Bamboo is structural gradient materials with hygroscopic properties. Understanding the variations in hygro-deformation behavior across the radial direction is crucial for managing the dimensional stability of bamboo. Herein, high-resolution microscopy and the digital image correlation (DIC) technique were combined to analyze the transverse shrinking and swelling of bamboo. Parenchyma cells were utilized as natural “tracking points” for DIC analysis to evaluate full-field strain at different radial positions, specifically the outer, middle and inner regions. The transverse shrinking and swelling of bamboo were found to exhibit a quasi-linear distribution in the tangential direction and a saddle-like distribution in the radial direction. The outer region, which had a higher fiber fraction, displayed greater and more isotropic hygro-deformation compared to the inner regions with fewer fibers. When relative humidity (RH) increased from 0% to 97%, the swelling ratio in the radial direction was 2.00, 1.55 and 1.22% for the outer, middle and inner regions, respectively. In the tangential direction, the swelling ratio was 1.75, 1.35 and 1.10%. The study also highlighted the differences in hygro-deformation between the fiber and parenchyma cells, with the fiber experiencing both greater shrinking and swelling compared to the parenchyma. Furthermore, the interactions between the fibers and parenchyma varied across different radial regions. Overall, this study demonstrated the use of individual bamboo cells as natural tracking points in DIC analysis and contributed to a better understanding of the relationships between bamboo and water, as well as the radial variation in shrinking and swelling of bamboo.

中文翻译：

---

利用数字图像相关技术评价竹子的横向收缩和膨胀

竹子是具有吸湿特性的结构梯度材料。了解径向方向上的湿变形行为的变化对于管理竹子的尺寸稳定性至关重要。本文结合高分辨率显微镜和数字图像相关（DIC）技术来分析竹子的横向收缩和膨胀。薄壁细胞被用作 DIC 分析的自然“跟踪点”，以评估不同径向位置（特别是外部、中间和内部区域）的全场应变。发现竹子的横向收缩和膨胀在切向方向呈现准线性分布，在径向方向呈现马鞍状分布。与纤维较少的内部区域相比，具有较高纤维分数的外部区域表现出更大且更多的各向同性湿变形。当相对湿度（RH）从0%增加到97%时，外、中、内区域径向膨胀率分别为2.00、1.55和1.22%。在切线方向上，溶胀率为1.75%、1.35%和1.10%。该研究还强调了纤维和薄壁组织细胞之间湿变形的差异，与薄壁组织相比，纤维经历了更大的收缩和膨胀。此外，纤维和薄壁组织之间的相互作用在不同的径向区域中有所不同。总的来说，这项研究证明了使用单个竹子细胞作为 DIC 分析中的自然跟踪点，有助于更好地理解竹子和水之间的关系，以及竹子收缩和膨胀的径向变化。