Evaluation and validation of multi-physics FE method to simulate bird strike on a wing leading edge

This work is the result of a collaborative research project between the universities (DIAS - Department of Aerospace Engineering, University of Naples "Federico II") and industrial partners (Alenia Aeronautica), to design a new aircraft wing leading edge structures with composite structure with the help of finite element analysis. Extensive experience has been gained with metallic leading edges subjected to bird strike. However, the impact damage in composite structures have been extensively studied in recent years, since composite structures are susceptible to impact damage due to fibre failure strains which lead to brittle failure modes with low energy absorption. The paper describes recent progress on materials modelling and numerical simulation of soft body impact on fibre reinforced composite structures. To reduce certification and development costs, computational methods are required by the aircraft industry which are able to predict structural integrity of composite structures under impact from soft bodies such as birds. In order to predict the damage of the structural components during a bird-strike event, it is necessary to create an appropriate model. This model must be able to reproduce both impact and loads generated in a bird-strike event. Current generation of nonlinear explicit finite element programs can greatly help designers and structural analysts for a more realistic and optimized design and verification of aircraft components to bird strike conditions. In this work the aircraft wing leading edge have been used to correlate the results, the layup consisted of three different plies, in this work we distinguish the ply as outboard skin, made aluminium alloy 2024 T3, the core skin was a honeycomb and inboard skin, the inboard skin was the fiber metal laminate. The approaches used the impact phenomena are different: the Lagrangian approach and the techniques based on Eulerian or Arbitrary Lagrangian Eulerian (ALE) approach. This article presented two approaches implemented in explicit solver MSC/Dytran [1]. For the Lagrangian bird technique the bird is modelled using Lagrangian brick finite elements with the properties of a fluid as reported in [2 and 3]. The imposition of boundary conditions is simplified since the boundary nodes remain on the material boundary. However, a Lagrangian description of this problem may result in loss of bird mass due to the fluid behaviour of the bird which causes large distortions in the bird. These excessive distortions cause failure due to volumetric strain in some elements of the modelled bird. In the Eulerian solver, the grid points are fixed in space and the elements are simply partitions of the space defined by connected grid points. The Eulerian mesh is a “fixed frame of reference.” The material of a body under analysis moves through the Eulerian mesh; the mass, momentum, and energy of the material are transported from element to element. The Eulerian solver, therefore, calculates the motion of material through elements of constant volume. Using the Eulerian bird technique, the bird flows through an Eulerian mesh to impact the structural finite element model. The Eulerian bird elements apply load to the structure elements through an ALE (Arbitrary Lagrange-Euler) coupling algorithm. This method does not need remeshing and is used for fluid dynamics simulations. The simulations correctly predicted the global behaviour of the test for the different materials and gave evidence of the important parameters and their sensitivity versus the design variables.