Assessment of mixed mode loading on macroscopic fatigue crack paths in thick section Al–Cu–Li alloy plate

Abstract

High strength, wrought 7xxx (Al-Zn-Mg) and Al-Li based alloys show a propensity for fatigue macroscopic crack deflections aligned along grain boundaries. The present work reports a study on a 3 rd generation Al-Li based alloy in the form of a thick AA2297 (Al-Cu-Li alloy) plate, where it was found that although the lithium containing material may indeed be more susceptible to mixed mode grain boundary failure (and by implication crack deflection in conventional tests), the AA2297 alloy fatigue behaviour is mechanistically and functionally equivalent to 7xxx alloy behaviour. It is shown that crack paths are controlled by a combination of crack loading mixity (K II /K I ratio) and maximum strain energy release rates (expressed as K eq.max ). Increasing K II /K I ratio is seen to favour sustained grain boundary failure. Crack growth rate behaviour is discussed in terms of extrinsic and intrinsic components of crack growth resistance. It is shown that the present approach can be successfully applied to predict crack deflection / crack paths for a range of sample geometries and orientations on a range of high strength orthotropic aluminium alloys, including 3 rd generation Al-Li based alloys and well-established 7xxx alloys).

Investigation on the fatigue crack behavior of Zr702/TA2/Q345R composite plate with a crack normal to interface

“…For metallic materials, the increase of load amplitude Δ F will result in a significant reduction in fatigue life, especially in the low cycle fatigue stage. It can be seen that with the increase of F max where R = 0.1, N f will decrease and interface debonding becomes serious (Figure A). R is often taken into account in the fatigue behavior because the change in R directly affects Δ F and Δ K .…”

“…It is worth noting that bifurcations occur at the TA2/Q345R interface for the crack propagates to the interface from the compliant material side (Type-A), which has been observed in many studies. 10,17,21 For this case, when crack propagates into the stiff material, the resistance of crack propagation increases, which results in the decrease of da/dN. When the interfacial mismatch is strong enough, the crack will be shielded and stopped, 17 or only propagates along the interface in the compliant material.…”

Crystal Plasticity Modeling of the Effects of Crystal Orientation and Grain-to-Grain Interactions on DSA-Induced Strain Localization in Al-Li Alloys

“…In relation (14), t D is a time scale characterizing solute diffusion. The switch is therefore controlled by the aging time, which in turn primarily depends on the magnitude of the local 139 plastic strain rateγ s .…”

“…However, strain localization phenomena occurring in these alloys which can result into reduced toughness, and the limited understanding of the complex relationships between localization, damage and material properties such as solute/precipitate hardening/softening and crystallographic/morphological texture, still hamper their widespread usage [8][9][10]. Extensive experimental and theoretical efforts have been made in the recent past for a better understanding of these relationships [11][12][13][14][15].…”

Fatigue Crack Propagation Behavior of the 2195-T8 Aluminum-Lithium Alloy with a Precorroded Hole

“…The combination of the properties of low density and high strength of Al-Li alloys provides potential applications in aerospace industry, thus resulting in the weight reduction and performance improvement of launch vehicles and missiles [1][2][3]. As metallic materials for aviation industry, their fatigue performance and resistance have tremendous influence on the component life [4][5][6].…”