Abstract:

Taking SEB samples of spruce (<i>Picea asperata</i>) for instance, the finite element software of ABAQUS was used to analyze the stress field of the samples, when the obliquity between the wood crack and the grain of wood were 90°, 60°, 30°, 0° respectively, “tangential normal stress intensity factor ratio criterion” was applied to predict the direction of the crack.The results showed the direction of the maximum Mises stress of four samples was along the grain of the wood when drawing a radial plane centered around the crack tip. It is also shown that the ratio of the tensile stress perpendicular to the crack (σ_Y) to the tensile stress parallel to the crack (<i>σ_X</i>) is approximately a constant within 1～5 in a large area around crack tip but except the singular point. No matter what is the angle of the initial crack to the grain of wood, the tangential normal stress intensity factor ratio (R) of the crack tip over the direction of the grain was the largest. Therefore, the initial crack direction along the grain had been verified either by theoretical prediction or by experiment. The role of toughening of low-interfacial strength between wood cells has been discussed.

Key words: wood fracture, finite element method, stress field, crack direction prediction