Modeling Shrinkage Response to Tensile Stresses in Wood Drying II. Stress–Shrinkage Correlation in Restrained Specimens

Abstract

This article reports on the effect of tensile stresses, temperature, and target moisture content on shrinkage behavior of short and thin Western hemlock specimens as part of a series of papers dealing with these issues. All tests were performed perpendicular to fiber grain while drying at 40, 60, and 80°C to 17, 11, and 5% final moisture contents at each temperature. Four matched specimens were subjected to different restraints during each drying experiment, namely, zero restraint (free shrinkage), two static restraints of 3 and 6 daN and a dynamic restraint controlled by the drying process. The resulting shrinkage was measured by pairs of resistive transducers located on the middle part of each specimen. Shrinkage percentages, obtained after the tensile stress was released and all the viscoelastic strain recovered, were proven to be a strong function of stress value, moisture, and temperature. The analytical fit yielded high coefficients of determination (R 2 = 0.83–0.85, p < 0.05) for both structural directions tangential and radial, respectively.