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.     

Modelling of impact forces and pressures in Lagrangian bird strike analyses

The paper aims at evaluating and improving the accuracy of bird impact numerical analyses performed with finite element explicit codes, focusing on the modelling of the spatial and temporal pressure distributions exerted on the target by the impacting body. A Lagrangian approach is adopted, interfacing the ESI/Pam-Crash solver code with an automatic trial-and-error procedure for the elimination of the excessively distorted elements. The theoretical formulation relevant to the impact of a cylindrical soft body against a rigid target is reviewed and this idealised case is adopted to validate the presented approach with increasingly refined finite element schemes. A sensitivity study is then carried out, adopting differently shaped bird models and varying the material hydrodynamic and deviatoric responses. A set of models is selected comparing the results with the experimental average values and the scattering reported in literature for the most significant loading parameters in impacts on rigid targets. The model shape and the calibration parameters of the bird material used in these models are subsequently adopted in the analyses of impacts on a deformable polycarbonate plate. The numerical results obtained with increasingly refined bird models are presented and discussed. A range of modelling parameters is finally suggested to perform reliable numerical analyses on aircraft structures and a criterion is proposed to select the models for a reasonably conservative approach to the design of a bird proof structure.     

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.     

Analysis of Bird Impact on a Composite Tailplane Leading Edge

One of the main structural requirements of a leading edge of a tailplane is to ensure that any significant damage caused by foreign object (i.e. birdstrike, etc...) would still allow the aircraft to land safely. In particular, leading edge must be certified for a proven level of bird impact resistance. Since the experimental tests are expensive and difficult to perform, numerical simulations can provide significant help in designing high-efficiency bird-proof structures. The aim of this research paper was to evaluate two different leading edge designs by reducing the testing costs by employing state-of-the-art numerical simulations. The material considered was a sandwich structure made up of aluminium skins and flexcore as core. Before each test was carried out, pre-test numerical analyses of birdstrike were performed adopting a lagrangian approach on a tailplane leading edge of a large scale aircraft using the MSC/Dytran solver code. The numerical and experimental correlation have shown good results both in terms of global behaviour of the test article and local evolution of some measurable parameters confirming the validity of the approach and possible guidelines for structural design including the bird impact requirements.     

基于欧拉—拉格朗日方法的复合材料机翼前缘鸟撞模拟

复合材料大面积用于飞机结构后,其鸟撞问题变得更加突出。利用大型通用有限元程序ABAQUS,采用耦合欧拉—拉格朗日方法（CEL）对某型无人机复合材料机翼前缘的鸟撞问题进行模拟,研究了鸟体速度、密度和蒙皮铺层形式等对鸟撞动响应的影响,计算了机翼前缘填充泡沫后的鸟撞损伤,对复合材料蒙皮的鸟撞破坏机理进行了分析,所得结果对工程设计具有参考意义。     

Bird's substitute tests results and evaluation of available numerical methods

Recent bird impact tests were conducted using gelatine as a bird substitute. A recipe for the gelatine is suggested in order to use as a reference in further bird test certification procedures. Results from the tests are also given so that they can be used to validate numerical models and promote the use of numerical tools in aircraft design and certification process.     

光学玻璃材料动态冲击试验与鸟撞研究

针对多光谱硫化锌(zinc sulfide,ZnS)光学玻璃材料用于飞行器时的鸟撞问题进行了研究。对多光谱硫化锌玻璃进行了中高应变率下的压缩试验获得其材料属性。鸟体采用光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)方法建模,引入Gruneisen状态方程定义鸟体本构模型。对建立的鸟体模型进行撞击铝板的仿真并进行试验验证,验证结果表明建立的鸟体模型具有较高的精度,可以用于其它碰撞情景下的仿真。建立鸟撞玻璃平板的模型对多光谱硫化锌玻璃的耐鸟撞性能进行预测分析,仿真结果表明ZnS玻璃撞击部位和边缘约束的地方容易达到极限应变并发生失效;另外,随着鸟体撞击角度的减小玻璃表面的接触力峰值也逐渐减小。该研究所得结果可以为鸟体SPH方法的数值模拟以及多光谱硫化锌玻璃在飞行器上的应用提供参考。     

