Hybrid approach in bird strike damage prediction on aeronautical composite structures

This paper deals with the problem of numerical prediction of bird strike induced damage on aeronautical structures. The problem of soft body impacts has been tackled by applying a hybrid Eulerian Lagrangian technique, thereby avoiding numerical difficulties associated with extensive mesh distortion. Eulerian modeling of the bird impactor resulted in a more realistic behavior of bird material during impact, which has lead to an enhanced response of the impacted structure. The work presented in this paper is focused on damage modeling in composite items of aeronautical structures. The bird impactor model and damage modeling approaches have been validated by comparison with experimental gas gun results available in the open literature, while the complete damage prediction procedure has been demonstrated on a complex airplane flap structure finite element model.     

Numerical simulation of bird strike damage prediction in airplane flap structure

Numerical analyses of bird impact damage in complex aircraft structures have been performed using ABAQUS/Explicit. A Lagrangian formulation was used for the bird model in combination with various material models. Several failure and damage modes have been considered for different material models used in the inboard flap of a typical large transport aircraft. A submodeling approach has been used to reduce computational time. Parametric analyses have been performed using different bird sizes, impact locations and velocity vectors.     

Impact damage prediction in carbon composite structures

This paper describes a strategy for predicting the extent of internal damage in a brittle carbon fibre laminated composite stucture, when subjected to low velocity impact by a single mass. The success of the predictions, which avoid expensive three-dimensional analysis, is validated by test for a wide range of structures from small stiff plates through to large flexible stiffened compression panels whose residual strength is affected much more by internal delamination than tension structures. It is shown that a numerical model needs to incorporate nonlinear behaviour due to both gross deformations and to in-plane material degradation.     

A damage prediction method for composite structures

Damage generally refers to the more or less gradual development of micro-voids and micro-cracks. Damage mechanics is the modelling of these phenomena on a structural analysis scale. In this paper we first recall the non-linear behaviour models we have developed to model composite laminates. Then we present two examples of implementations of such models in a structural analysis code in order to simulate the inner-failure of a structure, or to study delamination initiation.     

含雷击热-力耦合损伤复合材料层压板拉伸剩余强度预测

为了对含雷击热-力耦合损伤复合材料层压板的剩余强度进行预测,基于连续介质损伤力学法(CDM)和唯象分析法,建立了表征复合材料雷击热-力耦合损伤的刚度矩阵渐进损伤退化模型。基于该模型,通过ABAQUS有限元仿真软件,建立了含雷击热-力耦合损伤的复合材料层压板结构三维模型。结合UMAT子程序,完成了拉伸载荷下的剩余强度预测。结果表明:通过与试验对比,仿真结果与试验结果取得了良好的一致性。本文所建立模型,能够有效进行含雷击热-力耦合损伤复合材料层压板结构拉伸剩余强度预测。     

Numerical prediction of damage in composite structures from soft body impacts

The paper summarises recent progress on materials modelling and numerical simulation of soft body impact damage in fibre reinforced composite aircraft structures. The work is based on the application of finite element (FE) analysis codes to simulate damage in composite shell structures under impact loads. Composites ply damage models and interply delamination models have been developed and implemented in commercial explicit FE codes. Models are discussed for predicting impact loads on aircraft structures arising from deformable soft bodies such as gelatine (synthetic bird) and ice (hailstone). The composites failure models and code developments are briefly summarised and applied in the paper to numerical simulation of synthetic bird impact on idealised composite aircraft structures.     

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.     

Numerical simulation of damage and failure in aircraft windshield structure against bird strike

Based on the updated Lagrangian approach, the incremented form of a damage-modified nonlinear visco-elastic constitutive model and its failure criterion were deduced using the updated Kirchhoff stress tensors and strain tensors. The finite element model of a windshield structure including windshield, framework, arc-frame, gasket and rivets was established, in which the adaptive contact relation and boundary condition was defined. A contact–impact coupling algorithm and the explicit dynamic finite element program LS-DYNA were applied to simulate the damage and failure process of windshield structure under three kinds of bird strike velocities. The damage-modified nonlinear visco-elastic constitutive model and its failure criterion were implemented into the user material program. The results showed that the damage and failure of windshield under bird strike can be effectively simulated.     

