A comparative study on the modeling of matrix cracks in FRP plies

Paper in proceeding, 2017

In laminated composites, transverse compressive failure of a ply results in a wedge-shaped failure mechanism, formed from matrix cracking, which drives delamination between plies and can initiate local buckling on adjacent plies. In general, continuum damage methods have proven to be efficient in numerical models. However, as a consequence of the inherent homogenization, conventional continuum damage methods such as smeared crack modeling, may have difficulties in adequately capturing these inter-laminar effects due to their inability to replicate the wedge effect. Therefore, in this paper, a discrete method based on the extended finite element method, XFEM, is introduced to explicitly model an inclined crack and to approximate the material response during transverse compressive ply failure. The method is applied in 2D with a predefined inclined crack and a cohesive zone governed by a linear softening traction-separation law. The results of the model are then compared against ¬a similar XFEM approach, with a vertical crack utilizing a transformation in the cohesive zone, and a 3D smeared crack model. Results indicate that the smeared crack approach and the cohesive XFEM approaches successfully predict identical material responses when plies are meshed with one element per ply thickness. By further mesh refinement through the ply thickness, the XFEM approaches show a definitive mesh convergence whereas the smeared crack model is not applicable anymore and predictions become unreliable. Moreover, the proposed cohesive XFEM approach can accurately model the geometrical wedge explicitly, which provides an improved approximation of the wedge effect in comparison to the other two models. In summary, the combined benefits of a discrete XFEM model in terms of mesh objectivity and geometrical accuracy can prove to be significant in future progressive failure analyses involving laminates.