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Numerous investigations in the past decades have shown that the fatigue threshold is influenced by several external and internal parameters. The effect of closure as one of the dominating factors indicates the existence of ΔKth,eff as a material property. Due to the fact that the determination of closure is controversial a modified closure evaluation procedure was used in this investigation.
Using selected materials (dual phase steel, particulate reinforced Al-alloy) this modified closure procedure resulted in ΔKth,eff values of reduced scatter in comparison to conventional evaluation procedures.
An alternative concept to describe threshold conditions was suggested by introducing characteristic plastic strain contours. The dislocation configuration in the vicinity of a crack tip, revealed by the electron channeling contrast imaging (ECCI) technique in the scanning electron microscope, allowed to deduce such plastic strain values in poly crystalline Cu selected as model material.
The ECCI technique was also applied to quasi two-dimensional structures (thin foils) which may be of interest in microelectronic systems. Results show that for foils of the thickness in the magnitude of the grain size a crack growth behavior is observed which appears not to be affected by closure.
fatigue threshold, intrinsic threshold, closure, dislocation configuration, electron channeling contrast, plastic strain amplitude, thin foils
Research Scientist, Institute of Materialphysics, University of Vienna, Vienna,
Professor, Institute of Materialphysics, University of Vienna, Vienna,
Professor, Institute of Physical Chemistry — Material Science, University of Vienna, Vienna,