Combined Applications of Test and CAE for Assessing Performance of Aircraft Windshield-Like Structures under Bird Impacts

The present study deals with the CAE (computer-aided engineering)-based prediction of performance of aircraft windshield-like structures under simulated bird impact following a step-by-step procedure. In the investigations carried out here, stretched polyacrylic is chosen as the windshield material. It is assumed that impact occurs at room temperature, as a majority of bird strikes would take place at low altitudes of flight. Finite element-based simulation has been carried out with the explicit code LS-DYNA. A limited number of impact tests carried out with 2 lb (0.91 kg) and 4 lb (1.82 kg) cylindrical flat-head bird specimens striking flat but inclined polyacrylic plates at 103 m/s and 173 m/s are used for validating modeling procedures. It has been found that viscoelastic modeling of gelatinous test bird using a Lagrangian mesh yields good prediction of experimentally observed bird behavior. The engineering properties of windshield material are at first verified using quasi-static plate indentation tests. These properties are further modified to account for strain rate effects under impact conditions; in particular, the expected reduction of quasi-static failure strain at high loading rates is found to be crucial in realistically predicting failure of target plate and strain time histories. The verified modeling procedure is finally used for assessing the resistance to bird strikes of polyacrylic windshield components of curved design-intent geometry.