Reliability theory - failure rates, system reliability, reliability of growth models - One Line Questions

1. In Fault Tree Analysis, what does a 'top event' represent? — An undesirable system-level event (e.g., system failure)
2. What is the Bathtub Curve in reliability theory? — A graph of failure rate over time, typically showing initial high failure rates, followed by a constant period, and then increasing failure rates
3. What is the concept of 'failure modes and effects analysis' (FMEA)? — A systematic process of identifying potential failure modes in a system or product and their effects
4. What is the 'stress-strength' model in reliability theory? — A model for predicting reliability based on the relationship between applied stress and the strength of a component
5. The concept of 'graceful degradation' in system reliability refers to: — A system that maintains partial functionality even after some component failures
6. The constant failure rate period in the Bathtub Curve is often referred to as the: — Useful life period
7. The Weibull distribution has a shape parameter (beta). What does a beta > 1 typically indicate about the failure rate? — Increasing failure rate
8. The Duane model for reliability growth posits that the cumulative failure rate decreases as: — Development time increases
9. Which reliability model is often used to describe the lifetime of components subject to wear-out? — Weibull distribution
10. What is the significance of 'common-cause failures' in system reliability? — Failures where multiple components fail simultaneously due to a single event or cause
11. What is the common unit for measuring failure rate (lambda)? — Failures per unit time (e.g., failures per hour)
12. A beta = 1 in a Weibull distribution corresponds to a: — Constant failure rate (exponential distribution)
13. In the context of reliability growth, what does a 'corrective action' typically involve? — Identifying and fixing the root cause of a failure
14. The final period of increasing failure rate in the Bathtub Curve is typically due to: — Wear-out of components
15. What is the main advantage of predictive maintenance over preventive maintenance? — It avoids unnecessary maintenance tasks, reducing costs and downtime
16. In reliability growth models, what is the fundamental assumption about the system's reliability over time? — It increases as design changes and improvements are made
17. What is the main advantage of a parallel system configuration compared to a series system? — Higher reliability
18. What does a higher RPN value in FMEA generally indicate? — Higher risk and higher priority for action
19. Which of the following is a measure of system availability? — MTBF / (MTBF + MTTR)
20. What is the relationship between the failure rate (lambda) and the Mean Time To Failure (MTTF) for an exponential distribution? — MTTF = 1 / lambda
21. If a component has a constant failure rate, what type of distribution does its lifetime typically follow? — Exponential distribution
22. What is the primary focus of Reliability Theory in Operations Research? — Analyzing the probability of failure of components and systems
23. Which type of maintenance is characterized by performing maintenance tasks based on actual condition monitoring and analysis? — Predictive maintenance
24. If components A and B are in parallel with reliabilities R_A and R_B respectively, the reliability of the system R_S is: — R_S = 1 - (1 - R_A) * (1 - R_B)
25. If components A and B are in series with reliabilities R_A and R_B respectively, the reliability of the system R_S is: — R_S = R_A * R_B
26. The Risk Priority Number (RPN) in FMEA is typically calculated as: — Severity * Occurrence * Detection
27. In the stress-strength model, reliability is often calculated as the probability that: — Strength > Stress
28. What is the concept of 'k-out-of-n' systems in reliability? — Systems where k components must operate for the system to operate
29. What is Mean Time To Repair (MTTR)? — The average time required to repair a failed component or system
30. In FMEA, what does 'Occurrence' measure? — The likelihood or frequency of a failure mode occurring
31. In FMEA, what does 'Detection' measure? — The ability of existing controls to detect the failure mode before it reaches the customer
32. In FMEA, what does 'Severity' measure? — The impact of a failure mode on the system or customer
33. What is the 'learning curve' concept in reliability growth models? — The improvement in reliability achieved through repeated testing and correction of failures
34. System reliability refers to: — The probability that the entire system will perform its intended function for a specified period
35. For a series system, how is the system reliability calculated if the component reliabilities are independent? — The product of the component reliabilities
36. For a parallel system, how is the system reliability calculated if the component reliabilities are independent? — 1 minus the product of the probabilities of failure of each component
37. What does a high availability value indicate? — The system is operational for a high proportion of the time
38. A 2-out-of-3 system means: — The system operates if at least 2 components operate
39. In reliability theory, what does the 'failure rate' represent? — The rate at which a component is expected to fail at a specific time
40. Which of the following is a common type of reliability growth model? — The Duane model
41. What is the role of 'basic events' in a Fault Tree? — They represent fundamental failures or conditions that can lead to the top event
42. How do common-cause failures typically affect system reliability compared to independent failures? — They decrease system reliability
43. What is the primary goal of predictive maintenance in reliability theory? — To monitor equipment condition and predict potential failures to schedule maintenance proactively
44. What is the primary goal of applying reliability growth models? — To estimate how reliability will improve with testing and corrective actions
45. What is the purpose of Fault Tree Analysis (FTA)? — To identify potential causes of system failure by starting with an undesired event and working backward
46. In reliability theory, what does 'redundancy' typically refer to? — Using multiple components to perform the same function, often in parallel
47. Which of the following is NOT a typical method used in predictive maintenance? — Scheduled component replacement based on a fixed calendar time
48. The initial period of high failure rate in the Bathtub Curve is often attributed to: — Infant mortality or early failures due to manufacturing defects
49. A beta < 1 in a Weibull distribution typically indicates: — Infant mortality or decreasing failure rate
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