Exploratory Development on Application of Reliability Analysis to Aircraft Structures Considering Interaction of Cumulative Fatigue Damage and Ultramate Strength.
Final rept. 16 Nov 70-15 Mar 72,
BOEING COMMERCIAL AIRPLANE CO SEATTLE WASH
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An analysis method for determining the reliability of airplane structures, subjected to the cumulative and maximum operational loads and the resultant interaction of fatigue damage and strength, has been investigated. The design variables include the central tendency values of the fatigue performance, that is, the average lives to initiation and the growth of a major crack, and the effect of the crack on structural strength. Other variables include the standard operational procedure of periodic inspection of the structure and its repair when found to be damaged. Functions, based on the length of the fatigue crack, are used to describe both the residual strength of the structure and the probability of the crack being detected and the cracked structure being repaired. The times to initiation of a crack and the later time when the crack becomes critical, i.e., unstable, are taken as random variables. The derived reliability model considers that at any time the structure is either failed or unfailed. Author Modified Abstract