Bending creep behavior of hot-pressed wood under cyclic moisture change conditions

This study examined the bending creep behavior of hot-pressed wood during c yclic moisture changes. Sugi (Cryptomerica japonica D. Don) specimens were pressed in the radial direction under six combinations of nominal compressi ve strain (33% and 50%) and press temperatures (140 degreesC, 170 degreesC, 200 degreesC). Creep tests were conducted at 20 degreesC with three cyclic relative humidity changes between 65% and 95% under 25 % of short-breaking stress. The effect of moisture content (MC) change on elastic compliance a nd mechanosorptive (MS) compliance was investigated. The relation between M S compliance and thickness swelling was studied. The results indicated that total compliance increased over the history of cyclic moisture changes; an d its behavior was closely related to the changes in MC and thickness swell ing. The total compliance increased during adsorption and decreased during desorption. Elastic compliance increased linearly with MC and was dependent on press temperature and compression. With increasing MC change, MS compli ance increased during adsorption and decreased during desorption. The first adsorption led to greater MS compliance than did the subsequent adsorption with the same amount of MC change. In general, the elastic parameter K-E a nd the MS parameter K-M increased with compression and decreased as the pre ss temperature increased. The MS parameter K-M was apparently greater than the elastic parameter K-E. The MS parameter K-M increased with swelling coe fficient K-SW of the hot-pressed specimen during adsorption and decreased w ith an increasing shrinkage coefficient K-SH, during desorption.