Quality assurance for structural adhesively bonded joints by eddy current shearography

Abstract

To reduce weight of industrial appliances and to avoid thermally caused influences on the microstructure during the joining process, adhesive bonding has become increasingly important for the joining of mixed materials in recent years. Adhesive bonding is a joining process in which the quality of the process has to be ensured through sufficient surveillance and documentation of the manufacturing process. Apart from supervising the process, modern quality management and product liability demand that the quality of a manufactured product is recorded and documented fully. As the currently applied nondestructive testing (NDT) measurements such as ultrasonic testing (UT) or radiographic testing (RT) take too long to be used for serial productions, destructive testing methods are generally applied. As an optical method with good potential to become an automatable NDT method for adhesively joined bonds, shearography fulfills all necessary requirements. This contact-free method covers large areas and uses coherent illumination to detect the speckle pattern of the surface of the testing object. Changes in deformation can be determined by recording two stress scenarios. Thermal or mechanical forms of stimulation (e.g., flash lamps, low pressure) have proven reliable for putting stress on the testing object. Flaws in the bond cause local changes in deformation and can be detected with shearography. Thus, imperfections can be found due to the local change in the mechanical properties (e.g., stiffness) of the constructional element.