Influence of hygromechanical history on the longitudinal mechanosorptive creep of wood

Abstract

Abstract An experiment was performed on Norway spruce to simplify our understanding of mechanosorptive creep. Two well-matched sets of specimens were subjected to the same humidity history but loaded in four-point bending at different times. One set was loaded dry, and thus experienced a considerable creep at first adsorption (the so-called ++ effect). The other set was then loaded wet and only exhibited, together with the dry-loaded set, the usual pattern of creep increase during drying (- effect) followed by a partial recovery during remoistening (+ effect). Both sets converged to the same response after a few cycles. The results confirm that a single type of mechanosorption, combined with strain-dependent hygroexpansion and humidity-dependent viscoelascity, is sufficient to account for all observed features of longitudinal creep of wood at ambient temperature.