Notch Sensitivity and Fatigue in Austempered Ductile Iron 980685

The properties of ADI are suitable for automotive crankshafts, camshafts, and gears; but, like many high strength materials, ADI is notch-sensitive. In this study of notch sensitivity and fatigue, baseline properties were provided by smooth-wall, and ground and polished specimens. These specimens had a rotating-bending fatigue strength of 393 MPa (57.0 ksi) for a life of 10⁷ cycles. The fatigue strength of notched test bars was evaluated after fillet rolling and shot-peening. Notched specimens were tested with stress concentration factors ranging from 1.0 to 2.4. As the severity of the fillet radius increased from 3.05 mm. (0.120 in.) to 1.02 mm. (0.040 in.), the fatigue strength decreased from 335 MPa (48.6 ksi) to 230 MPa (36.7 ksi). The notch sensitivity factor, q, increased from 0.41 to 0.55. Shot-peening was performed with steel shot, with coverage ranging from 100-400%. Both fillet rolling and shot-peening decreased the notch sensitivity of the ADI and improved its fatigue resistance.