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An Improved Cohesive Zone Model for Residual Notched Strength Prediction of Composite Laminates with Different Orthotropic Lay-Ups

The traditional methods employing a characteristic length approach to predict residual strength of notched laminates did not recognize damage development prior to final failure. Due to this lack of physical basis, re-calibration is often needed when the specimen geometry and size are changed. More recent models such as the Damage Zone Model (DZM), Cohesive Zone Model (CZM) and the Effective Crack Growth Model (ECGM), have recognized the occurrence of progressive material softening ahead of the notch tip prior to catastrophic failure. However, since the anisotropic characteristic of the composite laminate has not been properly accounted for, these models may not be widely applicable for the laminates with different degrees of anisotropy. In this study, an Improved Cohesive Zone Model (ICZM) with proper consideration for anisotropy is proposed to predict the notched strength of composite laminate. Based on three fundamental parameters: namely the unnotched strength 0, the apparent fracture energy Gc and the effective longitudinal stiffness E0, this model successfully predicted the strength of notched composite laminates with various degrees of anisotropy. The current model also gives accurate prediction of the progressive damage zone size in quasi-isotropic and cross-ply laminates.