Constitutive modelling and computational simulation of nip mechanics and winding of paper rolls

摘要

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.