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- Title
Driving forces for localized corrosion-to-fatigue crack transition in Al-Zn-Mg-Cu.
- Authors
BURNS, J. T.; LARSEN, J. M.; GANGLOFF, R. P.
- Abstract
ABSTRACT Research on fatigue crack formation from a corroded 7075-T651 surface provides insight into the governing mechanical driving forces at microstructure-scale lengths that are intermediate between safe life and damage tolerant feature sizes. Crack surface marker-bands accurately quantify cycles ( Ni) to form a 10-20 μm fatigue crack emanating from both an isolated pit perimeter and EXCO corroded surface. The Ni decreases with increasing-applied stress. Fatigue crack formation involves a complex interaction of elastic stress concentration due to three-dimensional pit macro-topography coupled with local micro-topographic plastic strain concentration, further enhanced by microstructure (particularly sub-surface constituents). These driving force interactions lead to high variability in cycles to form a fatigue crack, but from an engineering perspective, a broadly corroded surface should contain an extreme group of features that are likely to drive the portion of life to form a crack to near 0. At low-applied stresses, crack formation can constitute a significant portion of life, which is predicted by coupling macro-pit and micro-feature elastic-plastic stress/strain concentrations from finite element analysis with empirical low-cycle fatigue life models. The presented experimental results provide a foundation to validate next-generation crack formation models and prognosis methods.
- Subjects
CORROSION fatigue of metals; CRACKING process (Petroleum industry); MICROSTRUCTURE; FINITE element method; NUMERICAL analysis
- Publication
Fatigue & Fracture of Engineering Materials & Structures, 2011, Vol 34, Issue 10, p745
- ISSN
8756-758X
- Publication type
Article
- DOI
10.1111/j.1460-2695.2011.01568.x