2020 Vol. 40, No. 11
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2020, 40(11): 115201.
doi: 10.11883/bzycj-2019-0315
Abstract:
Most of safety control standard studies for existing tunnels under blasting vibrations are based on the premise that the existing tunnels are intact, and the effects of existing defects under the dynamic response are not considered. Therefore, based on the proposed new tunnel next to the Xinling tunnel as the engineering background, according to the actual distribution characteristics of tunnel defects (cracks and back-cavities), the two-dimensional and three-dimensional numerical models were established to analyze the influence of defects under structural dynamic response. Moreover, the standard management system was established. The results show that the most unfavorable distribution position of cracks is the side wall of explosion-proof which mainly increases the response of the lining structure to stress S1 (tensile stress). The control standard should take the stress S1 and the propagation depth of crack as the quantitative indicators. When the propagation depth is (0−1/8)h, (1/8−1/2)h, and ＞(1/2)h (h represents the thickness of the lining structure), the corresponding vibration velocity limit value is 12, 10, and 8 cm/s, respectively. The most unfavorable distribution position of back-cavities is at the arch crown, which increases the dual response of the lining structure to the stress S1 and the vibration velocity, and the vibration velocity response is the main one. The control standard should take the vibration velocity, plane size and longitudinal length of the cavity as the quantitative indicators. The vibration velocity limit value is 12 cm/s. When the longitudinal length of the cavity is less than 7 m, the monitoring range is 3−4 times of the longitudinal length; when the longitudinal length of the cavity is greater than 7 m, the monitoring range is 1−1.5 times of the longitudinal length; when the longitudinal length of the cavity is small, the multiple takes a large value.
Most of safety control standard studies for existing tunnels under blasting vibrations are based on the premise that the existing tunnels are intact, and the effects of existing defects under the dynamic response are not considered. Therefore, based on the proposed new tunnel next to the Xinling tunnel as the engineering background, according to the actual distribution characteristics of tunnel defects (cracks and back-cavities), the two-dimensional and three-dimensional numerical models were established to analyze the influence of defects under structural dynamic response. Moreover, the standard management system was established. The results show that the most unfavorable distribution position of cracks is the side wall of explosion-proof which mainly increases the response of the lining structure to stress S1 (tensile stress). The control standard should take the stress S1 and the propagation depth of crack as the quantitative indicators. When the propagation depth is (0−1/8)h, (1/8−1/2)h, and ＞(1/2)h (h represents the thickness of the lining structure), the corresponding vibration velocity limit value is 12, 10, and 8 cm/s, respectively. The most unfavorable distribution position of back-cavities is at the arch crown, which increases the dual response of the lining structure to the stress S1 and the vibration velocity, and the vibration velocity response is the main one. The control standard should take the vibration velocity, plane size and longitudinal length of the cavity as the quantitative indicators. The vibration velocity limit value is 12 cm/s. When the longitudinal length of the cavity is less than 7 m, the monitoring range is 3−4 times of the longitudinal length; when the longitudinal length of the cavity is greater than 7 m, the monitoring range is 1−1.5 times of the longitudinal length; when the longitudinal length of the cavity is small, the multiple takes a large value.
2020, 40(11): 111101.
doi: 10.11883/bzycj-2020-0386
Abstract:
The “pump theory” and “wave theory” of cardiac function are analyzed. It is shown that the heart plays a role actually not as a pump but as a pulse generator, producing a series of pulse waves that carry energy. Each pulse wave consists of an ascending branch and a descending branch. The former corresponds to a loading process, in which the pressure, particle velocity, energy as well as oxygen saturation all increase with time. While the latter corresponds to an unloading process, in which the pressure, particle velocity, energy as well as oxygen saturation all decrease, up to zero. So the concepts proposed in the “pump theory”, such as the Windkessel effect, one engine-two pump and diastolic pump, all do not hold up. The cardiac power of about 1.5 W essentially represents the power of each pulse wave. Aimed at the characteristic that the pulse wave is a complex wave with fluid-solid coupling and longitudinal wave-transverse wave coupling, it is shown that the main part of energy (99.99%) is carried by the transverse waves, which propagate along the solid blood-vessel so that the dissipation is low and the efficiency is high. Moreover, it is shown that the increase of generalized wave impedance at the vascular branches may help to counteract the attenuation and dissipation of pulse waves and increase the pulse pressure propagating into the branches, which may be regarded as a kind of self-regulation mechanism of human body.
