A procedure has been developed to measure the fracture resistances of nominally brittle materials
(monolithics and composites) using chevron-notched, three-point bend specimens at room temperature
and elevated temperatures. The chevron-notched geometry promotes stable crack growth during quasi-static
fracture tests. For each test a continuous record of load versus crack mouth opening displacement
(CMOD) is obtained. The fracture toughness, work-of-fracture and the classical crack growth resistance
curves are then determined from the stable crack growth loading curves and previously established relations
between the CMOD compliance, the effective crack length, and the load point displacement (LPD).
Various materials have been tested which include monolithic ceramics: alpha silicon carbide, reaction bonded silicon nitride, and magnesium aluminate spine1 and composites: titanium diboride particle/ silicon carbide matrix, silicon carbide whisker / aluminium oxide matrix, and carbon fibre/ carbon matrix. The R-curves for the various materials show flat, rising linear, and rising non-linear behavior indicative of linear elastic fracture behavior, constant but increasing fracture mechanisms, and constantly developing fracture mechanisms, respectively.
(Received October 30, 1987)
Keywords: fracture toughness, work-of-fracture, carbon /carbon composites, heat engine component
* Institute of Industrial Science, The University of Tokyo, 7-22-l Roppongi, Minato-ku, Tokyo 106, Japan.