Fatigue Crack Paths 2003

shown schematically in Fig. 10(a). At high stress levels shear dominated fatigue cracks

originate at points C and remain within the plane of the weld, as shown schematically in

Fig. 10(b). At points C only ModeIII is present, but in general shear dominated fatigue

crack growth is in mixed ModesII and III. A high stress may be defined [25], as one in

which the average shear stress across the weld, at the maximumload in the fatigue

cycle, is greater than about 80 per cent of the shear yield stress.

Figure 8. Oscillating crack front families in high strength aluminium alloy. Crack

growth left to right.

Figure 9. Spot welded lap joint.

Figure 10. Crack paths in spot welded lap joints. (a) Maximumprincipal stress

dominated crack path. (b) Shear dominated crack path.