Regularised digital-level corrections for infrared image correlation

Abstract

Global digital image correlation (DIC) applied to infrared images is considered for a test where very significant and localised laser heating is applied. Because of temperature changes and high gradients, digital levels are to be corrected in addition to the displacement registration. Digital-level corrections and kinematics are decomposed over an unstructured mesh to account for steep gradients. A regularisation strategy is used to mend ill-posedness penalising rapid variation of corrections and displacements. High gradients motivate further softening of the regularisation (i.e. reduction of the regularisation length scale) based on prior estimates. The methodology is tested on different experimental cases in which DIC residuals are drastically reduced and systematic displacement errors are cut down to pixel after grey-level corrections (performed on numerical cases). Additionally, the regularisation improves the convergence speed as well as the quality of the sought fields. The capability of the code to account for blur corrections is illustrated on a practical case.

Keywords:

• Global DIC
• grey-level correction
• regularisation
• thermomechanical fields

Notes

No potential conflict of interest was reported by the authors.

1 In the context of thermal IR cameras, grey levels are more usually termed as digital levels, and after a suited calibration they are converted into temperatures under the assumption of observing a surface whose emissivity is known. In order to keep the discussion general, the ‘grey-level’ terminology is preferred hereafter and will be used all along the remainder of the paper.