In Situ Detection of the Flexural Fracture Behaviors of Inner and Outer Bamboo-Based Composites

Abstract

This paper investigated the fracture toughness and enhancement mechanism for each component in bamboo-based composites at the cellular level. In situ characterization techniques identified the fracture behaviors of bamboo-based composites in three-point bending tests, and scanning electron microscope (SEM) further visualized the crack propagation of the fracture surface. In addition, the improvement mechanism of bamboo-based composites was illustrated by mechanical properties at the cellular level assisted with nanoindentation tests. Our in situ test results showed that the bamboo-based composites exhibited a longer deformation and higher bending load compared with bamboo. The fracture was non-catastrophic, and crack propagated in a tortuous manner in bamboo-based composites. Microstructural analysis revealed that phenol-formaldehyde (PF) resin pulled out and middle lamella (ML) breaking rather than transverse transwall fracturing occurred in parenchymal cells. The higher density of fibers in the bamboo-based composites triggered massive interfacial delamination in the middle lamella (ML), which was a weak mechanical interface. Furthermore, indented modulus and hardness illustrated that phenol-formaldehyde (PF) resin improved the mechanical strength of cell walls, especially parenchymal cells. The crosslinks of PF resin with the cell walls and massive fibers were the primary mechanisms responsible for the fracture toughness of bamboo-based composites, which could be helpful for advanced composites.