Estimating lumber strength with radio frequency scanning

摘要

The amount of lumber graded by machine stress rating (MSR) has continued to increase since the development of the technology in the early 1960s. Accuracy of lumber strength estimation by this x-ray method is reported to be at least equal to that of MSR with an R-square relationship between estimated and actual MOR of 0.53 for southern yellow pine. This study examined whether lumber specific gravity and strength can be accurately estimated with radio frequency waves if the moisture content (MC) influence in the through-lumber-thickness signal can be eliminated. Through-lumber-thickness by radio-frequency capacitor was measured at 6.35mm intervals down the length of lumber center. A linear regression predictive equation was estimated relating MOR to measured signal voltage. Correction for the influence of moisture content on MOR resulted in a predictive equation with an R-square of 0.59. Validation results based on the developed equation gave an R-square of 0.67. The results indicate potential for accurate radio frequency estimation of MOR if adequate correction for moisture content influence is performed.