2021 Vol. 41, No. 7
Display Method:
Read OL
PDF 
Cited by
2021, 41(7): 071101.
doi: 10.11883/bzycj-2021-0023
Abstract:
Based on the research of Academician Tan Tjong-Kie on the long-term stability mechanics of underground tunnel and considering Academician Sadovsky’s structural hierarchy theories on complex geological rock masses, the inherent statistical mechanical properties of inhomogeneous structure and closed stress in deep rock masses were investigated. Two mechanical problems were mainly studied, i.e. characteristics of inherent non-uniform deformation and closed stress of rock masses, and long-term stability of deep tunnels. The quantitative mathematical characterization of inherent non-uniform deformation and closed stress of rock masses were given using the method of statistical mechanics. Based on the law of mass conservation, a general calculation method of long-term stability and deformation of rock masses surrounding deep level tunnels was proposed. The Maxwell model was used to calculate the threshold of splitting. A post-peak failure model of rock was established to estimate the in-situ stress at which rock undergoes post-peak failure. With the help of the theory of the hirerachical structure of rock masses, the maximum value of rock displacement due to splitting dilatation was obtained. A dimensionless energy factor was introduced to define the extent of zonal disintegration of surrounding rock masses. It was concluded that the splitting and dilatancy deformation is the main part of the deformation of surrounding rocks. The reasons why unloading splitting failure is more likely to take place in rock masses surrounding deep level tunnels were explained. The split evolution pattern of rock masses surrounding deep level tunnels and the calculation method of dilatancy displacement were obtained. The calculation results of the range of loosening zone, the location of the rupture zone in rock masses surrounding deep level tunnels, and the displacement of the sidewall were compared with the existing monitoring data in the underground powerhouse of the Jinping Ⅰ Hydropower Station, and the agreement is good.
Based on the research of Academician Tan Tjong-Kie on the long-term stability mechanics of underground tunnel and considering Academician Sadovsky’s structural hierarchy theories on complex geological rock masses, the inherent statistical mechanical properties of inhomogeneous structure and closed stress in deep rock masses were investigated. Two mechanical problems were mainly studied, i.e. characteristics of inherent non-uniform deformation and closed stress of rock masses, and long-term stability of deep tunnels. The quantitative mathematical characterization of inherent non-uniform deformation and closed stress of rock masses were given using the method of statistical mechanics. Based on the law of mass conservation, a general calculation method of long-term stability and deformation of rock masses surrounding deep level tunnels was proposed. The Maxwell model was used to calculate the threshold of splitting. A post-peak failure model of rock was established to estimate the in-situ stress at which rock undergoes post-peak failure. With the help of the theory of the hirerachical structure of rock masses, the maximum value of rock displacement due to splitting dilatation was obtained. A dimensionless energy factor was introduced to define the extent of zonal disintegration of surrounding rock masses. It was concluded that the splitting and dilatancy deformation is the main part of the deformation of surrounding rocks. The reasons why unloading splitting failure is more likely to take place in rock masses surrounding deep level tunnels were explained. The split evolution pattern of rock masses surrounding deep level tunnels and the calculation method of dilatancy displacement were obtained. The calculation results of the range of loosening zone, the location of the rupture zone in rock masses surrounding deep level tunnels, and the displacement of the sidewall were compared with the existing monitoring data in the underground powerhouse of the Jinping Ⅰ Hydropower Station, and the agreement is good.
2021, 41(7): 071102.
doi: 10.11883/bzycj-2020-0388
Abstract:
The damage mechanisms of structures under internal blast are important for the prediction and evaluation of damage effects of conventional weapons and the design of anti-explosion structures of buildings and ships. The researches status and existing problems are discussed in this paper, based on the following four aspects as the internal explosion loads on structures, the plastic responses of structures to internal explosion loads, the damage modes of box-wall structures under internal explosion loads, and the damage modes and distribution of multi-box structures under internal explosion loads. With respect to an internal blast load, it is recognized that the blast model can be divided into dynamic high-pressure stage and quasi-static pressure stage. The former is formed by the initial shock wave and reflection wave while the latter is mainly composed of expansion of detonation gas and chemical energy released by explosion. In regard to the plastic response of the structure under the internal blast load, the studies have shown that quasi-static pressure plays an important role in the response process. With respect to the damage mode of the internal blast loaded structure, the damage mode is greatly affected by the pressure relief mode and pressure relief speed, studies on the damage modes of the beam and plate were introduced. As regards the damage mode and distribution of multi-box structures under the internal blast load, the internal explosion damage of the metal box structure of ships was mainly introduced. Most of the current researches focus on the damage features and there is rarely systematic understanding and analysis for the damagemechanisms. Through the review of the research on the damage and damage of the structures under the internal blast load, suggestions are provided for further researches on: (1) the models to describe the internal explosion loads on more complex structures and the corresponding damage effects; (2) the mechanisms of dynamic response of the box walls to internal blast load; (3) the coupling effect of multi-box structures with internal explosion waves and detonation products; (4) the methods to quickly and accurately predict the damage mode, damage range and damage degree of structures under internal explosion loads.
