Fatigue Strength Prediction Formulae for Steels and Alloys in the Gigacycle Regime

Abstract—Most existing fatigue strength prediction models contain parameters related to the critical size of non metallic inclusions or defects. Finding the critical size of the inclusion or defect which causes the fatigue failure is not easy. Further, obtaining experimental stress life curves for gigacycles is expensive and time consuming. Therefore it is important to discover simple but reliable fatigue strength prediction formulae that use easily obtainable material parameters while being independent from the size of inclusions or defects. This paper proposes a new formula for predicting fatigue strengths of steels in the gigacycle regime using the ultimate tensile strength and Vickers hardness as material parameters while introducing a reliable substitute to the critical inclusion size. The formula is verified using published experimental results for forty five steels. Another formula for predicting fatigue strengths of steels and alloys is proposed using more than hundred experimental fatigue strength values at various numbers of failure cycles in the gigacycle regime.

Index Terms—Fatigue strength, gigacycles, inclusion and defect, stress life curve, tensile strength.

Chaminda S. Bandara is a Research Fellow of the National Research Council of Sri Lanka, Structural Engineering Laboratory, Faculty of Engineering, University of Peradeniya, Peradeniya 20400, Sri Lanka (e-mail: chamindasbandara@ yahoo.com; bandara@civil.pdn.ac.lk).
Sudath C. Siriwardane is an Associate Professor of the Department of Mechanical and Structural Engineering and Material Science, Faculty of Science and Technology, University of Stavanger, N-4036 Stavanger, Norway (e-mail: sasc.siriwardane@uis.no).
Udaya I. Dissanayake and Ranjith Dissanayake are with the Department of Civil Engineering, University of Peradeniya, Peradeniya 20400, Sri Lanka (e-mail: udissa@pdn.ac.lk, ranjith@fulbrightmail.org).