Effect of cross grain on stress waves in lumber

Abstract

An evaluation is made of the effect of cross grain on the transit time of longitudinal compression stress waves in Douglas-fir 2 by 8 lumber. Cross grain causes the stress wave to advance with a front or contour skewed in the direction of the grain angle, rather than to advance with a front normal to the long axis of lumber. Thus, the timing of the stress wave in lumber with cross grain is complicated. Based on the static bending modulus of elasticity of the lumber evaluated, an average of transit times for determining a stress wave modulus of elasticity (E) was better than two other timing bases. Another timing basis, however, was best in accounting for stress-wave measurements on 2 by 4’s cut with a 4.4° slope of grain bias from the 2 by 8’s. These results should aid in the development of lumber stress grading systems using E measurements based on stress waves.

Citation

Gerhards, C.C. 1980. Effect of cross grain on stress waves in lumber. Res. Pap. FPL-368. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, 1980: 8 pages