Effect of veneer quality and specimen type on compression properties of southern pine plywood in dry and wet conditions

Experimental evidence from 2- by 2- by 8-inch specimens and statistical analysis indicate that compressive stiffness of the different specimen types investigated are significantly different for specimens with different grades of face veneers. The average reduction in stiffness from dry to 48-hour-soaked condition is 30 percent. There is a special interaction between veneer grades and percentages of the parallel-oriented veneers on compressive strength. In the 3-ply basic construction with two-thirds parallel-oriented veneers, there is a significant increase in strength by improving the grades of the parallel veneers from C and D to B. In the 4-ply basic construction with one-half parallel-oriented veneers, no analogous increase in strength occurs with similar improvement in veneer grades. The average reduction in compressive strength from dry to 48-hour-soaked condition is 58 percent. In general, no significant differences were found between the compressive strength of large and small plywood specimens in the wet condition. In the dry condition, the strength of small specimens was generally 12 percent higher than that of the large-size specimens. Evidently, for determination of plywood compressive properties, preference should be given to small-size specimens because they require no special testing frame and provide both compressive stiffness and strength data in a single test.

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