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. 2. Geometry of sample.

Fig. 3. FEM mesh consisting of 7073 CPE3 linear plain strain elements.

principal stress resulting from the bending load. Initially, the unexpanded 16-mm hole appears to have minimal e ff ect on the direction of fatigue crack growth. After a few iterations, the crack turns in the direction of the hole. We believe that the physical significance of this phenomenon is that the 16-mm hole e ff ectively reduces the cross-section and therefore the crack moves toward the hole, as this is the path of least resistance. If we compare the results in the first iteration 0 without hole expansion in the figure 4 with the results with hole expansion in the figure 5, we can clearly see the presence of the RS field around the cold expanded hole. The main focus of cold expansion is on the compressive RS field at the surface of the hole. With each iteration, the magnitude of the compressive RS decreases, which is a twofold phenomenon. First, the combined nonlinear kinematic-isotropic model is able to predict the RS relaxation due to the externally applied load. Second, the stress-strain solution is mapped between iterations between meshes, so there is some error. Previous studies have shown that mapping between meshes with smaller elements reduces this error. Here, the artificial RS relaxation should be in the range of 10 % of the initial value. In this study, we focused on the crack progression for a crack that does not originate at the surface of a cold-widened hole. The original assumption was that the crack would grow around the cold expanded hole due to the high compressive RS. If we compare the condition at iteration 50 in Figure 5, we see that this is not the case. The crack originates at the notch and immediately turns toward the cold flared hole. The reason for this is the nature of the RS. Since these stresses must be in equilibrium, the compressive stress induced by the cold expansion is balanced by