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Metamorphic mechanisms have attracted considerable attention owing to their capability to switch their topology to adapt to different operational tasks. One feature of topological change is the re-contact of different bodies, which inevitably causes collisions affecting operation accuracy and service life. Consequently, in this study, a collision incidence matrix was introduced to describe the topology of a system involved in collisions, and a method for reducing the closed-loop system to an open-loop system was proposed. The complex movement of the metamorphic mechanism in a changing topology was classified into two different running stages of the source metamorphic mechanism. Based on the relative coordinate method, dynamic modeling of the source metamorphic mechanism considering the impact effects was conducted. Combining the classical collision theory and Newton–Euler equation, the generated impact impulse and the motion after collision were determined. Subsequently, a dynamic analytical method for the full configuration of metamorphic mechanisms was proposed to reflect the changes in the topological structure in the dynamic model. Finally, two typical metamorphic mechanisms used in packaging and spinning were considered as examples to verify the correctness and effectiveness of the proposed method, and their impact characteristics during configuration transformation were analyzed. The proposed analytical method of internal impact for a variable topology process provides effective theoretical guidance for the stability analysis of configuration transformation and structural design aimed at minimizing impacts. [ABSTRACT FROM AUTHOR]

Abstract Metamorphic mechanisms have attracted considerable attention owing to their capability to switch their topology to adapt to different operational tasks. One feature of topological change is the re-contact of different bodies, which inevitably causes collisions affecting operation accuracy and service life. Consequently, in this study, a collision incidence matrix was introduced to describe the topology of a system involved in collisions, and a method for reducing the closed-loop system to an open-loop system was proposed. The complex movement of the metamorphic mechanism in a changing topology was classified into two different running stages of the source metamorphic mechanism. Based on the relative coordinate method, dynamic modeling of the source metamorphic mechanism considering the impact effects was conducted. Combining the classical collision theory and Newton–Euler equation, the generated impact impulse and the motion after collision were determined. Subsequently, a dynamic analytical method for the full configuration of metamorphic mechanisms was proposed to reflect the changes in the topological structure in the dynamic model. Finally, two typical metamorphic mechanisms used in packaging and spinning were considered as examples to verify the correctness and effectiveness of the proposed method, and their impact characteristics during configuration transformation were analyzed. The proposed analytical method of internal impact for a variable topology process provides effective theoretical guidance for the stability analysis of configuration transformation and structural design aimed at minimizing impacts.

Copyright of Arab Journal for Scientific Publishing is the property of Research & Development of Human Recourses Center (REMAH) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Large-scale high-speed granular avalanches can be catastrophic; however, small-scale model tests cannot reproduce the high-speed impact effect, resulting in barrier designs lacking detailed knowledge considering the prototypical dynamic conditions of granular avalanches (e.g., high moving velocities and varied material volumes). In this paper, a well-designed centrifuge model is adopted to reproduce high-speed granular avalanches with variable flow velocities and material volumes, and a calibrated DEM model is also used to offer further insights. The results indicate that under high-speed impact conditions, the effect of granular volume on the pressure distribution pattern dominates, but its influence on the impact loading rate is less obvious. To estimate the high-speed impact force, a constant pressure coefficient of 1 can provide a reasonable estimation for the dynamic component if boulder impacts are excluded, and the static component can be calculated using the weight of the dead zone based on the assumption of a static state of the dead zone. In addition, considering the transition of the impact pressure distribution model caused by different granular volumes and flow velocities, a rectangular pressure profile is suggested for barrier design against high-speed dry granular avalanches when the peak total impact force is adopted as the design load. [ABSTRACT FROM AUTHOR]

Certain fox species plunge-dive into snow to catch prey (e.g., rodents), a hunting mechanism called mousing. Red and arctic foxes can dive into snow at speeds ranging between 2 and 4 m/s. Such mousing behavior is facilitated by a slim, narrow facial structure. Here, we investigate how foxes dive into snow efficiently by studying the role of skull morphology on impact forces it experiences. In this study, we reproduce the mousing behavior in the lab using three-dimensional (3D) printed fox skulls dropped into fresh snow to quantify the dynamic force of impact. Impact force into snow is modeled using hydrodynamic added mass during the initial impact phase. This approach is based on two key facts: the added mass effect in granular media at high Reynolds numbers and the characteristics of snow as a granular medium. Our results show that the curvature of the snout plays a critical role in determining the impact force, with an inverse relationship. A sharper skull leads to a lower average impact force, which allows foxes to dive head-first into the snow with minimal tissue damage. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to meet the higher requirements of energy-absorbing structures in the lightweight automobile design, the mechanical design and impact energy absorption of porous TPMS structures are studied. Eight kinds of porous TPMS structure elements, Gyroid, Diamond, I-WP, Neovius, Primitive, Fischer-Koch S, F-RD, and PMY, are designed based on Matlab, and the porous structure samples composed of eight elements are printed and molded using SLM. The deformation mechanism, mechanical response, and energy absorption characteristics of different porous TPMS structures are investigated. Gyroid and Primitive elements are selected to fill the internal structure of the energy-absorbing automobile boxes. Traditional thin-walled energy-absorbing boxes served as a control group and were subjected to low-speed impact testing. The results show that the peak load of the energy-absorbing box filled with TPMS porous structures is almost equal to the average load under a 4.4 m/s impact, and the SEA of the energy-absorbing box filled with TPMS porous structures is higher than the traditional thin-walled energy-absorbing box. The problems of excessive peak load and inconsistent load fluctuation of traditional thin-walled energy-absorbing structures are effectively solved by porous TPMS structures with the assurance that the lightweight and energy-absorbing requirements are still met. [ABSTRACT FROM AUTHOR]

