2022 Vol. 42, No. 10
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2022, 42(10): 102901.
doi: 10.11883/bzycj-2021-0521
Abstract:
The study of slow cook-off of composite propellant containing ammonium perchlorate (AP) is the focus of the research on propellant safety, while the pre-ignition is a common and effective way to reduce the intensity of reaction in slow cook-off of engine. To investigate the effect of pre-ignition temperature on its response characteristics, a set of slow cook off experiments of composite propellant was designed and carried out, and the response characteristics of ignition at different temperatures were studied. The temperature distribution of the propellant and the thermal damage law of propellant microstructure before ignition were investigated by numerical simulation and thermal decomposition experiment. The results show that the engine spontaneously ignited with a reaction level of violent explosion, and the reaction level was burning when it was ignited at 120 ℃. The intensity of the reaction could be reduced effectively by pre-ignition when the propellant temperature was low before auto-ignition. The thermal decomposition process and thermal structure damage evolution of the propellant during slow cook-off were studied by thermogravimetry analysis combined with morphological characterization. As the heating temperature increased, some components of the propellant were decomposed, causing the internal temperature of the propellant to be higher than that of the shell, while the breakdown of binders and AP in the propellant resulted in a porous structure of the propellant charge, more likely leading to convection combustion after ignition and increasing the intensity of the reaction. Due to the autothermal reaction of the propellant, the highest temperature of the propellant reached 150 ℃ when the shell temperature was only 138 ℃. The highest temperature first appeared near the tail of the nozzle. Considering the influence of porous structure caused by AP decomposition on the intensity of reaction, the ignition temperature in advance should be lower than 138℃. In order to avoid the decomposition in the propellant to produce porous structure, which would cause severe reaction after ignition, some measures should be taken in igniting the propellant before the main propellant reaches auto-ignition temperature, which can effectively reduce the intensity of reaction.
The study of slow cook-off of composite propellant containing ammonium perchlorate (AP) is the focus of the research on propellant safety, while the pre-ignition is a common and effective way to reduce the intensity of reaction in slow cook-off of engine. To investigate the effect of pre-ignition temperature on its response characteristics, a set of slow cook off experiments of composite propellant was designed and carried out, and the response characteristics of ignition at different temperatures were studied. The temperature distribution of the propellant and the thermal damage law of propellant microstructure before ignition were investigated by numerical simulation and thermal decomposition experiment. The results show that the engine spontaneously ignited with a reaction level of violent explosion, and the reaction level was burning when it was ignited at 120 ℃. The intensity of the reaction could be reduced effectively by pre-ignition when the propellant temperature was low before auto-ignition. The thermal decomposition process and thermal structure damage evolution of the propellant during slow cook-off were studied by thermogravimetry analysis combined with morphological characterization. As the heating temperature increased, some components of the propellant were decomposed, causing the internal temperature of the propellant to be higher than that of the shell, while the breakdown of binders and AP in the propellant resulted in a porous structure of the propellant charge, more likely leading to convection combustion after ignition and increasing the intensity of the reaction. Due to the autothermal reaction of the propellant, the highest temperature of the propellant reached 150 ℃ when the shell temperature was only 138 ℃. The highest temperature first appeared near the tail of the nozzle. Considering the influence of porous structure caused by AP decomposition on the intensity of reaction, the ignition temperature in advance should be lower than 138℃. In order to avoid the decomposition in the propellant to produce porous structure, which would cause severe reaction after ignition, some measures should be taken in igniting the propellant before the main propellant reaches auto-ignition temperature, which can effectively reduce the intensity of reaction.
2022, 42(10): 103101.
doi: 10.11883/bzycj-2021-0394
Abstract:
Electrochemical corrosion and fatigue tests were carried out to study the corrosion resistance and fatigue resistance of the pressure vessel material Q345R steel after laser shock peening (LSP). The material was cut into samples of 6 mm×10 mm×10 mm, with water as constraint layer and black tape as absorption layer. Laser shock peening was carried out for 1, 3, 5 and 7 times respectively. The samples were immerged in 3.5% NaCl solution for electrochemical corrosion. Tafel extrapolation method was used to obtain the polarization curves of the corrosion resistance of the reactive materials. The results show that the samples have the best corrosion resistance after a single shock, their corrosion resistances decrease after multiple shocks, the corrosion resistance without black tape decreases more obviously, the black tape serving as absorbing layer can effectively protect the sample from the LSP damage. The micro-observations show that surface cracks on corrosion specimen after LSP were significantly less than those on the untreated sample. S-N curves were obtained by MTS fatigue test of samples after different corrosion time and LSP times. The results show that under the same stress condition, the fatigue life of samples after 1- or 2-hours’ corrosion decreased 36.8% and 56.4%, respectively compared with that of the original sample. After one and three shocks, the fatigue life of the specimens increases 43.8% and 198.2%, respectively. X-ray diffraction (XRD) was used to analyze the residual stress on the surface of the sample. It was detected that the residual tensile stress on the surface of the untreated sample is 34.4MPa, and the residual compressive stresses on the surface of samples after one and three shocks were 205.6 and 288.5 MPa, respecitvely. It indicates that the residual compressive stress layer with a certain depth was formed on the surface, which inhibited the crack propagation and improved the fatigue life.
