The creep of wood destabilized by change in moisture content. Part 1: The creep behaviors of wood during and immediately after drying

Abstract

To better understand mechano-sorptive creep, creep behaviors were compared in wood samples during the drying process, immediately after drying, and after a long conditioning under constant humidity and temperature. Creep was greater in the sample tested immediately after drying than in the sample conditioned for a long time under relative humidity equal to that after drying, despite the fact that these samples had almost the same moisture content (MC). While the wood that has been moisture-conditioned for a long time is in a stable state, the wood tested immediately after the drying is presumed to be in an unstable state. Moreover, creep of the sample tested during the drying process was greater than that of the sample tested immediately after the drying. It has also been found that the instability decreased with time, indicating that stabilization and destabilization occur simultaneously during the drying process. In recent studies, a decrease in the elastic modulus and an increase in the fluidity of wood immediately after a change in MC or temperature have been reported. These findings are attributed to the instability caused by changes in MC or temperature. Based on the results of the present study and recent studies, we consider the increase in the fluidity of wood as the MC changes to be attributable to instability.

Variation of Drying Strains between Tangential and Radial Directions in Asian White Birch

“…Wu and Milota investigated the tangential MS deformations of Douglas fir in both desorption and absorption processes [4,5]. Takahashi et al found that the creep behaviors of Japanese cypress are different during the drying process, immediately after drying, and after a long period of conditioning under constant humidity and temperature [6]. Perre and Passard proposed a comprehensive model to predict drying stress evolution based on MS creep at different temperature levels [7].…”

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.…”

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).…”