Experimental and numerical investigations of the impact behaviour of composite frontal crash structures

The present paper deals with the lightweight design and the crashworthiness analysis of a composite impact attenuator for a Formula SAE racing car, in order to pass homologation requirements. The analysed impact attenuator is manufactured by lamination of prepreg sheets in carbon fibres and epoxy matrix, particularly used for sporting applications, and has a very similar geometry to a square frusta, so as to obtain a progressive and controlled deformation. During the design, attention was focused on the material distribution and gradual smoothing, but also on the lamination process, which can heavily affect the energy absorption capability. To reduce the development and testing costs of a new safety design, computational crash simulations for early evaluation of safety behaviour under vehicle impact test were carried out. The dynamic analysis was therefore conducted both numerically, using an explicit finite element code such as LS-DYNA, and experimentally, by means of an appropriately instrumented drop weight test machine, in order to validate the model in terms of deceleration values during crushing. To assess the quality of the simulation results, a comparative analysis was initially developed on simple CFRP composite tubes subjected to dynamic axial loading. The numerical analysis was conducted using both shell and solid elements, in order to reproduce not only the brittleness of the composite structure but also the effective delamination phenomenon. Both the analyses show a good capacity to reproduce the crushing process; this is confirmed by the fact that model estimated displacements and accelerations are in close agreement with observed values for these variables. This confirms the quality of the methodology and approach used for the design of a racing car impact attenuator.     

Progressive crushing of fiber-reinforced composite structural components of a Formula One racing car

The present paper describes an experimental and numerical investigation on energy absorbers for Formula One side impact and steering column impact. The crash tests are performed measuring the load-shortening diagram and the energy absorbed by the structure. A finite element model is then developed using the non-linear, explicit dynamic code LS-DYNA. To set up the numerical model, tubes crushing testing are conducted to determine the material failure modes and to characterise them with LS-DYNA. The results presented in this study show that the composite structural components of the investigated Formula One racing car possess high value of specific absorbed energy and crash load efficiency around 1.1. The finite element simulations accurately predict the overall shape, magnitude and pulse duration in all the types of impact as well as the deformation and failure of the structures. Comparing the numerical data of the specific absorbed energy to the experimental results, the differences are around 10%.     

Progressive failure modelling of woven carbon composite under impact

The design of composite structures or components, subject to extreme loading conditions, such as crash, blast, etc. requires a fundamental understanding of the deterioration mechanism within the composite meso-structure. Existing predictive techniques for the analysis of composite structures and components near and beyond their ultimate strength are either based on simple scalar stress functions, or use very complex damage formulations with many material constants, some of which may be difficult to characterise. This paper presents a simple damage mechanics based progressive failure model for thin woven carbon composites under impact loading. The approach is based on an unconventional thermodynamic maximum energy dissipation approach, which entails controlling damage evolution and hence energy dissipation per second, rather than damage. The method has been implemented into the explicit dynamic finite element code DYNA3D. Numerical simulation results using the proposed model are compared with two experimental impact tests.The analysis methodology proposed in this paper reflects a very simple, but effective technique that can be used to model a wide range of problems from extreme events, such as crash or blast, to birdstrike, when tearing and perforation are major failure mechanisms. As damage is cumulative, the technique allows initial or/and post-impact static loads to be applied to the composite structure or component, thus allowing a cradle-to-grave design methodology.     

Aircraft impact analysis of nuclear safety-related concrete structures: A review

Safety-related nuclear structures, including concrete nuclear containment vessels, constructed before September 11, 2001, were not purposely designed to resist any impact loading greater than a light aircraft crash. Since 2001, safety of nuclear facilities against a deliberate or accidental large civilian aircraft impact has drawn much attention worldwide. However, current design guides for nuclear structures provide limited information on analysis methodologies for such aircraft impact. This document presents basic general knowledge required to analyze concrete structures for an aircraft impact and provides a summary of available numerical and experimental investigations that may be used to benchmark an aircraft impact simulation. The methodologies available for an aircraft impact analysis are overviewed with an emphasis on structural damage analysis. Constitutive models used for concrete, reinforcing steel, and composite materials are addressed in this paper.     

