Natural composite rods extracted from the proximal section of the giant bamboo: statistical assessment of physical and mechanical properties

A statistical Design of Experiment (DOE) is innovatively applied to assess the physical and mechanical properties of natural composite rods extracted from the proximal section of the giant bamboo. The proximal section, roughly the first 2.4 m from the first usable culm above the soil, has the greatest wall thickness, allowing for the extraction of rods with larger transverse dimensions and sampling from different radial positions, resulting in composite rods with varying fibre volume fractions. A 31×21 full factorial design is conducted considering three levels of longitudinal position (base, middle, and top) along the proximal section, and two radial positions within the culms (inner and outer). The bulk density of the rods tends to increase (up to 12%) from the base to the top levels and from the in-extracted to the out-extracted rods, while water absorption exhibits the opposite behaviour, but increasing up to 25%. Tensile properties tend to increase up to 13% from the base-extracted rods to those extracted from the middle and top parts of the proximal section, and up to 24% from the in-extracted to the out-extracted specimens. Compressive properties increase up to 43% from the base to middle and top levels, and up to 45% from the in-extracted to the out-extracted rods. The impact resistance depends only on the longitudinal position, increasing by 11% from the top to the base levels. Specific tensile stiffness and strength are similar for any extraction position, while the specific compressive properties follow similar behaviour as the absolute compressive properties. The failure mode under tension is mostly characterised by delamination, whilst for compression the type of damage appears to be random and does not follow any discernible pattern. The impact specimens undergo a full rupture of the bamboo structure. These findings contribute valuable insights into the multi-scale characterisation of giant bamboo, laying the groundwork for its potential application in rod-based structural designs employing rods extracted from the culms of the plant.