Fracture Characteristics of Unidirectional CFRP Composites under Biaxial Tensile Load

Abstract

To clarify biaxial fracture properties of the unidirectional carbon-fiber-reinforced plastic (CFRP) composites, a cruciform specimen with two symmetric rectangular flat dents in the thickness direction was developed, and tensile tests were carried out under 0º and 90º loadings. The specimen showed three fracture modes, namely transverse crack (TC), fiber break (FB), and a mixture of TC and FB modes (TC&FB). According to the strain measurement result, regardless of the magnitude of the strain occurring in 0º direction, TC- and TC&FB-modes occurred when the strain occurring in 90º direction was positive, and FB-mode occurred when it was negative. It was concluded that when the strain along the 90º direction was zero, the straight line with slope ν₂₁ (Poisson’s ratio in the 1-direction when stressed in the 2-direction) can divide the fracture stress data occurring in the FB-mode and other two modes. A coefficient determining the elliptical rotation angle of the failure envelope was introduced, assuming that FB-mode occurs at levels comparable to the uniaxial tensile strength. The failure envelopes given by the coefficient correspond with average fracture stress data.