A finite element model was developed to simulate dynamic stress distributions in thermoplastic polyolefin (TPO) roofing systems subjected to severe impact events, e.g., hail and hard object strikes. In order to build an integrated TPO layered composite roofing system model, separate sub-models are developed that include: the TPO membrane, polyester reinforcement scrim, low modulus closed-cell foam and fiber-glass stiffened facer sheets. A hyperelastic Mooney-Rivlin model of the TPO membrane is utilized to simulate the membrane's large-deformation mechanical response during simple impact tests. Straightforward force-contact measurements on the TPO membrane material and low modulus foam backing, using spherical indenters, are shown to provide sufficient material properties for the impact model of interest. It is demonstrated that the local failure modes for the layered composite roofing system can be adequately characterized by using relatively simple failure criterion for each of the individual component layers in this type of roofing system. Both high-speed indentation and ice ball impact experimental tests have been performed to evaluate and verify the predicted performance of a single ply TPO roofing system. Excellent correlation is obtained between model predictions and experimental dynamic indentation tests.
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