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

J P M Hoefnagels,N Vonk,L Jacobs,K Van Dam

doi:10.1007/s11340-021-00781-y

J P M Hoefnagels, N Vonk + Show 2 more

Open Access

https://doi.org/10.1007/s11340-021-00781-y

Copy DOI

Abstract

Background95% 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.ObjectiveHere, 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.MethodsHigh 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.ResultsDemonstration 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.ConclusionsThe 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.

Highlights

Cold rolling is the most important processes considering metal forming
Over 95% of non-ferrous/ ferrous metals and alloys are processed by strip rolling into different shapes
The thickness of the strip is reduced by a certain amount, depending on the processing conditions, i.e. the work roll force, the entry and exit strip

Summary

Introduction

Cold rolling is the most important processes considering metal forming. Over 95% of non-ferrous/ ferrous metals and alloys are processed by strip rolling into different shapes, Generally, a tandem mill consisting of several rolling stands is used in strip rolling to achieve large thickness reductions. High industrial interest has led researchers to develop models that are used to better predict, analyze and understand the rolling process [3, 4, 6,7,8,9,10,11] Most of these models don’t take into account some key phenomena that are known to occur in the deformation zone: (i) pre-deformation in the material before it first touches the work roll, (ii) elastic recovery (spring-back) after the strip is processed, (iii) the gradient in strip velocity over the strip thickness. There is a continuous demand to further improve existing models To achieve this, it would be of great benefit if, by means of experiments, the full velocity and strain fields in the deformation zone between the work rolls could be accurately measured, which could be studied as a function of the various input parameters, e.g., the rolling force and strip tension. This data would allow direct identification of key strip rolling characteristics, including the neutral, entry, and exit point, and volume contraction

Objectives

Methods

Findings

Conclusion