Original paper(Vol.45 No.1 pp.16)
Effects of artificial small defect and graphite on torsional fatigue strength of ductile cast iron
Endo Masahiro
Abstract:Reversed torsion and rotating bending fatigue tests were performed on JIS FCD400 using both smooth and defect specimens containing an artificial hole whose diameter ranges from 100 to 500 mm.
Although this material has numerous spheroidal graphites in the structure, the effect of interaction between defects on the fatigue limit was so small that the fatigue limit of specimen containing an artificial hole was predicted from square root of area for the hole and the Vickers hardness of matrix by the equation that was proposed in this study assuming steels with a single defect. The fatigue limit of smooth specimens in torsion was controlled by graphites and the lower bound of the scatter was well predicted substituting the size of the maximum graphite, square root of areamax, for square root of area in the equation. The value of square root of areamax may correspond to the allowable defect size of this material.
Key Words:torsional fatigue, fatigue limit, prediction, ductile cast iron, small defects, small cracks, fracture mechanics, the square root of area parameter model