Stress intensity factors and strain energy release rates in single lap bonded joints in composite materials

In the first part of this work [Quaresimin M, Ricotta M. Fatigue behaviour and damage evolution of single lap bonded joints in composite material, Compos Sci Technol, in press] the fatigue behaviour of single lap bonded joints in composite materials was investigated. In this paper, the results of an extensive investigation on the stress intensity factors (SIFs) and strain energy release rate (SERR) for the same joints are presented and discussed. Linear elastic finite element analyses were carried out to evaluate generalised SIFs in the geometry of interest and the influence of overlap length, corner geometry, adhesive properties and thickness was investigated. Geometric non-linear analyses were instead used for the analysis of the SERR trends as a function of the crack length. On the basis of these results, a new equivalent formulation for the SERR was introduced, suitable to account for the mixed-mode loading condition as well as for the continuous variation of the mode-mixity during the fatigue life of the joints. The results presented here, together with the experimental results reported in the first part of the work, represent the basis for development and validation of a life prediction methodology, which is discussed in the third part of this work [Quaresimin M, Ricotta M. Life prediction of bonded joints in composite materials. Int J Fatigue, in press].