Oblique Impact Research Articles

Ballistic performance and damage behavior of three-dimensional angle-interlock woven fabric under ballistic impact: Numerical investigation

3D woven fabrics possess excellent specific performance and processability, making them highly favorable in the field of protective engineering, particularly in applications such as body armor. It is critical to evaluate their ballistic response under various impact loadings for both material manufacturing and application purposes. This paper presents a full-size mesoscale finite element model to investigate the dynamic damage behavior of 3D angle-interlock woven fabric (3DAWF) under ballistic impact. The effectiveness of the proposed numerical model is verified through a comparison with available experimental data in terms of ballistic performance and damage morphology. The effects of projectile shape, impact angle, and pre-stretching loading on the ballistic performance of 3DAWF are discussed. It is observed that 3DAWF demonstrates different impact resistance with different projectile shapes due to variations in the impact area and damage mechanism. The friction generated by projectile sliding plays a significant role in dissipating projectile kinetic energy under oblique impact. Moreover, pre-stretching is found to enhance the ballistic limit and energy absorption of 3DAWF to a certain extent.

Crashworthiness analysis and optimization of a novel “cake-cutting” multi-cell tube

Increasing the number of corners can effectively increase the energy absorption of thin-walled tubes. To obtain a thin-walled tube with better energy absorption performance, a novel type of multi-cell thin-walled tube is formed by adding three rib plates, imitating the way of cutting a cake. The rib plates can divide the circular tube into multi-cell tubes with different numbers of multi-cells, and numerical simulations are conducted for the crashworthiness analysis under the axial and oblique impact loadings. The results show that the deformation mode under axial impact is more stable when the number of "cakes" is maximum, and the specific energy absorption is increased by 46% compared with the traditional circular thin-walled tube. Then, a multi-objective optimization framework is employed to find the cutting configuration for better crashworthiness performance. It is found that the optimal multi-cell tube inspired by the “cake-cutting” method can increase energy absorption by 17.4% compared with the original tube. This cake-cutting method provides an innovative designing idea of a thin-walled structure for energy absorption.

Normal and oblique ballistic impact damage behaviour of functionally graded plates: Experimental and numerical

The present study discusses experimental and numerical investigations on the dynamic response of functionally graded plates subjected to normal and oblique ballistic impact. Functionally graded plates were produced in a step-wise manner with powder metallurgy method using powder stacking-hot pressing technique. An experimental configuration was developed where projectiles impact functionally graded plates with three different compositions at impact angles of 0°, 15°, 30°, 45°, and 60°. Ballistic tests of functionally graded plates were carried out with a single-stage gas gun system using fragment simulating projectile (FSP) at velocities of approximately 610 m/s. The effect of the material composition and obliquity on damage and deformation of functionally graded plates was studied by varying the Al 6061 and SiC volumetric ratios to metal-rich (n = 0.1), linear (n = 1.0), and ceramic-rich (n = 10.0). Finite element analyses of functionally graded plates were performed with ANSYS Ls-Dyna explicit solver by employing the Mori Tanaka method to determine local material properties in the graded region and the TTO model to define elasto-plastic material behavior. The normal and oblique ballistic tests of functionally graded plates were compared with the values predicted from the finite element model in terms of damage, deformation, and fracture mechanisms. According to both numerical and experimental studies, the impact angle and material composition were found to be significant influences on damage and deformation of functionally graded plates. Given the complexity of the modeling of the ballistic impact events, the numerical models developed to predict the penetration depth and failure mechanism of plates in the ballistic impact tests showed a good agreement for n = 0.1 and n = 1.0 material compositions due to their metal-rich compositions.

High-velocity impact damage and compression after impact behavior of carbon fiber composite laminates: Experimental study

In this paper, the impact resistance of carbon fiber/resin composite laminates with a thickness of 2.5 mm at different impact velocities, angles and positions was investigated experimentally. In the process of high-velocity impact, fiber shear failure and tension failure are the main failure modes. When the impact velocity is 300 m/s, the fiber tension failure and matrix compression failure under oblique impact are more than that under normal impact, and the energy absorption of laminates is also lager than that under normal impact. The ballistic limits, energy absorption and delamination area of the center and edge impact of laminate are similar. In addition, the CAI tests are conducted to study the influence of different positions on the residual compressive strength of laminates after high-velocity impact, and the fracture loads and failure modes of two impact positions are quite different. The failure modes of the center impact laminate are main buckling failure, and the failure modes of the edge impact laminate are compression failure near the bullet hole side of the fixture and buckling failure near the center of the laminate. The research results can provide a reference for the residual strength of laminates after impact at different locations in practical situations.

