Observation of Local Deformation and Crack Initiation in High-Cycle Torsional Fatigue of Carbon Steel Plain Specimen by Electron Microscope

Abstract

High-cycle torsional fatigue tests were carried out on carbon steel plain specimens (S45C). Local deformation in the crack initiation process was observed by an electron microscope. Fine grid lines were drawn on the specimen surface with a diamond point needle. The lines were fine enough not to influence the structure of the slip bands. The local strains were measured from the distorted grids. Cracks were generated in the area having large local deformation of several hundred % shearing strain. This occurs in the grain boundary between pearlite and ferrite or in the ferrite crystal grain sandwiched between pearlites.