The Use of Interference-Fit Bolts or Bushes and Hole Cold Expansion for Increasing the Fatigue Life of Thick-Section Aluminium Alloy Bolted Joints
AERONAUTICAL RESEARCH LABS MELBOURNE (AUSTRALIA)
Pagination or Media Count:
The detection of fatigue cracks at bolt holes in the main spar of the Mirage III wing during full-scale fatigue tests led to a requirement for refurbishment procedures to extend the fatigue lives at a number of critical locations. One of these, which is covered by this investigation, was the spar lower front flange. Flight-by-flight fatigue tests have been carried out to determine the relative fatigue performance of aluminum alloy bolted joint specimens of 28 mm thickness incorporating close-fit bolts, interference-fit bolts 0.4, hold cold-expansion 3, interference-fit steel bushes 0.3 and a combination of cold-expansion and interference-fit bushes. Fractographic measurements of crack development from the bores of holes in specimens incorporating close-fit bolts in non cold-expanded reamed and cold-expanded holes clearly indicated much slower fatigue crack propagation rates from the cold-expanded holes until the crack length was close to the nominal region of transition from the residual compressive to tensile stress zone around the cold- expanded holes. Fatigue tests on cold-expanded hole specimens at different spectrum scaling factors indicated that, under the loading sequence used, each 10 increase in stress reduced the life to about half that at the lower stress level.
- Metallurgy and Metallography
- Fabrication Metallurgy