Experimental study of the meso-scale heterogeneous deformation response of polymer composites

Meso-scale deformation response of an orthogonally woven carbon fiber reinforced composite is investigated using digital image correlation. The evolution of low and high strain domains within the material's structure are experimentally captured and analyzed. The meso-scale analyses are performed by studying the evolution of local normal and shear strain components for different off-axis specimens. Using the experimentally measured strains at meso-scale, the local stressstrain response is also quantified. Global tensile response and the bulk failure mechanisms present in the examined material are explained through the results obtained at meso-scales. The local deformation, irrespective of the fiber orientation, is highly heterogeneous, while the degree of inhomogeneity is found to be more remarkable in the case of ±45° off-axis specimen. It is revealed that the large magnitude of localized normal strain developed within the regions of soft polymer, confined with transverse fiber bundles, will eventually lead to fiber pull-out and formation of a rather flat fracture surfaces in specimens with loading direction parallel to the principal fiber directions. On the other hand, domains containing large magnitudes of shear strain formed within the polymer-rich regions of the off-axis ±45° specimen were shown to result in a shear type failure associated with a rough conical fracture surface.