INFLUENCE OF MICROSTRUCTURE OF Ti- AND Al-ALLOYS ON THE PROBLEM OF FATIGUE CRACK PROPAGATION LIFETIME CALCULATIONS USING MICROCRACK OR MACROCRACK DATA

摘要

The difference in fatigue crack propagation rates between naturally initiated small surface cracks in smooth specimens (microcracks) and large through-thickness cracks in CT-type of specimens (macrocracks) depends to a large extent on microstructure. This behavior is demonstrated on various microstructures of high strength Ti- and Al-alloys. In fatigue crack propagation lifetime calculations the use of the wrong da/dN-ΔK curve (macrocracks instead of microcracks) can lead to significant overestimation in lifetime which in turn could cause premature failure of a component. The microstructural influence on the magnitude of this overestimation is emphasized.