Abstract
Measurements of crack closure for small fatigue cracks were mode on fine and coarse grained materials of a low carbon steel, S 10 C, in the region of crack lengths of 2cm, above which the effect of grain boundaries on crack growth rate disappeared, to crack length of 2cc, above which crack growth rates for small cracks were consistent with those for large cracks. Crack opening stress increased with increasing crack length and tended to be constant at a crack length near 2cc. That is, small cracks in the region from 2cm to 2cc were in the process of increasing crack closure and then attained the same extent as large cracks. The reduction in crack closure of small cracks would be attributed to extensive plasticity surrounding the crack, and thus plasticity-induced crack closure was reduced because of decreased constraint by the surrounding elastic material on the plastic region.
