Mode I Strain Energy Release Rate in composite laminates in the presence of voids

The paper presents a methodology for evaluating the effects of voids on the fracture behaviour of woven fabric composites. The particular model studied consists of a double cantilever beam (DCB) in which voids are placed ahead of the crack tip and the Mode I Strain Energy Release Rate (SERR) is calculated. The standard beam-on-elastic-foundation theory is modified to account for shear compliance and material orthotropy, and the new formulation is used to evaluate the deformed shape, elastic deformation energy and SERR. The presence of the voids is simulated as an unsupported zone in the elastic-foundation. The validation of the new analytical model, in terms of the deformed shapes and SERR values, is successfully carried out by suitable 2D finite element (FE) analyses. The effect of size, location and shape of the voids is investigated by a parametric study that showed that the enhancement of SERR increases with the size of the voids and the proximity to the crack tip and that elongated (elliptical) voids are more critical than the circular voids. Finally, the influence of more complex void distributions on the fracture toughness is evaluated by FE analysis.