CQE Reliability and Risk Management 1 — Questions and Answers
Question 1: What does the 'bathtub curve' in reliability engineering represent?
- The cost of quality over product lifetime
- The failure rate pattern showing infant mortality, useful life, and wear-out phases (Correct answer)
- Warranty cost trends over time
- The relationship between reliability and price
Correct answer: The failure rate pattern showing infant mortality, useful life, and wear-out phases
The bathtub curve depicts three phases of product failure rate: early failures (infant mortality), random failures during useful life, and increasing failures during wear-out.
Question 2: Mean Time Between Failures (MTBF) is a reliability metric applicable to:
- Non-repairable items only
- Repairable items that can be restored to service (Correct answer)
- Items during burn-in testing only
- Software defect tracking
Correct answer: Repairable items that can be restored to service
MTBF applies to repairable systems and represents the average time between successive failures after repair, distinct from MTTF (Mean Time To Failure) used for non-repairable items.
Question 3: In a Failure Mode and Effects Analysis (FMEA), the Risk Priority Number (RPN) is calculated as:
- Severity + Occurrence + Detection
- Severity × Occurrence × Detection (Correct answer)
- Severity × Occurrence ÷ Detection
- Severity ÷ (Occurrence × Detection)
Correct answer: Severity × Occurrence × Detection
RPN is the product of three ratings: Severity (impact of failure), Occurrence (likelihood of cause), and Detection (ability to detect before reaching customer), each typically rated 1–10.
Question 4: What is the primary purpose of a Fault Tree Analysis (FTA)?
- To rank suppliers by quality performance
- To identify combinations of events that could lead to a top-level undesired event (Correct answer)
- To calculate process capability
- To create control charts for critical parameters
Correct answer: To identify combinations of events that could lead to a top-level undesired event
FTA is a top-down, deductive analysis that uses Boolean logic to identify all possible combinations of hardware failures, human errors, and external events that could cause a specific undesired top event.
Question 5: In reliability testing, accelerated life testing (ALT) is used to:
- Skip required reliability tests to save time
- Expose products to stresses above normal levels to induce failures faster and predict life (Correct answer)
- Test only a small fraction of production
- Verify supplier component reliability
Correct answer: Expose products to stresses above normal levels to induce failures faster and predict life
ALT applies elevated stress levels (temperature, voltage, vibration) to precipitate failures in a shorter time, allowing engineers to extrapolate reliability performance under normal use conditions.
Question 6: Which reliability metric describes the probability that a system will be operational at any given random point in time?
- MTBF
- MTTF
- Availability (Correct answer)
- Reliability function R(t)
Correct answer: Availability
Availability is the probability that a repairable system is in an operational state at a random point in time, combining both reliability (failure rate) and maintainability (repair rate).
CQE Reliability and Risk Management 1
What does the 'bathtub curve' in reliability engineering represent?