A Simple Approach for Determining the Characteristic Distance in the Point Stress Criterion for Holed CFRP Unidirectional Laminates

This paper presents a fracture criterion for predicting the strength of a CFRP unidirectional laminate with a hole. We formulated the point stress criterion (PSC) for notched composites with the characteristic distance at which the Tsai–Hill criterion for orthotropic materials was satisfied. The strengths of CFRP off-axis unidirectional laminates with a hole predicted by the PSC agreed well with the measured strengths, and the validity of the characteristic distance determined by the Tsai–Hill criterion was confirmed. Moreover, we observed the fractured surfaces of the holed specimens with small off-axis angles and found that the fracture mode within the characteristic distance (fiber breakage mode) was different from that away from the hole (shear fracture mode). These observations of the fractured surfaces suggested that the characteristic distance represented the size of the initially damaged area at the notch tip.