The damage mechanisms of structures under internal blast are important for the prediction and evaluation of damage effects of conventional weapons and the design of anti-explosion structures of buildings and ships. The researches status and existing problems are discussed in this paper, based on the following four aspects as the internal explosion loads on structures, the plastic responses of structures to internal explosion loads, the damage modes of box-wall structures under internal explosion loads, and the damage modes and distribution of multi-box structures under internal explosion loads. With respect to an internal blast load, it is recognized that the blast model can be divided into dynamic high-pressure stage and quasi-static pressure stage. The former is formed by the initial shock wave and reflection wave while the latter is mainly composed of expansion of detonation gas and chemical energy released by explosion. In regard to the plastic response of the structure under the internal blast load, the studies have shown that quasi-static pressure plays an important role in the response process. With respect to the damage mode of the internal blast loaded structure, the damage mode is greatly affected by the pressure relief mode and pressure relief speed, studies on the damage modes of the beam and plate were introduced. As regards the damage mode and distribution of multi-box structures under the internal blast load, the internal explosion damage of the metal box structure of ships was mainly introduced. Most of the current researches focus on the damage features and there is rarely systematic understanding and analysis for the damagemechanisms. Through the review of the research on the damage and damage of the structures under the internal blast load, suggestions are provided for further researches on: (1) the models to describe the internal explosion loads on more complex structures and the corresponding damage effects; (2) the mechanisms of dynamic response of the box walls to internal blast load; (3) the coupling effect of multi-box structures with internal explosion waves and detonation products; (4) the methods to quickly and accurately predict the damage mode, damage range and damage degree of structures under internal explosion loads.
2021, 41(7): 072101.
doi: 10.11883/bzycj-2020-0140
Abstract:
On the basis of revealing the effects of equivalence ratio on flame morphology, radius and maximum explosion overpressure, this work was aimed at establishing a theoretical model to predict hydrogen cloud explosion overpressure by considering self-accelerating flame propagation. The results indicated that the decreasing order of flame propagation velocity is Φ=2.0, Φ=1.0 and Φ=0.8. For Le＜1.0 and Le＞1.0, the cellular structures could be formed on the flame surface, which would increase flame surface area and result in self-accelerating flame propagation. When the equivalence ratio was fixed, the positive maximum explosion overpressure and absolute value of negative maximum explosion overpressure continue to decrease as the distance between pressure senor and ignition source increases. As the equivalence ratio changes, there are some differences for positive maximum explosion overpressure and absolute value of negative maximum explosion overpressure at the fixed distance. The absolute value of negative maximum explosion overpressure was relatively higher than positive maximum explosion overpressure. Before rupture of thin film, the explosion overpressure evolution at various monitoring points could be reproduced using the theoretical model considering self-accelerating flame propagation.
On the basis of revealing the effects of equivalence ratio on flame morphology, radius and maximum explosion overpressure, this work was aimed at establishing a theoretical model to predict hydrogen cloud explosion overpressure by considering self-accelerating flame propagation. The results indicated that the decreasing order of flame propagation velocity is Φ=2.0, Φ=1.0 and Φ=0.8. For Le＜1.0 and Le＞1.0, the cellular structures could be formed on the flame surface, which would increase flame surface area and result in self-accelerating flame propagation. When the equivalence ratio was fixed, the positive maximum explosion overpressure and absolute value of negative maximum explosion overpressure continue to decrease as the distance between pressure senor and ignition source increases. As the equivalence ratio changes, there are some differences for positive maximum explosion overpressure and absolute value of negative maximum explosion overpressure at the fixed distance. The absolute value of negative maximum explosion overpressure was relatively higher than positive maximum explosion overpressure. Before rupture of thin film, the explosion overpressure evolution at various monitoring points could be reproduced using the theoretical model considering self-accelerating flame propagation.
2021, 41(7): 072301.
doi: 10.11883/bzycj-2020-0215
Abstract:
The accumulation form of propellant grains has a great effect on the initial chamber pressure wave in the ignition and flame-spreading process of a modular charge. In this process, the grains distribution is determined by the dynamic characteristics of grains after the cartridge is broken. Therefore, a visualized ignition simulation experimental device was designed for the ignition test of the two-module charge with different initial loading positions. A high-speed camera system was used to observe the ignition and flame propagation, the rupture of combustible cartridge cases, and the moving process of the propellant grains. The experimental results show as follows. When the two-module charging position is far from the primer and the spacing between the two modules is increased, the time of flame propagation in the chamber is prolonged. And the cartridge cases are more completely burned and their rupture areas become larger. The propellant grains in the chamber are finally scattered in the axial 195–500 mm area starting from the end face of the primer side. The grains are mainly distributed in the steep-slope accumulation on the right side of the chamber. On the basis of the experiment, a three-dimensional unsteady gas-solid two-phase flow model for the modular charge was established. The dynamic process and distribution of the propellant grains was simulated. The calculation results are basically consistent with the test ones, which validate the rationality of the established model.
