Nonuniformity of Local Strain and Strain Concentration in Static Deformation of Plain Specimens of Rolled Round Carbon Steel Bars.

Abstract

Tensile and torsional tests were carried out on the plain specimens of rolled round carbon steel bars (S15C, S35C, S45C). Each specimen is regarded as an anisotropic material because it has a banded structure of ferrites and pearlites which were produced by rolling. Fine grid lines were drawn on the surface of specimen 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 elongated or distorted grids. The local deformations were not uniform in both tension and torsion, and most of the local strains were not the same as the given macroscopic strain. That is, there existed various local strains which were from near zero to several times the given macroscopic strain. The variety of local strains in torsion was greater than that in tension. The banded structure affected the local strain greatly in torsion, but hardly affected that in tension. Strain concentration in tension was small ; however, in torsion, this was large within the ferrite sandwiched between pearlite bands. When the materials had a clear banded structure and large binding force due to pearlites, the banded structure greatly influenced the local strain in torsion. The result of this study is important to the understanding of the fatigue of plain specimens of rolled round carbon steel bars.