Electrochemical corrosion and fatigue tests were carried out to study the corrosion resistance and fatigue resistance of the pressure vessel material Q345R steel after laser shock peening (LSP). The material was cut into samples of 6 mm×10 mm×10 mm, with water as constraint layer and black tape as absorption layer. Laser shock peening was carried out for 1, 3, 5 and 7 times respectively. The samples were immerged in 3.5% NaCl solution for electrochemical corrosion. Tafel extrapolation method was used to obtain the polarization curves of the corrosion resistance of the reactive materials. The results show that the samples have the best corrosion resistance after a single shock, their corrosion resistances decrease after multiple shocks, the corrosion resistance without black tape decreases more obviously, the black tape serving as absorbing layer can effectively protect the sample from the LSP damage. The micro-observations show that surface cracks on corrosion specimen after LSP were significantly less than those on the untreated sample. S-N curves were obtained by MTS fatigue test of samples after different corrosion time and LSP times. The results show that under the same stress condition, the fatigue life of samples after 1- or 2-hours’ corrosion decreased 36.8% and 56.4%, respectively compared with that of the original sample. After one and three shocks, the fatigue life of the specimens increases 43.8% and 198.2%, respectively. X-ray diffraction (XRD) was used to analyze the residual stress on the surface of the sample. It was detected that the residual tensile stress on the surface of the untreated sample is 34.4MPa, and the residual compressive stresses on the surface of samples after one and three shocks were 205.6 and 288.5 MPa, respecitvely. It indicates that the residual compressive stress layer with a certain depth was formed on the surface, which inhibited the crack propagation and improved the fatigue life.
2022, 42(10): 103102.
doi: 10.11883/bzycj-2021-0447
Abstract:
Aiming at a clarification of the differences in dynamic mechanical properties of rock specimens with different sizes when characterized by a large diameter split Hopkinson pressure bar system, sandstone specimens with three different diameters (50, 75 and 100 mm) and five kinds of length-diameter ratios (0.4, 0.5, 0.6, 0.8 and 1.0) were employed for impact experiments on a pressure bar of diameter 100 mm. The variations of stress versus strain and strain rate versus time of specimens with different sizes were analyzed. The concept of a superposition coefficient for comparing waveform alignment overlap was then proposed, and together with the equilibrium factor it was used to study dynamic stress equilibrium. Thus, the recommended size range of specimens was determined for large-diameter split Hopkinson pressure bar tests. Also, a high-speed camera was used to observe the dynamic damage of the specimens. The results show that when the length-diameter ratio of specimen remains the same, the tested dynamic compressive strengths are close for the specimens of diameter 75 mm and 100 mm, but it is affected by more pronounced specimen length for the specimens of diameter 50 mm. With the increase of specimen’s diameter, the curve of strain rate versus time changes from single peak to double peak. The small-size specimen is more prone to axial splitting failure, and the large-size specimen produces larger tensile stress due to the superposition of internal stress waves, which is prone to the composite failure of spallation tension and axial splitting. When the specimen with a diameter of 75 mm and the length-diameter ratio of 0.3–0.4 is used, the coincidence degree after waveform alignment is better, sufficient stress balance time is achieved before initial failure, and the strain rate loading is more effective. It is helpful to reveal the size effect on the rock dynamic compression mechanical properties with different sizes of specimens, as it can provide a good reference for the specimen size selection in large-diameter SHPB tests.
Aiming at a clarification of the differences in dynamic mechanical properties of rock specimens with different sizes when characterized by a large diameter split Hopkinson pressure bar system, sandstone specimens with three different diameters (50, 75 and 100 mm) and five kinds of length-diameter ratios (0.4, 0.5, 0.6, 0.8 and 1.0) were employed for impact experiments on a pressure bar of diameter 100 mm. The variations of stress versus strain and strain rate versus time of specimens with different sizes were analyzed. The concept of a superposition coefficient for comparing waveform alignment overlap was then proposed, and together with the equilibrium factor it was used to study dynamic stress equilibrium. Thus, the recommended size range of specimens was determined for large-diameter split Hopkinson pressure bar tests. Also, a high-speed camera was used to observe the dynamic damage of the specimens. The results show that when the length-diameter ratio of specimen remains the same, the tested dynamic compressive strengths are close for the specimens of diameter 75 mm and 100 mm, but it is affected by more pronounced specimen length for the specimens of diameter 50 mm. With the increase of specimen’s diameter, the curve of strain rate versus time changes from single peak to double peak. The small-size specimen is more prone to axial splitting failure, and the large-size specimen produces larger tensile stress due to the superposition of internal stress waves, which is prone to the composite failure of spallation tension and axial splitting. When the specimen with a diameter of 75 mm and the length-diameter ratio of 0.3–0.4 is used, the coincidence degree after waveform alignment is better, sufficient stress balance time is achieved before initial failure, and the strain rate loading is more effective. It is helpful to reveal the size effect on the rock dynamic compression mechanical properties with different sizes of specimens, as it can provide a good reference for the specimen size selection in large-diameter SHPB tests.
2022, 42(10): 103103.
doi: 10.11883/bzycj-2021-0464
Abstract:
The concrete damage plasticity (CDP) model, as commonly adopted in ABAQUS routine, fails to correlate damage parameters with strain rate. To accurately describe the damage of concrete under high strain rate, a modified CDP (MCDP) model considering the rate correlation of damage parameters was developed by defining a new strain rate field variable and compiling VUSDFLD subroutine. In the MCDP model, the tensile and compressive damage parameters can be obtained by the energy method, and the main solver can automatically update the damage parameters under different strain rates with the change of strain rate field variables. Under static load, the results calculated by the MCDP model are in good agreement with those by the CDP model. The MCDP model was then used to calculate the dynamic compression performance of concrete under high strain rate, indicating that the tensile and compressive damage parameters of concrete under different strain rates have a significant influence on its dynamic mechanical properties. The compiled VUSDFLD subroutine and the MCDP model can solve the problem of the correlation between damage and strain rate, investigate the dynamic response of reinforced concrete beams accurately, and provide a more reliable technical way in predicting the response and destruction of the concrete structures under severe dynamic loading such as explosion and impact.
