Next Article in Journal
Green Finance Empowering Forestry New Quality Productivity: Mechanisms and Practical Paths
Previous Article in Journal
An Empirical Study on the Effects of the “Sky Window” Policy on Household Income in Rural Communities: Evidence from Wuyi Mountain National Park
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Forests
Volume 16
Issue 9
10.3390/f16091444
forests-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

A Multiscale Investigation of Cross-Sectional Shrinkage in Bamboo Culms Using Natural-Speckle Digital Image Correlation During Drying

by
Chengjian Huang
1,2,
Yongjie Bao
1,2,
Neng Li
1,2 and
Junfeng Hou
3,*
1
China National Bamboo Research Center, Hangzhou 310012, China
2
Key Laboratory of High Efficient Processing of Bamboo of Zhejiang Province, Hangzhou 310012, China
3
College of Chemistry and Materials Engineering, Zhejiang A&F University, Hangzhou 311300, China
*
Author to whom correspondence should be addressed.
Forests 2025, 16(9), 1444; https://doi.org/10.3390/f16091444
Submission received: 7 August 2025 / Revised: 6 September 2025 / Accepted: 8 September 2025 / Published: 10 September 2025
(This article belongs to the Section Wood Science and Forest Products)
Browse Figures
Versions Notes

Abstract

Bamboo cracking is primarily attributed to the influence of moisture on its structure. Natural-speckle digital image correlation (DIC) was employed to characterize tangential shrinkage in cross-sections, using parenchyma cells as intrinsic speckle patterns. Shrinkage behavior during the 24 h drying process at a temperature of 103 °C across the external, middle, and internal layers was comparatively analyzed in bamboo nodal regions (NR), internodal regions (IR), and transitional zones (TZ, i.e., node–internode interfaces). Moisture had the most pronounced effect on NR, which consistently exhibited the highest moisture content and shrinkage ratios during the drying process. Notably, the drying shrinkage of the external layer was significantly greater than that of other layers. Specifically, the drying shrinkage strain ratio of the external layer of NR is 3.02 times higher than that of the internal layer, while for IR, it is 3.60 times higher. Furthermore, the external layer of NR exhibits substantial deformation during the initial stages of drying, with a drying shrinkage strain ratio of 5.96% for 2 h. The results demonstrated that shrinkage deformation in bamboo nodes was significantly greater than in other regions, offering valuable insights for developing strategies to mitigate bamboo cracking.