Numerical investigation of structural crash response of thin-walled structures on soft soil

Accident statistics show that although the certification of aircraft structures is based on crash scenarios on hard or rigid surfaces, in reality most of the crash cases occur on soft soil or water. Therefore a structure which is designed for hard surfaces may not be safe enough for a possible crash scenario on water or soft soil. Finite element method (FEM) has been used in several numerical investigations and promising results were obtained. However, since soil is a granular medium this work aims at numerical modeling of the experimentally observed soil behavior using particle-based numerical technique. In this work numerical simulations of the crash tests on idealized cones and hemispheres were used to validate the models and compare FEM-based models with particle-based models. The results of numerical simulations were compared with quasi-static and dynamic test results conducted on coarse sand sample at the Deutsches Zentrum fur Luft- und Raumfahrt e.V (DLR). After obtaining a stable and accurate particle-based numerical model for the soft soil the crash performance of deformable metallic energy absorbers on soft soil ground was investigated and compared with test data and numerical investigations of rigid ground impacts.     

Experimental testing and phenomenological modelling of the fragmentation process of braided carbon/epoxy composite tubes under axial and oblique impact

A new simulation technique is presented for the phenomenological modelling of stable fragmentation in fibre reinforced composite structures under dynamic compressive loading. An explicit crash code is used for implementation of a hybrid modelling technique, in which two distinct material models act simultaneously. The first model is implemented in a multi-layered shell element and uses a unidirectional composites fracture criterion to predict potential ply fracture mechanisms on a macroscopic scale. This model is, however, unable to represent the complex localised fracture mechanisms that occur on a meso (sub-ply) scale under compression fragmentation loading. Therefore, a second constitutive model is added to capture the energy absorbing process within the fragmentation zone, utilising an Energy Absorbing Contact (EAC) formulation between the composite structure and the impacting body. The essential benefits of the procedure are that it requires minimal input data that can be obtained from simple fragmentation tests, and that the procedure is computationally efficient enabling application to large scale industrial structures. The EAC theory is discussed, together with the required material model parameters. A series of dynamic axial and oblique impact tests and simulations of cylindrical continuous carbon fibre reinforced composite tubes have been performed to validate the approach. Furthermore, the application to more complex load cases including combinations of fragmentation and global structural fracture have also shown a good correlation with test results.     

具有隔震构造的安全壳飞机撞击耦合动力响应模拟分析

建筑物隔震构造主要用于削弱地基中地震荷载对上部结构的影响,而来自上部的飞机撞击对于安全壳隔震体系的影响如何是保证核电安全值得探讨的重要问题。为评价核电站安全壳隔震体系与飞机撞击的耦合动力效应,该文提供了一种细致的模拟耦合动力分析的手段,建立了安全壳细致的动力数值模型,针对不同刚度的隔震支座及无隔震条件,进行多种类型飞机撞击作用下安全壳的动力响应分析。结果显示,飞机撞击作用期间,不同刚度的隔震支座与无隔震条件相比,撞击位置中心节点位移与冲击力的大小具有相关性,因而存在差异,而对于安全壳混凝土结构损伤区域分布则差异不大;但在撞击荷载作用后,不同刚度的隔震支座则会对安全壳振动衰减过程有较大影响。研究表明在隔震体系设计阶段,不能片面的考虑隔震体系在削弱地震响应方面的需求,需要与飞机撞击振动衰减过程耦合分析,从而确定适宜的隔震支座水平刚度等参数。     

Explicit finite difference method in the dynamic analysis of composite structures

An approach for numerical analysis of composite thin-walled structural elements is presented. The analysis is based on the applied theory of composite shells and the grid-characteristic method of finite differences. The explicit and stable homogeneous method for numerical integration of dynamic equations of thin-walled composite structures is discussed. The splitting procedure is used to extract strongly oscillating components from the solution. Implementation of this procedure provides the stability of explicit finite differences schemes. The method considered makes it possible to carry out computations for a wide range of variation of structural parametres and could be used for the analysis of composite structures under dynamic loading.     

