球状黒鉛鋳鉄の微小き裂および長いき裂の下限界応力拡大係数幅に及ぼす硬さと応力比の影響

概要

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Threshold stress intensity factor ranges ⊿K_<th> on spheroidal cast irons, which are composed of ferritic, ferrite-pearlitic and pearlitic structures, have been measured by ⊿K-increasing tests for small cracks, and by ⊿K-increasing and ⊿K-decreasing tests for long cracks at several stress ratios. With respect to the effect of hardness and stress ratio, ⊿K_<th> for the long cracks under the ⊿K-decreasing tests and ⊿K_<th> for the small cracks are evidently different, while ⊿K_<th>s for the long cracks under the ⊿K-increasing tests and for the small cracks are similar. Moreover, regardless of the type of matrix structures, the values of ⊿K_<th> for the long cracks under the ⊿K-decreasing tests were larger than those for long cracks under the ⊿K-increasing tests. These tendencies are due to the fact that the long cracks under the ⊿K-decreasing tests have a relatively higher crack closure stress than those under the ⊿K-increasing tests. On the fracture surface of the long cracks under the ⊿K-decreasing tests, oxide layers caused by fretting were observed around the crack tip on the surface, although oxide layers were not observed under the ⊿K-increasing tests.
社団法人日本機械学会の論文
2005-11-25