New b-value parameter for quantitatively monitoring the structural health of carbon fiber-reinforced composites

Carbon fiber-reinforced composites have excellent mechanical properties but are vulnerable to the accumulation of small cracks. This study used acoustic emission (AE) signals to monitor and quantify composite damage. We subjected carbon fiber/epoxy specimens to cyclic loading (10 cycles/step, up to 700 MPa of tensile stress). We obtained AE signals over a wide frequency range that can be used to monitor failure modes. The conventional Ib-value decreased with increasing damage and shifted upward as the propagation distance increased. We introduced a new parameter, the composite b-value (Cb-value), to analyze AE amplitude distribution at the crack origin. It was demonstrated that the Cb-value is independent of sensor location, thus providing accurate information on the overall damage. Finally, a standard value based on the Cb-value was suggested as an index of the damage level in composite materials; this is a useful indicator of structural health.