Theoretical and experimental investigation of stress redistribution in open hole composite laminates due to damage accumulation

Abstract

Two methods were examined for the prediction of stress redistribution due to subcritical damage accumulation near open holes in composite laminates. A finite element analysis in conjunction with the method of material property degradation was performed to assess the accuracy of the fiber direction stress redistribution prediction due to formation of longitudinal splitting. A simple case of a unidirectional composite with an open hole was considered. The method was unable to accurately predict the fiber stress relaxation due to longitudinal splitting, which in the case of laminates with holes is of paramount importance for the accurate prediction of ultimate strength. Three-dimensional ply level modeling of discrete damage near an open hole in a quasi-isotropic composite laminate was subsequently considered. Normally the mesh configuration is dictated by the boundaries of the specimen, such as the presence of a hole, creating formidable difficulties to modeling matrix cracking, which is aligned with the fiber direction in a given ply. A mesh independent displacement discontinuity modeling method based on higher order shape functions was constructed for this purpose. The surface of the displacement jump associated with matrix cracking was defined in terms of the domain Heaviside function approximated by using higher order polynomial B-splines. Moiré interferometry was used to determine the strain and displacement fields in the surface layers of a quasi-isotropic composite, previously prestressed beyond the damage initiation load. Good correlation between the experimental data and the stress redistribution predicted by the mesh independent damage modeling technique was observed.