The concrete damage plasticity (CDP) model, as commonly adopted in ABAQUS routine, fails to correlate damage parameters with strain rate. To accurately describe the damage of concrete under high strain rate, a modified CDP (MCDP) model considering the rate correlation of damage parameters was developed by defining a new strain rate field variable and compiling VUSDFLD subroutine. In the MCDP model, the tensile and compressive damage parameters can be obtained by the energy method, and the main solver can automatically update the damage parameters under different strain rates with the change of strain rate field variables. Under static load, the results calculated by the MCDP model are in good agreement with those by the CDP model. The MCDP model was then used to calculate the dynamic compression performance of concrete under high strain rate, indicating that the tensile and compressive damage parameters of concrete under different strain rates have a significant influence on its dynamic mechanical properties. The compiled VUSDFLD subroutine and the MCDP model can solve the problem of the correlation between damage and strain rate, investigate the dynamic response of reinforced concrete beams accurately, and provide a more reliable technical way in predicting the response and destruction of the concrete structures under severe dynamic loading such as explosion and impact.
2022, 42(10): 103301.
doi: 10.11883/bzycj-2021-0275
Abstract:
The hypervelocity impact (HVI) of space debris is a typical extreme mechanics problem at high temperature, high pressure and high strain rate. The HVI involves the complex dynamic response of materials. Numerical methods have become very useful and important tools to predict the complex phenomena and look into the details of the entire process. However, the accurate simulation of the HVI is a grand challenge in scientific computing that places exacting demands on physics models, numerical solvers and computing resources. The optimal transportation meshfree (OTM) method is a meshfree updated-Lagrangian methodology for fluid and solid dynamic flows, possibly involving multiple phases, viscosity and general equations of state, general inelastic and history-dependent constitutive relations, arbitrary variable domains and boundary conditions and the interaction between fluid flows and highly deformable structures. The rationale behind the approach is combining concepts from the optimal transportation (OT) theory with material-point sampling, local maximum entropy (LME) approximation, the seizing contact, variational material point failure algorithm, and overcomes the essential difficulties in grid-based numerical methods like Lagrangian and Eulerian finite element method. Owing to those advantages, the OTM method provides an efficient and accurate solution for HVI simulation. In this paper, large scale three-dimensional numerical simulations on the HVI of the copper projectiles with different thicknesses (3.45, 5.13 mm), different masses (3, 10 g), different impact angles (5.4°, 11.7°) and different impact velocities (5.55, 5.12 km/s) impacting the Al6061-T6 plate with different thicknesses (2.87, 4.39 mm) were performed within the software ESCAAS based on the OTM method using a dynamic load balancing MPI/Pthreads parallel implementation. The dynamic response of material including phase transition in the high strain rate, high pressure and high temperature regime expected in this paper was described by the use of a variational thermomechanical coupling constitutive model with the SESAME equation of state, Grüneisen equation of state, rate-dependent J2 plasticity with power law hardening and thermal softening. The simulation results are in good agreement with the experimental measurements, which indicates the capacity of the OTM method and the ESCAAS software for HVI simulation.
The hypervelocity impact (HVI) of space debris is a typical extreme mechanics problem at high temperature, high pressure and high strain rate. The HVI involves the complex dynamic response of materials. Numerical methods have become very useful and important tools to predict the complex phenomena and look into the details of the entire process. However, the accurate simulation of the HVI is a grand challenge in scientific computing that places exacting demands on physics models, numerical solvers and computing resources. The optimal transportation meshfree (OTM) method is a meshfree updated-Lagrangian methodology for fluid and solid dynamic flows, possibly involving multiple phases, viscosity and general equations of state, general inelastic and history-dependent constitutive relations, arbitrary variable domains and boundary conditions and the interaction between fluid flows and highly deformable structures. The rationale behind the approach is combining concepts from the optimal transportation (OT) theory with material-point sampling, local maximum entropy (LME) approximation, the seizing contact, variational material point failure algorithm, and overcomes the essential difficulties in grid-based numerical methods like Lagrangian and Eulerian finite element method. Owing to those advantages, the OTM method provides an efficient and accurate solution for HVI simulation. In this paper, large scale three-dimensional numerical simulations on the HVI of the copper projectiles with different thicknesses (3.45, 5.13 mm), different masses (3, 10 g), different impact angles (5.4°, 11.7°) and different impact velocities (5.55, 5.12 km/s) impacting the Al6061-T6 plate with different thicknesses (2.87, 4.39 mm) were performed within the software ESCAAS based on the OTM method using a dynamic load balancing MPI/Pthreads parallel implementation. The dynamic response of material including phase transition in the high strain rate, high pressure and high temperature regime expected in this paper was described by the use of a variational thermomechanical coupling constitutive model with the SESAME equation of state, Grüneisen equation of state, rate-dependent J2 plasticity with power law hardening and thermal softening. The simulation results are in good agreement with the experimental measurements, which indicates the capacity of the OTM method and the ESCAAS software for HVI simulation.
2022, 42(10): 103302.
doi: 10.11883/bzycj-2021-0467
Abstract:
Concrete-filled double-skin steel tubular (CFDST) members are widely employed as load-bearing members in the ultra-high power transmission tower and offshore platform. The impact resistance of this type of members should be considered in the design stage. Based on the previous test results, in total 200 finite element (FE) models considering the coupling of axial and lateral impact loads were established with the ABAQUS software, and the damage mechanism of impact resistance was analyzed. Then, the parametrical studies were carried out to investigate the influences of key factors, including the nominal steel ratio, hollow ratio, cross-sectional diameter and material strength on the impact resistance of the members for the axial load ratio ranging from 0 to 0.7. Finally, the calculation formula for the impact bearing capacity is proposed and the dynamic response at the mid-span was predicted based on the methods of dynamic increase factor and an equivalent single degree-of-freedom model. In this work, the deflection at the mid-span and the plateau impact force were taken as the key indexes to evaluate the impact resistance. Results indicate that the impact resistance of the circular CFDST columns decreases with the increasing of axial load ratio. Under lateral impact, the CFDST members with the hollow ratio lower than 0.7 exhibit flexural failure. The interaction between the external steel tube and the inner concrete is stronger than that between the inner steel tube and the outer concrete. In addition, the nominal steel ratio, outer diameter of the cross-section, yield strength of the outer tube, impact velocity and impact mass all play significant roles on the maximum deflection at the mid-span and the plateau impact force when the axial load ratio ranges from 0 to 0.7. Effects of hollow ratio and concrete strength are marginal. The proposed calculation methods can reasonably predict the impact bearing capacity and mid-span displacement response of the CFDST members subjected to an impact.
