Fracture and mixed-mode resistance curve behavior of bamboo

Bamboo is a natural composite abundantly available in the world, and is a source of inspiration for design of new construction materials and structural composites for many applications. The microstructure of this Functionally Graded Material (FGM) evolves through its thickness in response to wind-induced stresses that arise in the plant during its lifetime. This paper presents the results of an experimental study on the structure and toughening mechanisms in Moso culm bamboo. The hierarchical and multi-scale structure of bamboo and the distribution of micron scale fibers are revealed via optical microscopy. Four-point bend fracture experiments are performed where the applied crack-driving forces are computed as a function of crack length. This experimental data are incorporated within a finite element framework in order to understand the fracture and deformation mechanisms of bamboo, and compute the Resistance-curves (R-curve)s. The resistance-curve behavior is shown to be dependent on the orientation of the fibers. In cases where the fibers are perpendicular to the crack growth toughening is observed to occur via crack bridging. Intermediate shielding levels are observed when toughening occurs by crack deflection for crack growth along the fiber orientation.