Bending creep behavior of wood under cyclic moisture changes

This study examined the bending creep behavior in the longitudinal directio n of six species under cyclic moisture content (MC) changes. For each speci es, tests were made at 20 degrees C with five cyclic relative humidity chan ges between 65% and 95%, beginning from moisture adsorption. A load corresp onding to 25% of short-term breaking load of the species was applied to the radial section of each specimen with four-point bending. The effect of MC change on instantaneous compliance was also investigated under the same con dition. The quantitative relation between mechano-sorptive (MS) compliance and MC change was examined, and the material parameter K-M for the relation in specific sorption was determined. Results indicated that the total comp liance in the six species with different behavior increases with sorption t ime. As an integral part of total compliance, instantaneous compliance chan ges linearly with MC and influences to a greater or lesser extent the total compliance behavior. In general, with increasing MC change, the MS complia nce linearly increases during the first adsorption and all desorption and d ecreases slightly during subsequent adsorption. The material parameter K-M varies markedly not only with species but also with specific sorption. The first adsorption causes the largest deformation, followed by desorption.