The accumulation form of propellant grains has a great effect on the initial chamber pressure wave in the ignition and flame-spreading process of a modular charge. In this process, the grains distribution is determined by the dynamic characteristics of grains after the cartridge is broken. Therefore, a visualized ignition simulation experimental device was designed for the ignition test of the two-module charge with different initial loading positions. A high-speed camera system was used to observe the ignition and flame propagation, the rupture of combustible cartridge cases, and the moving process of the propellant grains. The experimental results show as follows. When the two-module charging position is far from the primer and the spacing between the two modules is increased, the time of flame propagation in the chamber is prolonged. And the cartridge cases are more completely burned and their rupture areas become larger. The propellant grains in the chamber are finally scattered in the axial 195–500 mm area starting from the end face of the primer side. The grains are mainly distributed in the steep-slope accumulation on the right side of the chamber. On the basis of the experiment, a three-dimensional unsteady gas-solid two-phase flow model for the modular charge was established. The dynamic process and distribution of the propellant grains was simulated. The calculation results are basically consistent with the test ones, which validate the rationality of the established model.
2021, 41(7): 072302.
doi: 10.11883/bzycj-2020-0236
Abstract:
The amplitude-frequency characters of the seismic wave excited by the explosive source directly affect the seismic exploration accuracy. In order to reveal the characteristic law of the amplitude and frequency of the seismic wave field excited by an axially distributed explosive, the study on the calculation method of the seismic wave field of the axially distributed explosive was proposed. Based on the spherical cavity source model, the calculation method of the seismic wave field excited by the axially distributed explosive source was obtained by using the superposition method, and the seismic wave field model excited by the axially distributed charge was established. This model can describe the characteristics of the seismic wave field of distributed explosive sources in seismic exploration. Comparison with numerical simulation shows that the error between the theoretical model and the numerical model is within 5% in the radial direction, and the error between the theoretical model and the numerical model is within 3.4% in the axial direction. Compared with the field experiment results, the theoretical model seismic wave vibration velocity error is within 10% when the blast center distance is greater than 14 m. The calculation accuracy increases with the increase of the distance, and the error is less than 6% when the distance is greater than 24 m. When the blast center distance is the same, the vibration speed in the axial direction is greater than the vibration speed in the radial direction. The difference between the two decreases with the increase of the blast center distance. When the blast center distance is 9.8 times the total length of the charge, the axial direction is the vibration speed difference in the radial direction is within 5%, and the frequency of the seismic wave is higher. The research shows that the model can accurately describe the amplitude-frequency character of the seismic wave excited by the axially-distributed explosive.
The amplitude-frequency characters of the seismic wave excited by the explosive source directly affect the seismic exploration accuracy. In order to reveal the characteristic law of the amplitude and frequency of the seismic wave field excited by an axially distributed explosive, the study on the calculation method of the seismic wave field of the axially distributed explosive was proposed. Based on the spherical cavity source model, the calculation method of the seismic wave field excited by the axially distributed explosive source was obtained by using the superposition method, and the seismic wave field model excited by the axially distributed charge was established. This model can describe the characteristics of the seismic wave field of distributed explosive sources in seismic exploration. Comparison with numerical simulation shows that the error between the theoretical model and the numerical model is within 5% in the radial direction, and the error between the theoretical model and the numerical model is within 3.4% in the axial direction. Compared with the field experiment results, the theoretical model seismic wave vibration velocity error is within 10% when the blast center distance is greater than 14 m. The calculation accuracy increases with the increase of the distance, and the error is less than 6% when the distance is greater than 24 m. When the blast center distance is the same, the vibration speed in the axial direction is greater than the vibration speed in the radial direction. The difference between the two decreases with the increase of the blast center distance. When the blast center distance is 9.8 times the total length of the charge, the axial direction is the vibration speed difference in the radial direction is within 5%, and the frequency of the seismic wave is higher. The research shows that the model can accurately describe the amplitude-frequency character of the seismic wave excited by the axially-distributed explosive.
2021, 41(7): 073101.
doi: 10.11883/bzycj-2020-0198
Abstract:
The phenomena of repeated impacts are very common, especial in the field of ship and ocean engineering. When the ship structures suffering from repeated impact loadings, the deformation and damages will accumulate, leading to failure even damage of the structures, which may cause serious accident. In order to study the dynamic behaviors of metal foam sandwich beams (MFSBs) under repeated impact loadings, the nonlinear finite element model was established based on the material model of crushable foam by using Abaqus-Explicit, and the approach to achieve repeated impacts in the software was proposed. The accuracy of the numerical simulation was verified by comparing the permanent deflections of front and back face sheets. Based on the results of the numerical simulations, the deformation modes, loading and unloading process as well as the energy absorption behavior of the MFSBs under repeated impacts were analyzed. Results show that during repeated impacts, the deformation of the MFSBs is accumulated gradually, the front face sheet mainly experiences global bending and local indentation, and the metal foam core suffers from local compression, while the back face sheet is subjected to global bending. During the repeated impacts, the loading and unloading stiffness increases with the impact number. The energy absorption of front face is larger than that of back face and metal foam core in all the impacts. As the impact number increases, the energy absorbed by front face sheet and foam core declines gradually, while that of the back face sheet increases, approaching a constant value. The plastic deformation energy of the MFSBs decreases with the impact number, on the opposite, the rebound energy of the MFSBs increases gradually with the impact number, while both of them trends to be stable. The proposed finite element method can be applied to accurately predict the dynamic responses of the MFSBs suffering from repeated impact loadings, and provide technical supports for the anti-impact design of metal foam sandwich structures.
