Micromechanics-based structural analysis of thick laminated composites

Abstract

Thick filament wound cylinders, or local regions in structural laminates around cut-outs, fasteners or stiffeners may require three-dimensional (3D) analysis and evaluation, in order to fully characterize behavior and evaluate safety margins. This paper describes a particular approach to the 3D structural-level analysis of thick laminated composites that utilizes homogenization concepts and standard displacement-based finite element modeling. Hierarchical material modeling forms the basis of the procedure. The material model consists of two modules: 1. (1) a micro-model of a unidirectional lamina, containing the basic 3D constitutive information for fiber and matrix constituents 2. (2) a sublaminate model that enforces equilibrium of tractions between laminae, and delivers 3D homogenized stresses and strains and material tangent stiffnesses. This integrated approach provides the information required for evaluating damage and failure conditions at the microstructural level, and is essential for nonlinear analysis because of possible interactions between damage and failure modes. A nonlinear elastic material model is formulated, as an example; this nonlinear model, which is suitable for epoxy matrices, has been successfully implemented in a standard finite element code and used quite extensively. However, only elastic analysis results are presented, because the important characteristics of the modeling approach are clearly revealed in this setting. Comparisons are made between material model predictions and analytical, numerical, and experimental results for a unidirectional lamina, a thick laminate, and a thick cylinder under compression and bending. These results show that the accuracy of the procedure for thick laminates is quite satisfactory for practical purposes.