The strength properties of various adhesive-adherend combinations were determined as one phase of an investigation of the nature of adhesion. The adhesives were polyvinyl acetate, cellulose nitrate, resorcinol resin, casein, gum arabic, natural rubber, and neoprene. The adherends were stainless steel, aluminum alloy, paper-phenolic laminate, glass, birchwood, and hard rubber. The properties studied were double-lap shear, tensile, long-time loading shear, and impact strengths. The tensile-adhesion and shear-strength values for a given adhesive-adherend combination did not differ greatly except for wood and paper-phenolic laminate, which are nonisotropic. The highest values (up to 3600 psi) were obtained with polyvinyl-acetate and cellulose-nitrate adhesives. The thermosetting resorcinol resin showed no appreciable flow in supporting a load of 680 psi for 6 months, whereas the thermoplastic polyvinyl acetate failed in 45 days under a load of 200 psi. The rubber-type adhesives which were weak compared with the other adhesives in the static load tests were definitely superior in the impact tests. Better correlation of shear strengths was observed with the moduli of elasticity than with the dielectric constants of the materials used in the various adhesive-adherend combinations.

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