Strength and Fatigue Life Enhancements of Cracked Metal.
DEFENCE SCIENCE AND TECHNOLOGY ORGANIZATION CANBERRA (AUSTRALIA)
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Measures to reclaim both the static strength and the fatigue life of plates with cracks are examined experimentally on 2024 aluminum alloy specimens. The simple measure of stop drilling the crack tips restored most of the tensile strength of the plate. To enhance the fatigue life of a cracked plate the process of stop drilling the crack tips, cold expanding the resulting holes and inserting interference-fit steel plugs has dramatically increased fatigue resistance. For the same spectrum fatigue life the stresses in the life-enhanced plates need to be 2.6 times those in the plain cracked plates. This factor remains practically constant in the presence of secondary bending when the average bending stressaxial stress ratio is 0.5. Surprisingly, the secondary bending reduced the fatigue life by only about 25 for both unenhanced and enhanced specimens. These results have obvious application to the lower wing skin cracking in the F-111 aircraft.
- Properties of Metals and Alloys