Effects of natural weathering on the mechanical properties of Moso bamboo internodes and nodes

Bamboo structures are susceptible to natural weathering when exposed to outdoor conditions, making it imperative to comprehend the aging resistance of bamboo. In this paper, the study of Moso bamboo exposed to outdoor environment for one year illustrates the discoloration, expansion, mass loss and density reduction of the specimens. The changes of relative crystallinity (CrI) of bamboo were measured by using X-ray diffraction (XRD), the microstructural changes of bamboo were observed by scanning electron microscopy (SEM), and the computed tomography (CT) scanning technology was used to analyze the internal structure of the damaged specimens. Meanwhile, the damage and differences in the mechanical properties of bamboo internodes and nodes were evaluated by the tests of compression parallel to the grain, compression perpendicular to the grain and compressive elastic modulus parallel to the grain, taking into account the bamboo height. The results showed that natural weathering reduces cellulose crystallinity and has a detrimental effect on the cellular structure of bamboo, resulting in a weakening of the interfacial bonding between the vascular bundles and the parenchyma. Consequently, this leads to a decrease in the mechanical properties of bamboo. Compared to the internode specimens, the compressive strength perpendicular to the grain and compressive elastic modulus parallel to the grain are higher in the bamboo node specimens. However, the compressive strength parallel to the grain will be significantly reduced due to the complex fiber structure inside the bamboo nodes. In light of the experimental findings, a constitutive model is proposed to describe the relationship between uniaxial compressive stress and strain in Moso bamboo, both before and after weathering. The numerical results obtained from this model demonstrate a strong correlation with the experimental findings, thereby establishing a solid foundation for conducting finite element analysis on Moso bamboo structures.