One-dimensional discrete formulation of a hygrolock model for wood hygromechanics

Abstract

International audiencea new 1D discrete formulation of hygrolock models is proposed for modeling wood time-dependent behavior. This discrete formulation is compared to an integral formulation presented in a previously published paper. Simulations with various humidity cycles are performed under constant stress (creep) or constant strain (relaxation) using first a hygrolock spring and then a generalized Kelvin-Voigt model with a time-spectral distribution of hygrolocks springs. The discrete formulation presented here, based on original idea of mixed series/parallel rheological model, is shown to be very practical for implementation in scientific numerical codes. In order to compensate a lack of complete data-set on wood material, a generic time and moisture-dependent material is proposed to compare the various models: this dataset could be re-used in other studies. Finally the relevance of hygrolock models for wood time-dependent behavior is discussed: it appears that hygrolock models suits well to the upper part of wood hygroscopic domain, whereas further hypothesis should be tested for dry domain. A judicious choice in moisture activation of material parameters, combined with the blocking effect of hygrolock, agree with recent experimental results on simplifying the description of so-called ++ effect

Chemical, colloidal and mechanical contributions to the state of water in wood cell walls

“…But water uptake is also essential for biological functions by generating growth stresses in trees [3] or by providing seed mobility [4]. While hygromechanical properties of wood have been extensively studied [5,6], the physicochemical basis for the interaction of water with cell-wall components are poorly understood. Previous approaches mostly had the central objective of long-term wood protection against moisture uptake.…”

Coupled two-dimensional modeling of viscoelastic creep of wood

“…Viscoelastic creep is a pure creep response solely inflicted by a load's magnitude and its duration. Even though pure creep for load-carrying wood in ordinary varying climate is small in magnitude when compared to, for example, mechano-sorptive creep (Toratti and Svensson 2000), its formulation is a fundamental basis for the description of wood behavior, impacted by all sorts of environment variation (Hanhijärvi 1995;Bonfield et al 1996;Hunt and Gril 1996;Hanhijärvi and Hunt 1998;Dubois et al 2005Dubois et al , 2012Colmars et al 2014;Reichel and Kaliske 2015b). Several series of experimental data on viscoelastic creep strains in different orthotropic directions of wood under constant tensile loading are reported in Schniewind and Barrett (1972), Hayashi et al (1993), Ando (2010), andO_ zyhar et al (2013).…”

Numerical and experimental approaches to characterize the mass transfer process in wood elements

“…As a final step, specific thermo-hygro-mechanical behavior must be considered when estimating the thermo-hygro stresses (Dubois et al, 2012;Colmars et al, 2014).…”