Growth of Corner Cracks at a Hole

The two-dimensional growth characteristics of corner cracks emanating from an open hole were demonstrated by conducting constant amplitude cyclic crack growth tests on a set of 51 specimens. The specimens were machined from 2024-T851 aluminum alloy in three thicknesses (6.35, 12.7, and 19.30 mm) and three hole diameters (6.35, 12.7, and 19.05 mm). The precrack sizes are very small (typically 0.5 to 1.0 mm in either length or depth dimensions) having many arbitrary initiated length-to-depth ratios. Empirical stress intensity factors for various crack size, crack shape, and specimen geometry combinations were calibrated by back-tracking of the crack growth rate behavior in these specimens and the material baseline crack growth rate data (also in three thicknesses of the same heat) developed from compact specimens. Superposition principles were applied to separate the lumped stress intensity factors into a parametric functional form. It has been demonstrated that these empirically derived stress intensity expressions are capable of predicting the crack growth behavior in both the length (on specimen surface) and depth (on the hole wall) directions.