Page 26 - Research Report 2021 - Institut für Leichtbau und Kunststofftechnik

Fig. 02 In situ examination of different damage levels in a fibre composite.

new application possibilities and innovative processes to contrast microcracks, which are often closed in the
in scientific projects. We are primarily interested in the unstressed state, the ILK can use the in-situ computed
clarification of the so-called process-structure-property tomograph, which was developed in-house. With this
relationships, which will enable data- and model-based equipment, samples can be examined under mechanical
material and process developments in the future. Struc- loads such as tension, compression or torsion at resolu-
tural analysis with imaging methods plays an essential tions from 5 µm voxel size. Load tests with accompanying
role here in order to understand the essential mecha- xCT can be used to observe the initiation and evolution
nisms in the behaviour of the materials. of cracks in discrete stages (Fig. 02). However, scan times
of up to one hour have to be considered for high-con-
Basically, the aim of all NDT methods is to show the con- trast tomograms. Fast processes such as manufacturing,
dition of the material or component. For this purpose, deformation and structure formation processes can nev-
the interactions of the material with electromagnetic or ertheless be explored by recording an “x-ray film” – but at
mechanical waves are utilized. The NDT methods availa- the price of losing depth information.
ble at the ILK can be classified into the following groups:
Cost-effectiveness for xCT in series can be achieved, for
NDT with electromagnetic waves example, by using fast xCT, which requires only a few min-
utes for a scan, in combination with group examinations.
X-ray computer tomography
A considerable competitive advantage results from the
Shearography higher information content due to the volume resolution
compared to classical ultrasound examinations.
Optical measurement and by eye inspection
Thermography For further improving this xCT potential, the ILK is fo-
cusing on two priorities in its development: (1) reducing
image artefacts during acquisition, for example through
NDT with mechanical waves
helical CT or the use of filters, and (2) improving image
Ultrasound: Impuls-Echo, transmission, evaluation through the use of methods of 3D image cor-
water coupling, air coupling relation, correlative image analysis and the deeper inte-
gration of simulation results.
Ultrasound microscopy
Acoustic emission In contrast to xCT, NDT with ultrasound has a longer
tradition and is widely established in materials testing.
Vibration analysis
There are different variations of the method. The use of
air-coupled ultrasound in a transmission arrangement
The ILK has particular expertise in the field of X-ray com- is very efficient due to the low sample preparation ef-
puter tomography (xCT), which in principle can be used fort, especially for the analysis of flat, small to medium
to detect all relevant defects in fibre composites. How- size structures. Its spatial resolution is usually sufficient
ever, this method is limited in terms of spatial resolu- for the detection of all technically relevant defects such
tion, the ability to contrast defects and the analysis of as delaminations, pore fields or dry spots. The disadvan-
large components. We therefore have three devices in tage is that it usually cannot be used to inspect sandwich
use that complement each other's capabilities in this re- components and indicate the depth of the defect. In such
spect: We achieve the highest resolution of approx. 1 µm cases, the pulse-echo method is clearly at an advantage,
with the Nanotom, and we can examine particularly large which can also be used with only one-sided accessibil-
or heavy components with the V|tome|x 450L. In order ity. Its often lower efficiency can be compensated for by

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