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

Abstract

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.

Challenges and solutions of environmental scanning electron microscopy characterisation of biomaterials: Application to hygro‐expansion of paper

“…To cope with these contrast and brightness changes that make the correlation unstable, GDIC enables adding extra degrees of freedom to the correlation to match the grey value spectrum of the images, which have been found to be essential for finding convergence. In all correlations, a polynomial shape function is used to describe the displacement field of which the optimal kinematic regularisation is iteratively found, similar to earlier studies [45,46] . This optimisation resulted in a 12 th ‐ and 2 nd ‐order polynomial in, respectively, longitudinal and transverse directions for the single fibres, a 13 th ‐ and 2 nd ‐order polynomial in, respectively, longitudinal and transverse directions for both fibres of the interfibre bonds and a 5 th ‐order polynomial in horizontal and vertical directions for the interfibre bond CS.…”

“…In all correlations, a polynomial shape function is used to describe the displacement field of which the optimal kinematic regularisation is iteratively found, similar to earlier studies. [45,46] This optimisation resulted in a 12 th -and 2 nd -order polynomial in, respectively, longitudinal and transverse directions for the single fibres, a 13 th -and 2 nd -order polynomial in, respectively, longitudinal and transverse directions for both fibres of the interfibre bonds and a 5 th -order polynomial in horizontal and vertical directions for the interfibre bond CS. The obtained displacement fields are converted to strain fields using a Green-Lagrange strain definition.…”

Monitoring structural scale composite specimens in a post‐buckling regime: The integrated finite element stereo digital image correlation approach with geometrically non‐linear regularization

“…This type of regularization applied to DIC is often denoted as 'integrated'. [35,41,43,46,[49][50][51] Any prior information regarding the sought quantity can be used to improve the convergence of the algorithm and find a solution. In this particular case, the displacement of interest must satisfy some basic properties guaranteed by the mechanical principles.…”

“…The major advantage of the global approach to DIC, used hereafter, is that one can precisely inject in the formulation the expected regularity of the displacement field from the beginning (e.g., a more or less strong constraint on the search space), [34][35][36][37][38][39][40][41][42][43][44] rather than projecting it a posteriori on a reduced basis (e.g., to obtain smooth derivatives). This kind of approach allows us to limit the influence of image noise on the displacement measurement or even the identification of constituent parameters.…”

“…A generalization based on the exploitation of test displacement fields from FE simulation was later proposed by Leclerc et al [47] This type of approach has been widely exploited on many problems. [39][40][41][42][43]46,48] Pierré et al [28] took advantage of this approach to extract displacement and use them as boundary conditions. To the knowledge of the authors, this last reference reports the most advanced piece of research on such subject.…”