Ceramics With High Fracture Toughness

When evaluating ceramic or glass fracture toughness kic there are two major complications.

Ceramics with high fracture toughness.

The higher the fracture toughness the better the resistance to crack propagation. The fracture toughness of zirconia alumina and silicon nitride ceramics zirconia and alumina single crystals silicon carbide as well as silicon nitride ceramic particulate composites silicon nitride laminated composites and other ceramics materials were studied by a single edge v notched beam sevnb method. The fracture toughness values of the 3y tzp ceramics were determined to be in the range of 4 0 6 2 mp m 1 2 and these values did not vary significantly over a wide sintering range. 27 prepared laminated zrb 2 bn ceramics with a flexural strength of 381 mpa and a fracture toughness of 13 31 mpa m 1 2.

Fine ceramics generally have low toughness. The fracture toughness of composites made by combining engineering ceramics with engineering polymers greatly exceeds the individual fracture toughness of the constituent materials. However zirconia which is used to make ceramic knives exhibits high fracture toughness. High work of fracture fi ber reinforced ceramics consisting of carbon fiber rein forced glasses and glass ceramics were first demonstrated in 1972 accompanied by the first complete model of composite behavior.

A polished surface of the material under test is indented using a vickers hardness tester the cracks which emanate from the corners or the indents are then measured and provide an indication of the toughness of the material. Compared with monolithic ceramics laminated ceramics showed multiple fractures instead of typical brittle fractures. Ceramic materials are characterized with respect to fracture toughness by measuring the energy required for a defect of known dimensions to propagate and become a crack. Scg can cause stable crack extension at kiokic and thus can interfere with attempts to measure kic.

An understanding of the material s young s modulus and the length of the defect is required to measure what is known as the stress intensity factor.