Determination of mechano-sorptive coefficients in Eucalyptus nitens wood under isothermal conditions

New experimental data is presented for the mechano-sorptive coefficient of Eucalyptus nitens wood analyzed in the longitudinal direction through the principle of total deformation superposition. The procedure was based on the determination of the partial strain components: elastic strain, free shrinkage strain, and mechano-sorptive strain. The methodology included the design of cantilever flexion tests of a wooden beam in an air-conditioned environment with variable relative humidity. These conditions made it possible to estimate each of the deformation components separately and then to determine the mechano-sorptive coefficient using the rheological stress-strain model. Deformations and displacements were evaluated with extensometers and displacement sensors, respectively, in conditions of 0 to 30% of the breaking load applied perpendicularly to beams oriented in the longitudinal direction. The cross-section was positioned according to the relation between the action line of the load applied and the growth rings orientation. The variation of moisture content was considered, decreasing from 22 to 12%. The results exposed a direct proportionality between the intensity of the applied load and the mechano-sorptive strains. The values determined for mechano-sorptive coefficients were 0.1224 and 0.1746 GPa-1 for loads applied to radial and tangential directions, respectively.