Changes in the mechanical properties of wood during a period of moisture conditioning

Changes in the modulus of elasticity (MOE), modulus of rupture (MOR), and s tress relaxation in the radial direction of wood (hinoki: Chamaecyparis obt usa) moisture-conditioned by the adsorption process from a dry state and by the desorption process from a moisture content slightly below the fiber sa turation point were investigated. The MOE and MOR of wood conditioned by th e adsorption process showed significant increases during the later stages o f conditioning when the moisture content scarcely changed. However. with th e desorption process they did not increase as much during later stages of c onditioning, though they increased during early stages of conditioning when the moisture content greatly decreased. The stress relaxation of wood decr eased with an increase in the conditioning period with both the adsorption and desorption processes. These results suggest that wood in an unstable st ate. caused by the existing state of moisture differed from that in a true equilibrium state shows lower elasticity and strength and higher fluidity t han wood in a true equilibrium state. Furthermore. the present study demons trates that the unstable states of wood induced during the course of drying , desorption. and possibly adsorption of moisture are slowly modified as wo od approaches a true equilibrium state.