CRE (ASQ) flashcards
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31 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Reliability function R(t)
- Probability that an item performs its required function without failure for a stated time under stated conditions; ranges from 0 to 1.
- Failure rate lambda
- Instantaneous rate of failure at time t given survival to t; equals f(t)/R(t) and has units of failures per unit time.
- Exponential reliability model
- Model with constant failure rate where R(t) = exp(-lambda*t); MTBF equals 1/lambda and the distribution is memoryless.
- Weibull shape parameter beta
- Determines failure mode: beta below 1 indicates infant mortality, beta equal to 1 random failures, beta above 1 wear-out.
- Bathtub curve
- Failure-rate-over-time pattern with three phases: decreasing infant mortality, constant useful life, and increasing wear-out.
- Series system reliability
- For components in series, system reliability equals the product of component reliabilities; all components must function for success.
- Active parallel redundancy
- n identical units all operating; system reliability equals 1 minus (1 minus R) raised to the nth power.
- FRACAS
- Failure Reporting, Analysis, and Corrective Action System; a closed-loop process ensuring each failure is analyzed and corrective action verified.
- Duane reliability growth model
- Cumulative MTBF equals A times test time raised to slope alpha; plots as a straight line on log-log axes during growth.
- Design review gate
- Formal milestone where reliability analyses and test evidence are evaluated against requirements before proceeding to the next phase.
- Quantitative reliability requirement
- A measurable, verifiable statement of required reliability, such as MTBF or probability of success, traceable to mission needs.
- Derating
- Operating components below rated stress levels (power, voltage, temperature) to lower failure rate and extend useful life.
- Standby redundancy
- Backup units that are unpowered until switched on; reliability depends on the switch and failure-detection monitor.
- Risk Priority Number
- RPN equals severity times occurrence times detection, each scored 1 to 10 in FMEA; ranges from 1 to 1000.
- Fault tree analysis
- Top-down deductive method using AND/OR logic gates to model combinations of causes leading to an undesired top event.
- Stress-strength interference
- Failure occurs when applied stress exceeds component strength; probability of failure is the overlap of both distributions.
- Reliability allocation
- Distributing a system-level reliability target among subsystems using factors such as complexity, criticality, or prior data.
- Parts count prediction
- Early design method summing generic part failure rates multiplied by quality and environment factors to estimate system failure rate.
- k-out-of-n system
- System succeeds if at least k of n units function; reliability is the binomial sum from i equals k to n.
- Reliability block diagram
- Success-oriented model of series and parallel paths showing which component combinations permit the system to function.
- Markov reliability model
- State-transition model using failure and repair rates to compute state probabilities, availability, and system reliability.
- Producer's risk alpha
- Type I error in acceptance sampling; probability a good lot is rejected by the test, typically set at 0.05.
- Consumer's risk beta
- Type II error in acceptance sampling; probability a bad lot is accepted by the test, typically set at 0.10.
- Weibull probability plot
- Plot of ln(-ln R) versus ln t; a straight line indicates a Weibull fit, with slope estimating beta and intercept estimating eta.
- Arrhenius acceleration model
- Life-stress model where reaction rate depends exponentially on inverse absolute temperature; used to extrapolate accelerated test life.
- Censored life data
- Observations where the exact failure time is unknown, such as suspended or removed units; must be included to avoid biased estimates.
- Inherent availability
- A_i equals MTBF divided by the sum of MTBF and MTTR; excludes logistics and administrative downtime.
- Maintainability M(t)
- Probability a failed item is restored to operating condition within a stated time t, given maintenance resources and procedures.
- Reliability-centered maintenance
- Process selecting maintenance tasks based on failure modes and consequences: condition-based, scheduled, redesign, or run-to-failure.
- Operational availability
- Availability including logistics delay and administrative downtime in addition to repair time; reflects real field performance.
- Minimal cut set
- Smallest combination of fault tree basic events that causes the top event; a single-element cut set is a single point of failure.