高アルミナ室セラミックスの破壊面とアコースティックエミッション

概要

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Three-point bending fracture tests were carried out on three kinds of high alumina ceramics. The specimens were partially cracked by thermal shock before the fracture tests. The test results could be better evaluated in terms of nominal fracture stress, σ_c, using the effective transversal area, rather then the critical stress intensity factor, K_<IC>. The results evaluated through K_<Ic> depended on the pre-crack length. However, σ_c'S were almost independent of the crack length. Little topographic difference between the thermally-shocked and mechanically fractured surfaces was observed. For pure alumina specimens consisting of coarse grains, transgranular cracks were mainly observed on the thermally pre-cracked surface, while intergranular cracks were major on the mechanically fractured surface. Acoustic emissions were also monitored, and those signals were recorded using a transient memory recorder. The magnitude of the signals was large for porous mullite ceramics and small for fine-grain alumina ceramics. For mullite ceramics, the fracture stress obtained from cyclic loading was about 30% higher than that from monotonic loading. Cyclic step patterns with about 10 to 20 μm spacings were observed on the cyclic fracture surface.
1985-06-15