Study and modeling aurcraft structures under foreign objet impact (FOI : bird )

Abstract

The presented work is dedicated to industrial aspects and its goal designing aircraft leading edge structures that fully comply with bird strike’s airworthiness requirements. Designs developed in this work for ribless leading edge configurations made of alleviated compositions of sandwich material have demonstrated successful resistance to bird impact with a nominal weight of 4 lb and 8 lb at high velocity. The particularity of this work lies in a comprehensive study of the bird impact problem which includes: the bird impact, the interaction between bird and LE, and the dynamic response of the LE structure. For a complete understanding of the full impact process, that comprise: the shock phase- the release phase- the steady state phase- and the termination of impact, the fundamental principles of soft body impact process were first studied analytically, then numerically and this enabled an effective bird impact model development. SPH impact models for small and large sizes of bird were developed and validated against experimental test results, firstly: on a rigid steel flat plate (Barber 1975 and Challita 1979), secondly: on a FML composite leading edge bay (Guida 2009), and third: on a ribless configuration of a real aircraft leading edge made of sandwich material and principally composed of: FML outer skin- honeycomb flexcore- Aluminum inner skin (Guida 2013). This methodology was extended to perform six numerical impact tests with the help of the finite element code Ls-Dyna, where three material types were tested for the leading edge structure (metal with a thickness of 2.54 mm, a composite fiber metal laminate with a thickness of 1.4 mm, and a sandwich of a thickness of 8.05 mm) and the resultant damage was predicted for each material impact test, where two bird models were used for each material impact testing, the first with 4 lb and the second with 8 lb and the impact velocity was 129 m/s. Lastly, by the same methodology and taking into account the leading edge weight factor, three different innovative sandwich material configurations for an aircraft ribless leading edge were tested to high velocity impact of 4 lb and 8 lb birds. The first configuration was a single core and had a total thickness of 7.15 mm, the second configuration was a double core and had a total thickness of 13.7 mm, and the third configuration was a double core and had a total thickness of 13.95 mm. The important achievement in this work was the meet of these new developed configurations to the airworthiness requirements.