純チタンの微小疲労き裂成長挙動とその確率特性

概要

論文の詳細を見る
Rotating bending fatigue tests were conducted on smooth specimens of pure titanium in order to investigate the growth behaviour of small cracks and their statistical properties. Small cracks grow much faster than large cracks when subjected to the same nominal stress intensity. The former also grow below the threshold values of ΔK_<th> and ΔK_<eff, th> for large cracks. The early growth of small cracks is markedly affected by the microstructure in the region of crack length below 450 μm, and the growth rates often decrease at grain boundaries and due to crack deflection (a microstructurally small crack). Almost all of Stage I facet depths observed are of grain size, thus Stage I cracks do not correspond to microstructurally small cracks. This is clearly different from the results obtained in steels and aluminum alloys. The growth rates of small cracks follow a log-normal distribution, independent of maximum stress intensity or crack size. The coefficient of variation decreases with increasing the maximum stress intensity and then reaches a constant value. The largest scatter of the growth rates is obtained when the crack depth is comparable to grain size, thus it is attributed to grain boundary and grain orientation.
1990-03-25