Font Size: 

Designing short fibre reinforced plastic (SFRP) components against fatigue has becomea major concern during the last years. This is a difficult task because they exhibit acomplex mechanical response with a strong dependency on the service environment(temperature and humidity ratio) as well as on the complex microstructure induced bythe process and the complex geometries of the parts. Speeding-up the characterizationof the influences of these numerous parameters on the fatigue properties is of primaryimportance for the parts optimization and development.In a recent paper, a heat built-up protocol was developed to predict quickly the fatigueproperties from the temperature measurements: the dissipated energy is evaluated fromthe thermal measurements and the parameters of an energetic fatigue criterion areidentified. Proven very efficient (the full deterministic fatigue curve can be predictedfrom one sample, within 2 days) the protocol and the energy based criterion arechallenged in the present paper by several fatigue campaigns performed with variationsof numerous parameters (sample geometry, humidity ratio, fibers orientation). Theresults obtained validate both the criterion and the fast determination protocol. A verygood unification of the fatigue data is indeed obtained with the criterion.Then, heat build-up and fatigue tests were achieved on structural automotive parts andthe thermal fields were recorded. The localization of the hot spots were assessed bothby thermo-elastic and dissipation fields. A specific analysis of the thermal fields allowsfor describing the fields of the dissipated energy. The energy based criterion obtainedpreviously on samples is then applied to predict the fatigue lifetime from the local heatbuild-up curve measured on the parts. The agreement with the fatigue tests is very good,which validates both the energy based criterion and the use of thermal measurements toobtain quickly the fatigue curve for samples as well as for structures.