Strain-inducing mechanism of a rolling nip on a paper stack

The rolling of a cylindrical drum on a stack of separate paper sheets is studied using the finite element method. A two dimensional model under plane strain conditions is considered. The material of the sheets is modeled by a linearly elastic orthotropic constitutive law. The friction between the various contacting surfaces is modeled by the conventional Coulomb's law. As a result of the FEM-calculations the time development of the displacements, stresses and strains of the paper layers is obtained. The slip behavior at the various contacting surfaces is presented. The results indicate the existence of an instant center in the stack demonstrated earlier experimentally. The micro-slip pattern of the contacting surfaces in the nip area and, particularly, at the trailing edge of the nip, seems to be the main reason for the tightening effect of the nip. The results are compared to the corresponding results for a solid elastic block under the rolling cylinder