Abstract
The initial results (stage 1) of this research were presented in the 96 'SPIE's Symposium on Nondestructive Evaluation Techniques for Aging Infrastructure & Manufacturing.' It was shown, that aging of adhesives and bonded joints can be evaluated non-destructively by vibration analysis, based on the internal friction (damping) effect. Good correlation between the specific damping capacity (SDC) and the shear strength of bonded joints, consisting of flat aluminum slabs as adherends and two kinds of polyurethane adhesives was found for three aging procedures. The present work is an additional step towards the target application -- developing a tool for characterizing the aging effect on joint strength in bonded devices. Unlike the rapidly developing field of Resonance US, this work is concentrating mainly on the damping capacity, which is directly correlated with joint strength. Additional adhesives and adherends as well as various geometries and sizes of the bonded joints were tested. The effect of the following factors was established: adhesive aging or shear strength, adherends, temperature, sample size (up to diameter of 14') and sample shapes (flats and rings). The results show that the prospects of practical application of the method are most promising, although they are better for some structures and worse for others. Some guidelines were determined in this work. For more reliable wide ranging guidelines, theoretical analysis is required. The only generally applicable way to do it is by numerical simulation of vibrational stresses.
