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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Critical stress intensity factor range Equivalent stress intensity factor range Threshold stress intensity factor range

 K C  K eq  K th

Specimen length

L P R

Half corrosion pit length

Load/stress ratio Specimen width

W

Crack inclination angle

  

Poisson’s ratio   appl Applied tensile stress range ESIFR Equivalent Stress Intensity Factor Range FEM Finite Element Method SIF Stress Intensity Factor LEFM Linear Elastic Fracture Mechanics

2. Mixed-mode configuration For the analysis of the mutual interaction between a fatigue crack and a corrosion pit, a mixed-mode configuration was suggested. Particularly, a rectangular plate subjected to tensile loading was modelled in the FEM software ANSYS. The I+II mixed-mode conditions are ensured via the orientation of the short fatigue crack with regard to the tensile loading. Various inclination angles of the edge crack are considered in order to investigate configurations with various mixed-mode level. The corrosion pit has the shape of a circular segment and is located very close to the fatigue crack, because previous studies show that only such geometries enable to capture some mutual interaction between both defects. The scheme of the geometry can be seen in Fig. 2a, where the significant dimensions are marked. The length of the specimen was chosen to be large enough in comparison to its width ( L = 100 mm, W = 10 mm, L / W = 10). Dimensions of the corrosion pit were taken from literature, see e.g. Fatoba and Akid (2022) or Xue et al. (2021), but own observations of corroded surface on high-strength steel specimens are under operation to get more data. Nevertheless, in this work, the corrosion pit length was 2 P = 0.5, 2 and 4 mm and the corrosion pit depth was always one quarter of its length ( D = P /2 = 0.125, 0.5 and 1 mm). As mentioned above, some effect of the corrosion pit on the fatigue crack behavior can be observed only when both defects are very close to each other. Thus, and also with regard to the limitations of the FEM mesh, the distance of the corrosion pit edge from the crack at the specimen surface was chosen to be const = 0.1 mm. Then, the distance of the corrosion pit center from the fatigue crack, as marked in Fig. 1a, can be calculated as C = const + P . The last two geometrical parameters, that were varied, are the crack length and the initial crack inclination angle. In order to study their influence on the crack behavior, the following values were considered: Note that the negative values of the inclination angle represent the fatigue crack inclined towards the corrosion pit, whereas the positive values correspond to a fatigue crack deflected from the corrosion pit; see the scheme in Fig. 2a. The specimen described above was loaded on its upper and bottom side through tensile stress range of   appl = 300 MPa (load/stress ratio is considered to be R = 0, which is sometimes referred to as pulsating tensile loading), see Fig. 2a, and the material model of the high-strength steel material was defined as isotropic linear elastic with parameters:  Young’s modulus: E = 210 GPa  Poisson’s ratio:  = 0.3 2.1. Geometrical and material parameters  Crack length: a = 0.1, 0.25, 0.5, 1, 1.5, 2, 3 and 4 mm  Crack inclination angle:  = -45, -30, -15, 0, 15, 30 and 45°