Fatigue crack growth for straight-fronted edge crack in a round bar

In this paper, firstly fatigue crack growth for a straight-fronted edge crack in an elastic bar of circular cross-section is studied through experiments under pure fatigue axial loading. Three different initial notch depths are discussed. The relations between aspect ratio (b/c) and relative crack depth (b/D) are obtained, and it is shown that there is great difference in the growth of cracks with different front shapes and initial notch depths. Using the relations, predictions are made of the crack front shape and crack growth rate in the depth direction. Secondly, the variation of crack growth behavior is also studied under cyclic axial loading with steady torsion. Results show that Mode III loading superimposed on the cyclic Mode I leads to a significant reduction in the crack growth rates.