Research on a New Exponential Function Weighted Averaging Method Used for Full-Gradient Strain Measurement of DIC

Abstract

Background

In the implementation of Digital Image Correlation (DIC), several post-processing methods have been developed to calculate reliable strain field. Nevertheless, achieving effective and easy-to-implement strain measurement for full-gradient strain fields continues to be a challenge.

Objective

The widely used pointwise least square (PLS) method is hard to get a balance between smoothing and accuracy when dealing with different deformation fields. A large strain calculation window may lead to over-smoothing, whereas a small strain calculation window may be insufficient to suppress noise.

Methods

A new exponential function and the exponential function weighted averaging (EFWA) method are proposed. The shape of the exponential function can be either sharp-topped or flat-topped, allowing the EFWA method to either preserve or smooth the original strain results. A straightforward and effective selection strategy for parameters of the exponential function is also provided, enabling the EFWA method to achieve self-adaptive post-processing.

Results

The calculation examples of synthetic images indicate that, the proposed EFWA method can consistently yield high measurement accuracy for unidirectional and multi-directional complex deformation fields and exhibits superior spatial resolution compared to the PLS method. The minimum Metrological Efficiency Indicator (MEI) value for the EFWA method is 1.72, compared to 4.67 for original results and 5.10 for the PLS method. The results of a tensile experiment carried out on an open-hole specimen indicate that, after the EFWA method is implemented, the strain results in areas away from the hole are effectively smoothed and the strain results in areas around the hole are preserved.

Conclusions

The proposed EFWA method can achieve effective and easy-to-implement strain measurement for full-gradient strain fields.