Abstract
In this study, wood disks of 30 mm in thickness cut from white birch (Betula platyphylla Suk) logs were dried at a constant temperature (40 °C). The drying strains including practical shrinkage strain, elastic strain, viscoelastic creep strain and mechano-sorptive creep were measured both tangentially and radially. The effects of moisture content and radial position on each strain were also discussed qualitatively. Overall, the difference of the practical shrinkage strain between the tangential and radial directions was proportional to the distance from the pith. The tangential elastic strain and viscoelastic creep strain were higher than these strains in a radial direction, and they all decreased with the decrease of moisture content. Additionally, there were opposite mechano-sorptive creep between tangential and radial directions.
Highlights
Cutting wood logs into thin disks is advantageous to better understand the evolution of drying stresses because of the possibility to control the moisture content gradient longitudinally and compare drying strains between the tangential and radial directions
Rice and Youngs found that MS creep is the major component of strain and it is a function of moisture change during drying of red oak [3]
For wood disks of Betula platyphylla, the tangential shrinkage was 1.12–1.54 times that in a radial direction and the difference of shrinkage ratio between the tangential and radial directions increased with decreasing moisture content
Summary
Cutting wood logs into thin disks is advantageous to better understand the evolution of drying stresses because of the possibility to control the moisture content gradient longitudinally and compare drying strains between the tangential and radial directions It provides a better method for using small-diameter or crooked logs than when lumber is cut lengthwise; this occurs because waste is much less when logs are cut into cross sections during the logging and sawing processes [1]. The components of drying strains comprise free shrinkage strain, elastic strain, viscoelastic creep strain and mechano-sorptive (MS) creep The survey of these strains will provide an effective foundation for forecasting and analyzing drying stresses.
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