On the Invariance of Hardness at Vickers Indentation of Pre-Stressed Materials

Per-Lennart Larsson

doi:10.3390/met7070260

Abstract

The influence from residual surface stresses on global indentation properties, i.e., hardness and size of the contact area, have been studied quite frequently in recent years. A fundamental assumption when evaluating such tests is that the material hardness is independent of any residual stresses. This assumption has been verified in the case of cone indentation of classical Mises elastoplastic materials. However, a detailed investigation of this feature in the case of three-dimensional indentation, i.e., Vickers and Berkovic indentation, has not been presented previously. It is therefore the aim of the present study to remedy this shortcoming using finite element methods. The numerical results pertinent to Vickers indentation clearly show that the material hardness is independent of residual (or applied) stresses (also in case of three-dimensional indentation problems). The limitations of the validity of hardness invariance are also discussed in some detail.

Highlights

Residual stresses can be a very dangerous feature when it comes to the reduction of load-carrying capacity and strength in general
The behavior of the material hardness at Vickers indentation of elasticelastic-ideally modelled using the standard Prandtl-Reuss (Mises) plastic materials will be investigated in the presence of in-plane (X1-X3-plane) ideally Mises plastic materials will be investigated in the presence of in-plane (X1-X3-plane) equiequi-biaxial residual stresses
The investigation is based on the finite element method and the material properties are chosen to be investigation is based on the finite element method and the material properties are chosen to be

Summary

Introduction

Residual stresses can be a very dangerous feature when it comes to the reduction of load-carrying capacity and strength in general Such stresses can be introduced through mechanical and/or thermal loading, and during engineering, processing, and production of monolithic and composite materials. The best way to avoid any destructive influence from residual stresses is to substantially reduce the levels of the residual fields Very often this is not an easy task to undertake, and a more realistic approach to the problem is to quantify these stresses and account for them during design and dimensioning. There are many methods proposed for this purpose (hole-drilling, layer removal, beam bending, neutron and X ray tilt techniques, just to mention a few) but lately indentation testing has emerged as a strightforward and, non-destructive alternative.

Methods

Results

Conclusion