Mechano-sorptive behavior of solid wood stressed in compression perpendicular to the grain

End-matched samples 1.0 inch along the grain, either 2.0 or 2.5 inches perpendicular to the grain, and 0.15 inch thick, were stressed in compression perpendicular to the grain while cycled in moisture content (MC). The end grain of each sample was coated with phenolic resin plus a strip of aluminum foil to ensure perpendicular-to-grain moisture movement. Samples were prepared from air-dried red pine and ponderosa pine, air-dried redwood, and green redwood. There were three stress levels of 60, 80, and 120 psi and three temperature levels of 90?, 122?, and 150?F. In general, the stressed samples were cycled between 15, 5, 15 percent MC, etc. The only exception was for the green redwood samples, which were dried under load to 15 percent and then cycled between 15, 5, 15 percent, etc. For all sample types the first desorption/adsorption cycle produced the most mechano-sorptive (MS) creep. The higher the drying temperature and compressive stress, the greater the MS creep. The greatest amount of MS change occurred during the drying of redwood from green MC to 15 percent MC at 122?F and 120 psi. An attempt to dry green redwood at 150?F and 120 psi produced immediate chaotic buckling and collapse. The MS creep curves for these samples stressed in compression perpendicular to the grain are strikingly similar to those obtained for flexural samples. This suggests a common underlying mechanism for MS creep in the two types of samples despite the different methods of stressing the wood.

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