Examining the Effect of Pileup on the Accuracy of Sharp Indentation Testing

Zhongbin Tang,Qiuming Wei,Yulong Li,Zhaohu Jia,Yazhou Guo

doi:10.1155/2015/528729

Abstract

One essential problem related to instrumented indentation is the effect of pileup, which could introduce significant errors on the measured hardness and elastic modulus. In this work, we have assessed some critical issues associated with instrumented indentation by means of numerical simulation. Dimensional analysis is adopted to acquire the principal governing parameters of the process, such as the ratio of yield strength to elastic modulus(Y/E)and the ratio of indentation depth to maximum penetration depth(h/hmax). The dimensional analysis provides a general understanding on the relationships among these dimensionless variables and their influence on the test results. Three kinds of indenters, that is, conical, Berkovich, and Vickers indenter, are comparatively studied. The dependence of pileup on the dimensionless parameters and its effect on the simulation results are also given. These findings are instructive for measuring the mechanical properties by instrumented indentation, especially when the effect of pileup is involved.

Highlights

Instrumented indentation, nanoindentation, has been widely used for characterizing the mechanical properties of materials at small scales [1,2,3,4,5,6]
The geometry functions of Berkovich indenter and Vickers indenter can be designed to be the same as that of the conical indenter, the true projected contact areas at the same indentation depth may still be different considering the effect of pileup
Equation (17) indicates that the final indentation depth is proportional to the maximum indentation depth and is dependent on yield strength to elastic modulus (Y/E)

Summary

Introduction

Instrumented indentation, nanoindentation, has been widely used for characterizing the mechanical properties of materials at small scales [1,2,3,4,5,6]. The relationship between the effective elastic modulus and the projected contact area and unloading stiffness is given by [1, 4]. Bolshakov and Pharr [7] found by numerical simulation that pileup was significant for conical indenter if the ratio of final displacement to the maximum depth of penetration is larger than 0.7 (i.e., hf/hmax > 0.7). The geometry functions of Berkovich indenter and Vickers indenter can be designed to be the same as that of the conical indenter, the true projected contact areas at the same indentation depth may still be different considering the effect of pileup.

Dimensional Analysis

Numerical Analysis

Results and Discussion

Summary and Conclusion