Creep behavior of wood under cyclic moisture changes: interaction between load effect and moisture effect

Abstract

Load and moisture content (MC) changes are the essential conditions for the mechano-sorptive (MS) creep of wood. An experiment was carried out on poplar to comprehend the mechano-sorptive creep from our point view. To restore the truth of MS creep behavior especially in the first humidifying stage, three well-matched sets of specimens were loaded in third-point bending under different humidity cycles. For each set, the applied load varied from 15 to 35 % of the short-term breaking load. It was found that the wood specimens exhibited a partial recovery during all the adsorption phase and deflection increase during all the desorption phase when low load level was applied. This phenomenon was very different from that a considerable creep at first adsorption observed by large amounts of researchers, which can be ascribed to the pseudo-creep due to the difference in the normal longitudinal swelling and shrinkage of wood. The results also indicated that an amplified load effect existed within the creep under cyclic moisture changes, which usually resulted in a fast increasing rate of viscoelastic creep to veil pseudo-recovery in the first humidifying stage.