Mechanosorptive Creep of Hemlock under Conventional Drying: I. The Determination of Free Shrinkage Strain

Abstract

The dynamic free shrinkage behavior of Western hemlock (Tsuga heterophylla) was investigated in order to provide the theoretical basis for the determination of drying mechanosoptive creep mechanism. Small specimens taken from five distinct positions within a log were dried at three constant temperatures (40, 60, and 80°C) and stepwise decreasing relative humidity conditions and their free shrinkage strain S in the tangential and radial directions was determined. The anisotropic shrinkage ratios G were also calculated and analyzed as functions of moisture content and temperature. The influential mechanism of the drying temperature, moisture range, and specimen position on the free shrinkage behavior was revealed. Two different function types were chosen to simulate the relationship between the free shrinkage strain and its variables (temperature, moisture, wood positions) for the specified moisture ranges.

Keywords:

• Anisotropic shrinkage
• Free shrinkage strain
• Mechanosorptive creep strain
• Wood

ACKNOWLEDGMENT

This work was supported by the Fundamental Research Funds for the Central Universities of China (Northeast Forestry University, No. 070-41410079).

Notes

^a Data in air-dried conditions.

^a “T” refers to the tangential direction and “R” refers to the radial direction.

^b Because of the great variability of shrinkage data for the pith section, an exponential function () was chosen in this case.

^a Free shrinkage strain at 40°C.