An Investigation of Fatigue in a Supersonic Transport Operating Environment

The effects of aircraft-loading parameters on the fatigue behavior of titanium alloy have been investigated for a schedule of stresses representing the flight-by-flight variation of stress at a point in the lower wing surface of a supersonic airplane. The effects on fatigue life of design mean stress, minimum stress for ground-air-ground cycles, taxi stress, thermal stress, elevated temperature, salt corrosion, and flight duration were investigated. Of the loading parameters studied, the design mean stress and the minimum stress for ground-air cycles had the greatest effects on fatigue life. Simulated taxiing and thermal stresses, elevated temperature, and salt corrosion had smaller effects on fatigue life. Fatigue lives at 550 F (560 K) were about half as long as at room temperature for most conditions investigated. The effect of the difference in flight duration on fatigue life was less than a factor of 2.