The full-field swelling strains (in-plane) and displacements (out-of-plane) of a tropical hardwood [huayruro (Ormosia coccinea (Aubl.) Jacks.] were measured at a tissue level by three-dimensional digital image correlation (3D-DIC) technique. Swelling strains in tangential (Ɛxx) and radial (Ɛyy) directions and displacements in longitudinal direction (Z-axis) were measured on the cross section of wood samples from the dried condition under P2O5 to moisture adsorption condition under three steps of relative humidity (RH) (55%, 75%, and 90% RH) and at a constant temperature of 20 °C. Global swelling coefficients (α) were also calculated and compared with 3D-DIC strains. Ɛxx, Ɛyy, and Z-axis displacement data were separately extracted from fiber- and banded parenchyma-dominated zones. The density variation between tissues was determined by X-ray densitometry. Huayruro wood had a homogeneous Ɛxx, while a different Ɛyy was observed between fiber- and banded parenchyma-dominated zones at all RH conditions. The density of the fiber tissue was more than twice as high as that of the axial parenchyma tissue. Moreover, an opposite behavior was found between tissues in longitudinal directions (Z-axis displacement), showing that parenchyma tissue swells, while fiber tissue shrinks after moisture adsorption regardless of RH level. The fiber shrinkage in the longitudinal direction intensified with moisture adsorption increasing, while parenchyma swelled at the same proportion. Results revealed a complex interaction between fiber- and banded parenchyma-dominated tissues at the three principal directions of wood after moisture adsorption. The dimensional changes at a tissue scale appear to be governed by the stiffer cell component and will depend not only on stiffness/density values but also on the proportion of each tissue composing wood.

中文翻译：

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热带硬木红豆中纤维和薄壁组织的膨胀应变评估

组织之间的密度变化通过 X 射线密度测定法确定。Huayruro 木材具有均匀的 Ɛxx，而在所有 RH 条件下，在纤维和带状薄壁组织主导区域之间观察到不同的 Ɛyy。纤维组织的密度是轴向薄壁组织密度的两倍多。此外，在纵向（Z 轴位移）的组织之间发现了相反的行为，表明薄壁组织膨胀，而纤维组织在吸湿后收缩，而与 RH 水平无关。随着吸湿性的增加，纤维纵向收缩加剧，而薄壁组织以相同的比例膨胀。结果表明，吸湿后木材三个主要方向上的纤维和带状薄壁组织主导组织之间存在复杂的相互作用。