Improving the Fatigue Performance of Thick Aluminium Alloy Bolted Joints by Hole Cold-Expansion and the Use of Interference-Fit Steel Bushes
AERONAUTICAL RESEARCH LABS MELBOURNE (AUSTRALIA)
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Fatigue tests under a flight-by-flight loading sequence have been carried out on small bolted joint specimens of 23 mm thickness representing part of the spar rear flangeskin attachment in Mirage III aircraft. The investigation has shown that by cold-expanding the bolt holes to take standard oversize bolts, or by installing interference-fit bushes, the fatigue life can be more than doubled compared with the use of standard close-fit bolts in reamed holes. No significant differences were found between the fatigue lives of specimens embodying low-alloy steel or stainless steel bushes. When small-sized residual fatigue cracks are present, hole cold-expansion may be a suitable process for extending the fatigue life. The use of interference-fit bushes is not likely to be an effective method for extending the fatigue lives when large- size residual cracks are present. However, if such cracks can be machined out, the incorporation of large-size interference-fit bushes has the greater potential for providing not only significant extensions in life but also significantly longer lives than the original design detail.
- Metallurgy and Metallography
- Test Facilities, Equipment and Methods