Viscoelastic damping behavior of structural bamboo material and its microstructural origins

In this study, the intrinsic viscoelastic mechanical behavior of a hierarchical bio-composite, structural bamboo material, was experimentally investigated and correlated with its microstructural constituents and molecular building blocks. The macroscopic viscoelastic responses of bulk bamboo at ambient temperature and dehydrated condition were evaluated through dynamic compression experiments with various loading frequencies, whereas the localized viscoelasticity of bamboo's microstructural phases, viz. fibers and parenchyma cells, were evaluated separately through series of nano-indentation studies. The viscoelastic responses of the bamboo's building blocks were further evaluated at the molecular level, using the computational creep tests via constant force Steered Molecular Dynamics (SMD) simulations. A phenomenological viscoelastic model was then developed to explain the observed microstructure-viscoelastic property relationship. Based on the model and conducted microstructural characterizations, it was believed that the small evolved viscous phases within the parenchyma cells were mainly responsible for the smaller viscoelasticity in bulk bamboo at lower loading frequencies, whereas the exhibited larger viscoelasticity at higher loading frequencies was stemmed out from the concurrent contribution of fibers and parenchyma cells. The findings could be important for understanding the intrinsic viscoelasticity in other biological materials with hierarchical structures, as well as for optimizing the design of bio-inspired composites with favorable structural properties.