NONDESTRUCTIVE EVALUATION OF GREEN WOOD USING STRESS WAVE AND TRANSVERSE VIBRATION TECHNIQUES

Longitudinal stress wave and transverse vibration nondestructive testi ng (NDT) techniques have pl oven to be accurate means of evaluating th e quality of wood based pl odzlcts. Researchers have found strong rela tionships between stress wave and transverse vibration parameters (e.g ., wave velocity and modulus of elasticity predicted using NDT measure ments) with the actual static bending properties (e.g., modulus of ela sticity from static bending rests) of dry as well as green wood based materials. Therefore, these techniques may be used to presort or grade structural wood prior to drying, provided that cross correlation equa tions lions are developed to relate wood properties in the dry state w ith NDT measurements in the gl een state. Discarding wood with inferio r properties prior to drying can result in significant cost savings in the drying process. This paper presents the results of an experimenta l program designed to examine the relationships between stress wave an d transverse vibration characteristics (i.e., stress wave velocity, an d modulus of elasticity predicted from stress wave velocity and transv erse vibration measurements) with the static bending modulus of elasti city (MOE) and modulus of rupture (MOR) of green as well as dry southe rn pine dimension lumber. Also, cross correlations have been developed between green stress wave and transverse vibration properties with th e dry static bending MOE and MOR. Such doss correlations are important for grading wood in the green state itself, so that drying costs can be minimized. This research resulted in good cross correlation relatio nships between the static bending MOE values of dry southern pine and the nondestructive parameters in the green state (e.g., stress wave ve locity and derived MOE, and transverse vibration based MOE values for green wood). Also, ultrasonic tests were conducted over limited distan ces (300 mm [12 in.]) at three locations on the 2.4 m (8 ft) long spec imens to see if good correlations can be achieved. The low coefficient s of determination lend to the conclusion that ultrasonic testing is n ot suitable for grading of 1.8 to 2.4 m (6 to 8 ft) long dimension lum ber.