The crystallization degree in semi-crystalline thermoplastics plays an important role in determining the final properties of structural composite material (e.g. toughness, stiffness and solvent resistance). The main purpose of this work is to study different induced degrees of crystallinity in carbon fiber (CF) reinforced polyphenylene sulfide (PPS) composites, by using three different cooling rates during hot compression molding processing (51%, 58% and 62% of crystallinity). In this study, the morphology, thermal and mechanical properties of the produced laminates were investigated and compared. The results showed an increase in the storage modulus (9.8%), Young's modulus (9.2%) and ILSS (14.2%) for the lower cooling rates. Evidences of fiber/interface improvement and crystallites nucleation on the fiber reinforcement surface were also identified.

International audienceIn this paper, a non unified elasto-viscoplastic behavior model based on internal state variables, is investigated in order to describe the thermo-mechanical stress-strain fatigue response of 55NiCrMoV7 tempered martensitic steels (AISI L6). This model considers a quadratic yield criterion to define the elasticity domain. It allows the determination of two inelastic strain mechanisms resulting from two stress states which can be related to the typical continuous cyclic softening of the tempered martensitic steels. This cyclic softening is reproduced through an isotropic component (drag stress). A memory effect is also introduced to take into account the influence of the plastic strain range on the amount of the cyclic softening. The kinematic component (back stress) of the model allows the description of complex load conditions to which tool steels are subjected. Strain recovery (Baushinger effect), time recovery terms (cyclic behavior including tensile dwell times) and ratcheting effects are considered. The numerical implementation is addressed and two integration methods (explicit and implicit) of the constitutive equations are presented. Moreover, the identification methodology of the model parameters from only two sets of experimental data is presented; the coefficients of the kinematic and isotropic parts are determined successively. The main difficulty consists in reaching a good description both of the cyclic behavior for different strain rates and the ratcheting effect. Last, a validation stage of the three dimensional model is investigated from low cycle fatigue tests performed on different notched specimens

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