Separation of drying strains and the calculation of drying stresses considering the viscoelasticity of red pine wood during drying

ABSTRACT

The objective of this study was to separate drying strains into elastic, viscoelastic, and viscous strains using free shrinkage and recovery from the deformation of slices at stress relief. The apparent shrinkage deformation was obtained by measuring the change in width of drying specimens during drying. Using the slice method, elastic and viscoelastic deformation were defined as the instantaneous change in width of a slice right after cutting and the change in the width of a slice with constant moisture content during 48 h, respectively. Viscous deformation, permanent and nonrecoverable deformation of wood, was defined as the difference in deformation between free shrinkage and the sum of the apparent, elastic, and viscoelastic deformations. These elastic, viscoelastic, and viscous strains were applied to a viscoelastic model, and coefficients of viscoelasticity and viscosity were derived. The drying stress and deformation of red pine wood at specific times during the drying process can be predicted using each coefficients and modulus of elasticity obtained by experiment.

KEYWORDS:

• Drying stress
• kiln-drying
• red pine
• strain
• viscoelasticity

Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2013R1A1A2012630). This study was carried out with the support of “Forest Science & Technology Projects (Project no. S111215L100120)” provided by Korea Forest Service. This study was supported by the Research Fellowship Program of the National Institute of Forest Science in 2016.