Structural adhesive bonding has become increasingly important for the joining of dissimilar materials as well as for the reduction of weight of joined structures. To ensure the quality of these bonds, non-destructive testing (NDT) such as ultrasonic testing (UT) or radiographic testing (RT) is used. However, both testing methods have the disadvantage that the measurement takes too long to be used for mass productions. Shearography is an optical method with suitable capability for automated NDT of adhesively bonded joints. It is a contact-free method with an extensive measuring field. For the measurement, an object is illuminated with coherent light. The reflection on the surface causes a speckle pattern on a detector. During the measurement, the object is stressed with the help of thermal or mechanical excitation (e.g. flashlight, underpressure). Changes in deformation of the object’s surface can be calculated by recording two stress scenarios. Flaws in the bonding area cause a local change of deformation and can be detected with shearography. This paper presents the prospects and limitations of shearo-graphy for adhesively bonded structural joints. The stress in the specimen was achieved by thermal expansion caused by eddy currents. The evaluation included similar and dissimilar structural bonds of metal (e.g. deep drawing steel, aluminum) and CFRP substrates. The target of the examination is the characterization of the detectability of different bonding flaws such as missing adhesive, voids within the adhesive and kissing bonds.

In the present investigation, thin sheets of stabilized and unstabilized ferritic stainless steel were welded in butt joint configuration using irradiation of a 1070 $\mathrm{n}\mathrm{m}$ fiber-laser. Using optical microscopy, the microstructural evolution upon alternating heat input was characterized. In addition to that, hardness and tensile tests were carried out on the specimens. Detailed focus was given to the intergranular corrosion properties, which were investigated on basis of the Strauss test with different times of exposure to the corrosive environment. Following these tests, the mechanical properties of the joints were characterized using tensile tests. A combination of the latter with an inspection by $\mathsf{\mu }$-CT analysis allows for the proposition of an intergranular corrosion rate with regard to the degradation of the joint strength.

The effect of micro patterning of cemented carbide surface using nanosecond diode pumped solid-state pulsed laser on the strength of induction brazed carbide and steel joints has been investigated. Surface patterns increase the total surface area of the joint and, for an originally hydrophilic surface, increase the wettability of a liquid on a solid surface such that, instead of building droplets, the liquid spreads and flows on the surface. Microcomputed tomography (µ-CT) was used to observe the filler/carbide interface after brazing and to analyze the presence of porosity or remnant flux in the joint. Microstructures of the brazed joints with various surface patterns were analyzed using scanning electron microscopy. The strength of the joints was measured using shear tests. Results have shown that the groove pattern on the surface of carbide increases the joint strength by 70–80%, whereas, surface patterns of bi-directional grooves (grid) reduced the joint strength drastically. Dimples on the carbide surface did not show any improvement in the strength of the brazed joints compared to samples with no surface pattern.

In this paper, the potential of directional ultrasonic wave superposition by moving sound generators for laser beam welding of high-strength steel alloys 1.5528 (22MnB5) is studied. Steel sheets of identical thickness and in form of tailored blanks were joined in butt joint configuration. The influences of the various excitation parameters of the moving sound generators on the ultrasonic coupling and their influence on the distribution of the AlSi coating components within the melting zone and the weld seam characteristics are investigated. Etched cross-sections, scanning electron microscopy, energy dispersive X-ray spectroscopy, and electron backscattering measurements were used as the investigation methods to determine the AlSi distribution in the weld as well as its microstructure. The results presented a series of experiments which show that a suitable superposition of ultrasonic waves by the moving sound generators lead to a more homogeneous distribution of AlSi particles in the melt as well as to a finer microstructure within the weld, which improves the mechanical–technological properties.

Kurzfassung: In diesem Beitrag wird das Einsatzpotential der induktiv angeregten Shearografie mit dem der aktiven Thermografie zur zerstörungsfreien Prüfung von Klebverbindungen verglichen. Untersucht wird die Detektierbarkeit unterschiedlicher Fehlerbilder an Dickschicht- und Strukturverklebungen von Aluminium- und Tiefziehstahlsubstraten. Beide Verfahren zeigen für einen Einsatz bei strukturellen Klebungen gute Ergebnisse. Die Shearografie ermöglicht die Detektion von Fehlern, die zu lokalen Steifigkeitssprüngen in der Klebverbindung führen. Diese Steifigkeitssprünge können durch eine inhomogene Durchmischung oder durch Kissing Bonds verursacht werden. Der Nachweis dieser Fehler ist bei der angewendeten Messanordnung mittels Thermografie nur schwer bis gar nicht möglich. Mittels Thermografie ist hingegen eine eindeutige Detektion von ungleichmäßigen Klebschichtdicken möglich, die mittels Shearografie bisher nicht detektiert werden konnte. Bei den elastischen Klebungen zeigt die Thermografie bei vielen Fehlertypen deutlichere Messergebnisse als die Shearografie. Fehlertypen, die sich fast ausschließlich auf die Aushärtung des Klebstoffes auswirken, sind nur durch Shearografie nachweisbar. Da beide Verfahren unterschiedliche physikalische Grundlagen ausnutzen und sich dadurch für die Detektion unterschiedlicher Fehlertypen eignen, ist eine Kombination beider Verfahren sinnvoll. Die beiden Methoden ermöglichen so den Nachweis eines Großteils der für Klebverbindungen relevanten Fehlertypen.