Moisture-dependent orthotropic properties of four Korean softwood species measured by digital image correlation

Abstract This study determined the moisture-dependent orthotropic tensile behavior of four Korean softwood species—Korean pine ( Pinus koraiensis ), larch ( Larix kaempferi ), red pine ( Pinus densiflora ), and Japanese cedar ( Cryptomeria japonica )—at three moisture-content (MC) states (6%, 19%, and green/saturated) across six anatomical loading configurations (LR, LT, TR, RT, LRA, LTA). Full-field surface strains were measured using stereo digital image correlation (DIC) with a 15/8 pixel facet/step, a 0.024-pixel calibration residual, and 20 fps acquisition at a 0.5 mm/min loading rate. Ultimate tensile strength, longitudinal and transverse moduli, Poisson’s ratios, and shear moduli were extracted from the DIC. Longitudinal modulus and tensile strength decreased monotonically with increasing MC for all four species, whereas the matrix-controlled transverse moduli, shear moduli, and Poisson’s ratios decreased more steeply and with greater scatter, consistent with their stronger dependence on the moisture-plasticized cell wall matrix. Directional anisotropy ( E L / E R ) was amplified by moisture in three of the four species, and the four loading directions partitioned into moisture-independent (TR, LR) and moisture-dependent (LT, RT) failure regimes governed by the evolving earlywood/latewood modulus mismatch. The resulting moisture-adjusted orthotropic dataset provides direct constitutive input for finite-element analysis of CLT, glulam, and mass-timber connections under variable in-service moisture.