| The faces of red wood beams 18" long, 0.9" wide, and 0.5" thick were covered with the exception of one wide face. Tension-face-open or compression- face-open beams without an internal vapor barrier, and beams with an internal vapor barrier located either 1/16", 2/16", 3/16", or 4/16" from the open face, were centrally loaded over a 16" span to 1200 psi and cycled between moisture contents of 15% and 5%, at 91{dollar}spcirc{dollar}F for about 4500 hours. Sorption through the compression and tension faces produced opposite deflections. After accounting for the effect of shrinkage and the induced bending moment on beam deflections, the curves for all beam types became similar to that for conventional beams. For beams with an internal barrier, the amount of mechano-sorptive creep was greater for tension-face-open beams than compression-face-open beams. For beams without the internal barrier, the mechano-sorptive creep was the same for the two types of beams. The surface layer gave the greatest contribution to the total mechano-sorptive creep. As the internal barrier was moved toward the neutral axis, thereby increasing the amount of involved wood substance, the total amount of mechano-sorptive creep increased at a decreasing rate.; End-matched samples either 2.0" or 2.5" long, 1.0" along the grain, and 0.15" thick were tested in compressive stress perpendicular to the grain while the moisture content was cycled between about 5% and 15%. Three stress levels of 60, 80, and 120 psi were employed. Temperatures of 90, 122, and 150{dollar}spcirc{dollar}F were used. The mechano-sorptive creep curves in compression perpendicular to the grain for all three species were equivalent to those obtained for flexural beams. The first desorption/adsorption cycle produced the greatest amount of mechano-sorptive creep per cycle. The greatest absolute amount of mechano-sorptive creep for a single desorption occurred during the drying of redwood from the green condition to 15% moisture content at 122{dollar}spcirc{dollar}F and 120 psi. An increase in drying temperature increased the mechano-sorptive creep for samples from the same wood species. The higher the compressive stress, the greater the mechano-sorptive creep. |
