Improved relationship between Vickers hardness and yield stress for cold formed materials

Tekkaya A.

STEEL RESEARCH, vol.72, no.8, pp.304-310, 2001 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 72 Issue: 8
  • Publication Date: 2001
  • Doi Number: 10.1002/srin.200100122
  • Journal Name: STEEL RESEARCH
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.304-310
  • Middle East Technical University Affiliated: No


Cold-formed metal products are increasingly serving as high duty machine parts. Designers and users need to know their properties as accurately as possible. One such product property is the new yield strength, which can be approximated by the final flow stress of the workpiece material during forming. Vickers hardness measurements provide an easy and inexpensive method of evaluating the new local yield stress in cold-formed workpieces. The well-known available models given in literature to convert the measured hardness number into the corresponding yield stress have an error of up to 25%. This is basically due to the facts that cold formed material experiences large plastic strains in the main forming stage, the hardening behaviour is anisotropic and, moreover, the material properties are inhomogeneous especially at the workpiece surface. The purpose of this study is to improve the accuracy of the well-known available correlation models between Vickers hardness measurements and yield stress. This is achieved by utilizing finite element simulations of the indentation process. The models currently incorporate only the isotropic strain-hardening behaviour of the work material. The new suggested model decreases the theoretical conversion error to less than 10%.