An Approach to Strain Measurement Uncertainty for DIC Using the SPOTS Calibration Procedure

Abstract

As the validation of numerical simulations gets more important, the demand for more reliable experimental data with quantifiable uncertainty is increasing. For new materials and complex structures, full field deformation and strain results can be used to validate and ultimately improve computational modeling.

Digital Image Correlation (DIC) is a widely used experimental technique for measuring deformation and strain and many articles have been presented on how the influence of different parameters can affect the accuracy of results. To date, only single parameters have been considered in isolation, but for a more complete measure of full field uncertainty, a system approach must be used that considers all parameters together.

Within the SPOTS project a physical reference standard has been developed which can be used for calibration of optical full field techniques. The reference standard is a beam loaded in a four point bending configuration which is integrated into a monolithic frame structure. The strain distribution in the gauge section can be described analytically as a function of its displacement and thus forms the basis for the comparison with the measured results.

We used this approach to demonstrate the calculation for the full field uncertainty of a DIC setup at strain levels between 50 μstrain and 1,500 μstrain on a gauge area of about 25 × 15 mm. The DIC system used contained three cameras. In this way, using a single experimental setup, the difference between a single camera 2D and 3D configuarations using both two and three cameras could be made.