To improve the cushioning performance of soft-landing systems, a novel origami-inspired combined cushion airbag is proposed. The geometry size, initial pressure, and exhaust vent area of the cushion airbags are designed preliminarily using a theoretical model. The finite element models, including the returnable spacecraft and cushion airbags, are established via the control volume method (CVM) to analyze the impact dynamic behavior and cushioning performance during the landing attenuation process. The cushioning performance of the cushion airbags in complex landing environments are studied to investigate the influence of horizontal velocity, lateral velocity and nonhorizontal landing surfaces. Four design parameters of the cushion airbags, including the initial pressure, venting threshold pressure, exhaust vent area and polygon edge number, are employed to study their influence on the cushioning performance. A multi-objective optimization model of the cushion airbags based on the neural network and multi-objective water cycle algorithm is established to realize the rapid optimization design. The Pareto front of the maximum overload and specific energy absorption is obtained. The analysis results show that the maximum overload of the proposed combined cushion airbags is 7.30 g. The system with the anti-rollover design can avoid rollover and achieve outstanding cushioning performance in complex landing environments. The maximum overload of the returning spacecraft is decreased by 16.4% from 7.30 g to 6.10 g after multi-objective optimizations. This study could provide the technical support for the soft-landing system design of returnable spacecrafts. [ABSTRACT FROM AUTHOR]

General Aviation (GA) aircraft crashworthiness of the vehicle when it hits the ground after the parachute deployment is an important issue. The current dynamic emergency landing regulation (CS 23.562) defines the maximum human tolerant accelerations under both vertical and horizontal directions. This article aims to compare two different aircraft configurations: metal low-wing and composite high-wing ones. Both are two-seats and single-engine GA aircraft. The purpose of the analysis is to check whether the seats and restraint systems met human injury tolerance standards and to determine the possible impact on passengers in the cabin space due to shock loads. Finite element analysis of the fuselage sections for both configurations is performed using the commercial LS-Dyna solver. An extensive campaign of experimental tests has been performed on the composite samples for tuning and validating the model and to find the transition from an undamaged up to totally collapsed sample. The material of the composite fuselage has been characterized through experimental tests. The adopted material model has been refined to match with the performed experimental analysis, allowing high-fidelity modeling. A parametric analysis has been performed to determine the optimal impact angle in terms of lumbar injuries and loads transmitted by the seat belt due to aircraft contact with the ground, thereby increasing the level of safety. The investigations carried out may be an important indicator of the design of the parachute system. [ABSTRACT FROM AUTHOR]

Trochanteric soft tissue thickness (TSTT) is a protective factor against fall-related hip fractures. This study's objectives were to determine: (1) the influence of body posture on TSTT and (2) the downstream effects of TSTT on biomechanical model predictions of fall-related impact force (Ffemur) and hip fracture factor of risk. Ultrasound was used to measure TSTT in 45 community-dwelling older adults in standing, supine, and side-lying positions with hip rotation angles of −25°, 0°, and 25°. Supine TSTT (mean [SD] = 5.57 [2.8] cm) was 29% and 69% greater than in standing and side-lying positions, respectively. The Ffemur based on supine TSTT (3380 [2017] N) was 19% lower than the standing position (4173 [1764] N) and 31% lower than the side-lying position (4908 [1524] N). As factor of risk was directly influenced by Ffemur, the relative effects on fracture risk were similar. While less pronounced (<10%), the effects of hip rotation angle were consistent across TSTT, Ffemur, and factor of risk. Based on the sensitivity of impact models to TSTT, these results highlight the need for a standardized TSTT measurement approach. In addition, the consistent influence of hip rotation on TSTT (and downstream model predictions) support its importance as a factor that may influence fall-related hip fracture risk. [ABSTRACT FROM AUTHOR]

A quasi-static finite cavity cylindrical expansion model is proposed to investigate the lateral boundary effect during long-rod penetration. Analytical solutions for the cavity pressure in the elastic–plastic stage and plastic stage are obtained, through which a decay function for the lateral boundary effect is constructed. The resistance of the target with finite diameter RT is obtained by multiplying the decay function with the resistance of infinite target RT*. Then, a theoretical model for the penetration into the metal targets with finite diameters by long rods is proposed by substituting RT into the Alekseevskii–Tate model. The proposed model is verified by comparison with existing experimental results. Furthermore, the effect of the target diameter, initial impact velocity and yield criterion on the penetration depth and resistance are investigated. The results showed that the lateral boundary effect should be taken into account if the ratio of the target radius to the rod radius (rt0/RP) is less than 25. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study and theoretical analysis on the penetration behavior of a tungsten-alloy long-rod projectile into a concrete target with an impact velocity ranging from 900 to 1,700 m/s. Different penetration regimes are investigated in the experiment in order to have a better understanding of the penetration mechanism of tungsten-alloy projectiles with different impact velocities. The state of the projectiles during penetration and damage parameters of residual projectile and targets are analyzed. Penetration models during abrasion and deforming stages are modified by taking into account of the coupling effects of abrasion, deforming, and shape evolution. Furthermore, the model during the eroding penetration stage is improved to describe the penetration process by considering shape evolution and deforming characteristics of the projectiles. Finally, the improved models are validated against the corresponding experimental results. The results indicate that the crater depth, diameter, and volume of a target are proportional to the impact velocity and impact kinetic energy, separately. The abrasion and deformation of the projectile have a great influence on its penetration process, which cannot be ignored. The calculated depth of penetration (DOP) with different velocities is well-correlated with the experimental results. Residual projectile after erosion penetration still has a greater penetration ability to the concrete target and contributes a larger proportion in the penetration depth. [ABSTRACT FROM AUTHOR]