Experiment-Based Explicit Dynamics Analysis for Bird Strike Damage Prediction in Composite Structures

Bird strike analysis is a common type of analysis performed during the design and analysis of rotorcraft. These simulations are carried out in order to predict whether various designs will pass the necessary certification tests. In the past, the only way to determine whether forward-facing aeronautical composite structures could withstand bird strikes was with time-consuming physical tests. In the research of bird striking, the bird impact test is the most effective method. But the existing data of test results are highly disperse, so that they do less help for the design of aeronautical composite structures and also cost more. Tests usually needed to be repeated several times because components often failed and were required for each new design. There is a large variability in numerical bird models, composite modeling approaches and complexity of simulation processes to design the sandwich structures of an aircraft. This paper investigates the composite structures modeling for bird strike phenomenon by using state-of-the-art modeling tools capable of predicting the experiment-based composite structural damage, damage location, failure size and failure mode due to impact and addresses a critical review on analysis techniques. This paper also demonstrates the state-of-the-art bird strike simulation methodology developed, and the accuracy of modeling approaches available in explicit codes is discussed.     

复合材料加筋壁板鸟撞动响应分析

考虑复合材料蜂窝夹芯结构的冲击损伤,采用接触碰撞耦合方法研究了复合材料加筋壁板的抗鸟撞性能。鸟撞方式包括垂直冲击和斜冲击两种,复合材料的冲击损伤模型采用Chang-Chang模型,分析了三种鸟撞速度下鸟撞性能参数如复合材料壁板的失效单元数、鸟体剩余动能和筋条的变形,以及复合材料壁板和筋条在某一鸟撞速度下应力随筋条数的变化规律。计算结果表明：垂直冲击和斜冲击下复合材料加筋壁板的抗鸟撞性能不同,并非筋条越多越有利于改善抗鸟撞性能,筋条有时还可能起反作用。     

Soft body impact on laminated composite materials

A technique used to perform soft body impact tests has been described in this paper. Soft body impactor made of four parts water to one part of bovine hide gelatine was used to substitute bird. A series of tests on plates of different systems of CFRP materials have been conducted. Panels of each material system were impacted at velocities between 200 m/s and 330 m/s. Each panel was impacted only once, regardless of damage situation. Ultrasonic C-scan was used to interpret damage after impact. Damage modes are summarised and materials have been compared and ranked according to their impact behaviour.     

Modelling of Bird Strike on an Aircraft Wing Leading Edge Made from Fibre Metal Laminates – Part 2: Modelling of Impact with SPH Bird Model

Fibre Metal Laminates with layers of aluminium alloy and high strength glass fibre composite have been reported to possess excellent impact properties and be suitable for aircraft parts likely to be subjected to impacts such as runway debris or bird strikes. In a collaborative research project, aircraft wing leading edge structures with a glass-based FML skin have been designed, built, and subjected to bird strike tests that have been modelled with finite element analysis. In this second part of a two-part paper, a finite element model is developed for simulating the bird strike tests, using Smooth Particle Hydrodynamics (SPH) for modelling the bird and the material model developed in Part 1 of the paper for modelling the leading edge skin. The bird parameters are obtained from a system identification analysis of strikes on flat plates. Pre-test simulations correctly predicted that the bird did not penetrate the leading edge skin, and correctly forecast that one FML lay-up would deform more than the other. Post test simulations included a model of the structure supporting the test article, and the predicted loads transferred to the supporting structure were in good agreement with the experimental values. The SPH bird model showed no signs of instability and correctly modelled the break-up of the bird into particles. The rivets connecting the skin to the ribs were found to have a profound effect on the performance of the structure.     