Graphical Abstract

1. Introduction

Bamboo is a naturally abundant, fast-growing, and renewable resource widely distributed across the world [1]. Round bamboo is often used directly without modification for structural applications such as beams and columns [1,2], and after processing, it is applied in engineering contexts such as scaffolding, flooring, walls, windows, doors, ceilings, roofs, rafters, and trusses [3,4]. Additionally, round bamboo has been extensively used in furniture manufacturing, particularly in traditional designs that whole bamboo culms are utilized as the primary material. Round bamboo furniture products range from tables, doors, chairs, beds, stools, to kitchen cabinets and more [3]. However, the unique structural characteristics present several limitations in the utilization of round bamboo [5], among which cracking is a significant challenge. Cracks often develop either during the drying process prior to fabrication or after prolonged use, severely limiting the round bamboo’s applicability. To address this issue, various methods have been employed to improve the dimensional stability and hydrophobicity of bamboo. These include injecting low-molecular-weight polymers into vessels and parenchyma cells [6,7], and applying advanced technologies such as microwave drying [8], freeze-drying [9], high-frequency vacuum drying [10], and superheated steam treatment [11]. Surface coatings like paint and varnish are also commonly used to reduce moisture transmission and deformation [12]. While these methods improve bamboo’s dimensional stability or moisture resistance, none fully resolve the cracking problem. Effectively addressing this issue requires an understanding of the structural mechanisms through which moisture affects bamboo, a non-homogeneous material.
The phenomenon of wood cracking is attributed to structural characteristics that influence the processes of shrinking and swelling. These characteristics include the microfibril angle (MFA) [13], the arrangement of cells, and the intercellular interactions [14]. Concurrently, there are structural disparities between earlywood and latewood in wood, with latewood demonstrating higher wet deformation than earlywood [15,16,17]. This higher deformation is a significant cause of wood cracking. Numerous studies have examined the causes of bamboo cracking, focusing on moisture content (MC) and structural characteristics. These studies have laid a strong foundation for understanding the mechanisms behind cracking in round bamboo. Prolonged exposure to humidity fluctuations leads to hygroscopic swelling and desorption-induced shrinkage, which cause dimensional changes in bamboo. These are further influenced by the gradient distribution of fibers across the culm wall thickness [18,19]. At the cellular level, the moisture desorption causes bamboo cell deformation and displacement, concentrating shrinkage stress in the intercellular layers of fibers, thereby triggering cracks [20]. Additionally, fibers undergo greater shrinkage and swelling than parenchyma cells during deformation [21,22]. It has been shown that controlling the shrinkage of fiber cell walls and mitigating stress concentration in intercellular layers can effectively reduce cracking. On the macro scale, shrinkage and swelling strains increase from the inner to outer bamboo wall, based on microstructural changes [21]. Over 50% of cracks occur at the ends of round bamboo, while in the middle portion, 72% are concentrated at bamboo nodes [23]. Thus, bamboo nodes have been identified as key contributors to cracking. The bamboo culm features a unique structure, characterized by numerous nodes along its length. At the nodes, highly developed fibers form a complex three-dimensional network by intertwining conducting tissues [24]. Therefore, understanding the structural characteristics of bamboo nodes and their moisture response is crucial. However, there is currently a lack of research on node deformation under changing moisture conditions.
The digital image correlation (DIC) is an analytical method for non-contact measurement and analysis of images of objects during deformation [25]. Due to the advantages of simpler optical arrangement, easier specimen preparation, and lower experimental environment requirements compared to other non-contact full-field optical measurement techniques, DIC has a wide range of applications involving the quantification of microscopic deformation of wood [26], glue lines [27], elasticity [28,29], modulus of elasticity during bending [30], tensile [31] and compress strain [32], moisture strain due to moisture content, and even strain mapping in living trees [33]. It has also been used to assess delamination of man-made panels [34], porosity analysis [35], and other applications. It has recently been applied to assess shrinkage and swelling deformations in wood and bamboo materials [14,26,36,37,38], Since bamboo and wood are inherently porous materials, structures such as tracheid cells [39] and bamboo parenchyma cells [22] can serve as natural-speckles, which are used as tracking points in DIC analysis to calculate the strain characteristics of bamboo and wood. Data obtained through the natural-speckle method are unbiased [22,39], as confirmed by comparison with results from artificial speckle measurements. This greatly simplifies specimen preparation and makes the method suitable for studying the deformation characteristics of bamboo and wood under complex conditions, such as during drying and carbonization processes. When the ambient humidity changes, does bamboo undergo deformation due to its natural adsorption and desorption of moisture [22]. However, in practical applications, taking the drying process as an example, the accelerated loss of moisture inevitably leads to deformation that differs from that occurring under natural desorption. Therefore, employing a non-contact and natural-speckle DIC analysis to investigate the deformation characteristics of bamboo cross-sections during the drying process is of critical importance.
As evidenced by the literature review, moisture significantly influences bamboo cracking; however, there remains a scarcity of studies addressing its multi-scale effects on bamboo culms. This study aims to investigate the characteristics of cross-sectional dimensional shrinkage at multiple scales in Moso bamboo (Phyllostachys edulis) culms during the drying process, thereby testing the scientific hypothesis that moisture loss during drying exerts a more pronounced effect on the shrinkage deformation of nodal regions and the bamboo green layer. In this study, parenchyma cells were used as the natural speckles for DIC analysis to investigate tangential shrinkage characteristics of cross-section in bamboo during drying at three regions of bamboo culm: the nodal region, the internodal region, and the transitional zone. A comparative analysis of deformation characteristics at these locations was conducted with manual measurement testing. The results enhance understanding of the structure–moisture interaction of bamboo and provide a theoretical basis for developing technologies to suppress deformation and cracking in bamboo.

2. Materials and Methods

2.1. Materials

Four-year-old Moso bamboo was sourced from Huangshan, Anhui Province, China. Three bamboo culms, harvested from the same location, were utilized to prepare specimens, exhibiting a mean fresh density of 0.94 g/cm3, with diameters at breast height measuring 10.5, 11.1, and 10.8 mm, and a mean wall thickness of 8.24 mm. A total of three to four intact nodes and three to four intact internodes were observed in culms measuring between 1500 and 2500 mm above the ground, in accordance with Chinese National Standards [40]. The intact nodes and internodes in the middle of the culms were utilized to prepare the specimens. Specimens were taken from three distinct morphological regions of the culm: the nodal region (NR), the internodal region (IR), and the transitional zone (TZ), corresponding to the bamboo node, internode, and node–internode interface, respectively, as illustrated in Figure 1. The specimens were cut to dimensions of 20 × 20 × t (longitudinal × tangential × radial) mm, where t represents the culm wall thickness.

