Abstract

Design and manufacture of a variable-thickness composite laminate such as a helicopter yoke or a robot arm involves tapering the laminate by dropping certain individual plies at discrete internal locations, in order to tailor the stiffness of the laminate to the design and performance requirements. The ply drop in the laminate creates geometric and material discontinuities and results in large stress concentration. These in turn cause changes in the response and failure strengths of the laminate. For achieving economical, safe and reliable design, the progressive failure and post-buckling response of tapered laminated plates are important design considerations. Therefore, there is a necessity to investigate the progressive failure of tapered laminates and its effect on the post-buckling response. The present thesis concerns with these aspects. In the present thesis, a nonlinear finite element formulation is developed based on the first-order shear deformation theory and the geometric nonlinearity in the von Karman sense for the analysis of tapered laminated plates. The tensor polynomial form of failure criterion is used in conjunction with a progressive failure simulation methodology to study the progressive failure. The developed formulation and progressive failure simulation methodology are validated. A detailed parametric study of the deterministic progressive failure of tapered laminates under the action of uni-axial and bi-axial compression, in-plane positive shear, and in-plane negative shear loadings is conducted. A detailed parametric study on the deterministic progressive failure of tapered laminates under the action of bi-axial compression combined with in-plane shear loading is also conducted. The first-ply failure load, the ultimate failure load, the buckling load, the associated maximum transverse displacements, and the locations and modes of failure of tapered laminated plates are determined for each case. The effects of different taper and laminate configurations, fiber orientations, boundary conditions, addition of uniform-thickness sections are determined. Stochastic progressive failure of tapered laminated plate under the action of bi-axial compression combined with in-plane positive shear loading is investigated. The mean and standard deviation values of failure strengths are calculated considering the material properties as stochastic processes in space