The detection of aeronautical defects in situ on composite structures using Non Destructive Testing

A study of three Non Destructive Testing methods (Ultrasonic Testing, InfraRed Thermography and Speckle Shearing Interferometry, known as Shearography) was carried out on different specific types of composite specimens having a variety of defects. The aim of this study is to evaluate the efficiency of these NDT methods in the detection of in site defects resulting from Barely Visible Impact Damages (BVID) or in-service damages to complex surfaces such as wings or rods. The size and position of all the defects were determined by GVI (General Visual Inspection): GVI being the reference. The evaluation of the three NDT techniques enabled conclusions to be drawn regarding defect detection and size. The first part of the study deals with determining and measuring defects. It appears that only the ultrasonic method enables the depth of a defect to be determined. In the second part of the study, the results obtained by the three NDT methods are compared. Finally, the feasibility and the time taken to set up the experimental protocol are analyzed. The study shows that all the defects were revealed by, at least, one of the three NDT methods. Nevertheless it appears that InfraRed Thermography and Shearography produced results very quickly (in about 10 s) compared to Ultrasonic Testing.     

A multi-scale finite element approach for modelling damage progression in woven composite structures

A significant challenge in the numerical modelling of composite structures with a multi-axis fibre architecture is the reproducibility of the textile mechanics [1]. A numerical analysis procedure for woven composite structures using a multi-scale finite element approach has been developed, and is presented in this paper. The approach is demonstrated for a flat two-dimensional woven glass/epoxy laminate. Digital microscopy is used to estimate tow cross-section and path, and quantify the amount of variation of these parameters. This data is used to generate both a meso-scale model of a single unit cell as well as a macro-scale model of the complete structure. Numerical results from the proposed approach are compared to experimental stress-strain data, which show good agreement in the lower strain range.     

复合材料三维损伤模型在大开口结构强度预测中的应用

为了预测复合材料大开口结构的强度及损伤扩展情况,开展了3种不同复合材料三维损伤退化模型(瞬间退化模型、渐进损伤退化模型和连续损伤退化模型)在复合材料大开口结构强度预测中的应用研究,完成了含口框加强件的复合材料大开口结构面内纯剪切试验,并采用3种损伤退化模型对试验件及相关文献算例进行了数值模拟。数值模拟结果与试验结果的对比表明:3种损伤退化模型均可以较为精确地预测复合材料大开口结构的极限强度;与其他模型相比,连续损伤退化模型的预测精度最高、通用性最好且网格依赖度最低。研究结果为复合材料大开口结构力学性能的研究提供了理论指导。     

Fibre optic damage detection in composite structures

A system of thin, light-conducting fibres, integrated into a composite structure during its manufacturing process, can serve as a reliable, automatic and remote working long-term monitoring device for structural damage. Fractures, cracks or delaminations in a structure area can destroy the optical fibres installed there and thus interrupt the light flow. Various examples of applications in gfrp aircraft components are described. The outline of a complete fibre optic nervous system (fons) for large Airbus cfrp components shows how fibre optic damage detection can contribute to future aircraft maintenance and inspection philosophies. Following the example of other aircraft systems including engines and computers, the structure can also be included in the permanent and automatic working central fault detection system (cfds).     

Homogenization and damage for composite structures

After presenting shortly the main results of the homogenization theory for periodic media, we give two applications related to damage evaluation and simulation for composite materials: (i) simulation of the evolution of damage by fibre rupture in a unidirectional composite, involving parameters defined on the microscale; and (ii) prediction of debonding near an unloaded boundary in a stratified structure, using boundary layer asymptotic expansions.     

Characterisation of impact damage in skin-stringer composite structures

In studies aimed at understanding the impact performance of structures made from carbon-fibre composites, effects of structural geometry, material type and impact location have been investigated in skin-stringer panels representative of aircraft structure. Effects were investigated for low-velocity impacts to the skin in the bay between stringers, over a stringer foot, and over a stringer centreline. Detailed studies of the impact damage at these locations were investigated using ultrasonic techniques, and optical and electron microscopy. The damage characteristics were explained in terms of the proportion of energy absorbed through damage, such as delamination, and elastic effects, such as structural response of the panel.     

基于剩余应变的复合材料结构寿命预测

为实现对复合材料结构的寿命预测,对已有的复合材料疲劳寿命预测模型进行了研究,确定了基本的刚度降模型,提出了剩余应变的概念,并将其应用到渐进疲劳损伤方法中,以Abaqus为平台,编写UMAT子程序,实现了对复合材料结构的寿命预测及疲劳损伤扩展分析.针对某碳纤维增强复合材料TS800开展相关试验,试验结果与预测结果吻合较好.研究表明,本文所改进的渐进疲劳损伤方法能较好地完成对复合材料结构的寿命预测.     

