gms | German Medical Science

To obtain long term mechanical degradation parameters form implants and implant material requires some severe effort in performing and analyzing time-evolved multi circle load tests. A good example are Archard’s wear depth parameter kd usually extracted via complex tribological experiments. Analytical analyzing these tests in order to come to a sufficiently generic description allowing the generalization and simulation of real life (in vivo) applications still is a quest of almost unrivaled difficulties. What is more, in the case of soft implants or nano-composites we also have the problem of principle time dependency of the materials used due to their usually highly viscous properties and inhomogeneous structure.

The talk features an approach where such parameters are extracted from effective interaction potentials [1], which themselves are built up and fed from more physical-oriented contact measurements like Nanoindentation and PHYSICAL scratch. By using such effective material potentials one can derive critical loading situations leading to failure (decomposition strength) for any contact situation also the typical ones occurring in vivo. A subsequent connection of these decomposition or failure states with the corresponding stress or strain distributions allows the development of rather comprehensive tribological and degradation parameter models applicable in wear and fatigue simulations as demonstrated in this work.

From this a new sophisticated practical and in vivo wear model has been developed on the basis of the effective indenter concept [1], [2] by using the extended Hertzian approach [3], [4]. The models do not only allow to analyze certain tribological experiments like the well known pin-on disk test or the more recently developed nano-fretting tests, but also to forward simulate such tests and even give hints for better implant life-time predictions. The work will show how the procedure in principle is to be applied and a few examples will be presented in the corresponding talk. Thereby also newest results of an international EU-project about long term deformation behaviour of viscous materials [5] are going to be presented.