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

A 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 an original idea of a 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 suit well to the upper part of the wood hygroscopic domain, whereas further hypothesis should be tested for the dry domain. A judicious choice in moisture activation of material parameters, combined with the blocking effect of hygrolock, agrees with recent experimental results on simplifying the description of the so-called ++ effect.