Influence of asymmetric bending behavior of bamboo on performance of curved components

Objective The quality of curved components produced under identical process conditions exhibits instability due to the structural heterogeneity of bamboo, such as its asymmetric bending behavior. This study aimed to explore the forming regulations of bamboo strips derived from different parts of bamboo culms under varied bending modes, aiming to enhance the controllability of producing bamboo strip curved components and to provide a scientific foundation for process optimization.

Method A one-piece bending forming process was employed to fabricate curved components. The bending properties of bamboo strips from different parts of bamboo culms were investigated under two bending modes, namely compression on bamboo outer layer (Type Ⅰ) and compression on bamboo inner layer (Type Ⅱ). Additionally, the bending pass rate, minimum bending radius range, and bending stability of curved components were also examined.

Result The fiber volume fraction of bamboo strips was the highest in the middle part, followed by the root part, and the lowest in top part. Additionally, there was a positive correlation between bending properties of bamboo strips and their fiber volume fraction. For the same parts of bamboo culms, the bending strength and modulus of bamboo strips were higher under Type Ⅰ mode compared with those under Type Ⅱ mode, while bamboo strips under Type Ⅱ mode exhibited higher bending toughness. Bamboo strip curved components were more likely to be successfully bent and shaped when compressed under Type Ⅱ mode rather than Type Ⅰ mode, resulting in achieving smaller bending radii. The bending pass rate of curved components fabricated from the middle part of bamboo strips was higher compared with that of root and top part of bamboo strips, and the minimum bending radius of the middle part of bamboo strips was in the range of 30 mm < R ≤ 60 mm when they were bent under Type Ⅱ mode. The bending stability of curved components was negatively correlated with fiber volume fraction of bamboo strips, and the middle bamboo strip curved components with the highest fiber volume fraction exhibited the largest springback angle.

Conclusion Bamboo strips from different parts of bamboo culm exhibit significant asymmetric bending behavior under radial bending loads. When fabricating bamboo strip curved components, bamboo strips from different parts of bamboo culms and bending modes can be selected according to the desired degree of bending, in which the use of bamboo strips in the middle of bamboo culms under Type Ⅱ mode can effectively produce curved components with higher degree of curvature.