The bending mechanism of bamboo based on X-ray micro-tomography (µCT) and digital image correlation technique (DIC)

The asymmetric distribution of the vascular bundles in bamboo significantly contributes to the nonlinear characteristics of its bending deformation behavior. However, there is still a lack of the correlation between crack propagation paths and the gradient layered structure, as well as the regulatory role of pore network in crack bifurcation. In this study, the asymmetric bending behavior of bamboo was investigated from bamboo green (Type I) and bamboo yellow (Type II) surfaces, respectively. Elastic segments, yield points and damage points were analyzed, and the crack propagation paths were visualized via the digital image correlation (DIC) and X-ray micro-tomography (µCT) techniques. Results indicated that the bending strength of type II (160.70 MPa) was significantly higher than that of type I (122.61 MPa), and the yield point of type I and type II occur at 446 N and 425 N, respectively. DIC and µCT analysis revealed the fracture modes correlated with the gradient layered structure and the pore networks. Fibre debonding, fibre bridging, fibre pull-out, and crack deflection were prominent fracture modes. The fibres demonstrated a strong inhibitory effect on crack propagation. The parenchyma cells provided a buffering role. The µCT results further indicated that the hollow vessel and phloem within vascular bundles modified the fracture properties by deflecting the crack propagation and absorbing the energy at the crack tip, thereby delaying bending damage. This study provided valuable insights for the biomimetic design of impact-resistance composites with enhanced energy absorption, promoting multi-scale simulation technology to achieve the lightweight, high strength and toughness materials. • Employing μCT with DIC analysis to predict and visualize the dynamic failure process and crack propagation within bamboo. • Cell structure traits and crack propagation mechanisms synergistically affect bamboo's bending mechanical properties. • The strain is transmitted more quickly in homogeneous cell units. • The hollow structure (vessels and phloem) is crucial in adjusting the fracture properties.