The paper presents a model for the prediction of the fatigue life of composite bonded joints. The model was developed on the basis of extensive experimental and numerical investigations, presented in the first [Quaresimin M, Ricotta M. Fatigue behaviour and damage evolution of single lap bonded joints in composite material. Compos Sci Technol, 2006;66:176-87] and second [Quaresimin M, Ricotta M. Stress intensity factors and strain energy release rates in single lap bonded joints in composite materials. Compos Sci Technol, 2006;66:647-56] part of this work.
The model is based on the actual mechanics of the fatigue damage evolution and describes the joint lifetime as the sequence of a crack nucleation phase followed by a propagation phase. The nucleation phase was modelled by using a generalised stress intensity factor (SIF) approach, summarising the fatigue data to crack initiation in scatter bands in terms of generalised SIFs. The life spent in the propagation phase was obtained by integration of a Paris-like power law relating the strain energy release rate (SERR) to the rate of the crack growth. The Paris curves were obtained by combination of crack propagation data measured on the joints and functions describing the SERR variations with the crack length calculated via FE analysis. Several alternative combinations of crack propagation data and SERR components were compared to investigate their possible influence on the life prediction. The model validation provided a good agreement between predictions and experimental fatigue data obtained for single lap joints with different overlap length and corner geometry.