PSI - Issue 41

Peter Zobec et al. / Procedia Structural Integrity 41 (2022) 208–214 Peter Zobec / Structural Integrity Procedia 00 (2022) 000–000

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Fig. 4. Maximum principal stress magnitude for fatigue crack growth simulation without hole expansion.

a region of tensile stress. This condition can be clearly seen in iteration 0 in figure 5. Thus, the tensile region around the cold-expanded hole ”pulls” the crack toward the hole. On further iterations, we find that the crack continues to grow toward the hole and the RS field decreases. In the final stages of the simulation, here iteration 150, another crack appears on the surface of the hole. However, this is considered a simulation error because the current state of the YAA2FCG algorithm fails to simulate a crack growing in the direction of the free surface, in this case the surface of the hole.

4. Conclusions

A di ff erent light is shed on the process of CHE. The beneficial results of these techniques are well documented and researched in terms of delaying crack formation near a CHE. However, when we focus on a crack growing near a CHE, the CHE appears to have a decreasing e ff ect on component fatigue and fracture life. The resulting tensile RS around the CHE appears to pull the crack toward the hole and the notch e ff ect of the crack may overcome the induced compressive RS. These conclusions are based only on the results of the YAA2FCG algorithm and should be thoroughly tested in the laboratory. But if the physics is correct, this could mean that CHE is beneficial for safety critical structures, but could also be a major safety problem when viewed from the other side.