CONCURRENT INFLUENCE OF AN INCREASE IN TENSILE-STRENGTH AND THICKNESSREDUCTION ON FATIGUE-STRENGTH OF HOT-ROLLED STEEL

Plane bending fatigue tests were conducted on smooth and notched speci mens made with combinations of tensile strength and thickness of 440 N /mm2 and 2.6 mm, 590 N/mm2 and 2.3 mm2 and 780 N/m2 and 2.0 mm, respec tively. A change in the fatigue limit load (moment) was investigated. In smooth specimens, the fatigue limit moment did not change with the variation of steel. In the notched specimen having an 8 mm(phi) pierce d hole, however, the fatigue limit moment decreased drastically with t he increase in tensile strength in combination with the reduction of t hickness. An improvement in the fatigue limit stress of the notched sp ecimen was then studied from the point of view of the stamping process . It was found that coining the pierced hole is one effective method.