Dynamic Test for Evaluating Decay in Wood

Strength loss has frequently been used as a criterion in the laboratory evaluation of the effectiveness of a preservative or the durability of wood because the loss in strength due to decay often occurs before significant weight loss. The static strength test methods, as used by several workers, do not allow a direct measure of strength loss. The original strength value of each decayed specimen is estimated based on the non-decayed controls. Since wood is a variable material, this estimated value may differ significantly from the true original strength of the decay specimen. Thus, a non-destructive test should result in improved reliability. This report introduces a non-destructive test for the laboratory evaluation of wood decay. A preliminary test was conducted using specimens of white pine sapwood, 5″ long, 0/16″ wide and 1/16″ thick, exposed to Poria lacenta. The amount of decay was measured by the loss in e values of natural frequency observed from the bending vibration caused by an external force of the wood specimen before and after infection. Frequency losses after decay for 7, 17, 27 and 37 days were 4 percent, 11 percent, 27 percent and 41 percent, respectively. Their corresponding weight losses were 0 percent, 3 percent, 8 percent and 14 percent.

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