Original Article

Friction dependence of measured hardness: Brinell vs. Rockwell indentation tests

Faculty of Engineering and Natural Sciences, Department of Mechanical Engineering, Ankara Yıldırım Beyazıt University, Ayvalı District 150 St. Etlik-Keçiören, Ankara 06010, Türkiye

^* e-mail: fkvarol24@aybu.edu.tr

Received: 18 January 2025
Accepted: 14 March 2025

Abstract

Hardness testing is crucial in materials science and mechanical engineering, providing valuable insights into material properties and performance. Over time, various hardness tests have been developed, that compare applied load to the measured indentation depth or diameter to determine a hardness value. Prominent examples of these methods are the Rockwell and Brinell tests, each known for being convenient in various applications. In this study, DIN 50125 tensile test specimens and a hardness test block were extracted from a single ST52 rod. Tensile tests were performed on the specimens, and the average true stress-strain curve was extrapolated from the onset of diffuse necking. This extrapolation was then corrected using an inverse method. The input for the indentation simulation was defined as a piecewise function including the corrected extrapolation and a Lüder plateau. Brinell 2.5/187.5 and Rockwell 30T indentation tests, along with corresponding simulations, were conducted. Tests were performed both in dry conditions and with motor oil applied to the surface of the test block. In the simulations, friction coefficients between 0 and 0.5 were considered. The numerical results were found to be consistent with the experimental results. A higher friction coefficient increased Brinell hardness by about 3%, while Rockwell hardness showed almost no change. The effect of element sizes on both the numerical hardness values and the indentation profiles was also investigated.