Experimental study of bird strike response of sandwich structures: overall trends

Nowadays sandwich structures are used as bird shields to protect aircraft nose bulkhead. They are usually made of aluminum honeycomb and sheets. In order to optimize mass, cost and efficiency of such bird shields, aircraft manufacturers want to explore new materials and designs. In this context, this work aims at exhibiting influences of material and design parameters on the bird strike response of sandwich structures. Based on previous finite element calculations that enabled to determine the most influential parameters, a design of experiment has been defined to span a parameter space in 4 dimensions, namely the thickness of the front skin, the thickness of the core, the yield stress of the front skin and the crushing stress of the core. 13 configurations of sandwich structures are then tested according to this design of experiment. These samples are 800 mm x 800 mm square sandwiches simply supported on a rigid square frame. The impactor is a 1.6 kg gelatin bird substitute, thrown at a speed of 160 m/s. Based on high speed camera image correlation, an original approach is developed to measure and quantify the responses of the samples. For each configuration, the full displacement field of the rear face of the sandwich is calculated during the impact event. The final shapes for both rear and front faces of the shield are also reconstructed, enabling to compare the behaviors of the different structures regarding bending, indentation and core crushing… The exhibited trends in terms of influences of material and design parameters open prospects for pre-selection of candidate materials and designs for bird shield applications which could lead to mass and cost reduction while satisfying aircraft design constraints (no failure, low rear face displacement…)