Failure behavior analysis of variable-stiffness composite open-hole plates based on an anisotropic phase-field model

This study investigates the failure behavior of open-hole Variable-Stiffness Composite (VSC) laminates. A fiber placement path was fitted based on the distribution of principal stresses, and an anisotropic and quasi-brittle phase-field model was developed to predict the damage evolution in VSCs. First, a direction-dependent crack surface density function was introduced into the unified phase-field framework to capture the anisotropic characteristics during crack propagation. Then, a phase-field driving force and damage constitutive relationship suitable for mixed failure modes were constructed, enabling the model to analyze coupled failure mechanisms. By implementing an alternate solution scheme and a layered element structure in the UEL subroutine, the phase-field model was numerically solved using ABAQUS. To verify the accuracy and applicability of the model, damage and failure analyses were conducted on single-edge-notched plates made of straight-fiber and curved-fiber composites, respectively. The results indicate that the model can reasonably predict the mechanical behavior and crack propagation paths of composite laminates. Finally, the model was used to simulate the tensile failure and damage evolution of open-hole plates with constant and variable stiffness. The results show that the predicted crack paths agree well with experimental observations, and the tensile strength of the variable stiffness plate is significantly improved compared to that of the constant stiffness plate.