The phenomena of repeated impacts are very common, especial in the field of ship and ocean engineering. When the ship structures suffering from repeated impact loadings, the deformation and damages will accumulate, leading to failure even damage of the structures, which may cause serious accident. In order to study the dynamic behaviors of metal foam sandwich beams (MFSBs) under repeated impact loadings, the nonlinear finite element model was established based on the material model of crushable foam by using Abaqus-Explicit, and the approach to achieve repeated impacts in the software was proposed. The accuracy of the numerical simulation was verified by comparing the permanent deflections of front and back face sheets. Based on the results of the numerical simulations, the deformation modes, loading and unloading process as well as the energy absorption behavior of the MFSBs under repeated impacts were analyzed. Results show that during repeated impacts, the deformation of the MFSBs is accumulated gradually, the front face sheet mainly experiences global bending and local indentation, and the metal foam core suffers from local compression, while the back face sheet is subjected to global bending. During the repeated impacts, the loading and unloading stiffness increases with the impact number. The energy absorption of front face is larger than that of back face and metal foam core in all the impacts. As the impact number increases, the energy absorbed by front face sheet and foam core declines gradually, while that of the back face sheet increases, approaching a constant value. The plastic deformation energy of the MFSBs decreases with the impact number, on the opposite, the rebound energy of the MFSBs increases gradually with the impact number, while both of them trends to be stable. The proposed finite element method can be applied to accurately predict the dynamic responses of the MFSBs suffering from repeated impact loadings, and provide technical supports for the anti-impact design of metal foam sandwich structures.
2021, 41(7): 073201.
doi: 10.11883/bzycj-2020-0136
Abstract:
Bubble curtain is an important means for protection against underwater explosion shock wave. It is of great significance to study the mechanism and technical parameters of bubble curtain regarding the safety and application of underwater blasting. By using high-speed photography technology and video framing processing technology, indoor small underwater bubble curtain model is photographed and analyzed. It is found that the gas curtain is highly discontinuous and inhomogeneous in both the formation process and the interaction process with the underwater explosion shock wave. The gas and liquid are mixed in the air curtain area, and the interface contour is complex and diverse. Air displacement will directly affect the quality of the air bubble curtain. The larger the air displacement, the better the continuity and quality of air curtain. On this basis, considering the influences of bubble shape, interface, and gas-liquid coexistence, programming is carried out through the APDL language that comes with the LS-DYNA finite element software. By setting the variation range of bubble diameter and the minimum difference between bubble diameters, a certain number of bubbles of different diameters are randomly positioned to simulate the bubble distributions in the real air curtain. The air curtain quality under different gas source pressure can be simulated by changing the number of bubbles in the set air curtain area. It is found that this method can better reflect the protection mechanism of air curtain against the shock wave. Comparing the protective performance of air curtain with different bubble numbers on the same shock wave, it shows that the protective performance increases with the increase of bubble density. However, when the number of bubbles reaches a threshold number, the overall continuity and stability of the air curtain are basically fixed, and the protection effect tends to be stable.
Bubble curtain is an important means for protection against underwater explosion shock wave. It is of great significance to study the mechanism and technical parameters of bubble curtain regarding the safety and application of underwater blasting. By using high-speed photography technology and video framing processing technology, indoor small underwater bubble curtain model is photographed and analyzed. It is found that the gas curtain is highly discontinuous and inhomogeneous in both the formation process and the interaction process with the underwater explosion shock wave. The gas and liquid are mixed in the air curtain area, and the interface contour is complex and diverse. Air displacement will directly affect the quality of the air bubble curtain. The larger the air displacement, the better the continuity and quality of air curtain. On this basis, considering the influences of bubble shape, interface, and gas-liquid coexistence, programming is carried out through the APDL language that comes with the LS-DYNA finite element software. By setting the variation range of bubble diameter and the minimum difference between bubble diameters, a certain number of bubbles of different diameters are randomly positioned to simulate the bubble distributions in the real air curtain. The air curtain quality under different gas source pressure can be simulated by changing the number of bubbles in the set air curtain area. It is found that this method can better reflect the protection mechanism of air curtain against the shock wave. Comparing the protective performance of air curtain with different bubble numbers on the same shock wave, it shows that the protective performance increases with the increase of bubble density. However, when the number of bubbles reaches a threshold number, the overall continuity and stability of the air curtain are basically fixed, and the protection effect tends to be stable.
2021, 41(7): 073301.
doi: 10.11883/bzycj-2020-0191
Abstract:
In order to study the influence of the cavity on the explosion effect caused by the penetration of concrete target, model tests of penetration and explosion of concrete target at the velocity of 450–700 m/s were carried out. Based on 10 sets of test results and dimensional analysis, the effect of penetration result on the depth of blast hole is studied. Results indicate that the dimensionless impact coefficient Ip can be used to characterize the penetration effects such as penetration depth, hole volume and penetration damage value, regardless of length-diameter ratio of charge, the increase of damage depth is mainly influenced by dimensionless impact coefficient Ip and explosion coefficient Ie. Based on the experimental data, influence rule of the depth of crater is obtained for the length-diameter ratio of 5: (1) when the Ip is small, the penetration depth is small, the change of Ie has little influence on the depth of crater he; (2) with the increase of Ip, he increases at a decreasing rate, influence of Ie on he increases; (3) with the increase of Ip to a certain extent, he tends to reachsaturation value, influence of Ie on he tends to be stable.
