In-situ observation on the morphological behavior of bamboo under flexural stress with respect to its fiber-foam composite structure

Abstract

An in-situ observation on the morphological behavior of bamboo’s fiber-foam composite structure under flexural stress was conducted, and the respective contribution of parenchymatous tissues and sclerenchyma fibers to the flexural ductility of bamboo was evaluated. Fibers or parenchymatous cells at the bottom suffered tensile stress during bending process, where initial microcracks occurred. The results suggested that the bottom parenchymatous tissues experienced a perforative tear along the loading direction, while fibers continued to stretch until several fibrous tensile failure cracks were observed. The subsequent crack growth mode was similar to that of the horizontal crack transmission that began when it reached fibers or somewhere between fibers, until another weak load-bearing point appeared, and then it expanded up through parenchymatous tissues. As a whole, the crack acted ladder-like in its growth, and the propagation paths were not restricted to a coherent one. Images of the morphological changes of the upper parenchymatous tissues and sclerenchyma fibers, which suffered compressive stress during bending process, indicated that parenchymatous tissues and sclerenchyma fibers made different contributions to the flexural ductility of bamboo. Sclerenchyma fibers supplied deformation resistance for bamboo’s macroscopic deformation, while parenchymatous tissues offered deformation space due to the variation of cellular morphology and location.