SYMPOSIA PAPER Published: 01 January 1976
STP33382S

Spectrum Fatigue Crack Growth in Lugs

Source

Analytical and experimental investigations were conducted to determine the crack growth behavior in lug joints subjected to a randomized flight-by flight spectrum. Specific objectives were to evaluate capabilities for analyzing spectrum crack growth in lugs and to assess the effects on crack growth of KIc and cold working the material surrounding the lug holes. Stress intensity solutions were developed for cracks radiating from lug holes using Bueckner's weight function approach for various stress distributions surrounding the lug hole. The stress distributions were determined using an elastic/plastic finite element analysis. Included in these analyses were residual stress distributions following either large lug loads or mandrel hole enlargement. Spectrum crack growth calculations were made using the resulting stress intensity values and the Wheeler retardation crack growth model.

Lug specimens were fabricated from two heats of 6Al-4V mill annealed titanium representative of material having low and high fracture toughness levels. Basic mechanical properties including ultimate and yield strength, percent elongation, and reduction in area and fracture characteristics, including KIc and constant-amplitude crack growth rates, were determined for each heat of material. EDM cuts in the lug specimens were used as points of stress concentration where precracks were developed by low-level constant-amplitude fatigue loading. The lug holes of selected specimens were cold worked to determine the effect of compressive residual stresses on the crack growth rate. Plots of crack growth versus spectrum hours were obtained for each specimen by post-failure examination of the fracture surfaces using the scanning electron microscope.

Author Information

Impellizzeri, LF
McDonnell Aircraft Company, McDonnell Douglas Corporation, St. Louis, Mo.
Rich, DL
McDonnell Aircraft Company, McDonnell Douglas Corporation, St. Louis, Mo.
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Details
Developed by Committee: E08
Pages: 320–336
DOI: 10.1520/STP33382S
ISBN-EB: 978-0-8031-4672-3
ISBN-13: 978-0-8031-0344-3