In order to study the influence of the cavity on the explosion effect caused by the penetration of concrete target, model tests of penetration and explosion of concrete target at the velocity of 450–700 m/s were carried out. Based on 10 sets of test results and dimensional analysis, the effect of penetration result on the depth of blast hole is studied. Results indicate that the dimensionless impact coefficient Ip can be used to characterize the penetration effects such as penetration depth, hole volume and penetration damage value, regardless of length-diameter ratio of charge, the increase of damage depth is mainly influenced by dimensionless impact coefficient Ip and explosion coefficient Ie. Based on the experimental data, influence rule of the depth of crater is obtained for the length-diameter ratio of 5: (1) when the Ip is small, the penetration depth is small, the change of Ie has little influence on the depth of crater he; (2) with the increase of Ip, he increases at a decreasing rate, influence of Ie on he increases; (3) with the increase of Ip to a certain extent, he tends to reachsaturation value, influence of Ie on he tends to be stable.
2021, 41(7): 073302.
doi: 10.11883/bzycj-2020-0247
Abstract:
To investigate the strain rate sensitivity of mechanical properties and the breaking mechanisms of brittle hollow particles (BHPs) at mesoscopic level, low-velocity impact tests and the corresponding numerical simulation using finite element method (FEM) were performed on the fly ash cenospheres (CPs). Characteristics of the mechanical response and the mesoscopic crushing behavior of brittle hollow particles under dynamic loadings were observed and discussed based on the impact tests. Additionally, the mechanism of producing strain rate sensitivity of cenosphere was interpreted through the mesoscopic numerical simulations. The results are as follows. (1) At the strain rate of 0.001−300 s−1, the breaking ratio and the Hardin relative breaking potential was improved by 12% and 10%−30%, respectively. Meanwhile, the specific energy absorption of two types of cenospheres increased 50%−125%. The extra improvement of energy absorption should be attributed to the increase of the friction energy dissipation which was caused by the dynamic slipping rearrangement of BHPs. Also, the cenosphere specimens with larger particles size distribution exhibited more remarkable strain rate sensitivity. (2) The stress-strain response of BHPs at the initial collapse stage obtained from the numerical simulation coincided well with the experimental results. It was suggested that the dynamic secondary collapse stress was mainly caused by the particle slippage and its dependence on the loading velocity. (3) In addition, the numerical simulation shown that the damage extent of packing particles under dynamic loadings was much higher than that under static loadings at the same compression strain level. This was in good agreement with the experimental results that the relative breaking potential, characterizing the crushing extent of particles, increased with the strain rate. By combining the potential analysis of the testing cenosphere specimens and the mesoscopic simulation, it can be concluded that the intrinsic mechanism of the macro strain rate effect of BHPs is the decrease in energy utilization of particle breaking and the rate-dependence of the particles crushing behavior.
To investigate the strain rate sensitivity of mechanical properties and the breaking mechanisms of brittle hollow particles (BHPs) at mesoscopic level, low-velocity impact tests and the corresponding numerical simulation using finite element method (FEM) were performed on the fly ash cenospheres (CPs). Characteristics of the mechanical response and the mesoscopic crushing behavior of brittle hollow particles under dynamic loadings were observed and discussed based on the impact tests. Additionally, the mechanism of producing strain rate sensitivity of cenosphere was interpreted through the mesoscopic numerical simulations. The results are as follows. (1) At the strain rate of 0.001−300 s−1, the breaking ratio and the Hardin relative breaking potential was improved by 12% and 10%−30%, respectively. Meanwhile, the specific energy absorption of two types of cenospheres increased 50%−125%. The extra improvement of energy absorption should be attributed to the increase of the friction energy dissipation which was caused by the dynamic slipping rearrangement of BHPs. Also, the cenosphere specimens with larger particles size distribution exhibited more remarkable strain rate sensitivity. (2) The stress-strain response of BHPs at the initial collapse stage obtained from the numerical simulation coincided well with the experimental results. It was suggested that the dynamic secondary collapse stress was mainly caused by the particle slippage and its dependence on the loading velocity. (3) In addition, the numerical simulation shown that the damage extent of packing particles under dynamic loadings was much higher than that under static loadings at the same compression strain level. This was in good agreement with the experimental results that the relative breaking potential, characterizing the crushing extent of particles, increased with the strain rate. By combining the potential analysis of the testing cenosphere specimens and the mesoscopic simulation, it can be concluded that the intrinsic mechanism of the macro strain rate effect of BHPs is the decrease in energy utilization of particle breaking and the rate-dependence of the particles crushing behavior.
