Effect of Loading Rate on Bending Performance of Moso Bamboo

After millennia of evolution, bamboo has developed a multifunctional gradient distribution structure from the macroscopic to the nanoscale. This structure endows it with high strength and good toughness, providing a natural model for optimizing engineered materials and structural designs. Using moso bamboo (phyllostachys edulis) as the target material, this study elucidated the fracture mechanisms at varying strain rates via three-point bending tests under different loading directions and rates. The results demonstrate that as the loading rate increases, the bending strength and fracture energy under the “positive” loading direction gradually increase. In contrast, the fracture energy under the “negative” direction initially increases then decreases. Macroscopically, fracture surfaces from positive loading exhibit increased crack length with multiple deflections and bifurcations, revealing the structural origin of the high strength and toughness. Furthermore, the fiber-sheath fracture surface becomes smoother under positive loading. At the single-fiber level, the failure mode transitions from wall tearing and lamellar splitting to fiber pull-out and direct fracture, indicating distinct failure mechanisms under different loading rates.