Reliability Fundamentals Flashcards
7 cards from real CRE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Reliability Fundamentals flashcards as text
A k-out-of-n system requires at least k of n identical components to work. Which scenario describes a 2-out-of-3 system?
Answer: The system works if at least 2 of 3 components function
A 2-out-of-3 system succeeds when at least 2 of its 3 components are operational, providing redundancy against single failures.
The conditional reliability R(t|T) represents the probability that a component will survive an additional time t given it has already survived to time T. For an exponential distribution, R(t|T) equals:
Answer: R(t), independent of T
Due to the memoryless property of the exponential distribution, R(t|T) = R(t) regardless of prior survival time T.
Which reliability growth model uses a non-homogeneous Poisson process (NHPP) to track cumulative failures during development testing?
Answer: Crow-AMSAA model
The Crow-AMSAA model applies an NHPP with a power-law intensity function to characterize and project reliability growth during testing.
When performing a reliability apportionment for a series system, what is the primary goal?
Answer: Allocate a system reliability requirement among subsystems or components
Reliability apportionment distributes the overall system reliability goal to lower-level elements so each has a target to design toward.
A component has a lognormal failure distribution. This is most commonly associated with which failure mechanism?
Answer: Fatigue crack growth and corrosion failures
Lognormal distributions commonly model fatigue, corrosion, and repair time distributions where failure results from multiplicative degradation processes.
What is the effect of adding a warm standby redundant component (versus cold standby) on system reliability?
Answer: Warm standby has a higher failure rate while idle than cold standby, so it is generally less reliable
Warm standby components operate at reduced stress but still fail at some rate while idle, making them less reliable than cold standby (zero standby failure rate) but faster to switch.
In the context of the exponential distribution, what is the relationship between the failure rate λ and the MTTF?
Answer: MTTF = 1/λ
For the exponential distribution, MTTF = 1/λ, so a failure rate of 0.001/hr yields an MTTF of 1000 hours.