NiTi SMA Wires Coupled with Kevlar Fabric: a Real Application of an Innovative Aircraft LE Slat System in SMAHC Material

This paper investigates experimentally and numerically the response of a smart hybrid thermoplastic aircraft slat system subjected to a short-duration and high-frequency event like a birdstrike. The focus of the paper is to exploit the ability that superelastic shape memory alloys have to absorb and dissipate energy compared to conventional composite structures. The final objective of the work is to develop an innovative thermoplastic wing leading edge slat able to resist to an impact of 4-lb (1.8 kg) bird at speed of 350 kts (132 m/s), as requested by the aeronautical requirements. Aircraft leading edges must be certified for a proven level of bird impact resistance. In particular, the main structural requirement is to protect the torsion box and control devices from any significant damage caused by birdstrike in order to allow the aircraft to land safely. A clear increase of the composites toughness and higher absorbed energy levels before failure were also observed. This is due to the fact that SMA wires can absorb kinetic energy during the impact due to their remarkably large failure and recoverable strain and to their superelastic and hysteretic behaviour. The activities have been performed within the European Project COALESCE “Cost Efficient Advanced Leading Edge Structure”, funded by the Seventh Framework Program Theme 7 Transport (incl. Aeronautics).     

大型商用飞机撞击核电站屏蔽厂房荷载研究

采用有限元方法建立飞机与核电站屏蔽厂房非线性模型,利用发动机以不同速度撞击钢筋混凝土板试验验证撞击分析中飞机与核电站屏蔽厂房有限元模型非线性材料本构及参数,并分析飞机网格尺寸效应。对大型商用飞机以200m/s速度撞击核电站屏蔽厂房非线性撞击过程模拟计算及假设核电站分别为线弹性、刚性本构模型撞击过程计算。获得大型商用飞机撞击核电站屏蔽厂房的荷载时程曲线,分析飞机撞击力及核电站屏蔽厂房结构变形特点及核电站结构刚度对撞击力影响规律,并讨论在核电站初步设计中常用飞机撞击力计算方法-Riera方法的适用性。     

FE analysis of geometry effects of an artificial bird striking an aeroengine fan blade

Bird strike resistance of aeroengines is a strict certification requirement. Apart from costly experimental bird strike tests, explicit numerical modeling techniques have been employed. However, due to the complicated bird geometry, artificial bird models are still not well defined and it is a perennial problem selecting an appropriate representative artificial bird geometry for the simulations. To examine the relative effects of the artificial bird geometry, explicit 3-D finite element analyses are conducted herein using the commercial code LS-DYNA. As a validation test, we first studied the nonlinear transient dynamic response of an artificial bird striking a rigid flat target. Following the validation, we studied the impact behavior of an artificial bird impinging a flexible aeroengine fan blade. The study focused on the three most-frequently used configurations in the literature: namely, hemispherical-ended cylinder, straight-ended cylinder, and ellipsoid, at various length-to-diameter aspect ratios. The results show that the initial contact area between the bird and target in the early phase of the impact event would have a significant effect on the peak impact force. The aspect ratio of the bird striking both rigid panel and flexible fan blade was found to have little influence on the normalized impact force and impulse.     

State-of-the-Art Finite Element Modeling of Rotorcraft Main Rotor Blade for Bird Strike Damage Analysis

This paper demonstrates the state-of-the-art composite modeling methodology to investigate the bird strike phenomenon using available numerical bird models through experimental tests and simulation tools. The present work is based on the application of nonlinear explicit finite element analysis to simulate the response of rotorcraft main rotor blade root end under high velocity impact load. The damage behavior of blade made of composites under soft body impact depends upon bird size, blade size, blade span-wise location of impact and bird orientation with respect to hitting location, blade rotational speed and rotorcraft cruise speed. Bird model is considered as hydrodynamic with length-to-diameter ratio of 2. A bird strike event is characterized by loads of high intensity and short duration. A transient explicit nonlinear finite element-based impact analysis using Autodyn has been carried out to predict bird strike resistance to withstand 1.0 kg bird at critical flight condition. Numerical analysis indicates that blades do not tear which agrees well with the physical test conducted.     

