破壊じん性値がき裂速度に依存するセラミックスのJIS三点曲げ破壊じん性試験の問題点

概要

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In the fracture toughness tests of perfectly brittle and crack-rate sensitive ceramics(R∝a^^・^m^*, R;the crack resistance force, a^^・;the crack velocity), it has been analytically as well as experimentally clarified that an initial crack begins to extend befor a maximum load appears in load-deflection curve. This crack-extension phenomenon was named PSP(psuedo-stable phenomenon) in the previous paper. The amount of the crack-extension due to the PSP depends on the crack-rate sensitivity parameter m^*, the non-dimensional compliance of testing machine EBΛ^* and the initial crack length x_0. Nevertheless, the fracture toughness value, K_<IC> has been currently determined by the maximum load and the precracked crack-length measured before testing. In the testing regulation for high performance ceramics in JIS, the K_<IC> is also evaluated in the same way. For a single edge cracked 3 point bending specimen of JIS, the amount of crack-extension is numerically calculated as a function of m^*, EBΛ^* and x_0, and it is studied whether or not the K_<IC> is evaluated exactly. The results obtained show that the K_<IC> is reasonably evaluated when both m^* and EBΛ^* are small enough, but the K_<IC> is considerably underestimated when these values are large.
社団法人日本材料学会の論文
1994-01-15