2.2. Methods

Following fabrication, the specimens were systematically marked at designated test points across three distinct anatomical layers through the wall thickness: external, middle, and internal layers, as defined in reference [18], as shown in Figure 1. To ensure that the fresh bamboo remained in a consistently moist state, all specimens were conditioned by immersion in distilled water for 48 h at ambient temperature (25 ± 1 °C) [22]. After immersion, the water on the surface of the specimens was removed. Initial mass and dimensional measurements at the marked locations were recorded by using precision instruments (±0.1 g for mass, ±0.001 mm for dimensions). The specimens were then placed in a forced-convection drying oven maintained at 103 ± 2 °C. Mass and dimensional data were subsequently recorded at 2, 6, 12, and 24 h intervals. After the drying process, the moisture content of each stage is obtained by calculating the ratio of the difference between the mass of specimens at each stage and the final adiabatic mass to the adiabatic mass. Additionally, the tangential drying shrinkage was calculated from the ratio of the difference between the tangential dimensions of specimens at each stage and the adiabatic tangential dimensions to the tangential dimension of the adiabatic material.
The tangential shrinking ratio was estimated as follows:
Δ L = L t − L 0 L 0 × 100
where ∆L represents the tangential shrinkage ratio of bamboo during the drying process, Lt denotes the tangential dimension of the specimen in the drying process, and L0 refers to the initial tangential dimension of the specimen.
Specimens for DIC analysis were randomly selected from the previously marked samples. The surface of each specimen was smoothed by a sliding microtome (HM 430, Microm, Walldorf, Germany). During the drying process at 103 ± 2 °C for 24 h, the cross-sections were examined once per minute by using a digital microscope (Vimba, Stuttgart Germany) to capture surface images through the glass window of the drying oven, following the methodology described in reference [39]. The images obtained during the drying process were imported into VIC-2D software (Version 7, Correlated Solutions Inc., Irmo, SC, USA) and analyzed in accordance with references [14,36,39]. Specifically, the step size and subset size were set to 2 and 27, respectively, for comparison of shrinking strain results.
The tangential shrinking strain was estimated as follows:
ε = l t − l 0 l 0 × 100
where ε represents the tangential shrinkage strain of bamboo during the drying process, lt denotes the tangential dimension of the specimen for DIC in the drying process, and l0 refers to the initial tangential dimension of specimen for DIC.
In this study, Welch-corrected simple effects analysis was employed to examine the variability of moisture content among different culm sections and the effect of different culm regions and wall layers on the cross-sectional drying shrinkage of bamboo. This analysis was conducted due to the violation of the assumption of chi-square (Levene’s test, p < 0.05). The analysis was then followed by a Games-Howell post hoc test performed at a significance level of p = 0.05.

3. Results

3.1. Moisture Content (MC)

As shown in Figure 2, the specimens tended toward an oven-dry state after approximately 6 h of drying, with significant differences in drying shrinking behavior observed among the three distinct bamboo regions. As demonstrated in Table 1 and Table 2, the statistical analyses revealed that there were significant differences in MC among the various sections of bamboo culms during the initial stage and the 2 h drying stage. Notably, the NR consistently exhibited significantly higher MC than both the IR and TZ throughout the drying process, regardless of whether the MC was above or below the fiber saturation point (FSP). While MC remained comparable between IR and TZ when above the FSP, a clear divergence emerged once MC fell below the FSP, particularly after 2 h of drying, with the TZ demonstrating a faster desorption rate.

3.2. Shrinkage Behavior Measured Manually

As shown in Figure 3a and Table 3 and Table 4, the external shrinkage did not differ significantly (p > 0.05) among the three sections of bamboo culms. However, Figure 3b and Table 3 and Table 4 demonstrate that the drying shrinkage ratio of both the middle-layer and internal layer in NR was significantly greater than that in both IR and TZ. The shrinkage ratio of the middle layer in NR was 26.17% and 24.71% higher than that of the middle layers in TZ and IR after a 24 h drying process, respectively. Meanwhile, the shrinkage ratio of the internal layer in NR was, respectively, 55.37% and 82.12% higher than that of the internal layers in TZ and IR.
Overall, Figure 3 revealed a consistent trend across all bamboo regions: the drying shrinkage ratios decreased sequentially from the external to the internal layers as drying time increased. Importantly, Table 3 and Table 5 showed that external shrinkage consistently exceeded both the middle and internal shrinkage across all specimens. significantly (p < 0.01). Subsequent to a drying period of 24 h, the external layer shrinkage ratios of the NR, TZ, and IR sections were 1.51, 2.25, and 2.71 times those of the internal layer, respectively.

3.3. Deformation Analysis by DIC

The tangential shrinkage characteristics of bamboo cross-sections in the drying process had been studied in detail by utilizing natural-speckle DIC analysis. The shrinkage strain cloud map was displayed in Figure 4. All regions, NR, IR, and TZ, exhibited significant shrinking deformation during the drying process. A progressive accumulation of strain was observed over time, with stabilization occurring after 12 h of drying. This trend was further supported by the results shown in Figure 5. As illustrated in Figure 4, the edges of the external layers in the IR and NR specimens appear red, indicating that the external layer in the NR and IR specimens exhibited abrupt changes in tangential shrinkage, with strain of 5.96% and 5.09%, respectively, after 2 h. In contrast, the TZ region demonstrated a more gradual progression. In all regions, the tangential strain consistently decreased from the external to the internal layers, a pattern also evident in Figure 5. Notably, Figure 5 highlights substantially greater strain magnitudes in the external and middle layers of NR compared to its internal layer. After a 24 h drying period, the drying shrinkage strain of the external layer in NR was 3.02 times that of the internal layer. The disparity between the external and internal layers in the TZ region is minimal, with the external layer’s drying shrinkage strain being merely 2.41 times that of the internal layer. Notably, the discrepancy between the external and internal layers in IR was the most significant, with the external layer exhibiting a dry shrinkage strain that was 3.60 times greater than that of the internal layer.

