In Situ Investigation of the Kinematics of Ply Interfaces During Composite Manufacturing

The kinematics of composite ply interfaces critically affects both the manufacturing processes and deformation mechanisms and is often responsible for the formation of defects such as wrinkles and delamination. In the present work, processing-induced defects in a carbon fiber prepreg composite are evaluated by devising a novel in situ experimental approach. Carbon fiber prepreg laminates are cured in a specially designed autoclave with viewports with plies laid up on a mold with cylindrical tooling set up to maximize the ply-movement. Four-ply layup orientations of [90/90]_s, [90/0]_s, [90/45]_s, and [90/−45]_s and three-mold configurations with cylindrical tools of diameter 9.5 mm (3/8 in.), 12.7 mm (1/2 in.), and 15.9 mm (5/8 in.) are used for the parametric study. Strains, ply-movement, and formation of defects are observed in situ using digital image correlation (DIC) during the autoclave cure cycle, through the viewports. The processing-induced defects in the composite are further characterized by X-ray micro-computed tomography (micro-CT). We observed that the mold with the larger radius of curvature (15.9 mm cylinder) leads to higher strains in both in-plane directions and higher displacement in out of plane directions. The maximum average out-of-plane ply movement, as well as the largest wrinkle, are observed for [90/−45]_s layup on the mold with the highest radius of curvature.