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Abstract
The mechanical behavior of a flexible epoxy-resin adhesive system was observed in joints of plywood to lumber. The joints were subjected to internal swelling stresses caused by an increase in moisture content. Previous experimental work at the U.S. Forest Products Laboratory has shown that this adhesive system acts as a strain-absorbing cushion and thus has a significant stress-relieving effect in the joint. An attempt was made to use this adhesive as a calibrated tool for measuring shear strain as a function of lumber size, lumber specific gravity, and glueline thickness in a plywood-to-lumber joint. The strain was then converted to shear stress. Photographic results showed that the adhesive acted as a strain-absorbing component by straining in shear up to 0.625 inches per inch without failure. The calibration of the adhesive was complicated because the adhesive performed viscoelastically rather than elastically under a sustained load. Even with this difficulty, certain stress relations were obtained by calibrating the adhesive on a viscoelastic basis using an average sustained load. The technique of using a calibrated adhesive has great potential in studying adhesive behavior; however, it is necessary to have an adhesive system whose performance would he primarily elastic under a sustained load.
Keywords
Shear,
strain,
specific gravity,
calibration,
adhesives,
moisture content,
creep,
joints (timber),
bond strength,
glued joints,
glueline thickness,
Douglas-fir,
epoxy resin
Citation
Krueger, Gordon P. 1965. Behavior of an epoxy-polysulfide adhesive in wood joints exposed to moisture content changes. Res. Pap. FPL-RP-24. Madison, WI : U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 24 pages
