Fatigue crack growth and fracture toughness behavior of an Al-Li-Cu alloy

A comparison of fatigue-crack propagation behavior in sheet and plate aluminum-lithium alloys

“…Accordingly, it is concluded that differences in fatigue-crack growth behavior between Al-Li sheet and plate alloys are principally associated with microstructurally-induced variations in crack-path deflection and resulting roughness-induced crack closure from the wedging of fracture-surface asperities [3][4][5][6]. For both plate alloys, the planar nature of slip (due to coherent o' -particle hardening) results in faceted crack growth along slip bands, which promotes periodic deflection in the crack-growth direction (Figs.…”

“…Compared to traditional aluminum alloys, Al-Li alloys exhibit remarkably superior (long-crack) fatigue-crack propagation resistance [1][2][3][4][5][6][7]; in fact, at equivalent stress-intensity levels, growth rates can be up to three orders of magnitude slower. This behavior was originally attributed to their higher elastic modulus and consequently lower crack-tip opening displacements, and to less accumulated crack-tip damage per cycle from a greater degree of reversible slip, due to marked planar-slip deformation arising from the shearable nature of coherent, ordered o' (Al 3 Li) strengthening precipitates [1,2].…”

“…This behavior was originally attributed to their higher elastic modulus and consequently lower crack-tip opening displacements, and to less accumulated crack-tip damage per cycle from a greater degree of reversible slip, due to marked planar-slip deformation arising from the shearable nature of coherent, ordered o' (Al 3 Li) strengthening precipitates [1,2]. More recent studies [3][4][5][6][7], however, have shown that their superior fatigue properties of slip. In Al-Li alloys, such shielding occurs primarily from crack deflection and resulting (asperityinduced wedging) crack-closure mechanisms.…”

The effect of inhomogeneous plastic deformation on the ductility and fracture behavior of age hardenable aluminum alloys

“…The most effective method of reducing strain localization is to minimize the slip length or the distance between concurrent non-sheared events on the active slip plane. The slip length is a key microstructural parameter used in many fracture models to quantify the degree of strain localization (Duva et al, 1988;Sugamata et al, 1993;Jata and Starke, 1986;Roven, 1992;Hornbogen, 1975). For microstructures containing both shearable and non-shearable precipitates, the slip length can be considered the interparticle spacings between the non-shearable precipitates.…”

On the behavior of small fatigue cracks in commercial aluminum-lithium alloys

“…The newly developed advanced aluminum-lithium alloys are of particular interest in this regard, as despite their unquestionably superior (long) fatigue crack growth properties compared to traditional high strength aluminum alloys (8)(9)(10)(11)(12)(13)(14), the discrepancy between long and small crack propagation behavior in these alloys has recently been shown to be extremely large (15,16). In view of the importance of the "small crack" effect in potential airframe and fuel tank materials, the objective of this study was thus to document the growth rate characteristics of small (1-1000 llm), naturally-occurring surface cracks in a series of commercial aluminum-lithium alloys,…”