About the fatigue crack propagation threshold of metals as a design criterion – A review

The Merging of Fatigue and Fracture Mechanics Concepts: A Historical Perspective

Fatigue properties of TiAl alloys

The effect of orientation, applied stress state, environment, and temperature on the crack growth and crack-path behavior of single-crystal specimens of UDIMET 720 has been examined. Stage I cracking has been promoted by mixed-mode loading, plane stress, and vacuum conditions; increasing the test temperature to 600 °C does not suppress stage I crack growth in vacuum. Consideration of the local resolved shear-stress intensity and local resolved normal-stress intensity for each slip system as it intersects the nominal crack-growth plane allows the prediction of stage I crack paths, clarifying the importance of secondary single-crystal testing orientation (i.e., nominal crack-growth direction as well as effective tensile axis). A combination of both opening and shearing are found to promote stage I crack growth, and boundary conditions have been established within which stage I cracking is promoted. Highly deflected stage I cracking gives rise to significant shielding effects, but under suitable mixed-mode loading, highly oriented, coplanar stage I crack growth can be produced. Intrinsic stage I cracking under mixed-mode loading appears to be greatly accelerated compared with mode I-dominated stage II crack growth for comparable stress-intensity levels.

Fatigue crack path prediction in UDIMET 720 nickel-based alloy single crystals

Influence of surface and internal casting defects on the fatigue behaviour of A357-T6 cast aluminium alloy

Stage II intrinsic fatigue crack propagation

Stage II crack propagation of AlZnMgsingle crystals in dry and wet atmospheres

A clear identification has been achieved for intrinsic stage I fatigue-crack propagation in single crystals of a high-purity Al-Zn-Mg alloy. The intrinsic stage I regime is noted to be much faster than intrinsic stage II for comparable loading conditions. The 'shielding' effect related to stage I-like propagation is significantly more important than anticipated on the basis of the conventional comparison to stage II. The propagation of a small surface crack growing in stage I is comparable to that of intrinsic stage I in single crystals rather than to either stage I or stage II in polycrystals. 11 refs.

Intrinsic stage I crack propagation in Al-Zn-Mg single crystals

Fatigue crack growth behaviour of Ti6Al4V at elevated temperature in high vacuum

Fatigue studies, performed at 35 and 100 Hz on peak-aged Al-Zn-Mg single crystals in vacuum, have shown that crystallographic crack initiation and propagation dominate under all circumstances. Crack closure measurements undertaken with these specimens have shown that crystallographic cracks propagate in the near-threshold region even in a «closed manner», i.e. the effective stress intensity factor ΔK eff approaches zero. Obviously, the propagation of these cracks cannot be sufficiently described by a ΔK eff concept any more. Normally, a persistent slip band is initiated by cyclic deformation on the specimen surface and acts as seed for a crystallographic crack

J. Petit

Papers

Stage II intrinsic fatigue crack propagation

Stage II crack propagation of AlZnMgsingle crystals in dry and wet atmospheres

Intrinsic stage I crack propagation in Al-Zn-Mg single crystals

Fatigue crack growth behaviour of Ti6Al4V at elevated temperature in high vacuum

Microstructural aspects of fatigue crack propagation in Al-Zn-Mg alloys