Influence of assemble patterns on bonding strength of glued bamboo

Abstract

As a kind of natural composite material, the outer side of bamboo was quite different from its inner side in microscopic structure and mechanical properties. In order to research the effect of these differences on bonding strength of glued bamboo, bamboo strips were bonded by three different forms: outer side to outer side, outer side to inner side and inner side to inner side. Shear strength results indicated that the bamboo sample glued by inner side to inner side has the greatest shear strength value, which is 18.35 MPa, and the other two types have similar shear strength values (approximately 14 MPa). In particular, for the sample glued by outer side to inner side, the broken part is always the outer side. The scanning electron microscope (SEM) images indicated that bamboo fiber cells and parenchyma cells have different failure patterns in compression shear test. For bamboo fiber cells, dominant destruction occurred at the interface between the fibers. And for parenchyma cell, fracture occurred on cell wall and broken the parenchyma cell itself. The interface between bamboo fiber cells was very weak, thus parenchyma cell was the major contributor to shear strength of bamboo. The inner side had higher shear strength because it had higher content of parenchyma cells. The SEM image and shear strength curve also indicated that in the early period of shearing process, the deformed parenchyma cells are in a relax status, and until the later period of shearing process, the parenchyma cells begin to contribute to shear strength.