The “pump theory” and “wave theory” of cardiac function are analyzed. It is shown that the heart plays a role actually not as a pump but as a pulse generator, producing a series of pulse waves that carry energy. Each pulse wave consists of an ascending branch and a descending branch. The former corresponds to a loading process, in which the pressure, particle velocity, energy as well as oxygen saturation all increase with time. While the latter corresponds to an unloading process, in which the pressure, particle velocity, energy as well as oxygen saturation all decrease, up to zero. So the concepts proposed in the “pump theory”, such as the Windkessel effect, one engine-two pump and diastolic pump, all do not hold up. The cardiac power of about 1.5 W essentially represents the power of each pulse wave. Aimed at the characteristic that the pulse wave is a complex wave with fluid-solid coupling and longitudinal wave-transverse wave coupling, it is shown that the main part of energy (99.99%) is carried by the transverse waves, which propagate along the solid blood-vessel so that the dissipation is low and the efficiency is high. Moreover, it is shown that the increase of generalized wave impedance at the vascular branches may help to counteract the attenuation and dissipation of pulse waves and increase the pulse pressure propagating into the branches, which may be regarded as a kind of self-regulation mechanism of human body.
2020, 40(11): 111401.
doi: 10.11883/bzycj-2020-0105
Abstract:
Large naval warships are severely threatened by underwater weapons. Especially, the hull structures will suffer excessive local damage in the case of underwater contact explosion, which brings severe challenges to the combat effectiveness and even vitality of ships. In this paper, the underwater protective structures of large naval warships were taken as the research object. The development history of underwater protective structures in various countries was briefly introduced. The damage loading generated by underwater contact explosion and the damage mechanism of underwater protective structures were analyzed. Based on the specific structures and different damage loading, the corresponding protective measures were summarized. In view of the present research situation, some problems were put forward for the future investigation. This may provide a reference for the design of underwater protective structures so as to improve the anti-explosion ability of large naval warships.
Large naval warships are severely threatened by underwater weapons. Especially, the hull structures will suffer excessive local damage in the case of underwater contact explosion, which brings severe challenges to the combat effectiveness and even vitality of ships. In this paper, the underwater protective structures of large naval warships were taken as the research object. The development history of underwater protective structures in various countries was briefly introduced. The damage loading generated by underwater contact explosion and the damage mechanism of underwater protective structures were analyzed. Based on the specific structures and different damage loading, the corresponding protective measures were summarized. In view of the present research situation, some problems were put forward for the future investigation. This may provide a reference for the design of underwater protective structures so as to improve the anti-explosion ability of large naval warships.
2020, 40(11): 111402.
doi: 10.11883/bzycj-2020-0110
Abstract:
To address the problem of double-structures subjected to underwater explosion, the interaction mechanism between explosion bubbles and double-layer structures with circular hole was studied. And the characteristics such as cabin inrush and flow field change were analyzed by an Eulerian finite element numerical model. First of all, the numerical model was verified through discharge experiments, and it turned out that the numerical results agreed well with the experimental results. Then, the interaction behaviors under different initial conditions were summarized. Under the combined action of internal air, fluid inertia and breach induction, the bubble’s segmentation occurs during the bubble evolution process. When the size coefficient of the inner-layer breach is less than 0.5, the secondary water hump phenomenon occurs in the inner-cabin and the shape of the inrush is slender. When the explosive detonation position coefficient is less than 0.1, the re-closing and breaking of the free surface will take place. The influence of the free surface in the shell on the cabin inrush is complicated and when the water level is full, the rapid surge will reduce the emergency time of the ship.
To address the problem of double-structures subjected to underwater explosion, the interaction mechanism between explosion bubbles and double-layer structures with circular hole was studied. And the characteristics such as cabin inrush and flow field change were analyzed by an Eulerian finite element numerical model. First of all, the numerical model was verified through discharge experiments, and it turned out that the numerical results agreed well with the experimental results. Then, the interaction behaviors under different initial conditions were summarized. Under the combined action of internal air, fluid inertia and breach induction, the bubble’s segmentation occurs during the bubble evolution process. When the size coefficient of the inner-layer breach is less than 0.5, the secondary water hump phenomenon occurs in the inner-cabin and the shape of the inrush is slender. When the explosive detonation position coefficient is less than 0.1, the re-closing and breaking of the free surface will take place. The influence of the free surface in the shell on the cabin inrush is complicated and when the water level is full, the rapid surge will reduce the emergency time of the ship.
