B. Vieille

Correlation between physical properties, microstructure and thermo-mechanical behavior of PPS-based composites processed by stamping

This work focuses on the influence of stamping process on physical (glass transition temperature, and degree of crystallinity) and mechanical properties (Young’s modulus, tensile and compressive strengths, and in-plane and interlaminar shear strengths) of polyphenylenesulfide-based carbon fiber fabric laminates under severe environmental conditions (120℃ and hygrothermal ageing). The results show that stamping as well as hygrothermal ageing increase the glass transition temperature and the degree of crystallinity. Mechanical investigations coupled with fractography studies highlight significant improvements in both interlaminar and compressive properties. Finally, stamping can be considered as a second thermo-compression of consolidated laminates, and the resulting changes in the microstructure can be correlated with higher mechanical properties of polyphenylenesulfide-based laminates under severe conditions.

Investigations on Crack Propagation and Strain Energy Release Rate in Notched Woven-Ply Thermoplastic Laminates at High-Temperature

The strain energy release rate G is of prime importance in composite materials fracture mechanics. In order to experimentally and numerically evaluate this parameter in the case of quasi-isotropic and angle-ply (AP) woven-ply thermoplastic (TP) laminates, single edge notched (SEN) specimens have been subjected to monotonic tensile loading at T > Tg when the toughness and the viscous behavior of the (TP) matrix are exacerbated. From the simulation standpoint, a particular attention was paid to the type of meshing as well as its refinement in the vicinity of the crack tip where the triaxiality rate leads to significant stress concentrations. For this purpose, a linear spectral viscoelastic and a generalized Norton-type viscoplastic models have been used. A comparison between two types of meshing (radiant and concentric) has been conducted. Both types of meshing allow us to define crowns in order to represent the surface of the integration ring around the crack tip. These crowns are necessary to evaluate the strain energy release rate GI in opening mode using Gθ-integral computation. Both overstress and overstrain profiles near the crack tip were investigated and validated using theoretical stress fields derived from the linear elastic fracture mechanics (LEFM) framework and overstrain fields obtained from digital image correlation (DIC) to verify the model’s ability to provide accurate mechanical fields at singularity zones.

Influence of matrix ductility on the high-temperature fatigue behaviour of notched and unnotched thermoplastic and thermoset laminates

An experimental study has been conducted on notched and unnotched carbon woven-ply PolyPhenylene Sulfide (PPS) and Epoxy laminates subjected to fatigue loadings at a test temperature T such as T g | C / PPS < T < T g | Epoxy . Depending on matrix nature, the obtained results confirm that matrix ductility is prominent to rule the fatigue response of notched woven-ply laminates at high temperature. In C/PPS laminates whose behaviour is very ductile at T > Tg, the presence of a stress concentrator improves their fatigue life, whereas it reduces the fatigue life in C/Epoxy laminates. During cycling loadings, the dissipated energy is about four times as high in C/PPS laminates as in C/Epoxy laminates. The overstresses relieving known to be primarily due to diffuse damage around the hole in C/Epoxy is not efficient at high frequency, contrary to the overstresses accommodation due to the fibres rotation and to the plastic deformation along the ±45° oriented fibres in C/PPS, resulting in a longer fatigue life with respect to unnotched laminates.

LR models of pseudoelasticity for SMAs at finite strains. Formulation and implementation

Publisher Summary This chapter presents an extension of RL models of pseudoelasticity accounting for large strains. The mechanical model is reformulated in an intermediate configuration to recover a small strain-like format of the constitutive relationship. Alloys capable of undergoing phase transformations between a highly ordered austenitic (parent) phase and a less ordered martensitic (product) phase exhibit macroscopic phenomena not present in traditional metals. In particular, the alloys known as “shape memory alloys” (SMAs) possess exceptional strain-recovery capabilities. This is because of the fact that, as opposite to conventional metals, they can respond to severe deformations by simply changing the orientation of the crystal structure through the movement of twin boundaries. This unique behavior is the basis of the so-called “pseudoelasticity.”