Issue 37

Y. Hos et alii, Frattura ed Integrità Strutturale, 37 (2016) 234-240; DOI: 10.3221/IGF-ESIS.37.31 239 C ONCLUSION atigue crack growth under non-proportional loading cases lead to crack paths, which are not understood fully. A collection of results was presented in this paper. A number of conclusions can be derived from these results: - The assumption of planar symmetrical crack growth in axial specimens is quite plausible, in spite of bending effects. In [20], another similar experiment with a larger load was discussed and simulated. A change in crack path because of the bending load, which increases with increasing crack length, was not observed. - The crack that was loaded proportionally undergoes a non-negligible shear mode (about %20), as the crack growth pattern with zigzags suggest. A final conclusion, why the crack sees this as a second option is though not clear. - A general tendency for cracks under non-proportional loadings is difficult to derive from the morphology. However, DIC [19] and FE-simulations (ongoing) can lead to some important conclusions. Such simulations can be compared with the DIC results in [19] and a clearer answer for this alternating crack growth pattern might be found. A CKNOWLEDGEMENTS he German Research Foundation (Deutsche Forschungsgemeinschaft) is greatly acknowledged by the authors for financial support under grant Vo729/13-1. R EFERENCES [1] Zerres, P., Vormwald, M., Review of fatigue crack growth under non-proportional mixed-mode loading, Int. J. Fatigue, 58 (2014) 75-83. [2] Qian, J., Fatemi, A., Mixed mode fatigue crack growth: a literature survey, Eng. Fract. Mech., 55(6) (1996) 969-990 [3] Highsmith, J., PhD Thesis, Georgia Institute of Technology, USA, (2009). [4] Richard, H.A., Fulland, M., Sander, M., Theoretical crack path prediction, Fatigue Fract. Eng. Mater. Struc., 28 (2005) 3-12 [5] Roberts, R., Kibler, J., Mode II fatigue crack propagation, J. Basic Eng., 93D (1971) 671-680 [6] Tanaka, K., Fatigue crack propagation from a crack inclined to the cyclic tensile axis, Eng. Fract. Mech., 6 (1974) 493-507 [7] Brown, M.W., Miller, K.J., Initiation and growth of cracks in biaxial fatigue, Fatigue Fract. Eng. Mater. Struc., 1 (1979) 231- 246. [8] Otsuka, A., Tohgo, K., Fatigue Crack Initiation and Growth Under Mixed Mode Loading in Aluminum Alloys 2017-T3 and 7075-T6, Eng. Fract. Mech., 28 (1987) 721-732. [9] Socie, D.F., In: Fatigue 87, proc. 3 rd int. conf. fatigue and fatigue thresholds, 2 (1987) 599-616,. [10] Doquet, V., Bertlino, G., Local approach to fatigue cracks bifurcation, Int. J. Fatigue, 30 (2008) 942-950 [11] Hoshide, T., Socie, D.F., Mechanics of mixed mode small fatigue crack growth, Eng. Fract. Struc., 26 (1987) 841-850. [12] Savaidis, G., Seeger, T., Consideration of multiaxiality in fatigue life prediction using the closure concept, Fatigue Fract. Eng. Mater. Struc., 20 (1997) 985-1004. [13] Döring, R., Hoffmeyer, J., Seeger, T., Vormwald, M., Short fatigue crack growth under nonproportional multiaxial. elastic- plastic strains, Int. J. Fatigue, 28 (2006) 972-982. [14] Hertel, O., Vormwald, M., Short-crack-growth-based fatigue assessment of notched components under multiaxial variable amplitude loading, Eng. Fract. Mech. 78 (2011) 1614-1627. [15] Hertel, O., Vormwald, M., Multiaxial fatigue assessment based on a short crack growth concept, Theor. Appl. Fract. Mech., 73 (2014) 17-26. [16] Dowling, N.E., Begley, J.A., Fatigue crack growth during gross plasticity and the J-integral, ASTM STP 590 (1976) 82-103. [17] Wüthrich C., The Extension of the J-Integral Concept to Fatigue Cracks, Int. J. Fract., 20 (1982) R35-7. [18] Hertel, O., Döring, R., Vormwald, M., Cyclic J-integral under nonproportional loading, Proc. 7th Int. Conf. Biaxial/Multiaxial Fatigue Fract. (2004) 513-518. [19] Hos, Y., Freire, J.L.F., Vormwald, M., Measurements of strain fields around crack tips under proportional and non- proportional mixed-mode fatigue loading, Int. J. Fatigue (2016) (in press). F T