EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

95% of non-ferrous/ferrous metals and alloys are processed by strip rolling, arguably the most important metal forming process. Various models have been developed to optimize the multi-pass deformation process, yet further model advancement requires direct, accurate in-situ measurement of the full deformation and strain fields of the strip between the rolls. Standard (Local) DIC algorithms fail at this task, due to the harsh environment (oil, vibrations), high material velocity, challenging imaging conditions (obstructed viewing angle and field of view), unavoidable light reflections, and poor Digital Image Correlation (DIC) speckle pattern.

Therefore, building on our long-standing experience in developing advanced Global and Integrated DIC frameworks (e.g., Neggers et al. IJNME, 2016; Kleinendorst et al. CMAME, 2019), we derived (in a consistent mathematical setting) a novel Integrated DIC framework that fully exploits the knowledge of continuous, recurring material motion during strip rolling. High robustness against the above-mentioned challenges as well as high strain accuracy is achieved by simultaneous correlation of many (e.g. 200) image pairs, each correlated with the same average global displacement field but multiplied with a separate velocity multiplicator to account for (slight) differences in material velocity between image pairs.

The potential of the IDIC framework for recurring material motion is successfully demonstrated on two very different strip rolling experiments (operated at various settings), by unraveling subtle changes in the deformation and strain fields due to variations in pre-deformation, elastic recovery, and geometrical irregularities. Interestingly, these high-fidelity full-field results revealed that the residual stresses, which result from plastic bending on guiding rolls used to bring the strip to the pass line, cause asymmetric feeding of the strip into the mill, thereby altering the lubrication condition of the top/bottom strip surface.