Force and work to shear green southern pine logs at slow speed

Abstract

When logs of three diameter classes and two specific gravity classes were sheared with a 3/8-inch-thick knife travelling at 2 inches per minute, shearing force and work averaged greatest for dense 13.6-inch logs cut with a knife having a 45^o sharpness angle (73,517 pounds; 49,838 foot-pounds). Force and work averaged at least 5.1-inch bolts of low density when cut with a knife having 22-1/2^o sharpness angle (9,975 pounds; 2,885 foot-pounds). Values for 9.7-inch bolts were intermediate. Shear force reached a maximum about three-fourths the way through the log; it then dropped rapidly as the knife traveled the reamining distance. Momentary peaks of force commonly occurred near the three-quarter point. The greatest observed force to shear was 92,000 pounds required for a 13.6-inch log of 0.51 specific gravity (ovendry weight and green volume) when cut with a knife having 45^o sharpness angle. when sheared logs were viewed in radial section, each annual ring showed a check at the earlywood-latewood boundary. Checks were least severe in small logs sheared with the 22-1/2^o knife, where they averaged 0.8 inch deep; they were most severe in large logs of low density sheared with the 45^o knife, where they averaged 1.4 inches deep. Each sheared log generally also had one to several rather lengthy checks that formed just prior to emergence of the knife. Regression expressions were developed to predict force and work to shear as well as average and maximum check depth-all in terms of sharpness angle, wood specific gravity, and log diameter.

Citation

Koch, Peter. 1971. Force and work to shear green southern pine logs at slow speed. Forest Products Journal, Vol. 21(3): 21-26