Quasi-ductile fracture behavior of glubam due to transverse fiber distribution

Abstract

Abstract The cracking of fibrous composites is inevitable, and the cracking mode is depended on its fiber distribution. In this study, bamboo fibrous composites are selected to investigate the effect of fiber distribution on crack propagation. Glued-laminated bamboo (Glubam) is a bi-directional bamboo fibrous composites, usually used as a board member, its vertical thickness (V direction) is about 28 mm, and with the longitudinal fiber layers (L direction) to transverse fiber layers (T direction) setting a 4:1. Considering that there are fewer transverse fibers in glubam, it is more prone to cracking under transverse load, this study researches the mode-I fracture characteristics of glubam in the TV direction. The three-point bending (3-p-b) fracture test of glubam specimens with single-edge notches (SEN) was carried out in this study. 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, the tensile strength ft and fracture toughness KIC of glubam in the softening and quasi-ductile stages are calculated using nonlinear elastic fracture mechanics (Non-LEFM) method, and the prefabricated crack length a0 is modified according to the location of the transverse fibers. The deviations of the fracture parameters in the two stages are within 10%, which indicates that the modification of the prefabricated crack length is correct and indirectly demonstrates the correlation between the fracture parameters of the quasi-ductile stage and the transverse fiber position. On the other hand, quasi-ductile fractures exist in other materials and structures, and they all have staggered structures. This staggered structure makes the crack in the form of semi-stable propagation, while the load decreases in a step-like manner.