Moisture-induced strains in earlywood and latewood of mature and juvenile woods in jack Dine from 3D-DIC measurements

The aim of this study was to evaluate the full-field swelling and shrinkage strains on the earlywood (EW) and latewood (LW) bands of juvenile and mature woods in jack pine. Moisture-induced strains in the tangential (epsilon(xx)) and radial (epsilon(yy)) directions were assessed by a 3D digital image correlation device composed of two high-resolution stereo-vision cameras on the cross-section of wood samples. The accuracy of strain measurements was verified by comparison with the conventional swelling/shrinkage coefficients. Matched samples were used to compare the growth ring strains with the radial density profiles of juvenile and mature woods. The results showed that swelling and shrinkage epsilon(xx) differed between juvenile and mature woods, for both EW and LW. Moreover, the shrinkage epsilon(yy) of EW differed from that of LW for both wood types. A significant interaction between wood type and EW-LW bands was found for swelling epsilon(yy), which was lower in EW and higher in LW of juvenile wood than of mature wood. Regression models revealed that swelling/shrinkage epsilon(yy) is more governed by growth ring features (width, density, and proportion of EW and LW) than epsilon(xx). Better correlations were obtained to predict epsilon(yy) in juvenile wood than for mature wood.