A comparative study of energy absorption characteristics of foam-filled and multi-cell square columns

A comparative study of energy absorption characteristics between foam-filled square columns and multi-cell square columns was conducted by using nonlinear finite element codes LS-DYNA. The columns and the foam were made of the same material aluminum and the thickness of all sidewalls of columns was kept 1.5 mm. Numerical results compared well with theoretical predictions and showed that the energy absorption efficiency of multi-cell columns was about 50–100% higher than that of foam-filled columns. It means that multi-cell columns were more attractive than foam-filled columns and the reason for this was analyzed by a comparison of the collapse modes. Furthermore, a type of pre-crushed trigger was introduced and modeled for multi-cell columns. This type of trigger was found to be effective to eliminate the initial peak force and improve the efficiency of a multi-cell column as an energy absorber.     

椭圆形泡沫填充薄壁管斜向冲击吸能特性仿真研究

为了提高汽车在斜向碰撞中的防撞性,提出了一种新型的椭圆形泡沫填充管。以比吸能和冲击力峰值作为评价指标,采用有限元仿真的方法分析了椭圆向心率、壁厚和泡沫铝密度等参数对其斜向冲击吸能特性的影响。结果表明:向心率的减小,在小角度冲击时,可降低冲击力峰值,大角度冲击时,能提高比吸能量;比吸能和冲击力峰值与壁厚近似为线性关系;泡沫铝密度为0.153 g/cm~3时,泡沫填充管的综合比吸能最小,而冲击力峰值则随着泡沫密度的增大而增大。因此,合理地设计椭圆形泡沫填充管参数有利于提高汽车的防撞性,从而提高乘员安全性能。     

Dynamic simulation and energy absorption of tapered thin-walled tubes under oblique impact loading

In real-world impact loading situations the structure could be subjected to both axial and off-axis loads. Tapered thin-walled rectangular tubes have been considered desirable impact energy absorbers due to their ability to withstand oblique impact loads as effectively as axial loads. Despite this, relatively few studies have been reported on the response of such structures under oblique loading. The aim of this paper is to compare the energy absorption response of straight and tapered thin-walled rectangular tubes under oblique impact loading, for variations in the load angle, impact velocity and tube dimensions. It is found that the mean load and energy absorption decrease significantly as the angle of applied load increases. Nevertheless, tapering a rectangular tube enhances its energy absorption capacity under oblique loading. The outcome of the study is design information for the use of straight and tapered thin-walled rectangular tubes as energy absorbers in applications where oblique impact loading is expected.     

FEA of oblique impact tests on a motorcycle helmet

In accidents, motorcycle riders full-face helmets often make oblique impacts with road surfaces. Finite element analysis was used to predict the rotational and linear acceleration of a Hybrid II headform, representing a motorcyclist's head, in such impacts, considering the effects of friction at the head/helmet and helmet/road interfaces. Simulations of the oblique impact test in British Standard BS 6658 were validated by comparison with published data. This showed that COST 327 experimental data was largely determined by the friction coefficient (0.55) between the helmet shell and abrasive paper, and hardly affected by that between the head and helmet. Slip was predicted at the shell/paper interface throughout the impact, due to the high angular inertia of the helmet, and the normal force remaining below 3.5 kN. Simulations of more severe motorcycle helmet impacts explored the effects of impact site and direction, impact velocity components, helmet fit and the scalp. In these impacts, the higher velocity component normal to the road caused high frictional forces on the helmet shell, eventually causing it to roll on the road. The peak headform rotational accelerations, at some impact sites, were potentially injurious. The most effective method of reducing head rotational acceleration could be a reduction in the linear acceleration limit of the helmet standards.     

Crushing response of foam-filled conical tubes under quasi-static axial loading

Foam-filled thin-walled tubes are considered to be desirable energy absorbers under axial loading due to their higher energy absorption compared with empty tubes. This paper treats the axial crushing and energy absorption response of foam-filled conical tubes under quasi-static axial loading, using non-linear finite element models. Influence of important parameters such as wall thickness, semi-apical angle and density of foam filler was investigated and the results highlight the advantages of using foam-filled conical tubes as energy absorber. Results also indicate that the crush and energy absorption performances of conical tubes are significantly enhanced by foam filling. The primary outcome of the study is new research information and development of empirical relations which will facilitate the design of foam-filled conical tubes as energy absorbers in impact applications.     

