A Computational Cost-effective numerical methodology for the simulation of the fatigue behaviour in composite materials.

Carbon fibre reinforced polymers (CFRPs) are widely employed in aeronautical structural load-bearing components, thanks to their properties in terms of strength, stiffness, weight, and corrosion resistance, if compared to the commonly used metallic materials. Among the other failure mechanisms, fatigue is one of the main causes for CFRPs components collapse. Indeed, when subject to cyclic loading, CFRPs exhibit gradual degradation of the mechanical properties as a result of microcracks propagation. In this work, the empirical model, proposed by Shokrieh and Lessard, for the evaluation of the fatigue induced strength and stiffness degradation, has been implemented in the commercial Finite Element Code ANSYS MECHANICAL, by means of Ansys Parametric Design Languages (APDL). A cycle jump strategy, named SMART CYCLE strategy, has been introduced in the numerical model to avoid the simulation of every single cycle and save computational resources. The SMART CYCLE routine is able to predict cycles where fatigue failure criteria are likely to be verified and to limit the numerical simulation to these cycles where damages propagation in terms of fibre and matrix breakage is expected. The proposed numerical approach has been validated on 30° fibre oriented unidirectional coupons subjected to tensile-tensile fatigue loading condition. The numerical results have been compared with experimental data in terms of number of cycles at failure for different percentage of the static strength. Then, the proposed numerical methodology has been used to investigate the fatigue behaviour of a quasi-isotropic open hole composite panel under compression-compression fatigue loading conditions