EFFECT OF CREEP AND MECHANOSORPTIVE EFFECT ON STRESS DEVELOPMENT DURING DRYING

Constitutive equations to quantify wood deformation under combined mec hanical loading and moisture content change [1] were coupled with the moisture distribution developed during drying to predict stress and st rain in 50 by 190-mm Douglas-fir heartwood lumber. Two combinations of temperature and relative humidity were used to dry the wood. The over all board shrinkage and the immediately released and set strains were measured as a function of time. Those strains were compared with analy tic results, which showed good agreement. The roles that four strain c omponents played in the development of stress both at board surface an d center were compared for different drying conditions. The significan ce of creep and mechano-sorptive strain in relieving the stress was de monstrated by varying the model parameters.