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

Plane bending fatigue tests were conducted on smooth and notched specimens 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, respectively. 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) pierced hole, however, the fatigue limit moment decreased drastically with the increase in tensile strength in combination with the reduction of thickness. An improvement in the fatigue limit stress of the notched specimen was then studied from the point of view of the stamping process. It was found that coining the pierced hole is one effective method.