Analyzing the accumulative roll bonding deformation zone behavior by FEM, upper bound, and experimental methods

Abstract

Kinematically admissible velocity field assumption is a significant step in analyzing metal forming processes by the upper bound method (UBM). While the rotational triangular velocity field is the most compatible one in simple rolling, there is no evidence for prevailing of this velocity field in accumulative roll bonding (ARB). Accordingly, in this article, the geometry of the prevailing velocity field at the deformation zone of simple rolling (SR), and twice-rolled ARB samples were investigated through two distinct methods including experimental tests, and finite element simulation (FEM). It was proved that: 1) rotational triangle velocity field is quietly detectable in SR and ARB samples, 2) at the strip contact surfaces of ARB samples, the surface discontinuities affect the geometry of velocity field, and 3) the number of appeared rotational triangles at the deformation zone can be related to the initial roll diameter/initial sheet thickness ratio (D0/H0 while ignoring roller flattening). These results were used to propose an angular velocity field containing a discontinuity at the ARB strip interfaces. In the next step, the effects of three independent parameters including strip/rollers friction, the angular velocity of rollers, and strip's yield strength on the geometry of the prevailing velocity field were evaluated for both SR and ARB at two different D0/H0 and thickness reductions.