Self-Shifting Neutral Axis and Negative Poisson’s Ratio in Hierarchical Structured Natural Composites: Bamboo

Bamboo is a light weight, high strength natural composite. Although it has been wildly used in the world for thousand years, the mechanism of material enhancement and microstructure/property relationships has not been well understood yet. In this study, triple points bending tests were conducted for mechanical behavior characterization of natural composite-bamboo. Digital Image Correlation was utilized to determine the deformation and strain of a bamboo beam. It was found that (a) the material responses to the applied load had both a linear and a non-linear range, (b) the beam was stiffer when it had node at two ends, (c) the neutral axis shifted toward the tensile side of the beam during loading process, (d) when samples were reloaded, the material responses to the load were different, (e) negative Poisson’s ration was found in the high fiber density of the beam.