純チタンの微小疲労き裂成長挙動の結晶粒径依存性

概要

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The growth behaviour of small fatigue cracks was studied on both fine- and coarse-grained materials of pure titanium under axial loading (R=-1), and the growth behaviour and its statistical properties on coarse-grained material were also investigated under rotating bending and were compared with the results of fine-grained material in a previous report. As the growth rate data are plotted in terms of an effective stress intensity range, small cracks still grow faster than large cracks in a small crack regime. Small cracks of coarse-grained material show higher growth rates than fine-grained material due to a much smaller effect of microstructures such as the grain boundary and crack deflection. Stage-I facets are observed in all specimens and their depths are less than the maximum grain size estimated by the statistics of extreme values. However, the distribution of Stage-I facet depths corresponds to the maximum distribution of grain size of the materials. The growth rates of small cracks follow a log-normal distribution independent of grain size. The coefficient of variation of the crack growth rate in coarse-grained material is less than that in fine-grained material. The coefficient of variation is significantly large at a/d < 3 ( a : crack depth, d :grain size) , showing that the relative size of microstructurally small cracks is not dependent on grain size.
一般社団法人日本機械学会の論文
1992-02-25