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Abstract

Bamboo is a unidirectional fibre-reinforced composite with radially graded and almost transversely isotropic elastic properties. The cracks originated in bamboo under bending due to wind loads propagate along the fibre direction. This process is controlled by interlaminar fracture toughness. In order to observe the spatial distribution of the fracture toughness in bamboo, energy release rate is theoretically deduced from the general equations for crack-tip stress fields in anisotropic bodies. The analysis shows that the fracture toughness has graded distribution and the trend is opposite to that of axial modulus. To verify this, the energy release rate (or fracture toughness) is experimentally calculated for double cantilever beam specimens (with a crack placed in different fibre density region) in mode-I i.e. crack opening mode. It is observed that the crack propagation parallel to fibres (splitting) develops easily and the energy release rate decreases with increased density of fibre bundles. The observed trend closely corroborates the results from theoretical analysis. From the results of real-time wind load simulations (reported elsewhere) on tapered bamboo-like structure it is concluded that with the help of radially graded fracture toughness bamboo converts flaws of all orientations into splitting mode.

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