PSI - Issue 66

Guido Dhondt et al. / Procedia Structural Integrity 66 (2024) 102–107 Author name / Structural Integrity Procedia 00 (2025) 000–000

106

5

max criterion performs better than the max criterion. This is particularly noticeable for the tests with R axial =0, for which one can show that da/dN* in the mission extends into the negative range. It also looks like FRANC3D uses the min max criterion as well.

5. Simulating the cruciform tests To further validate the min-max criterion cruciform tests were performed with static loading along one set of arms “A” and cyclic loading along the other set of arms “B”, Figure 8. The cyclic loading was fixed to 16 kN, the static loading gradually increased from test to test from 2 kN to 12 kN. Pre-cracking was performed under overall tension. From the pre-cracks primary cracks grew perpendicular to the cyclic loading. However, it was observed that due to the increasing static loading secondary cracks spontaneously grew perpendicular to the static loading. These secondary cracks mostly initiated directly from the notch (i.e. no crack branching) and grew the faster the higher the static load.

Figure 8: Experimental crack propagation due to static/cyclic loading conditions.

From these results it was expected that at very high static loading cracks will grow perpendicular to the static load. This was confirmed in an additional experiment with a static loading of 24 kN and a cyclic loading of 8 kN (Figure 9).

Figure 9: Experimental crack propagation at high static/cyclic load ratios.