Mixed mode crack growth in a circular shaft

This example is demonstrates the effect of mixed mode loading on a crack in a circular shaft. This analysis is typical of many industrial applications. The initial crack is a shallow but straight through crack at the centre of a test specimen. The full uncracked mesh is shown in Figure 1. The cut-away cross section at the crack location is shown in Figure 2 for the uncracked mesh and in Figure 3 for the mesh containing the initial straight crack.

Figure 2 - Uncracked model cut along the mid section showing the plane that will contain the initial crack front

Figure 3 - The initial cracked model showing (one side of) the straight crack front in the crack plane

The component is loaded by cyclic torsion. This generates anti-symmetric mixed mode conditions at the crack front. The result is that the crack skews and twists as it grows through the section. Figure 4 shows the calculated profiles from the growth analysis. Plots of the meshing part way through the analysis are shown in Figure 5 and demonstrate the way that Zencrack is able to propogate an awkward 3D crack shape through a structure. Animations of the re-meshing during the crack growth prediction are available by clicking on the movie icons in Figure 5.

Figure 5 - Analysis with cyclic torsion load resulting in non-planar crack growth

Of course the mixed mode case is a challenging one but Zencrack also allows study of the simpler mode I scenario. By changing a few input parameters the analysis can be re-run using a cyclic tension load. This results in the prediction shown in Figure 6.

Figure 6 - Analysis with cyclic tension load resulting in planar crack growth