Extended Study of Flaw Growth at Fastener Holes. Volume I: Fid-Bau Portal

Extended Study of Flaw Growth at Fastener Holes. Volume I

T. M. Hsu / W. M. McGee / J. A. Aberson

An analytical and experimental investigation was conducted to characterize the fracture and cyclic-growth behavior of cracks emanating from various types of fastener holes, such as open, close-tolerance, interference-fit, and cold-worked fastener holes. An analytical approach was developed for estimating stress intensity factors for through cracks emanating from these types of fastener holes. Approximate stress intensity factors for quarter- elliptical cracks emanating from a corner of the same types of fastener holes were derived from corresponding through-crack solutions. Two alloy plates (2219-T851 aluminum and 6Al-4V (ELI) beta annealed titanium) with and without intentional initial flaws were tested under constant amplitude cyclic load and flight-by-flight fighter and bomber spectrum loads. Two initial flaw shapes corresponding to a quarter-circular corner crack and a through-the-thickness crack and three initial crack lengths (small, intermediate and large) were used in the test program. Three levels of cold working and interference and one level of fastener load transfer were included for each alloy. The amount of load transferred through the loaded fastener was maintained uniformly at the level which produced a bearing stress equal to the far-field stress. Correlations between calculated stress intensities and those reduced from fatigue crack growth data were good, except for very small cracks growing from the cold-worked holes. Also, the natural cracks initiated in the fatigue tests were most commonly corner and embedded types whose shapes corresponded quite closely to the quarter- and semi-elliptical shapes used in the analyses. (Author)