乘用车-载货汽车追尾碰撞相容性结构优化设计

对一种已获得专利的新型货车后防护结构进行碰撞相容性优化设计,建立了该结构的乘用车-货车追尾碰撞有限元模型,并通过实车碰撞试验验证了模型有效性。为提高碰撞相容性,制定了防护架最大的吸能和乘用车前部最小的变形量两个优化目标函数,并设计了优化设计参数变量及其变化范围,采用正交化试验方法对16组参数进行了有限元仿真,并对优化目标的影响因素进行了显著性分析,最后,对得到最优的设计方案进行了实车碰撞试验     

Numerical simulation of impact tests on GFRP composite laminates

The design of advanced composite structures or components subjected to dynamic loadings requires a deep understanding of the damage and degradation mechanisms occurring within the composite material. The present paper deals with the numerical simulation of low-velocity impact tests on glass fabric/epoxy laminates through the LS-DYNA Finite Element (FE) code. Two laminates of different thickness were subjected to transverse impact at different energy levels and modeled by FE. Solid finite elements combined with orthotropic failure criteria were used to model the composite failure and stress based contact failure between plies were adopted to model the delamination mechanism. The final simulation results showed a good correlation with experimental data in terms of both force–displacement curves and material damage.     

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。      

基于Campbell模型的卡车与防撞柱最大碰撞力修正计算方法

为探究卡车冲击防撞柱过程中的最大碰撞力,开展了63组碰撞数值试验。根据碰撞后卡车变形特征分析,采用卡车等效变形对Campbell模型进行参数修正,提出了卡车与防撞柱最大碰撞力的修正计算方法,并对国内外相关规范建议的最大碰撞力计算方法的适用性进行了评估。研究表明,碰撞后卡车变形沿宽度呈中间大、两端小的不均匀分布。卡车等效变形不仅受卡车碰撞速度影响,还与防撞柱高度和直径、钢管屈服强度和厚度以及基础深度有关。与实车碰撞试验和数值模拟试验得到的最大碰撞力对比表明,《欧规1》附录B建议方法计算结果严重偏小,《欧规1》附录C和《公路规范》建议方法计算结果离散性较大,该文建议方法计算结果更加准确保守,适用于防撞柱结构设计。     

直升机机身下部复合材料典型结构耐坠特性研究

抗坠性能是武装直升机的一项重要要求,设计具有较高抗坠吸能性能的机身下部结构是实现直升机抗坠要求的主要技术途径。研究了多种形式的复合材料结构元件抗坠特性,在元件研究基础上优化选择复合材料波纹梁和厚蜂窝结构组合,提出了一种新颖的具有较高抗坠吸能性能的复合材料组件形式,并利用有限元理论及试验的方法进行了对比研究分析,计算结果和试验结果吻合较好。     

Automobile intersection collisions—An analytical and experimental investigation of the crash phase

In this study an investigation is made into the crash phase of automobile intersection collisions in which the predominant force is due to the impact; and the external forces on the vehicle, such as tire friction, may be neglected. Analytical as well as experimental methods were used to show that the automobile crash phenomena may be explained macroscopically by rigid body impact theory. Analysis of experimental results indicated the numerical range of the coefficient of friction between the colliding vehicles and the coefficient of restitution necessary to explain the crushing characteristics of the automobile structures and the final socities at the end of the crash phase for different modes of intersection collisions.     

