Interfacial evaluation of electrodeposited single carbon fiber/epoxy composites by fiber fracture source location using fragmentation test and acoustic emission

Fiber fracture is one of the dominant failure phenomena to determine total mechanical performance inside composites. Fiber fracture locations were measured and compared via either conventional optical microscopic method or nondestructive acoustic emission (AE) by pencil-lead-break method as functions of epoxy matrix modulus and surface treatment by the electrodeposition (ED). Two AE sensors were attached on single carbon fiber reinforced various epoxy composites and consecutive fiber fracture signals were monitored with the elapsing time and strain. The interfacial shear strength (IFSS) was measured using tensile fragmentation test and AE method. In ED-treated case, the numbers of the fiber fracture measured by optical method and AE were more than those of the untreated case. The signal number of fiber fracture measured by AE method was smaller than the number of fragments measured by an optical method, since some fiber fracture signals were lost during AE monitoring. However, the correspondence between AE detected location and optically observed location was generally established well with small error range. Wave speed was relied on the impact direction and the existence of induced defects, i.e., surface and internal damages of epoxy specimen. The fiber break source location and wave analysis by AE can be a valuable method to measure IFSS and mechanical properties of matrix indirectly for non-, semi- and/or transparent polymer composites nondestructively.