Stress wave nondestructive evaluation of Douglas-fir peeler cores

With the need for evaluating the utilization of veneer peeler log cores in higher value products and the increasing importance of utilizing round timbers in poles, posts, stakes, and building construction components, we conducted a cooperative project to verify the suitability of stress wave nondestructive evaluation techniques for assessing peeler cores and some mechanical properties of lumber that might be derived from peeler cores. Longitudinal stress waves were used to evaluate peeler cores from 111 Douglas-fir stems. Supplementary dynamic and static tests were then conducted on 2 by 4 lumber sawn from the cores. Stress wave testing of peeler cores was found to be a good predictor of static and dynamic modulus of elasticity (MOE) of lumber sawn from the cores. However, correlations between stress wave MOE of the peeler cores and bending and tensile strength of derived standard-size lumber were low. Nonetheless, based on past experience, the data derived could establish a means for classifying peeler cores into three stress classes, which would have higher levels of confidence for assigned bending and tensile design strength. For lumber stress wave MOE compared with peeler core stress wave MOE, the coefficient of determination (r²) value was 0.81. In the comparison of transverse vibration MOE of lumber with stress wave MOE, peeler cores had a corresponding r² of 0.72. Comparison of statically determined tensile MOE of the lumber with stress wave MOE of the cores showed an r ² of 0.70, but for ultimate tensile strength of the lumber taken as one large group compared with stress wave MOE, the r² was only 0.38. For statically determined modulus of rupture of the derived lumber taken as a single group compared with dynamic stress wave MOE of the peeler cores, the r² was 0.32.