Compressive Strength and Failure Mechanisms of Laminated C/C Composites by using Acoustic Emission Method

摘要

Compressive tests are conducted on the laminated unidirectional C/C composite of two shapes, block and tab specimens. Acoustic emission (AE) is monitored during the tests to investigate microscopic failure mechanisms. Compressive strengths in block specimens are within the range between 70 to 180 MPa. The Compressive strength has no significant influence of the height of the specimens, but is dependent on the failure procedure. Two types of stress-strain curves are observed. In type-1 of lower strength, initial deformation is linear elastic with AE signals of low amplitude ( < 60dB). As AE events increases, the curve becomes non-linear, and the stress decreases gradually after peak stress. In type-2 of higher strength, stress falls to zero after peak stress. The location of initial dela-mination is found to affect the failure mechanism and strength considerably. With increasing stress, AE events of relatively high amplitude ( > 60dB), corresponding to the initiation of delamination are observed. Compressive strengths in the tab specimens are within the range between 260 to 300MPa, higher than that of the block specimens. Due to the constraint of edges by the tabs, delamination can not propagate to the edges, resulting in higher strengths. In the present C/C composites, main failure mechanism is found to be de-lamination, whereas kink-band formation is observed only partially.