Highly Nonlinear Solitary Waves for the Inspection of Adhesive Joints

In this paper we propose the use of highly nonlinear solitary waves (HNSWs) to monitor the curing process of an adhesive layer utilized to bond two aluminum sheets, and to inspect an adhesively-bonded aluminum lap-joint. HNSWs are mechanical waves that can form and travel in highly nonlinear systems, such as a chain of spherical particles where they are generated by means of a mechanical impact. They are characterized by a constant spatial wavelength and possess the important property that their speed, amplitude, and duration can be tuned by modifying the particles’ material or size, or the velocity of the impact. In the study presented in this paper, we investigate the feasibility of HNSWs for the nondestructive testing of adhesively-bonded structures. Two experiments are illustrated. In the first experiment we observe the curing process of a commercial 2-Ton Clear epoxy used to bond two aluminum sheets. In the second experiment, six types of bond quality were created on an aluminum lap-joint. In both experiments we noted that certain characteristics of the HNSWs such as time-of-flight and amplitude are affected by the physical conditions of the test specimen.

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