CRACKING PATH AND FRACTOGRAPHY OF SPLITTING FAILURE OF WOOD

Abstract

Three-point bending tests were performed for beams made of Japanese cedar, in which the beam axis is inclined to the grain of the wood. Followings were observed with respect to the cracking path. Splitting starts at the point on the tension edge where the stresses satisfy the fracture criterion for orthotropic plates. When the beam is not restrained, in other words, the beam has an entirely free path of cracking, the crack suddenly propagates into the compression edge, resulting in the total failure of the beam. However, when plywood panels are attached to the sides of the beam in its half span in order to interrupt the anticipated cracking path, the splitting crack stops on its way and then bending failure is developed slowly. The first splitting, even when the cracking path is interrupted, can be initiated only if a small trigger length equivalent to the interval of annual rings is latent in the possible cracking path. From fractography by means of SEM, it was found that the initial crack of splitting is the fibrous crack with honeycomb patterns, which is followed by the progressive crack with split bamboo patterns.