抄録
It is well known that the first moisture increase of wood under constant bending load causes an increase in deflection, but the second and later adsorption of moisture tends to produce some recovery of deformation. This suggests that creep during adsorption depends upon the loading history of wood during past desorption/adsorption.
So, to clarify the effect of past loading history on recovery and creep of wood during adsorption, two types (D-set and A-set) of small bending-set wood specimens (0.3cm by 1.0cm by 12cm: Tx Lx R) were prepared from air-dried Hinoki (Chamaecyparis obtusa Endl.) and Buna (Fagus crenata Bl.). D-set specimens were subjected to desorption (MC 16%→8%) under constant loads. A-set specimens were subjected to adsorption (MC 8%→16%) under constant loads and then to the following desorption (MC 16%→8%) after unloading at about 16% MC. Then, the recovery of deflection and the creep during adsorption (from about 8% MC to about 25% ) were measured on these two types of bending set wood.
The recovery of D-set specimens during adsorption was significant at MCs below about 16% (the upper limit of MC interval where bending load was applied), but was not so significant at MCs above this value. On the other hand, the recovery of A-set specimens was not so significant at MCs below about 16%, but was significant at MCs above this value.
After making compensation for the effect of recovery of set, the resultant creep curves during adsorption for the two types of set specimens were similar to those for the control specimens with no loading-history. From these results, it is concluded that the experimental creep curve of wood subjected to bending set is the resultant of the superposition of recovery of set and mechano-sorptive creep deflection of wood with no loading-history.
