Fatigue crack growth behavior of aluminum alloy 2020 (AlCuLiMnCd)

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.…”

Fatigue crack propagation in aluminum- lithium alloy 2090: Part I. long crack behavior

“…Although most studies on aluminum-lithium alloys to date have reported generally improved fatigue resistance compared to traditional 2000-and 1000-series alloys (4)(5)(6)(7)(8)(9)(10)(11)(12), due to their marked anisotropy, some concern has been raised over their crack propagation resistance as a function of plate orientation, and specifically with regard to short-transverse properties (i.e., involving crack propagation in the rolling plane). Accordingly, the objective of the current study is to investigate the mechanics and mechanisms of fatigue crack propagation behavior in an Al-Li-Cu-Zr alloy 2090-T8E41 as a function of orientation.…”

“…planar slip characteristics (also induced by ordered o' precipitation), which enhances slip-reversibility (and hence creates less "damage") at the crack tip (5,6,9), and the tortuous nature of the crack path, which promotes crack tip shielding via crack deflection and closure mechanisms (7,(9)(10)(11)(12). Whereas all three mechanisms undoubtedly act in concert to various degrees, in view of the high measured levels of closure and deflection, the large load ratio dependence of near-threshold growth rates, and the anomalously high small crack effects (15,23), it would now appear that enhanced shielding is the prominent factor for the excellent fatigue crack growth properties of these alloys (see also refs.…”