Three dimensional finite element modelling of crack growth and geometry induced closure in notched specimens

This paper presents the results of finite element analyses made of fatigue crack growth, and geometry induced closure in double-edged notch tension specimens. The paper supports previous experimental studies of crack-growth and closure in the double-edged notch specimen. The experimental testing proved the cracks roughly grew as quarter ellipses. The largest axis (a) being along the notch root and the shortest axis (b) along the plain face. However, the experiments also showed, the (alb) ratio of the ellipses was influenced by the nominal stress of the test. A three-dimensional small strain, elastic-plastic finite element program was used to study the axial stress distributions across the thickness, for arbitrary shaped cracks. The finite element analyses, of the experimentally measured crack shapes, simulated the applied loading cycles. The results of the analyses, coupled with fatigue life predictions made in previous publications, and experimental testing at high and low R ratios, provide an insight into why a particular shape is adopted by a crack.