Theoretical and Experimental Study of the Acoustic Nonlinearities at an Interface with Poor Adhesive Bonding

Abstract

The problem of characterizing adhesion bonds nondestructively is of ever increasing importance, as industry moves towards the use of adhesive technology as a means of efficiently bonding all types of materials. While conventional ultrasonic methods seem to provide adequate inspection for delaminations or missing glue, it doesn’t appear capable of distinguishing poorly cured adhesion, “kissing” delaminations, or weak adhesive bonds. It has long been speculated that nonlinear ultrasonic inspection might provide a solution to these problems. Numerous recent papers have been devoted to these proposals, dealing with both the experimental and the theoretical difficulties they pose, which are significant1–4. It is our view that the main difficulties are inherent in the interpretation of the origin of tiny harmonic distortions being produced in a complicated structure with numerous frequency dependent effects such as resonance, attenuation, reflection, diffraction, and possibly dispersion, as well as filtration in the generating and recieving electro-mechanical systems. The approach we propose is therefore to couple a simple and flexible time-domain theory, hopefully capable of providing recognizable predictions, with a minimalist experimental approach which is clear and interpretable, based on powerful input signals and sizeable distortion of the waveform.