Influence of free edge intralaminar stresses on damage process in CFRP laminates under thermal cycling conditions

The purpose of this study is to understand the damage mechanisms of CFRP laminate subjected to repeated thermo-mechanical loads. Thermal cycling tests in oxygen show that the oxidation at high temperature associated with the “fatigue” phenomenon due to the cyclic thermal stresses lead to many matrix cracks. By means of optical microscopy and X-ray technique, some observations permit to characterize and quantify the initiation, build-up and propagation kinetics of these transverse cracks.A thermo-elastic calculation of the initial intralaminar transverse thermal stresses has been carried out in 3D finite-element models of the undamaged specimens. The comparison of experimental data and FEM results highlights a significant “free edge effect” on transverse matrix cracking onset, depending on both the direction of the edge referred to the fibres and the position of the layer in the lay-up. From this observation, a scenario of damage development dealing with a coupling between the local transverse stresses and the oxidation process is proposed.