13th International Conference on Fracture June 16–21, 2013, Beijing, China 7 Figure 11. Crack growth behavior of rod specimen. 6. Conclusions The fatigue crack growth in AISI304 specimens is investigated experimentally. The surface crack in 3D rod under tension is characterized by the fatigue crack data from the CT specimen. 3D finite element models are generated in compliance with the surface crack configurations and the stress intensity factor along the crack front is calculated through virtual crack closure technique. The present work confirms: 1. The stress intensity factor along the surface crack front non-uniformly varies with crack growth. Crack growth rate is proportional to the stress intensity factor distribution in the 3D cracked specimen. After crack grows up over the crack front, the maximum of the stress intensity factor appears near the free surface of the tensile rod, so that the crack front curvature becomes smaller. 2. Experiments confirm that the fatigue crack growth in surface cracked specimens can be described by the Forman model identified in conventional CT specimens. For crack growth in the free specimen surface the arc length seems more suitable to quantify crack progress. 3. Geometry and loading configuration of the surface cracked specimen seem to not affect the fatigue crack growth substantially. The Forman model can predict local crack front growth rather precisely. Acknowledgements The authors thank financial support of the German Science Foundation (DFG) under the contact number YU119/5-2. References [1] R. G. Forman, V. E. Kearney and R. M. Engle (1967). Numerical analysis of crack propagation in cyclic-loaded structures. Journal of Basic Engineering 89(3): 459-464. [2] T. L. Mackay and B. J. Alperin (1985). Stress intensity factor for fatigue cracking in high strength bolts. Engineering Fracture Mechanics 21(2): 391-397. [3] C. S. Shin and C. Q. Cai (2004). Experimental and finite element analyses on stress intensity factors of an elliptical surface crack in a circular shaft under tension and bending. International Journal of Fracture 129: 239-246. [4] E. F. Rybicki and M. F. Kanninen (1977). A finite element calculation of stress intensity factors by a modified crack closure integral. Engineering Fracture Mechanics 9: 931-938. [5] E. F. Rybicki, D. W. Schmueser and J. Fox (1977). An energy release rate approach for stable crack growth in the free-edge delamination problem. Journal of Composite Materials 11: 470-487.
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