Thermal treatment (TMT) impacts the mechanical strength of wood. Investigating the compressive strength (CS) of thermally treated wood with variable growth ring orientation is helpful to better understand the effect of TMT on mechanical performance of wood. Specimens, cut from spruce wood, were classified according to two growth ring orientations, namely 10 degree (f_c10) and 40 degree (f_c40), these two situations commonly exist in practice. Six replicates from each type were thermally treated with saturated steam at two different temperatures (180 °C and 210 °C), respectively. Dimensional changes, chemical composition, and microstructure of the specimens were monitored before and after TMT using FTIR spectroscopy and optical microscopy. Compressive stress of specimens was determined and, simultaneously, strain distribution was recorded using digital image correlation. The results show that TMT caused mass loss and shrinkage in tangential and radial directions. Changes in chemical composition were mainly due to hemicellulose degradation. For both treated and untreated samples, the CS perpendicular to the grain and deformation of f_c10 samples were higher and smaller than that of f_c40 samples, respectively. TMT results in brittle wood tissue, which hampered strain transfer along growth rings and changed failure modes of samples. Mechanical strength of f_c40 samples was sensitive to be impacted by TMT. Prior to TMT, failure modes of f_c10 and f_c40 specimens were shear deformation and growth ring buckling, respectively. After TM, failure modes of all specimens changed to shear failure parallel to growth ring boundaries. These structural changes mainly occurred in earlywood. The output of this work contributes to the effective application and scientific evaluation of mechanical performance of TMT wood by considering growth ring orientations.

热处理 (TMT) 会影响木材的机械强度。研究具有可变年轮取向的热处理木材的抗压强度 (CS) 有助于更好地了解 TMT 对木材机械性能的影响。从云杉木上切下的标本根据两个年轮方向进行分类，即 10 度 ( f _c 10) 和 40 度 ( f _c40），这两种情况在实践中普遍存在。每种类型的六个重复样品分别在两种不同的温度（180 °C 和 210 °C）下用饱和蒸汽进行热处理。使用 FTIR 光谱和光学显微镜监测 TMT 前后样品的尺寸变化、化学成分和微观结构。确定试样的压应力，同时使用数字图像相关性记录应变分布。结果表明，TMT 引起了切向和径向的质量损失和收缩。化学成分的变化主要是由于半纤维素降解。对于处理和未处理样品，f _c 10 样品的垂直于晶粒和变形的 CS高于和小于f _c分别为 40 个样本。TMT 导致木材组织变脆，这阻碍了应变沿年轮的传递并改变了样品的失效模式。f _c 40 样品的机械强度对TMT 的影响很敏感。在 TMT 之前，f _c 10 和f _c 40 试样的破坏模式分别是剪切变形和年轮屈曲。TM 后，所有试样的破坏模式都变为平行于年轮边界的剪切破坏。这些结构变化主要发生在早材中。通过考虑年轮取向，这项工作的成果有助于 TMT 木材机械性能的有效应用和科学评估。