Stress wave techniques for determining quality of dimensional lumber from switch ties

Abstract

Researchers at the Forest Products Laboratory, USDA Forest Service, have been studying nondestructive techniques for evaluating the strength of wood. This report describes the results of a pilot study on using these techniques to determine the quality of large dimensional lumber cut from switch ties. First, pulse echo and dynamic (transverse vibration) techniques were used to determine the modulus of elasticity (MOE) of 12 untreated red oak switch ties. The ties were then sawn into nominal 2 by 8 specimens, which were later resawn into nominal 2 by 4 specimens. Pulse echo and transverse vibration techniques were used to determine the MOE of the individual lumber members. Positive correlations were observed between the pulse echo MOE of a switch tie and the full-length parallel-tograin pulse echo MOE and dynamic MOE of the lumber sawn from the tie. The accuracy of the prediction of lumber MOE decreased with a reduction in the size of the members: the greater the number of members cut from the tie, the less accurate the prediction. Strong relationships were seen between pulse echo and dynamic MOE of both green and dry lumber. The data also demonstrate that the speed of sound can be useful in predicting internal degradation of a tie and can be correlated to the specific gravity of the tie. The latter finding may be useful to hardwood crosstie producers who have expressed interest in a simple species-independent technique for nondestructive grading of ties on the basis of density.

Citation

Schad, K. C.; Kretschmann, D. E.; McDonald, K. A.; Ross, R. J.; Green, D. W. 1995. Stress wave techniques for determining quality of dimensional lumber from switch ties. (Research note FPL ; RN-0265):12 p. : ill. ; 28 cm.