Concrete-filled double-skin steel tubular (CFDST) members are widely employed as load-bearing members in the ultra-high power transmission tower and offshore platform. The impact resistance of this type of members should be considered in the design stage. Based on the previous test results, in total 200 finite element (FE) models considering the coupling of axial and lateral impact loads were established with the ABAQUS software, and the damage mechanism of impact resistance was analyzed. Then, the parametrical studies were carried out to investigate the influences of key factors, including the nominal steel ratio, hollow ratio, cross-sectional diameter and material strength on the impact resistance of the members for the axial load ratio ranging from 0 to 0.7. Finally, the calculation formula for the impact bearing capacity is proposed and the dynamic response at the mid-span was predicted based on the methods of dynamic increase factor and an equivalent single degree-of-freedom model. In this work, the deflection at the mid-span and the plateau impact force were taken as the key indexes to evaluate the impact resistance. Results indicate that the impact resistance of the circular CFDST columns decreases with the increasing of axial load ratio. Under lateral impact, the CFDST members with the hollow ratio lower than 0.7 exhibit flexural failure. The interaction between the external steel tube and the inner concrete is stronger than that between the inner steel tube and the outer concrete. In addition, the nominal steel ratio, outer diameter of the cross-section, yield strength of the outer tube, impact velocity and impact mass all play significant roles on the maximum deflection at the mid-span and the plateau impact force when the axial load ratio ranges from 0 to 0.7. Effects of hollow ratio and concrete strength are marginal. The proposed calculation methods can reasonably predict the impact bearing capacity and mid-span displacement response of the CFDST members subjected to an impact.
2022, 42(10): 103303.
doi: 10.11883/bzycj-2022-0030
Abstract:
The penetration resistance of concrete can be greatly improved by lateral confinement, and it would be continued to increase when pre-stress is further applied. However, the existing methods are difficult to realize the pre-stress on the confined concrete. In this paper, a relatively simple method for pre-stress confinement is proposed. Based on the principle of wedging the wedge-shaped block, a truncated cone-shaped concrete target with a cone inclination of 3° and a diameter slightly larger than the ferrule was squeezed into the matching steel ferrule, so the concrete target was pre-stressed along the radial direction by means of cone-shaped fitting and tightening, while the pre-stress was controlled by the indicators such as the pressing depth of the concrete target, the margin, and the pressing force. The feasibility of this method is then verified by simulation using LS-DYNA, and the penetration resistance of pre-stressed confined concrete is studied by the so-called restart algorithm. Numerical results demonstrate that the proposed method can provide enough radial pre-stress to the confined concrete target, and the pre-stress of the target increases approximately linearly with the increase of the pressing depth or the margin. Furthermore, within a certain range, the penetration resistance of the concrete target increases with the increase of pre-stress, while it decreases rapidly when the pre-stress is too high, which causes the damage of the concrete target. Parametric study on the parameters such as steel ferrule strength, concrete strength, steel ratio and projectile velocity, shows that reasonable matching of the steel ferrule strength with the concrete strength and selection of appropriate steel ratio of the target can effectively improve the pre-stress, penetration resistance of the target and the efficiency of steel; the higher the projectile velocity, the more obvious the effect of pre-stress on the improvement of the anti-penetration performance of the target. The proposed method for applying pre-stress provides a new approach to improve the anti-penetration capability of brittle materials such as concrete.
The penetration resistance of concrete can be greatly improved by lateral confinement, and it would be continued to increase when pre-stress is further applied. However, the existing methods are difficult to realize the pre-stress on the confined concrete. In this paper, a relatively simple method for pre-stress confinement is proposed. Based on the principle of wedging the wedge-shaped block, a truncated cone-shaped concrete target with a cone inclination of 3° and a diameter slightly larger than the ferrule was squeezed into the matching steel ferrule, so the concrete target was pre-stressed along the radial direction by means of cone-shaped fitting and tightening, while the pre-stress was controlled by the indicators such as the pressing depth of the concrete target, the margin, and the pressing force. The feasibility of this method is then verified by simulation using LS-DYNA, and the penetration resistance of pre-stressed confined concrete is studied by the so-called restart algorithm. Numerical results demonstrate that the proposed method can provide enough radial pre-stress to the confined concrete target, and the pre-stress of the target increases approximately linearly with the increase of the pressing depth or the margin. Furthermore, within a certain range, the penetration resistance of the concrete target increases with the increase of pre-stress, while it decreases rapidly when the pre-stress is too high, which causes the damage of the concrete target. Parametric study on the parameters such as steel ferrule strength, concrete strength, steel ratio and projectile velocity, shows that reasonable matching of the steel ferrule strength with the concrete strength and selection of appropriate steel ratio of the target can effectively improve the pre-stress, penetration resistance of the target and the efficiency of steel; the higher the projectile velocity, the more obvious the effect of pre-stress on the improvement of the anti-penetration performance of the target. The proposed method for applying pre-stress provides a new approach to improve the anti-penetration capability of brittle materials such as concrete.
