Stress analysis of the Outwater-Murphy fiber/matrix debond specimen

Abstract

The distribution of stress at the fiber/matrix interface in the Outwater-Murphy specimen is determined using finite element analysis. Stresses due to mechanical loading as well as residual stresses due to cure shrinkage and water swelling of the matrix are determined and used to predict the fiber/matrix interface stress state at the site where fiber/matrix debonding initiates. Stress analysis of all-resin Outwater-Murphy specimens and Outwater-Murphy specimens with a super element with homogenized fiber and matrix properties point to the dominance of a biaxial tensile stress field at the apex of the hole. A 2D plane stress analysis of the fiber exit element assuming the dominating stresses are tensile indicates that the initiation of fiber/matrix debonding is due to a radial tensile stress acting on the fiber/matrix interface. Experimental test on glass and carbon fiber/vinylester OM specimens were conducted at dry and water-saturated conditions, which provided fiber/matrix interface tensile strengths. It was found that absorbed moisture substantially reduces the strength of the fiber/matrix interface.