ITPEC IP October 2022 Question 16
The life cycle of a device is divided in terms of failures into three (3) periods, namely, the initial failure period, the random failure period, and the wear-out failure period, as time goes by. In the first initial failure period, the failure rate decreases as time goes by. Then, the device reaches a stable state, and the failure rate is effectively constant in the subsequent random failure period while time goes by. In the final wear-out failure period, the failure rate increases as time goes by, and the life of the device eventually ends. Which of the following is a representation of the relation between the failure rate and time?
Explanation
Bathtub curve — the failure rate plotted against time falls, stays flat, then rises, the outline of a bathtub.
The curve has three periods:
- •Initial failure period: the failure rate is high and falls as defects from design, manufacturing and installation show up and are removed
- •Random failure period: a low, nearly constant failure rate from chance failures, the device's useful life
- •Wear-out failure period: the failure rate rises again as parts age and wear
Answer (c)
Why not others:
- •(a) Gantt chart — a schedule chart, a bar for each task along a time axis; it shows work planned and done, not failures
- •(b) Reliability growth curve — the cumulative number of bugs found plotted against test time during software testing; it flattens as the software stabilises, but it never rises again like the wear-out period
- •(d) Radar chart — compares several items on axes drawn from a centre, such as scores on several criteria; it has no time axis
Key rule: Burn-in before shipping screens out initial failures, and replacing parts before they wear out keeps a device at the flat bottom of the bathtub.
System Component · AI-written, may contain errors
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