Versatile fatigue strength evaluation of unidirectional CFRP specimen based on micro-stress analysis of resin

Abstract A versatile methodology for fatigue strength prediction is proposed to enable the optimal use of the high specific stiffness and strength of unidirectional carbon fiber-reinforced plastic (CFRP). We assumed that the fatigue strength of CFRP is governed by the strength of its resin matrix, and employed a microscopic approach to evaluate the stress using a micro-scale model that considers the carbon fibers and resin separately. Fatigue tests were performed on resin and unidirectional CFRP specimens by making the reinforcement direction deviate 0°, 30°, 45°, 60°, and 90° from the loading axis. Fatigue strength prediction was successfully performed using the interfacial normal stress, which is the normal stress on a plane perpendicular to the line segment connecting the center axes of two carbon fibers. The inadequate test results for fatigue strength prediction by stress criteria of the first principal stress, Tresca stress, or von Mises stress demonstrate the superiority of the proposed methodology.