Distinguishing Strain Field Visualization Stability from Condition-Level Incremental Strain Accuracy in High-Temperature 2D Digital Image Correlation.

Abstract

High-temperature two-dimensional digital image correlation (2D-DIC) can produce spatially unstable strain fields and biased condition-averaged incremental strains, but these error signatures need not respond to the same processing. A smoother strain field is therefore not, by itself, evidence of improved scalar accuracy. We evaluated strain field visualization stability separately from extensometer-referenced, condition-level incremental strain accuracy. An MA956 specimen was tested at 600, 700 and 800 °C under 12 loading conditions spanning 500-2000 µε, with four manually triggered snapshots acquired per condition. The field path used affine registration, pixelwise four-snapshot median fusion and strain radius sensitivity analysis. The scalar path used only the original unfused images and compared four prespecified models under leave-one-temperature-out internal assessment. Increasing the strain radius from 10 to 15 grid points reduced the spatial standard deviation and P₉₅-to-median span by 22.7% and 16.6%, respectively, with little change in scalar RMSE. Controlled simulations with known ground truth showed that local non-affine disturbances primarily increased field dispersion, whereas isotropic scale changes induced approximately common-mode axial and transverse strain drift. Across 20 mechanical strain-magnification conditions, a common-mode-suppressed axial-transverse feature reduced RMSE from 439.7 to 49.8 µε. Guided by this mechanistic evidence, combining the feature with temperature terms yielded the lowest pooled out-of-fold RMSE of 76.27 µε in the experimental data, 69.7% below the raw axial strain baseline. Within the conditions examined, these results demonstrate that improved strain field visualization is insufficient evidence of scalar accuracy and support separate validation of field stability and condition-level incremental strain error.