2024 Vol. 44, No. 3
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2024, 44(3): 031401.
doi: 10.11883/bzycj-2023-0324
Abstract:
High-entropy alloy (HEA) materials exhibit different failure modes and mechanical properties under high strain rate dynamic response. Because its potential mechanism cannot be fully explained from a macro perspective, it is necessary to study the atomic structure change, dislocation distribution change, evolution mechanism and deformation mechanism in the dynamic response process from a microscopic perspective. This study provides a reference for optimizing the processing technology and preparation method of HEA protective materials. The molecular dynamics simulation is adopted to design the compression, tensile at different strain rates and impact tests of [110], [111] and [100] three oriented Al0.3CoCrFeNi HEA. The atomic structure changes, dislocation distribution change, evolution mechanism and deformation mechanism in the dynamic response process are then analyzed. In the compression test: the yield strength of Al0.3CoCrFeNi high-entropy alloy with [110] orientation structure is the highest, followed by [111] and [100]. The main deformation mechanism of the [100] orientation structure is twin deformation, [110] orientation structure is slip deformation, and [111] orientation structure is dislocation deformation. In the tensile test: the yield strength of Al0.3CoCrFeNi high-entropy alloy with [111] orientation structure is the highest, followed by [100] and [110]. [100] orientation structure presents more twin structure during the tensile process; [110] exhibits more regular hexagonal close-packed structure slip surface; while [111] does not produce any slip surface. With the increase of strain rate, the compressive and tensile yield strength increased greatly, and the corresponding elongation increased, too. The plastic deformation mechanism at low strain rate (1×109 s−1) is mainly slip deformation, but the number of slip systems is small. The plastic deformation mechanism at medium strain rate (1×1010 s−1) is mainly slip deformation mechanism, but many slip systems appear. The plastic deformation mechanism at high strain rate (1×1011 s−1) is induced by amorphous atoms with disordered atomic arrangement. The Al0.3CoCrFeNi high-entropy alloy with [110] orientation structure has the best impact resistance, which is attributed to its highest yield strength and the highest stress at the end of the yield stage.
High-entropy alloy (HEA) materials exhibit different failure modes and mechanical properties under high strain rate dynamic response. Because its potential mechanism cannot be fully explained from a macro perspective, it is necessary to study the atomic structure change, dislocation distribution change, evolution mechanism and deformation mechanism in the dynamic response process from a microscopic perspective. This study provides a reference for optimizing the processing technology and preparation method of HEA protective materials. The molecular dynamics simulation is adopted to design the compression, tensile at different strain rates and impact tests of [110], [111] and [100] three oriented Al0.3CoCrFeNi HEA. The atomic structure changes, dislocation distribution change, evolution mechanism and deformation mechanism in the dynamic response process are then analyzed. In the compression test: the yield strength of Al0.3CoCrFeNi high-entropy alloy with [110] orientation structure is the highest, followed by [111] and [100]. The main deformation mechanism of the [100] orientation structure is twin deformation, [110] orientation structure is slip deformation, and [111] orientation structure is dislocation deformation. In the tensile test: the yield strength of Al0.3CoCrFeNi high-entropy alloy with [111] orientation structure is the highest, followed by [100] and [110]. [100] orientation structure presents more twin structure during the tensile process; [110] exhibits more regular hexagonal close-packed structure slip surface; while [111] does not produce any slip surface. With the increase of strain rate, the compressive and tensile yield strength increased greatly, and the corresponding elongation increased, too. The plastic deformation mechanism at low strain rate (1×109 s−1) is mainly slip deformation, but the number of slip systems is small. The plastic deformation mechanism at medium strain rate (1×1010 s−1) is mainly slip deformation mechanism, but many slip systems appear. The plastic deformation mechanism at high strain rate (1×1011 s−1) is induced by amorphous atoms with disordered atomic arrangement. The Al0.3CoCrFeNi high-entropy alloy with [110] orientation structure has the best impact resistance, which is attributed to its highest yield strength and the highest stress at the end of the yield stage.
2024, 44(3): 031402.
doi: 10.11883/bzycj-2023-0308
Abstract:
Stiffened panels are widely used in the explosion and impact protection, thus a fast and accurate method for solving their dynamic response is highly desired in engineering. Based on the idea of stiffness superposition, a novel equivalent-isotropic-plate method is proposed in this paper to convert the radial and uniformly stiffened circular plate into an isotropic flat plate, so as to analyze its dynamic response in the elastic stage under uniform pulse loading. Since obtaining the dynamic response of an isotropic plate is mature and convenient, the equivalent analysis can overcome the computational difficulty of anisotropy in direct modeling, thus greatly improving the solving efficiency. Through the linear superposition of the plate and stiffener dynamic equations, a concise formula of the equivalent plate thickness is derived explicitly. The equivalent parameter in the formula is obtained with the assistance of simulation and numerical fitting, which directly measures the strengthening effect of the stiffeners on the plate. Employing the equivalent-isotropic-plate model, the overall dynamic response of a stiffened circular plate can be represented by that of an equivalent isotropic plate with acceptable accuracy, especially for low-order vibrations and center deflections. It is verified that the equivalent method can be successfully applied to a variety of stiffening types, materials, and load forms. The deviation of the maximum deflection response of the equivalent flat plate from that of the original stiffened circular plate does not exceed 6%, and the deviation of the response frequency does not exceed 10%. This completely meets the engineering requirements. The equivalent-isotropic-plate model verifies the feasibility of isotropic equivalence, and reveals the intrinsic connection between the radial stiffened circular plate and the homogeneous circular plate, which is of great significance in engineering applications such as response prediction and structural optimization.
Stiffened panels are widely used in the explosion and impact protection, thus a fast and accurate method for solving their dynamic response is highly desired in engineering. Based on the idea of stiffness superposition, a novel equivalent-isotropic-plate method is proposed in this paper to convert the radial and uniformly stiffened circular plate into an isotropic flat plate, so as to analyze its dynamic response in the elastic stage under uniform pulse loading. Since obtaining the dynamic response of an isotropic plate is mature and convenient, the equivalent analysis can overcome the computational difficulty of anisotropy in direct modeling, thus greatly improving the solving efficiency. Through the linear superposition of the plate and stiffener dynamic equations, a concise formula of the equivalent plate thickness is derived explicitly. The equivalent parameter in the formula is obtained with the assistance of simulation and numerical fitting, which directly measures the strengthening effect of the stiffeners on the plate. Employing the equivalent-isotropic-plate model, the overall dynamic response of a stiffened circular plate can be represented by that of an equivalent isotropic plate with acceptable accuracy, especially for low-order vibrations and center deflections. It is verified that the equivalent method can be successfully applied to a variety of stiffening types, materials, and load forms. The deviation of the maximum deflection response of the equivalent flat plate from that of the original stiffened circular plate does not exceed 6%, and the deviation of the response frequency does not exceed 10%. This completely meets the engineering requirements. The equivalent-isotropic-plate model verifies the feasibility of isotropic equivalence, and reveals the intrinsic connection between the radial stiffened circular plate and the homogeneous circular plate, which is of great significance in engineering applications such as response prediction and structural optimization.
2024, 44(3): 031403.
doi: 10.11883/bzycj-2023-0317
Abstract:
To adjust the fragment lethality field of the anti-ground ammunition, the paper studies the power characteristics of a drum-shaped warhead under static and dynamic detonation. Aiming at the ground armored vehicles, the damage efficiency of the drum-shaped warhead under different initiation modes is analyzed. The fragment power characteristics of a drum-shaped warhead under static detonation and the damage area to vehicle target under dynamic detonation are studied by numerical simulation under two initiation modes of end face center single point and center single point compared with cylindrical warhead of the same caliber. On this basis, further by adjusting the drum-shaped warhead initiation mode into three kinds of eccentric two-line synchronous initiation, eccentric two-line sequential initiation and eccentric two-line synchronous-sequential initiation. The fragment velocity and dispersion angle of the drum-shaped warhead during static detonation, the damage area to the vehicle target and the distribution of the effective fragment landing kinetic energy during dynamic detonation are calculated under different eccentric initiation. The effect of adjusting the detonating mode on the destruction power field of the fragment of the drum-shaped warhead is analyzed by comparing the power characteristics of the fragment of the drum-shaped warhead during the static detonation and the damage results of the vehicle target during dynamic detonation with the corresponding results under the end face center single-point initiation of the drum-shaped warhead. The results show that compared with the cylindrical warhead structure with the same caliber, the fragment dispersion angle of the drum-shaped warhead is increased by 55.98%, and the damaged area of the ground military vehicles is increased by the maximum 59.3%. Compared with the eccentric two-line synchronous initiation, the drum-shaped warhead with eccentric two lines synchronous-sequential initiation can increase the fragment dispersion angle by 18.0%, and increase the dispersion of fragments by 11.48%. Compared with the single-point initiation of charge center, the damage area of the drum-shaped warhead under eccentric two-line sequential initiation is less affected by the burst height, and the damage area reaches 47.15 m2 when the falling angle is 50°, the falling velocity is 200 m/s and the burst height is 9 m. By adjusting the structure and the initiation mode of the warhead, the dispersion angle of fragments can be effectively increased, the coverage area of fragments to the target can be increased, and the damage efficiency of the warhead can be improved.
To adjust the fragment lethality field of the anti-ground ammunition, the paper studies the power characteristics of a drum-shaped warhead under static and dynamic detonation. Aiming at the ground armored vehicles, the damage efficiency of the drum-shaped warhead under different initiation modes is analyzed. The fragment power characteristics of a drum-shaped warhead under static detonation and the damage area to vehicle target under dynamic detonation are studied by numerical simulation under two initiation modes of end face center single point and center single point compared with cylindrical warhead of the same caliber. On this basis, further by adjusting the drum-shaped warhead initiation mode into three kinds of eccentric two-line synchronous initiation, eccentric two-line sequential initiation and eccentric two-line synchronous-sequential initiation. The fragment velocity and dispersion angle of the drum-shaped warhead during static detonation, the damage area to the vehicle target and the distribution of the effective fragment landing kinetic energy during dynamic detonation are calculated under different eccentric initiation. The effect of adjusting the detonating mode on the destruction power field of the fragment of the drum-shaped warhead is analyzed by comparing the power characteristics of the fragment of the drum-shaped warhead during the static detonation and the damage results of the vehicle target during dynamic detonation with the corresponding results under the end face center single-point initiation of the drum-shaped warhead. The results show that compared with the cylindrical warhead structure with the same caliber, the fragment dispersion angle of the drum-shaped warhead is increased by 55.98%, and the damaged area of the ground military vehicles is increased by the maximum 59.3%. Compared with the eccentric two-line synchronous initiation, the drum-shaped warhead with eccentric two lines synchronous-sequential initiation can increase the fragment dispersion angle by 18.0%, and increase the dispersion of fragments by 11.48%. Compared with the single-point initiation of charge center, the damage area of the drum-shaped warhead under eccentric two-line sequential initiation is less affected by the burst height, and the damage area reaches 47.15 m2 when the falling angle is 50°, the falling velocity is 200 m/s and the burst height is 9 m. By adjusting the structure and the initiation mode of the warhead, the dispersion angle of fragments can be effectively increased, the coverage area of fragments to the target can be increased, and the damage efficiency of the warhead can be improved.
2024, 44(3): 031404.
doi: 10.11883/bzycj-2023-0316
Abstract:
When assessing the damage effectiveness of blast-fragmentation ammunitions against ground targets, the traditional approach involves calculating the overall target damage probability based on component damage criteria. Typically, the shooting line tracing method is used to determine the specific location on the target where fragments from the munition hit. However, this computation process is time-consuming. Therefore, to rapidly and accurately evaluate the ammunition damage effectiveness on the target, this study proposes a method called the multiple rectangular cookie cutter damage function. This method adopts the concept of the trapezoidal rule and performs equivalent processing on different regions corresponding to different damage probability intervals based on the gradient of damage probability changes within the actual damage area. This method can effectively retain the distribution pattern of damage probability values in the practical damage area, thus ensuring the accuracy of the computations. When describing ammunition delivery accuracy, a two-dimensional normal distribution is commonly employed to simulate the impact point locations of projectiles. Therefore, when calculating the mean of damage probability of the ammunition on the target, integration operations on the normal distribution function are necessary. However, due to the absence of an analytical solution for integrating the normal distribution function, polynomial equations are introduced as substitutes to enhance computational efficiency. The effects of ammunition drop angle and accuracy on the mean of damage probability of the target were investigated through example analysis, and the results were compared with those of methods based on the rectangular cookie cutter and Carlton damage function. The results show that within the ammunition drop angle range from 30° to 75°, and the circular error probable (CEP) precision range from 5 m to 50 m, compared with the rectangular cookie cutter damage function, the calculation method based on the multiple rectangular cookie cutter damage function improves the accuracy of damage effectiveness calculation by up to 26.4%. At the same time, the computational efficiency is improved by a factor of 518 compared with the Carlton damage function.
When assessing the damage effectiveness of blast-fragmentation ammunitions against ground targets, the traditional approach involves calculating the overall target damage probability based on component damage criteria. Typically, the shooting line tracing method is used to determine the specific location on the target where fragments from the munition hit. However, this computation process is time-consuming. Therefore, to rapidly and accurately evaluate the ammunition damage effectiveness on the target, this study proposes a method called the multiple rectangular cookie cutter damage function. This method adopts the concept of the trapezoidal rule and performs equivalent processing on different regions corresponding to different damage probability intervals based on the gradient of damage probability changes within the actual damage area. This method can effectively retain the distribution pattern of damage probability values in the practical damage area, thus ensuring the accuracy of the computations. When describing ammunition delivery accuracy, a two-dimensional normal distribution is commonly employed to simulate the impact point locations of projectiles. Therefore, when calculating the mean of damage probability of the ammunition on the target, integration operations on the normal distribution function are necessary. However, due to the absence of an analytical solution for integrating the normal distribution function, polynomial equations are introduced as substitutes to enhance computational efficiency. The effects of ammunition drop angle and accuracy on the mean of damage probability of the target were investigated through example analysis, and the results were compared with those of methods based on the rectangular cookie cutter and Carlton damage function. The results show that within the ammunition drop angle range from 30° to 75°, and the circular error probable (CEP) precision range from 5 m to 50 m, compared with the rectangular cookie cutter damage function, the calculation method based on the multiple rectangular cookie cutter damage function improves the accuracy of damage effectiveness calculation by up to 26.4%. At the same time, the computational efficiency is improved by a factor of 518 compared with the Carlton damage function.
2024, 44(3): 031405.
doi: 10.11883/bzycj-2023-0289
Abstract:
The explosion of missiles penetrating the interior cabin could cause extensive damage to the warship structure. How to evaluate the damage range of the ship structure under the coupling of multiple loads in the inner explosion is a big challenge for engineering researchers. In order to establish a theory method of ship structural damage caused by cabin inner implosion, a large-scale cabin model was designed in this paper, and an inner explosion experiment was carried out on the cabin model. The damage range of the cabin structure was measured and typical failure models were acquired. The damage mechanism of the ship structure under the coupling effect of multiple loads (including extensive shock wave loading and quasi-static pressure loading) under inner implosion was analyzed. Based on experimental results, the theory method of ship structure damage range under inner blast was established. It was indicated that: (1) the cabin model would be subjected to shock wave and quasi-static pressure loadings after the explosive charge was detonated, which led to large area damage and complex failure models; (2) quasi-static pressure was the major destroying element for cabin model damage under inner blast; (3) the theory analysis method proposed by this paper simultaneously considered the coupling effect of shock wave and quasi-static pressure loadings for the damage of the cabin model, the theory results well coincided with the experimental ones. The established calculation method can be applied to evaluate the damage range of ship structure subjected to implosion loading.
The explosion of missiles penetrating the interior cabin could cause extensive damage to the warship structure. How to evaluate the damage range of the ship structure under the coupling of multiple loads in the inner explosion is a big challenge for engineering researchers. In order to establish a theory method of ship structural damage caused by cabin inner implosion, a large-scale cabin model was designed in this paper, and an inner explosion experiment was carried out on the cabin model. The damage range of the cabin structure was measured and typical failure models were acquired. The damage mechanism of the ship structure under the coupling effect of multiple loads (including extensive shock wave loading and quasi-static pressure loading) under inner implosion was analyzed. Based on experimental results, the theory method of ship structure damage range under inner blast was established. It was indicated that: (1) the cabin model would be subjected to shock wave and quasi-static pressure loadings after the explosive charge was detonated, which led to large area damage and complex failure models; (2) quasi-static pressure was the major destroying element for cabin model damage under inner blast; (3) the theory analysis method proposed by this paper simultaneously considered the coupling effect of shock wave and quasi-static pressure loadings for the damage of the cabin model, the theory results well coincided with the experimental ones. The established calculation method can be applied to evaluate the damage range of ship structure subjected to implosion loading.
2024, 44(3): 031406.
doi: 10.11883/bzycj-2023-0287
Abstract:
Data quality is the basis for the validity and accuracy of data-driven models, and there may be a large number of anomalies in the raw concrete targets penetration depth data. Therefore, to ensure the accuracy of the subsequent data-driven model, it is necessary to eliminate the outlier of the raw data. Compared with the traditional anomaly detection method, the anomaly detection method based on neural network models is more suitable for complex multi-dimensional and unevenly distributed concrete target penetration depth data. However, relying only on the neural network model to fit the raw experimental data ignores the abundant and effective expert prior knowledge, which will reduce the accuracy of the model, and even lead to wrong prediction results due to the limited amount of data of the training sample, data bad pixels, poor data distribution, etc. To this end, an algorithm for outlier detection of concrete target penetration depth data combined with prior knowledge was proposed. Firstly, the back propagation (BP) neural network model is used to fit the distribution of the experiment samples, then the outlier is screened out based on the deviation index, and at last, the anomaly detection performance of the model is evaluated by the empirical algorithm. Based on the characteristics of the experimental data, the batch gradient descent combined with the momentum optimization method is selected to improve the stability and efficiency during training. Furthermore, by adding domain prior knowledge with the BP neural network model to constrain the fitting of the sample data, the model can reflect the influence of additional features during training. The research results show that the BP neural network model is suitable for the outlier detection of the rigid projectile penetrating concrete experiment data. The fusion of reasonable prior knowledge can improve the detection accuracy and the convergence speed of the model, furthermore, integrating different prior knowledge will cause different results.
Data quality is the basis for the validity and accuracy of data-driven models, and there may be a large number of anomalies in the raw concrete targets penetration depth data. Therefore, to ensure the accuracy of the subsequent data-driven model, it is necessary to eliminate the outlier of the raw data. Compared with the traditional anomaly detection method, the anomaly detection method based on neural network models is more suitable for complex multi-dimensional and unevenly distributed concrete target penetration depth data. However, relying only on the neural network model to fit the raw experimental data ignores the abundant and effective expert prior knowledge, which will reduce the accuracy of the model, and even lead to wrong prediction results due to the limited amount of data of the training sample, data bad pixels, poor data distribution, etc. To this end, an algorithm for outlier detection of concrete target penetration depth data combined with prior knowledge was proposed. Firstly, the back propagation (BP) neural network model is used to fit the distribution of the experiment samples, then the outlier is screened out based on the deviation index, and at last, the anomaly detection performance of the model is evaluated by the empirical algorithm. Based on the characteristics of the experimental data, the batch gradient descent combined with the momentum optimization method is selected to improve the stability and efficiency during training. Furthermore, by adding domain prior knowledge with the BP neural network model to constrain the fitting of the sample data, the model can reflect the influence of additional features during training. The research results show that the BP neural network model is suitable for the outlier detection of the rigid projectile penetrating concrete experiment data. The fusion of reasonable prior knowledge can improve the detection accuracy and the convergence speed of the model, furthermore, integrating different prior knowledge will cause different results.
2024, 44(3): 031407.
doi: 10.11883/bzycj-2023-0331
Abstract:
To address challenges in the field of large-scale explosive building damage assessment, where the explosion process is too complex for high-precision numerical simulation, and relying solely on change detection from remote sensing imagery cannot capture detailed internal information and lacks the capability of predicting in advance, this paper establishes a building damage assessment model for large-scale explosive events by coupling empirical mechanics models with remote sensing image interpretation and big data analysis. The study initially constructs a damage dataset based on specific historical cases of large-scale explosions. This involves extracting building damage information (including building types and damage levels) from remote sensing imagery and supplementing damage details with additional big data sources such as collected online images, videos, and news reports to enhance the precision of the sampled data. Geographic information systems spatial analysis is employed to digitize the damage information, obtaining data on building types, damage levels, and the distance from the target building to the explosion center, forming the damage dataset. Subsequently, the empirical model parameters are refined based on the training samples from the damage dataset, creating damage assessment models applicable to different building types for large-scale explosive events. The performance of the model is then tested using validation samples from the damage dataset. Experimental results demonstrate a model fitting goodness of over 96%, accuracy on validation samples exceeding 84%, and an overall error within an acceptable range. The model, under certain accuracy requirements, can provide guidance for site selection of storage locations for chemicals and hazardous materials, emergency evacuation of people in the event of a risk of large-scale explosions, critical equipment evacuation during an emergency, resource dispatching for rescue and relief after an accident, and building damage assessment.
To address challenges in the field of large-scale explosive building damage assessment, where the explosion process is too complex for high-precision numerical simulation, and relying solely on change detection from remote sensing imagery cannot capture detailed internal information and lacks the capability of predicting in advance, this paper establishes a building damage assessment model for large-scale explosive events by coupling empirical mechanics models with remote sensing image interpretation and big data analysis. The study initially constructs a damage dataset based on specific historical cases of large-scale explosions. This involves extracting building damage information (including building types and damage levels) from remote sensing imagery and supplementing damage details with additional big data sources such as collected online images, videos, and news reports to enhance the precision of the sampled data. Geographic information systems spatial analysis is employed to digitize the damage information, obtaining data on building types, damage levels, and the distance from the target building to the explosion center, forming the damage dataset. Subsequently, the empirical model parameters are refined based on the training samples from the damage dataset, creating damage assessment models applicable to different building types for large-scale explosive events. The performance of the model is then tested using validation samples from the damage dataset. Experimental results demonstrate a model fitting goodness of over 96%, accuracy on validation samples exceeding 84%, and an overall error within an acceptable range. The model, under certain accuracy requirements, can provide guidance for site selection of storage locations for chemicals and hazardous materials, emergency evacuation of people in the event of a risk of large-scale explosions, critical equipment evacuation during an emergency, resource dispatching for rescue and relief after an accident, and building damage assessment.
2024, 44(3): 032101.
doi: 10.11883/bzycj-2023-0123
Abstract:
There are frequent gas explosion accidents in urban rain and sewage drainage pipes, which pose a serious threat to people’s lives and property safety. To study the propagation characteristics of gas explosion and the law of gas-liquid two-phase coupling in urban underground drainage pipes, based on the gas-liquid two-phase flow theory and computational fluid dynamics method, a numerical simulation study of the explosion-acceleration-decay process of gas/air mixture under different water depth ratio was conducted. The results show that when the water depth ratio is less than 0.7, as the water depth ratio increases, the long-diameter ratio of the gas phase space increases, the fuel combustion intensifies, and the flame acceleration phenomenon gradually becomes significant, which leads to a gradual increase in peak overpressure, a gradual reduction in peak overpressure time, and a more significant effect of peak overpressure along the axial direction. When the water depth ratio reaches 0.7, the propagation of the flame in the pipeline is blocked, and the fluctuation caused by the water shock and the fine water column quickly occupy a small gas phase space, blocking the continuous propagation of the flame, which makes the explosion overpressure appear only near the ignition source. Under different water depth ratios, in the same zone of the pipeline and at the same moment, the height of the water being rolled up and the velocity field of the gas phase region is different, and the cryogenic liquid is rolled up to cool and block the high-temperature flame in the adjacent zone. Then, due to the macroscopic flow of the gas, the cryogenic gas adjacent to the liquid surface flows to the high-temperature region in the pipeline, resulting in a decrease in the flame temperature in the pipeline. The shock of water and the flying of fine water columns greatly reduce the risk of explosion overpressure. The research results provide a scientific basis for the explosion protection of urban gas lifelines.
There are frequent gas explosion accidents in urban rain and sewage drainage pipes, which pose a serious threat to people’s lives and property safety. To study the propagation characteristics of gas explosion and the law of gas-liquid two-phase coupling in urban underground drainage pipes, based on the gas-liquid two-phase flow theory and computational fluid dynamics method, a numerical simulation study of the explosion-acceleration-decay process of gas/air mixture under different water depth ratio was conducted. The results show that when the water depth ratio is less than 0.7, as the water depth ratio increases, the long-diameter ratio of the gas phase space increases, the fuel combustion intensifies, and the flame acceleration phenomenon gradually becomes significant, which leads to a gradual increase in peak overpressure, a gradual reduction in peak overpressure time, and a more significant effect of peak overpressure along the axial direction. When the water depth ratio reaches 0.7, the propagation of the flame in the pipeline is blocked, and the fluctuation caused by the water shock and the fine water column quickly occupy a small gas phase space, blocking the continuous propagation of the flame, which makes the explosion overpressure appear only near the ignition source. Under different water depth ratios, in the same zone of the pipeline and at the same moment, the height of the water being rolled up and the velocity field of the gas phase region is different, and the cryogenic liquid is rolled up to cool and block the high-temperature flame in the adjacent zone. Then, due to the macroscopic flow of the gas, the cryogenic gas adjacent to the liquid surface flows to the high-temperature region in the pipeline, resulting in a decrease in the flame temperature in the pipeline. The shock of water and the flying of fine water columns greatly reduce the risk of explosion overpressure. The research results provide a scientific basis for the explosion protection of urban gas lifelines.
2024, 44(3): 032201.
doi: 10.11883/bzycj-2023-0230
Abstract:
To effectively characterize the propagation characteristics of the explosion shock waves in tunnels at different altitudes, nonlinear explicit dynamics finite element software AUTODYN and dimensional analysis were used to study the influence of altitude on the propagation of explosion shock waves in long straight tunnels, and the influence characteristics of high altitude environments on the propagation of shock waves in tunnels were explored. First of all, the accuracy of the computational method was verified by comparing the peak overpressure and the time of overpressure rise of the small-scale shock tube test and the numerical simulation at the same measurement point. Then based on the AUTODYN-2D Euler symmetric algorithm and standard atmospheric parameters, the shock wave parameters of TNT explosion with 10 kg TNT spherical charge explosion in a tunnel with a diameter of 2.5 m and a length of 40 m at altitudes from 0 to 4000 m were computed, which were arranged with gauges with an axial interval of 2 m and a radial interval of 0.25 m, such as plane wave formation distance, peak overpressure, shock wave front propagation velocity, impulse, etc. In the end, a polynomial theoretic calculation model for shock wave peak overpressure in a tunnel at different altitudes was proposed with coefficients least-squares fitted from numerical simulation data at sea level, and the variables were obtained by dimensional analysis and the extended Sachs scaling law. The results show that, with the increase of altitude, the deviations between the propagation velocity of the explosion shock wave front and the radial parameters of the shock wave in the tunnel increases, the formation distance of the plane wave increases, and the peak overpressure of the shock wave decreases. Within the altitude range of 0 to 4000 m, the average value of shock wave impulse decreases by about 0.91% for every 1000 m increase. By combining the extended Sachs scaling law with dimensional analysis, a theoretical analysis model for calculating peak overpressure of shock waves at different altitudes with no more than 10% deviation is derived, which can provide a theoretical basis for explosion shock wave propagation in tunnels at high altitudes.
To effectively characterize the propagation characteristics of the explosion shock waves in tunnels at different altitudes, nonlinear explicit dynamics finite element software AUTODYN and dimensional analysis were used to study the influence of altitude on the propagation of explosion shock waves in long straight tunnels, and the influence characteristics of high altitude environments on the propagation of shock waves in tunnels were explored. First of all, the accuracy of the computational method was verified by comparing the peak overpressure and the time of overpressure rise of the small-scale shock tube test and the numerical simulation at the same measurement point. Then based on the AUTODYN-2D Euler symmetric algorithm and standard atmospheric parameters, the shock wave parameters of TNT explosion with 10 kg TNT spherical charge explosion in a tunnel with a diameter of 2.5 m and a length of 40 m at altitudes from 0 to 4000 m were computed, which were arranged with gauges with an axial interval of 2 m and a radial interval of 0.25 m, such as plane wave formation distance, peak overpressure, shock wave front propagation velocity, impulse, etc. In the end, a polynomial theoretic calculation model for shock wave peak overpressure in a tunnel at different altitudes was proposed with coefficients least-squares fitted from numerical simulation data at sea level, and the variables were obtained by dimensional analysis and the extended Sachs scaling law. The results show that, with the increase of altitude, the deviations between the propagation velocity of the explosion shock wave front and the radial parameters of the shock wave in the tunnel increases, the formation distance of the plane wave increases, and the peak overpressure of the shock wave decreases. Within the altitude range of 0 to 4000 m, the average value of shock wave impulse decreases by about 0.91% for every 1000 m increase. By combining the extended Sachs scaling law with dimensional analysis, a theoretical analysis model for calculating peak overpressure of shock waves at different altitudes with no more than 10% deviation is derived, which can provide a theoretical basis for explosion shock wave propagation in tunnels at high altitudes.
2024, 44(3): 032301.
doi: 10.11883/bzycj-2023-0011
Abstract:
Multiple damage effects can be generated when thermobaric explosives (TBX) detonated inside a tunnel, posing serious threats to people and equipment. Based on the explosion tests with different explosive masses, the explosion characteristics of the TBX detonated inside a tunnel are investigated. The thermal effects of fireball and the propagation law of the shock wave inside the tunnel are analyzed, the reduction degree of oxygen concentration is elucidated as well. Besides, the constraint effect of the tunnel on the afterburning of aluminum powders and the explosive mass conditions for the formation of afterburning effects at high intensity are discussed. It is shown that the radiation brightness of the fireball induced by the TBX is higher than TNT, and the temperature peak of TBX fireball is 1.3 times higher than that of TNT. During the process of fireball evolution, the temperature peak of the TBX fireball in the afterburning stage can increase by more than 10% compared to the temperature peak at the moment when the fireball is just stable. Regarding the propagation law of shock waves, the TNT equivalent coefficients of the overpressure peak and positive pressure time are approximately 1.4 and 1.65, respectively. In addition, the compressive waves generated by the afterburning of aluminum powders can provide various supplementary effects on the propagation of shock wave. The compressive wave with quickly rising process can be benefit for the increase in the pressure peak of the shock wave. In terms of the compressive wave with long duration and slow rising process, it can limit the attenuation of the shock wave and can extend the overall positive pressure time. Due to the constraint effect of the tunnel, the TBX fireball could interact with tunnel walls. As a consequence, the combustion intensity of aluminum powders will be enhanced. When the ratio between the cubic root of the TBX mass and the equivalent tunnel diameter is greater than 0.28 kg1/3/m, the afterburning effect at high intensity will emerge.
Multiple damage effects can be generated when thermobaric explosives (TBX) detonated inside a tunnel, posing serious threats to people and equipment. Based on the explosion tests with different explosive masses, the explosion characteristics of the TBX detonated inside a tunnel are investigated. The thermal effects of fireball and the propagation law of the shock wave inside the tunnel are analyzed, the reduction degree of oxygen concentration is elucidated as well. Besides, the constraint effect of the tunnel on the afterburning of aluminum powders and the explosive mass conditions for the formation of afterburning effects at high intensity are discussed. It is shown that the radiation brightness of the fireball induced by the TBX is higher than TNT, and the temperature peak of TBX fireball is 1.3 times higher than that of TNT. During the process of fireball evolution, the temperature peak of the TBX fireball in the afterburning stage can increase by more than 10% compared to the temperature peak at the moment when the fireball is just stable. Regarding the propagation law of shock waves, the TNT equivalent coefficients of the overpressure peak and positive pressure time are approximately 1.4 and 1.65, respectively. In addition, the compressive waves generated by the afterburning of aluminum powders can provide various supplementary effects on the propagation of shock wave. The compressive wave with quickly rising process can be benefit for the increase in the pressure peak of the shock wave. In terms of the compressive wave with long duration and slow rising process, it can limit the attenuation of the shock wave and can extend the overall positive pressure time. Due to the constraint effect of the tunnel, the TBX fireball could interact with tunnel walls. As a consequence, the combustion intensity of aluminum powders will be enhanced. When the ratio between the cubic root of the TBX mass and the equivalent tunnel diameter is greater than 0.28 kg1/3/m, the afterburning effect at high intensity will emerge.
2024, 44(3): 032901.
doi: 10.11883/bzycj-2023-0222
Abstract:
The issue of charge launch safety under the environment of high rifling pressure, high overload and high initial velocity has been one of the research hot topics. To investigate the impact mechanism of bottom gap on charge launch safety, a thermo-mechanical-solid coupling combustion model of the charge affected by bottom gap under impact loads based on the material point method is established. In this procedure, the formula for calculating temperature of air in the bottom gap during adiabatic compression is deduced, the relationship between the compression amount and the air temperature is quantitatively analyzed, the criteria and equation of state of the multi-material hybrid is constructed, and the calculation method of the temperature at the charge bottom affected by bottom gap in the launch process is established. The launch process of PBX charge with different bottom gap thicknesses is simulated by using the model, and the bottom temperature variation of PBX charge under different conditions are consistent with the experimental results, which verifies the correctness of the model. This model is then used to simulate the launch process of Composition B (COM B) charge with different bottom gap thickness in the launch environment, and the bottom temperature variation of charge is analyzed. The simulation results show that the charge temperature decreases gradually from the bottom to the top in the launch process and the area most likely to experience an ignition reaction is located at the charge bottom. The bottom temperature of COM B charge increases with the increase of the bottom gap thickness. The thickness of the bottom gap shall not be greater than 0.062 cm when the charge is in the launch safety state under the action of loading peak value of 324.7 MPa, which means that the presence of bottom gap seriously affects charge launch safety. From the simulation results, it is clear that the air in the bottom gap can be compressed in the launch process, and its temperature can rise rapidly; while in turn, it transfers heat to the charge bottom adjacent to the air, causing the temperature of the charge bottom to rise and making the charge bottom more susceptible to ignition reactions. The combustion model provides a theoretical basis for studying the charge launch safety.
The issue of charge launch safety under the environment of high rifling pressure, high overload and high initial velocity has been one of the research hot topics. To investigate the impact mechanism of bottom gap on charge launch safety, a thermo-mechanical-solid coupling combustion model of the charge affected by bottom gap under impact loads based on the material point method is established. In this procedure, the formula for calculating temperature of air in the bottom gap during adiabatic compression is deduced, the relationship between the compression amount and the air temperature is quantitatively analyzed, the criteria and equation of state of the multi-material hybrid is constructed, and the calculation method of the temperature at the charge bottom affected by bottom gap in the launch process is established. The launch process of PBX charge with different bottom gap thicknesses is simulated by using the model, and the bottom temperature variation of PBX charge under different conditions are consistent with the experimental results, which verifies the correctness of the model. This model is then used to simulate the launch process of Composition B (COM B) charge with different bottom gap thickness in the launch environment, and the bottom temperature variation of charge is analyzed. The simulation results show that the charge temperature decreases gradually from the bottom to the top in the launch process and the area most likely to experience an ignition reaction is located at the charge bottom. The bottom temperature of COM B charge increases with the increase of the bottom gap thickness. The thickness of the bottom gap shall not be greater than 0.062 cm when the charge is in the launch safety state under the action of loading peak value of 324.7 MPa, which means that the presence of bottom gap seriously affects charge launch safety. From the simulation results, it is clear that the air in the bottom gap can be compressed in the launch process, and its temperature can rise rapidly; while in turn, it transfers heat to the charge bottom adjacent to the air, causing the temperature of the charge bottom to rise and making the charge bottom more susceptible to ignition reactions. The combustion model provides a theoretical basis for studying the charge launch safety.
2024, 44(3): 033101.
doi: 10.11883/bzycj-2023-0124
Abstract:
Lattice sandwich structures often exhibit discontinuous characteristics under impact, with damage behaviors involving multiple scales, from micro-scale cell fracture to macro-scale structural collapse. Traditional methods based on continuum mechanics have difficulty in accurately describing non-continuum problems such as material interfaces and fracture behavior, so usually they can only handle single-scale problems. Besides, lattice materials have complex geometric shapes, and mesh-dependent numerical methods such as finite element analysis may suffer mesh sensitivity and may even struggle to obtain an ideal mesh. In order to effectively simulate the damage behavior of 3D printed lattice sandwich structures under projectile impact, a lattice sandwich structure modeling method based on the theory of peridynamics and micro-polar model, and by considering plastic bonds, is proposed. The simulation results of uniaxial compression and large-mass low-speed impact tests are compared with experimental results to verify the accuracy of the peridynamics model for lattice sandwich structures. This model is then used to analyze the damage patterns and failure mechanisms of lattice sandwich panels under projectile impact from low to high velocities. The results show that under low-speed impact, the failure mode of 3D printed lattice sandwich structures is mainly localized plastic deformation, which causes small-scale fractures in the lattice structure near the impact location after arriving at a certain level of strain; while under high-speed impact, it usually exhibits collapse, hole piercing, and fragment ejection, accompanied by extensive plastic deformation. The plastic yield range of 3D printed lattice sandwich structures shows different patterns under high-speed and low-speed impacts, with the plastic deformation range increasing as the impact velocity increases under low-speed impact, and decreasing under high-speed impact. This is mainly influenced by the characteristics of the lattice structure and the material crack propagation during the impact process. Under high-speed impact, the process of projectile penetration will go through four stages; i.e., panel contact, local yield, core material compression, and penetration. Because the material characteristics at each stage are different, the projectile will experience a “sharp-slow-sharp” deceleration process featured by to two acceleration peaks, with the second peak value being 50% lower than the first. Compared with high-speed impact, the projectile under low-speed impact only experiences one deceleration process, and the peak acceleration increases with increasing impact velocity. When the plastic deformation and damage process of the lattice sandwich structure cannot fully dissipate the kinetic energy of the projectile, the release of elastic strain energy in the sandwich structure will cause the projectile to bounce back. The rebound speed in this study is less than 30% of the initial velocity. The research results can provide theoretical support and new analytical methods for the design and application of lattice materials.
Lattice sandwich structures often exhibit discontinuous characteristics under impact, with damage behaviors involving multiple scales, from micro-scale cell fracture to macro-scale structural collapse. Traditional methods based on continuum mechanics have difficulty in accurately describing non-continuum problems such as material interfaces and fracture behavior, so usually they can only handle single-scale problems. Besides, lattice materials have complex geometric shapes, and mesh-dependent numerical methods such as finite element analysis may suffer mesh sensitivity and may even struggle to obtain an ideal mesh. In order to effectively simulate the damage behavior of 3D printed lattice sandwich structures under projectile impact, a lattice sandwich structure modeling method based on the theory of peridynamics and micro-polar model, and by considering plastic bonds, is proposed. The simulation results of uniaxial compression and large-mass low-speed impact tests are compared with experimental results to verify the accuracy of the peridynamics model for lattice sandwich structures. This model is then used to analyze the damage patterns and failure mechanisms of lattice sandwich panels under projectile impact from low to high velocities. The results show that under low-speed impact, the failure mode of 3D printed lattice sandwich structures is mainly localized plastic deformation, which causes small-scale fractures in the lattice structure near the impact location after arriving at a certain level of strain; while under high-speed impact, it usually exhibits collapse, hole piercing, and fragment ejection, accompanied by extensive plastic deformation. The plastic yield range of 3D printed lattice sandwich structures shows different patterns under high-speed and low-speed impacts, with the plastic deformation range increasing as the impact velocity increases under low-speed impact, and decreasing under high-speed impact. This is mainly influenced by the characteristics of the lattice structure and the material crack propagation during the impact process. Under high-speed impact, the process of projectile penetration will go through four stages; i.e., panel contact, local yield, core material compression, and penetration. Because the material characteristics at each stage are different, the projectile will experience a “sharp-slow-sharp” deceleration process featured by to two acceleration peaks, with the second peak value being 50% lower than the first. Compared with high-speed impact, the projectile under low-speed impact only experiences one deceleration process, and the peak acceleration increases with increasing impact velocity. When the plastic deformation and damage process of the lattice sandwich structure cannot fully dissipate the kinetic energy of the projectile, the release of elastic strain energy in the sandwich structure will cause the projectile to bounce back. The rebound speed in this study is less than 30% of the initial velocity. The research results can provide theoretical support and new analytical methods for the design and application of lattice materials.
2024, 44(3): 034101.
doi: 10.11883/bzycj-2023-0089
Abstract:
The Asay foil has been a widely applied diagnostic in ejecta measurement since its design was first reported in 1976. An Asay foil is a foil of a known mass (or areal density), whose velocity changed when it is impacted by ejecta. The Foil velocity is measured using velocimetry and the ejecta velocity is inferred from the initial gap between foil and free surface and the ejecta fly time. The mass of the impacting ejecta can then be inferred from the change in momentum of the foil. In some cases, the ejecta spray out from complex loading conditions such as double shock loading condition, the initial gap and fly time are unable to measure accurately, thus the Asay foil method doesn’t work. Therefore, it is necessary to develop an Asay foil method that does not depend on the initial gap and fly time. An improved Asay foil method is then developed based on the traditional Asay foil method. This method uses photonic Doppler velocimetry (PDV) to obtain the ejecta velocity in the testing area of the Asay foil probe, and the Asay foil probe obtains the foil velocity curve after the ejecta collides with the foil. Based on spatial position constraints and precise temporal correlation, the combination of the two velocity curve results can provide the total amount and distribution of ejecta under complex loading conditions. A numerical experimental method was used to generate ejecta particle groups with different distribution states, as well as the PDV velocity curve and Asay foil velocity curve to analyze the applicability of the method. In addition, the numerical experimental analysis results were verified using light gas gun experiments. The numerical experimental analysis results show that this method has good applicability in three typical ejecta distribution cases, with a deviation of less than 20% between the measured value and the theoretical value. The results of the light gas gun tests indicate that the deviation between the improved method and the traditional Asay foil method is less than 20%.
The Asay foil has been a widely applied diagnostic in ejecta measurement since its design was first reported in 1976. An Asay foil is a foil of a known mass (or areal density), whose velocity changed when it is impacted by ejecta. The Foil velocity is measured using velocimetry and the ejecta velocity is inferred from the initial gap between foil and free surface and the ejecta fly time. The mass of the impacting ejecta can then be inferred from the change in momentum of the foil. In some cases, the ejecta spray out from complex loading conditions such as double shock loading condition, the initial gap and fly time are unable to measure accurately, thus the Asay foil method doesn’t work. Therefore, it is necessary to develop an Asay foil method that does not depend on the initial gap and fly time. An improved Asay foil method is then developed based on the traditional Asay foil method. This method uses photonic Doppler velocimetry (PDV) to obtain the ejecta velocity in the testing area of the Asay foil probe, and the Asay foil probe obtains the foil velocity curve after the ejecta collides with the foil. Based on spatial position constraints and precise temporal correlation, the combination of the two velocity curve results can provide the total amount and distribution of ejecta under complex loading conditions. A numerical experimental method was used to generate ejecta particle groups with different distribution states, as well as the PDV velocity curve and Asay foil velocity curve to analyze the applicability of the method. In addition, the numerical experimental analysis results were verified using light gas gun experiments. The numerical experimental analysis results show that this method has good applicability in three typical ejecta distribution cases, with a deviation of less than 20% between the measured value and the theoretical value. The results of the light gas gun tests indicate that the deviation between the improved method and the traditional Asay foil method is less than 20%.
2024, 44(3): 035201.
doi: 10.11883/bzycj-2023-0206
Abstract:
Due to the deficiency that dynamic processes of rock blasting and rock failure zones around a blasthole are not simultaneously considered, the explosion load history of rock blasting considering rock failure zones and its reliability were investigated. Combining theoretical solutions of the dynamic processes of rock blasting and the rock failure zones around a blasthole, a theoretical formula of the explosive load history considering rock failure zones was derived, and a comparison was made between the derived explosive load history and a measured explosion pressure curve inside a blasthole. Both the field test on an ideal site and the numerical simulation including three explosion load conditions of single hole blasting were carried out, and the field and numerical results of blasting vibration were compared. The results show that the explosive load history considering rock failure zones consists of an ascending stage and three attenuation stages Ⅰ, Ⅱ, and Ⅲ, among which the ascending stage lasts for an extremely short time, while the attenuation stages last for a long time and are controlled by the stemming conditions. The change tendency of the calculated explosive load history considering rock failure zones is consistent with that of the measured explosion pressure curve, indicating the reliability of the explosive load history considering rock failure zones. The numerical results of single hole blasting vibration waveforms under the theoretical explosive load condition are consistent with the filed results, and the deviation ratios between the calculated peak particle velocity (PPV) results under the theoretical explosive load condition and the field PPV results are the smallest, most of which are within 7%, indicting the explosive load history considering rock failure zones has strong reliability. The explosive load history considering rock failure zones can be adjusted as the rock blasting system changes, and it has wide adaptability and good application potentials. The research results may help provide a theoretical basis for realizing efficient and accurate calculation about rock blasting.
Due to the deficiency that dynamic processes of rock blasting and rock failure zones around a blasthole are not simultaneously considered, the explosion load history of rock blasting considering rock failure zones and its reliability were investigated. Combining theoretical solutions of the dynamic processes of rock blasting and the rock failure zones around a blasthole, a theoretical formula of the explosive load history considering rock failure zones was derived, and a comparison was made between the derived explosive load history and a measured explosion pressure curve inside a blasthole. Both the field test on an ideal site and the numerical simulation including three explosion load conditions of single hole blasting were carried out, and the field and numerical results of blasting vibration were compared. The results show that the explosive load history considering rock failure zones consists of an ascending stage and three attenuation stages Ⅰ, Ⅱ, and Ⅲ, among which the ascending stage lasts for an extremely short time, while the attenuation stages last for a long time and are controlled by the stemming conditions. The change tendency of the calculated explosive load history considering rock failure zones is consistent with that of the measured explosion pressure curve, indicating the reliability of the explosive load history considering rock failure zones. The numerical results of single hole blasting vibration waveforms under the theoretical explosive load condition are consistent with the filed results, and the deviation ratios between the calculated peak particle velocity (PPV) results under the theoretical explosive load condition and the field PPV results are the smallest, most of which are within 7%, indicting the explosive load history considering rock failure zones has strong reliability. The explosive load history considering rock failure zones can be adjusted as the rock blasting system changes, and it has wide adaptability and good application potentials. The research results may help provide a theoretical basis for realizing efficient and accurate calculation about rock blasting.
