On a simple power law for macroscopic crack propagation rate due to stress-corrosion cracking in unidirectional GFRP composites

This paper is concerned with a micromechanical theory of macroscopic crack propagation due to stress-corrosion cracking in unidirectional glass-fiber-reinforced polymer composites on the basis of a physically-sound model of crack propagation in glass fibers as a result of stress-corrosion cracking. The premise is that a stress-corrosion crack initiates at a pre-existing surface flaw in a glass fiber, grows and finally leads to breakage of the fiber. We derive theoretically an equation for the macroscopic crack propagation rate as a function of the apparent stress intensity factor. It is emphasized that the size of the inherent surface flaw affects significantly the macroscopic crack propagation rate. For glass fibers free of pre-existing flaws, the relationship between the macroscopic crack propagation rate and the apparent stress intensity factor can be represented by a simple power law with the value of power of 2. Assuming that the relationship is represented by a simple power law for any size of pre-existing flaw, we obtain the power as a function of the size of pre-existing flaw, which is presented in diagrammatic forms. Using the diagrams, the experimental results of power in previous studies are examined. We conclude that the size of pre-existing surface flaw is not the same in the previous studies.