Interfacial evaluation and microfailure mechanisms of single carbon fiber/bismaleimide (BMI) composites by tensile and compressive fragmentation tests and acoustic emission

Interfacial properties and microfailure modes of carbon, SiC, and glass fibers/bismaleimide (BMI) composites were evaluated using both tensile fragmentation and compressive Broutman tests with acoustic emission (AE). Since brittle BMI is a difficult matrix to apply for the conventional fragmentation test, dual matrix composites (DMC) were applied due to their too brittleness and high modulus. By curing further from two- to three-stage, the interfacial shear strength (IFSS) between the fiber and the BMI matrix increased under both tension and compression, whereas the number of the vertical crack spacings of the BMI matrix decreased under tension. It was considered that the IFSS increased due to further progressed curing at the three-stage. The typical microfailure modes including fiber break, matrix crack, and interfacial failure were observed in tension. Due to transverse tensile stress at the interface in compression, many overlapped diagonal slippages were observed only at the broken carbon fiber ends without a BMI vertical crack. In tension, SiC and glass fibers were never broken due to their rather longer elongation to failure than carbon fiber. AE amplitudes of the brittle BMI matrix fracture were even higher than those of carbon fiber fracture in tension because of high modulus of the BMI matrix to fracture and geometrical effect due to thick rod shape. The waveform of signals coming from BMI matrix fractures in tension was consistent with AE amplitude result. (C) 2002 Elsevier Science Ltd. All rights reserved.