The Investigation And Research On Mode ? Interlaminar Fracture Toughness Of Wood And Bamboo

Wood and bamboo as natural bio-composite material,they have unique advantages in structure and they have significant differences in different parts of the structure,which result the differences in their physical and mechanical properties.Wood and bamboo during using often come up with a variety of cross-section cracking along the grain.These cracking behavior were also known as interlaminar fracture on composite materials science.And once there were crack along the grain,its interlamination spread was not controlled by the strength but it was controlled by the interlaminar fracture toughness of wood and bamboo.Therefore,researching on wood and bamboo fracture behavior and testing the interlaminar fracture toughness of wood and bamboo were very important for wood and bamboo structural strength design,the usability of wood and bamboo and so on.For fiber-reinforced composite materials,a variety of methods were applied to assess their mode ? fracture toughness,these were commonly used such as elastic beam theory,Timoshenko beam theory,the method of substituting test parameters into formula equation and compliance calibration method.However,for the mode ? interlaminar fracture toughness of natural biological composite,which method is more appropriate and accurate processing method needs to be explored and studied.In this paper,firstly we took MSCB?Modified Split Cantilever Beam?method and self-improved SCB?Split Cantilever Beam?method to test the mode ? interlaminar fracture toughness of Tsuga chinensis wood respectively,investigated thoroughly the differences between the two methods to test mode ? interlaminar fracture toughness and analyzed the crack surface of specimen after fracture;secondly we used SCB method to test the mode ? interlaminar fracture toughness of bamboo?Phyllostachs pubescens?inter-bamboo section and applied the compliance calibration method and area method to calculate the mode ? interlaminar fracture toughness of bamboo inter-bamboo section along the grain and analyzed the crack surface after the specimen fracture as well.The results are as follows:?1?The result by using the MSCB method is as follows: G_?-SCB=1804.25J/m2?SD=359.66J/m2?;?2?The results by using the SCB method is as follows: G_?-SCB=659.79J/m2?SD=128.59J/m2?;?3?The interlaminar fracture toughness tested by MSCB method was higher thanthe interlaminar fracture toughness tested by SCB method and the main reason for this difference is the difference F_cr-MSCB and F_cr-SCB caused,and the reason F_cr-MSCB and F_cr-SCB difference remains to be further explored;?4?With the analysis of Tsuga chinensis wood mode ? interlaminar fracture surface,mode ? crack's propagation was accompanying with the tearing of middle lamella,the breaking of tracheid cells in basic tissues and the tearing of cytoderm;?5?By using SCB method,we tested the mode ? interlaminar fracture toughness of bamboo,and respectively calculated its mode ? interlaminar fracture toughness with compliance method and area method,obtained:?1?G_?-comp=2380.97J/m2?SD=741.35J/m2?,G_?-area=2199.65J/m2?SD=365.62J/m2?.The calculation results of the two analysis methods was insignificant,but from the dispersion of the data,the area method is superior;?6?With the analysis of bamboo mode ? interlaminar fracture characteristics and fracture surface,mode ? crack's propagation was accompanying with the tearing of long cells and the cracking of short cells in basic tissues,the cracking of fiber bundles wrapped by basic tissues and the interlaminar of fiber bundles and vascular bundles with the interfaces of basic tissues;?7?Mode ? interlaminar fracture toughness was the properties of material,substantially it was independent of crack size.