Bird strike damage analysis in aircraft structures using Abaqus/Explicit and coupled Eulerian Lagrangian approach

The subject of this paper is numerical prediction of bird strike induced damage in real aeronautical structures using highly detailed finite element models and modern numerical approaches. Due to the complexity of today’s aeronautical structures, numerical damage prediction methods have to be able to take into account various failure and degradation models of different materials. A continuum damage mechanics approach has been employed to simulate failure initiation and damage evolution in unidirectional composite laminates. Hashin’s failure initiation criteria have been employed in order to be able to distinct between four ply failure modes. The problem of soft body impacts has been tackled by applying the Coupled Eulerian Lagrangian technique, thereby avoiding numerical difficulties associated with extensive mesh distortion. This improvement in impactor deformation modelling resulted in a more realistic behaviour of bird material during impact. Numerical geometrical and material nonlinear transient dynamic analyses have been performed using Abaqus/Explicit. The main focus of the work presented in this paper is the application of the damage prediction procedure in damage assessment of bird impact on a typical large airliner inboard flap structure. Due to the high cost of gas-gun testing of aircraft components, experimental testing on the real flap structure could not have been performed. In order to evaluate the accuracy of the presented method, the bird and composite damage model have been validated against experimental data available in the literature.     

Prediction of impact damage on sandwich composite panels

Sandwich structures are extensively employed in the aerospace and automobile industries. The understanding of their behaviour under impact conditions is extremely important for the design and manufacturing of these engineering structures since impact problems are directly related to structural integrity and safety requirements. This paper investigates the damage behaviour of composite sandwich panels with aramid paper honeycomb (NOMEX) and polyetherimide (PEI) foam cores under transverse impacts at high velocities. A numerical model was developed using the dynamic explicit finite element (FE) structure analysis program PAM-CRASH. For both sandwich structures numerical analysis reproduces physical behaviour observed experimentally in high velocity impact tests.     

瓦斯爆炸冲击作用下新型复合结构防护外壳的动态响应

为了降低和防止瓦斯爆炸冲击波对矿难救生系统的破坏,提高防爆抗冲击能力,提出新型复合结构防护外壳。运用有限元数值分析方法,对新型复合结构防护外壳在瓦斯爆炸冲击波作用下的动态响应进行研讨。分析冲击波作用下新型防护外壳的变形、应力和应变,并与单层防护外壳的动态响应进行了对比。结果表明: 采用中间柔性材料缓冲层的新型复合防护结构,能够延缓瓦斯爆炸冲击波对矿难救生系统的冲击作用,保护系统内部模块不受严重破坏,制造工艺简单且成本低。运用数值分析的方法,可以为救生系统设计建立一个仿真的实验环境,为优化救生系统设计、提高设计效率提供参考数据。     

Topology optimization for nonlinear dynamic problems: Considerations for automotive crashworthiness

Crashworthiness of automotive structures is most often engineered after an optimal topology has been arrived at using other design considerations. This study is an attempt to incorporate crashworthiness requirements upfront in the topology synthesis process using a mathematically consistent framework. It proposes the use of equivalent linear systems from the nonlinear dynamic simulation in conjunction with a discrete-material topology optimizer. Velocity and acceleration constraints are consistently incorporated in the optimization set-up. Issues specific to crash problems due to the explicit solution methodology employed, nature of the boundary conditions imposed on the structure, etc. are discussed and possible resolutions are proposed. A demonstration of the methodology on two-dimensional problems that address some of the structural requirements and the types of loading typical of frontal and side impact is provided in order to show that this methodology has the potential for topology synthesis incorporating crashworthiness requirements.     

Electric-field-controlled magnetoelectric microwave attenuator

The electric-field-induced shift of the magnetic resonance line in ferrite-piezoelectric composites has been studied by experimental and theoretical methods. It is shown that such structures provide a basis for the creation of a magnetoelectric attenuator in mictrostrip design for the microwave range. The device operation is based on a phenomenon in which the magnetic resonance line shifts upon application of an external electric field to the ferrite-piezoelectric composite structure, which plays the role of a resonator. The dependence of the attenuation level on the applied field has been calculated.