Issue 38

X. Yu et alii, Frattura ed Integrità Strutturale, 38 (2016) 148-154; DOI: 10.3221/IGF-ESIS.38.20 154 It is noted that under most loading cases, a second crack also emanated from the far edge of the circular hole. However, the second crack only emerged after more than 4000 cycles of the applied mixed mode load. Therefore, their effect on crack path deviation was ignorable in this study. C ONCLUSION his study clarifies that for AA7075-T651, the FCG under non-proportional mixed mode I and II loads is significantly different from the open mode FCG commonly expected under mode I or proportional mixed mode loads. Similarly to previous results for mild steel, a long and stable shear mode FCG can be produced in AA7075- T651 under non-proportional loads. The commonly accepted MTS criterion does not apply under most non-proportional load cases. Further investigations are needed to gain sufficient understanding, including those under in-service multiaxial loading spectra, to better support durability assessment of primary aircraft structures subjected to severe non-proportional multiaxial loads. R EFERENCES [1] Nayeb-Hashemi, H., Taslim, M.E., Effects of the transient Mode II on the steady state crack growth in Mode I, Engng Fract Mech, 26(6) (1987) 789-807. doi:10.1016/0013-7944(87)90029-4. [2] Wong, S.L., Bold, P.E., Brown, M.W., Allen, R.J., A branch criterion for shallow angled rolling contact fatigue cracks in rails, Wear, 191 (1-2) (1996) 45-53. doi: 10.1016/0043-1648(95)06621-7 [3] Yu, X., PhD thesis, the University of Sydney, Australia, (1999). [4] Doquet, V., Pommier S., Fatigue crack growth under non-proportional mixed-mode loading in ferritic-pearlitic steel Fatigue Fract Engng Mater Struct, 27(11) (2004) 1051-1060. doi: 10.1111/j.1460-2695.2004.00817.x. [5] Highsmith, S., Jr., PhD thesis, Georgia Institute of Technology, USA (2009). [6] Doquet, V., Abbadi, M., Bui, Q. H., Pons, A., Influence of the loading path on fatigue crack growth under mixed- mode loading, Int J Fract, 159 (2009) 219-232. doi: 10.1007/s10704-009-9396-6. [7] Shamsaei, N., Fatemi, A., Small fatigue crack growth under multiaxial stresses. Int J Fatigue, 58 (2014) 126–135. doi: 10.1016/j.ijfatigue.2013.02.002. [8] Zerres, P., Vormwald, M., Review of fatigue crack growth under non-proportional mixed-mode loading, Int J Fatigue, 58 (2014) 75-83; doi: 10.1016/j.ijfatigue.2013.04.001. [9] Erdogan, F., Sih, G.C., On the Crack Extension in Plates Under Plane Loading and Transverse ShearJ Basic Engng, 85(4) (1963) 519-525. doi:10.1115/1.3656897. [10] Otsuka, A., Mori, K., Miyata T., The condition of fatigue crack growth in mixed mode conditions, Engng Fract Mech, 7(3) (1975) 429-439; doi:10.1016/0013-7944(75)90043-0. [11] Smith, M.C., PhD thesis, University of Cambridge, UK, (1984). [12] Yu, X., On the Fatigue Crack Growth Analysis of Spliced Aircraft Wing Panels under Sequential Axial and Shear Loads, Engng Fract Mech, 123 (2014) 116-125. doi: 10.1016/j.engfracmech.2014.03.018. [13] Anderson, T.L. (1995) Fracture Mechanics: Fundamentals and Applications, 2nd Edition, CRC Press, Inc. [14] Yu, X., Abel, A., Mixed-mode crack surface interference under cyclic shear loads, Fatigue Fract Engng Mater Struct, 23(2) (2000) 151-158. doi: 10.1046/j.1460-2695.2000.00236.x. [15] Yu, X., Abel, A., Modelling of crack surface interference under cyclic shear loads, Fatigue Fract Engng Mater Struct, 22(3) (1999) 205-213; doi: 10.1046/j.1460-2695.1999.00152.x. [16] Otsuka, A., Mori, K., Ohshima, T., Tsuyama, S., Mode II fatigue crack growth in aluminium alloys and mild steel, In: Advances in Fracture research, Fracture 81, ICF5, Francois, D. (Ed), (1981) 1851-1858.