ITPEC IP October 2018 Question 14
Topic: System Component
In reliability engineering, which of the following is the index represented by the y-axis of a bathtub curve?
Explanation
Failure rate — the bathtub curve plots how often a device fails over its life: high at first, low and flat for a long time, then rising again.
The curve has three periods:
- •Early failure period: the failure rate is high and falls as defects from manufacturing and installation are found and removed
- •Random failure period: a low, nearly constant failure rate, the device's useful life
- •Wear-out failure period: the failure rate rises again as parts age
Answer (a)
Why not others:
- •(b) Reliability — the probability that the device is still working at a given time; it starts at 1 and only decreases, so it cannot dip and rise like a bathtub
- •(c) Mean time between failures — a single average for a device (in the random failure period, the reciprocal of the constant failure rate), not a value that changes with time
- •(d) Mean time to repair — the average time to restore a failed device; it measures maintainability, not how failures occur over time
Key rule: Burn-in before shipping screens out early failures, and replacing parts before they wear out keeps the failure rate at the flat bottom of the bathtub.
System Component · AI-written, may contain errors
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