Interlaminar fracture behavior of 3D C/C composites using z-pins as through-thickness reinforcements

A preform consisting of plain weave fabric and z-pin through-thickness reinforcements was prepared. The carbon matrix was derived from a combination of isothermal chemical vapor infiltration and high-pressure impregnation-carbonization of coal tar pitch. The interlaminar shear strength of the composites was characterized by a short beam interlaminar shear test and a double edge-notched tensile shear test. Hyper pseudoplastic fracture behavior of short beam interlaminar shear of 3D C/C composites was found, which is ascribed to the propagation of microcracks formed between laminations within and between bundles. Z-pins can have effective control over the progress of pseudoplastic fracture. True shear failure, which is characterized by the double edge-notched tensile test, shows non-pseudoplastic fracture progress that is ascribed to shear sliding occurring only within one interlamination. Both short beam interlaminar strength and double edge-notched tensile strength are 40%-50% higher for a z-pin density of 1.5 mm interval than those for a z-pin density of 2.5 mm interval. Employing z-pins as through-thickness reinforcements has advantages over a 3D weave.