In-plane hygro-viscoelasticity of paper at small deformations
2005 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 20, no 2, 139-149 p.Article in journal (Refereed) Published
A classic hygro-viscoelastic constitutive model applicable for the analysis of time and humidity-dependent stresses of paper structures using the finite element method (FEM) was investigated. For the evaluation of the parameters required to model two-dimensional behaviour, a procedure based on the interconversion of experimental creep source data at different moisture ratios is described. The procedure enables the selection of parameters for stable performance of the constitutive model to promote convergence of FEM simulations with combined mechanical and moisture boundary conditions such as prescribed tractions, displacements and moisture ratios. In order to account for the dependence of the moisture ratio of paper, an internal variable was used to shift the continuous spectral components of the relaxance matrix. Despite the assumption of orthotropic symmetry, a minor asymmetric behaviour was found on the transverse response during model validation of paperboard behaviour at uniaxial tensile testing conditions and constant levels of moisture ratio between 0.07 and 0.15. This phenomenon was found to be present when the time-dependent behaviour of the in-plane viscoelastic components differed. At higher strain levels (> 0.15% strain) and beyond the operating window of the model, the experimental findings show more profound asymmetry of the transverse response: this was probably caused by inelastic material behaviour. The model response to strain histories included some hereditary effects of the stress, which was found to agree well with the experimental results at small deformations. A numerical scheme was derived and used during implementation of the constitutive model in commercial FEM software. The solutions converged rapidly for the conditions investigated. After imposing higher moisture ratio at a given strain level, the stress levels were reduced and stress relaxation was shown during short-term simulations. Residual stress states were shown in the numerical simulations after unloading and changed moisture ratios, when hygroexpansion and the effect of clamped test pieces were included.
Place, publisher, year, edition, pages
2005. Vol. 20, no 2, 139-149 p.
creep, relaxation, measurement, mechanical properties, generating line spectra, experimental responses, stress, hygroexpansivity, interconversion, relaxation, moisture, behavior
IdentifiersURN: urn:nbn:se:kth:diva-14885ISI: 000230271800002ScopusID: 2-s2.0-20744432475OAI: oai:DiVA.org:kth-14885DiVA: diva2:332926
QC 201005252010-08-052010-08-05Bibliographically approved