Criteria for Crack Branching in Cylindrical Rods: II, Flexure

The angular and radial dependencies of the mirror‐mist and mist‐hackle boundaries predicted by the stress intensity criterion for crack branching were compared with those of experimentally determined boundaries in cylindrical specimens fractured in flexure. The analysis models the reduction of branching radii near the surface caused by reduced constraint and the elongation toward the neutral axis caused by the stress distribution except that it underestimates the elongation in a range of angles for specimens fractured at relatively low stresses. This difference is believed to result from changes in crack shape that are not accounted for in the analysis. As in the case of rectangular bars fractured in tension and flexure and cylindrical rods fractured in tension, the stress intensity criterion continues to provide better predictions than the Johnson and Holloway criterion.