Study on the Quasi-Ductile Fracture Behavior of Glubam: The Role of Fiber Distribution

Abstract

Cracking in fibrous composites is inevitable, and the fracture pattern is influenced by its fiber distribution. Bamboo fibrous composites have a distinct fiber distribution, which makes them an excellent material for studng the relationship between fiber distribution and fracture mode. Glued laminated bamboo is a bi-directional bamboo fibrous composite, which is called glubam for short. Its vertical thickness is about 28 mm, and the ratio of the number of longitudinal fiber layers to the number of transverse fiber layers is 4:1. This study conducted three-point bending fracture tests on single-edge notched specimens of glubam to investigate its mode-I fracture characteristics in the transverse vertical direction. The deformation curves show that the specimens still have the load-carrying capacity after reaching the maximum load, and the load shows a trend of step-like decrease, exhibiting a quasi-ductile fracture behavior. Overall, the fracture process can be divided into four stages, including linear, softening, quasi-ductile, and failure stages. In this study, based on certain assumptions, the prefabricated notch length a0 was adjusted according to the position of the transverse fibers. Subsequently, the non-linear elastic fracture mechanics method was employed to calculate the fracture parameters of glubam during the softening and quasi-ductile stages, including the fracture toughness KIC* and fiber tensile strength ft. The deviation of the fracture parameters between the two stages is within 10%, indicating that the correction of the a0 is correct. This indirectly proves that the staggered structure formed by longitudinal and transverse fibers is responsible for the quasi-toughness fracture of glubam. Finally, this study summarized and analyzed the quasi-ductile fracture behavior and found that materials or structures exhibiting quasi-ductile fracture behavior often possess a staggered structure. This staggered structure makes the crack in the form of semi-stable propagation, while the load decreases in a step-like manner.