PSI - Issue 42

Lucie Malíková et al. / Procedia Structural Integrity 42 (2022) 1082–1089 Lucie Malíková et al. / Structural Integrity Procedia 00 (2022) 000–000

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2.2. FEM model

The fracture behavior of the fatigue crack and its interaction with the near-by corrosion pit was investigated by means of the FEM simulations in the commercial computational system ANSYS, see Ansys (2022). The model geometry and material model are described in the previous section. An example of the meshed specimen can be seen in Fig. 2b, where both the whole numerical model and the detail of the refined mesh at the corrosion pit and fatigue crack tip for a selected geometry is presented. A two-dimensional numerical model was created in accordance with the dimensions and plane strain conditions were define. The angled edge crack was modelled as ideally sharp in the vicinity of the corrosion pit of a circular segment shape. The model of the steel specimen was loaded via tensile stress on its both sides. The 8-nodes quadrilateral PLANE183 elements were utilized within the model, because they enable to shift the mid-side nodes in the first row of elements at the crack tip towards the crack tip, which ensures more accurate approximation of the square root singularity of the stress/displacement field. Of course, the mesh was refined at the critical locations, i.e. at the crack tip and at the surface of the corrosion pit, see Fig. 2b.

(a)

(b)

Fig. 2. (a) Scheme of the mixed-mode geometry with the fatigue crack and the corrosion pit; (b) example of the FEM mesh with applied boundary conditions and detail of the crack and pit. 3. Stress intensity factor range concept The fatigue behavior of the angled crack influenced by the presence of the corrosion pit in its vicinity was investigated within the concept of the stress intensity factor ranges. As a consequence of both the arbitrary orientation of the crack with regard to the applied stress range and the presence of the nearby corrosion pit, the crack is subjected to I+II mixed mode fatigue loading. Thus, in order to assess its fracture/fatigue behavior, it is necessary to determine the appropriate stress intensity factor ranges that control the crack propagation. When the mixed mode fatigue behavior shall be evaluated, it is crucial to combine both stress intensity factor ranges (  K I and  K II, see Qian & Fatemi (1996), Rozumek and Macha (2009), etc.) into one parameter that can be additionally compared to some material constant deciding about stable/unstable crack propagation (threshold stress intensity factor range  K th and/or critical value of the stress intensity factor range  K C ). For mixed mode stress intensity factor