Wechselverformung und Gefügeänderungen von Ck 15 und Ck 45

Microstructural Changes and Cyclic Deformation The crack initiation starts due to weakening and strengthening process during rotating bending. However a smaller plastic deformation amplitude is noticed at the same nominal stress compared to tension-compression stressed specimens. This results in a higher fatigue life. The different cyclic deformation behaviour was proofed by SEM (rotating bending specimens showed a lower slip line density compared to tension-compression specimens at the same nominal stress) and TEM investigations (the rotating bending specimens showed a smaller dislocation density at the same nominal stress). Furthermore it is showed, a correlation of cyclic stress strain data σ(ε_pls) between tension-compression and rotating bending specimens exists. This is also valid for the Manson-Coffin-relationship. the relation between lg ε_pls and lg N_B depends on the material (Ck 15, Ck 45) but not on the state of stress.