Progressive failure analysis of thick composite plates using the spline finite strip method

A spline finite strip method for the progressive failure analysis of thick composite plates is developed based on Cho’s higher-order zigzag laminate theory and Lee’s failure criterion. Cho’s theory satisfies the interlaminar continuity conditions of transverse shear stress and the shear free surface conditions, so that the transverse shear stresses can be calculated directly and correctly from the constitutive equations. The initial failure load is calculated by means of an elastic stress analysis. The load is increased step by step. For each given load, the stresses at each integration point are evaluated and the appropriate failure criterion is applied to inspect for possible failure. At the point with failure, the material properties are modified according to the failure mode using a non-zero stiffness degradation factor. Then, the modified Newton–Raphson iteration is carried out until convergence is reached. This analysis is repeated for each load increment until the final failure occurs and the ultimate strength is determined. The present method yields results in reasonable agreement with the 3D finite element solutions. The effects of length-to-thickness ratio, fibre orientation, number of plies and boundary conditions on the failure loads are investigated through numerical examples.