Abstract
Bamboo is a biological system and a naturally occurring composite, however its microstructure is very complex compared to manmade composites. This complexity arises from nature's way of adapting itself to perform various functions with maximum efficiency, which is popularly termed as optimization. Due to optimization, it can be assumed that the variation in properties transition smoothly along the thickness of bamboo culm. This assumption simulates better bonding strength between layers and prevents non-uniform stress concentrations. Biological structures are complicated and non-uniform, which makes it difficult to propose a realistic model that can capture the mechanical performance correctly. This paper presents the results of experimental and numerical studies on basic bending properties, fatigue properties and torsional properties of bamboo. The hierarchical and multi-scale structure of bamboo and the distribution of nano-scale fibers are revealed via laser scanning and atomic force microscopy. The information from the imagery was used to incorporate the experimental investigations with finite element modeling to analyze the mechanical behavior of bamboo under bending and torsion, and to estimate the shear modulus of bamboo. Additionally, the effect of humidity and therefore the water content on the mechanical properties of bamboo was investigated by performing torsion tests on samples kept in a controlled environment with 25, 40, 60, 80 and 100 percent humidity. The strength of the samples increases at an optimum humidity between 60 to 80 percent, while beyond this range the strength undergoes a significant drop. The samples behave more ductile within the higher humidity range while they behave more brittle at the lower humidity range. Additionally, an increase in humidity has little effect on the modulus of rigidity. Further multiscale analysis is needed to determine the effect of water content on mechanical performance of bamboo. Finally, the results of this study can provide insight to the use and design of bamboo for different applications, and to take advantage of the effect of water on natural materials, and to design and make bio-inspired composites with remarkable mechanical properties.