4. Discussion

In this study, DIC based on the natural-speckle method was employed to investigate the drying shrinkage behavior of different structural regions of the bamboo culms and wall during the drying process. The influence of moisture on the deformation of bamboo nodes was found to be notably greater than that on other regions. The external layer of the bamboo wall exhibited the highest ratio of drying shrinkage, followed by the middle layer, with the internal layer showing the least. Moreover, the external layer of the bamboo node experienced the most significant shrinkage deformation, which plays a critical role in the cracking behavior of bamboo materials.
A comparison of the results obtained from the DIC analysis and manual measurement revealed a general consistency in the trend of shrinkage ratio across the bamboo culms and bamboo wall layers. The degree of shrinkage deformation in the NR region was greater than that observed in the other two sections. Additionally, the shrinkage ratio and strain in the bamboo wall exhibited a gradient distribution from the external layer to the internal layer, which was consistent with the fiber distribution, this finding aligned with the observations reported by Zhu et al. [22]. Natural-speckle DIC had been demonstrated to be a suitable method for studying the drying shrinkage characteristics of bamboo in complex environments due to the advantages of non-contact and simpler optical arrangement. However, the DIC method is only capable of acquiring data regarding the surface shrinkage of the sample, it is limited in its ability to study the interior of the sample, as well as the cell and water migration processes. Consequently, it is necessary to employ DIC in conjunction with other methods to obtain a more comprehensive understanding of the subject.
The tangential shrinkage strain in wood is primarily constrained by transverse tis-sues such as rays [13,36,41]. In contrast, bamboo lacks ray tissue [42], and its shrinkage variability arises mainly from the gradient distribution of fibers across the bamboo wall [43]. From the internal to the external layers, the fiber volume fraction increases progressively [44]. Since fibers are composed predominantly of Hemicelluloses, which are rich in hydroxyl groups and highly sensitive to moisture fluctuations [45], the drying process consequently induces distinct deformation patterns. The external layer, with the highest fiber content, underwent the greatest water loss and shrinkage, followed by the middle layer, while the internal, with the lowest fiber content, exhibited the smallest shrinkage. This distribution resulted in a clear shrinkage ratios gradient across the bamboo wall, with the external layer having the highest shrinkage ratio, followed by the middle layer, and the internal layer having the lowest.
Furthermore, bamboo culms were distinguished by the presence of periodic nodes, a feature that distinguishes them from wood. The bamboo node’s enlargement was primarily attributable to the development of its fibers [24], resulting in an elevated initial moisture content. Simultaneously, the well-developed vascular bundles [24], including vessels for water transport, accelerated moisture loss during the drying process, thereby inducing more severe deformation. Although nodes partially retained the structural traits of internodes [46], the morphology of vascular bundles changed axially within the nodes [24,47]. The enlargement of conductive tissues further amplified deformation. While the width of vascular bundles remained relatively constant, their length, as well as that of vessels, decreased progressively from node to internode [24,48], potentially affecting the moisture transport efficiency. Consequently, both direct measurements and DIC analyses consistently showed that shrinkage and strain at nodes were significantly greater than those in the transition zones and internodes.

5. Conclusions

In this study, the nature-speckle DIC analysis was found to be a suitable approach for studying the deformation of bamboo in relatively complex application scenarios, such as drying and heat treatment processes, with the results obtained from the DIC analysis and manual measurement revealed a general consistency in the trend of shrinkage ratio across the bamboo culms and bamboo wall layers during drying. A salient finding of this study is that, during the drying process, the drying shrinkage deformation of bamboo nodes was greater than that of other parts of the bamboo culms (p < 0.1). Furthermore, a gradient distribution of the drying shrinkage was exhibited on the bamboo wall. This phenomenon was a primary cause of cracking and necessitated heightened attention during the drying process. The present study is subject to certain limitations imposed by the experimental conditions. The present study examined the macroscopic-scale drying shrinkage characteristics of bamboo during the drying process. Future research endeavors should integrate sophisticated measurement techniques to investigate the mechanisms of drying shrinkage in bamboo from the perspectives of various tissue types, cell types, and cell wall structure interactions.

