本文通过高分辨率显微镜和数字图像相关(DIC)分析了杉木环内收缩和膨胀的变化。管胞细胞不使用人工斑点图案,而是用作 DIC 分析的自然“跟踪点”,以评估全场应变作为生长环相对位置的函数。广角 X 射线衍射表征显示整个生长环的微纤维角度一致(约 11°)。随着从早材(EW)到过渡材和晚材(LW)湿变形的增量,获得了应变的高分辨率变化。在前一个生长环的 EW 和 LW 界面处观察到应变浓度。径向和切向的湿变形从之前的LW开始急剧减小,直到EW内的某个位置,即,由于先前的LW对EW的抑制作用,在界面处观察到较大的EW的湿变形。在水分解吸过程中,约束效应和各向异性变形与相对湿度(RH)水平无关。然而,随着吸湿过程中相对湿度的增加,对EW的约束作用减弱,导致受约束的EW的各向异性变形更大。当考虑湿变形作为含水量的函数时,没有发现明显的膨胀滞后。这项研究证明了在没有人工散斑图案的情况下使用 DIC 来表征环内收缩和膨胀的可行性。这些发现为解释木材与水的关系以及分层木材结构在调节湿气变形方面的适应性潜力提供了见解。由于先前的LW对EW的抑制作用,在界面处观察到较大的EW的湿变形。在水分解吸过程中,约束效应和各向异性变形与相对湿度(RH)水平无关。然而,随着吸湿过程中相对湿度的增加,对EW的约束作用减弱,导致受约束的EW的各向异性变形更大。当考虑湿变形作为含水量的函数时,没有发现明显的膨胀滞后。这项研究证明了在没有人工散斑图案的情况下使用 DIC 来表征环内收缩和膨胀的可行性。这些发现为解释木材与水的关系以及分层木材结构在调节湿气变形方面的适应性潜力提供了见解。由于先前的LW对EW的抑制作用,在界面处观察到较大的EW的湿变形。在水分解吸过程中,约束效应和各向异性变形与相对湿度(RH)水平无关。然而,随着吸湿过程中相对湿度的增加,对EW的约束作用减弱,导致受约束的EW的各向异性变形更大。当考虑湿变形作为含水量的函数时,没有发现明显的膨胀滞后。这项研究证明了在没有人工散斑图案的情况下使用 DIC 来表征环内收缩和膨胀的可行性。这些发现为解释木材与水的关系以及分层木材结构在调节湿气变形方面的适应性潜力提供了见解。
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A close-up view of the intra-ring variation of transverse shrinking and swelling in Chinese fir using digital image correlation without artificial speckle pattern
Herein, an intra-ring variation of shrinking and swelling in Chinese fir was analyzed through high-resolution microscopy and digital image correlation (DIC). Instead of using artificial speckle patterns, tracheid cells were utilized as natural “tracking points” for DIC analysis to assess full-field strain as a function of the relative position in the growth ring. Wide-angle X-ray diffraction characterization showed consistent microfibril angle (~ 11°) throughout the growth ring. High-resolution changes of strain were obtained as increments of hygro-deformation from earlywood (EW) to transition wood and latewood (LW). Strain concentrations were observed at the interface of EW and LW from the previous growth ring. The hygro-deformations in both radial and tangential directions decreased sharply from the previous LW until a certain position within EW, i.e., larger hygro-deformation of EW at the interface was observed due to the restraining effect of the previous LW on EW. During moisture desorption, the restraining effect and anisotropic deformation were independent of the relative humidity (RH) level. However, the restraining effect on EW was weakened with increasing RH levels during moisture absorption, resulting in greater anisotropic deformation of the restrained EW. No obvious swelling hysteresis was found when considering hygro-deformation as a function of moisture content. This research demonstrated the feasibility of using DIC without artificial speckle patterns to characterize the intra-ring shrinking and swelling. The findings provide insight into explaining wood–water relations and the adaptive potential of hierarchical wood structure in modulating hygro-deformation.