2020, 40(11): 111403.
doi: 10.11883/bzycj-2019-0119
Abstract:
Four types of polyurea coated composite armor structures were designed based on steel plates, SiC ceramic tiles and polyurea coatings. The near-field explosion damage characteristics of the composite armor structures were experimentally studied using the method of charge driven prefabricated fragments. The failure modes of the components of the armor structures were proposed, the protection performances of the armor structures were comparatively analyzed and the protection mechanisms were investigated. The experimental results indicate that the impact energy acted on the structures by the prefabricated fragments is far greater than that of the blast wave. The protection performances of the polyurea coated composite armor structures are much better than those of the multi-layer steel structures. Increasing the thickness of ceramic tiles can enhance the protection performance more efficiently than increasing the thickness of the front plate or back plate. Under the impact of fragment cluster, ceramic tiles are damaged on a large scale, and the anti-penetration capability against subsequent hitting fragments will be severely weakened.
Four types of polyurea coated composite armor structures were designed based on steel plates, SiC ceramic tiles and polyurea coatings. The near-field explosion damage characteristics of the composite armor structures were experimentally studied using the method of charge driven prefabricated fragments. The failure modes of the components of the armor structures were proposed, the protection performances of the armor structures were comparatively analyzed and the protection mechanisms were investigated. The experimental results indicate that the impact energy acted on the structures by the prefabricated fragments is far greater than that of the blast wave. The protection performances of the polyurea coated composite armor structures are much better than those of the multi-layer steel structures. Increasing the thickness of ceramic tiles can enhance the protection performance more efficiently than increasing the thickness of the front plate or back plate. Under the impact of fragment cluster, ceramic tiles are damaged on a large scale, and the anti-penetration capability against subsequent hitting fragments will be severely weakened.
2020, 40(11): 111404.
doi: 10.11883/bzycj-2020-0106
Abstract:
The loading of bubble jet is an important part of the whole loading induced by the middle-field and near-field underwater explosion. Due to the fact that the period of the bubble jet is extremely short and the jet occurs inside the complicated underwater explosion bubble, it is hard to investigate the bubble jet through the direct underwater explosion bubble. Therefore, simplifying underwater explosion bubble jet into a high-speed water column has been widely adopted by many researchers to investigate the bubble jet. Based on the in-cavity explosion, a new high-speed water jet experimental methodology was proposed, and the experimental device design, method and system were presented as well. The details about how to carry out the pertinent experiments were also illustrated. Based on the proposed experimental system, the experimental research on high-speed water jet under different conditions were carried out. It is found that the shapes of the generated high-speed water jet vary with the outlet position and the depth of the cavity. Three experiments with three different cavity depths but same outlet position, and other two experiments with same cavity depth but different outlet positions were carried out. According to the results, the shape of the water jet generated in the experiments with short cavity depth and surface-above outlet position cannot meet the requirements of the investigation. The influence of outlet position and depth of the cavity on the shape of the water jet was investigated and the mechanism of the water jet shape was analyzed. According to the requirements of the investigation of the bubble jet wall pressure, the adoptable outlet position and cavity depth were got. In the experiments, the piezoelectric wall pressure sensor was used to measure the wall pressure of the water jet. The whole water jet wall pressure can be divided into two phases: the initial impact pressure period and the later hydrodynamical pressure period. According to the results, the outlet position and the depth of the cavity are the two main factors affecting on the shape of the water jet. The initial impact pressure of the water jet meets the water hammer theory. The proposed water jet experimental methodology based on the in-cavity explosion can be used to investigate the shape of the high-speed water jet and wall pressure characteristics including the underwater explosion bubble jet.
