Prediction of fatigue S-N curves of composite laminates by Super Mic-Mac

Super Mic-Mac (SMM), an Excel-based program that has extended the original classical laminated plate theory in Mic-Mac to a new capability in durability predictions, was used to demonstrate the capability in predicting fatigue S-N curves of various composite materials, layups of laminates subject to combined loading and hot-wet environmental conditions at various frequency and stress ratios. The prediction agrees well with experimental data for different materials, layups and loading conditions. Parametric study was performed to show how the SMM could be utilized in the design of composites structures. It was shown that the prediction of fatigue strength is not obvious with the change of the loading and environmental conditions because of complex nature of load-carrying mechanism in the laminate composites. It was also shown that the normalized S-N curves, whose fatigue strengths were normalized by a static strength, approximately coalesce together for all loading and environmental conditions. Despite of need for further verification, this finding is encouraging because it may be acceptable to measure the static strength first and use the SMM predictions to estimate the life of the structures.