Elastic response in wood under moisture content variations: analytic development

Abstract : Creep evolution of timber structures results from the interaction between mechanical stresses due to different loads and hydric stresses due to moisture content variations. This paper deals with a thermodynamic approach in order to take into account a realistic elastic behavior under moisture content variations. In this context, memory effect, experimentally observed, is introduced employing a mechano-sorptive stress driven by a function dependent of the moisture content variations. This new internal thermodynamic variable enables to define an original separation of the free energy into an instantaneous recoverable part and a stored part during the last drying phase. This energy enables the modeling of the nonreversible strain process during the unloading phase. The locate state method is employed in order to define the thermodynamic function which traduces an indirect hereditary behavior between moisture content history and the stress state in the material.