The Effect of Clamping Pressure and Orthotropic Wood Structure on Strength of Glued Bonds


  • R. J. Rabiej
  • H. D. Behm


Clamping pressure, glueline strength, glueline testing, optimum clamp pressure, orthotropic wood structure, percentage of wood failure, wood bonding


Reference values for compression strength perpendicular to the grain were determined for radial and tangential sections of samples of sugar maple and ponderosa pine. Samples to be glued were matched according to specific gravity and orthotropic structure and bonded along the grain in tangential or radial sections. Magnitude of clamp pressure was controlled throughout a range of pressures commonly applied in industry, up to about 80% of the compression strength of the wood sample. Tests were conducted on the bonded samples to determine glueline shear strength and percent of wood failure at the bonded surfaces. Results were subjected to regression analysis to ascertain relationships. It was determined that clamping pressure had a different effect on both shear strength and percent of wood failure depending on species and orthotropic section. It is possible to maximize joint strength by applying proper clamping pressure. Results similar in direction but differing in magnitude were obtained with both PVAc and U-F adhesives. A generalized measure of clamping pressure was defined as the ratio of applied clamping pressure to the compression strength (CP/CS) of the wood section to be glued. Using this concept, the optimum clamping pressure for sugar maple was found to be 0.3 times compression strength using U-F glue and 0.5 times using PVAc glue. This approach to determining reliable clamping pressure data can lead to improved gluing practice and more precise testing procedures.


American Society for the Testing of Materials. 1983, 1989. ASTM D 2016-83: Moisture content. ASTM D 2395-83: Specific gravity. ASTM D 143-83: Compression strength. ASTM D-905-89: Glue line shear strength and estimated percentage of wood failure.nBaumann, H., and J. E. Marian. 1961. Gluing pressure with wood as a function of physical factors. Holz Roh Werkst. 11:441-446.nBrady, D. E., and F. A. Kamke. 1989. Effect of hot-pressing parameters on resin penetration. Forest Prod. J. 38(11/12):63-68.nBrown, H. P., A. T. Panshin, and C. C. Forsaith. 1952. Textbook of wood technology, vol. II. McGraw-Hill Book Company, New York.nCagle, C. V. 1968. Adhesive bonding. McGraw-Hill Book Company, New York.nForest Products Lab. 1974. Wood handbook—Wood as an engineering material. U.S. Department of Agriculture.nKollmann, F. P., and W. C. Côté, Jr. 1968. Principles of wood science and technology, I. Solid wood. Springer-Verlag, New York.nKollmann, F. P., E. W. Kuenzi, and A. J. Stamm. 1975. Principles of wood science and technology. II. Wood-based materials. Springer-Verlag, New York.nMarra, A. A. 1980. Adhesives for wood composites. "Wood adhesives research, application and needs" Symposium, Sept. 23-25. Madison, WI.nMetrak, C. 1975. Furniture—Bases of construction and design. W. N. T., Warszawa.nOkkonen, E. A., and B. H. River. 1989. Factors affecting the strength of block-shear specimens. Forest Prod. J. 39(1):43-50.nPanshin, A. J., and C. de Zeeuw. 1970. Textbook of wood technology, Vol I. McGraw-Hill Inc., New York.nPerkitny, T., and R. S. T. Kingston. 1972. Review of the sufficiency of research on the swelling pressure of wood. Wood Sci. Technol. 6:215-229.nRabiej, R. J., and H. D. Behm. 1989. A test method for orthotropic wood properties. Proceedings of the X Inter-American Conference on Materials Technology. South-west Research Institute, San Antonio, TX.nRabiej, R. J., and P. T. Brown. 1986. Factors affecting setting rate of poly (vinyl acetate) adhesives in wood joints, (Wood Adhesives in 1985: Status). Proceedings of a Conference by FPRS.nSelbo, M. L. 1975. Adhesive bonding of wood. USDA Bulletin No. 1512.nStasiak, H. 1963. The method of surface machining of wood and its influence on the shearing strength of the glue line. Przemysl Drzewny. 14(1): 15-18.nSuchsland, O. 1958. On the penetrating of glue in wood and the significance of the penetration depth for the strength of glue joints. Holz Roh Werst. 16(3): 101-108.nTruax, T. R. 1929. The gluing of wood. USDA Bulletin No. 1500.nZenkteler, M. 1968. Technology of wood gluing. PWRiL. Poland.n






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