Inspection of Debonds in Adhesive Joints and Loosened Mechanical Fasteners Using Shearography with Multiple Frequency Vibrational Excitation

To reduce costs and facilitate automation of joining processes, adhesive bonding has gained popularity as a replacement for conventional mechanical fastener, especially for bonding parts made of plastics and polymer composites. However, the adhesive bonding process is more susceptible to quality variations during manufacturing than traditional joining and fastening methods. Shearography, an optical technique that measures full-field surface deformation, has been extended to inspecting debonds. It detects a debond by measuring the debond's response to applied stresses. This paper describes a technique of shearography using multiple frequency vibration excitation as a means of stressing for detecting debonds with closed boundaries as well as open boundaries. The technique can also be used to detect loosened mechanical fasteners. This process can be fully automated for rapid inspection on factory floors.