Investigation of damage development of polymer foams using interrupted in-situ X-ray tomography

Salaberger, Dietmar; University of Applied Sciences Upper Austria; Austria

Salaberger, D.; University of Applied Sciences Upper Austria ; Austria
Gerner, S.; University of Applied Sciences Upper Austria ; Austria
Kahlen, S.; Borealis Polyolefine GmbH; Austria
Kastner, J.; University of Applied Sciences Upper Austria ; Austria

ID: ECNDT-0466-2018
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Session: CT-Applications 2
Room: G3
Date: 2018-06-13
Time: 11:30 - 11:50

Polymeric foams are used intensively for a widespread of different applications. In order to extend the range of applications further, especially for novel polymeric materials, knowledge about microstructure and change in microstructure during mechanical loading is needed.
This contribution uses X-ray tomography to characterise the cell structures while interrupted compression testing.

The investigated specimens were punched out of 3 mm thick sheets of polypropylene and had cylindrical shape.
From a first compression test without stopping the experiment the positions on the force-extension curve were defined for interrupting. Figure 1 shows the curve of the interrupted compression test. After the desired force was reached, a delay time was applied to prevent relaxation during CT scanning. The resolution is depending on the cell size and the cell wall thickness. For the investigated materials a voxel edge length of 2.5 µm was reasonable. CT scans were performed at a laboratory CT device.

The slice images in Figure 2 (left) show collapsing of cells which is pronounced in the centre of the sheet. The segmentation of each separated cell is done using MAVI (Fraunhofer ITWM, Kaiserslautern) and a watershed approach. The image processing of deformed cells requires adapted pre-processing and parameter optimization compared to the undamaged state.

Quantitative results in terms of changes in cell size distributions for several materials tested by interrupted in-situ CT will be shown.