Comparison of inductive shearography and thermography for the detection of flaws in structural and elastic adhesive bonds

Kryukov, Igor; University of Kassel; Germany

Böhm, S.; University of Kassel; Germany
Kryukov, I.; University of Kassel; Germany

ID: ECNDT-0165-2018
Session: Microwave, Terahertz, and Infrared NDE
Room: H1
Date: 2018-06-13
Time: 16:20 - 16:40

For bonding of different materials in lightweight constructions in materially optimized designs, adhesive bonding has become increasingly important for industrial appliances. However, the bonding process needs a high degree of supervision. The DIN 2304 standard, which came into force 2016, defines four classes of bonds and lists the requirements for the supervision of measurement and testing instruments. One possibility to proof the correctness of bonding is non-destructive testing. Unfortunately, the established methods ultrasound and radiographic examination can only be integrated into very few serial productions as the testing period is too long. This, in turn, brings the testing methods “active thermography” and “shearography” into the focus of the bonding industry.
Both testing methods are contact-free and can test large areas in short time, but focus on different physical variables. Active thermography disturbs the thermal balance of the testing sample and focuses on the thermal diffusibility. Shearography, on the other hand, evaluates the deformation gradient as a reaction to a certain stress on the surface of the sample. Local deviances in the thermal diffusibility or the deformation gradient indicate flaws in the bond seam.
This paper aims at comparing the potential of shearography and active thermography for non-destructive testing of bonding. Inductive loading in transmission arrangement are used as excitation for both methods. Different types of flaws and irregularities are examined (e.g. missing adhesive, voids as well as “Kissing Bonds”) in similar and dissimilar structural and elastic bonding. The boundaries of detection for each type of flaw and testing method will be evaluated as well as a possible advantage of combining both systems.