Accurate Strain Field Measurement During Strip Rolling by Exploiting Recurring Material Motion with Time-Integrated Digital Image Correlation

Background: 95% Of all metals and alloys are processed using strip rolling, explaining the great number of existing strip rolling optimization models. Yet, an accurate in-situ full-field experimental measurement method of the deformation, velocity and strain fields of the strip in the deformation zone is lacking. Objective: Here, a novel time-Integrated Digital Image Correlation (t-IDIC) framework is proposed and validated that fully exploits the notion of continuous, recurring material motion during strip rolling. Methods: High strain accuracy and robustness against unavoidable light reflections and missing speckles is achieved by simultaneously correlating many (e.g. 200) image pairs in a single optimization step, i.e. each image pair is correlated with the same average global displacement field but is multiplied by a unique velocity corrector to account for differences in material velocity between image pairs. Results: Demonstration on two different strip rolling experiments revealed previously inaccessible subtle changes in the deformation and strain fields due to minor variations in pre-deformation, elastic recovery, and geometrical irregularities. The influence of the work roll force and entry/exit strip tension has been investigated for strip rolling with an industrial pilot mill, which revealed unexpected non-horizontal material feed. This asymmetry was reduced by increasing the entry strip tension and rolling force, resulting in a more symmetric strain distribution, while increased distance between the neutral and entry point was found for a larger rolling force. Conclusions: The proposed t-IDIC method allows for robust and accurate characterization of the strip’s full-field behavior of the deformation zone during rolling, revealing novel insights in the material behavior.