Swelling and shrinking behaviour of bamboo and its application on a hygro-mechanical model

Bamboo exposed to variations in humidity is prone to cracking, which can reduce its usability. As a natural material, bamboo’s hygroscopicity causes dimensional changes, influenced by the gradient distribution of fibres throughout the wall thickness. This study evaluated the dimensional changes resulting from variations in moisture content. Hygroscopic coefficients were extracted and applied in a finite element model to assess the circumferential stresses generated during sorption and desorption processes. Conditioning tests showed that open ring samples tend to close during sorption and open during desorption, due to the predominant swelling and shrinking behaviour of the fibre cells. The developed finite element model successfully replicated the aperture behaviour and dimensional changes in the thickness of open ring bamboo samples. The optimized parameters were subsequently used to predict the stresses under varying humidity conditions in closed-ring samples. The circumferential stresses ranged from 9.8 MPa to -12.5 MPa from the inner to the outer layer in the saturated condition, and from − 7.1 MPa to 11.4 MPa in the dried condition. The values achieved reflect stresses that can lead to cracks and the failure of bamboo, thereby demonstrating the model’s ability to predict the hygroscopic behaviour of the material.