COMPRESSIVE STRENGTH AND FAILURE MECHANISMS OF LAMINATED C C COMPOSITES BY USING ACOUSTIC-EMISSION METHOD/

Compressive tests are conducted on the laminated unidirectional C/C co mposite of two shapes, block and tab specimens. Acoustic emission (AE) is monitored during the reals to investigate microscopic failure mech anisms. Compressive strengths in block specimens are within the range between 70 to 180 MPa. The compressive strength has no significant inf luence 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 signa ls 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 delamination is found to affect the failure mecha nism and strength considerably. With increasing stress, AE events of r elatively high amplitude (>60dB), corresponding to the initiation of d elamination are observed Compressive strengths in the tab specimens ar e within the range between 260 to 300MPa, higher than that of tile blo ck 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 delamin ation, whereas kink-band formation is observed only partially.