The study presents an experimental and theorical study conducted on a PolyPhenylene Sulfide with 40%wt of short glass fibers (PPS GF40) and its matrix. Widely used for under-the-hood applications in the automotive industry, those materials are subjected to high temperatures and aging effects of cooling liquid. Therefore, the understanding of those phenomena are essential to design mechanical parts. Thus, an experimental campaign in tensile mode has been carried out with different temperatures and glycol proportions in the cooling liquid, for monotonic and cyclic loadings on neat and reinforced PPS. The results of these tests allowed us to highlight some of the main physical phenomena occurring during these solicitations under tough hydrothermal conditions. Taking into account this analysis, a visco-elasto-pseudo-plastic model is proposed. Moreover, this model allows the consideration of the cooling liquid effects and its constituents by a temperature/humidity equivalence and allows to take into account the consequences on the mechanical behavior of the glass transition. The accuracy of the model was confronted to another phenomenological model and an artificial intelligence based one, in order to study the maximal accuracy physically reachable. Finally, the evolution of the model parameters has been studied with the adjunction of short glass fibers and for specifics orientation distribution.

It was thus shown that:

• The behavior of the PPS is considerably influenced by temperature and also sensitive to humidity.

• The more the cooling liquid contains water, the more the mechanical behavior will be affected as the PPS shows more sensitivity to absorption than to chemical aggressiveness of the cooling liquid.

• Two kinds of behavior have been noted: an elasto-plastic type under the glass transition temperature and a visco-pseudo-plastic one above this temperature.

• Viscosity is the leading phenomenon above the glass transition temperature for the PPS and can also be important under Tg, under cyclic conditions and when the stress rate is low.

• The high temperatures are decreasing the advantages of the presence of fibers.

The model shows a good prediction as its global error is between 1% and 2% regarding the AI prediction. Studying the evolution of the parameters with the adjunction and the orientation of fibers had shown that the fiber orientation has an important impact on the mechanical resistance under the glass transition temperature and a more important impact above this temperature. The damping of the material, showing the same evolution trend under and above Tg, showed more sensitivity to the fiber ratio than the orientation. These observations will have to be taken into account for the integration of this kind of model in a homogenization model.

Such results have a strong interest regarding the non-linear mechanical characterization of polymers, from the matrix to the composite, for a wide range of hydrothermal conditions, which is required for reliable fatigue design of industrial components.