Experimental study of the low-velocity impact behaviour of primary sandwich structures in aircraft

The susceptibility of sandwich structures to localised (impact) damage is one of the main reasons why the sandwich concept is not yet used in large primary aircraft structures of airliners. The objective of this work is to experimentally investigate the damage tolerance of representative composite sandwich panels for primary aircraft structures. Instrumented low-velocity impact tests were performed on sandwich specimens consisting of carbon Non-Crimp Fabric/epoxy facings and a Rohacell (PMI) foam core. Both internal and external damage resulting from these impact events was evaluated.The foam core material has a considerable influence on the amount of damage detected by ultrasonic TTU C-scan. CAI tests however showed that this core damage has no significant influence on the residual compressive strength of the specimens.     

Hypervelocity impact response of spaced composite material structures

The design of a spacecraft for a long-duration mission must take into account the possibility of high-speed impacts by meteoroids and orbiting space debris and the effects of such impacts on the spacecraft structure. With the advent of many new high-strength composite materials and their proliferation in aircraft applications, it has become necessary to evaluate their potential for use in long-duration space and aerospace structural systems. One aspect of this evaluation is the analysis of their response to hypervelocity projectile impact loadings. The analyses performed in this study indicate that the extent of damage to a dual-wall composite structure can be written as a function of the geometric and material properties of the projectile/structure system. A comparative analysis of impact damage in composite specimens and in geometrically similar aluminum specimens is also performed to determine the advantages and disadvantages of employing certain composite materials in the design of structural wall systems for long-duration spacecraft.     

Comparing different fidelity models for the impact analysis of large commercial aircrafts on a containment building

Three Boeing 767 finite element models with different fidelities are built using CATIA, Hypermesh and LS-DYNA in this study. The impacts of these models on a rigid wall and a containment building are simulated with LS-DYNA. The simulation results show that the time histories of the impact forces and impulses differ significantly among these models for the low-speed impact case. With the increase of the impact velocity, the time histories of impact forces and the damage of the containment building become similar. Moreover, the impact on the back side of the containment building will occur only when the high fidelity model impacts the containment building with a high velocity. The over-simplified aircraft models will underestimate the impact load and induce a different failure mode compared to the high fidelity model. The internal structures of an aircraft should be accounted for in the impact simulation. This investigation provides a reference for further studies of aircraft impacts on containment buildings.     

飞机尾翼前缘结构鸟撞仿真与改进设计

基于疏散鸟体动能的防鸟撞策略,以提高结构刚度和抑制变形为目标,采用光滑粒子流体动力学(SPH)方法对现有飞机尾翼前缘结构鸟撞过程进行了数值研究。根据模拟结果,通过增加单向斜支板结构和采用纤维/金属复合材料,实现了从结构和材料两个方面对尾翼前缘结构进行改进设计。结果表明,前缘增加的单向斜支板结构可以通过疏散鸟体动能来降低鸟撞冲击对尾翼内部结构的破坏,而采用纤维金属复合材料则减轻了前缘曲翼约10%的质量,且提高了整体刚度,并使结构在鸟撞过程中最大变形降低到原始构型的25%。通过分析不同铺层方式下材料的破坏模式和吸能效果,发现合理的铺层设计可显著提高尾翼前缘结构的抗鸟撞性能。     

Numerical Analysis of Bird Impact on Glass-Reinforced Leading Edge of an Aircraft Wing

The paper describes the methodology of modeling and simulation of bird impact mechanism of GLARE laminate structures. The bird is modeled using Lagrangian concept. Explicit finite element techniques have been developed to simulate the impact mechanics. The study involves deeper understanding of impact dynamics and contact mechanics. The bird impact analysis has been carried out on typical configuration of GLARE 3/2, 4/3, 5/4, 6/5, 7/6 and 8/7. The results of stress propagation and material deformation at high strain rate have been obtained. Results from the numerical analysis are compared with experimental results, and the material is found to be capable of absorbing the impact energy. The results also show that the bird material model chosen to simulate for carrying out impact mechanics analysis is found to be capable of capturing most of the complex behavior exhibited by functional structural material GLARE.