Abstract
The correlation between the diameter of a hole drilled perpendicular to the axis of a bar and its fatigue limit under repeated bending or torsion was inves igated experimentally for Ni-Cr steel especially the fatigue limit under rcpcated torsion and small hole diameter, which experiment has not been conducted was cleared. It was cleared that the quantitative recovery of fatigue limit is due to compression of the edge of the hole by steel ball, the fatigue limit increased straightly with the pressure of the ball, and by Ni-Cr steel with 12mm rod dianTeter, 15mm hole diameter, and 5.5mm ball diameter, the stress concentration factor attained almost unity at 2.500kgs_??_2.700kgs of ball pressure.
