The study on in situ asymmetric bending behavior of structural bamboo materials under combined tension-bending loads

As a growing structural material in the engineering field, bamboo materials are mainly subjected to tension, bending, and a combination of the two during the service process when used as a beam structure. However, the asymmetric bending behavior of bamboo materials under combined loads has not been thoroughly investigated. Therefore, this paper aims to systematically study the asymmetric deformation and fracture of bamboo materials under tension, bending, and combined tension-bending loads. The tests were conducted on a novel self-made in situ apparatus. The periodic stresses fluctuations under three-point bending when loading on the lower fiber density side were analyzed, and the correlation between the shape, size and buckling performance of parenchymal cells was revealed from a mechanical point of view. Microscopy-based in situ three-point bending tests revealed a rich energy dissipation mechanism in the fracture process. It was found that the bending resistance and bending bearing capacity of the bamboo materials under combined tension-bending were significantly improved attributed to the coupling effect of tension and bending. The specimens under combined tension-bending exhibited a composite fracture mode with the combination of tensile fracture and three-point bending fracture mode. Additionally, an expression for the finite stress intensity factor was derived, which allows to characterize the fracture toughness of bamboo materials under tension, bending and combined tension-bending. This work is expected to provide new insights into the deformation and damage of bamboo materials, as well as guide the engineering applications of raw bamboo materials and the development of bionic bamboo structural materials. Graphical abstract