Characterizing Microscopic Behavior of Wood Under Transverse Compression. Part II. Effect of Species and Loading Direction
Keywords:Radial compression, tangential compression, cellular structure, cell-wall collapse, stress-strain response
AbstractSpecimens of four species with different cellular structures (white spruce, jack pine, white ash, and aspen) were tested in radial compression. Deformation characteristics were observed and measured using a microscope at different magnifications. The magnified images were recorded with a video recorder, which were then played back for deformation measurements. Stress-strain responses of these specimens were determined from the measured load and deformation. As expected, the softwood and hardwood responses to radial compression were influenced by the anatomical features. Tangential compression tests were also conducted on white spruce and jack pine specimens. It was found that the mechanisms of deformation in radial and in tangential compression were distinctly different for these softwood species. In radial compression, cell-wall deformation dominated elastic behavior, and collapse of the weakest cells in earlywood coincided with the onset of yielding observed in the stress-strain curve. Cell collapse developed only in earlywood, while latewood cells mainly underwent elastic deformation. In tangential compression, elastic deformation was dominated by the bending of the latewood layers. For the two hardwood species, the measured elastic strain under radial compression was dominated by deformations in the vessels. Yield point on stress-strain curves was related to the collapse of these vessels.
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