Anisotropic Linear Viscoelasticity of Paper Sheet

• Published in: Nihon Reoroji Gakkaishi Vol. 7; no. 2; pp. 64 - 68
• Main Authors: UESAKA, Tetsu, MURAKAMI, Koji, IMAMURA, Rikizo
• Format: Journal Article
• Language: English; Japanese
• Published: The Society of Rheology, Japan 30.06.1979
• ISSN: 0387-1533; 2186-4586
• DOI: 10.1678/rheology1973.7.2_64

Anisotropic relaxation functions for some machine made papers were determined experimentally on the basis of the theory of linear viscoelasticity. For a material which has the orthotropic anisotropy and is subject to in-plane stresses, there are five independent in-plane relaxation functions, of which two (G12, G21) must be equal if the relaxation functions are symmetric (Gijkl=Gklij). These relaxation functions can be determined from the measurements of stress relaxation under the strip biaxial tensile condition in the three directions: the machine direction, the cross machine direction and the direction at 45 degrees to the machine direction. Measurements were made using a biaxial tensile tester for regular kraft paper samples, untreated filter paper samples, and the filter paper samples which had been immersed in water and then dried without restraints in order to release the so called dried-in stress.5) The estimated relaxation functions G11(t), G22(t) and G33(t) for filter paper samples (treated and untreated) showed similar time dependence which was expressed as Gii(t)=Giig(t), whereas those for kraft paper samples showed large differences among them. The differences between G12(t) and G21(t) were of the order of experimental errors. Anisotropic relaxation functions for these paper samples at t=1(sec) were represented schematically and compared with each other.