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Monitoring Of Adhesive Cure Process and Following Evaluation of Adhesive Joint Structure by Acoustic Techniques

Structural adhesives become more popular in automotive production as a part of body assembling process. The development of new adhesive bonding technologies shows the necessity for effective non-destructive quality assessment of the joints. In the present work, curing reactions of the epoxy structural adhesive were investigated by acoustic methods in pulse-echo mode at 20 MHz at isothermal and non-isothermal conditions. The changes of acoustic properties at the reaction reflect all phenomenological changes, which occur in epoxy adhesive during cure. Method will help to determine optimal cure regime to achieve maximum conversion and develop high adhesion strength. A metal/adhesive interface of adhesive joints and bulk adhesive properties were then investigated by high resolution acoustic microscopy in frequency range of 25-250 MHz. Joints that have undergone thermal and hydrothermal degradation were also analyzed. Capability of acoustic microscopy to detect all major defects and damages, both in the interface and in bulk, was demonstrated. Results presented in this paper can be useful as a basis for development of NDT technique for monitoring adhesive joints quality in the automotive industry.