Prediction of Creep Deformation of Short Fiber Reinforced Thermoplastic Parts

Short fiber reinforced thermoplastic parts that are submitted to thermal and mechanical loadings during a long period of time develop creep deformation. Creep depends on the nature of the thermoplastic material, but also on the type of reinforcement, the amount and orientation of fibers. At the structural part level, the amount and orientation of fibers are governed by the injection process. For instance, the position of the gates, flow rates, pressure and temperature parameters influence the dispersion and orientation of the fibers in the mold. In order to take into account the effects of these material and manufacturing process parameters on the creep behavior of the part, a multiscale approach is required. The characterization of the creep behavior of reinforced thermoplastic materials is a very expensive process. The experimental tests must be performed at various levels of stress, for various specimen orientations and various temperatures. Hence, the experimental test campaign can quickly ramp up to more than 50 tests, where each test can run for 1h to 1000h, representing a huge investment in testing for material suppliers, Tiers1 and OEM. In addition, these experimental test campaigns do also have a significant ecological impact due to the consumed energy and the wasted materials. In this paper, the multiscale material modelling approach is developed in order to calibrate a viscoelastic-viscoplastic material model that accurately predicts the creep behavior of reinforced thermoplastic materials. Moreover, the approach that is used enables to reduce the experimental test campaign by replacing some physical tests with virtual tests. By combining both experimental and virtual material data, the approach aims to offer a solution to predict the creep behavior of reinforced plastic materials based on a reduced experimental test campaign, lowering its ecological impact and benefiting from additional time and cost savings. Finally, this advanced viscoelastic-viscoplastic material model is used to predict the thermo-mechanical response and creep behavior of a short fiber reinforced thermoplastic part.