About the applicability of a simple model to predict the fatigue life and behavior of woven-ply thermoplastic laminates at T > Tg

Through the application of a simple model, the concept of damage accumulation has been used to predict the fatigue life of TP-based composite materials at a test temperature higher than its glass transition temperature. This work was aimed at studying the off-axis tension–tension fatigue behavior of woven-ply C/PPS laminates which consists of three primary stages: (i) In the initial phase of cyclic loading, damage accumulates rapidly along with a matrix plasticization under the form of intra-laminar cracking which may initiate in multiple locations, but preferably at the interfaces between fibers and matrix at the crimps – (ii) The second stage is characterized by a steady damage growth rate and little damage accumulation – (iii) Damage (mostly debonding and interlaminar cracks) generalizes rapidly during the last stage ultimately resulting in extensive delamination and fiber bundles pull-out. It also appears that the fatigue behavior is ascribed to the highly ductile and time-dependent behavior of matrix-rich regions due to the non-planar structure of woven plies. Finally, a simple analytical model was applied, and proved to be adequate to capture the different stages of damage scenario, with excellent correlation to the experimental data.