Nanostructured and ultrafine-grained metals are of great interest as they show improved mechanical and physical properties compared to their coarse grain counterparts. Not many studies concentrate on the crack propagation properties of ultrafine-grained materials, although it is an important aspect in many engineering applications and difficult to derive from other properties.

For this reason fatigue crack growth of ultrafine-grained metals, produced by high pressure torsion is investigated. In order to take the texture of high pressure torsion produced materials into account, specimens with different orientations in respect to the shear direction are tested. To learn more about the effect of the loading condition, crack growth experiments with different load ratios are performed.
The potential drop method is used to determine the crack length in the crack propagation investigations. For guaranteeing accurate measurements, the calculation of the crack length of small CT specimens based on the electrical potential drop is closely studied.
After the tests, specimens are studied using a scanning electron microscope. Thereby fracture mechanisms can be identified and differences between specimens tested at different load ratios and with different orientations can be determined.

The results should help to better understand the crack propagation process and to optimize the architecture of nanostructured materials in respect to fatigue.