PSI - Issue 28

F. Conrad et al. / Procedia Structural Integrity 28 (2020) 2195–2205 Author name / Structural Integrity Procedia 00 (2019) 000–000

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To increase comparability, the geometry of the crack-path from the DIC (Fig. 5c) is transferred as a discrete seam to the FEM mesh, Fig. 6b. In the center, quadratic-quadrilateral CPS8-Elements are used in combination with a focused meshing approach at the crack-tips. The analysis with linear-elastic material behaviour functions as a first approach to compare the DIC-measured displacement fields. Fig. 7 compares displacement fields in A-direction of the FEM simulation with DIC results from Fig. 5 transformed to ሺܽǡ ܾሻ coordinates by equations (7). In the center, the crack contour is visible with the initial crack starter notch and the fatigue crack that turned out to grow perpendicular to the higher loaded axis A. As the analysis references to the state of maximum tension loading, the crack itself is fully open and the distribution of the displacement in A-direction above and below the crack corresponds very well with FEM-Data, Fig. 7 The displacements increase in positive A- and B-direction and decrease in negative directions indicating a correct axis transformation. A random measurement of the crack opening (between the yellow points) outlines very similar results of 19.6 µm in the FEM simulation and 21.0 µm in the DIC evaluation.

Fig. 7: Comparison displacement field in A-Direction. FEM-Simulation results (left) and DIC-Evaluation (right).

Fig. 8 Comparison shear-strain field in A-B-direction. FEM-Simulation results (left) and DIC-Evaluation (right).

The FEM simulation outlines shear strains almost at zero-levels with pole-like peaks near the crack tip, showing opposite signs (white circles in Fig. 8, left). This underlines, that the above mentioned rotation-criteria can be