Stress Intensity Factors for semi-elliptical surface cracks in round bars under bending and torsion

Stress Intensity Factor calculations for semi-elliptical surface cracks in round bars subjected to bending and torsion using a three-dimensional finite element model are presented. The configuration of the semi-ellipse follows the equation b=(2s)/pi, experimentally obtained, where b is the crack depth and 2s is the are crack length. First, Stress Intensity Factors are obtained for bending loading (Mode I) and compared with available literature results in order to validate the proposed model. Second, Stress Intensity Factors under torsion (Mode III) are computed by employing a finite element model of the whole round bar, since such loading is nonsymmetrical. Results showed that in torsion case the Mode III loading also induces a significant K-II at the points where the crack front intercepts the free surface of the round bar, whereas at the deepest point only K-III exits. The aims of this study have in view the determination of the crack growth rate in rotating load-transmission devices with this type of crack. (C) 1999 Elsevier Science Ltd. All rights reserved.