The fracture of rice grains and other cereals is a common phenomenon during various processes such as seeding, harvesting, and processing. With the objective of elucidating the underlying fracture mechanisms involved, this paper aimed at simulating the fracture of rice grain caused by impacts at different locations on the surface using the discrete element method (DEM) and a bonded particle model (BPM). The aim was to establish an accurate BPM of rice grain using an impact bench test combined with the DEM. To uncover the mechanisms underlying the fracture of rice grains, the fracture process of rice grains at different locations was visualised using impact simulation. The findings demonstrated that this BPM can replicate the fracture behaviour of rice grains. The impact fracture velocity of rice grains varied across different locations, with the highest fracture velocity observed at the centre of the grain, reaching a maximum of 39.5 m s−1. The propagation of cracks played a crucial role in the occurrence of fractures in rice grains. The impact force and kinetic energy were concentrated in the impact zone, resulting in the formation of fracture surfaces in rice grains. The impact toughness of the impact zone in rice grains exhibited a direct correlation with the impact fracture velocity of the rice grains. This study elucidated the fracture mechanism of rice grains and determined the impact fracture velocities at different locations, thereby establishing a reliable foundation for minimising losses in various agricultural stages including seeding, harvesting, and processing. [Display omitted] • Process of crack propagation under rotational impact was studied. • Effect of different locations of rice grains on crack propagation was studied. • Fracture velocity of different locations of rice grains was compared. • Correlation between contact area and impact toughness of rice grains. [ABSTRACT FROM AUTHOR]

Failure of composite not only includes tensile or compression failure of fiber matrix, but also the delamination between plies. The current study investigates a methodology for the Ply-Delamination of Dyneema material due Ballistics impact using LSDYNA. A new methodology was implemented in order to effectively capture the ply delamination and the damage caused due to the impact for different velocities. Numerical results obtained were correlated with previous existing simulation results. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The rebound phenomenon of droplet impacting on super-hydrophobic surfaces is a common flow phenomenon in nature and engineering fields, and is also a frontier research in fluid mechanics. In this paper, the spread deformation, rebound and vibration of viscoelastic droplets on a heated superhydrophobic surface are studied by using high-speed camera and image processing technology. The corresponding impact phenomena of droplets with different impact velocities on various temperature surfaces are explored. The phase diagram of droplet rebound is summarized, and the relationship between velocity, temperature and droplet rebound is demonstrated. The important influence of superhydrophobic surface temperature on the vibration of viscoelastic droplets is revealed. The experimental results can provide a reference for the research of droplet control technology. [ABSTRACT FROM AUTHOR]

The plastic deformation of the spherical tungsten alloy projectile during penetration results in the change of penetration rule. To accurately calculate the penetration depth of the projectile into the low carbon steel target, the concept of projectile shape coefficient was introduced according to the shape of the experimentally recovered projectile, and the deformation penetration process of the projectile was simplified into the rigid penetration process with different shape coefficients at different impact velocities. The rigid penetration model of the spherical, ellipsoidal, and truncated sphere projectile was constructed. The calculation results show that the accuracy of the three models is close to each other. On this basis, the heat map analysis method is used to correlate the impact velocity with the projectile shape coefficient, and a piecewise calculation model of the penetration depth of the spherical projectile is constructed. The error between calculation results and experiment results is less than 10%. [ABSTRACT FROM AUTHOR]

This study investigates the microscopic morphology of a hydraulic servo spool valve caused by particle erosion. The microscopic morphology of spool working edges and solid particle characteristics in oil of a typical hydraulic servo system were experimentally studied. The formation mechanism was analyzed using dynamic impact calculation. The results reveal that the erosion micro-morphology of the spool working edge was mainly characterized by surface peeling, notches, grooves, and chamfers. The contour of the working edge was rounded. The average and variance of the radius of the old spool's working edges were obviously higher than those of the new spool. The main distribution range of solid particle size in typical servo-hydraulic system oil was 5–50 μm, and the number of particles decreased sharply with an increase in particle size, up to 90.89%. The actual shape of particles was close to an ellipsoid with strong erosion destructive power. When a single solid particle collided with the working edge, a large amount of stress was generated at the collision center point, and the stress can reach 1500 MPa when the pressure differential at the valve orifice was 3.5 MPa. The working edges were subjected to cyclic stress of high-frequency particle pulses, resulting in fatigue erosion. [ABSTRACT FROM AUTHOR]