2021, 41(7): 073303.
doi: 10.11883/bzycj-2020-0219
Abstract:
An experimental study on the impact force and penetration of falling rocks with three typical shapes, including spherical, conical and flat shapes, against the cushion was carried out. The experimental results show that the shape of the falling rock has a significant influence on the impact results. Under the same conditions, the flat blocks have the highest impact force, the lowest penetration depth and the shortest peak impact time, and the opposite for the conical falling rocks, with spherical blocks are between the two. The dimensionless analysis method was adopted to convert the mass, velocity, shape, size of the falling rock, the strength and density of the cushion layer into the dimensionless strength impact factor I, density impact factor λ and shape impact factor ψ. The correlation analysis between the impact factors and penetration test data shows that: (1) The effects of the impact factors I and λ on the final depth of penetration zm/d are similar. (2) The analysis of the impact factors I and λ effects on penetration depth shows that I and λ are relatively independent. The pattern of the I effects on the depth of penetration is generally consistent for different λ values.
An experimental study on the impact force and penetration of falling rocks with three typical shapes, including spherical, conical and flat shapes, against the cushion was carried out. The experimental results show that the shape of the falling rock has a significant influence on the impact results. Under the same conditions, the flat blocks have the highest impact force, the lowest penetration depth and the shortest peak impact time, and the opposite for the conical falling rocks, with spherical blocks are between the two. The dimensionless analysis method was adopted to convert the mass, velocity, shape, size of the falling rock, the strength and density of the cushion layer into the dimensionless strength impact factor I, density impact factor λ and shape impact factor ψ. The correlation analysis between the impact factors and penetration test data shows that: (1) The effects of the impact factors I and λ on the final depth of penetration zm/d are similar. (2) The analysis of the impact factors I and λ effects on penetration depth shows that I and λ are relatively independent. The pattern of the I effects on the depth of penetration is generally consistent for different λ values.
A rapid system identification method for measuring explosion heat by the constant temperature method
2021, 41(7): 074101.
doi: 10.11883/bzycj-2020-0249
Abstract:
In order to reduce the risk of measurement failure caused by system failure in the classical constant temperature method for measuring explosion heat, a measurement method was developed for identifying the explosion heat value based on the water temperature rise curve of an inner barrel before failure. Firstly, the heat transfer mechanism of the measurement process was analyzed, and the heat transfer model of the calorimeter was established, and the water temperature rise curve of the inner barrel in each measurement stage was obtained. Then, based on the system identification theory, the identification algorithm of intermediate parameters was proposed, and based on the idea of isolating easily oscillating parameters, a fast system identification algorithm was given to correct the temperature rise and explosion heat. And it is proved that the identification value of explosion heat approximately converges to the classical value. Finally, the test data of 8 explosive samples with explosion heat values ranging from 4 to 9 kJ/g were used to test the algorithm, and the test criterion for judging the convergence time was put forward. The simulation results show that the identification algorithm can effectively isolate the influence of the oscillation parameters and has a strong prediction ability on the temperature change of the water in the inner barrel, and that the identification value of explosion heat can quickly and stably converge to the upper limit of relative error of 3.5% within 40 min (1/3 of the main end stage), and that the test criterion can accurately judge the convergence time of the identified value of explosion heat. This method can also be extended to the adiabatic method for calculating explosion heat.
In order to reduce the risk of measurement failure caused by system failure in the classical constant temperature method for measuring explosion heat, a measurement method was developed for identifying the explosion heat value based on the water temperature rise curve of an inner barrel before failure. Firstly, the heat transfer mechanism of the measurement process was analyzed, and the heat transfer model of the calorimeter was established, and the water temperature rise curve of the inner barrel in each measurement stage was obtained. Then, based on the system identification theory, the identification algorithm of intermediate parameters was proposed, and based on the idea of isolating easily oscillating parameters, a fast system identification algorithm was given to correct the temperature rise and explosion heat. And it is proved that the identification value of explosion heat approximately converges to the classical value. Finally, the test data of 8 explosive samples with explosion heat values ranging from 4 to 9 kJ/g were used to test the algorithm, and the test criterion for judging the convergence time was put forward. The simulation results show that the identification algorithm can effectively isolate the influence of the oscillation parameters and has a strong prediction ability on the temperature change of the water in the inner barrel, and that the identification value of explosion heat can quickly and stably converge to the upper limit of relative error of 3.5% within 40 min (1/3 of the main end stage), and that the test criterion can accurately judge the convergence time of the identified value of explosion heat. This method can also be extended to the adiabatic method for calculating explosion heat.
2021, 41(7): 074201.