Author Contributions

Conceptualization, C.H.; methodology, C.H.; validation, Y.B. and N.L.; formal analysis, Y.B.; investigation, C.H. and Y.B.; resources, C.H.; data curation, N.L. and C.H.; writing—original draft preparation, C.H.; writing—review and editing, C.H. and J.H.; visualization, N.L. and J.H. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by the Fundamental Research Funds for the Central Non-profit Research Institution of Chinese Academy of Forestry, CAFYBB2020MB009.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Fahim, M.; Haris, M.; Khan, W.; Zaman, S. Bamboo as a Construction Material: Prospects and Challenges. Adv. Sci. Technol. Res. J. 2022, 16, 165–175. [Google Scholar] [CrossRef]
  2. Simi, A.; Shirehjini, R.M.; Shi, D.; Demartino, C.; Li, Z. A Review on Round Bamboo Structural Applications and Perspectives. In 2019 International Bamboo Construction Competition; Springer: Cham, Switzerland, 2022; pp. 29–40. ISBN 978-3-030-91990-0. [Google Scholar]
  3. Akinlabi, E.T.; Anane-Fenin, K.; Akwada, D.R. Applications of Bamboo. In Bamboo; Springer International Publishing: Cham, Switzerland, 2017; pp. 179–219. ISBN 978-3-319-56807-2. [Google Scholar]
  4. Chaowana, K.; Sungkaew, S.; Chaowana, P. Bamboo—A Sustainable Building Material. In Multifaceted Bamboo: Engineered Products and Other Applications; Md Tahir, P., Lee, S.H., Osman Al-Edrus, S.S., Uyup, M.K.A., Eds.; Springer Nature: Singapore, 2023; pp. 85–110. ISBN 978-981-19-9327-5. [Google Scholar]
  5. Hauptman, J.; Haghnazar, R.; Marggraf, G.; Ashjazadeh, Y. Lightly Modifying Thick-Walled Timber Bamboo: An Overview. In Bamboo and Sustainable Construction; Palombini, F.L., Nogueira, F.M., Eds.; Springer Nature: Singapore, 2023; pp. 157–183. ISBN 978-981-99-0232-3. [Google Scholar]
  6. Su, N.; Fang, C.; Yu, Z.; Zhou, H.; Wang, X.; Tang, T.; Zhang, S.; Fei, B. Effects of Rosin Treatment on Hygroscopicity, Dimensional Stability, and Pore Structure of Round Bamboo Culm. Constr. Build. Mater. 2021, 287, 123037. [Google Scholar] [CrossRef]
  7. Yang, X.; Huang, Y.; Ye, C.; Lin, X.; Su, N.; Fei, B. Improving the Dimensional Stability of Round Bamboo by Environment-Friendly Modified Rosin. Constr. Build. Mater. 2023, 365, 130078. [Google Scholar] [CrossRef]
  8. Lv, H.-F.; Ma, X.-X.; Zhang, B.; Chen, X.-F.; Liu, X.-M.; Fang, C.-H.; Fei, B.-H. Microwave-Vacuum Drying of Round Bamboo: A Study of the Physical Properties. Constr. Build. Mater. 2019, 211, 44–51. [Google Scholar] [CrossRef]
  9. Xu, J.; He, S.; Li, J.; Yu, H.; Zhao, S.; Chen, Y.; Ma, L. Effect of Vacuum Freeze-Drying on Enhancing Liquid Permeability of Moso Bamboo. BioResources 2018, 13, 4159–4174. [Google Scholar] [CrossRef]
  10. Chang, F.; Liu, Y.; Zhang, B.; Fu, W.; Jiang, P.; Zhou, J. Factors Affecting the Temperature Increasing Rate in Arc-Shaped Bamboo Pieces during High-Frequency Heating. BioResources 2020, 15, 2656–2667. [Google Scholar] [CrossRef]
  11. Xue, Z.; Sun, F.; Liu, C.; Shang, L.; Yang, S. Enhancing Bamboo Properties through Rapid Steam Heat Treatment: A Study on Physical and Mechanical Performance. Constr. Build. Mater. 2025, 473, 140990. [Google Scholar] [CrossRef]
  12. Sain, A.; Gaur, A.; Khichad, J.S.; Somani, P. Treatment of Bamboo for Sustainable Construction Practise: A Comprehensive Review. IOP Conf. Ser. Earth Environ. Sci 2024, 1326, 12049. [Google Scholar] [CrossRef]
  13. Eder, M.; Schäffner, W.; Burgert, I.; Fratzl, P. Wood and the Activity of Dead Tissue. Adv. Mater. 2021, 33, 2001412. [Google Scholar] [CrossRef]
  14. Garcia, R.A.; Rosero-Alvarado, J.; Hernández, R.E. Full-Field Moisture-Induced Strains of the Different Tissues of Tamarack and Red Oak Woods Assessed by 3D Digital Image Correlation. Wood Sci. Technol. 2020, 54, 139–159. [Google Scholar] [CrossRef]
  15. Zhan, T.; Lyu, J.; Eder, M. In Situ Observation of Shrinking and Swelling of Normal and Compression Chinese Fir Wood at the Tissue, Cell and Cell Wall Level. Wood Sci. Technol. 2021, 55, 1359–1377. [Google Scholar] [CrossRef]
  16. Patera, A.; Derome, D.; Griffa, M.; Carmeliet, J. Hysteresis in Swelling and in Sorption of Wood Tissue. J. Struct. Biol. 2013, 182, 226–234. [Google Scholar] [CrossRef] [PubMed]