Deep coal is mostly in a three-dimensional unequal stress state. In order to study the dynamic characteristics of coal under impact load, the dynamic failure mechanics experiment of coal was carried out by true triaxial Hopkinson experimental system. This system can be used to provide uniaxial (σ1≥σ2=σ3=0), biaxial (σ1≥σ2 > σ3=0) and true triaxial (σ1≥σ2≥σ3 ≠ 0) pre-stressing for coal samples respectively(where, σ1 is axial prestress; σ2 is vertical prestress; σ3 is horizontal prestress), so as to realize the mechanical property test of coal samples at high strain rates. By analyzing the dynamic mechanical characteristics and differences of coal under uniaxial and true-triaxial static pre-stress, the relationships of dynamic peak strength, peak strain and macroscopic fracture morphology with three-dimensional static pre-stress and strain rate were studied. The results show that the mechanical curves of coal under true triaxial impact load are basically the same, including three stages: linear elastic stage, plastic stage and failure stage. The peak strength and strain of coal samples under uniaxial and true triaxial impact loads have obvious strain rate effects .With the increase of strainrate, the peak strength and peak strain of coal under uniaxial and true triaxial impact loading increase gradually. Compared with uniaxial and true triaxial impact, the three-dimensional static load pre-stress has obvious constraint on the dynamic failure of coal specimen, and the mechanical strength of coal specimen is higher than that of uniaxial impact. The mechanical peak strength and strain of the coal sample decrease with the increase of the principal stress σ1 while the stress σ2 and σ3 remain unchanged. With the increase of strain rate, the coal under uniaxial impact load is gradually broken into particles or powder, and the average particle size of the fragments decreases linearly with the increase of strain rate. However, the coal under three-dimensional static pre-stress presents soma macroscopic fractures, and the average particle size of fragments decreases linearly with the increase of σ1 while the damage degree is lower than that of uniaxial impact.

In order to meet the higher requirements of energy-absorbing structures in the lightweight automobile design, the mechanical design and impact energy absorption of porous TPMS structures are studied. Eight kinds of porous TPMS structure elements, Gyroid, Diamond, I-WP, Neovius, Primitive, Fischer-Koch S, F-RD, and PMY, are designed based on Matlab, and the porous structure samples composed of eight elements are printed and molded using SLM. The deformation mechanism, mechanical response, and energy absorption characteristics of different porous TPMS structures are investigated. Gyroid and Primitive elements are selected to fill the internal structure of the energy-absorbing automobile boxes. Traditional thin-walled energy-absorbing boxes served as a control group and were subjected to low-speed impact testing. The results show that the peak load of the energy-absorbing box filled with TPMS porous structures is almost equal to the average load under a 4.4 m/s impact, and the SEA of the energy-absorbing box filled with TPMS porous structures is higher than the traditional thin-walled energy-absorbing box. The problems of excessive peak load and inconsistent load fluctuation of traditional thin-walled energy-absorbing structures are effectively solved by porous TPMS structures with the assurance that the lightweight and energy-absorbing requirements are still met.

X-ray radiography and computed tomography have become well-established methods for investigation of internal structure of objects and for defectoscopy. Recently, the methods have even been used for in-situ analysis of materials under mechanical loading. Although the techniques would be very suitable for analysis during dynamic events, their application is constrained by typical achievable frame rates. Therefore, fast imaging is usually limited to facilities providing sufficient flux like particle accelerators. In this paper, we test imaging performance of a laboratory-based setup with a high-power X-ray tube, a scintillation panel, and an optical camera. Fast-rotating object and typical specimens for impact testing are irradiated with different power settings and quality of captured images is evaluated and analyzed. It is found out that the system can be successfully used for imaging at several hundred frames per second allowing for inspection of slow impact dynamics experiments.

X-ray radiography and computed tomography have become well-established methods for investigation of internal structure of objects and for defectoscopy. Recently, the methods have even been used for in-situ analysis of materials under mechanical loading. Although the techniques would be very suitable for analysis during dynamic events, their application is constrained by typical achievable frame rates. Therefore, fast imaging is usually limited to facilities providing sufficient flux like particle accelerators. In this paper, we test imaging performance of a laboratory-based setup with a high-power X-ray tube, a scintillation panel, and an optical camera. Fast-rotating object and typical specimens for impact testing are irradiated with different power settings and quality of captured images is evaluated and analyzed. It is found out that the system can be successfully used for imaging at several hundred frames per second allowing for inspection of slow impact dynamics experiments. [ABSTRACT FROM AUTHOR]

Frequently appearing fragile hail, ice and other foreign objects pose great threats to advanced turboprop aircraft when they enter the intake system of the engine. However, it is difficult to simulate the effects of these objects as complicated aerodynamic and dynamic impact coupling phenomena are involved. Regarding a turboprop aircraft inlet with a bypass duct as the subject of the research reported in this article, a coupled Computational Fluid Dynamics–Computational Structural Dynamics (CFD–CSD) numerical simulation method is established based on an unstructured dynamic mesh and impact dynamics technology to solve the phenomena of ‘motion–collision–fragmentation–fragment motion’ for foreign objects such as fragile ice and hail entering the inlet. Based on airworthiness specifications, external hail and ice at the lip and inner lower wall of the inlet are modelled. Moreover, the dynamic motion of these foreign objects and their effects on the aerodynamic performance of the inlet system during the process are simulated and analysed in depth. The results show that high-speed hail breaks into small debris after collision, which may not cause a serious threat to the engine. In addition, the total pressure recovery coefficient and distortion rate are not heavily changed during the process. However, large pieces of ice at the lip of the inlet may lead to large-size fragments that impact the inner wall of the inlet, thus increasing the threat to the safety of the engine. Also, serious shielding and interference of large pieces debris with the inner flow in the dynamic process decrease the total pressure recovery coefficient while increasing the distortion rate, especially in the junction area between the inlet and the bypass duct. In particular, ice in the icing zone located in the inner lower part of the inlet should be of much more concern owing to the fact that ice in this region is more likely to fly directly into the main engine and cause a serious threat.

