Torsional fatigue behaviour in gigacycle regime and damage mechanism of the perlitic steel

Purpose: This paper gives a comprehensive study based on the damage mechanism under torsional fatigue behaviour of D38MSV5S steel in very high cycle regime (VHCF). Torsional fatigue tests have been carried out at 20 kHz ultrasonic fatigue testing device, and these results were compared with that of the conventional torsional fatigue test machine at 35 Hz as to whether the discrepancy due to the frequency effects between two test results. All of the fatigue tests were carried out up to 1010 cycles at room temperature. Design/methodology/approach: Damage mechanism in torsional fatigues crack initiation and propagation in different mode was evaluated by Scanning Electron Microscopy (SEM). Findings: The experimental results have shown that the S-N curves exhibited a considerable decrease in fatigue strength beyond 107 cycles. Practical implications: These results give a precise data for the safety design of the pieces. Originality/value: Damage mechanism under torsional fatigue loading composes two stages, crack initiation and crack propagation, contrary to the damage under axial loading that exposes only crack initiation mechanism in the VHCF range.