Free edge stresses in composite laminates with imperfect interfaces under extension, bending and twisting loading

An accurate analytical three-dimensional elasticity solution is presented for the free edge stresses in composite laminates under extension, bending and twisting loading, accounting for possible bonding imperfections at the layer interfaces. The bonding imperfection is modeled using the linear spring-layer model. A mixed formulation with both displacements and stresses as primary variables is developed using the Reissner-type variational principle and the solution is obtained using the recently developed mixed-field multiterm extended Kantorovich method (MMEKM). The method ensures exact and point-wise satisfaction of the traction-free edge boundary conditions and interlaminar stress continuity conditions, which is key to the accurate solution of free edge stresses. A detailed numerical study established excellent convergence characteristics of iterative series solution. The presence of bonding imperfection at an interface leads to nonsingular free edge interlaminar stresses at that interface, in contrast with the singular stress field occurring at a classical perfect interface. The effect of loading type on the relative reduction of free edge stresses with the increase in imperfection compliance is investigated for cross-ply and angle-ply laminates. The effect of ply-angle of angle-ply laminates on the same is also ascertained.