Component Failure Rate (FR) and MTBF
.No data available for comparative MTBF. Data sources for predictive MTBF were ADD Fatigue and Durability (FD) Analysis data, Mil-Std-1388-2b App. F (Ref 1) and the Reliability Analysis Center (RAC) Failure Mode/Mechanisms Distribution (Ref 2)
MTBF is the total functional life of a population of an item divided by the number of failures during the measurement interval. Failure rate is the inverse of MTBF. (Ref 1)
RAC (Ref 2) indicates that failure causes for typical structure items, in an aerospace application envelope, consists of 50% cracks (FD), 30% accidental damage (AD) and 20% aging/ environmental deterioration (ED)
This analyst, in consensus with his ADD counterpart, formulated the following computation using RAC distribution of failure (Ref 2) and LOGISTICS ENGINEERING by Benjamin Blanchard (Ref 3):
Where Item fatigue test life= N Let FD= 50%, AD= 30%, ED= 20%
Then FR= 1/(2N x 0.5) + 1/(2N x 0.3) + 1/(2N x 0.2) MTBF= 1/FR
See Figure 1
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