A Rapid, Continuous Method of Testing Glued End Joints

A nondestructive testing procedure and a simple machine for rapidly proof-loading lumber products is the subject of this report. Developed particularly to insure the bending strength of end-jointed lumber, the article also points out the relationship between flexural deflection and inherent strength of joints. Proof loading is accomplished by applying a load to induce the allowable stress for the piece, suitably adjusted for rate of loading. To prevent breakage of weak pieces, which deflect excessively, a limit switch system discontinues load application if there is any tendency for excessive deflection. The procedure then evolves into a system of sequential loading, to prevent damage by the strength test. Data on the effectiveness of using deflection as a determinant in proof-loading without damaging peices are presented. The system can be used to stress grade unjointed lumber more precisely and with more discrimination than conentional visual grading methods, according to the authors. The interaction of shrinkage and strength to prevent confounding of results by moisture variation is suggested. This is a pioneer work in the development of nondestructive machine stress grading.

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