2022, 42(10): 104101.
doi: 10.11883/bzycj-2022-0015
Abstract:
The impact force transducers are widely used in aerospace, national defense engineering, auto industry and other important fields involving national security and people livelihood. Those transducers usually need to be calibrated before being put into practical use. Realizing synchronous loading and developing an accurate mathematical model to describe the input-output relationship are the major challenges in the calibration of triaxial impact force transducers at this stage. In this paper, a method for the synchronous excitation of three-dimensional impact force loads was established based on a modified Hopkinson bar technique and the principle of vector decomposition. The triaxial impact force transducer being calibrated was mounted at an angle to the axis of the Hopkinson bar, the one-dimensional force excited in the Hopkinson bar was then decomposed onto each sensitive axis of the transducer, thus realizing its synchronous loading. The coupling effect between the sensitive axes of the transducer was assumed to be linear. A linear decoupling calibration model of the triaxial impact force transducer was built based on a sensitivity matrix containing three main sensitivity coefficients and six transverse sensitivity coefficients. The sensitivity matrix was solved using the least squares method. The amplitude and pulse width of the impact force pulses excited in the Hopkinson bar were adjusted by varying the structure and the impact velocity of the bullet. Reference impact force pulses with varied amplitudes and pulse widths were then used to calibrate the triaxial impact force transducer. Characteristics were revealed that both the main sensitivity coefficients and the transverse sensitivity coefficients of the transducer are related to the amplitude and the pulse width of the reference impact force. The amplitude and pulse width information of the input force pulses that the transducer was subjected to can be reflected by the output voltage pulses of the transducer. Therefore, the amplitude and pulse width of the output voltages of the sensitive axes of the transducer were taken as influencing factors and added to the input layer of the artificial neural network (ANN) in form of artificial neurons. A nonlinear decoupling calibration model for the tri-axial impact force transducer was then built based on an ANN model. The calibration results show that the ANN model has higher calibration accuracy compared to the least squares model. It is feasible and valid to use ANNs to calibrate the tri-axial impact force transducers.
The impact force transducers are widely used in aerospace, national defense engineering, auto industry and other important fields involving national security and people livelihood. Those transducers usually need to be calibrated before being put into practical use. Realizing synchronous loading and developing an accurate mathematical model to describe the input-output relationship are the major challenges in the calibration of triaxial impact force transducers at this stage. In this paper, a method for the synchronous excitation of three-dimensional impact force loads was established based on a modified Hopkinson bar technique and the principle of vector decomposition. The triaxial impact force transducer being calibrated was mounted at an angle to the axis of the Hopkinson bar, the one-dimensional force excited in the Hopkinson bar was then decomposed onto each sensitive axis of the transducer, thus realizing its synchronous loading. The coupling effect between the sensitive axes of the transducer was assumed to be linear. A linear decoupling calibration model of the triaxial impact force transducer was built based on a sensitivity matrix containing three main sensitivity coefficients and six transverse sensitivity coefficients. The sensitivity matrix was solved using the least squares method. The amplitude and pulse width of the impact force pulses excited in the Hopkinson bar were adjusted by varying the structure and the impact velocity of the bullet. Reference impact force pulses with varied amplitudes and pulse widths were then used to calibrate the triaxial impact force transducer. Characteristics were revealed that both the main sensitivity coefficients and the transverse sensitivity coefficients of the transducer are related to the amplitude and the pulse width of the reference impact force. The amplitude and pulse width information of the input force pulses that the transducer was subjected to can be reflected by the output voltage pulses of the transducer. Therefore, the amplitude and pulse width of the output voltages of the sensitive axes of the transducer were taken as influencing factors and added to the input layer of the artificial neural network (ANN) in form of artificial neurons. A nonlinear decoupling calibration model for the tri-axial impact force transducer was then built based on an ANN model. The calibration results show that the ANN model has higher calibration accuracy compared to the least squares model. It is feasible and valid to use ANNs to calibrate the tri-axial impact force transducers.
2022, 42(10): 104201.
doi: 10.11883/bzycj-2021-0415
Abstract:
A computational model of simulating the structural damage and the propagation of shock wave was developed in order to study the interaction between blast wave and building. A damage-load criteria of building structures was used to evaluate the destruction of the structure under blast wave, with shock wave impulse used as an indicator of structural failure. Then, the mechanism of the interaction between shock wave and structural fragments was investigated via the simulations of unstructured dynamic grid according to the distribution of pressure field. It has been recognized that there mainly exist three categories of physical effects, i.e., the effect of rarefaction wave caused by the motion of fragments; the impediment effect of structure fragments to shock wave; and the effect of plane wave resulting from the realignment of diffraction wave. Based on the aforementioned analysis, an interface algorithm of fluid-structure coupling was employed to assess the first effect in terms of pressure relief, and “virtual mesh ventilation method” is utilized to deal with the second effect of impediment to shock wave. The results show that the developed model can effectively simulate the propagation of shock wave and reduce the computational cost. Compared to the rigid wall assumptions, the developed model reaches relatively closer agreement with the physical reality. Moreover, the model is simpler and more efficient than the strict coupling method of CSD (computational structural dynamics) / CFD (computational fluid dynamics). Reasonable consistence of the pressure prediction was found between the application of the model and the unstructured dynamic grid simulation. The accuracy, therefore, can meet the engineering requirements. When applied to numerical simulations of the damage process of typical buildings, this model effectively leads to the building damage and shock wave overpressure distributions. The results conform well with the structural damage characteristics, which can provide reference and basis for the damage assessment of explosion shock wave and the building structure.
A computational model of simulating the structural damage and the propagation of shock wave was developed in order to study the interaction between blast wave and building. A damage-load criteria of building structures was used to evaluate the destruction of the structure under blast wave, with shock wave impulse used as an indicator of structural failure. Then, the mechanism of the interaction between shock wave and structural fragments was investigated via the simulations of unstructured dynamic grid according to the distribution of pressure field. It has been recognized that there mainly exist three categories of physical effects, i.e., the effect of rarefaction wave caused by the motion of fragments; the impediment effect of structure fragments to shock wave; and the effect of plane wave resulting from the realignment of diffraction wave. Based on the aforementioned analysis, an interface algorithm of fluid-structure coupling was employed to assess the first effect in terms of pressure relief, and “virtual mesh ventilation method” is utilized to deal with the second effect of impediment to shock wave. The results show that the developed model can effectively simulate the propagation of shock wave and reduce the computational cost. Compared to the rigid wall assumptions, the developed model reaches relatively closer agreement with the physical reality. Moreover, the model is simpler and more efficient than the strict coupling method of CSD (computational structural dynamics) / CFD (computational fluid dynamics). Reasonable consistence of the pressure prediction was found between the application of the model and the unstructured dynamic grid simulation. The accuracy, therefore, can meet the engineering requirements. When applied to numerical simulations of the damage process of typical buildings, this model effectively leads to the building damage and shock wave overpressure distributions. The results conform well with the structural damage characteristics, which can provide reference and basis for the damage assessment of explosion shock wave and the building structure.
