A study of effect factors on thermal drift rates during cryogenic indentation via Taguchi design and finite element method

Abstract

Although nanoindentation at cryogenic temperatures has been widely used to evaluate mechanical deformation behaviors and damage mechanism, thermal drift has a significant effect on accuracy and reliability of measurements. In order to acquire high-quality data of indentation, this paper proposes a novel evaluation method on the significance of effect factors and their interactions for thermal drift rates during cryogenic indentation using a Taguchi robust design combined with finite-element analysis. The results of signal-to-noise (S/N) and analysis of variance (ANOVA) are indicated that the effects of the five control factors on the measurement of thermal drift are ranked as: specimen material > indenter tip assembly’s material > loading rate > testing temperature > peak of load. It demonstrates that temperature-dependent material properties for the contact pair are the most important factors in determining the thermal drift rate. Therefore, an upgraded indenter tip assembly with the Invar 36 shaft and the diamond tip is proposed for the cryogenic indentation of different materials. To further reduce thermal drift, an atmosphere pre-cooling method for tip assembly and specimen during cryogenic indentation is recommended owing to its minimum thermal drift and high homogeneity of temperature.

Keywords

• Cryogenic indentation
• Thermal drift rate
• Taguchi robust design
• Finite element method
• Pre-cooling method