Optimisation of an elastomeric pre-buckled honeycomb helmet liner for advanced impact mitigation

Advances in computational modelling now offer an efficient route to developing novel helmet liners that could exceed contemporary materials’ performance. Furthermore, the rise of accessible additive manufacturing presents a viable route to achieving otherwise unobtainable material structures. This study leverages an established finite element-based approach to the optimisation of cellular structures for the loading conditions of a typical helmet impact. A novel elastomeric pre-buckled honeycomb structure is adopted and optimised, the performance of which is baselined relative to vinyl nitrile foam under direct and oblique loading conditions. Results demonstrate that a simplified optimisation strategy is scalable to represent the behaviour of a full helmet. Under oblique impact conditions, the optimised pre-buckled honeycomb liner exceeds the contemporary material performance when considering computed kinematic metrics head and rotational injury criterion, by up to 49.9% and 56.6%. Furthermore, when considering tissue-based severity metrics via finite element simulations of a human brain model, maximum principal strain and cumulative strain density measures are reduced by 14.9% and 66.7% when comparing the new material, to baseline.

Child occupant safety in unconventional seating for vehicles with automated driving systems

The objective of this study was to use computational models to study how unconventional seating positions and orientations in vehicles with Automated Driving System (ADS) may affect occupant response metrics of children with various restraint conditions.A literature review was first conducted to frame a simulation plan, including selections of surrogate ADS-equipped vehicles, potential seating arrangements, impact scenarios, anthropomorphic test device (ATD) models, and child restraint system (CRS) models that are relevant to the selected ATD models. Due to the lack of impact tests with child ATDs and CRS in farside, oblique, and rear impacts, 17 sled tests were conducted with CRS harness-restrained ATDs and vehicle belt-restrained ATDs in frontal, farside, oblique, and rear impact conditions. The sled tests were then used to validate a set of MADYMO (MAthematical DYnamic MOdels) v7.7 models. A total of 550 simulations were then conducted with four child ATDs and various CRS conditions across a range of conventional and unconventional seating locations and orientations under five impact directions. We did not find major safety concerns with ATDs restrained by harnessed CRSs based on the nature of ATD contacts. Compared with frontal and rear impacts, CRSs may rotate laterally in farside and oblique impacts, which could result in higher head and chest injury measures than frontal due to inertial loading to the CRS, and the larger lateral rotation of the CRS may lead to a contact between the CRS and vehicle interior. The major safety concern for vehicle belt-restrained ATDs (with and without booster) is that they have the potential to contact the seat next to them or the instrument panel behind them in a farside or oblique impact. Unconventional seating does not necessarily create additional safety concerns beyond what we know with the conventional seating. However, due to the orientation of the unconventional seats, the occupants on those seats may be involved in a higher percentage of oblique and rear-oblique impacts relative to their seating orientations than conventional seats, which may be considered in the future safety design process.This is the first study using different child ATDs and CRSs to investigate child occupant responses in a wide range of impact directions and seating orientations. Results from the sled tests and simulations provide a better understanding of child occupant responses in those crash conditions, but also identified several limitations of using frontal ATDs in other crash directions.

Numerical study on the effects of oblique impact on the ballistic behavior of 3D angle interlock woven fabric

3D angle interlock woven fabric(3DAWF) has great potential for impact protection. This paper investigates the ballistic mechanism of 3DAWF(5 layers of angle interlock – through the thickness) under normal and oblique impact. The full-size mesoscale model of 3DAWF under different impact directions and angles was established and systematically studied to reveal the 3DAWFs’ ballistic mechanism. The numerical studies of 3DAWF subjected to 0°, 15°, 30°, 45°, and 60° oblique impacts from two impact directions along 3DAWF structure configurations were carried out. We found that 3DAWFs’ ballistic performance increases non-linearly with impact obliquity. The ballistic mechanisms change with impact directions because of 3DAWFs’ anisotropic structure. This work also demonstrates the impact damage mechanism, energy absorption evolution, and stress wave distribution of the 3DAWF under oblique high-velocity impact. The findings are constructive for the 3DAWF applicated in ballistic protection.

Independent friction-restitution description of billiard ball collisions

The oblique impact of a cue ball moving on a horizontal surface with an arbitrary spin on an object ball at rest is described using the independent friction-restitution modeling of impact. The model yields theoretical expressions for the post-collision linear and angular velocities in terms of ‘constant’ coefficients of normal restitution, tangential restitution, and friction for both stick and slip regimes of impact. The model also predicts the post-impact velocities reached by the balls when, as a result of friction with the supporting surface, the pure rolling motion is established. Theoretical predictions are in satisfactory agreement with experimental data for collisions between regulation billiard balls, steel, brass, and rubber spheres.

