The Effect of Anatomy on the Initial Stress-Strain Relationship in Transverse Compression

Four species were selected on the basis if anatomical characteristics to study anatomical effects on the shape of the stress-strain curve in both radial and tangential compression perpendicular to the grain. The 3/4 by 1/2 by 1/2 inch (1, r, t) specimens of western redcedar (Thuja plicata Donn.), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), Oregon ash (Fraxinus latifolia Benth), and red alder (Alnus rubra Bong.) were tested at approximately 10 percent moisture content on an Instron Testing machine at a loading rate of 0.01 in./min. Stress-strain curves were recorded continuously and photographs were taken at different stages of compression. The results show that loading direction within a species can be more important than between species differences. All four species showed a maximum stress point in radial compression and, in tangential compression, the two softwoods showed a maximum stress. Failure in the tangential direction is similar to failure in long columns with the boards of summerwood acting as spaced columns. In radial compression, failure occurs in the weakest springwood layer initially. If compression continues, every springwood layer will fail, causing a progressive failure.

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