The effect of specific gravity upon modulus of rupture, modulus of elasticity in static bending, and maximum crushing strength in compression parallel to the grain was examined for commercially important timbers of various world-wide origins. Data sets were compiled from world literature according to geographic origin. The logarithmic regression of specific gravity vs. the particular mechanical property was calculated by least squares for each data set in the green and air-dry condition. For all data sets, the calculated regression proved to be significant at a 95% confidence level as determined by correlation analyses.
Published relationships (U.S. Forest Products Laboratory 1974) were compared to the calculated regressions for the commercially important timber species of the United States and were found to fall within our 95% limits of confidence for each property and moisture content. Covariance analyses revealed significant differences in specific gravity-mechanical property relationships between hardwood and softwood groups. Covariance analyses between data sets from different geographic locations revealed no conclusive trends. Global equations for specific gravity-mechanical property relationships for all data included in this study were shown by correlation analyses to be valid at 95% level of confidence. * The authors wish to express their appreciation to Dr. John F. Siau for his assistance with the analytical procedures employed in this study 1 Specific gravity as referred to in this study is based on oven-dry mass and volume at the indicated moisture content (green or 12 percent)