泡沫填充多边形单锥管与双锥管斜向加载下耐撞性分析

锥形泡沫填充结构结合了泡沫填充结构与锥形结构的优势,具有优异的吸能性和抵抗失稳变形的能力。研究了具有不同横截面的泡沫填充多边形单锥管(FSPTTs)与泡沫填充多边形双锥管(FBPTTs)在四种冲击角度下的耐撞性。采用多准则评估方法(COPRAS)对不同横截面的泡沫填充单锥管与泡沫填充双锥管的综合耐撞性进行了评估。评估表明:综合考虑多种冲击角度时,圆形截面泡沫填充单锥管较其他截面泡沫填充单锥管具有更好的耐撞性;圆形截面泡沫填充双锥管较其他截面泡沫填充双锥管具有更好的耐撞性。最后,针对圆形截面泡沫填充单锥管与圆形截面泡沫填充双锥管,以最大比吸能和最小峰值力为目标,采用非支配遗传算法对这两种结构在四种冲击角度下进行了多目标优化。结果表明:当冲击角度从0°变化到10°时,两种结构的Pareto曲线变化不大,而当冲击角度从10°变化到30°时,冲击角度对Pareto曲线形状和位置有显著影响;在冲击角度为0°和10°时,圆形截面泡沫填充双锥管的耐撞性优于圆形截面泡沫填充单锥管,而在冲击角度为20°和30°时,圆形截面泡沫填充单锥管的耐撞性优于圆形截面泡沫填充双锥管。实际应用中,可以根据工程需要选择合适的结构。     

Numerical simulation of normal and oblique ballistic impact on ceramic composite armours

This paper presents three-dimensional finite element models that investigate the performance of ceramic–composite armours when subjected to normal and oblique impacts by 7.62 AP rounds. The finite element results are compared with experimental data from different sources both for normal and oblique impact, respectively. Simulation of the penetration processes as well as the evaluation of energy and stresses distributions within the impact zones highlight the difference between normal and oblique ballistic impact phenomena. The findings show that the distributions of global kinetic, internal and total energy versus time are similar for normal and oblique impact. However, the interlaminar stresses at the ceramic–composite interface and the forces at the projectile–ceramic interface for oblique impact are found to be smaller than those for normal impact. Finally, it is observed that the projectile erosion in oblique impact is slightly greater than that in normal impact.     

Ballistic limit for oblique impact of thin sandwich panels and spaced plates

Ballistic perforations of monolithic steel sheets, two-layered sheets and lightweight sandwich panels were investigated both experimentally and numerically. The experiments were performed using a short cylindrical projectile with either a flat or hemispherical nose that struck the target plate at an angle of obliquity. A total of 170 tests were performed at angles of obliquity 0–45°. The results suggest that during perforation by a flat-nosed projectile, layered plates cause more energy loss than monolithic plates of the same material and total thickness. There was no significant difference in the measured ballistic limit speed between monolithic plates and layered plates during oblique impact perforation by a hemispherical-nosed projectile.     

填充泡沫铝的多层铝管动态压溃吸能特性研究

采用数值模拟的方法研究和分析了无填充物的多层铝管结构的吸能特性,结果发现多层铝管相比单层铝管,不但具有较大的吸能量,而且还具有较高的比吸能率;在此基础上,设计了不同层数的多层管泡沫铝填充结构,研究发现泡沫铝不但受轴向压溃变形,同时也受到了铝管层之间的相互作用力使其在径向发生了变形;之后对多层管填充3种不同密度的泡沫铝,采用变参分析的方法研究了多层管层数和泡沫铝密度对整个结构吸能特性的影响;研究结果表明:填充泡沫铝的多层管,随着层数的增加,其比吸能率和吸能量也随之有所增加,随着泡沫铝密度的提高,比吸能率的提高量开始下降,但仍高于填充相同泡沫铝的单层管。     

高g值冲击下泡沫铝填充铝壳吸能特性研究

在弹体高速侵彻硬目标和弹箭爆炸抛撒过程等环境中,弹载测控电路将承受数万g的冲击加速度作用,因此需要对测控电路模块进行缓冲保护.为了设计较优的保护结构,提出了3种不同厚度的铝壳和不同密度泡沫铝的填充结构,利用LS-DYNA有限元软件,从载荷效率、比吸能、隔冲效率以及最大加速度响应等4个评价指标对泡沫铝填充铝壳缓冲吸能效果进行评估.结果表明,厚度为0.8mm、密度为1.1g/cm3填充结构的缓冲吸能效果在不同组合中最好.     

