Residual strength after fatigue in composites: Theory vs. experiment

State-of-the-art phenomenological residual strength models are discussed in this paper. The presentation focus is on probabilistic and deterministic theories that predict strength degradation under various loading conditions. In an effort to improve the predictions, simple modifications on existing models as well as a new one are implemented in computational schemes and predictions are compared to experimental data from C/Ep and Gl/Ep laminates. Theoretical aspects either as deterministic degradation curves or probability distributions are evaluated. The results show that no model is consistent in accurately predicting residual strength degradation behaviour of the different composite laminates, even though some models appear to be more fit to purpose. Statistical predictions at various stress levels and life fractions are also poor. The main conclusion is that the use of complicated phenomenological models requiring large experimental data sets for implementation does not necessarily pay back in terms of accurate predictions and consequently simple models requiring limited experimental effort should be preferred.