resulting in a great increase in the explosion pressure behind the membrane. The experimental data show that the difference in the maximum explosion pressure between the locations before and after the membrane is five times and the corresponding difference of flame velocity is seven times. In addition, it is found that the incentive effect can be enhanced by adding an additional membrane after the original one with a prescribed distance and the essential role of the additional membrane is to increase the interaction numbers between the shock wave and the flame.
In order to study the incentive effect of flexible obstacles on methane-air explosion waves, a biaxially oriented polypropylene ( BOPP) film was used as a flexible obstacle to separate the methane-air premixed gas from the air in the pipeline, the difference of the flame and shock wave before and after they propagated through the obstacle was compared, and the mechanism of the incentive effect of the flexible membrane obstacle was analyzed. The experimental results show that the incentive effect of this flexible obstacle with certain pressure-bearing capacity on the methane explosion wave cannot be ignored. Multiple reflections of shock wave before the rupture of the flexible membrane can result in the formation of turbulent flame, and thus greatly increase the explosion pressure. After the rupture of the flexible membrane, the velocity of the flame increases suddenly under the action of the concomitant flow and approaches the shock wave, resulting in a great increase in the explosion pressure behind the membrane. The experimental data show that the difference in the maximum explosion pressure between the locations before and after the membrane is five times and the corresponding difference of flame velocity is seven times. In addition, it is found that the incentive effect can be enhanced by adding an additional membrane after the original one with a prescribed distance and the essential role of the additional membrane is to increase the interaction numbers between the shock wave and the flame.
