A new non-contact measuring method for the evaluation of the curing status of glued lightweight components based on ultrasound

摘要

The curing of adhesives depends mainly on the application conditions such as temperature or humidity. Manufacturers' information on pot life and processing time are therefore not always directly transferable to the real application, so that large safety factors in the curing time are observed. This unnecessarily ties up resources such as production and storage areas and delays subsequent process steps, which is accompanied by a significantly reduced added value. There are only a few non-destructive test methods that can be used to monitor the curing processes of adhesives in laboratory. Their main disadvantages are the lack of process capability, the low penetration depth, the high system costs and finally the lack of applicability for real component structures with complex geometries. On the other hand, contact-based ultrasound methods enable monitoring of the curing process with high temporal and spatial resolution and thus offer decisive advantages over laboratory technologies. The sound attenuation and the sound velocity provide material-dependent information that can be correlated directly with the degree of curing. However, disadvantages are a lack of process capability, as between the test head and the component a coupling medium must be present, and the acquisition of locally limited point information. Guided waves by using non-contact air ultrasonic technology are an alternative approach that overcomes these disadvantages. A corresponding test set-up and an evaluation method for determination of ultrasonic characteristics, which allow conclusions to be drawn on the degree of curing, are presented. The referencing is done by rheological investigations.