2022, 42(10): 104202.
doi: 10.11883/bzycj-2022-0059
Abstract:
As a non-contact, non-interference full-field non-destructive optical measurement technology, digital image correlation (DIC) technology can obtain the dynamic deformation information on the surface of materials and failure process. Aiming to evaluate the ballistic performance of armor steel and explore the application of high-speed three-dimensional digital image correlation (3D-DIC) technology in perforation test of armor steel plates, impact tests by seven shots on high strength and hardness armor steel plates with different thicknesses were conducted, in which 15-mm-caliber deformable projectile at various velocities were fired by using hydrogen-oxygen detonation ballistic gun, whilst the high-speed 3D-DIC measurement technology with frame rate of 144000 s−1 was adopted to extract the out-of-plane displacement and strain field-time histories of the target. Then, based on the calibrated and validated constitutive model parameters of armor steel obtained in previous work, the current impact test is numerically simulated and the corresponding finite element model is validated by comparing with the simulated residual projectile velocities and lengths with test data. Furthermore, by comparing the out-of-plane displacement-time histories and strain contours at the rear of target obtained by numerical simulation and test, the accuracy of results obtained by high-speed 3D-DIC is validated. Finally, the relationship between maximum out-of-plane displacement with projectile impact velocity and armor steel plate thickness is analyzed. The results show that the relatively smaller out-of-plane displacements were obtained due to the shear plugging failure for 8 mm-thick targets. Under the identical impact energy, the unperforated targets with the thickness of 10 mm absorb the most of energy and exhibit larger out-of-plane displacements compared with those in targets with the thicknesses of 5 mm and 8 mm. The application of high-speed 3D-DIC technology in this study can provide a reference for related tests, and the analysis result of maximum out-of-plane displacement of target can be used as the experimental basis for the analysis, verification and optimal design in protective barrier structures.
As a non-contact, non-interference full-field non-destructive optical measurement technology, digital image correlation (DIC) technology can obtain the dynamic deformation information on the surface of materials and failure process. Aiming to evaluate the ballistic performance of armor steel and explore the application of high-speed three-dimensional digital image correlation (3D-DIC) technology in perforation test of armor steel plates, impact tests by seven shots on high strength and hardness armor steel plates with different thicknesses were conducted, in which 15-mm-caliber deformable projectile at various velocities were fired by using hydrogen-oxygen detonation ballistic gun, whilst the high-speed 3D-DIC measurement technology with frame rate of 144000 s−1 was adopted to extract the out-of-plane displacement and strain field-time histories of the target. Then, based on the calibrated and validated constitutive model parameters of armor steel obtained in previous work, the current impact test is numerically simulated and the corresponding finite element model is validated by comparing with the simulated residual projectile velocities and lengths with test data. Furthermore, by comparing the out-of-plane displacement-time histories and strain contours at the rear of target obtained by numerical simulation and test, the accuracy of results obtained by high-speed 3D-DIC is validated. Finally, the relationship between maximum out-of-plane displacement with projectile impact velocity and armor steel plate thickness is analyzed. The results show that the relatively smaller out-of-plane displacements were obtained due to the shear plugging failure for 8 mm-thick targets. Under the identical impact energy, the unperforated targets with the thickness of 10 mm absorb the most of energy and exhibit larger out-of-plane displacements compared with those in targets with the thicknesses of 5 mm and 8 mm. The application of high-speed 3D-DIC technology in this study can provide a reference for related tests, and the analysis result of maximum out-of-plane displacement of target can be used as the experimental basis for the analysis, verification and optimal design in protective barrier structures.
2022, 42(10): 105101.
doi: 10.11883/bzycj-2021-0502
Abstract:
The blast shock wave will be transmitted to the ground through the vent as a gas explosion accident occurs in an urban shallowly-buried pipe trench, and cause serious disaster consequences. However, there are few studies on the propagating law of the explosion load outward through the explosion vent in the long and straight space. Thus, it is necessary to reveal the explosion load distribution law on the ground of such accidents. Based on the combustible gas explosion test in the long and straight venting space conducted in the previous period, the applicability of parameters and grid size in FLACS software were verified. Then the FLACS software was used to carry out numerical simulations of the gas explosion process in the urban shallow buried pipe trench. The propagation process of shock wave was divided into three stages: stable stage, Δp1 stage and Δp2 stage, and the mechanism of shock wave was analyzed by fuel, flame, flow velocity and density. The results show that the value of Δp1 is small, mainly caused by compression waves, and Δp2 is the maximum overpressure peak, mainly caused by flame waves. The characteristics of the overpressure time-history curve were studied. The results show that Δp1 has smaller differences in each direction than Δp2, and the wave propagation has obvious directionality in X and Z directions, while symmetrical in the y direction. The attenuation law of shock waves in space was studied and the attenuation formula in each direction was obtained by data fitting. The results show that Δp2 gradually decreases with the increase of the distance from the venting port, and the value of the value in each direction varies greatly, among which, it shows a symmetrical attenuation trend along the short side of the pipe trench section; Δp2 and distance roughly satisfy the exponential function relationship, and the fitting degree is above 98.8%.
