CRE Reliability Fundamentals 3

Question 1

A non-repairable component has a Weibull distribution with β = 2.5 and η = 1000 hours. What does η represent?

Accepted Answer

The characteristic life at which 63.2% of units have failed

Answer

The Weibull scale parameter η (characteristic life) is the time at which 63.2% of units will have failed, regardless of β.

Question 2

Which of the following is the correct formula for the reliability of a two-component active parallel system?

Accepted Answer

R_sys = 1 - (1 - R₁)(1 - R₂)

Answer

For an active parallel system, the system fails only if all components fail: R_sys = 1 - (1-R₁)(1-R₂).

Question 3

The B10 life of a bearing is the time by which what percentage of bearings will have failed?

Accepted Answer

10%

Answer

BX life is the time by which X% of a population will have failed, so B10 life corresponds to 10% failure.

Question 4

A system's hazard function h(t) is constant. What does this imply about its failure behavior?

Accepted Answer

Failures are memoryless and occur randomly

Answer

A constant hazard rate implies the exponential distribution and memoryless property — past operation does not affect future failure probability.

Question 5

What is the primary purpose of accelerated life testing (ALT) in reliability engineering?

Accepted Answer

To precipitate failures quickly by applying elevated stress to estimate normal-use life

Answer

ALT applies stresses above normal use levels to induce failures faster, then uses models to extrapolate life at normal conditions.

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