Dissipation analysis in SFRP structural samples : thermomechanical analysis and comparison to numerical simulations

Design of SFRP [short fibre reinforced polymer] parts against fatigue is clearly not an easy task due to the numerous dissipation mechanisms involved and to the strong anisotropy induced by the injection process. Another difficulty is to evaluate a relevant scale to compute the thermomechanical data, as the complex geometry of the parts can induce a variation within a distance comparable to or lower than the representative scale of the microstructure. In this study, injected samples with a geometry leading to a theoretical stress concentration factor Kt=2.5Kt=2.5 are under consideration. The samples are submitted to several cyclic blocks and the temperature fields are measured using an infrared camera. Taking advantage of the good thermal and spatial resolutions, a first analysis is performed on the temperature fields, allowing to highlight the hot spot location and to follow the crack propagation. A specific adiabatic analysis is then suggested in order to measure directly the fields of dissipated energy. To predict this field, a numerical chain is then applied involving the simulation of the injection process and finite elements analysis using an anisotropic elasto-viscoplastic model. The predicted heat sources are compared to the experimental ones for several loading amplitudes and the ability of the approach to catch the experimental fields is finally discussed.