Damage prediction in thermoplastics under impact loading using a strain rate-dependent GISSMO

With the increasing use of polymers in structural parts in areas ranging from automotive and aviation to electronic and common household goods a clear understanding of their mechanical behavior under dynamic conditions has become important. While the study of damage and fracture in metals has a long history, the prediction of damage in polymers is still in its fledging stages, not least due to the very complex microstructure. Owing to similarities in their behavior from a continuum mechanics perspective, applying models originally developed for metals is expedient but needs justification and validation. Further, rate-dependence must be accounted for. In this study, the damage and fracture behavior of two thermoplastic is investigated. The focus lies on the high strain and high strain rate regions. The GISSMO (generalized incremental stress-strain damage model) is applied to model the damage-induced softening of the material. Rate-dependence is accounted for by expanding the triaxiality failure diagram (TFD) to the strain rate dimension. Elastoplastic and damage parameters are obtained from tensile tests with different specimen geometries. Viscoelastic and viscoplastic behavior is neglected. The material model is validated by comparing the responses from FE simulation with experimental data from 3-point bending and ball drop tests with notched specimens and actual parts. It is found that this relatively simple model with straightforward parameter evaluation is capable of predicting damage and fracture under various conditions to some good accuracy. © 2023