Evaluation of an Improved Filtering Method for Strain Measurement at High Temperatures Using 2D-DIC

Background

The Two-Dimensional Digital Image Correlation (2D-DIC) method is widely used as a non-contact full-field kinematic measurement, but it presents significant errors related to temperature effects including the image con- trast and heat waves. Consequently, results of mechanical displacement or strain measured by the 2D-DIC method, especially strains in the elastic domain of materials, is significantly dispersed.

Objective

The aim of this study is to propose a very simple 2D-DIC method, using commercial DIC software with no need of additional storage to accurately measure strain and displacements at high temperatures, typically at the hot metal forming temperatures, from 400 ^◦C to 750 ^◦C.

Methods

This study demonstrates the influence of temperature effects (radiation and heat waves) on strain measurements obtained with the 2D-DIC method in the elastic regime (ε < 0.05) of the TA6V titanium alloy material at high temperatures. Furthermore, the strain measurement errors at different temperatures were characterized by the Background Oriented Schlieren technique (BOS). Correction methods using temperature-dependent low-pass filters for strain measurement errors are suggested.

Results

The correction methods allow separating mechanical strain fields and strain measurement errors caused by temperature effects. The efficiency of the correction methods is demonstrated by identifying the Young’s modulus (E) and the Thermal Expansion Coefficient (TEC) of the TA6V. After corrections, E and the TEC of the TA6V are close to the reference values found in the literature. Conclusion: The coefficient R² from the linear regression method to determine the Young’s modulus from tensile test at 600 ^◦C increases from 0.783 to 0.989, revealing the great potential of using the improved-2D-DIC method for full-field kinematic measurements of mechanical tests at high temperatures.