707 セラミックス表面層の破壊強度に関する研究(GS-3 強度・破壊(2))

概要

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The purpose of this study is to investigate the relationship between the sphere indentation diameter 2R and the crack length c_i that is an origin of the ring crack in the ceramics specimen. The sphere indentation tests using HIP sintered Si_3N_4 specimens were carried out to obtain the ring crack initiation load for various 2R. On the assumption that a ring crack initiate from a micro-crack in the surface layer, the crack length of c_i was estimated by using the experimental data (ring crack initiation load, ring crack radius) in terms of a stress intensity factor K_1 obtained for a surface crack under the sphere-plate contact loading condition. It was found that the crack length c_i was 5-6 μm using the threshold fracture strength K_<th> of 5.3 Mpa・m^<1/2> and was almost independent of the sphere indentation diameter 2R in the case of large 2R.
2004-03-17