Improvement in Calibration Procedure in Nanoindentation: An Indenter Bluntness Indicator

Background

Nanoindentation experiments require the calibration of the tip area function, which involves up to 9 fitting coefficients following classical method. These coefficients are determined from indentation tests on a reference material. However, their values may vary from one test batch to another. Consequently, these coefficients cannot describe the amplitude of the indenter tip defect.

Objective

The main objective of this study is to propose a contact area function that uses only one fitting coefficient to represent the indenter tip defect. This coefficient corresponds to the distance between the blunt and ideal indenter tip.

Methodology

To demonstrate the efficiency of the proposed contact area function, we reanalyzed nearly 40 calibration procedures, while keeping the same experimental protocol, performed between 2014 and today. A novel two-step calibration methodology is advanced. We compared the results of the proposed method to those obtained with the classic methodology.

Results

This two-step methodology was applied to a fused silica calibration sample. The values of the Young's modulus and instrumented hardness are equals to 71 and 10 GPa, respectively. The length of the indenter tip defect increases gradually from 5 to 30 nm accordingly to the frequency of use of the indenter. The values of the mechanical properties calculated by this methodology are in good agreement with those obtained using the classical contact area function.

Conclusion

The methodology presented in this paper demonstrates its ability to accurately calibrate the tip area function. This new calibration procedure considers both the Young’s modulus and the tip defect parameter as free parameters. Furthermore, the calibration parameters have a clear physical meaning and their values remain stables from one batch to another.