Mechanism for deformation of wood as a honeycomb structure I: Effect of anatomy on the initial deformation process during radial compression

The mechanism for radial compression of coniferous wood was examined from the viewpoint of the porous structure of wood. The compressive test was carried out in a wet-type scanning electron microscopy (WET-SEM) chamber to observe continuously the deformation process of wood. The initial stress-strain relation of the cellular solids or single cell was measured with image analyses of SEM photographs. The first fracture occurred in one tangential row of earlywood tracheids just after the load-displacement curve exceeded the proportional limit. The fracture occurred because of abrupt breaks of the radial cell walls. The first fractured cells had a tendency to have the smallest percentage of cell wall within an annual ring, and the cells suffered shearing deformation in a radial direction until the occurrence of the first fracture. On the basis of the results of image analyses, it was concluded that this shearing deformation of cells was almost Linearly related to the compressive load.