Experimental characterization of microscopic damage progress in quasi-isotropic CFRP laminates: effect of interlaminar-toughened layers

Microscopic damage progress under static tensile loading in quasi-isotropic CFRP laminates was observed by an optical microscope and a scanning acoustic microscope (SAM). Material systems used were toughened-type CFRP, T800H/3631 and newly developed CFRP with interlaminar-toughened layers, T800H/3900-2. The laminate configurations were quasi-isotropic [0/45/90/-45](s2) for T800H/3631 and [0/45/90/-45](s) for T800H/3900-2. Both plain specimens and specimens with a circular hole were tested. By the edge observation of the plain specimens, transverse crack density was measured as a function of laminate strain. The effect of interlaminar-toughened layers on the behavior of the microscopic damage was clarified experimentally. By the SAM observation of specimens with a hole, delamination onset and growth were detected. To discuss the delamination onset from the edge of the open hole, the energy release rate associated with delamination growth was calculated following O'Brien and Raju. The energy release rate predictions of delamination onset and growth was qualitatively consistent with the experimental observation.