Time-dependent damage development during creep in carbon woven-ply polyphenylene sulfide laminates above the glass transition temperature

In order to understand the coupling between time-dependent behaviours (viscoelasticity, viscoplasticity) and damage mechanisms within carbon woven-ply polyphenylene sulfide (C/PPS) thermoplastic composites subjected to creep loadings at T > T _g (Glass transition temperature), it is necessary to develop experimental protocols adapted to high temperature conditions. To this aim, the present study combines different complementary techniques (acoustic emission, edge replication, fractographic analysis, tomography) allowing in-situ analyses of the damage mechanisms that coexist and interact during the different phases of creep-type loadings. These techniques provide information to quantify and dissociate the different material behaviours (viscoelasticity, viscoplasticity, damage). Two main damage mechanisms are identified: intra-bundle cracking and inter-bundle cracking leading to extensive meta-delamination. Image analyses based on morphological operations allow the evaluation of the surface cracking density (intra- and inter-strand) from edge replicas. At macroscopic scale, the thermo-mechanical response is little influenced by the viscous behaviour of angle-ply C/PSS laminates though their thermo-mechanical behaviour is mainly driven by the PPS matrix. At micro and mesoscopic scales, the results clearly show the onset and propagation of time-dependent damage in C/PPS specimens. By implementing this protocol, the acoustic emission monitoring associated with the quantification of the cracking density proved to be relevant and complementary to study the coupling between viscous effects and damage within C/PPS laminates subjected to high temperature loading.