Experimental and numerical study on crashworthiness of bionic hedgehog spine thin-walled structures

Natural impact-resistant biomaterials, with ingenious and exquisite geometric configurations, have resistance to external impact, and thus provide a perfect bionic example for the optimization design and crashworthiness improvement of new thin-walled structures. Based on the configuration characteristics of hedgehog spine, this paper designed the bulkheaded hedgehog spine thin-walled structure and studied the dynamic behavior of thin-walled structures under axial and oblique impact compression by combining 3D metal printing, quasi-static compression test and finite element simulation. The results show that the combined effect of the ribs, inner walls and bulkheads of the bulkheaded hedgehog spine thin-walled structure effectively improves its deformation coordination ability and crashworthiness. The specific energy absorption of the bulkheaded hedgehog spine thin-walled structure under axial or oblique impact is about 4.1, 2.1 and 1.4 times that of the single-wall cylinder, spider web and simplified hedgehog spine thin-walled structures, respectively.

A novel oblique impact model for elastic solids

Hertzian contact theory is a key step in modeling low-velocity impact on structures. This study presents an oblique contact model for simulating the oblique impact contact between two elastic solids. The presented model can be used for analyzing contact responses between rigid and non-rigid bodies. The contact force and indentation predicted by the presented model were compared to available oblique impact experimental results in the literature. The results demonstrated high accuracy in predicting the impact response of a plane subjected to an impactor with different obliquely velocities. The numerical results show that with increase in the incident angle, the contact force and local indentation decrease significantly, while the contact time increases. The elastic modulus ratio between the indenter and the plane significantly affects the prediction of the contact force and indentation. Hence, it is essential to choose an impact contact model that will facilitate accurate evaluation of its impact response. The present results represent a useful method to assess the safety of different materials. In addition, the oblique impact model can also provide a theoretical framework for evaluating the obliquely low-velocity impacting the performance of beam, plate, and shell structural elements.

Water droplet impact on perfluoropolyether-based liquid-like surfaces

Water droplet impact on water-repellent surfaces is of relevance to many important engineering applications. Although the droplet impact behavior on water-repellent surfaces has been extensively investigated, in particular, textured superhydrophobic surfaces, that on water-repellent liquid-like surfaces has been barely reported. In this study, we experimentally investigated the oblique impact of water droplets on a surface with a liquid-like perfluoropolyether coating using a high-speed camera. The direct observation showed that all the impinging water droplets released from various heights exhibited similar outcomes, including an inelastic collision without rebound as well as a continuous sliding over the liquid-like surface. The liquid-like perfluoropolyether molecular chain on the surface was suggested to behave like a high viscosity oil layer that could cause more intense energy dissipation during the impact process. The crucial impact parameters of the maximum tangential droplet extension, the spreading time and the sliding length were further analyzed quantitatively by the methodology widely adopted in the exploration of the impact behavior in previous studies. It was indicated that the process of the impinging droplet spreading on the liquid-like surface was more likely dominated by the competition between the inertial and capillary forces although the increased viscous dissipation arising from the liquid-like layer significantly suppressed the rebound of the impinging droplet. Compared to superhydrophobic surfaces, the liquid-like surface could generate a stronger friction force for the slide motion of the impinging water droplet. The triboelectric effect arising from the water-solid contact was proven to inhibit the retraction of the impinging droplet with relatively higher impact velocities. This study is expected to improve the fundamental understanding of the droplet impact process and facilitate us to make more rational designs of liquid-like surfaces for relevant applications.

Numerical Simulation of Material Ejection into the Atmosphere Induced by Oblique Impacts of Ten-Kilometer-Diameter Asteroids into the Ocean

Numerical Simulation of Material Ejection into the Atmosphere Induced by Oblique Impacts of Ten-Kilometer-Diameter Asteroids into the Ocean

Oblique impact of a buckling table-tennis ball on a rigid surface.

We report on the rebound of a table-tennis ball impinging without any initial spin in oblique incidence on a rigid surface. We show that, below a critical incidence angle, the ball rolls without sliding when bouncing back from the surface. In that case, the reflected angular velocity acquired by the ball can be predicted without any knowledge of the properties of the contact between the ball and the solid surface. Beyond the critical incidence angle, the condition of rolling without sliding is not reached within the time of contact with the surface. In this second case, one can predict the reflected angular and linear velocities, as well as the rebound angle, provided the supplementary knowledge of the friction coefficient associated with the ball-substrate contact.

Numerical Simulation of Material Ejection into the Atmosphere Induced by Oblique Impacts of Ten-Kilometer-Diameter Asteroids into the Ocean

The results of a three-dimensional numerical simulation of the oblique impacts of ten-kilometer asteroids at an angle of 45° onto a solid surface and into an ocean with a depth of 1 to 6 km are presented. The maximum masses of water, impactor, and soil ejected into the atmosphere and the masses of water, impactor material, and soil remaining in the atmosphere 10 minutes after the impact are calculated. The mass of vaporized ejecta is determined. It is shown that there are 2–5 times more impactor material and soil ejected into the atmosphere during oblique impacts than during vertical impacts.

