Fatigue damage accumulation in nickel prior to crack initiation

Quantitative assessment of fatigue damage accumulation in wavy slip metals from acoustic harmonic generation

“…From the data of Grobstein et al (1991) for uniaxial, fully reversed, stress-controlled loading at 154MPa, we obtain A ≈ 8.6 x 10 -10 MPa -3 m -0.5 cycle -1 assuming from the data that ∆N ≈ 3.3 x 10 3 cycles, N total ≈ 2.23 x 10 4 cycles, and C crk ≈ 10 7 m -3 (Nazarov and Sutin 1963).…”

“…It is these basic building blocks that determine the magnitude of the nonlinearity parameters. In this view we naively assume that since AA2024-T4 is also a wavy slip metal, the nonlinearity parameters of the alloy may be obtained from the substructural evolution data of nickel Grobstein et al (1991) and the elastic constants, Poisson ratio, and Burgers vector for AA2024-T4.…”

“…Grobstein et al (1991) published an extensive study of substructural evolution in fatigued polycrystalline nickel, a wavy slip metal, cyclically stressed from the virgin state to fracture using various specimens subjected to a variety of loading conditions. Their data include volume fractions of dislocation substructures (veins and PSBs) and dislocation densities within the substructures formed as a function of percent full life.…”

“…For stress-controlled cyclic loading at 241MPa we use the dislocation substructure-related parameters previously ascertained by Cantrell (2004) for polycrystalline nickel from the data of Grobstein et al (1991) and the published works of Winter (1974), , Antonopoulos, Brown and Winter (1976), Brown (1981), and . The vein structure attains a volume fraction f vein = 0.35 at 10 percent full life and remains at that volume fraction to fracture.…”

“…The substructural contribution to β in the plots are obtained by substituting into Eq. (15) the substructural evolution data of Grobstein et al (1991) and the above-calculated values of the nonlinearity parameters and gamma factors. The contributions from crack growth are calculated from Eqs.…”