Joining Techniques

Elastic waves can be used to determine the thickness and elastic properties of layered structures.
Even if the thickness of a layer is too small for pulse-echo measurements, the thickness or elastic properties of a layer can be calculated from the propagation behavior of surface waves. Depending on the frequency, surface waves penetrate the layer and substrate material below the surface to different depths. Low frequencies correspond to large penetration depths, high frequencies correspond to small penetration depths (see graph).
The different properties of the layer and substrate result in a frequency-dependent phase velocity of the surface wave. This can be measured and numerically modeled, and thus the thickness and elastic properties can be determined.
For more information, see our publication: https://doi.org/10.1115/QNDE2021-74927

Optical pump-probe spectroscopy on the picosecond timescale (picosecond laser ultrasound “PLUS”) enables the study of elastic phenomena in the GHz- and even up to the THz-range.
We apply different detection schemes to investigate a large variety of materials from metals, semiconductors and polymers to novel nano- and low dimensional materials.
This gives us access to material intrinsic parameters like acoustic damping, heat diffusion and other dissipation mechanisms, doping profiles, as well as to structural properties like layer thicknesses in the sub-nm to low um range, the adhesion quality of thin coatings and other interface related properties.
Further information about a possible application can be found in https://doi.org/10.1016/j.pacs.2023.100464

The homogeneity of adhesive layers, which is not visible or accessible after the joining process of the components, should often be tested. The modern technique of Photoacoustic Imaging provides a solution in such cases. For example you can see here (b) errors in the adhesive layer between (a) a non-transparent plastic component and a metal component – and (c) the adhesive surface in a PAI-Scan.

Non-destructive testing of welds is possible with Laser-Ultrasound. Thanks to the good automation capacity also inline measurements at high speed can be carried out, depending on the required resolution. With a repetition rate of 10 Hz, 100 Hz or even higher, flaws, inclusions, hot cracks and pore concentrations can be found. 

By means of Laser-Ultrasound also spot welds can be scanned in a short time and zones of actual material connection (weld nugget) can be imaged and evaluated.

The Laser-Ultrasonics technology is also applicable for the testing of adhesion and bonding layers, e.g., solder joints. As the high-frequency ultrasonic waves are influenced at the interfaces, an image of this critical inner zone can be generated.

With the Terahertz technology (THz) it is possible to look through relatively thick plastic layers and test hidden layers non-destructively (e.g. adhesive layers). The terahertz waves used are not harmful for health (no ionizing radiation), but still make it possible to look inside many optically non-transparent materials.

Multilayer-films carry great importance especially in the food industry. For example, the thickness and homogeneity of barrier layers have a great influence on the shelf-life of food. With the OCT technology you can measure the thickness of the individual layers with high-resolution inline during the process. Moreover, you can see and detect delaminations and welding seams in real-time and possibly regulate and optimize the production process based on this measurement data.

An adhesive bond can only be as good as the production process in which it was produced. Besides the optimum choice and quality of the adhesive agent, the preparation of the surfaces and the perfect process control also play important roles in ensuring utmost performance of the bond in terms of load capacity and fatigue strength.
By utilizing spectroscopic technologies we can help you to monitor and control all chemical parameters (e.g., in mixtures, reaction monitoring, cleanliness of surfaces, hardening) directly inline during the process.

Do you want to know the exact local distribution (in micrometer range) of your chemical components? With Mid-Infrared-Microscopy we can chemically characterize and measure materials and cross-sections (e.g. residues or inclusions) with a spatial resolution as small as 5 µm.