Novel multiscale modeling schemes for damage evolution in composite laminates

Microscale damage mechanism of the multi-layer composite laminates is one of the active areas of research. Micromechanics theory is extensively used for the prediction of elastic response and to perform damage analysis of unidirectional laminae via representative volume element (RVE). The present state of the art in the micromechanics theory is extended in this study for the damage analysis of the multi-fiber multi-layer laminates to capture the local damage mechanisms which include matrix failure, fiber-matrix debonding, fiber failure, and delamination. A multi-fiber multi-layer representative volume element (M2RVE) representing a multi-layer cross-ply laminate is developed. Each layer in the M2RVE is represented by a unit cube with multiple randomly distributed fibers of same diameter at specified angle ensuring specified volume fiber fraction. Periodic boundary conditions are applied to the all six M2RVE surfaces to model the directional periodicity. All the simulations are performed by using FE analysis code ABAQUS®. A maximum principal stress criterion is used for modeling fiber failure. Mohr-coulomb failure criterion is used for matrix failure and standard traction-separation law is used for fiber-matrix debonding and for modeling delamination between plies. Numerical results from the FE analysis are found to be in good agreement with the experimental data obtained. Note that this technique is valid for periodic structures. The periodic boundary condition is not a suitable assumption, especially in the regions of high gradients like free edges, interfaces, material discontinuities. The periodicity of simple unit cells is also unrealistic for non-uniform microstructures, due the presence of randomness, clustering or evolving micro-structural behavior. Consequently, this approach has limited utility in identifying local damage in real structural members. To address the limitations of the M2RVE, a micromacro multiscale scale multilevel model is proposed. The multilevel model is comprised of two levels, namely, microscale, and macroscale. The micro-macro model is an effective and computationally efficient technique for modeling the deformation and local damage in real composite structures. Thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy of the Indian Institute of Technology Bombay, India and Monash University, Australia.