Preliminary estimation of rock-fall lateral dispersion by laboratory test

Lateral dispersion significantly directs the assessment of rockfall hazard and design of countermeasures. In the present study, the dependence of lateral dispersion on different controlling factors has been systematically evaluated by performing laboratory tests using three different rock block types, namely circular block, and two types of elliptical block. The three types of rock block are released onto an inclined surface with the identical initial status. Parallel, anti-parallel, and oblique impact tests set at slope angles of 22.5° and 45°are conducted to study the block-slope interaction of rockfall. Lateral dispersion of rockfall is less influenced by the block shape for the oblique impact, while the post-impact behaviors are greatly affected by the block shape. The key factors influencing the deviation of the post-impact trajectory direction are the slope angle (θ) and direction difference (Δφ). An empirical model is then developed to characterize the deviation distribution of lateral dispersion by 5th and 95th percentile values with the inclusion of the two key factors. Linear function can be used to describe the 5th percentile boundary, while hyperbolic function is good for the 95th percentile boundary, which need to be validated by field tests in the subsequent research.

Contact characteristics and interfacial motion states during sphere oblique impact with initial spin

Contact characteristics and interfacial motion states during sphere oblique impact with initial spin

On the ricochet of sharp-nosed rigid projectiles from metallic plates

We present a numerical study on sharp-nosed rigid projectile obliquely impacting ductile metallic plates. We followed the trajectory changes of these projectiles including their ricochet behavior and we determined their threshold ricochet angles. These are the impact obliquities at which the projectile moves along a trajectory parallel to the plate's face. These angles were found to be related to the normalized impact velocities of the projectile/plate pair, which are defined by the ratio between the impact velocity and the ballistic limit velocity, at normal incidence, for the given pair. This numerically-derived empirical relation was shown to account for various rigid projectiles, with different nose shapes and aspect ratios, impacting aluminum and steel plates of various strengths. We also found that this relation accounts for experimental data with aluminum and steel plates obliquely impacted by 7.62 mm AP projectiles.

Finite Element Analysis of Low-Speed Oblique Impact Behavior of Adhesively Bonded Composite Single-Lap Joints

Finite Element Analysis of Low-Speed Oblique Impact Behavior of Adhesively Bonded Composite Single-Lap Joints

Numerical Study of Heat Transfer During Oblique Impact of a Cold Drop on a Heated Liquid Film

Abstract A three-dimensional study of a cold droplet impacting obliquely on a heated solid flat surface covered with a hot liquid layer has been performed. The drop Weber number, liquid film thickness, and drop impact angle are set to a range from 100 to 800, 0.1 to 0.4, and 0 deg to 60 deg, respectively. The interface evolution and thermal behavior of the drop impingement is well captured using coupled level set and volume of the fluid method (CLSVOF). The code is validated against previously published results both qualitatively and quantitatively. The results show that in the case of oblique drop impact, the crown dynamics and wall heat flux distribution exhibit an asymmetric pattern, with secondary droplets generated solely on the downstream side, as opposed to normal drop impact in which the secondary drops generated around the circumference of the crown. Based on heat flux values, two distinct region within the liquid film exist: (i) impact region around the impact point and (ii) undisturbed region far from the impact region characterized by the impact dynamics. A parametric analysis further reveals that for a moderate Weber number, asymmetric behavior increases as the drop impact angle increases, resulting in a reduction in heat transfer from the solid surface. However, for a drop impacting at an angle of 28 deg, increased asymmetry due to a increase in the Weber number results in significant cooling of the impact region. Furthermore, it is also found that a thinner liquid film promotes higher heat transfer from the solid surface, resulting in a higher wall heat flux.

Heat generation during oblique particle impact

Granular flows are characterised by particle interactions that involve sliding and collisions. In such events, heat is generated from friction and plastic deformation. Despite the importance of such self-heating mechanisms, our understanding of the fundamental principles of heat generation from friction and plastic dissipation is still limited. This work explores this problem at the particle level for oblique impacts between a spherical particle and a rigid substrate. In the first part, theoretical models and a finite element method (FEM) model are used to predict the amount of heat generated and contact temperatures at various impact angles. The theoretical and the FEM models are in good agreement for all impact cases considered. A parametric study of the influence on heat generation and temperature distributions is also carried out. It is shown that the temperature profiles are dependent not only on the amount of the generated heat but also on the material’s thermal properties, such as thermal conductivity and specific head capacity. Apart from a good insight into heat generation during oblique impacts, this study also identifies simple theoretical solutions that can be used in other numerical tools, such as discrete element methods, for studying heat generation problems in bulk granular flows.