AN ULTRASONIC TECHNIQUE FOR PREDICTING TENSILE STRENGTH OF SOUTHERN PINE LUMBER

The goal of this research was to develop nondestructive evaluation (NDE) technology to enhance mechanical stress rating of lumber. An ultrasonic NDE technique was developed that is sensitive to grain angle and edge knots in lumber — two primary determinants of lumber strength. The presence of edge knots increased the acoustic wave travel time and selectively attenuated the higher frequency ultrasonic energy. NDE measurements and tension tests were performed on 200 pieces of nominal 50 × 150 mm Southern Pine lumber. Statistical models were developed from localized stress wave indices to predict lumber tensile strength. The ultrasonic method compared favorably with other NDE methods, including static modulus of elasticity (MOE), impact stress wave MOE and transverse vibration MOE.