Experimental Procedure for the In-Shear Adhesive Strength Evaluation Under High-Frequency Cyclic Loading

The procedure for evaluating the adhesive strength in shear under high-frequency cyclic loading is advanced. Such loading can speed up the gaining of its characteristics. The problem on the longitudinal vibrations of a compound bar, with its elements joined by elastic shear bonds is the theoretical grounds of this procedure. The longitudinal vibrations of the experimental symmetrical bar system, which is the working block of a high-frequency resonance test unit, are analyzed. It is a structure consisting of a carrying half-wave rod with concentrated weights on the ends to which test specimens are rigidly fixed symmetrically about the former. General solution results for the vibration problem of such a system are cited. The displacement functions for its parts, including test specimens, which are made as compound bars with adhesive bonds, were derived. The two kinds of frequency equations of the system for its symmetric and antisymmetric natural vibration modes are constructed. As an example used in the experiment, the frequency parameters of the system at its fundamental vibration modes are found based on the antisymmetric vibration relations, the displacements of system elements at this mode are graphically presented. The experimental investigation that completes the algorithm of the procedure implementation is performed after a familiar scheme of determining the endurance limit, if frequencies, displacement functions, and numerical vibration amplitudes in any point of the system are known. The performance and efficiency of the procedure are verified by the example of finding the cyclic adhesive strength of bonded flat metallic specimens. For an Al alloy and cyanoacrylate adhesive at a 10-kHz frequency and 10(7)number of cycles, the limiting value of tau(-1) approximate to 60 MPa was obtained.