复合材料薄壁管冲击断裂分析与吸能特性优化

为实现不同冲击载荷下的吸能管结构逆向设计, 应用复合材料强度和刚度理论, 计算得到树脂基纤维增强复合材料正交各向异性的力学参数, 同时应用非线性显式有限元算法模拟了轴向冲击载荷作用下管件的动态断裂过程。根据正交设计原理, 得到了管件比吸能与其几何参数之间的非线性映射关系, 并构造出了相应的响应表面。按照汽车正面碰撞对冲击加速度的要求, 应用序列二次规划算法对吸能管进行了优化设计, 得到了具有较优吸能效率和较小冲击力峰值的吸能管结构参数。结果显示: 方管的变形模式、吸能量、冲击载荷-位移曲线变化趋势、冲击载荷峰值等与试验结果吻合很好; 当管件的壁厚、截面长度、管长分别选取2.1、44、200 mm时, 可得到设计域内的最大比吸能29.23 J/g。      

Effective elastic properties of foam-filled honeycomb cores of sandwich panels

Filling with foams of honeycomb structures has been proposed as some enhancement of honeycomb-cored sandwich material systems. The present study considers aluminum honeycomb cores filled with polyvinyl chloride foams with the aim to predict their material elastic properties. The displacement-based homogeneous technique using 3D finite element analysis is applied to evaluate the effective elastic properties of foam-filled honeycomb cores. The special attention is paid to stress predictions at the skin/core interface and the stress distributions within the honeycomb cell walls. The influence of the foam filler on distribution of local stresses within the cell is examined. The FE modelling is performed with the commercial available software ABAQUS. The structural benefits of the foam-filled honeycomb cores are also discussed.     

Concepts for enhanced energy absorption using hollow micro-lattices

We present a basic analysis that establishes the metrics affecting the energy absorbed by multilayer cellular media during irreversible compaction on either a mass or volume basis. The behaviors at low and high impulse levels are distinguished through the energy dissipated in the shock. The overall mass of an energy absorbing system (comprising a cellular medium and a buffer) is minimized by maximizing the non-dimensional dissipation per unit mass parameter for the cellular medium, Λ≡Umρs/σY$\Lambda \equiv U_{\text{m}}{\rho }_{\text{s}}/{\sigma }_{\text{Y}}$, where U_m is the dissipation per unit mass of the cellular medium, ascertained from the area under the quasi-static compressive stress/strain curve, σ_Y the yield strength of the constituent material and ρ_s the density of the material used in the medium. Plots of Λ$\Lambda$ against the non-dimensional stress transmitted through the medium, σtr/σY${\sigma }_{\text{tr}}/{\sigma }_{\text{Y}}$ demonstrate the relative energy absorbing characteristics of foams and prismatic media, such as honeycombs. Comparisons with these benchmark systems are used to demonstrate the superior performance of micro-lattices, especially those with hollow truss members. Numerical calculations demonstrate the relative densities and geometric configurations wherein the lattices offer benefit. Experimental results obtained for a Ni micro-lattice with hollow members not only affirm the benefits, but also demonstrate energy absorption levels substantially exceeding those predicted by analysis. This assessment highlights the new opportunities that tailored micro-lattices provide for unprecedented levels of energy absorption for protection from impulsive loads.     

Dynamic energy absorption characteristics of hollow microlattice structures

Hollow microlattice structures are promising candidates for advanced energy absorption and their characteristics under dynamic crushing are explored. The energy absorption can be significantly enhanced by inertial stabilization, shock wave effect and strain rate hardening effect. In this paper we combine theoretical analysis and comprehensive finite element method simulation to decouple the three effects, and then obtain a simple model to predict the overall dynamic effects of hollow microlattice structures. Inertial stabilization originates from the suppression of sudden crushing of the microlattice and its contribution scales with the crushing speed, v. Shock wave effect comes from the discontinuity across the plastic shock wave front during dynamic loading and its contribution scales with v². The strain rate effect increases the effective yield strength upon dynamic deformation and increases the energy absorption density. A mechanism map is established that illustrates the dominance of these three dynamic effects at a range of crushing speeds. Compared with quasi-static loading, the energy absorption capacity at dynamic loading of 250 m/s can be enhanced by an order of magnitude. The study may shed useful insight on designing and optimizing the energy absorption performance of hollow microlattice structures under various dynamic loads.     

Crushing and energy absorption performance of different geometrical shapes of small-scale glass/polyester composite tubes under quasi-static loading conditions

This paper presents the quasi-static crushing performance of nine different geometrical shapes of small-scale composite tubes. The idea is to understand the effect of geometry, dimension and triggering mechanism on the progressive deformation of small-scale composite tubes. Different geometrical shapes of the composite tubes have been manufactured by hand lay-up technique using uni-directional E-glass fabric (with single and double plies) and polyester resin. Dedicated quasi-static tests (144 tests) have been conducted for all nine geometrical shapes with different t/D (thickness–diameter) ratios and two triggering profiles (45° chamfering and tulip pattern with an included angle of 90°). From this unique study, it was found that the crushing characteristics and the corresponding energy absorption of the special geometrical shapes are better than the standard geometrical shapes such as square and hexagonal cross sections. Furthermore, the tulip triggering attributed to a lower peak crush load followed by a steady mean crush load compared to the 45° chamfering triggering profile which resulted into a higher energy absorption in most of the geometrical shapes of the composite tubes.     

