Closed-Form Analysis and Assessment of the Free-Edge Effect in Angle-Ply Laminates

In composite laminates the layerwise discontinuous stiffness properties cause highly localized, singular concentrations of interlaminar stresses. These stress singularities occur in the vicinity of free edges and may induce interfacial cracks, often referred to as delaminations. For the analysis and assessment of composite materials, this work suggests a computational tool that describes effectively both the free-edge effect and reliably predicts the onset of delaminations. A new displacement-based multilayer method based on third-order shear deformation theory is developed to determine displacements and stresses near the free edges of angle-ply laminates. In a comprehensive comparison it is demonstrated that the analytical method reproduces the typical warping deformation and the dominant interlaminar shear stress in agreement with the numerical reference results. Based on these findings, a concept for predicting interlaminar crack nucleation in symmetric angle-ply laminates is developed using the framework of finite fracture mechanics. The excellent prediction accuracy of the new method is highlighted using experimental as well as numerical reference data.