The loading of bubble jet is an important part of the whole loading induced by the middle-field and near-field underwater explosion. Due to the fact that the period of the bubble jet is extremely short and the jet occurs inside the complicated underwater explosion bubble, it is hard to investigate the bubble jet through the direct underwater explosion bubble. Therefore, simplifying underwater explosion bubble jet into a high-speed water column has been widely adopted by many researchers to investigate the bubble jet. Based on the in-cavity explosion, a new high-speed water jet experimental methodology was proposed, and the experimental device design, method and system were presented as well. The details about how to carry out the pertinent experiments were also illustrated. Based on the proposed experimental system, the experimental research on high-speed water jet under different conditions were carried out. It is found that the shapes of the generated high-speed water jet vary with the outlet position and the depth of the cavity. Three experiments with three different cavity depths but same outlet position, and other two experiments with same cavity depth but different outlet positions were carried out. According to the results, the shape of the water jet generated in the experiments with short cavity depth and surface-above outlet position cannot meet the requirements of the investigation. The influence of outlet position and depth of the cavity on the shape of the water jet was investigated and the mechanism of the water jet shape was analyzed. According to the requirements of the investigation of the bubble jet wall pressure, the adoptable outlet position and cavity depth were got. In the experiments, the piezoelectric wall pressure sensor was used to measure the wall pressure of the water jet. The whole water jet wall pressure can be divided into two phases: the initial impact pressure period and the later hydrodynamical pressure period. According to the results, the outlet position and the depth of the cavity are the two main factors affecting on the shape of the water jet. The initial impact pressure of the water jet meets the water hammer theory. The proposed water jet experimental methodology based on the in-cavity explosion can be used to investigate the shape of the high-speed water jet and wall pressure characteristics including the underwater explosion bubble jet.
2020, 40(11): 111405.
doi: 10.11883/bzycj-2020-0066
Abstract:
In order to explore the damage and failure model of warship under close-in underwater explosion from shipboard direction attacting, a cabin model was designed and applied to close-in underwater explosion experiments. The results including demolishing regions of cabin model, shock environment data from typical positions, together with strain datas were acquired. It was indicated that: (1) Only the regions around the charge suffered serious damage, majorly characterized by the local damage model; (2) Water jetting phenomenon was found in this experiment, but the mechanism responsible for the formation of water jetting was quite different from traditional one induced by the bubble collapsing. The reasons may be due to the coupling interactions between bubble movement and incomplete boundary and free surface; (3) The crevasse calculation based on energy method was built. The calculated results were in good agreement with the experimental results; (4) The distance of charge had an important influence on the failure model of shipboard plate.
In order to explore the damage and failure model of warship under close-in underwater explosion from shipboard direction attacting, a cabin model was designed and applied to close-in underwater explosion experiments. The results including demolishing regions of cabin model, shock environment data from typical positions, together with strain datas were acquired. It was indicated that: (1) Only the regions around the charge suffered serious damage, majorly characterized by the local damage model; (2) Water jetting phenomenon was found in this experiment, but the mechanism responsible for the formation of water jetting was quite different from traditional one induced by the bubble collapsing. The reasons may be due to the coupling interactions between bubble movement and incomplete boundary and free surface; (3) The crevasse calculation based on energy method was built. The calculated results were in good agreement with the experimental results; (4) The distance of charge had an important influence on the failure model of shipboard plate.
2020, 40(11): 111406.
doi: 10.11883/bzycj-2020-0067
Abstract:
Experiment of cabin model subjected to close-in underwater explosion from bottom attacting was investigated to explore the damage failure model of warship, The demolishing region datas of cabin model together with shock environment information were obtained. Furthermore, by contrasting the experimental results from the case of close-in underwater explosion from ship broadside attacting and far-mild field shock environment trial. It is concluded that: (1) the typical failure of cabin model mainly contains the whole deformation, tearing in the middle along with local dish on both sides; (2) the bottom attacting method has more destruction ability in contrast to the ship broadside attacting way, it is found more than 40% damage effect can be increased according to the experimental results; (3) the variation tendency of measuring point shock spectra between close-in and far-mild field bottom underwater explosion at middle and high frequency level, Unfortunately, for the low frequency level the values of close-in underwater explosion are greater than the latter.
Experiment of cabin model subjected to close-in underwater explosion from bottom attacting was investigated to explore the damage failure model of warship, The demolishing region datas of cabin model together with shock environment information were obtained. Furthermore, by contrasting the experimental results from the case of close-in underwater explosion from ship broadside attacting and far-mild field shock environment trial. It is concluded that: (1) the typical failure of cabin model mainly contains the whole deformation, tearing in the middle along with local dish on both sides; (2) the bottom attacting method has more destruction ability in contrast to the ship broadside attacting way, it is found more than 40% damage effect can be increased according to the experimental results; (3) the variation tendency of measuring point shock spectra between close-in and far-mild field bottom underwater explosion at middle and high frequency level, Unfortunately, for the low frequency level the values of close-in underwater explosion are greater than the latter.
