Effect of dents on crack growth in aluminum alloy under constant-amplitude loading

Abstract

The purpose of this study was to determine the effect of dents on the stable crack growth in 0.04-in.-thick 2024-T3 bare aluminum sheet. The test specimens were either pristine, dented, or reworked. The edge-cracked pin-loaded specimens of 8 in. in width were tested at constant-amplitude loading with a stress ratio of 0.2, producing stable crack growth aldose to 4 in. completely through two dents on the crack line. Dents were produced with a drop tower having a 0.5 in. spherical hardened-steel indenter head. Dent depths ranged from 0.03 to 0.0325 in., measured on the convex side of the specimen. A starter notch of 0.3 in. was produced at the edge of the specimen with a jeweler's saw blade. The specimen was fatigue-loaded under constant-amplitude loading to produce an initial crack length of 0.37 in., at which time readings of crack length vs cycles began. The same constant-amplitude cyclic loading used to produce the initial crack length was used during the testing. The crac! k lengths were measured with an optical microscope at 160 K magnification. Nine specimens were tested, including three replications for each of the three conditions. Crack growth data are given in both tabular and graphical forms for all specimens. Crack growth rate data are also presented in graphical form. The overall crack growth in the dented specimens was significantly greater than in the pristine specimens. It was also faster, on average, in the reworked specimens; reworking, in general, did not recapture the life displayed by the pristine specimens.