This paper on "A Model for Predicting the Fatigue Life of CFRP Components" was presented at the NAFEMS World Congress on Design, Simulation & Optimisation: Reliability & Applicability of Computational Methods - 9-11 April 1997, Stuttgart, Germany.

Summary

A recently developed technique for predicting the fatigue damage growth in fibre-reinforced plastic-composite (CFRP) materials due to matrix cracking is presented. The model has been applied to two CFRP components: (a) a notched I-beam subjected to a four-point bending load, and (b) a notched coupon subjected to a tensile load. The basis of the method is to first use a fracture-mechanics approach to obtain experimentally the relationship between the maximum strain-energy release rate experienced during a fatigue cycle and the rate of growth of the damage area. This information can be obtained in a relatively short time-scale. The component is then analysed using finite element (FE) analysis and the local stresses and strains around the notch are determined. The extent of any damage is modelled by using an experimentally-determined value for the strain for microcracking to occur. The elastic properties of the damage zone are then suitably degraded, and the FE analysis is run again to determine the growth of the damage area. As the modelled damage-area grows, the maximum strain experienced by the fibres is ascertained from the FE analysis, and when this reaches the known ultimate strain for the fibres, final fracture of the component is assumed to occur. Hence, the ultimate strain capability of the fibres provides the failure criterion to determine when the fatigue life of the component is reached. By combining the results from the experimental fracture-mechanics approach and the theoretical FE analyses, the number of cycles to failure for the component may be theoretically predicted. The results from the modelling studies for the fatigue life of the components are in good agreement with the experimentally measured fatigue lives.