Granite, as a typical anisotropic hard and brittle rock, is generally in a uniaxial, biaxial, or triaxial state of stress in deep underground engineering and is frequently influenced by extreme dynamic loads including earthquakes, occasional burst, and excavation disturbance. A series of dynamic compression tests were conducted on granite using a true triaxial split Hopkinson pressure bar (SHPB) system on initially anisotropic granite. Using X-ray three-dimensional (3-d) computed tomography (CT) scanning technology and ultrasonic testing, the mechanical properties and fracture behaviors of anisotropic granite under combined dynamic and static loading conditions were studied. Results show that the failure mode of granite changes from damage, to splitting failure, and finally to crushing failure with the rising strain rate under dynamic uniaxial compression. In addition, the axial prestress increases the proportion of transmitted energy in the rock and significantly influences failure strain of the rock. Under biaxial static prestresses, the granite is split along the direction of its free faces and the failure mode is affected by the value of the anisotropy index in the direction of free faces. Under the triaxial static prestresses, the rock is very unlikely to be damaged and the damage effect occurs only after multiple impacts. In the same prestress state, the strain rate of granite increases with the increasing impact velocity and the prestress constraint reduces the dynamic strain rate in the granite. The initial anisotropy of the longitudinal wave velocity of granite is gradually enhanced as the cyclic impact continues. Increasing the strain rate will induce more significant evolution of initial anisotropy of granite, while the prestress constraint restricts the development of initial anisotropy. The results improve understanding of the evolution of impact damage and the dynamic failure characteristics of anisotropic rocks under high geostress. Highlights: Conducted a series of dynamic fracture tests of granite under unprestressed, uniaxial, biaxial and triaxial prestressed conditions. Revealed the dynamic impact damage evolution mechanism of granite under multi-axial stress constraints from a microscopic perspective. Investigated the confining pressure effect and strain rate effect on dynamic damage anisotropy of granite under multi-axial stress constraint. [ABSTRACT FROM AUTHOR]

To improve the cushioning performance of soft-landing systems, a novel origami-inspired combined cushion airbag is proposed. The geometry size, initial pressure, and exhaust vent area of the cushion airbags are designed preliminarily using a theoretical model. The finite element models, including the returnable spacecraft and cushion airbags, are established via the control volume method (CVM) to analyze the impact dynamic behavior and cushioning performance during the landing attenuation process. The cushioning performance of the cushion airbags in complex landing environments are studied to investigate the influence of horizontal velocity, lateral velocity and nonhorizontal landing surfaces. Four design parameters of the cushion airbags, including the initial pressure, venting threshold pressure, exhaust vent area and polygon edge number, are employed to study their influence on the cushioning performance. A multi-objective optimization model of the cushion airbags based on the neural network and multi-objective water cycle algorithm is established to realize the rapid optimization design. The Pareto front of the maximum overload and specific energy absorption is obtained. The analysis results show that the maximum overload of the proposed combined cushion airbags is 7.30 g. The system with the anti-rollover design can avoid rollover and achieve outstanding cushioning performance in complex landing environments. The maximum overload of the returning spacecraft is decreased by 16.4% from 7.30 g to 6.10 g after multi-objective optimizations. This study could provide the technical support for the soft-landing system design of returnable spacecrafts.

A quasi-static finite cavity cylindrical expansion model is proposed to investigate the lateral boundary effect during long-rod penetration. Analytical solutions for the cavity pressure in the elastic–plastic stage and plastic stage are obtained, through which a decay function for the lateral boundary effect is constructed. The resistance of the target with finite diameter RT is obtained by multiplying the decay function with the resistance of infinite target RT*. Then, a theoretical model for the penetration into the metal targets with finite diameters by long rods is proposed by substituting RT into the Alekseevskii–Tate model. The proposed model is verified by comparison with existing experimental results. Furthermore, the effect of the target diameter, initial impact velocity and yield criterion on the penetration depth and resistance are investigated. The results showed that the lateral boundary effect should be taken into account if the ratio of the target radius to the rod radius (rt0/RP) is less than 25.

In order to study the influence of the bolt joint mode on low-velocity projectiles penetrating the composite protective structure, two bolt joint models which connect the composite target to the fixed frame were designed, the ballistic test of the bolted composite protective structure with limited span was carried out, and the bearing and failure characteristics of the bolted region, as well as the energy dissipation of each part of the structure, were analyzed. The results show that in the condition of low-velocity impact, there are three failure modes for the bolted composite protective structure subjected to projectile penetration, including failure of the impact point of the composite target, failure of protective structure connecting components and failure of the holes in the bolted region of the composite target; the failure mode of bolt holes in the bolted region has a great influence on the protection performance, and the allowable value of the bearing capacity of the bolted region depends on the sum of the minimum failure load in the failure modes and the friction force; shear-out failure occurring in the bolt holes in the bolted region exerts the greatest effect on ballistic performance, which should be avoided; When simultaneous failure occurs in the bolted region and the free deformation region of the composite protective structure, the energy absorption per unit surface density of the composite protective structure reaches the maximum, which can give full play to its anti-penetration efficiency.

