Fracture characteristics of SiC particle reinforced oxynitride glass usingchevron-notch three-point bend specimens

The fracture toughness K-1c and the effective fracture surface energy gamma (eff), of oxynitride glass(m)/SiC(p) brittle particulate composites were me asured by means of stable fracture tests, using chevron-notch three-point b end specimens. In comparison to oxide glasses, the oxynitride glass matrix is noticeably tougher: K-1cm = 1.2 MPa.root m and gamma(eff) = 5 J/m(2). Th e addition of SiC particles, 6 mu m in diameter, results in a significant t oughening: K-1c = 2.5 MPa.root m and gamma(eff) = 9.1 J/m(2) for the compos ite with 40 vol% SiC. In such systems, with strong particle-matrix interfac ial bonding, and where (E-p, K-1cp, sigma(rp)) > (E-m, K-1cm, sigma(rm)), t he main toughening contribution is due to a discrete pinning of the crack b y particles near the crack tip in conjunction to bowing of the crack front between particles, and to a small scale bridging mechanism.