2020, 40(11): 111407.
doi: 10.11883/bzycj-2019-0378
Abstract:
In order to study the damage mechanism of a caisson wharf under underwater contact explosion, the damage characteristic caisson wharf subjected to underwater contact explosion was simulated by using the LS-DYNA software. The credibility of simulation results was verified by comparative analysis of experimental results. The results show that numerical simulation can reflect the experimental result effectively. The failure process of caisson wharf can be divided into two stages. The circumferential cracks and crater appear in the blast side during the shock wave propagation. During the bubble expansion stage, the detonation products flow into the caisson bin from break accelerating the deformation and damage of the caisson cage. The deformation of the cage seriously led to the damage of the wharf panel. The bubble rush out of water and collapse. Accordingly, the severest damage is stopped when it is about 14% of the first pulsation period of underwater explosion bubble. When the location of charge detonation is in the middle of water depth, underwater contact explosion causes more overall damage to the caisson. When the location of charge detonation is near water face, it causes more damage to wharf panel.
In order to study the damage mechanism of a caisson wharf under underwater contact explosion, the damage characteristic caisson wharf subjected to underwater contact explosion was simulated by using the LS-DYNA software. The credibility of simulation results was verified by comparative analysis of experimental results. The results show that numerical simulation can reflect the experimental result effectively. The failure process of caisson wharf can be divided into two stages. The circumferential cracks and crater appear in the blast side during the shock wave propagation. During the bubble expansion stage, the detonation products flow into the caisson bin from break accelerating the deformation and damage of the caisson cage. The deformation of the cage seriously led to the damage of the wharf panel. The bubble rush out of water and collapse. Accordingly, the severest damage is stopped when it is about 14% of the first pulsation period of underwater explosion bubble. When the location of charge detonation is in the middle of water depth, underwater contact explosion causes more overall damage to the caisson. When the location of charge detonation is near water face, it causes more damage to wharf panel.
2020, 40(11): 111408.
doi: 10.11883/bzycj-2019-0467
Abstract:
In order to study the failure mode and damage mechanism of a high-piled wharf subjected to underwater explosion, the experimental study on two models of the high-piled wharf under different explosive positions was conducted. The data collection and analysis for underwater loads and damage phenomenon of wharf models were recorded. The influence of explosive position on the damage effect and damage mechanism of high-piled wharf was analyzed. The results show the followings: The wharf is subjected to two times of loads under underwater explosive, which are the shock wave load composed of initial shock wave and underwater reflected wave, and bubble pulse load. The main damaged parts of the high-piled wharf are the middle and top of the piles, panel, longitudinal beams and the connection of the panel and beams. The explosive position directly affects the damage form of the wharf. Reducing the distance between the explosive and pile will increase the damage of the pile. When the explosive is located under the panel, the beams and panel of the high-piled wharf is seriously damaged.
In order to study the failure mode and damage mechanism of a high-piled wharf subjected to underwater explosion, the experimental study on two models of the high-piled wharf under different explosive positions was conducted. The data collection and analysis for underwater loads and damage phenomenon of wharf models were recorded. The influence of explosive position on the damage effect and damage mechanism of high-piled wharf was analyzed. The results show the followings: The wharf is subjected to two times of loads under underwater explosive, which are the shock wave load composed of initial shock wave and underwater reflected wave, and bubble pulse load. The main damaged parts of the high-piled wharf are the middle and top of the piles, panel, longitudinal beams and the connection of the panel and beams. The explosive position directly affects the damage form of the wharf. Reducing the distance between the explosive and pile will increase the damage of the pile. When the explosive is located under the panel, the beams and panel of the high-piled wharf is seriously damaged.
