Microscale experimental results and their implications for mesoscale modeling of damage initiation in cross-ply fiber reinforced composites

The results from a combined experimental and computational study to evaluate local in-plane variations of elastic properties (at the microscale fiber/matrix level) in mesoscale progressive failure analysis models of composites due to local fiber volume fraction variations are reported. A rectangular cross-ply specimen subjected to tensile loading is used as a case study in this investigation. Experimental results in support of understanding the correlation between local fiber volume fraction and in-plane strain field variations, by using specimens with small length scales is reported. A micromechanics computational model is used to understand and explain the experimental findings. The microscale finite element results suggest that the strain variations on the surface of the outer 90 plies prior to damage initiation are caused by local geometrical changes caused by the fibers nonuniformly packed and lying closest to the surface and not by the through-ply thickness local fiber volume fraction variations. Implications of this finding for homogenized mesoscale models for damage and failure are discussed.