The blast shock wave will be transmitted to the ground through the vent as a gas explosion accident occurs in an urban shallowly-buried pipe trench, and cause serious disaster consequences. However, there are few studies on the propagating law of the explosion load outward through the explosion vent in the long and straight space. Thus, it is necessary to reveal the explosion load distribution law on the ground of such accidents. Based on the combustible gas explosion test in the long and straight venting space conducted in the previous period, the applicability of parameters and grid size in FLACS software were verified. Then the FLACS software was used to carry out numerical simulations of the gas explosion process in the urban shallow buried pipe trench. The propagation process of shock wave was divided into three stages: stable stage, Δp1 stage and Δp2 stage, and the mechanism of shock wave was analyzed by fuel, flame, flow velocity and density. The results show that the value of Δp1 is small, mainly caused by compression waves, and Δp2 is the maximum overpressure peak, mainly caused by flame waves. The characteristics of the overpressure time-history curve were studied. The results show that Δp1 has smaller differences in each direction than Δp2, and the wave propagation has obvious directionality in X and Z directions, while symmetrical in the y direction. The attenuation law of shock waves in space was studied and the attenuation formula in each direction was obtained by data fitting. The results show that Δp2 gradually decreases with the increase of the distance from the venting port, and the value of the value in each direction varies greatly, among which, it shows a symmetrical attenuation trend along the short side of the pipe trench section; Δp2 and distance roughly satisfy the exponential function relationship, and the fitting degree is above 98.8%.
2022, 42(10): 105102.
doi: 10.11883/bzycj-2021-0524
Abstract:
In order to study the influence of bilinear resistance model on the vibration displacement of beam members under air blast loading, both the theoretical elast-plastic displacement solutions of the flexible and rigid members in forward and rebound stages were deduced, respectively. According to the relationship between blast duration and elastic duration from static position to maximum elastic displacement for members, the vibration situations could be divided into elastic forced vibration, elastic free vibration, plastic forced vibration, plastic free vibration, elastic rebound and plastic rebound. The equivalent single degree of freedom method was used to establish the vibration equations of each stage and the theoretical solutions of each stage were derived for different initial conditions. The method of the general solution plus the special solution was applied to solve each differential equation. Based on the theoretical solutions and the representative plastic strengthening coefficient, the elastoplastic vibration displacements of two types of beam members under different plastic strengthening degrees in the bilinear resistance model were verified under typical calculation cases. The corresponding complete vibration curves were finished for comparative analysis. The influence of the degree of plastic strengthening on the vibration representative value was analyzed. The results show that the displacement theoretical solution based on the bilinear resistance model has a wider range of application. With the increase of plastic strengthening coefficient of the bilinear resistance model, the maximum elastic-plastic displacement and residual deformation of the two types of beam members decrease gradually, and the reduction degree of residual deformation is higher than that of the maximum elastic-plastic displacement. When the plastic strengthening coefficient increases to a certain extent, the plastic vibration displacement will appear in the rebound stage of the beam members, further reducing the residual deformation. Compared with the bilinear resistance model, the elastic-perfectly plastic resistance overestimates the residual deformation of beam members under air blast loading.
In order to study the influence of bilinear resistance model on the vibration displacement of beam members under air blast loading, both the theoretical elast-plastic displacement solutions of the flexible and rigid members in forward and rebound stages were deduced, respectively. According to the relationship between blast duration and elastic duration from static position to maximum elastic displacement for members, the vibration situations could be divided into elastic forced vibration, elastic free vibration, plastic forced vibration, plastic free vibration, elastic rebound and plastic rebound. The equivalent single degree of freedom method was used to establish the vibration equations of each stage and the theoretical solutions of each stage were derived for different initial conditions. The method of the general solution plus the special solution was applied to solve each differential equation. Based on the theoretical solutions and the representative plastic strengthening coefficient, the elastoplastic vibration displacements of two types of beam members under different plastic strengthening degrees in the bilinear resistance model were verified under typical calculation cases. The corresponding complete vibration curves were finished for comparative analysis. The influence of the degree of plastic strengthening on the vibration representative value was analyzed. The results show that the displacement theoretical solution based on the bilinear resistance model has a wider range of application. With the increase of plastic strengthening coefficient of the bilinear resistance model, the maximum elastic-plastic displacement and residual deformation of the two types of beam members decrease gradually, and the reduction degree of residual deformation is higher than that of the maximum elastic-plastic displacement. When the plastic strengthening coefficient increases to a certain extent, the plastic vibration displacement will appear in the rebound stage of the beam members, further reducing the residual deformation. Compared with the bilinear resistance model, the elastic-perfectly plastic resistance overestimates the residual deformation of beam members under air blast loading.
2022, 42(10): 105401.
doi: 10.11883/bzycj-2022-0012
Abstract:
To investigate the influence of gasoline-air mixture volume fraction, ignition position and liquid level on explosion overpressure parameters and flame development in vertical dome oil tank, a series of experiments with nine initial hydrocarbon volume fractions, four ignition positions and five liquid levels were carried out in a transparent imitated oil tank. Dynamic data acquisition system and high-speed camera were employed to detect the changes of internal and external field pressure, and to record the transformation of flame shape. The following results were found. (1) 1.7% is the most dangerous gasoline-air mixture volume fraction under any working condition. The development of overpressure in the inner field can be divided into three stages: overpressure rise, overpressure release and oscillation attenuation. The formation and spatial distribution of free radicals such as CH, C2 and OH during the explosion process make the flame show different color changes under different initial volume fractions or at different explosion stages. (2) Ignition position has a great influence on explosion overpressure parameters. The lower the ignition position is, the greater the explosion power is. When the ignition position is in the center of the bottom of the tank, the average pressure boost rate of the internal and external fields reaches the maximum value, being 0.464 MPa/s and 0.053 MPa/s, respectively. (3) The change of liquid level has a great influence on the overpressure of the internal and external field of oil and gas explosion. When the position ignition is located at the top of the side wall of the oil tank, the 50% liquid level is the most dangerous level. At any liquid level, the outfield overpressure decreases exponentially with the increase of scaled distance. The relationship among the maximum overpressure peak of the outfield shock wave of gasoline-air mixture explosion at different liquid levels, the distance and the volume of gasoline-air mixture can be expressed by a unified expression. Compared with gas space, the overpressure in liquid space has the characteristics of delay, enhancement of negative overpressure and faster oscillation attenuation frequency.
