The creep of wood destabilized by change in moisture content. Part 2: The creep behaviors of wood during and immediately after adsorption

Abstract

The fluidity of wood remarkably increases during moisture changes. This phenomenon is termed mechano-sorptive creep. The mechanism of mechano-sorptive creep has been studied, including a previous report by our group. Here, creep tests in bending were carried out for wood during and immediately after adsorption of moisture and after a long moisture conditioning. The effects of the rate of moisture adsorption on creep were also examined. The results and conclusions are as follows: (I) Greater creep occurred immediately after the adsorption process as compared with that after a long moisture conditioning, whereas much greater creep occurred during the same adsorption process, similar to the case of drying. Therefore, during the changes in moisture, not only destabilization but also stabilization should occur simultaneously, so that the wood during the changing process is in a remarkably unstable state. (II) Smaller creep occurred immediately after a slower adsorption as compared with that immediately after a more rapid adsorption. This suggests that wood is more stabilized during a slower versus a more rapid adsorption process. However, difference in creep between the final stages of the slower and the more rapid adsorption process was scarcely found. This is considered to result from the difference in degree of stabilization caused by the different duration of both adsorptions. In other words, this result is only an outward appearance. (III) Greater creeps were recognized during larger changes in moisture content (Δu) during the adsorption processes corresponding to the drying process. Therefore, mechano-sorptive creep depends not only on Δu but also on the range of relative humidity (RH). Larger stabilization was found during the changing process of larger Δu.

The variation of tangential rheological properties caused by shrinkage anisotropy and moisture content gradient in white birch disks

“…In conclusion, for the nearly steady-state S 1 , where temperature was lower and RH was constant, V-C strain did not easily recover, whereas, for the non-steadystate S 2 , where temperature was higher and RH and MC varied significantly, V-C strain recovered easier and produced reverse V-C strain. Theoretically, compared with the steady-state, the creep is large for the non-steady-state (Takahashi et al 2004(Takahashi et al , 2005(Takahashi et al , 2006. This is the main cause for the differences in creep between the two schedules.…”

The creep of wood destabilized by change in moisture content. Part 3: The influence of changing moisture history on creep behavior

“…In our previous paper (Takahashi et al 2005) we described findings in relation to point (2). Greater creep occurred in tests under constant MC immediately after rapid adsorption of moisture than after slow adsorption, but the degree of creep during the changing processes was similar, regardless of the changing rate of moisture.…”

“…A memory effect of the 0% RH state was apparent, as outlined above. Takahashi et al (2005) reported that samples showed greater stabilization during slower and longer adsorption Brought to you by | University of Queensland -UQ Library Authenticated Download Date | 6/18/15 7:46 AM than in rapid and shorter processes. Accordingly, destabilization and stabilization occur simultaneously during adsorption processes, and the balance between them is affected by the adsorption rate.…”

“…Therefore, the apparent independence of MS creep on the changing moisture rate is in reality time-dependent. Takahashi et al (2004Takahashi et al ( , 2005 found that in both desorption and adsorption processes, greater Du causes greater bending creep deformations, and that the creep was greater in a higher RH range when the same amount of moisture was exchanged. At larger Du the stabilization effect was higher.…”

Time dependence of the orthotropic compression Young’s moduli and Poisson’s ratios of Chinese fir wood

“…A lot of investigations concentrated on the experimental determination and analytical expressions of the mechano-sorptive creep (Mukudai and Yata 1988;Hunt 1989;Toratti and Svensson 2000;Navi et al 2002;Takahashi et al 2004Takahashi et al , 2005Takahashi et al , 2006Dong et al 2010;Kaboorani et al 2013;Violaine et al 2015). However, the pure visco elastic creep is usually neglected in numerical models and received much less attention compared to the mechanosorptive effects (Liu 1993).…”