Determination of linear viscoelastic material properties of paper for web mechanics in printing presses

Abstract

Analysis of multispan web handling systems such as printing presses requires that viscoelasticity is considered. Guided by the plane and anisotropic nature of paper webs and the relatively small strain levels in a printing press suggests the use of a two dimensional anisotropic linear viscoelastic constitutive model for a first order analysis of the web behavior.

In the present paper a novel procedure for determination of the material functions in such a model, based upon biaxial measurements during small uniaxial sinusoidal excitations of paper strips symmetrically around zero stress, was presented. The drawbacks of buckling of the paper strip during the compressive part of the load cycle was avoided by supporting the paper specimen between glass plates. The method enables in-plane viscoelastic characterization of paper grades in the frequency range 0.000238-10 Hz. The experimental set-up was tested for newsprint and paperboard. The results showed that the method offers the determination of the material functions during a steady-state response which is not the case in conventional set-ups using a static pre-strain in order to avoid buckling.

The experimental data were used for determination of appropriate material functions. The usefulness of the material model was verified by comparing model simulations with different driving stimuli in a tensile tester. The time dependent transverse strain response of paper due to stress relaxation was demonstrated. The comparison between model and experiments indicated that newsprint and paperboard exhibit some non-linear material behavior at the strain amplitude of 0.075 % chosen for obtaining the material parameters. The linear viscoelastic model described the Behaviour of the tested papers within the requirements of engineering accuracy for strain levels typical for many printing applications.