On microstructural control of near-threshold fatigue crack growth in 7000-series aluminum alloys

Fatigue Crack Growth Simulation of Aluminium Alloy under Cyclic Sequence Effects

“…The table-lookup form is used because many materials, especially aluminum alloys, show sharp changes in the crack-growth-rate curves at unique values of rates. These sharp changes have been associated with monotonic and cyclic-plastic-zone sizes, grain sizes, and environments [Yoder, et al, 1982]. The Functional relations for geometry factors (F (a, w)) are given in the FASTRAN manual [Newman, 1992] [Ray & Patankar, 2001b], which is a cycle-by-cycle structural crack growth fracture mechanics computer program developed at the Air Vehicles Directorate of the United States Air Force Research Laboratory (AFRL), and is widely used to predict the fatigue life of components [Harter, 2003].…”

Environment and R-ratio effects on fatigue crack propagation transitions in Ti-6A1-4V (ELI)

“…Yoder et al [4,6,7] and Irving et al [8] argue that a transition is due to the change in structure-sensitive to structure-insensitive crack propagation as the reversed plastic zone ~ plastic zone* approaches a critical value (e.g., the effective size of t~ grain in conventional ~13 titanium alloys and the size of Widmanstatten packet for beta annealed Ti-6-4). Yoder et al further developed a model to predict the transition stress intensity factor range, AK~, according to: AKT = 5.5~y.~(1) r~ (2) where oy~ is the yield stress and I is the mean free path between barriers to slip band transmission.…”

“…Several mechanisms have been proposed for changes in the FCP power-law exponent with increasing AK, including transitions: (1) from plane strain to plane stress [3], (2) from a damage accumulation-discontinuous crack advance process to per cycle FCP [15], (3) from microstructure sensitive to microstructure insensitive FCP associated with the plastic zone diameter exceeding the spacing of one or more dominant barriers to slip [4][5][6][7][8], (4) in plastic deformation mode which in turn affects a microscopic damage mechanism change [9], (5) in the microscopic paths and proportions of environmental damage mechanisms [1,2], (6) involving superposition of time-cycle-dependent [10] or time-dependent [14] environmental cracking modes, (7) involving the mass transport rate limiting process [18], and (8) …”

Transitional behavior of fatigue crack growth in welded joint of 25Cr2Ni2MoV steel

“…Therefore, a transition point is inevitable between the near-threshold and Paris regimes of a da/dN À DK curve [9,10]. According to Liu and Liu [11] and Yoder et al [12], FCG data below such a kind of transition point denote the onset of real threshold regime, while those above the transition point belong to the Paris regime by considering the similarity of fracture morphology [13].…”