Finite element modelling of the progressive crushing of braided composite tubes under axial impact

Composite tubular structures are of interest as viable energy absorbing components in vehicular front rail structures to improve crashworthiness. Desirable tools in designing such structures are models capable of simulating damage growth in composite materials. Our model (CODAM for COmposite DAMage), which is a continuum damage mechanics based model for composite materials with physically based inputs, has shown promise in predicting damage evolution and failure in composites. In this study, the model is used to simulate the damage propagation, failure morphology and energy absorption in triaxially braided composite tubes under axial compression. The model parameters are based on results from standard and specialized material testing and a crack band scaling law is used to minimize mesh sensitivity (or lack of objectivity) of the numerical results. Axial crushing of two-ply and four-ply square tubes with and without the presence of an external plug initiator are simulated in LS-DYNA. Refinements over previous attempts by the authors include the addition of a pre-defined debris wedge, a distinguishing feature in tubes displaying a splaying mode of failure, and representation of delamination using a tiebreak contact interface that allows energy absorption through the un-tying process. It is shown that the model adequately predicts the failure characteristics and energy absorption of the crushing events. Using numerical simulations, the process of damage progression is investigated in detail and energy absorptions in different damage mechanisms are presented quantitatively.     

Energy loss in vehicle to vehicle oblique impact

Since the seventies, many methodologies have been developed for estimating from energy loss the delta V produced in a vehicle to vehicle impact. Normal energy loss, is calculated by a discrete number of residual crush measurements in the direction parallel to the vehicle's axis, using the stiffness coefficients. In the case of oblique impact, a correction factor is applied to the normal energy loss to determine energy loss in the impulse direction. In this paper the concept of principal direction of deformation is introduced, presenting a new method for estimating energy loss in vehicle to vehicle collision, starting from a discrete number of crush measurements, which are, however, performed considering the effective displacement of the points during the crush. This novel approach, in addition to providing a more rigorous model of the physical phenomena, leads to improvement in the results: with the new approach, the mean error committed in estimating energy loss is about 10%, as compared to the 20% of the previous methodology.     

In-plane impact behavior of honeycomb structures filled with linearly arranged inclusions

Honeycomb structures filled with linearly arranged inclusions were analyzed with a finite element method (FEM) to study how the arrangement of rigid inclusions affects the in-plane impact behavior of honeycomb structures. Each model was divided into several cell regions by inclusion lines. The analysis revealed the effect of inclusion lines on the mean stress of the cell region, maximum displacement of the cell region, and the order of deformed cell regions. Maximum displacement of the cell region was proportional to the width of the cell region, and mean stress of the cell region decreased as the width of the cell region increased. Approximate equations for the maximum displacement and mean stress of the cell region were derived. The approximations accounted for the deformation process of the honeycomb models with inclusion lines and revealed the dependence of the order of the deformed cell region on the mean stress of the regions. The validity of the approximate equations was confirmed by comparing them with experimental results. It was found that the approximate equations enabled us to design the in-plane impact behavior of honeycomb structures filled with linearly arranged inclusions.     

方孔蜂窝夹层板在爆炸载荷下的吸能特性

通过有限元数值模拟方法,对方孔蜂窝夹层板在爆炸冲击载荷下的变形机理和吸能特性进行了分析。在单位面积质量以及夹层板芯层薄壁间距、高度给定的情况下,通过对不同夹芯层相对密度下夹层板的吸能率以及上、下面板最大变形的比较,得出了最优的夹芯层相对密度。在此相对密度下,夹芯层吸能率最高,下面板变形最小,夹层板的抗冲击性能最优。同时还讨论了夹层板芯层薄壁间距、厚度、高度以及面板厚度对其各部分吸能率的影响,以得到最优化的夹层板结构。     

Impact energy absorption characteristics of composite structures

The tensile and compressive tests of glass–epoxy composites with 1–200 s⁻¹ strain rates which are typical strain rate range during automobile crash accidents were performed in order to measure the strength variation with respect to strain rate. The tests were performed using both a horizontal type pneumatic impact tester and a conventional dynamic universal test machine with strain-rate-increase mechanisms. Also, the impact energy absorption characteristics of glass fiber reinforced composites were estimated using the newly proposed progressive impact fracture model. From the experiments and predictions, it was found that the proposed method predicted relatively well the experimental results.