SUBSURFACE DEFORMATION PATTERNS AROUND INDENTATIONS IN WORK-HARDENED MILD-STEEL

By using specially prepared specimens of work-hardened mild steel, subsurface deformation patterns around Vickers, conical and spherical indentations of millimetre dimensions have been determined. It has been shown that in no case does the deformation pattern agree with the predictions of the plasticity theory for a rigid-perfectly plastic material; the material flow pattern is also inconsistent with the radial flow models. Also, plastic natural strains of 2+/-0.01 and 4.1+/-0.001 have been estimated at the tips of a Vickers and a conical (included angle, 45-degrees) indentations respectively. In the case of a spherical indentation of size a/R = 0.5, where a and R are the radii of contact and the indenter, respectively, the plastic natural strains are estimated to be 0.1+/-0.05 and 0.15+/-0.06 at z/a = 0.5 and 0.65 respectively, where z is the distance measured from the undeformed surface along the load axis.