1. IntroductionFuture customer requirements for higher quality of flat rolledproducts (i.e. strip thickness, strip flatness and strip surface freefrom defects) need a better understanding of the interactionbetween strip deformation in the roll bite and work roll surface(Fig. 1). This need is also due to the current trend of rolling millsto combine higher rolling speeds, larger reduction, harder steelgrades and thinner rolled strips, that all affect the three strip qual-ities (thickness, flatness and surface). The final goal is to decreaseproduct yield associated to these rolled strip quality defects andto improve mill productivity by minimizing roll degradation. Typi-cally, three main rolling conditions are used to produce flat steelproducts: hot, cold and temper rolling. Thick strips (thicknessfrom 30 cm to 1 cm) are rolled at around 1500 K under hot rollingconditions. The contact between the strip and the roll is a few∗Corresponding author. Tel.: +33 169335805.E-mail address: weisz@lms.polytechnique.fr (D. Weisz-Patrault).centimeters long. Thinner strips (thickness from 5 mm to 1 mm)are rolled at around 400 K under cold rolling conditions. Shortercontact lengths are obtained (around 10 mm). Finishing steps, forpacking for instance, are done under temper rolling conditions forvery thin strips (a few hundreds of micrometers) with very shortcontact lengths (a few millimeters). Product quality is quantifiedby terms of flatness, defect free surface and thickness homogene-ity. The different rolled materials (low or high alloy steels, lowor high carbon steels, stainless or special steels) behave differ-ently with respect to defects. Rotation speed of work rolls, rollingforce (pressure applied by backup rolls), incoming strip speed, striptemperature, cooling and lubrication systems orientation are sig-nificant parameters regarding quality issues. Modern rolling millscombine higher rolling speeds, larger reduction ratios, harder steelgrades and thinner rolled strips. Empirical settings do not applyanymore, thus to ensure a better product quality, knowledge offriction and lubrication in the roll gap becomes a very significantissue. Indeed, unknown shear stress and normal pressure as wellas lubrication conditions take place in the strip/roll contact, whereplastic deformations are generated, determining product quality.