Investigations of the fracture mechanism of carbon/epoxy composites by AE signal analyses.

Although the AE method provides useful information on the operating fracture processes of materials, a synthesized evaluation of AE signals using several AE parameters is necessary for composite materials because AE signals arise from various fracture processes. In this paper, the relationships between several AE paramaters and AE original sources were investigated, and fracture mechanisms of CFRP are discussed in terms of observations of fracture surfaces and internal damage of the laminates by a SEM and a scanning acoustic microscope (SAM), respectively. Synthesized AE signal wave analyses including the distributions of AE amplitude, AE event duration, and counts/duration (corresponding to frequency), give us useful and powerful information to analyze the complicated fracture mechanisms of composite materials. The fracture in tensile tests and cyclic tensile tests of unidirectionally reinforced carbon/epoxy composites goes through fiber/matrix interface debond and fiber breaking.