Shape evolution of surface cracks in fatigued round bars with a semicircular circumferential notch

The shape of the fronts of surface cracks in semicircularly notched round bars under fatigue loading is predicted by a numerical procedure developed recently by the authors. This procedure utilizes a linear elastic three-dimensional finite element analysis to estimate the stress intensity factor along the crack front, and then employs an experimental Paris-type fatigue crack growth relation to calculate local crack advances at a few points along the crack front. Re-creating a finite element model for the new crack front and repeating the calculation of the crack growth increment simulates further crack propagation. This method can avoid making the usually necessary assumption of crack shape during the fatigue life calculation for surface cracks in notched round bars. Both remote cyclic tension and bending loads are considered. Characteristics of the crack shape change are also investigated by examining deviations of the crack profiles from the widely assumed elliptical-arc shape, and aspect ratio changes with crack growth.

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