The variation of tangential rheological properties caused by shrinkage anisotropy and moisture content gradient in white birch disks

Abstract

Abstract The focus of this study is the variation of practical shrinkage strain, elastic strain, viscoelastic creep strain, and mechanosorptive creep characteristics of white birch (Betula platyphylla Suk) disks caused by shrinkage anisotropy (ShrA) and its interaction with moisture content (MC) gradient. The rheological properties of white birch disks have been analyzed as a function of MC based on two different drying schedules at constant and increasing temperature. The drying conditions influence the strains remarkably. The stress characteristics and stress reversal mechanism under the conditions of increasing temperature are discussed based on stress analysis diagrams. Under both drying schedules, the wood disks are initially subjected to tangential tensile stress, and with decreasing MC, the tensile stress turns into compressive stress. Before stress reversal, the stresses of ShrA and MC gradient are aligned in the same direction and then point in opposite directions.