Fast Prediction of the Fatigue Behavior of Short Fiber Reinforced Thermoplastics from Heat Build-up Measurements

The fatigue design of short fiber reinforced thermoplastics components for structural applications in the automotive industry requires an accurate knowledge of the numerous factors affecting the fatigue lifetime (process, loading type, environment, etc). This paper aims at describing a method based on thermal measurements (using an infrared camera) that will reduce substantially the characterization duration of the fatigue properties compare to classical methods. Recent publications illustrated the relevancy of using an energy based criterion to predict the fatigue properties. In this study, a simple way to get the cyclic dissipated energy from thermal measurements is suggested, usable for homogeneous and heterogeneous dissipation fields. A so-called heat build- up protocol is used to relate the cyclic stress amplitude to the cyclic dissipated energy. The parameters of an energy based criterion can be obtained within one day and using only one specimen, which is of course of huge interest to investigate quickly the influence of numerous factors on the fatigue behavior. In this study, this protocol is applied on one sample geometry, for one given orientation, and one humidity conditioning, and should be challenged by tests lead for several variations of first order parameters (fibers orientation, water uptake).