Issue 37

Y. Hos et alii, Frattura ed Integrità Strutturale, 37 (2016) 234-240; DOI: 10.3221/IGF-ESIS.37.31 237 Multiaxial Loading Three types of multiaxial loading were conducted: proportional loading, 90° out-of-phase loading and 45° out-of-phase loading, namely the specimens R-004, R-005 and R-006 respectively. The amplitudes of the loadings are F max = 33 kN, M max = 382 Nm and R F = R M = -1. The nominal stresses in the gross section corresponding to these loads are σ n,max = 101.5 MPa and τ n,max = 62.6 MPa. Again two cracks were initiated at the notch. The different crack paths can be seen in Figs. 5-7 with a summary in Fig. 8. The crack growth directions in Fig. 5 are inclined 17° and 18° to the cross-section plane, respectively for crack 1 and 3. Some cyclic mode II loading is expected to have contributed to the fatigue crack growth. This argument was discussed with more detail in the forthcoming chapters about simulation. Figure 5 : Cracks in specimen R-004, proportional loading with F max = 33 kN, M max = 382 Nm and R F = R M = -1, steel S235. After putting a 90° phase shift between the two loadings, the cracks stopped growing symmetrically, as shown in Fig. 6. Crack 1 grew straight, with an angle of 45° approximately to the specimen axis, and after a crack length of 17 mm, the crack changes direction to a direction perpendicular to the specimen axis, and soon after that the specimen fails. Figure 6 : Cracks in specimen R-005, 90° out-of-phase non-proportional loading with F max = 33 kN, M max = 382 Nm and R F = R M = -1, steel S235. Last but not least, the specimen, which was loaded with 45° out-of-phase loading, was shown in Fig. 7. Crack 1 had a kink quite early, but crack 3 continued linearly, and after some time, it made a kink too. Crack 1 continued in a zigzag pattern after the kinking, which leads to an argument that the crack cannot decide between two options and switches back and forth continuously. Fig. 8 shows a comparison of these three cracks and this zigzag pattern is more obviously visible. Figure 7 : Cracks in specimen R-006, 45° out-of-phase non-proportional loading with F max = 33 kN, M max = 382 Nm, R F = R M = -1, steel S235.