Stiffness Reduction in Laminates at High Intralaminar Crack Density: Effect of Crack Interaction

Abstract

The previously developed closed form expressions for thermo-elastic properties of laminates with intralaminar cracks (Lundmark and Varna, 2005) contain crack surface opening and sliding as main local parameters. The dependence of these parameters on various material and geometrical characteristics was in (Lundmark and Varna, 2005) described by power functions valid only for noninteractive cracks in a given layer (low crack density). In this article the 90-layer crack interaction in terms of its effect on the crack opening displacement (COD) is discussed. The effect on COD is described by the introduced ‘interaction function’ which is determined fitting results of finite element (FE) analysis for cross-ply laminates. To simplify the application in stiffness predictions, the numerically found weak dependence of the interaction on geometrical and material parameters is neglected and the interaction function is presented as a function of crack density only. Using the interaction function to determine the COD, the previously developed calculation scheme (Lundmark and Varna, 2005) has been used to predict stiffness reduction in the entire crack density region. The results are validated comparing with tests and FE simulations.