13th International Conference on Fracture June 16–21, 2013, Beijing, China -10- 6. Conclusions and further work Fatigue crack paths in thin sheets of aluminium alloy and mild steel were characterized in 3D in air and salt water. Crack twisting was delayed by a corrosive environment, which makes normal mode I crack growth more stable. Real 3D crack geometries were taken into account in an X-FEM model allowing the computation of KI, KII, KIII at any point along the front. Both the opening and shear modes contribute to slanted crack growth, whose rate correlates much better with (1 ) 2 2 2 ν− Δ Δ = Δ +Δ + III II I eq K K K K than with ΔKI. 3D elastic-plastic F.E. simulations and a local application of a fatigue criterion with a strain range-dependent critical plane qualitatively predicted the transition in crack growth mode and the twist angles. The challenge is now to develop incremental 3D simulations of mixed-mode slanted crack growth in a unified framework. The X-FEM method has to be modified to incorporate cyclic plasticity. This should allow predictions of both the crack growth kinetics and crack paths, based on the local approach mentioned above. References [1] J. Schijve, Shear lips on fatigue fractures in aluminium alloy sheet metal, Eng. Fract. Mech. 14 (1981), 789-800 [2] L.B. Vogelesang, J. Schijve, Environmental effects on fatigue fracture mode transitions observed in aluminium alloys, Fat. Fract. Eng. Mat. & Struct. 3 (1980) 85-98 [3] J. Zuidema, H.S. Blauw, Slant fatigue crack growth in Al 2024 sheet material, Eng. Fract. Mech. 29 (1988) 401-413 [4] J. Zuidema, M. Mannesse, Interaction of fatigue crack growth properties and crack surface geometry in Al 2024 , Engng. Fract. Mechanics 40 (1991) 105-117 [5] A.A. Shanyavsky, M.Z. Koronov, Shear lips on fatigue fractures of aluminium alloy sheets subjected to biaxial cyclic loads at various R-ratios, Fat. Fract. Engng. Mat. Struct. 17 (1994) 1003-1013 [6] S. Horibe, M. Nakamura, M. Sumita, The effect of seawater on fracture mode transition in fatigue, Int. J. Fatigue 7 (1985) 224-227 [7] K. Walker, S. Pendleberry, R. McElwee , Tensile and shear-mode cracking of titanium sheet in air and in salt water, in: Effects of environment and complex load history on fatigue life, p234-240, ASTM STP 462, ASTM Philadelphia (1970) [8] L.P. Pook (1993), A finite element analysis of the angle crack specimen in“Mixed-mode fracture and fatigue” p 285-302, H.P. Rossmanith and K.J. Miller eds, ESIS 14, MEP, London [9] A.Bakker, Three dimensional constraint effects on stress intensity distributions in plate geometries with through-thickness cracks, Fat. Fract. Engng. Mat. Struct., 15 (1992) 1051-1069 [10] N. Moes, J. Dolbow and T. Belytschko, A finite element method for crack growth without remeshing Int. Journ. Numerical Methods in Engineering 46 (1999) 131-150 [11] Ph. Destuynder, M. Djaoua, S. Lescure, Quelques remarques sur la mécanique de la rupture elastique, Journ. Mécanique Théorique & Appliquée 2 (1983) 113-135 [12] T. Zhao, Y. Jiang Fatigue of 7075-T651 aluminum alloy Int. J. Fatigue 30 (2008) 834–849
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