Latest PhD Defenses

date: 20.12.2018

In December 2018 a PhD thesis defence took place within the Laboratory for Tribology and Interface Nanotechnology.

Dr. Dejan Poljanec: Tribological optimization of axial slip ring for automotive alternators

In the PhD thesis we have studied the influence of operating parameters (sliding velocity, normal contact force, electrical current and direction of the current) on the tribological and electrical properties of the innovative design of sliding electrical contact. A dedicated tribological test rig was developed for this purpose, and is also presented in this thesis. Out of the initial eight graphite materials, three graphite materials (hard carbon, electrographite and polymer-bonded graphite) were selected under the demanding operating conditions and were further tested and studied in detail. They were running against self-mated contacts and against copper. In all conditions, a specific surface film formation was detected, which have a key effect on the properties of the sliding electrical contact. Smooth, well-compacted film, that overlaps most of the contact, usually gives good tribological properties and stable contact operation. With graphite/graphite combinations better tribological and electrical properties than with graphite/copper combinations can be achieved. The chosen polymer-bonded graphite has proved to be the most suitable, both in pair with copper, and especially in contact with itself. The direction of the electrical current has no influence on the behaviour of the graphite/graphite combinations. Meanwhile, in the case of the graphite/copper combinations, the negative graphite surfaces wear more than the positive graphite surfaces, and the positive copper surfaces wear more than the negative copper surfaces. The results demonstrate the great potential of graphite/graphite material combinations in the disc-disc sliding electrical contact, as it is possible to achieve a good efficiency of the contact and very low wear.