| Abstract: | Fatigue Crack Propagation of High Strength Alloys Investigations of the crack propagation behaviour under variable amplitude loading conditions show a strong influence of sequence effects. The fatigue crack propagation as a consequence of changes in the loading conditions is not linear. New continuum mechanical analyses enable an interpretation of the influence of sequence effects on fatigue crack propagation by considering the plastic deformations and displacements around the crack tip and their correlation to the crack closure behaviour. In order to enable a direct investigation of the crack propagation and crack closure behaviour in the scanning electron microscope a special loading equipment was designed. The investigations led to the following results: - there existed only a weak correlation between the crack propagation rates and mechanisms at the side surfaces and on the fracture surfaces of the specimens,
- the crack propagation behaviour was significantly influenced by the microstructural constitution of the alloy,
- the continuum mechanical analyses could be corroborated in the tests.
For the tests the high strength aluminum alloys 2024-T3 and X-7075 were applied. |
