Johannes Reiser

The Fatigue Behaviour of a High Strength CrNi-Steel Regarding Fretting Fatigue

In many assemblies of moving components, contact problems under various lubrication conditions are lifetime-limiting. There, relative motion of contacting bodies, combined with high loads transmitted via the contact surface lead to fretting fatigue failure. For a reliable prediction of in service performance load type, different damage and failure mechanisms that may be activated during operation have to be known. In this contribution selected results of a currently conducted research project are presented. The aim of this study was to examine the material behaviour of a surface stressed steel. The influence of the fretting regime on fatigue properties has been investigated.Copyright

A testing apparatus for SEM in-situ fatigue testing of small scale specimens and a derived application

The prediction of fatigue strength and fatigue life of materials was the key motivation in this study. Several approaches for fatigue limit prediction at mesoscopic scale have been proposed. All of them incorporate microstructure and grain features. For the purpose of studying plastic local strain accumulation and therefore fatigue behaviour at the grain scale a new testing rig was developed. A key point for understanding fatigue behaviour and crack initiation even at higher load cycles is basic knowledge on strain localization in the grain structure of the material. Till now low testing frequencies of SEM in-situ testing rigs limited tests at higher load cycles. The developed in-situ tension-compression testing apparatus for in-situ SEM use allows testing at higher frequencies and therefore to perform even higher load cycles with less time consumption. Oxygen free high conductivity copper (OFHC) grade 99,99% was chosen for investigation. In addition cuts with a focus ion beam (FIB) were made in distinct orientations representing material defects to get an idea of the influence of micro notches on fatigue behaviour and crack initiation. The results of in-situ fatigue tests will be presented.Copyright