Very high cycle fatigue tests with smooth and notched specimens and screws made of light metal alloys

Results of several fatigue tests using a new servohydraulic testing machine (VHF 50 D) are presented. Investigations were done at room temperature with
• smooth and notched (Kt = 1.8) specimens made of aluminium wrought alloy EN AW 6082,
• screws M 8 made of EN AW 6056 and
• smooth specimens made of die cast magnesium AZ91 hp (here also at 125 °C).Used frequencies were between 250 and 400 Hz and number of cycles were measured up to N = 8 × 108. Fatigue strength values were determined according to the staircase method. Crack initiation sites were investigated and could be found below the surface for smooth magnesium and aluminium specimens, but not for screws and other notched specimens.