Frequently appearing fragile hail, ice and other foreign objects pose great threats to advanced turboprop aircraft when they enter the intake system of the engine. However, it is difficult to simulate the effects of these objects as complicated aerodynamic and dynamic impact coupling phenomena are involved. Regarding a turboprop aircraft inlet with a bypass duct as the subject of the research reported in this article, a coupled Computational Fluid Dynamics–Computational Structural Dynamics (CFD–CSD) numerical simulation method is established based on an unstructured dynamic mesh and impact dynamics technology to solve the phenomena of 'motion–collision–fragmentation–fragment motion' for foreign objects such as fragile ice and hail entering the inlet. Based on airworthiness specifications, external hail and ice at the lip and inner lower wall of the inlet are modelled. Moreover, the dynamic motion of these foreign objects and their effects on the aerodynamic performance of the inlet system during the process are simulated and analysed in depth. The results show that high-speed hail breaks into small debris after collision, which may not cause a serious threat to the engine. In addition, the total pressure recovery coefficient and distortion rate are not heavily changed during the process. However, large pieces of ice at the lip of the inlet may lead to large-size fragments that impact the inner wall of the inlet, thus increasing the threat to the safety of the engine. Also, serious shielding and interference of large pieces debris with the inner flow in the dynamic process decrease the total pressure recovery coefficient while increasing the distortion rate, especially in the junction area between the inlet and the bypass duct. In particular, ice in the icing zone located in the inner lower part of the inlet should be of much more concern owing to the fact that ice in this region is more likely to fly directly into the main engine and cause a serious threat. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Ballistics / Dandao Xuebao is the property of Journal of Ballistics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The global impact dynamics of multibody system is challenging due to the multi-scale characteristics of slow-changing non-contact process and fast-changing impact process. To solve the contradiction between the impact accuracy and the global simulation efficiency, a novel quasi-static contact model is proposed where the local contact domain is finely discretized and the energy loss caused by elastoplasticity is considered, and the real-time force-displacement interaction is established to execute the global integration capably. Through the experimental case of flexible pendulum impact, the proposed model is compared with measurements and existing methods, including impulse method, continuous contact force method and nonlinear finite element method. It is shown that the impulse method and continuous contact force method are both sensitive to the coefficient of restitution, yielding uncertain results. The nonlinear finite element method can accurately describe the impact process, but its calculation scale is too large to apply to the global simulation. The quasi-static model can accurately describe the response of the global process and does not rely on artificial selection of any parameters, and the calculation efficiency is greatly improved compared with the nonlinear finite element method. [ABSTRACT FROM AUTHOR]

Atmospheric ice collisions on exposed outdoor infrastructure are a rarely explored surface design challenge. A primary obstacle to realistic ice particles in the laboratory setting is freezing a droplet without a solid surface present and then allowing it to impact a substrate without physical intervention. Using acoustically levitated ice formation with subsequent release onto a controlled area, a third class of ice-countering system called "ice-impacting" is introduced. Stainless steel 316 (SS), epoxy resin-coated (ER), and laser-textured (LT) surfaces with known surface roughness, hardness, and structural characteristics were subjected to 40 ice droplet impacts each. The impact effect on surface properties and the effect of these properties on solid-solid interfacial impact dynamics, in turn, were examined using an analysis framework based on fundamental conservation laws. Elasticity was the most significant factor in droplet behaviour as the ER surface exhibited rebounding for 78 % of impacts, nearly double the rates of the stainless steel surfaces. However, surface roughness also played a role, particularly for droplets with rotational motion, as immobilization occurred for 66 % of impacts on the rougher LT surface. Moreover, the nanostructures on that textured surface resulted in droplet redirection perpendicular to the surface directionality. In contrast, the other surfaces experienced no consistent change in rebound angle. Elasticity also affected momentum retention: the ER surface had a translational restitution coefficient of 0.32 compared to 0.17 for the SS/LT surfaces. Surface roughness was a predominant aspect of energy retention, as the LT surface had a translational-to-rotational energy transfer coefficient of 0.07 (0.23 for the smoother surfaces), resulting in an overall energy retention coefficient of 0.09 compared to 0.28 for the SS and ER surfaces on average. The results show that the interplay between elasticity, roughness, and structure at a dynamic solid-solid interface must be considered to optimize their effectiveness when designing ice-countering surfaces. [Display omitted] • Surface properties affecting solid, atmospheric-like ice impacts are investigated. • Impact dynamics are analyzed using a momentum and energy conservation framework. • Rebounding and immobilization behavior were governed by elasticity and roughness. • Momentum restitution was greatest for more elastic, resin-coated surfaces. • Roughness affected energy retention, limiting translational-to-rotational transfer. [ABSTRACT FROM AUTHOR]

N -methyl pyrrolidone was proposed as a new carbon source for efficiently preparing the diamond-like carbon (DLC) films by a one-step electrodeposition technique at a low voltage. The responses of surface morphology, microstructure and surface wettability of the DLC films on the variation of the area ratio of anode to cathode were investigated in terms of current density in the process of electrodeposition. Especially, the dynamic behaviors of water droplets impacting on one of the superhydrophobic DLC films were studied in detail as a function of Weber number and inclined angle. Results revealed that either a larger or a smaller area ratio than 1.56 could facilitate the formation of hierarchical structure with more hydrocarbon features, which is in favor of creating superhydrophobicity with low surface adhesion. Further, it was found that a competitive strategy between deformation and movement depending on Weber number and inclined angle, where the movement is balanced by sliding with rolling, dominates the impact dynamics of water droplets. This work provides new insight and explanation for the efficient electrodeposition of DLC films at low voltage and the dynamic evolution of impacting droplets on the inclined superhydrophobic surface. • Low-voltage electrodeposited DLC films from a new carbon source – NMP. • Performances regulation of DLC films by changing area ratio of two electrodes. • Droplet deformation competing with movement dominates impact dynamics. • Droplet movement is balanced by sliding with rolling. [ABSTRACT FROM AUTHOR]

