Flexural deformation and fracture behaviors of bamboo with gradient hierarchical fibrous structure and water content

Natural gradient fibrous bamboo bended from two opposite directions (divided as Type I and Type II samples) showed pronounced asymmetric flexural performances as the water contents gradually increased (0%, 6%, 22% and 35%). The real-time flexural deformation and fracture behaviors were detected and analyzed with the aid of acoustic emission (AE). Results indicated that there were three kinds of mechanical behaviors during the flexural deformation and fracture process of bamboo: matrix (parenchyma cells) failure, fiber interfacial dissociations (fiber/matrix and fiber/fiber wall dissociations) and fiber breakage. They showed different sequences within the Type I and Type II samples, which were caused by the gradient fibrous structure. The AE energy was dramatically declined and the fiber interfacial dissociations showed exponential-like growth as the water content increased. Upon certain content of water, the gradient hierarchical fibrous structures were toughened through detailed mechanisms of micro-fiber pull-out, debonding and bridging, laminar debonding, local cell wall buckling and micro wart swelling. The study provides critical experimental evidences on the effects of gradient fibrous structure and water content on the flexural performance and fracture behaviors of the natural bamboo.