Influence of Flaw Geometries on Hole-Crack Stress Intensities

The problem geometry of a crack emanating from the intersection of a hole with a plate surface has received considerable attention in recent years. Approaches to the problem have included frozen stress photoelasticity, crack growth rate correlations, and approximate analytical studies. A comparison of results from the various approaches indicates reasonable agreement except for the case where the aspect ratio of the flaw (that is, ratio of flaw depth to length) approaches unity. Moreover, this problem and the geometries of this problem which were specified recently as benchmarks for three-dimensional cracked body analysis at a 3D fracture workshop at Battelle include this aspect ratio and also very deep flaws. For an aspect ratio ≃ 1, the analytical solution is found to yield significantly higher results than either of the experimental methods. This paper describes a frozen stress photoelastic study of this class of flaw shapes where the ratio of hole diameter to plate thickness is approximately unity. The study utilizes a technique developed by the senior author and his associates for estimating stress intensity factor variations along the border of flaws in three-dimensional problems. Results reveal that, for deep flaws, flaw shapes are not simple and flaw growth is not self-similar. The influence of this effect and its implications are discussed.