Non-destructive Evaluation of Adhesive Bonding Using Reflective Fringe Pattern Technique

Adhesive bonding is an important fabrication technique for traditional and modern engineering materials in most industrial applications. Compared to the traditional joining methods (such as mechanical fastening or welding), adhesive bonding is rather simple, low cost and time-saving. The performance of the adhesive bonded assemblies strongly depends upon both the material and adhesive properties, and also the bond quality. An excessive gap between the joined elements could result in local stress concentration, and consequently reduce the bond strength. This paper suggests a full-field and optical technique, Reflective Fringe Pattern (RFP) technique, for evaluating adhesive bonding. RFP is based on reflecting the fringe pattern from a specularly reflective surface. In the measurement, two sets of the reflected fringe patterns (i.e. one before and the other after deformation) are recorded to produce the corresponding fringe phase distributions. The difference of these phase distributions depicts the surface deformation. As an adhesive disbond affects the surface deformation, the presence of adhesive disbond can be located by identifying the flaw-induced deformation anomalies in the phase-change distribution map. The potential of using RFP for inspecting adhesive bonding is demonstrated and compared with the conventional non-destructive testing technique—thermography.