Hybrid carbon fiber composite lattice truss structures

Carbon fiber reinforced polymer (CFRP) composite sandwich panels with hybrid foam filled CFRP pyramidal lattice cores have been assembled from linear carbon fiber braids and Divinycell H250 polymer foam trapezoids. These have been stitched to 3D woven carbon fiber face sheets and infused with an epoxy resin using a vacuum assisted resin transfer molding process. Sandwich panels with carbon fiber composite truss volumes of 1.5–17.5% of the core volume have been fabricated, and the through-thickness compressive strength and modulus measured, and compared with micromechanical models that establish the relationships between the mechanical properties of the core, its topology and the mechanical properties of the truss and foam. The through thickness modulus and strength of the hybrid cores is found to increase with increasing truss core volume fraction. However, the lattice strength saturates at high CFRP truss volume fraction as the proportion of the truss material contained in the nodes increases. The use of linear carbon fiber braids is shown to facilitate the simpler fabrication of hybrid CFRP structures compared to previously described approaches. Their specific strength, moduli and energy absorption is found to be comparable to those made by alternative approaches.     

A reduced basis approach to quantifying damage dependent dynamic response of laminated composite structures

A finite element (FE) based formulation is utilized to represent the damage-dependent response of laminated composite structures. An internal-state-variable (ISV) approach provides a definition of the stiffness reduction caused by intralaminar crack propagation at the ply level. These ISVs are combined with simple stress criteria to accommodate ply property changes caused by fiber fracture, fiber microbuckling and interior delaminations. A set of orthogonal Ritz vectors are chosen as basis vectors to transform the dynamical equations of motion to a reduced coordinate space. The reduced basis form of the equations provides significant numerical efficiencies, especially for large ordered systems. Furthermore, damping and its variation with damage can be generally represented in any number of vibratory modes. The Newmark integration operator is used to solve the dynamic equations of motion, and equilibrium iterations are performed in each incremental time step to assure convergence. Results are given for laminated beam and plate geometries subjected to dynamic loads.     

复合材料胶接修补航空铝合金的疲劳性能与损伤监测实验研究

针对航空铝合金在疲劳载荷作用下易发生疲劳裂纹快速扩展引起突发断裂破坏的问题,采用碳纤维复合材料来胶接修补受损航空铝合金,以提高其疲劳性能。同时,使用红外热成像技术结合数字图像处理,对复合材料与铝合金界面脱粘进行在线监测,尝试建立脱粘缺陷发展与疲劳裂纹扩展之间的关系。进行无修补和有修补受损铝合金试件的疲劳实验对比研究,结果表明:复合材料胶接修补铝合金试件的疲劳寿命比未修补试件提高60%,从实验曲线走势和破坏形态看,可认为复合材料的疲劳性能优于复合材料/铝合金界面的疲劳性能,而界面的疲劳性能优于铝合金的疲劳性能,脱粘缺陷的像素增加与金属的裂纹长度延伸规律一致、高度相关,可以为后续疲劳裂纹扩展监测提供参考。     

Numerical damage prediction in dowel connections of wooden structures

The behaviour of timber connections is very complex because of the interaction between brittle and ductile failure modes that develop within the contact areas between the timber and the dowel. Simulating this behaviour numerically requires the use of multidimensional failure criteria as well as the use of coupled constitutive equations accounting for both non-linear isotropic hardening and isotropic ductile damage. Such a formulation is proposed in the present work and implemented within a Vumat user-defined subroutine in Abaqus/Explicit. The model is used to simulate the behaviour of a double shear timber steel connection. Good agreement was found between the FE results and experimental ones, which showed the good capability of the model to predict the onset of ductile damage and growth. It was found that failure results from ductile defects initiation, growth and propagation inside narrow shear bands wherein the plastic strain is highly localised.     

基于改进空间滤波器的复合材料结构损伤成像方法

为降低Lamb波在复合材料结构中传播时存在的频散现象和各方向传播特性的不一致性给损伤监测带来的困难, 提出一种利用Hilbert变换改进的空间滤波器对复合材料结构损伤进行成像的方法。分析了基于空间滤波器的信号合成成像原理, 在此基础上利用Hilbert变换构造传感器时域响应信号的解析信号参与到信号合成成像过程中。通过对仿真声源的成像实验, 验证了该方法的可行性, 通过对碳纤维复合材料板结构上激励源和损伤的成像实验, 验证了该方法的功能。研究表明该方法能够识别损伤相对于压电传感器阵列的角度位置和损伤散射信号的到达时刻。