Microstructure based fatigue life predictions for thick plate 7050-T7451 airframe alloys

Relationship between Defect Size and Fatigue Life Distributions in Al-7 Pct Si-Mg Alloy Castings

“…However, pores found on fracture surfaces were larger than the largest pores found on polished sections by an order of magnitude. Similar results were found by Yi et al [9] in A356 castings and Przystupa et al [16] in 7050-thick plate. Hence, more research is needed before the size of fatigue-initiating (largest) pores can be estimated in a nondestructive manner.…”

“…To model the effect of structural defects on the fatigue performance of metals, two main approaches have been taken by researchers in the literature: (1) taking the entire pore size distribution into account [8,13,14] or (2) modeling the distribution of the largest defects or inclusions [4,15,16] that initiate fracture. For instance, the model of Yi et al [8,9] assumes that pore size follows the lognormal distribution, which is consistent with their histograms as well as statistical analysis of pore sizes for Mg alloy castings.…”

“…They measured the size of crack-initiating pits and found that the Gumbel distribution, an extreme value distribution, provided excellent fits to the measured size of the crackinitiating pits. Przystupa et al [16] suggested that the pores in 7050-T7451 alloy components follow a logGumbel distribution, and they estimated the largest pores from this distribution. The authors did not provide a reason why this distribution was selected.…”

The role of competing mechanisms in the fatigue-life variability of a titanium and gamma-TiAl alloy

“…The apparent behavior is typically assumed to be due to a single mechanism. In some cases, it may be appropriate to describe fatigue behavior by a single scatter band, for example, in materials where crack nucleation predominantly occurs from constituent particles or pores [11][12][13][14][15][16] and the crack nucleation and early (microstructurally small crack) propagation life can be considered negligible. In such cases, the uncertainty in life has been shown to arise from variability in the crack growth lives due to the distribution in size of the crack-nucleating particle.…”

“…In such cases, the uncertainty in life has been shown to arise from variability in the crack growth lives due to the distribution in size of the crack-nucleating particle. 11,15,16 There are a few studies that have incorporated the variability from both the crack nucleation as well as the growth life 17,18 to estimate the overall variability. However, the crack nucleation lives were empirically 17,18 as a single distribution that was governed by the defect size and shape distributions.…”