The Research On The Influence Of Wood Microstructure To Fracture

This paper discussed the influence of wood microstructure to the fracture. It coulddiscover the wood fracture process in the microcosmic level and supply the design basis forwood use security. Pine, popular, Manchurian Walnut and Amur cork-tree were tested in thetensile and bending experiments with the LR and LT fracture mode. It utilized the in-situobservation of wood fracture process in ESEM by presetting a notch, adjusting thespecifications of specimen and load speed. Crack propagation was analyzed by thecorresponding analysis of the fracture images and stress-strain curve. The crack developmenttrending and the shape of crack such as line, curved and zig-zag could be estimated accordingto the wood structure traits. The influences of the vessel, spindly ray, the border of earlywoodand latewood, wood fiber, wood ray and tracheid to the fracture were also researched. In thecrack propagation process the intracellular level of force should be significantly less than thecell wall. The vessel, border of earlywood and latewood and spindly ray always delayed thecrack propagation. Sometimes the path could deviate from original direction. The crack wouldbe propagated along the edge of the wood microstructure. The specimen sometimes could besplitted into two parts. The vessel wall was easy to engender micro cracks in the primary loadwhile it was located near the notch or the surface layer of the tensile part. Because the micro-fibers grew around the pit, the crack always turned around the pit and the integrated pit couldbe seen after the fracture. The fracture along the outer edge of the wood ray group was mucheasier than the internal parts when crack extended to a group of wood ray. Due to the higherstrength of wood fiber the linear vertical fiber breakage was hard to form in addition to thenotch influence or high power. The arc crack between the fibers and vessels were easy to formwith the inertia effect.