Abstract
The evaluation of cyclic crack propagation due to missions with varying mixed-mode conditions is an important topic in industrial applications. This paper focuses on the determination of the resulting propagation direction. Two criteria are analyzed, the dominant step criterion and the averaged angle criterion, and compared with experimental data from tension-torsion tests with and without phase shift. The comparison shows that the dominant step criterion yields better results for small to moderate values of the phase shift. For a large phase shift of 90°, the experimental results are not very consistent, and therefore, no decisive conclusions can be drawn.
Highlights
In aircraft engine components, the accurate prediction of the propagation of potential cracks has gained much importance in recent decades
Life prediction in terms of the number of cycles is crucial, and the accurate prediction of the crack propagation direction is a target. This applies for instance to blisks, in which a crack initiated in the blade due to vibrations may grow into the disk and lead to a catastrophic failure due to the centrifugal loading [2]
A switch from a 0◦ to a 40◦ phase shift leads to an increase of the deflection angle. This indicates that the time at maximum tensile force, which corresponds to a higher tension/torsion stress ratio compared to zero phase shift, is not dictating the crack propagation direction
Summary
The accurate prediction of the propagation of potential cracks has gained much importance in recent decades. A special problem in the case of three-dimensional mixed-mode loading is the geometry-dependent coupling of Mode II and Mode III at the surface, which was demonstrated, for example, in [34,35,36] This is currently not generally taken into account in the crack propagation concepts developed or in the determination of the crack growth curves. To take the temperature effect into account, the weight in each loading step is taken to be the crack propagation rate obtained by substituting the equivalent Kfactor into a simple Paris-type law (this is similar to the way the dominant step is identified in the dominant step approach). R-value correction axial force critical value equivalent stress intensity factor
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