  17. Rafsanjani, A.; Derome, D.; Wittel, F.K.; Carmeliet, J. Computational Up-Scaling of Anisotropic Swelling and Mechanical Behavior of Hierarchical Cellular Materials. Compos. Sci. Technol. 2012, 72, 744–751. [Google Scholar] [CrossRef]
  18. Do Amaral, L.M.; Molari, L.; Savastano, H. Swelling and Shrinking Behaviour of Bamboo and Its Application on a Hygro-Mechanical Model. Wood Sci. Technol. 2025, 59, 36. [Google Scholar] [CrossRef]
  19. Chen, Q.; Fang, C.; Wang, G.; Ma, X.; Chen, M.; Zhang, S.; Dai, C.; Fei, B. Hygroscopic Swelling of Moso Bamboo Cells. Cellulose 2020, 27, 611–620. [Google Scholar] [CrossRef]
  20. Yuan, J.; Chen, L.; Mi, B.; Lei, Y.; Yan, L.; Fei, B. Synergistic Effects of Bamboo Cells during Shrinkage Process. Ind. Crops Prod. 2023, 193, 116232. [Google Scholar] [CrossRef]
  21. Huang, B.; Wang, X.; Chen, L.; Su, N.; Liu, L.; Luan, Y.; Ma, X.; Fei, B.; Fang, C. Impact of the Natural Structure of Cortex and Pith Ring on Water Loss and Deformation in Bamboo Processing. Constr. Build. Mater. 2024, 411, 134396. [Google Scholar] [CrossRef]
  22. Zhu, J.; Tan, Y.; Chen, K.; Peng, H.; Li, Z.; Jiang, J.; Lyu, J.; Zhan, T. Evaluation of Transverse Shrinking and Swelling of Bamboo Using Digital Image Correlation Technique. Ind. Crops Prod. 2024, 211, 118274. [Google Scholar] [CrossRef]
  23. Chen, Q.; He, Y.; Jiang, Y.; Qi, J.; Zhang, S.; Huang, X.; Chen, Y.; Xiao, H.; Jia, S.; Xie, J. Effect of Bamboo Nodes on Crack Generation of Round Bamboo and Bamboo-Based Composites during Drying. Eur. J. Wood Wood Prod. 2023, 81, 1201–1210. [Google Scholar] [CrossRef]
  24. Li, S.; Yang, S.; Shang, L.; Liu, X.; Ma, J.; Ma, Q.; Tian, G. 3D Visualization of Bamboo Node’s Vascular Bundle. Forests 2021, 12, 1799. [Google Scholar] [CrossRef]
  25. Schreier, H.; Orteu, J.-J.; Sutton, M.A. Image Correlation for Shape, Motion and Deformation Measurements: Basic Concepts, Theory and Applications; Springer: Boston, MA, USA, 2009; ISBN 978-0-387-78746-6. [Google Scholar]
  26. Garcia, R.A.; Rosero-Alvarado, J.; Hernández, R.E. Swelling Strain Assessment of Fiber and Parenchyma Tissues in the Tropical Hardwood Ormosia Coccinea. Wood Sci. Technol. 2020, 54, 1447–1461. [Google Scholar] [CrossRef]
  27. McKinley, P.; Sinha, A.; Kamke, F.A. Understanding the Effect of Weathering on Adhesive Bonds for Wood Composites Using Digital Image Correlation (DIC). Holzforschung 2019, 73, 155–164. [Google Scholar] [CrossRef]
  28. Li, L.; Gong, M.; Chui, Y.H.; Schneider, M.; Li, D. Measurement of the Elastic Parameters of Densified Balsam Fir Wood in the Radial-Tangential Plane Using a Digital Image Correlation (DIC) Method. J. Mater. Sci. 2013, 48, 7728–7735. [Google Scholar] [CrossRef]
  29. Zhu, J.; Peng, H.; Lyu, J.; Zhan, T. Evaluation of Orthotropic Elasticity of Gradient-Structured Bamboo by Microtensile Testing Combined with Digital Image Correlation Technique. Ind. Crops Prod. 2023, 203, 117097. [Google Scholar] [CrossRef]
  30. Hu, M.; Johansson, M.; Olsson, A.; Oscarsson, J.; Enquist, B. Local Variation of Modulus of Elasticity in Timber Determined on the Basis of Non-Contact Deformation Measurement and Scanned Fibre Orientation. Eur. J. Wood Wood Prod. 2015, 73, 17–27. [Google Scholar] [CrossRef]
  31. Nagai, H.; Murata, K.; Nakano, T. Strain Analysis of Lumber Containing a Knot during Tensile Failure. J. Wood Sci. 2011, 57, 114–118. [Google Scholar] [CrossRef]
  32. Tinkler-Davies, B.; Shah, D.U. Digital Image Correlation Analysis of Laminated Bamboo under Transverse Compression. Mater. Lett. 2021, 283, 128883. [Google Scholar] [CrossRef]
  33. Dahle, G.A. Influence of Bark on the Mapping of Mechanical Strain Using Digital Image Correlation. Wood Sci. Technol. 2017, 51, 1469–1477. [Google Scholar] [CrossRef]
  34. Davim, J.P.; Campos Rubio, J.; Abrão, A.M. Delamination Assessment after Drilling Medium-Density Fibreboard (MDF) by Digital Image Analysis. Holzforschung 2007, 61, 294–300. [Google Scholar] [CrossRef]
  35. Hass, P.; Wittel, F.K.; McDonald, S.A.; Marone, F.; Stampanoni, M.; Herrmann, H.J.; Niemz, P. Pore Space Analysis of Beech Wood: The Vessel Network. Holzforschung 2010, 64. [Google Scholar] [CrossRef]
  36. Garcia, R.A.; Rosero-Alvarado, J.; Hernández, R.E. Moisture-Induced Strains in Earlywood and Latewood of Mature and Juvenile Woods in Jack Pine from 3D-DIC Measurements. Wood Mater. Sci. Eng. 2023, 18, 570–579. [Google Scholar] [CrossRef]
