Experimental investigation on macroscopic fracture behavior of wood plates under tensile load using digital image correlation method

Abstract

Wood is a kind of composite material in nature. Variations of latewood distribution and grain orientation are due to the climate and environment changes. The fracture behavior of the wood is difficult to observe and predict. In this paper, Japanese cedar (Cryptomeria japonica), a kind of conifers, was used to prepare the tensile test specimen to investigate the macroscopic fracture behavior under tensile load. During the tensile test, both the three-dimensional digital image correlation (3D-DIC) and two-dimensional digital image correlation (2D-DIC) methods were employed simultaneously. The 3D-DIC method was used to observe the specimen from the beginning of the tensile test to failure. The 2D-DIC method was employed to record the fracture mechanism by using a high-speed camera. According to the 3D-DIC results, higher longitudinal and radial strains occurred on the location of fewer latewood of the specimen. Based on the captured images of the fracture process obtained from the high-speed camera, both mode I and mode II fracture behaviors were observed. It is obvious that the mode I fracture occurred at the very beginning of the equivalent defect on the specimen. Then, the crack extended along the boundary of earlywood and latewood. Later on, the mixed mode I and II fracture occurred passing the latewood. Finally, the mode I fracture occurred on the crack passing the latewood.