Fundamentals of Reliability

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  • 1. Chapter 13 ReliabilityTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 1
  • 2. Reliability • Generally defined as the ability of a product to perform as expected over time • Formally defined as the probability that a product, piece of equipment, or system performs its intended function for a stated period of time under specified operating conditions 2THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 3. Maintainability • The probability that a system or product can be retained in, or one that has failed can be restored to, operating condition in a specified amount of time. 3THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 4. Types of Failures • Functional failure – failure that occurs at the start of product life due to manufacturing or material detects • Reliability failure – failure after some period of use 4THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 5. Types of Reliability • Inherent reliability – predicted by product design • Achieved reliability – observed during use 5THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 6. Reliability Measurement • Failure rate (λ) – number of failures per unit time • Alternative measures – Mean time to failure – Mean time between failures 6THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 7. Cumulative Failure Rate Curve 7THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 8. Failure Rate Curve “Infant mortality period” 8THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 9. Average Failure Rate 9THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 10. Reliability Function • Probability density function of failures f(t) = λe-λt for t > 0 • Probability of failure from (0, T) F(t) = 1 – e-λT • Reliability function R(T) = 1 – F(T) = e-λT 10THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 11. Series Systems 1 2 n RS = R1 R2 ... Rn 11THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 12. Parallel Systems 1 2 n RS = 1 - (1 - R1) (1 - R2)... (1 - Rn) 12THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 13. Series-Parallel Systems C RA RB RD RC A B D C RC • Convert to equivalent series system RA RB RD A B C’ D RC’ = 1 – (1-RC)(1-RC) 13THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 14. Reliability Engineering • Standardization • Redundancy • Physics of failure • Reliability testing • Burn-in • Failure mode and effects analysis • Fault tree analysis 14THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 15. 15THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 16. 16THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 17. Reliability Management • Define customer performance requirements • Determine important economic factors and relationship with reliability requirements • Define the environment and conditions of product use • Select components, designs, and vendors that meet reliability and cost criteria • Determine reliability requirements for machines and equipment • Analyze field reliability for improvement 17THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 18. Configuration Management • Establish approved baseline configurations (designs) • Maintain control over all changes in the baseline programs (change control) • Provide traceability of baselines and changes (configuration accounting) 18THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 19. Maintainability • Maintainability is the totality of design factors that allows maintenance to be accomplished easily • Preventive maintenance reduces the risk of failure • Corrective maintenance is the response to failures 19THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 20. Design Issues • Access of parts for repair • Modular construction and standardization • Diagnostic repair procedures and expert systems 20THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM
  • 21. Availability • Operational availability MTBF MTBM = mean time between AO = maintenance MTBM + MDT MTD = mean down time • Inherent availability MTBF = mean time between MTBF failures AO = MTBF + MTTR MTTR = mean time to repair 21THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM