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2025,
45(8):
081001.
doi: 10.11883/bzycj-2024-0277
Abstract:
The explosion limit serves as a key parameter for assessing explosion risks and prevention strategies of combustible gases. Through a self-developed 5-liter experimental platform for flammable gas explosion characteristics, the upper explosive limits (UELs) of CH4/C2H6 and C2H6/H2O gas mixtures under high-temperature and high-pressure conditions were investigated, revealing the influence mechanisms of methane blending ratios and steam concentrations on the UELs of ethane under such extreme environments. The results demonstrate that methane blending ratios (0−0.5) exhibit minimal influence on the UELs of CH4/C2H6 mixtures at 200 ℃ and 0.4−0.6 MPa, and the UELs of CH4/C2H6 mixtures increase with increasing initial pressure, while exhibiting a progressively diminishing rate of UEL increment. Under identical thermal conditions (200 ℃, 0.4−0.6 MPa), the UELs of C2H6/H2O mixtures decrease approximately linearly with increasing water vapor concentrations (0−40%). Conversely, higher initial pressures enhance the UELs of C2H6/H2O mixtures. Notably, under 0.5 MPa pressure, as temperature increases from 200 ℃ to 270 ℃, the UELs of both pure ethane and C2H6/H2O mixtures containing 40% water vapor increase with a rise in temperature, with pure ethane demonstrating an accelerating UEL increase rate.
The explosion limit serves as a key parameter for assessing explosion risks and prevention strategies of combustible gases. Through a self-developed 5-liter experimental platform for flammable gas explosion characteristics, the upper explosive limits (UELs) of CH4/C2H6 and C2H6/H2O gas mixtures under high-temperature and high-pressure conditions were investigated, revealing the influence mechanisms of methane blending ratios and steam concentrations on the UELs of ethane under such extreme environments. The results demonstrate that methane blending ratios (0−0.5) exhibit minimal influence on the UELs of CH4/C2H6 mixtures at 200 ℃ and 0.4−0.6 MPa, and the UELs of CH4/C2H6 mixtures increase with increasing initial pressure, while exhibiting a progressively diminishing rate of UEL increment. Under identical thermal conditions (200 ℃, 0.4−0.6 MPa), the UELs of C2H6/H2O mixtures decrease approximately linearly with increasing water vapor concentrations (0−40%). Conversely, higher initial pressures enhance the UELs of C2H6/H2O mixtures. Notably, under 0.5 MPa pressure, as temperature increases from 200 ℃ to 270 ℃, the UELs of both pure ethane and C2H6/H2O mixtures containing 40% water vapor increase with a rise in temperature, with pure ethane demonstrating an accelerating UEL increase rate.
2025,
45(8):
081101.
doi: 10.11883/bzycj-2024-0225
Abstract:
With its high design freedom and rapid prototyping capabilities, additive manufacturing (AM) offers significant advantages in manufacturing critical components with complex geometries for the aerospace and defense industries. Ti-6Al-4V alloy, leveraging its exceptional combination of low density, high specific strength, and creep resistance, are extensively employed in critical structures that are frequently subjected to impact loading in aerospace and defense systems. A thorough understanding of the mechanical properties and underlying mechanisms of the additively manufactured Ti-6Al-4V alloy under static and dynamic loading is crucial for enhancing the service performance of these components. This paper systematically reviews and summarizes the latest advancements in the mechanical response of AM Ti-6Al-4V titanium alloys. Firstly, a brief overview of the classification and working principles of typical metal additive manufacturing (AM) technologies is provided. Subsequently, research efforts on the quasi-static tensile and dynamic compressive properties of additively manufactured Ti-6Al-4V titanium alloy are systematically reviewed, followed by a comparative analysis of its mechanical performance against cast and forged Ti-6Al-4V components. Furthermore, the mechanisms of correlation between the microstructure and mechanical behaviors of typical metal additive manufactured titanium alloys. Additionally, the commonly used post-processing techniques to mitigate the anisotropic mechanical response of AM Ti-6Al-4V alloy under static loading are summarizes.
With its high design freedom and rapid prototyping capabilities, additive manufacturing (AM) offers significant advantages in manufacturing critical components with complex geometries for the aerospace and defense industries. Ti-6Al-4V alloy, leveraging its exceptional combination of low density, high specific strength, and creep resistance, are extensively employed in critical structures that are frequently subjected to impact loading in aerospace and defense systems. A thorough understanding of the mechanical properties and underlying mechanisms of the additively manufactured Ti-6Al-4V alloy under static and dynamic loading is crucial for enhancing the service performance of these components. This paper systematically reviews and summarizes the latest advancements in the mechanical response of AM Ti-6Al-4V titanium alloys. Firstly, a brief overview of the classification and working principles of typical metal additive manufacturing (AM) technologies is provided. Subsequently, research efforts on the quasi-static tensile and dynamic compressive properties of additively manufactured Ti-6Al-4V titanium alloy are systematically reviewed, followed by a comparative analysis of its mechanical performance against cast and forged Ti-6Al-4V components. Furthermore, the mechanisms of correlation between the microstructure and mechanical behaviors of typical metal additive manufactured titanium alloys. Additionally, the commonly used post-processing techniques to mitigate the anisotropic mechanical response of AM Ti-6Al-4V alloy under static loading are summarizes.
2025,
45(8):
082101.
doi: 10.11883/bzycj-2024-0102
Abstract:
In order to reduce the great threat of gas explosion to coal mine operators and coal safety mining, the law of explosion overpressure and impact airflow velocity attenuation with the propagation distance of different volumes of gas-air mixed gas in roadway was deeply studied. Firstly, based on dimensional analysis, factors affecting the single-direction propagation attenuation of gas explosion overpressure in roadway were comprehensively considered, such as mixed gas energy, gas accumulation amount, measuring point distance and related parameters of roadway, and a dimensionless formula of single-direction propagation attenuation of gas explosion overpressure in roadway was obtained. Based on the regression analysis of the test data of gas explosion overpressure in large-size roadway, the mathematical model of unidirectional overpressure propagation attenuation in roadway was established, and the mathematical model of bidirectional overpressure propagation attenuation in roadway was established according to the law of energy similarity. According to the analysis process of influencing factors of single-direction propagation attenuation of gas explosion overpressure in roadway, a dimensionless formula of single-direction propagation attenuation of impact airflow velocity in roadway was obtained. Through regression analysis of test data of gas explosion impact airflow velocity in large-size roadway, a mathematical model of single-direction propagation attenuation of impact airflow velocity in roadway was established. According to the law of energy similarity, the mathematical model of the bidirectional propagation attenuation of the impact airflow velocity in the roadway was established. Secondly, according to the establishment process of the mathematical model of the unidirectional and bidirectional propagation attenuation of overpressure and impact airflow velocity in the roadway, the impact airflow velocity was included as one of the influencing factors in the consideration of the unidirectional propagation attenuation of gas explosion overpressure in the roadway in addition to the mixed gas energy, gas accumulation amount, measuring point distance and relevant parameters of the roadway. Based on the energy similarity law, the overpressure-airflow velocity relation of overpressure propagation attenuation in roadway was established. According to the establishment process of the overpressure-airflow velocity relation of the single and bidirectional propagation attenuation of gas explosion overpressure in roadway, the airflow velocity relation of the single and bidirectional propagation attenuation of the impact airflow velocity in roadway was established. Finally, the attenuation model and the mathematical relationship between overpressure and impact airflow velocity were verified. The results show that the energy of gas mixture, gas accumulation amount, the distance of measuring point, the hydraulic diameter and the cross-sectional area of roadway are the main factors affecting the attenuation of overpressure and impact airflow velocity. Both overpressure and impact airflow velocity are positively correlated with the amount of mixed gas accumulation. The greater the initial overpressure and impact airflow velocity, the faster the attenuation. The relative errors between the theoretical value and the test value of the attenuation model and the relative errors between the theoretical value and the test value of the relation are controlled at about 10%, and the overall consistency of the data is high, which verifies the reliability of the model and the mathematical relation, and can describe the law of gas explosion propagation more simply and intuitively, and realize the rapid calculation of overpressure and impact airflow velocity.
In order to reduce the great threat of gas explosion to coal mine operators and coal safety mining, the law of explosion overpressure and impact airflow velocity attenuation with the propagation distance of different volumes of gas-air mixed gas in roadway was deeply studied. Firstly, based on dimensional analysis, factors affecting the single-direction propagation attenuation of gas explosion overpressure in roadway were comprehensively considered, such as mixed gas energy, gas accumulation amount, measuring point distance and related parameters of roadway, and a dimensionless formula of single-direction propagation attenuation of gas explosion overpressure in roadway was obtained. Based on the regression analysis of the test data of gas explosion overpressure in large-size roadway, the mathematical model of unidirectional overpressure propagation attenuation in roadway was established, and the mathematical model of bidirectional overpressure propagation attenuation in roadway was established according to the law of energy similarity. According to the analysis process of influencing factors of single-direction propagation attenuation of gas explosion overpressure in roadway, a dimensionless formula of single-direction propagation attenuation of impact airflow velocity in roadway was obtained. Through regression analysis of test data of gas explosion impact airflow velocity in large-size roadway, a mathematical model of single-direction propagation attenuation of impact airflow velocity in roadway was established. According to the law of energy similarity, the mathematical model of the bidirectional propagation attenuation of the impact airflow velocity in the roadway was established. Secondly, according to the establishment process of the mathematical model of the unidirectional and bidirectional propagation attenuation of overpressure and impact airflow velocity in the roadway, the impact airflow velocity was included as one of the influencing factors in the consideration of the unidirectional propagation attenuation of gas explosion overpressure in the roadway in addition to the mixed gas energy, gas accumulation amount, measuring point distance and relevant parameters of the roadway. Based on the energy similarity law, the overpressure-airflow velocity relation of overpressure propagation attenuation in roadway was established. According to the establishment process of the overpressure-airflow velocity relation of the single and bidirectional propagation attenuation of gas explosion overpressure in roadway, the airflow velocity relation of the single and bidirectional propagation attenuation of the impact airflow velocity in roadway was established. Finally, the attenuation model and the mathematical relationship between overpressure and impact airflow velocity were verified. The results show that the energy of gas mixture, gas accumulation amount, the distance of measuring point, the hydraulic diameter and the cross-sectional area of roadway are the main factors affecting the attenuation of overpressure and impact airflow velocity. Both overpressure and impact airflow velocity are positively correlated with the amount of mixed gas accumulation. The greater the initial overpressure and impact airflow velocity, the faster the attenuation. The relative errors between the theoretical value and the test value of the attenuation model and the relative errors between the theoretical value and the test value of the relation are controlled at about 10%, and the overall consistency of the data is high, which verifies the reliability of the model and the mathematical relation, and can describe the law of gas explosion propagation more simply and intuitively, and realize the rapid calculation of overpressure and impact airflow velocity.
2025,
45(8):
083101.
doi: 10.11883/bzycj-2024-0207
Abstract:
To investigate the dynamic mechanical characterization of non-pure and non-intact ice materials under impact loads, a modified split Hopkinson pressure bar (SHPB) was used. Rapid loading, rod end cooling and waveform shaping techniques were used to ensure the stability of the ice material and achieve dynamic stress balance during loading. The impact mechanical properties of complete ice (pure water, containing 2.5%, 3.5%, 4.5% salt, containing 2.0%, 4.5%, 8.5% coconut) and spliced ice (splicing interface inclination 30°, 60°) at freezing temperature of −10 ℃ were studied. The strain rate ranges from 150−250 s−1. The failure process was recorded by using the high-speed camera triggered simultaneously with the pressure rod. The correlation between the stress and strain of the sample, along with the failure process, was determined by analyzing the time history curve of sample. The failure mode of the spliced ice sample was analyzed by combining the Mohr-Coulomb strength criterion. The results show that the pure water ice exhibits the highest compressive strength, followed by the ice with coconut shreds, and both of them show a positive strain rate effect. However, the compressive strength of the ice with salt addition decreases significantly due to its loose structure and the strain rate effect is not obvious. The dynamic compressive strength of ice samples added with coconut fiber increases firstly and then decreases with the increase of coconut fiber content. Ice samples with high coconut fiber content are prone to “double peak” phenomenon due to the binding effect of coconut fiber on broken ice with small particle size. The splicing plane affects the crack growth, resulting in lower compressive strength than the intact ice sample, and affects the failure mode as well. The ice with small interface inclination is mainly damaged by interface slip, while the ice with large interface inclination is mainly damaged by whole ice, which is similar to the intact ice. The research results provide theoretical basis and method reference for the dynamic mechanical properties of non-pure and non-intact ice materials under impact loads.
To investigate the dynamic mechanical characterization of non-pure and non-intact ice materials under impact loads, a modified split Hopkinson pressure bar (SHPB) was used. Rapid loading, rod end cooling and waveform shaping techniques were used to ensure the stability of the ice material and achieve dynamic stress balance during loading. The impact mechanical properties of complete ice (pure water, containing 2.5%, 3.5%, 4.5% salt, containing 2.0%, 4.5%, 8.5% coconut) and spliced ice (splicing interface inclination 30°, 60°) at freezing temperature of −10 ℃ were studied. The strain rate ranges from 150−250 s−1. The failure process was recorded by using the high-speed camera triggered simultaneously with the pressure rod. The correlation between the stress and strain of the sample, along with the failure process, was determined by analyzing the time history curve of sample. The failure mode of the spliced ice sample was analyzed by combining the Mohr-Coulomb strength criterion. The results show that the pure water ice exhibits the highest compressive strength, followed by the ice with coconut shreds, and both of them show a positive strain rate effect. However, the compressive strength of the ice with salt addition decreases significantly due to its loose structure and the strain rate effect is not obvious. The dynamic compressive strength of ice samples added with coconut fiber increases firstly and then decreases with the increase of coconut fiber content. Ice samples with high coconut fiber content are prone to “double peak” phenomenon due to the binding effect of coconut fiber on broken ice with small particle size. The splicing plane affects the crack growth, resulting in lower compressive strength than the intact ice sample, and affects the failure mode as well. The ice with small interface inclination is mainly damaged by interface slip, while the ice with large interface inclination is mainly damaged by whole ice, which is similar to the intact ice. The research results provide theoretical basis and method reference for the dynamic mechanical properties of non-pure and non-intact ice materials under impact loads.
2025,
45(8):
083102.
doi: 10.11883/bzycj-2024-0119
Abstract:
H-section steel columns have been widely employed in industrial buildings and parking lots, etc., which are vulnerable to crane-loading or vehicle collisions. Based on above background and previous experimental studies, the lateral impact model and residual load-carrying capacity model are established by using Abaqus finite element software to analyze the performance of H-section steel columns during and after impact loading. Firstly, the working mechanism, including the deformation characteristics, stress evolution and energy dissipation, is analyzed. Results indicate that under impact loading, the deformation pattern is mainly dominated by the global deformation, with the local deformation of the upper flange and out-of-plane buckling of the web. The time history curve of impact force exhibits an obvious plateau phase, and the existence of the pre-axial compression clearly reduces the impact resistance of the specimens. In general, H-section steel columns present favorable ductility performance during impact loading. Subsequently, a total of 108 parametric models are constructed, and the effects of load parameters (impact mass, impact velocity and axial load ratio), material parameter (steel yield strength) and geometric parameters (sectional area and specimen length) on the impact force, deformation, and residual load-carrying capacity are emphatically studied. The results show that as the impact mass, impact velocity, and/or pre-axial loading ratio increase, both the global and local deformations of H-section steel column will increase, while the residual load-carrying capacity will decrease. Finally, by considering the multi-factor interactions, the formulas for predicting global deformation and local deformation during impact and the residual load-carrying performance after impact are proposed by using response surface method. Results show that pre-axial loading is a key factor affecting global deformation, while the impact velocity mainly affects local deformation. In addition, both the pre-axial loading and impact velocity significantly interact with other parameters. The proposed formulas can be employed for the damage evaluation and design of H-section steel columns during the whole impact process and after impact event.
H-section steel columns have been widely employed in industrial buildings and parking lots, etc., which are vulnerable to crane-loading or vehicle collisions. Based on above background and previous experimental studies, the lateral impact model and residual load-carrying capacity model are established by using Abaqus finite element software to analyze the performance of H-section steel columns during and after impact loading. Firstly, the working mechanism, including the deformation characteristics, stress evolution and energy dissipation, is analyzed. Results indicate that under impact loading, the deformation pattern is mainly dominated by the global deformation, with the local deformation of the upper flange and out-of-plane buckling of the web. The time history curve of impact force exhibits an obvious plateau phase, and the existence of the pre-axial compression clearly reduces the impact resistance of the specimens. In general, H-section steel columns present favorable ductility performance during impact loading. Subsequently, a total of 108 parametric models are constructed, and the effects of load parameters (impact mass, impact velocity and axial load ratio), material parameter (steel yield strength) and geometric parameters (sectional area and specimen length) on the impact force, deformation, and residual load-carrying capacity are emphatically studied. The results show that as the impact mass, impact velocity, and/or pre-axial loading ratio increase, both the global and local deformations of H-section steel column will increase, while the residual load-carrying capacity will decrease. Finally, by considering the multi-factor interactions, the formulas for predicting global deformation and local deformation during impact and the residual load-carrying performance after impact are proposed by using response surface method. Results show that pre-axial loading is a key factor affecting global deformation, while the impact velocity mainly affects local deformation. In addition, both the pre-axial loading and impact velocity significantly interact with other parameters. The proposed formulas can be employed for the damage evaluation and design of H-section steel columns during the whole impact process and after impact event.
2025,
45(8):
083103.
doi: 10.11883/bzycj-2024-0002
Abstract:
To understand the dynamic fracture characteristics of nodular cast iron structures such as the spent nuclear fuel storage and transportation vessels under low temperatures and dynamic loads, the mode I dynamic fracture toughness (DFT) of nodular cast iron was tested at different temperatures (20, −40, −60 and −80 ℃) using an improved split Hopkinson pressure bar technique, and focused on studying the ductile-brittle transition behavior of the material. Standard three-point bending specimens with a fatigue crack were pre-fabricated before the experiment. A special fixture was used to replace the transmitter bar, while the temperature was controlled by a specially designed environmental chamber. The crack initiation time of the specimen was determined by the strain gauge method, and the dynamic stress intensity factor (DSIF) at the crack tip was determined using the experimental-numerical method. Mesh refinement and element transition were used at the crack tip region to ensure a high-accuracy result of the displacement field. On this basis, the mode Ⅰ DFT of the material was finally determined. The results show that under the same impact velocity, the DFT and the fracture initiation time of nodular cast iron decrease significantly with the decrease in temperature. As the temperature decreases, the macroscopic fracture surface of nodular cast iron changes from rough to relatively flat, indicating a change in the failure modes of the material. The effect of temperature on the failure mode is further verified by quantitative microscopic analysis of fracture surfaces. As the temperature decreases, the number of dimples on the fracture surface decreases, while river patterns and cleavage steps increase. It means that the ductility of the material is weakened, but the brittleness is enhanced at low temperatures. This ductile-brittle transition phenomenon is consistent with the tendency of the measured toughness of the material.
To understand the dynamic fracture characteristics of nodular cast iron structures such as the spent nuclear fuel storage and transportation vessels under low temperatures and dynamic loads, the mode I dynamic fracture toughness (DFT) of nodular cast iron was tested at different temperatures (20, −40, −60 and −80 ℃) using an improved split Hopkinson pressure bar technique, and focused on studying the ductile-brittle transition behavior of the material. Standard three-point bending specimens with a fatigue crack were pre-fabricated before the experiment. A special fixture was used to replace the transmitter bar, while the temperature was controlled by a specially designed environmental chamber. The crack initiation time of the specimen was determined by the strain gauge method, and the dynamic stress intensity factor (DSIF) at the crack tip was determined using the experimental-numerical method. Mesh refinement and element transition were used at the crack tip region to ensure a high-accuracy result of the displacement field. On this basis, the mode Ⅰ DFT of the material was finally determined. The results show that under the same impact velocity, the DFT and the fracture initiation time of nodular cast iron decrease significantly with the decrease in temperature. As the temperature decreases, the macroscopic fracture surface of nodular cast iron changes from rough to relatively flat, indicating a change in the failure modes of the material. The effect of temperature on the failure mode is further verified by quantitative microscopic analysis of fracture surfaces. As the temperature decreases, the number of dimples on the fracture surface decreases, while river patterns and cleavage steps increase. It means that the ductility of the material is weakened, but the brittleness is enhanced at low temperatures. This ductile-brittle transition phenomenon is consistent with the tendency of the measured toughness of the material.
2025,
45(8):
083301.
doi: 10.11883/bzycj-2024-0062
Abstract:
In order to study the deformation characteristics of thin-walled ellipsoidal shells under localized impact loading, experimental investigations and numerical simulations were conducted. The global deformation characteristics, central dent depth and dent boundary of the recovery ellipsoidal shell impacted by cylindrical projectiles at different velocities were obtained by projectile impact tests on a light gas gun apparatus and three-dimensional digital image correlation (DIC) technology for deformation process record. The simulation analysis focused on the effects of three different curvature radii on the depression depth and the lengths of the major and minor axes of the ellipsoidal shell. The primary dimensionless independent variables on which the dimensionless deformation characteristics depend were determined by means of dimensional analysis. The influence of less significant parameters was reduced through parameter sensitivity analysis. Under the condition of maintaining consistent scaling ratios for material properties, projectile dimensions, and shell thickness, specific response surface function expressions between dimensionless deformation characteristics vs. three curvature radii and velocity parameters were derived. A formula for predicting global deformation based on the depth of the depression and the depression boundary was proposed. The established expression can well describe the size effect and has a high prediction accuracy, and can provide reference for the design of impact load protection of large-sized curved thin shells in engineering.
In order to study the deformation characteristics of thin-walled ellipsoidal shells under localized impact loading, experimental investigations and numerical simulations were conducted. The global deformation characteristics, central dent depth and dent boundary of the recovery ellipsoidal shell impacted by cylindrical projectiles at different velocities were obtained by projectile impact tests on a light gas gun apparatus and three-dimensional digital image correlation (DIC) technology for deformation process record. The simulation analysis focused on the effects of three different curvature radii on the depression depth and the lengths of the major and minor axes of the ellipsoidal shell. The primary dimensionless independent variables on which the dimensionless deformation characteristics depend were determined by means of dimensional analysis. The influence of less significant parameters was reduced through parameter sensitivity analysis. Under the condition of maintaining consistent scaling ratios for material properties, projectile dimensions, and shell thickness, specific response surface function expressions between dimensionless deformation characteristics vs. three curvature radii and velocity parameters were derived. A formula for predicting global deformation based on the depth of the depression and the depression boundary was proposed. The established expression can well describe the size effect and has a high prediction accuracy, and can provide reference for the design of impact load protection of large-sized curved thin shells in engineering.
2025,
45(8):
083302.
doi: 10.11883/bzycj-2024-0261
Abstract:
Tolerances in machining and assembly often result in gaps within engineering structures. Under strong dynamic loading, gap jets may form within these gaps, thereby posing a threat to the reliability and safety of the structure. However, the formation mechanism of gap jets differs from that of traditional high-speed metal jets, and its formation process still requires systematic study. Hypervelocity impact loading experiments on tungsten samples with gaps were conducted using a two-stage light gas gun, and the formation and evolution of the gap jet were recorded using a high-speed framing camera. A numerical model for predicting the formation of gap jets was established using ANSYS Autodyn, and the applicability of the numerical simulation method was validated by comparing the numerical results with the jet morphology and head velocity history data obtained from a representative experiment. The effects of flyer velocity, gap width, and gap half-angle on the formation of the gap jet were investigated by adjusting these parameters in the numerical model, and the variations in the gap jet head velocity and mass with respect to these factors were obtained. The limitations of the steady-state jet model were analyzed, and an empirical model was developed to predict the jet head velocity and mass based on the findings from numerical simulations. The results show that the numerical model based on the Eulerian method can accurately predict the formation of the gap jet under strong dynamic loading. Loading pressure is found to be the main factor controlling the jet head velocity and mass; as the loading pressure increases, both the jet head velocity and mass increase accordingly. The gap width and half-angle have little effect on the jet head velocity, but the mass increases linearly with the gap width and half-angle. Due to significant errors in estimating the gap closing velocity, the steady jet model fails to accurately predict the formation of the gap jet. In contrast, the developed empirical model shows good agreement with the numerical results.
Tolerances in machining and assembly often result in gaps within engineering structures. Under strong dynamic loading, gap jets may form within these gaps, thereby posing a threat to the reliability and safety of the structure. However, the formation mechanism of gap jets differs from that of traditional high-speed metal jets, and its formation process still requires systematic study. Hypervelocity impact loading experiments on tungsten samples with gaps were conducted using a two-stage light gas gun, and the formation and evolution of the gap jet were recorded using a high-speed framing camera. A numerical model for predicting the formation of gap jets was established using ANSYS Autodyn, and the applicability of the numerical simulation method was validated by comparing the numerical results with the jet morphology and head velocity history data obtained from a representative experiment. The effects of flyer velocity, gap width, and gap half-angle on the formation of the gap jet were investigated by adjusting these parameters in the numerical model, and the variations in the gap jet head velocity and mass with respect to these factors were obtained. The limitations of the steady-state jet model were analyzed, and an empirical model was developed to predict the jet head velocity and mass based on the findings from numerical simulations. The results show that the numerical model based on the Eulerian method can accurately predict the formation of the gap jet under strong dynamic loading. Loading pressure is found to be the main factor controlling the jet head velocity and mass; as the loading pressure increases, both the jet head velocity and mass increase accordingly. The gap width and half-angle have little effect on the jet head velocity, but the mass increases linearly with the gap width and half-angle. Due to significant errors in estimating the gap closing velocity, the steady jet model fails to accurately predict the formation of the gap jet. In contrast, the developed empirical model shows good agreement with the numerical results.
2025,
45(8):
083303.
doi: 10.11883/bzycj-2024-0294
Abstract:
To accurately predict the initial velocity distribution of cylindrical casing under central point detonation at one end with different length-diameter ratios (L/D), it studied the impact of L/D on the initial velocity of fragments and the applicability of existing empirical models for the initial velocity of fragments founded on the numerical model of experimental verification. On this basis, a correction term related to L/D, which was often influenced by the axial rarefaction waves, was added to the fragment initial velocity index model. By fitting the data obtained from numerical simulations, the function expression of the correction term was derived and the calculation model for the initial velocity distribution of cylindrical casing with L/D≥1 was obtained. Finally, the applicability of the established fragment initial velocity calculation model was validated through experimental data and numerical simulations. The research results indicate that the initial velocity distribution of fragments under different L/D exhibits a trend where the initial velocities are lower at both ends and higher in the middle. Additionally, as the L/D raises, the initial velocity of the fragment also increases. When the L/D reaches 5, the relative error between the maximum initial velocity of the fragments and the calculated result using the Gurney formula is only 1.99%. However, the existing models for calculating initial velocities of fragment display significant errors when predicting smaller L/D in cylindrical casing. The average error between the formula calculation results and the experimental and numerical simulation results does not exceed 6%, indicating that the proposed model is reliable for predicting the initial velocity distribution of fragments under different L/D.
To accurately predict the initial velocity distribution of cylindrical casing under central point detonation at one end with different length-diameter ratios (L/D), it studied the impact of L/D on the initial velocity of fragments and the applicability of existing empirical models for the initial velocity of fragments founded on the numerical model of experimental verification. On this basis, a correction term related to L/D, which was often influenced by the axial rarefaction waves, was added to the fragment initial velocity index model. By fitting the data obtained from numerical simulations, the function expression of the correction term was derived and the calculation model for the initial velocity distribution of cylindrical casing with L/D≥1 was obtained. Finally, the applicability of the established fragment initial velocity calculation model was validated through experimental data and numerical simulations. The research results indicate that the initial velocity distribution of fragments under different L/D exhibits a trend where the initial velocities are lower at both ends and higher in the middle. Additionally, as the L/D raises, the initial velocity of the fragment also increases. When the L/D reaches 5, the relative error between the maximum initial velocity of the fragments and the calculated result using the Gurney formula is only 1.99%. However, the existing models for calculating initial velocities of fragment display significant errors when predicting smaller L/D in cylindrical casing. The average error between the formula calculation results and the experimental and numerical simulation results does not exceed 6%, indicating that the proposed model is reliable for predicting the initial velocity distribution of fragments under different L/D.
2025,
45(8):
083304.
doi: 10.11883/bzycj-2024-0128
Abstract:
In the near-field explosion of improvised explosive device, the protective structure is often subjected to the combined action of blast wave and fragments. To improve the protection performance of the structure, a composite structural material containing foamed aluminum/fiber sandwich was designed and prepared. The explosion and penetration experiment was carried out to study the failure mode of the composite structure under the combined action of explosion shock wave and high-speed fragments. In the experiment, the time for the explosive shock wave to reach the surface of the composite plate and the pressure attenuation before and after passing through the material were tested by installing PVDF pressure gauges on the upper and lower surfaces of the composite plate. Meanwhile, the time for the shock wave to reach the surface of the composite plate was measured by piezoelectric probes for the purpose of verification. The time for fragments to reach the surface of the composite plate was tested using a comb-shaped target, and the velocity attenuation of fragments after penetrating the target plate was obtained. The influence of the two loading’s timing sequence of explosion shock wave and fragment on the failure mode was discussed, and the energy absorption mechanism of different materials was analyzed. The results show that the change of detonation distance directly affects the timing sequence of the action of explosion shock wave and fragment. In the conditions discussed in this paper, when the detonation distance is greater than 600 mm, the fragment acts before the shock wave. Under the combined action of shock wave and fragment, the aluminum plate is accompanied by local sag deformation in addition to the penetration failure of fragments. The cellular structure of foamed aluminum was crushed and deformed under the impact load. The fibers at the bullet hole are stretched and fractured under the penetration of fragments, and are accompanied by high temperature failure. Under the two sequential effects, the existence of bullet holes weakens the effect of shock wave on the front aluminum plate, and the deformation and damage degree of the later sandwich structural material and the rear aluminum plate are more serious than that of the previous material. This research provides a technical basis for the application and functional design of lightweight composite structural materials in the field of near-burst protection in limited space.
In the near-field explosion of improvised explosive device, the protective structure is often subjected to the combined action of blast wave and fragments. To improve the protection performance of the structure, a composite structural material containing foamed aluminum/fiber sandwich was designed and prepared. The explosion and penetration experiment was carried out to study the failure mode of the composite structure under the combined action of explosion shock wave and high-speed fragments. In the experiment, the time for the explosive shock wave to reach the surface of the composite plate and the pressure attenuation before and after passing through the material were tested by installing PVDF pressure gauges on the upper and lower surfaces of the composite plate. Meanwhile, the time for the shock wave to reach the surface of the composite plate was measured by piezoelectric probes for the purpose of verification. The time for fragments to reach the surface of the composite plate was tested using a comb-shaped target, and the velocity attenuation of fragments after penetrating the target plate was obtained. The influence of the two loading’s timing sequence of explosion shock wave and fragment on the failure mode was discussed, and the energy absorption mechanism of different materials was analyzed. The results show that the change of detonation distance directly affects the timing sequence of the action of explosion shock wave and fragment. In the conditions discussed in this paper, when the detonation distance is greater than 600 mm, the fragment acts before the shock wave. Under the combined action of shock wave and fragment, the aluminum plate is accompanied by local sag deformation in addition to the penetration failure of fragments. The cellular structure of foamed aluminum was crushed and deformed under the impact load. The fibers at the bullet hole are stretched and fractured under the penetration of fragments, and are accompanied by high temperature failure. Under the two sequential effects, the existence of bullet holes weakens the effect of shock wave on the front aluminum plate, and the deformation and damage degree of the later sandwich structural material and the rear aluminum plate are more serious than that of the previous material. This research provides a technical basis for the application and functional design of lightweight composite structural materials in the field of near-burst protection in limited space.
2025,
45(8):
083305.
doi: 10.11883/bzycj-2024-0156
Abstract:
Abrasive water jet (AWJ) perforation is an effective mean for stimulation in oil and gas wells. However, the mechanism of perforation formation and the regulation of its parameter remain poorly understood. This study investigates the variation in hole shape during AWJ perforation through a series of experimental designs and analyses. By analyzing the variation in perforation shape with injection time, the rock-breaking damage caused by AWJ and the flow characteristics in the perforation were quantitatively characterized. The results show that the process of perforation formation is governed by the coupling of three physical effects. The inflow increases the hole depth by vertically impacting the hole tip, while the backflow enlarges the hole diameter by eroding the hole wall. As the fluid mechanical energy dissipates along the path, the evolution of the perforation slows down during the later perforation period. Because the rock breaking ability of inflow is stronger than that of backflow, the ratio of hole depth to hole diameter of AWJ perforation increases with the increase of injection time. Specifically, when the injection time ranges from 5 s to 300 s, the ratio increases from 7 to 28. The rock breaking ability of the backflow decreases from the tip to the orifice, whereas the duration of the backflow’s action on the hole wall increases in the same direction. Under the combined influence of rock breaking ability and rock breaking time, the hole evolves from a conical shape to a spindle shape, and the degree of spindle increases. With the increase of injection time and hole depth, the fluid mechanical energy loss becomes more severe. The change rate of hole depth decreased to 11.3% and the change rate of hole diameter decreased to 4.3%. The evolution of the AWJ perforation became slow.
Abrasive water jet (AWJ) perforation is an effective mean for stimulation in oil and gas wells. However, the mechanism of perforation formation and the regulation of its parameter remain poorly understood. This study investigates the variation in hole shape during AWJ perforation through a series of experimental designs and analyses. By analyzing the variation in perforation shape with injection time, the rock-breaking damage caused by AWJ and the flow characteristics in the perforation were quantitatively characterized. The results show that the process of perforation formation is governed by the coupling of three physical effects. The inflow increases the hole depth by vertically impacting the hole tip, while the backflow enlarges the hole diameter by eroding the hole wall. As the fluid mechanical energy dissipates along the path, the evolution of the perforation slows down during the later perforation period. Because the rock breaking ability of inflow is stronger than that of backflow, the ratio of hole depth to hole diameter of AWJ perforation increases with the increase of injection time. Specifically, when the injection time ranges from 5 s to 300 s, the ratio increases from 7 to 28. The rock breaking ability of the backflow decreases from the tip to the orifice, whereas the duration of the backflow’s action on the hole wall increases in the same direction. Under the combined influence of rock breaking ability and rock breaking time, the hole evolves from a conical shape to a spindle shape, and the degree of spindle increases. With the increase of injection time and hole depth, the fluid mechanical energy loss becomes more severe. The change rate of hole depth decreased to 11.3% and the change rate of hole diameter decreased to 4.3%. The evolution of the AWJ perforation became slow.
2025,
45(8):
084201.
doi: 10.11883/bzycj-2024-0191
Abstract:
For the estimation of blast loading in complex structures, traditional numerical simulation methods were computationally intensive whereas rapid estimation methods based on neural networks can only provide estimates at local points without providing confidence intervals for the predicted results. To achieve fast and reliable estimation of the blast loading in complex structures, Bayesian theory was combined with deep learning to develop a Bayesian deep learning approach for rapid estimation of blast loading in complex structures. The approach initially utilized open-source numerical simulation software to generate a dataset of blast loading in complex structures, encompassing a wide range of parameters such as explosion equivalents, locations, and velocities. During this process, mesh sizes that balanced computational accuracy and speed were determined through mesh sensitivity analysis and the verification of the numerical simulation accuracy. Then, the deep learning model was extended into a Bayesian deep learning model based on Bayesian theory. By introducing probability distributions over the weights of the neural network, the model parameters were treated as random variables. Variational Bayesian inference was then employed to efficiently train the model, ensuring the accuracy of rapid blast loading estimation while also equipping the model with the ability to quantify uncertainty. Finally, metrics such as mean absolute percentage error (MAPE), normalized mean prediction interval width (NMPIW) and prediction interval coverage probability (PICP) were adopted to quantitatively assess the model's estimated accuracy and the precision of the uncertainty quantification. Additionally, an error decomposition of the estimation results was conducted to analyze model’s performance based on target parameters and scaled distance. The results indicate that the proposed method achieved an estimation error of 12.2% on the test set, with a confidence interval covering over 81.6% of true values, and less than 20 milliseconds of the estimation time for a single sample point. This method provides a novel approach for fast and accurate estimation of blast loading in complex structures with sufficient confidence for the estimation results.
For the estimation of blast loading in complex structures, traditional numerical simulation methods were computationally intensive whereas rapid estimation methods based on neural networks can only provide estimates at local points without providing confidence intervals for the predicted results. To achieve fast and reliable estimation of the blast loading in complex structures, Bayesian theory was combined with deep learning to develop a Bayesian deep learning approach for rapid estimation of blast loading in complex structures. The approach initially utilized open-source numerical simulation software to generate a dataset of blast loading in complex structures, encompassing a wide range of parameters such as explosion equivalents, locations, and velocities. During this process, mesh sizes that balanced computational accuracy and speed were determined through mesh sensitivity analysis and the verification of the numerical simulation accuracy. Then, the deep learning model was extended into a Bayesian deep learning model based on Bayesian theory. By introducing probability distributions over the weights of the neural network, the model parameters were treated as random variables. Variational Bayesian inference was then employed to efficiently train the model, ensuring the accuracy of rapid blast loading estimation while also equipping the model with the ability to quantify uncertainty. Finally, metrics such as mean absolute percentage error (MAPE), normalized mean prediction interval width (NMPIW) and prediction interval coverage probability (PICP) were adopted to quantitatively assess the model's estimated accuracy and the precision of the uncertainty quantification. Additionally, an error decomposition of the estimation results was conducted to analyze model’s performance based on target parameters and scaled distance. The results indicate that the proposed method achieved an estimation error of 12.2% on the test set, with a confidence interval covering over 81.6% of true values, and less than 20 milliseconds of the estimation time for a single sample point. This method provides a novel approach for fast and accurate estimation of blast loading in complex structures with sufficient confidence for the estimation results.
2025,
45(8):
084202.
doi: 10.11883/bzycj-2024-0147
Abstract:
In order to improve the quantitative characterization of the penetration process of tungsten alloy projectile into the target, the numerical methods such as FEM (finite element method), SPG (smoothed particle Galerkin), SPH (smoothed particle hydrodynamics), and FE-SPH (finite element-smoothed particle hydrodynamics) adaptive simulation methods were employed to simulate the penetration of tungsten alloy projectiles into Q235A steel targets. Based on numerical simulations, a comparison was made of the advantages and disadvantages of the four numerical simulation methods for calculating the residual velocity of the projectile after penetrating the target, the perforation diameter of the target, and the distribution of secondary fragments by the projectile penetration. The results show that, for calculating the residual velocity of the projectile, FEM and FE-SPH adaptive methods strictly rely on the selection of failure criteria and corresponding parameters, as FEM employs an element erosion algorithm to model material failure, while SPG method, as it does not require adjusting the failure parameters in bond failure mode, can obtain relatively accurate calculations; for predicting perforation diameter, FEM and FE-SPH adaptive methods accurately represent material boundaries and perforation morphology, although the perforation diameter varies significantly under different failure criteria, while the SPG method can accurately predict the perforation diameter of target plates due to its insensitive to failure parameters; for analzing secondary fragments generation and distribution, both FE-SPH adaptive and SPH methods effectively characterize these phenomena, while the FE-SPH adaptive method provides detailed information on large fragments, it is less computationally efficient than the SPH method.
In order to improve the quantitative characterization of the penetration process of tungsten alloy projectile into the target, the numerical methods such as FEM (finite element method), SPG (smoothed particle Galerkin), SPH (smoothed particle hydrodynamics), and FE-SPH (finite element-smoothed particle hydrodynamics) adaptive simulation methods were employed to simulate the penetration of tungsten alloy projectiles into Q235A steel targets. Based on numerical simulations, a comparison was made of the advantages and disadvantages of the four numerical simulation methods for calculating the residual velocity of the projectile after penetrating the target, the perforation diameter of the target, and the distribution of secondary fragments by the projectile penetration. The results show that, for calculating the residual velocity of the projectile, FEM and FE-SPH adaptive methods strictly rely on the selection of failure criteria and corresponding parameters, as FEM employs an element erosion algorithm to model material failure, while SPG method, as it does not require adjusting the failure parameters in bond failure mode, can obtain relatively accurate calculations; for predicting perforation diameter, FEM and FE-SPH adaptive methods accurately represent material boundaries and perforation morphology, although the perforation diameter varies significantly under different failure criteria, while the SPG method can accurately predict the perforation diameter of target plates due to its insensitive to failure parameters; for analzing secondary fragments generation and distribution, both FE-SPH adaptive and SPH methods effectively characterize these phenomena, while the FE-SPH adaptive method provides detailed information on large fragments, it is less computationally efficient than the SPH method.
2025,
45(8):
085201.
doi: 10.11883/bzycj-2024-0254
Abstract:
To address the issues of over-excavation at the tunnel arch foot due to the difficulty of forming the perimeter hole blasting and under-excavation at the tunnel face bottom, the damage characteristics of the surrounding rock caused by perimeter hole blasting at the arch foot of a horseshoe-shaped tunnel were studied through a combination of theoretical calculations and numerical simulations. On the theoretical level, an in-depth analysis of the stress distribution and crack radius in the arch foot area was conducted based on the principles of blasting mechanics, and the theoretical charge length for the perimeter holes at the arch foot was derived. Building on this, a 3D numerical model of the perimeter holes at the arch foot was established through numerical simulation. During the modeling process, the damage evolution in the surrounding rock during blasting was simulated by introducing an appropriate damage model, along with the generation of post-blast damage cloud maps. By comparing the damage cloud maps under different conditions, the relationship between blasting effectiveness and parameters such as free surface shape, charge amount, and void deflection angle was analyzed, further revealing the mechanisms by which these parameters influence the blasting formation results, which were validated through field experiments. The research results indicate that the shape of the free surface significantly affects the extent of surrounding rock damage and the energy utilization efficiency of explosives. A concave free surface results in a smaller damage range compared to a flat free surface, with greater rock confinement, making it difficult for the explosives to effectively fracture the surrounding rock, leading to an energy utilization rate of only 78%. The blasting effectiveness shows a trend of first increasing and then decreasing with the increase in charge amount, with the optimal blasting effectiveness achieved when the linear charge density of the perimeter holes at the arch foot is 0.624. Additionally, by setting voids and adjusting the void deflection angle, the blasting effectiveness of the perimeter holes at the arch foot can be improved. With the optimized blasting parameters, the maximum linear over-excavation at the arch foot was reduced by 53.1%, resulting in a smooth tunnel contour. The research outcomes are engineeringly feasible and provide valuable insights for similar projects.
To address the issues of over-excavation at the tunnel arch foot due to the difficulty of forming the perimeter hole blasting and under-excavation at the tunnel face bottom, the damage characteristics of the surrounding rock caused by perimeter hole blasting at the arch foot of a horseshoe-shaped tunnel were studied through a combination of theoretical calculations and numerical simulations. On the theoretical level, an in-depth analysis of the stress distribution and crack radius in the arch foot area was conducted based on the principles of blasting mechanics, and the theoretical charge length for the perimeter holes at the arch foot was derived. Building on this, a 3D numerical model of the perimeter holes at the arch foot was established through numerical simulation. During the modeling process, the damage evolution in the surrounding rock during blasting was simulated by introducing an appropriate damage model, along with the generation of post-blast damage cloud maps. By comparing the damage cloud maps under different conditions, the relationship between blasting effectiveness and parameters such as free surface shape, charge amount, and void deflection angle was analyzed, further revealing the mechanisms by which these parameters influence the blasting formation results, which were validated through field experiments. The research results indicate that the shape of the free surface significantly affects the extent of surrounding rock damage and the energy utilization efficiency of explosives. A concave free surface results in a smaller damage range compared to a flat free surface, with greater rock confinement, making it difficult for the explosives to effectively fracture the surrounding rock, leading to an energy utilization rate of only 78%. The blasting effectiveness shows a trend of first increasing and then decreasing with the increase in charge amount, with the optimal blasting effectiveness achieved when the linear charge density of the perimeter holes at the arch foot is 0.624. Additionally, by setting voids and adjusting the void deflection angle, the blasting effectiveness of the perimeter holes at the arch foot can be improved. With the optimized blasting parameters, the maximum linear over-excavation at the arch foot was reduced by 53.1%, resulting in a smooth tunnel contour. The research outcomes are engineeringly feasible and provide valuable insights for similar projects.
