Transient wrinkling analysis of steel web rolling

Abstract

In this study a mechanism of wrinkles were studied in terms of stress wave propagations and interactions between web edges using the explicit time integration finite element code, LS-DYNA. During the hot rolling of steel web for thickness reduction, the roller speed is constantly changing for constant gage control. It was shown from this study that this sudden change of speed itself could cause wrinkling without in-plane shear stress introduced to the web span from outside. Tensile stress wave is generated by sudden increase of roller speed, and the wave propagates and reflects back and forth while interacting with free edges of the web to generate compressive stress in CMD resulting in wrinkling in MD. As the thickness reduction of the web repeats, front and end edges are no longer on a straight line. The edge of either end of web span may change to the shape of tongue or fishtail. The width of the web is relatively constant except very front and end. Tail-out phase, when the very last part of the web exits the roller, causes sudden change of web width followed by complete release of tensile force. These extreme disturbances cause complete different behaviors of web: severe wrinkling and large vibration. A precise analysis by using the LS-DYNA is carried out and it is concluded that these are sufficient for the permanent wrinkling, fold-over[1] [2].