Mechanical Characterisation of Polycarbonate for Helicopter Windshields

Kurzfassung

Transparent thermoplastics like polycarbonate are widely used as windshields for its optical properties and for their higher specific mechanical properties compared to glass. Under use in airframe front windshields, plastics transparencies can be exposed to impact scenarios such as bird-strikes. The resulting load can lead to a complex loading of the material dominated by tension and bending. In order to generate input for realistic simulation results, experiments have been performed to characterise the materials under these loading modes at coupon level in the elastic and plastic domain. On the simulation side, numerical models comprising a discretisation with elements applying Reissner’s plate bending theory have been used in the explicit finite-element method within the LS-DYNA framework with latest solver version R10.1. Experiments were performed at different strain-rates ranging from quasi-static to approx. 75 1/s. The numerical modelling has been done with thin and thick shell elements. The thin shell element approach used the Reissner-Mindlin kinematic assumption in fully-integrated shells. Additionally, some thick shell formulations with various approaches were applied. To cover the strain-rate sensitive behaviour, a material model based on the Johnson-Cook theory was applied. The influence of the modelling was investigated and compared to the experimental characterisation.