Micromechanical study and simulation of the interlaminar failure of a woven composite laminate

The laminate load bearing capability is often compromised by the interlaminar failure even though the integrity of the individual lamina remains intact. The out-of-plane components of the stress tensor, defined at the interfaces between plies, are typically responsible for the delamination of multi-layered materials. Failure models for delamination usually make use of both shear and normal interlaminar stresses but their reliable calculation by finite element analysis requires cautions and special techniques. This is particularly true for woven composites in which the fabric architecture may generate unexpected local normal stresses and consequently influence the fracture occurrence. In this paper a numerical analysis was performed using layered solid elements to predict the global response of the laminate. Then sub-modeling techniques are used with several solid elements through the layer thickness in order to obtain accurate interlaminar stresses in the critical regions. As case study, the short-beam configuration under three-point bending condition was selected. Experimental tests show a reduction of the maximum interlaminar shear stress at failure as effect of the span-depth ratio increase for a given laminate thickness. That evidence, assuming a homogenized material behavior, is unpredicted because the span-depth ratio increase has no significant influence on the interlaminar stresses. The work aims to clarify this not well explained phenomenon with a micromechanics approach.