• Exponential equations of the liquid properties were used for model modification. • The electric field will induce the pinch-off, tiny jet, and stretching phenomena. • Correlations of the maximum spreading for the charged condition were proposed. • The heat transfer model of droplet impact under an electric field was modified. In this study, the effects of the electric field on the impact dynamics and heat transfer of a single droplet impinging on hot substrates in the film evaporation regime were numerically investigated with phase-field method. According to the simulation results, many fancy impact behaviors of the droplets under a vertical electric field were observed. A strong electric field was found to induce upward pinch-off or even tiny jet phenomena on the hydrophilic substrates. In contrast, the bouncing droplet on hydrophobic substrate would be vertically stretched before leaving the substrates. The maximum spreading ratio of impacting droplets was always inversely proportional to the applied electric field intensity. Correlations of the maximum spreading for the charged condition were proposed by considering the effects of the electric force. In addition, the total heat transfer from hot substrates to the impacting droplet was verified as closely related to the maximum spreading area, spreading time, and instantaneous local heat flux. However, the broken droplets from the induced tiny jet would eventually fall back to disturb the sessile droplet, enhancing the droplet cooling efficiency. The modified heat transfer model of impacting droplets under the effect of an electric field on hydrophilic substrates was established. Finally, the surface charge distribution and electric force loading of the impacting droplets were also discussed. This work delved deep into the underlings of droplet spreading heat transfer under an electric field, and the main findings promised to advance high-efficiency cooling technology. [ABSTRACT FROM AUTHOR]

Under argon conditions, the Taylor impact test for ZrCuAlNiNb amorphous alloy with impact velocity range of 78.9-155 m/s was carried out, the failure fracture process of the material was recorded by high-resolution high-speed photography, and the fractured samples after fracture were recovered. The microscopic morphology of the section was observed by scanning electroscope, and the fracture behavior of the material at different impact speeds was analyzed. ZrCuAlNiNb amorphous alloy breaks from a single main shear band under low-speed impact to a multi-shear band break at high speed (≥ 150 m/s), and several secondary shear straps are formed along the axial direction of the sample. Its complex force leads to a variety of fractured forms, and dynamic temperature rise aggravates the thermal softening effect of the material. ZrCuAlNi crystal alloy is transmitted by axial cracks, which cause the crystal alloy to fracture under the interaction of multiple cracks, and the fractured morphology presents a river-like cleavage fracture. The study of the mechanical properties of ZrCuAlNiNb amorphous alloys and their failure behavior provide theoretical guidance and experimental basis for the application of ZrCuAlNiNb amorphous alloys.

From an offensive point of view, increasing the impact velocity of the projectile is an effective way to enlarge its penetration depth. However, as the projectile penetrates the target, there often exists an angle of attack, the resultant force on the projectile is in a different direction from that of projectile velocity, which causes the deflection of the projectile, and thus the strike effect is greatly weakened. From the other perspective, the deflection of the projectile can contribute to proactive protection of key targets from damage caused by a deeper penetration which has been an important consideration for actual protective structure. Presently, investigations on the deflection mechanism of the impact projectile are relatively few, and there is especially a lack of more comprehensive theoretical and experimental studies. In this paper, the mechanism of projectile deflection when penetrating a composite concrete target is thoroughly analyzed. The composite concrete target composed of a concrete fixed target and multiple diamond-shaped moving targets, similar to the structural system for multi-layer overlay extension, showed better anti-penetration performance in practical protective structures. The analytical model of projectile deflection during penetrating the target is established through simultaneously resolving the dynamic equations for the projectile and moving target. Penetration tests of the composite concrete target plate impacted by a 76 mm projectile were conducted to examine the effectiveness of the analytical model, where impact velocity and point and the size of the moving target were considered. On this basis, the influences of impact velocity and point on the deflection of the projectile are disclosed, and the effects of parameters of moving target are discussed. These findings can provide significant references for optimization of advanced protective structures and improvement of their anti-penetration performance. [ABSTRACT FROM AUTHOR]

The protective performance of a three-layer explosive welded composite plate consisting of steel and aluminum plates is studied in ballistic experiments and numerical simulations. The mechanism of target plate failure under the impact of spherical fragments is investigated. [ABSTRACT FROM AUTHOR]

In the context of green aviation, as an internationally recognized solution, hydrogen energy is lauded as the "ultimate energy source of the 21st century", with zero emissions at the source. Developed economies with aviation industries, such as Europe and the United States, have announced hydrogen energy aviation development plans successively. The study and development of high-energy hydrogen fuel cells and hydrogen energy power systems have become some of the future aviation research focal points. As a crucial component of hydrogen energy storage and delivery, the design and development of a safe, lightweight, and efficient hydrogen storage structure have drawn increasing consideration. Using a hydrogen-powered Unmanned Aerial Vehicle (UAV) as the subject of this article, the crash characteristics of the UAV's hydrogen storage structure are investigated in detail. The main research findings are summarized as follows: (1) A series of crash characteristics analyses of the hydrogen storage structure of a hydrogen-powered UAV were conducted, and the Finite Element Analysis (FEA) response of the structure under different impact angles, internal pressures, and impact speeds was obtained and analyzed. (2) When the deformation of the hydrogen storage structure exceeds 50 mm, and the strain exceeds 0.8, an initial crack will appear at this part of the hydrogen storage structure. The emergency release valve should respond immediately to release the gas inside the tank to avoid further damage. (3) Impact angle and initial internal pressure are the main factors affecting the formation of initial cracks. [ABSTRACT FROM AUTHOR]