To investigate the influence of gasoline-air mixture volume fraction, ignition position and liquid level on explosion overpressure parameters and flame development in vertical dome oil tank, a series of experiments with nine initial hydrocarbon volume fractions, four ignition positions and five liquid levels were carried out in a transparent imitated oil tank. Dynamic data acquisition system and high-speed camera were employed to detect the changes of internal and external field pressure, and to record the transformation of flame shape. The following results were found. (1) 1.7% is the most dangerous gasoline-air mixture volume fraction under any working condition. The development of overpressure in the inner field can be divided into three stages: overpressure rise, overpressure release and oscillation attenuation. The formation and spatial distribution of free radicals such as CH, C2 and OH during the explosion process make the flame show different color changes under different initial volume fractions or at different explosion stages. (2) Ignition position has a great influence on explosion overpressure parameters. The lower the ignition position is, the greater the explosion power is. When the ignition position is in the center of the bottom of the tank, the average pressure boost rate of the internal and external fields reaches the maximum value, being 0.464 MPa/s and 0.053 MPa/s, respectively. (3) The change of liquid level has a great influence on the overpressure of the internal and external field of oil and gas explosion. When the position ignition is located at the top of the side wall of the oil tank, the 50% liquid level is the most dangerous level. At any liquid level, the outfield overpressure decreases exponentially with the increase of scaled distance. The relationship among the maximum overpressure peak of the outfield shock wave of gasoline-air mixture explosion at different liquid levels, the distance and the volume of gasoline-air mixture can be expressed by a unified expression. Compared with gas space, the overpressure in liquid space has the characteristics of delay, enhancement of negative overpressure and faster oscillation attenuation frequency.
2022, 42(10): 105901.
doi: 10.11883/bzycj-2021-0527
Abstract:
To improve the crashworthiness of thin-walled tube structures, a series of bio-inspired multi-cell thin-walled tubes with sinusoidal cells (abbreviated BSTs) were designed based on the dactyl club microstructure of Odontodactylus scyllarus (O. scyllarus) using bionic design methods. By taking initial peak load, specific energy absorption and crushing force efficiency as crashworthiness indexes, the influences of cell numbers on the crashworthiness of the BSTs under different impact angles (0º, 10º, 20º and 30º) conditions were analyzed under low-velocity impact condition using the nonlinear finite element (FE) method through LS-DYNA. The optimal number of bionic cells was obtained using complex proportion assessment. A complex proportional assessment (COPRAS) method was used to select the optimal number configuration under multiple loading angles. Base on the combination of weight factor values of different impact angles, four single-angle cases (1–4) and three multi-angle cases (5–7) were set. A metamodel-based multi-objective optimization method based on polynomial regression (PR) metamodels and a multi-objective particle optimization (MOPSO) algorithm were employed to optimize the dimensions of the optimal cell number configuration, where the initial peak load, specific energy absorption and crushing force efficiency were taken as objectives and the height-width ratio and thickness were regarded as the design variables. According to the results of the COPRAS method, the BST with four sinusoidal cells was determined to be the best design based on the multi-criteria process. The optimization results of single-angel cases show that, the optimal height-width ratio ranges from 0.88 to 1.50, and the optimal thickness ranges from 0.36 mm to 0.60 mm. The optimal height-width ratios of cases 1–2 are significantly smaller than those of cases 3–4 . The BST with four sinusoidal cells has the maximum optimal thickness of 0.6 mm when the impact angles is 0º. For multi-angel cases, the optimal height-width ratio ranges from 1.01 to 1.10, and the optimal thickness ranges from 0.49 mm to 0.57 mm. The results above are helpful for exploring the lightweight design of new thin-walled tube structures and providing new ideas for their application in energy absorption and crashing field.
To improve the crashworthiness of thin-walled tube structures, a series of bio-inspired multi-cell thin-walled tubes with sinusoidal cells (abbreviated BSTs) were designed based on the dactyl club microstructure of Odontodactylus scyllarus (O. scyllarus) using bionic design methods. By taking initial peak load, specific energy absorption and crushing force efficiency as crashworthiness indexes, the influences of cell numbers on the crashworthiness of the BSTs under different impact angles (0º, 10º, 20º and 30º) conditions were analyzed under low-velocity impact condition using the nonlinear finite element (FE) method through LS-DYNA. The optimal number of bionic cells was obtained using complex proportion assessment. A complex proportional assessment (COPRAS) method was used to select the optimal number configuration under multiple loading angles. Base on the combination of weight factor values of different impact angles, four single-angle cases (1–4) and three multi-angle cases (5–7) were set. A metamodel-based multi-objective optimization method based on polynomial regression (PR) metamodels and a multi-objective particle optimization (MOPSO) algorithm were employed to optimize the dimensions of the optimal cell number configuration, where the initial peak load, specific energy absorption and crushing force efficiency were taken as objectives and the height-width ratio and thickness were regarded as the design variables. According to the results of the COPRAS method, the BST with four sinusoidal cells was determined to be the best design based on the multi-criteria process. The optimization results of single-angel cases show that, the optimal height-width ratio ranges from 0.88 to 1.50, and the optimal thickness ranges from 0.36 mm to 0.60 mm. The optimal height-width ratios of cases 1–2 are significantly smaller than those of cases 3–4 . The BST with four sinusoidal cells has the maximum optimal thickness of 0.6 mm when the impact angles is 0º. For multi-angel cases, the optimal height-width ratio ranges from 1.01 to 1.10, and the optimal thickness ranges from 0.49 mm to 0.57 mm. The results above are helpful for exploring the lightweight design of new thin-walled tube structures and providing new ideas for their application in energy absorption and crashing field.
