セラミックスの即時破壊強度に関する理論的考察

概要

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As fracture strength of ceramics σ_f measured in bending or tension tests decreases with decrease in stress rate σ^^., σ^^. should be sufficiently high if σ_f&sirne;σ_<f0> is to be realized, where σ_<f0> is true fast fracture strength (inert strength) which will be obtained when unstable crack extension occurs directly from an existing crack without preceeding stable crack growth. However, magnitude of σ^^. needed to obtain σ_f&sirne;σ_<f0> has not been clarified. In this paper, a general equation of σ_f as a function of σ^^. was obtained for testing in which σ^^.=const assuming that dependence of σ_f on σ^^. results from stable crack growth. Based on this equation, it was shown that σ^^. should be higher than (0.95)^<n+1> σ^^._0 if σ_f≧0.95σ_<f0> is to be realized, where n is the exponent in da/dt=AK^n, and σ^^._0 is given by Eq, in this paper. It was then pointed out that the stress rate in usual tests of ceramics is considerablly lower than this required value. It was also shown that the range of σ^^. in which the power relation σ_f∝σ^^.^λ(λ>0) holds is given by σ^^.&sirne;0.1 σ^^._0.
一般社団法人日本機械学会の論文
1991-03-25