Driving forces for localized corrosion-to-fatigue crack transition in Al-Zn-Mg-Cu

作者：Burns J T^*; Larsen J M; Gangloff R P

来源：Fatigue and Fracture of Engineering Materials and Structures, 2011, 34(10): 745-773.

DOI：10.1111/j.1460-2695.2011.01568.x

• AFGROW
• aluminium
• corrosion fatigue
• finite element analysis
• fatigue at notches
• fatigue crack initiation
• hydrogen embrittlement
• life prediction

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 (N(i)) to form a 10-20 mu m fatigue crack emanating from both an isolated pit perimeter and EXCO corroded surface. The N(i) 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.

• 出版日期2011-10