COD-based simulation of transverse cracking and stiffness reduction in [S/90n]s laminates

Closed-form expressions for the thermo-elastic properties of [S/90n]s laminates with transverse cracks in the 90° layers are derived. Provided the normalised average crack-opening displacement (COD) is known, expressions contain only crack density, geometrical parameters and elastic constants of layers. The average COD dependence on the crack spacing and constraint effect of adjacent sub-laminates is analysed by using finite-element method in plane stress formulation. It is found that the out-of-plane elastic constants have an insignificant effect on COD. A simple power law relating average COD to elastic and geometrical parameters of constituents is derived. The obtained power law and the developed methodology are successfully used to predict the reduction of thermo-elastic properties and damage evolution of [±θ/904]s laminates. The crack-closure technique and Monte-Carlo simulations are used to model the damage development. The 90° layer is divided in to a large number of elements and Gc values are assigned to each element according to a Weibull distribution. Parameters in the Weibull distribution are determined by using experimental crack density versus strain curve for glass-fibre/epoxy [02/904]s cross-ply laminates. Damage development in [S/904]s laminates of the same material, containing sub-laminates with ±θ layers only, is modelled by using these Weibull parameters and the results are in good agreement with test data. The effect of the thickness of the 90° layer on damage development is discussed in strength and fracture mechanics formulation.