Regensburg 2007 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 39: Mechanical properties I

MM 39.4: Vortrag

Donnerstag, 29. März 2007, 17:00–17:15, H6

Local stress incompatibilities as source of dislocation nucleation and damage — •Markus Welsch, Michael Marx, and Horst Vehoff — Universität des Saarlandes, Werkstoffwissenschaft und Methodik, Postfach 15 11 50, 66041 Saarbrücken, Deutschland

During high cycle fatigue of polycrystalline materials local inhomogeneities cause localized additional stresses. For instance due to elastic anisotropy orientation differences at grain boundaries work as additional driving forces for damage mechanisms. This was shown by experiments and simulations in a previous work, where cracks initiated exactly at grain boundaries with the highest incompatibility stresses calculated by finite element method (FEM). In the further work these experiments are extended to local plastic deformation at higher loads. The stress distribution of an elastic anisotropic material is calculated by FEM. This calculation uses the 3-dimensional arrangement of the grain boundaries and the orientation of the grains determined by electron backscatter diffraction. In the range of beginning elastic-plastic deformation, the local additional stresses are absorbed by the formation of dislocation structures (DS). DS and persistent slip bands develop, which also act as preferential crack initiation sites. These DS are examined by electron channelling contrast imaging. During fatigue in the grains of different orientation strongly varying DS are formed. But also inside these grains the arrangement of the structures is not uniform. Near grain boundaries seams with different DS are generated. The influence of incompatibility stresses on DS and their influence on crack initiation and propagation are presented in this work.