doi: 10.11883/bzycj-2020-0220
Abstract:
In order to study the fracture mechanism of the projectile melted by the electron beam, a parameterized modeling method based on the micromechanical characteristics of the projectile was proposed. Scanning electron microscope and hardness tester were used to accurately obtain the characteristics of the electron beam melted zone. The typical electron beam controlled area was composed of the melting zone, the transition zone, the hollow zone and the matrix zone. Three hypotheses were proposed based on the mesoscopic characteristics of the electron beam controlled projectile. First, the structural characteristic parameters of the electron beam controlled projectile were summarized. Second, diamond-shaped finite element mesh elements were constructed through translation nodes. Third, the electron beam controlled pattern was constructed by combining diamond-shaped finite elements. Finally, the materials of melting zone and transition zone are defined, and finite elements of the hollow zone were deleted. A three-dimensional finite element model of the projectile with matrix, melting zone, transition zone and hollow zone was established. The explosion driving and fracture process of the typical projectile was simulated and analyzed by LS-DYNA software. The results show that the fracture process of the projectile can be divided into three stages: the tensile fracture in the hollow zone after the expansion of the projectile under the action of the circumferential tensile stress; the crack propagation and tensile fracture in the transition area; and the shear failure of the matrix at the bottom of the cavity area under the action of the tensile stress at both sides and the compressive stress at the bottom, which is 45° to the normal of the inner wall of the projectile. The numerical simulation results are in good agreement with the recovered fragment section shape and failure mode. The research results are of reference value to the forming control of projectile fragments by electron beam controlled.
In order to study the fracture mechanism of the projectile melted by the electron beam, a parameterized modeling method based on the micromechanical characteristics of the projectile was proposed. Scanning electron microscope and hardness tester were used to accurately obtain the characteristics of the electron beam melted zone. The typical electron beam controlled area was composed of the melting zone, the transition zone, the hollow zone and the matrix zone. Three hypotheses were proposed based on the mesoscopic characteristics of the electron beam controlled projectile. First, the structural characteristic parameters of the electron beam controlled projectile were summarized. Second, diamond-shaped finite element mesh elements were constructed through translation nodes. Third, the electron beam controlled pattern was constructed by combining diamond-shaped finite elements. Finally, the materials of melting zone and transition zone are defined, and finite elements of the hollow zone were deleted. A three-dimensional finite element model of the projectile with matrix, melting zone, transition zone and hollow zone was established. The explosion driving and fracture process of the typical projectile was simulated and analyzed by LS-DYNA software. The results show that the fracture process of the projectile can be divided into three stages: the tensile fracture in the hollow zone after the expansion of the projectile under the action of the circumferential tensile stress; the crack propagation and tensile fracture in the transition area; and the shear failure of the matrix at the bottom of the cavity area under the action of the tensile stress at both sides and the compressive stress at the bottom, which is 45° to the normal of the inner wall of the projectile. The numerical simulation results are in good agreement with the recovered fragment section shape and failure mode. The research results are of reference value to the forming control of projectile fragments by electron beam controlled.
2021, 41(7): 075101.
doi: 10.11883/bzycj-2021-0059
Abstract:
To study the blast resistance and damage rule of ultra-high toughness cementitious composites (UHTCC) subjected to blast by embedded explosives, blast resistance tests of embedded explosives were carried out on UHTCC and high-strength concrete (HSC) with different embedded depths of explosives. The damage patterns of the targets of the two materials were obtained. Using the test results of contact explosion, the blast resistance parameters of the above two materials were calculated. The test results show that UHTCC has better blast resistance than high-strength concrete under the same test conditions. To further explore the influence of compressive strength, tensile strength and tensile toughness on the blast resistance of UHTCC targets to embedded explosives, the improved K&C model was used to numerically simulate the UHTCC target subjected to blast by explosives with an embedded depth of 40 mm. The simulation results were basically consistent with the experimental results. According to the results of numerical simulation, the rule that the attenuation speed of the explosion shock wave along the radial direction of target was greater than that along the axial direction was obtained, which verified the validity of the model. Then, by adjusting the parameters related to the compressive strength, tensile strength and tensile toughness in the modified K&C model, the damage patterns of the UHTCC targets with different compressive and tensile strengths and tensile toughness were predicted. It is found that enhancing the toughness of UHTCC can effectively prevent the target from undergoing overall damage, increasing the tensile strength of UHTCC can reduce the cratering diameter of the blasting surface, and increasing the compressive strength of the material has no obvious effect on reducing the cratering size. These studies can provide a basis for the application of UHTCC materials in protection engineering.
To study the blast resistance and damage rule of ultra-high toughness cementitious composites (UHTCC) subjected to blast by embedded explosives, blast resistance tests of embedded explosives were carried out on UHTCC and high-strength concrete (HSC) with different embedded depths of explosives. The damage patterns of the targets of the two materials were obtained. Using the test results of contact explosion, the blast resistance parameters of the above two materials were calculated. The test results show that UHTCC has better blast resistance than high-strength concrete under the same test conditions. To further explore the influence of compressive strength, tensile strength and tensile toughness on the blast resistance of UHTCC targets to embedded explosives, the improved K&C model was used to numerically simulate the UHTCC target subjected to blast by explosives with an embedded depth of 40 mm. The simulation results were basically consistent with the experimental results. According to the results of numerical simulation, the rule that the attenuation speed of the explosion shock wave along the radial direction of target was greater than that along the axial direction was obtained, which verified the validity of the model. Then, by adjusting the parameters related to the compressive strength, tensile strength and tensile toughness in the modified K&C model, the damage patterns of the UHTCC targets with different compressive and tensile strengths and tensile toughness were predicted. It is found that enhancing the toughness of UHTCC can effectively prevent the target from undergoing overall damage, increasing the tensile strength of UHTCC can reduce the cratering diameter of the blasting surface, and increasing the compressive strength of the material has no obvious effect on reducing the cratering size. These studies can provide a basis for the application of UHTCC materials in protection engineering.
