FATIGUE PREDICTION FOR COMPOSITE MATERIALS AND STRUCTURES

O. SALOMON; F. RASTELLINI; S. OLLER; E. OÑATE

Simposio; NATO Research and Technology Organization (RTO) Air Vehicle Technology; 2005

The objective of this paper is to present a new computational methodology for predicting the durability of structures made of composite materials based on epoxy matrix with long carbon fibres.To analyse the behaviour of composite materials an Advanced Serial-Parallel Mixing Theory (ASPMT) has been developed assuming components behave as parallel materials in the fibres alignment direction and as serial materials in orthogonal directions. It allows equal component strains in the fibre direction and equal stresses in the transverse directions. The ASPMT brings answers on the non-linear behaviour of composites, where Classical Micro-mechanics Formulas are restricted to their linear elastic part. Constitutive tensors ofthe composite materials are obtained from mechanical properties and internal variables of their components within a continuum framework. Anisotropy and different constitutive models (plasticity, damage and fatigue) for each phase are considered.The fatigue prediction model is based in a continuum mechanic stress life approach for each of the component materials. S-N curves are proposed for each phase. A cumulative fatigue damage index is used to update the mechanical properties of the components and with these properties update layers properties and compute residual stiffness of the laminate.Constitutive models for the composite materials have been implemented into a general purpose finite element code (COMET) and a user friendly interface for composite material data input in a pre-post processing module (GiD) has been developed. The methodology is validated using experimental data from tests on CFRR composite material samples.