A three-dimensional mathematical model of the hygro-thermo-mechanical behavior of wood during drying

In the process of lumber drying, deformations and stresses are induced. Checking and warp are the most detrimental defects. The purpose of this study is to develop a three-dimensional mathematical model to predict the evolution of the hygro-thermomechanical behavior of wood during drying. This mechanical model will be used for the prediction of warp, maximum stresses, and residual stresses. The main characteristics of the model are that it takes into account the coupling effect between the directional creep strains (i.e., axial and transverse strains), the effect of external load, and it introduces the concept of a threshold plastic (permanent) strain which is dependent on stress level and time. The constitutive law for viscoelastic strain is based on a modified Burger model while the mechano-sorptive behavior is described through the Ranta-Maunus' approach. A cantilever-type wood specimen is proposed for the determination of the viscoelastic and mechano-sorptive parameters of the model, by measuring the surface strain both in tension and in compression.