Analysis of radial compression behavior of wood using digital image correlation method

Strain distributions in wood under an applied load were studied by means of a digital image correlation method (DIC). Cross sectional surfaces of wood specimens under compressive stress in the radial direction were observed u sing a video microscope. The video images were digitized with an image digi tizer board on a personal computer. Strain distributions were calculated by the DIC and visualized. The results of the analysis were as follows : Arra ys of high strain concentration area were observed below the proportional l imit and they shifted with the increase of load. The arrays consisted of no t only compression but also tension strains near the strain concentrated ar ea. In shear strain distributions either of positive or of negative strains were observed. This observation indicates that the deformations of the rad ial-tangential section in compression had something to do with the cellular arrangements like honeycomb and that properties of the high concentration area were related to complex tissue of wood. The ordinary DIC was improved so that it makes it possible to calculate the strain distribution efficiently with a personal computer. This study showe d that strain measurement with the DIC can be applied to analyze the behavi or of wood under a stress in different dimensions, from micrometer to meter , if a suitable way of applying a random speckle pattern and suitable equip ment to take digital images are chosen. It will have great use in future st udies concerning the mechanical properties of wood.