Edge effects and fatigue delamination of composite laminates and bonded assemblies

Finite Element Analysis (FEA) of multilayer structures using plates and shells is not able to quantify the singular stresses distribution, especially the local overstresses near the boundaries. This critical design parameter is taken into account by 3D FEA models, which are not used for systematic computations due to a very long calculation time. The software CLEOPS (Composites Local Effects Of Plates and Shells) is developed by MEDYSYS (MEchanics and DYnamics of SYStems) to address this problem for composite laminates and their bonded assemblies involved in aerospace or defense industry. It is used as a post-processor of Finite Element computations on plates and shells to calculate the 3D stresses within multilayer structures subjected to mechanical plane or bending loadings. The edge effects are computed at the mesoscale based on a semi-analytical asymptotic method with one-dimensional finite elements in the through-thickness direction. The software includes quadratic failure criteria in order to evaluate the delamination initiation and anticipate whether the laminates can withstand a fatigue load. The calculation of the stresses distribution near the edges of multilayer structures and the fatigue delamination are key issues developed in this article. Results provided by CLEOPS are compared to 3D FEA results.