The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Constitutive Modelling and Computational Simulation of Nip Mechanics and Winding of Paper Rolls

Kilwa Ärölä

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Mechanical Engineering for public examination and debate in Auditorium K3/118 at Helsinki University of Technology (Espoo, Finland) on the 1st of December, 2006, at 12 noon.

Overview in PDF format (ISBN 951-22-8513-4)   [145 KB]
Dissertation is also available in print (ISBN 951-22-8512-6)

Abstract

In this thesis the behaviour of paper rolls under different loading conditions as well as the winding process are studied using computational simulations. First, the mechanics of a rolling nip contact on a paper stack is investigated. The development of the micro-slip pattern of the contacting surfaces under the rolling nip is elaborated, in particular. It is found that the interlayer slippage between paper layers below the surface of the paper roll substantially influences the events taking place in the nip contact. This implies that a purely elastic, continuous simulation model cannot accurately describe the nip contact phenomena.

Second, the modelling of paper rolls is studied. Due to the immense computational cost of a full contact mechanical analysis of a paper roll, a much more effective continuum model with interlayer slippage for wound rolls of orthotropic material is developed. The constitutive behaviour of the roll is modelled using the theory of plasticity, with plastic shear deformation used to describe the layer-to-layer slippage. The model can be readily implemented in a modern finite element analysis software. The proposed model is used to study the stresses, interlayer slippage and permanent deformations in paper rolls loaded by nip rollers and clamping devices. To validate the model, the calculated nip contact results are compared to experimental findings. The advantages of the new model are computational efficiency as compared to a full contact mechanical model and the ability to effectively simulate the interlayer slippage, permanent deformations as well as hysteresis in repeated loading, any of which cannot be simulated using a purely elastic model.

Finally, a two-dimensional large deformation axisymmetric winding model for wound rolls of hyperelastic orthotropic material is developed. The roll build-up is modelled as an incremental accretion process, where successive pre tensioned hoops are shrunk-fit onto the underlying roll. The model is used to study the effects of the material parameters, winding speed, and tension profiles of the incoming paper web to the stresses in the finished paper roll.

This thesis consists of an overview and of the following 4 publications:

  1. K. Ärölä, R. von Hertzen. Development of sheet tension under a rolling nip on a paper stack. International Journal of Mechanical Sciences 47 (1) 2005, 110-133.
  2. K. Ärölä, R. von Hertzen. An elastoplastic continuum model for a wound roll with interlayer slippage. Finite Elements in Analysis and Design 42 (6) 2006, 503-517.
  3. K. Ärölä, R. von Hertzen. Deformation of a paper roll loaded against a nip roller. Journal of Structural Mechanics 38 (3) 2005, 55-58. © 2005 by authors.
  4. K. Ärölä, R. von Hertzen. Two-dimensional axisymmetric winding model for finite deformation. Helsinki University of Technology, Laboratory for Mechanics of Materials Research Reports, TKK-LO-38, 2006. Computational Mechanics, submitted for publication. © 2006 by authors.

Keywords: nip, winding, constitutive model, paper roll

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© 2006 Helsinki University of Technology

Last update 2011-05-26