2020, 40(11): 113101.
doi: 10.11883/bzycj-2020-0045
Abstract:
In order to study the relationship between the failure and action loading characteristics of thin circular plates subjected to internal explosion, the experiments on aluminum and steel thin circular plates were carried out in a double-cylinder device. The failure modes and the specific impulse characteristics of the circular plates were analyzed. Based on the principle of equal loading under the same deformation, the effective specific impulse and action time under the ultimate deformation of the circular plate were obtained, and the prediction model of the circular plate deformation under this condition was proposed. The results show that, under the action of internal explosion load, the stress concentration zone is the boundary and geometric center of the thin circular plate, which leads to the failure mode of large plastic deformation, tensile tear and shear fracture. The specific impulse on the circular plate gradually changes from the initial wave growth to linear growth, and the effective specific impulse action time is in the range of 2.26–2.93 ms for a certain thermobaric explosive charge of 30–80 g making the steel circular plate with the thickness of 1 mm produce the ultimate deformation. The empirical results show that the deviation between the charge mass obtained by the prediction model and the experimental charge mass is less than 13.3%.
In order to study the relationship between the failure and action loading characteristics of thin circular plates subjected to internal explosion, the experiments on aluminum and steel thin circular plates were carried out in a double-cylinder device. The failure modes and the specific impulse characteristics of the circular plates were analyzed. Based on the principle of equal loading under the same deformation, the effective specific impulse and action time under the ultimate deformation of the circular plate were obtained, and the prediction model of the circular plate deformation under this condition was proposed. The results show that, under the action of internal explosion load, the stress concentration zone is the boundary and geometric center of the thin circular plate, which leads to the failure mode of large plastic deformation, tensile tear and shear fracture. The specific impulse on the circular plate gradually changes from the initial wave growth to linear growth, and the effective specific impulse action time is in the range of 2.26–2.93 ms for a certain thermobaric explosive charge of 30–80 g making the steel circular plate with the thickness of 1 mm produce the ultimate deformation. The empirical results show that the deviation between the charge mass obtained by the prediction model and the experimental charge mass is less than 13.3%.
2020, 40(11): 113102.
doi: 10.11883/bzycj-2020-0035
Abstract:
Some achievements have been made in the study on mechanical properties of antler, but they have not been applied in engineering practice, especially in the study of thin-walled tubes similar to antler crashworthiness. In order to improve the crashworthiness and energy absorption of the thin-walled tube structures, a bionic thin-walled tube with the same inner diameter and equal gradient of outer diameter was designed based on the structural characteristics of antler bone and the principle of structural bionics. The finite element method was used to simulate the energy absorption characteristics of 75 kinds of bionic thin-walled tube structures under the oblique impacts with the impact angles of 10°, 20° and 30°. The polynomial regression element model and multi-objective particle swarm optimization algorithm were used to optimize, and the Pareto front optimization principle was used to obtain the optimal allocation scheme of each target. The minimum distance selection method was used in optimization analysis to obtain the optimal structural design parameters of each scheme. The optimization method used in this study can provide reference for the follow-up research on the crashworthiness of thin-walled tubes, and the optimal structure of bionic thin-walled tubes can provide reference for practical engineering application. The results show that when only considering a single impact angle, the optimal number of biomimetic layers n is 6, and the parameter combination of maximum wall thickness and thickness gradient tmax-a is 2.84 mm-0.38 mm, 2.89 mm-0.29 mm, 2.91 mm-0.34 mm, respectively under 10°, 20° and 30° impact angles. Considering various impact angle weight factors and different configuration schemes, the optimal number of biomimetic layers n is 6, and the parameter combination of maximum wall thickness and thickness gradient tmax-a is 2.95 mm-0.28 mm, 2.92 mm-0.30 mm and 2.85 mm-0.33 mm, respectively.
Some achievements have been made in the study on mechanical properties of antler, but they have not been applied in engineering practice, especially in the study of thin-walled tubes similar to antler crashworthiness. In order to improve the crashworthiness and energy absorption of the thin-walled tube structures, a bionic thin-walled tube with the same inner diameter and equal gradient of outer diameter was designed based on the structural characteristics of antler bone and the principle of structural bionics. The finite element method was used to simulate the energy absorption characteristics of 75 kinds of bionic thin-walled tube structures under the oblique impacts with the impact angles of 10°, 20° and 30°. The polynomial regression element model and multi-objective particle swarm optimization algorithm were used to optimize, and the Pareto front optimization principle was used to obtain the optimal allocation scheme of each target. The minimum distance selection method was used in optimization analysis to obtain the optimal structural design parameters of each scheme. The optimization method used in this study can provide reference for the follow-up research on the crashworthiness of thin-walled tubes, and the optimal structure of bionic thin-walled tubes can provide reference for practical engineering application. The results show that when only considering a single impact angle, the optimal number of biomimetic layers n is 6, and the parameter combination of maximum wall thickness and thickness gradient tmax-a is 2.84 mm-0.38 mm, 2.89 mm-0.29 mm, 2.91 mm-0.34 mm, respectively under 10°, 20° and 30° impact angles. Considering various impact angle weight factors and different configuration schemes, the optimal number of biomimetic layers n is 6, and the parameter combination of maximum wall thickness and thickness gradient tmax-a is 2.95 mm-0.28 mm, 2.92 mm-0.30 mm and 2.85 mm-0.33 mm, respectively.