  37. Peng, M.; Ho, Y.-C.; Wang, W.-C.; Chui, Y.H.; Gong, M. Measurement of Wood Shrinkage in Jack Pine Using Three Dimensional Digital Image Correlation (DIC). Holzforschung 2012, 66, 639–643. [Google Scholar] [CrossRef]
  38. Gao, Y.; Fu, Z.; Zhou, Y.; Gao, X.; Zhou, F.; Cao, H. Moisture-Related Shrinkage Behavior of Wood at Macroscale and Cellular Level. Polymers 2022, 14, 5045. [Google Scholar] [CrossRef] [PubMed]
  39. Zhan, T.; Liu, H.; Zhu, J.; Sun, F.; Peng, H.; Lyu, J. 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. Wood Sci. Technol. 2023, 57, 1369–1383. [Google Scholar] [CrossRef]
  40. GB/T 15780-1995; Testing Methods for Physical and Mechanical Properties of Bamboos. Standards Press of China: Beijing, China, 1995.
  41. Derome, D.; Griffa, M.; Koebel, M.; Carmeliet, J. Hysteretic Swelling of Wood at Cellular Scale Probed by Phase-Contrast X-Ray Tomography. J. Struct. Biol. 2011, 173, 180–190. [Google Scholar] [CrossRef]
  42. Ramful, R.; Sunthar, T.P.M.; Zhu, W.; Pezzotti, G. Investigating the Underlying Effect of Thermal Modification on Shrinkage Behavior of Bamboo Culm by Experimental and Numerical Methods. Materials 2021, 14, 974. [Google Scholar] [CrossRef]
  43. Darwis, A.; Iswanto, A.H.; Jeon, W.-S.; Kim, N.-H.; Wirjosentono, B.; Susilowati, A.; Hartono, R. Variation of Quantitative Anatomical Characteristics in the Culm of Belangke Bamboo (Gigantochloa pruriens). BioResources 2020, 15, 6617–6626. [Google Scholar] [CrossRef]
  44. Nogata, F.; Takahashi, H. Intelligent Functionally Graded Material: Bamboo. Compos. Eng. 1995, 5, 743–751. [Google Scholar] [CrossRef]
  45. Zhang, C.; Chen, M.; Keten, S.; Coasne, B.; Derome, D.; Carmeliet, J. Hygromechanical Mechanisms of Wood Cell Wall Revealed by Molecular Modeling and Mixture Rule Analysis. Sci. Adv. 2021, 7, eabi8919. [Google Scholar] [CrossRef]
  46. Huang, P.; Chang, W.-S.; Ansell, M.P.; Chew, Y.M.J.; Shea, A. Density Distribution Profile for Internodes and Nodes of Phyllostachys Edulis (Moso Bamboo) by Computer Tomography Scanning. Constr. Build. Mater. 2015, 93, 197–204. [Google Scholar] [CrossRef]
  47. Chen, S.-M.; Zhang, S.-C.; Gao, H.-L.; Wang, Q.; Zhou, L.; Zhao, H.-Y.; Li, X.-Y.; Gong, M.; Pan, X.-F.; Cui, C.; et al. Mechanically Robust Bamboo Node and Its Hierarchically Fibrous Structural Design. Natl. Sci. Rev. 2023, 10, nwac195. [Google Scholar] [CrossRef]
  48. Zhang, Y.; Xu, H.; Li, J.; Wang, H. Unraveling the Inhibition of Bamboo Node on Dry Shrinkage: Insights from the Specific Vascular Structure of Bamboo Node. Ind. Crops Prod. 2024, 211, 118193. [Google Scholar] [CrossRef]
Forests 16 01444 g001
Figure 1. Diagram of specimens and manual measurement: (a) internodal regions (IR), (b) transitional zones (TZ, i.e., node–internode interfaces), (c) nodal regions (NR); and (d) manual measurement. Author’s drawings.
Figure 1. Diagram of specimens and manual measurement: (a) internodal regions (IR), (b) transitional zones (TZ, i.e., node–internode interfaces), (c) nodal regions (NR); and (d) manual measurement. Author’s drawings.
Forests 16 01444 g001
Forests 16 01444 g002
Figure 2. Moisture content of specimens during the drying process. Author’s drawings.
Figure 2. Moisture content of specimens during the drying process. Author’s drawings.
Forests 16 01444 g002
Forests 16 01444 g003
Figure 3. The variation in dimensions of bamboo (a) the external layer, (b) the middle layer; and (c) the internal layer. Author’s drawings.
Figure 3. The variation in dimensions of bamboo (a) the external layer, (b) the middle layer; and (c) the internal layer. Author’s drawings.
Forests 16 01444 g003
Forests 16 01444 g004
Figure 4. In-plane shrinking-deformation. E: the location of the external tangential plane, M: the location of the middle tangential plane; and I: the location of the internal tangential plane. Author’s drawings.
Figure 4. In-plane shrinking-deformation. E: the location of the external tangential plane, M: the location of the middle tangential plane; and I: the location of the internal tangential plane. Author’s drawings.
Forests 16 01444 g004
Forests 16 01444 g005
Figure 5. In-plane shrinking strain during drying. Author’s drawings.
Figure 5. In-plane shrinking strain during drying. Author’s drawings.
Forests 16 01444 g005
