16th International Conference on Composite Structures ICCS 16

A. J. M. Ferreira (Editor) © FEUP, Porto, 2011

HYBRID APPROACH IN BIRD STRIKE DAMAGE PREDICTION ON AERONAUTICAL COMPOSITE STRUCTURES

I. Smojver* and D. Ivančević* * Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb

I. Lučića 5, HR-10000 Zagreb, Croatia e-mail: ismojver@fsb.hr, web page: http://aerodamagelab.fsb.hr

Key words: Composite structures, Impact damage, Bird strike, Aeronautical structures.

Summary. 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.

1 INTRODUCTION

Bird strikes present still present a major concern to the air transport safety due to changes in migration routes of flocking birds. In order to reduce the costs involved with assessment of bird strike resistance of critical aeronautic components, numerical bird strike simulations are subjected to continuous improvements. A hybrid Eulerian Lagrangian approach has been employed in this work as to overcome excessive distortion of bird impactor elements. Application of this methodology enables modelling of the impacted structure using traditional Lagrangian finite elements, while the bird impactor is modelled as an Eulerian material. Eulerian modelling of the impactor avoids all unwanted consequences associated with extensive mesh distortion, as the Eulerian material is free to move through the stationary mesh. This paper illustrates the improvements of the damage prediction approach presented in [1]. The nonlinear transient dynamic simulations have been performed in Abaqus/Explicit.

2 BIRD MODELING The Eulerian model in CEL (Coupled Eulerian Lagrangian) analyses is usually represented

by a stationary cube containing Eulerian elements. Abaqus provides multi-material EC3D8R volume elements to model Eulerian problems, which may be completely or partially occupied

First A. Author, Second B. Author and Third C. Coauthor.

2

by the Eulerian material. The generally accepted approach in the numerical bird simulation to replace the impactor with an equivalent mass of water and air mixture (e.g. [2,3]), has been employed in this paper as well.

3 DAMAGE MODELLING 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. Consequently, Hashin’s failure criterion has been employed for the CFRP parts, while a strain rate dependent plasticity model and element deletion criterion based on equivalent plastic strain have been used for metallic structural items. Failure of the Nomex honeycomb core has been modeled by a simplified criterion based on equivalent plastic strain.

4 RESULTS Figure 1 shows the bird deformation upon impact on the flap model. The kinetic energy of

the 1.81 kg bird at 100 m/s is sufficient to cause damage on a wide area around the impact location as demonstrated by contours of Hashin’s tensile fiber damage initiation criterion. Despite the fact that some elements have fulfilled the element deletion criterion, the bird doesn’t protrude through the composite flap skin.

(Avg: 75%)Multiple section pointsHSNFTCRT

+0.000e+00+2.000e-01+4.000e-01+6.000e-01+8.000e-01+1.000e+00

XY

Z

Figure 1: Impact of a 1.81 kg bird. Contours of Hashin’s fibre tensile initiation criterion are shown.

REFERENCES [1] I. Smojver and D. Ivancevic, “Numerical simulation of bird strike damage prediction in

airplane flap structure”, Compos. Struct., 92, 2016 – 2026 (2010). [2] A.F. Johnson and M. Holzapfel, “Modelling soft body impact on composite structures”,

Compos. Struct., 63, 103-113 (2003). [3] A. Airoldi and B. Cacchione, “Modelling of impact forces and pressures in Lagrangian

bird strike analyses”, Int. J. Imp. Eng., 32, 1651-1677 (2006).