Evaluation Method for Residual Stresses Induced by Surface Treatments of Crankshafts and Effect of These Stresses on Fatigue Strength

Abstract

Nowadays, crankshafts are required to use materials with higher fatigue strength to increase the output and efficiency of marine engines in an attempt to reduce of greenhouse gas emissions. Surface treatment is one of the means to fulfill this requirement. However, instead of giving rise to compressive residual stresses on treated parts, surface treatment causes tensile residual stresses to be produced around boundary positions between treated and non-treated parts. This report presents the distribution of residual stress when induction hardening is performed on a specimen. It also highlights ways to measure X-ray stress using the cosα method that is applicable to crankshafts. Moreover, it shows the axial and torsional fatigue test results of specimens with different sizes of artificial defects using compressive and tensile mean axial stress as a substitute for residual stress. The end of the report introduces the fatigue strength assessment of specimens treated by induction hardening using the Murakami’s equation with a modified coefficient, concluding that the defect in the tensile residual stress region of the specimen could be a starting point of failure.