Numerical analysis of the influence of friction conditions on the pile-up effect in Vickers hardness measurements

Vickers indentation load-depth curve may be used to determine basic mechanical properties of metallic materials such as hardness, yield stress, modulus of elasticity, and elastic and plastic work. The pile-up phenomenon observed during indentation causes underestimation of the projected contact area and the diagonal dimensions of the impression in different hardness measurement scales (nano-, micro-, and macro-). The aim of this paper is to conduct a numerical analysis of the effect of friction conditions on the pile-up phenomenon during testing of DC04 steel sheet. The mechanical properties of the sheet metal used for the modelling purpose were first characterized by tensile tests on samples cut along the rolling direction (0°), transverse to the rolling direction (90°) and at an angle of 45° to the rolling direction. The numerical computation was conducted using ABAQUS, which is one of the powerful finite element-based programs. A wide range of variation of friction coefficients, i.e. 0-0.3 has been used in the analysis. It has been observed that the results of indentation of anisotropic materials are significantly affected by friction. The difference in the pile-up height measured at rolling direction of sheet metal and transverse to the rolling direction decreases with the reduction of the maximum displacement of the indenter. For higher values of the coefficient of friction, the higher the value of the indenter displacement, the lower becomes the increase in the pile-up height value.