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Hierarchical multiscale modeling of the elastic properties of bamboo Khajouei Nezhad, Mohammad


Bamboo, a hierarchically organised material with a distinct cylindrical shape, exhibits anisotropic behaviour due to its unique anatomical structure. Bamboo culm walls are reinforced by vascular bundles densely in the outer region and sparsely in the inner region, resulting in a gradient structure along the radial direction of the culm. This research investigates the elastic behaviour of bamboo at four different scales, namely nanoscale, microscale, mesoscale and macroscale, by combining microstructural investigations, image analysis of bamboo microstructure and finite element modeling (FEM) techniques. The focus is to understand the orthotropic elastic properties at each specific scale. This study utilises representative volume element (RVE) homogenisation to extract nine independent elastic parameters and analyse stress and strain contours, providing valuable insights into the elastic deformation behaviour of bamboo. Moreover, to ensure robust validation, the experimental data are compared with the predicted elastic properties at each scale, aiming to achieve a satisfactory level of agreement. The results reveal that among the different cell wall layers, the broad layer of fiber exhibits the highest homogenised elastic properties due to its lower microfibril angle (MFA) and higher cellulose content. Layer-structured composition of different cell walls within a fiber, parenchyma, and vessel are modeled. Consequently, fiber cells exhibit the highest elastic properties among these three cell types. Anatomical-based homogenisation of vascular bundles at the mesoscale level reveals that increasing the fiber content from 8% to 56% results in 2.6 times increase in longitudinal Young's modulus and 1.7 times increase in transverse Young's modulus. Experimental results at the macroscale level, using a non-contact, in-situ digital image correlation (DIC) system for strain measurements, reveals a high accuracy of 94.7% for estimating the experimental Young’s modulus. Overall, this research contributes to a better understanding of bamboo's elastic behaviour at different scales, offering valuable insights for bamboo structural analyses, material designs, and potential applications.

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