2021, 41(7): 075201.
doi: 10.11883/bzycj-2020-0214
Abstract:
The topics such as fragmentation degree, active energy consumption and energy consumption efficiency of rock mass under explosive load have attracted increasing attention in recent years. However, it is very difficult to conduct such research due to its instantaneity, high temperature and high pressure characteristics. Systematic analysis and research on broken blocks of rock mass and the variation of energy utilization under explosion load with the different minimum resistance lines have been carried out. Plain concrete material was used to construct the model and carry out the model experiment. Theory of energy consumption in fracture mechanics was used to calculate the crushing energy. The basic fractal theory was used to calculate and analyze the fragmentation distribution law. Research results indicate that: the fractal dimension of broken blocks is between 1.2 and 1.7, exhibiting a good linear attenuation trend with the increase of the minimum resistance line from 120 mm to 200 mm; the crushing energy consumption increases first and then decreases. More specifically, the crushing energy consumption is 440.0 J at 120 mm, and increases to the maximum of 1 106.5 J at 180 mm, and then decreases to 1 084.8 J at 200 mm. The explosive energy utilization rate is between 4.57% and 12.51% and the maximum value corresponds to the minimum resistance line of 180 mm, the variation trend is consistent with that of the energy consumption value. The trend of broken fragmentation and utilization rate of energy consumption is opposite. There is an optimum minimum resistance line, corresponding to the optimized fragmentation degree and energy consumption utilization rate, in the model experiment is 160 mm which is 26.7 times the diameter of the charge. The research results can provide a theoretical basis for improving the explosive energy utilization rate and guide the design and construction processes in future engineering applications.
The topics such as fragmentation degree, active energy consumption and energy consumption efficiency of rock mass under explosive load have attracted increasing attention in recent years. However, it is very difficult to conduct such research due to its instantaneity, high temperature and high pressure characteristics. Systematic analysis and research on broken blocks of rock mass and the variation of energy utilization under explosion load with the different minimum resistance lines have been carried out. Plain concrete material was used to construct the model and carry out the model experiment. Theory of energy consumption in fracture mechanics was used to calculate the crushing energy. The basic fractal theory was used to calculate and analyze the fragmentation distribution law. Research results indicate that: the fractal dimension of broken blocks is between 1.2 and 1.7, exhibiting a good linear attenuation trend with the increase of the minimum resistance line from 120 mm to 200 mm; the crushing energy consumption increases first and then decreases. More specifically, the crushing energy consumption is 440.0 J at 120 mm, and increases to the maximum of 1 106.5 J at 180 mm, and then decreases to 1 084.8 J at 200 mm. The explosive energy utilization rate is between 4.57% and 12.51% and the maximum value corresponds to the minimum resistance line of 180 mm, the variation trend is consistent with that of the energy consumption value. The trend of broken fragmentation and utilization rate of energy consumption is opposite. There is an optimum minimum resistance line, corresponding to the optimized fragmentation degree and energy consumption utilization rate, in the model experiment is 160 mm which is 26.7 times the diameter of the charge. The research results can provide a theoretical basis for improving the explosive energy utilization rate and guide the design and construction processes in future engineering applications.
2021, 41(7): 075301.
doi: 10.11883/bzycj-2020-0197
Abstract:
A theoretical model for shock wave propagation was established to study the airflow in the gap between the base and cladding plates of explosive welding, and the gas shock wave channel effect between the base and cladding plates was proposed and explained by theoretical analysis and calculation. The results show that the channel effect can push up the tail of the cladding plate before the collision point of explosive welding, and then causes the welding energy of the plate tail to increase too high or the explosive on the plate tail to be pressed dead. Therefore, the channel effect in explosive welding is the primary reason for the failure or quality reduction of the tail welding of long and large clad plates. In addition, other simplified theoretical models were used to further analyze various factors influencing on the channel effect, like clad plate width, various shielding gases and explosive welding in coarse vacuum. The optimization principle of shielding gas for explosive welding was explained, and also the helium-shielded explosive welding of titanium/steel and aluminum/magnesium was processing as experimental verification. The theoretical foundation for the further development and research of gas-shielded explosive welding and vacuum explosive welding was built up in this paper.
A theoretical model for shock wave propagation was established to study the airflow in the gap between the base and cladding plates of explosive welding, and the gas shock wave channel effect between the base and cladding plates was proposed and explained by theoretical analysis and calculation. The results show that the channel effect can push up the tail of the cladding plate before the collision point of explosive welding, and then causes the welding energy of the plate tail to increase too high or the explosive on the plate tail to be pressed dead. Therefore, the channel effect in explosive welding is the primary reason for the failure or quality reduction of the tail welding of long and large clad plates. In addition, other simplified theoretical models were used to further analyze various factors influencing on the channel effect, like clad plate width, various shielding gases and explosive welding in coarse vacuum. The optimization principle of shielding gas for explosive welding was explained, and also the helium-shielded explosive welding of titanium/steel and aluminum/magnesium was processing as experimental verification. The theoretical foundation for the further development and research of gas-shielded explosive welding and vacuum explosive welding was built up in this paper.
