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. 1. The Co ffi n-Manson strain-life curve. ϵ a denotes the strain amplitude and N f cycles to failure.

Table 2. Non-linear kinematic material model’s parameters.

Young’s modulus [GPa] 213.7 Initial yield stress [MPa] 265 C 1 [MPa] 104736

γ 1 [MPa] 1269 C 2 [MPa] 10575 γ 2 [MPa] 132 C 3 [MPa] 366 γ 3 [MPa] 0

nucleation based on the strain-life approach. Here, the direct cyclic algorithm routine calculates the average response of the area subjected to cyclic loading. This means that only proportional and non-variable cyclic loads can be simu lated. Crack initiation is modelled by node separation in conjunction with damaging cohesive contact. The allowable damage jump or damage forward step in the cohesive contact controls the resolution of crack growth. Since only the evolution of the crack and not its velocity is of interest in this study, a damage jump of ∆ D = 0 . 5 was specified. This means that the crack grows over the entire length of the cohesive contact in two iterations.

2.3. Numerical simulation

The geometry of the area is similar to that of CT specimens used in fatigue crack growth experiments. The dimen sions are shown in figure 2. Since the YAA2FCG approach only allows for a 2D simulation, the domain is reduced to the simple strain state. The mesh is shown in figure 3. The domain is loaded through holes with a diameter of 24 mm. The loading is in vertical direction with sinusoidal shape (R = -1) and amplitude of 7500 N. Two examples are presented, one with and one without hole expansion. The 16 mm hole was expanded by 0.16 mm in the radial direction using displacement boundary conditions, corresponding to an expansion of 1%. The expansion was simulated before any fatigue loading.

3. Results and discussion

The results show the simulated crack growth for both the unexpanded case and the case expanded with hole. Figure 4 shows the trend of crack growth in the unexpanded case. The crack appears to originate in the notch. The crack growth continues in the horizontal direction. The crack grows in the direction perpendicular to the maximum