Growth of Physically Short Corner Cracks at Circular Notches

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Abstract
This paper presents and discusses experimental results concerning the initiation and continued growth of cracks in thin circularly notched sheets. Data are reported for specimens and test conditions selected to examine the influence of (1) free surface and (2) inelastic action on the behavior of cracks at notch roots. Results of the study suggest that proximity to a free surface causes first a decrease and then an increase in the growth rate of physically short cracks at notches. This is postulated as being due to blunting of very short cracks and growth in a plane stress field, respectively. Inelastic action at notch roots, by contrast, is associated with increased growth rate within the notch plastic field. Its influence, therefore, is felt over distances equal to the plastic zone size so that its effect need not be restricted to physically short cracks. It is shown that current models which attempt to account for the influence of inelastic action and free surface on crack growth rate through empirical modifications to linear elastic fracture mechanics analysis are, in general, both inappropriate and inadequate.

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