How variability in OSB mechanical properties affects biological durability testing

Loss in bending strength of wood has been shown to be a more sensitive measure of decay than is weight loss. Using modulus of rupture as the decay criterion is problematic for oriented strandboard (OSB) because of variation in mechanical properties due to particle orientation and size. Moreover, the small specimen size required for such tests increases the variance in mechanical properties. This study compared the variance in bending strength of ASTM D1037 standard-sized specimens and small specimens from two samples of commercial OSB. The small specimens were found to have a significantly higher level of variance in bending strength than the standard-sized specimens. A simple method of sorting the specimens based on strand orientation on the tensile surface significantly reduced the level of variance measured. The effects of differing levels of variance on the size, design and limitations of the experimental study are presented.