Reliability of Repairable Systems
Consider a system (or unit) which fails at random times. After each failure the system is repaired (renewed). The repair time is a random variable with some repair-time distribution (instantaneous or fixed-time repairs are special cases). After each renewal the system starts a new cycle, independent of the previous ones. Thus, let T1 be the time till failure (TTF) of the system in the first cycle; let S 1 be the length of time till repair (TTR); T 2 and S 2 the TTF and TTR in the second cycle, etc. (See Figure 4.1.)
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