2020, 40(11): 113301.
doi: 10.11883/bzycj-2020-0047
Abstract:
The hail impact has become a realistic threat for aerospace industries. Natural hail ice has a spherically-layered construction. In order to study the impact failure characteristics and damage ability of hail ice, spherically-layered ice spheres with two layers were created. A series of high- velocity impact experiments were conducted for the simulated hail ice spheres (both monolithic and spherically layered ice) through a smooth barrel gas gun. The dynamic failure properties of ice spheres were studied using high-speed video images during the impact event. Based on the experimental results, it is found that both the monolithic and layered ice spheres present the similar macroscopic crushing characteristics. The ice fragments are formed in the early impact stage. Fragments trajectories lie almost in the target plane. The angle between the fragment trajectories and the plane of the target increases with the increase of impact kinetic energy. A possible explanation for this phenomenon could be attributed to the release rate of projectile kinetic energy. The impact force histories of ice spheres under different velocities were recorded by a force measurement bar apparatus. The impact force curves of monolithic ice show a trend of a sudden increase of the force reaching a maximum, followed by a more gradually decreasing force versus time decay. However, the impact force curves of layered ice show a second rising signal at the last stage. The formation mechanism of the secondary rise signal is hypothesized that the internal small ball is not completely fragmented due to the deflection of failure front at the interlayer interface during impact process. The measured peak impact force is observed to increase with the increase of the projectile kinetic energy. The maximum peak force is reached at very early stage of the impact. Then the ice is actually fragmented, which can not transfer more momentum in the impact direction. In addition, there is a suggestion of higher impact forces for layered ice. This result is expected that the fragmentation process of layered-ice spheres is delayed by the interlayer interface, which is able to transfer much more momentum in the direction of the impact. The achievements of the study are helpful to better understand the dynamic mechanical behaviors of ice under impact loading, and can also provide reference for the safe design of aerocraft structure.
The hail impact has become a realistic threat for aerospace industries. Natural hail ice has a spherically-layered construction. In order to study the impact failure characteristics and damage ability of hail ice, spherically-layered ice spheres with two layers were created. A series of high- velocity impact experiments were conducted for the simulated hail ice spheres (both monolithic and spherically layered ice) through a smooth barrel gas gun. The dynamic failure properties of ice spheres were studied using high-speed video images during the impact event. Based on the experimental results, it is found that both the monolithic and layered ice spheres present the similar macroscopic crushing characteristics. The ice fragments are formed in the early impact stage. Fragments trajectories lie almost in the target plane. The angle between the fragment trajectories and the plane of the target increases with the increase of impact kinetic energy. A possible explanation for this phenomenon could be attributed to the release rate of projectile kinetic energy. The impact force histories of ice spheres under different velocities were recorded by a force measurement bar apparatus. The impact force curves of monolithic ice show a trend of a sudden increase of the force reaching a maximum, followed by a more gradually decreasing force versus time decay. However, the impact force curves of layered ice show a second rising signal at the last stage. The formation mechanism of the secondary rise signal is hypothesized that the internal small ball is not completely fragmented due to the deflection of failure front at the interlayer interface during impact process. The measured peak impact force is observed to increase with the increase of the projectile kinetic energy. The maximum peak force is reached at very early stage of the impact. Then the ice is actually fragmented, which can not transfer more momentum in the impact direction. In addition, there is a suggestion of higher impact forces for layered ice. This result is expected that the fragmentation process of layered-ice spheres is delayed by the interlayer interface, which is able to transfer much more momentum in the direction of the impact. The achievements of the study are helpful to better understand the dynamic mechanical behaviors of ice under impact loading, and can also provide reference for the safe design of aerocraft structure.
