Effects of Mean Stress and Defect Sizes on Fatigue Properties of Forged Steel Crankshafts

Abstract

Recently solid-type crankshafts for 4-stroke diesel engines are required to have higher fatigue strength to increase output of marine and power generator engines and make them more compact. Due to these requirements, surface treatment methods that can induce residual stresses have been well-studied. To study the effect of surface treatment methods on fatigue strength, fatigue tests, under mean stress, were conducted using fatigue specimens, namely artificial defects with different sizes. The result found that in the compressive mean stress region, fatigue strength of the specimens corresponded well with modified Goodman equation and that in the tensile mean stress region, their fatigue strength matched well with Gerber equation. Moreover, it was found that fatigue strength of the specimens with artificial defects, can be evaluated with the square root of defect area.