Geophysical mass flows impacting flexible barriers can create complex flow patterns and multiway solid‐fluid‐structure interactions, wherein estimates of impact loads rely predominantly on analytical or simplified solutions. However, an examination of the fundamental relations, applicability, and underlying mechanisms of these solutions has been so far elusive. Here, using a coupled continuum‐discrete method, we systematically examine the physical laws of multiphase, multiway interactions between geophysical flows of variable natures, and a permeable flexible ring net barrier system. This model well captures the essential physics observed in experiments and field investigations. Our results reveal for the first time that unified bi‐linear laws underpin widely used analytical and simplified solutions, with inflection points caused by the transitions from trapezoid‐shaped to triangle‐shaped dead zones. Specifically, the peak impact load increases bi‐linearly with increasing Froude number, peak cable force, or maximum barrier deformation. Flow materials (wet vs. dry) and impact dynamics (slow vs. fast) jointly drive the patterns of identified bi‐linear correlations. These findings offer a physics‐based, significant improvement over existing solutions to impact problems for geophysical flows. Plain Language Summary: Flexible barriers are increasingly used worldwide to mitigate debris flows, debris/rock/snow avalanches, and rockfalls. Although many methods exist to estimate critical design factors of flexible barriers, a systematic examination of their applicability and underlying relations remains elusive. The status quo has been largely caused by the challenges of capturing and quantifying the multiphase, multiway flow‐barrier interactions. Here, we perform a series of hybrid solid‐fluid simulations to explore the impact of debris flows/avalanches and rock avalanches on a flexible barrier system. Our numerical predictions of critical physical processes show reasonable consistency with experimental and field observations. For the first time, the physics‐based numerical measures of the flow‐barrier forces, in‐barrier forces, and barrier load‐deformation relations reveal the unified bi‐linear laws behind widely used methods. We find that the flow‐specific turning points of the bi‐linear laws are due to the changes from trapezoid‐shaped to triangle‐shaped jammed regions formed upstream of the barrier. Our findings quantitatively explain how flow properties (e.g., wet vs. dry and slow vs. fast) control the obtained bi‐linear laws. This study provides a crucial improvement over widely used methods for geohazard scientists and engineers to impact problems for geophysical flows. Key Points: We present numerical measures of the impact loads of debris flows/avalanches and rock avalanches on a flexible ring net barrier systemBi‐linear laws relate peak impact to Fr, peak cable force, or maximum barrier deformation with turning points due to shifts of dead zonesFlow materials and dynamics jointly control the obtained bi‐linear laws, which underpin widely used analytical and simplified solutions [ABSTRACT FROM AUTHOR]

In this study, a rapid prediction method for the damage range evaluation of steel box structures under internal blast load was proposed. First, we carried out a dimensional analysis of the damage range, determined the main influencing factors, and built a predictive model. Then, a large number of numerical simulations were conducted with consideration of different steel grades, structural dimensions, plate thicknesses, and explosive weights. After that, according to the damage range data for all the working conditions obtained with the simulation, the failure mode diagrams were drawn on a dimensionless coordinate axis and a two-dimensional dimensionless number coordinate system. Based on this, the damage range for different working conditions was observed, and empirical equations were proposed to quickly predict the damage range of the steel box structure during a blast load. Finally, the correctness of the proposed quick prediction method was verified through field blast experiments result. [ABSTRACT FROM AUTHOR]

[Display omitted] The impact dynamics of droplets containing nonionic surfactants are dependent on their molecular weight and concentration. This study investigates the role of these key parameters on the droplet dynamic behavior of nonionic surfactant solutions on non-wettable alkyl ketene dimer surfaces. Aqueous solutions of 3 nonionic surfactants, MEGA-10, Brij C10 and Brij O20, with molecular weights of ∼ 350, 683 and 1150 g/mol, were prepared at various concentrations. The droplet impact dynamics of these solutions were observed using a high-speed camera. The results show that neither the concentration nor the molecular weight can noticeably change the spreading of the surfactant-laden droplets. A strong correlation was established between droplets' maximum spreading factor (β max) and Weber number (β max = 0.76 We 0.29). In addition, with a slight modification, we adopted two existing analytical models to predict β max. While the model of Pasandideh-Fard et al. overpredicts β max , especially at We < 40, the statistical analyses showed the reasonable accuracy of the model of Ukiwe and Kwok. Furthermore, as the molecular weight decreases, the surfactants more noticeably weaken the vertical oscillation of the droplets in the retraction phase. Surfactant solutions can act similar to dampers and limit the complete/partial rebound of the droplets with no effect on their splashing behavior. [ABSTRACT FROM AUTHOR]

Closed-cell cellular materials gained tremendous interest in their application in aerospace, shipbuilding and defence industries due to their exceptional impact energy absorption and lightweight characteristics. To assess the suitability of these materials in practical utilisation, a proper characterisation in dynamic loading is necessary. This paper investigates closed-cell aluminium foam's deformation behaviour due to low-velocity projectile impact in experimentation and finite element analysis. The collapse mechanism was numerically and empirically examined. The experiment and the finite element analysis were found to be in good agreement. The lowvelocity projectile impact tests were conducted using an instrumented drop-tower with several projectile tips with an impact energy of 105 J. Finite Element modelling using ABAQUS explicit was undertaken. The results reveal that FE modelling of true foam properties using solid geometry has a good correlation with experimental results. In this study, four impactors/indenters (flat-faced, hemispheric, conical, and truncated-conical) were used. A detailed structural collapse during the low-velocity dynamic impact has been explored with XCT data and finite element tools. [ABSTRACT FROM AUTHOR]