ECCM15 - 15 TH EUROPEAN CONFERENCE ON COMPOSITE MATERIALS, Venice, Italy, 24-28 June 2012 1 HEAT BUILT-UP MEASUREMENTS AND ENERGETIC CRITERION USED TO EVALUATE QUICKLY THE FATIGUE LIFE OF PA66 GF50 Y. Marco 1* , L. Jégou 1,2 , S. Calloch 1 1 Université Européenne de Bretagne, ENSTA Bretagne, Laboratoire Brestois de Mécanique et des Systèmes EA 4325, 2 rue François Verny 29806 Brest Cedex 9 France 2 Université Européenne de Bretagne, IUT Saint-Brieuc (Université de Rennes1), Département Sciences et Génie des Matériaux, 18 rue Wallon BP406 22004 Saint-Brieuc Cedex *e-mail address of the corresponding author: yann.marco@ensta-bretagne.fr Keywords: Injection, SFRP, Heat build-up, Energetic fatigue criterion Abstract The goal of this paper is to apply a heat built-up protocol on a SFRP used for structural automotive applications (PA66GF50, a polyamide filled with 50% of glass fiber in mass) to predict quickly the fatigue properties from the temperature measurements. In order to provide a relation between the full heat build-up curve and the Wöhler curve, the dissipated energy is then evaluated from the thermal measurements and the parameters of an energetic fatigue criterion are identified from the results obtained from one single sample. The fatigue curve predicted from the heat build-up curve is compared to the one obtained from a classical fatigue campaign and the agreement is very good. The energy based criterion as well as the identification of the dissipation sources from the temperature measurements are finally challenged by an experimental campaign achieved on a sample with a different geometry. 1 Introduction Designing short fibre reinforced plastic (SFRP) components against fatigue has become a major concern during the last years as these materials, filled up to 50% in mass with glass fibers, are now used for structural components [1-4]. A first difficulty comes from the thermoplastic and hydrophilic nature of the PA66 matrix, which leads to a strong environmental dependency [10] and a complex behavior exhibiting viscous, plastic and damage features [9]. A second difficult point arises from the very strong coupling between the microstructure on the one hand and the geometry and the process parameters on the other hand. The characterization of the influences of these numerous environment and process parameters on the fatigue properties therefore requires wide fatigue campaigns, which are even longer than for metallic materials as the test frequency has to be limited in order to reduce the influence of the temperature rise [7]. A way to speed up the characterization of the fatigue properties of these materials would be more than useful. Thermal measurements to evaluate quickly the fatigue properties has been used for several years for metallic materials (see [18] and references therein) and are clearly reaching now maturity [14, 18]. For composite materials, following the temperature fields is usually a way