Evaluation of the mechanical properties of different parts of bending bamboo culm by nanointendation

Abstract Bamboo is a flexible natural material, which has high potential value. However, manufacturing processes for bent bamboo products are highly reliant on manual labor. The main challenge in the industrial processing of raw bamboo is that bamboo’s characteristics have not yet been extracted accurately. This mainly originates from bamboo’s complexity and its response to bending, which depends on chemical composition, structure, and properties of bamboo. In order to understand the response of bamboo to bending, samples from different parts of manual processed bent bamboo culm ring were studied through nanoindentation tests. In this regard, elastic modulus, hardness, irreversible work, and residual depth on different bamboo parts were analyzed. The results show that bending has different effects on the tension side (TS, the convex side) and compression side (CS, the concave side) of the bamboo culm. Moreover, the bending effect was different on the green (GBP) and middle bamboo parts (MBP). It was found that bending improved the elastic modulus of GBP in TS by 101%. Moreover, the hardness of GBP in TS decreased by 21% while that of MBP increased by 12.4%. In CS, the hardness of GBP increased by 10% while that of MBP decreased by 19%. The performed analyses reveal that the ratio of irreversible work to total work increased in the bent bamboo and the difference between GBP and MBP was not large for both TS and CS. The relative residual depth was about 60% for the neutral side (NS) and increased to above 70% in TS and CS. It was proposed that either TS or CS formed a respective complete tension-compression stress system in the bent bamboo specimen.