Table 1. Average moisture content values (%), standard deviation, and number of samples.
Table 1. Average moisture content values (%), standard deviation, and number of samples.
Sample0 h (M ± SD, n) 12 h (M ± SD, n)6 h (M ± SD, n)12 h (M ± SD, n)
NR68.35 ± 2.08, 1821.35 ± 3.63, 180.69 ± 0.23, 180.17 ± 0.21, 18
TZ60.24 ± 1.04, 177.95 ± 1.87, 170.55 ± 0.24, 170.07 ± 0.33, 17
IR58.74 ± 1.22, 1814.73 ± 2.08, 180.66 ± 0.33, 180.04 ± 0.30, 18
Total62.48 ± 4.54, 5314.80 ± 6.08, 530.63 ± 0.27, 530.09 ± 0.28, 53
1 M: mean value, SD: standard deviation, n: number of samples.
Table 2. Results of simple effects analysis (Welch’s Correction) for the effect of drying duration on MC within different regions of bamboo culms.
Table 2. Results of simple effects analysis (Welch’s Correction) for the effect of drying duration on MC within different regions of bamboo culms.
DurationWelch’s F 1df1df2p-ValuePost Hoc Comparisons
(Games-Howell)
0 h143.467231.9650.000NR > TZ > IR **
2 h112.220232.0430.000NR > IR > TZ **
6 h1.751232.7440.189n.s.
12 h1.243232.5690.302n.s.
1 df: degrees of freedom, n.s.: not significant, ** p < 0.01.
Table 3. Average shrinkage ratios values (%), standard deviation, and number of samples.
Table 3. Average shrinkage ratios values (%), standard deviation, and number of samples.
SectionLayer2 h (M ± SD, n) *6 h (M ± SD, n)12 h (M ± SD, n)24 h (M ± SD, n)
NRExternal−5.30 ± 0.45, 11−8.73 ± 0.35, 11−8.19 ± 0.33, 11−8.32 ± 0.35, 11
Middle−4.59 ± 0.47, 11−6.27 ± 0.46, 11−6.37 ± 0.44, 11−6.46 ± 0.41, 11
Internal−4.50 ± 0.71, 11−5.40 ± 0.77, 11−5.43 ± 0.75, 11−5.50 ± 0.77, 11
TZExternal−6.27 ± 0.31, 14−8.28 ± 0.33, 14−7.85 ± 0.31, 14−7.97 ± 0.30, 14
Middle−4.13 ± 0.16, 14−4.91 ± 0.21, 14−5.04 ± 0.25, 14−5.12 ± 0.22, 14
Internal−3.18 ± 0.48, 14−3.46 ± 0.56, 14−3.45 ± 0.57, 14−3.54 ± 0.59, 14
IRExternal−5.67 ± 0.21, 12−8.47 ± 0.28, 12−8.04 ± 0.27, 12−8.18 ± 0.26, 12
Middle−3.77 ± 0.32, 12−4.85 ± 0.27, 12−5.05 ± 0.33, 12−5.18 ± 0.30, 12
Internal−2.31 ± 0.21, 12−2.86 ± 0.21, 12−2.95 ± 0.24, 12−3.02 ± 0.27, 12
* M: mean value, SD: standard deviation, n: number of samples.
Table 4. Results of simple effects analysis (Welch’s Correction) for the effect of region on shrinkage ratios within different layers of bamboo cells.
Table 4. Results of simple effects analysis (Welch’s Correction) for the effect of region on shrinkage ratios within different layers of bamboo cells.
DurationWelch’s Fdf1 1df2p-ValuePost Hoc Comparisons
(Games-Howell)
External0.016285.3030.984NR > TZ > IR
Middle32.085282.998<0.01NR > TZ **, NR > IR **, TZ > IR
Internal161.740285.728<0.01NR > TZ > IR **
1 df: degrees of freedom, ** p < 0.01.
Table 5. Results of simple effects analysis (Welch’s Correction) for the effect of layer on shrinkage ratios within different regions of bamboo culms.
Table 5. Results of simple effects analysis (Welch’s Correction) for the effect of layer on shrinkage ratios within different regions of bamboo culms.
DurationWelch’s Fdf1 1df2p-ValuePost Hoc Comparisons
(Games-Howell)
NR47.239282.926<0.01External > Middle > Internal **
TZ481.8172104.709<0.01External > Middle > Internal **
IZ476.058280.763<0.01External > Middle > Internal **
1 df: degrees of freedom, ** p < 0.01.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Huang, C.; Bao, Y.; Li, N.; Hou, J. A Multiscale Investigation of Cross-Sectional Shrinkage in Bamboo Culms Using Natural-Speckle Digital Image Correlation During Drying. Forests 2025, 16, 1444. https://doi.org/10.3390/f16091444

AMA Style

Huang C, Bao Y, Li N, Hou J. A Multiscale Investigation of Cross-Sectional Shrinkage in Bamboo Culms Using Natural-Speckle Digital Image Correlation During Drying. Forests. 2025; 16(9):1444. https://doi.org/10.3390/f16091444

Chicago/Turabian Style

Huang, Chengjian, Yongjie Bao, Neng Li, and Junfeng Hou. 2025. "A Multiscale Investigation of Cross-Sectional Shrinkage in Bamboo Culms Using Natural-Speckle Digital Image Correlation During Drying" Forests 16, no. 9: 1444. https://doi.org/10.3390/f16091444

APA Style

Huang, C., Bao, Y., Li, N., & Hou, J. (2025). A Multiscale Investigation of Cross-Sectional Shrinkage in Bamboo Culms Using Natural-Speckle Digital Image Correlation During Drying. Forests, 16(9), 1444. https://doi.org/10.3390/f16091444

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop