ReliabilityReliability: DefinitionFactors Impacting ReliabilityProduct Life CycleMeasures of ReliabilityTime-Dependent PerformanceSlide 7System ReliabilitySlide 9Redundant Systems ReliabilityReliability ProgramsSlide 12ReliabilityA. A. ElimamReliability: DefinitionThe ability of a product to perform its intended function over a period of time and under prescribed environmental conditionsFactors Impacting Reliability Initial design Complexity of design Manufacturing process Handling during shipping Environment of use Its end userProduct Life Cycle Early Failure (infant Mortality) : Exponential  Chance Failure Wear-out: As the product agesMeasures of Reliability Failure-terminated testsWhen a predetermined number of failures occur in sample  Time-terminated tests when an established number of hours is reached.Time-Dependent Performance Mean Life Mean Time between Failures Mean Time to Failures (non-repairable systems) Availability = mean time to failure (MTTF) MTTF + mean time to repairTime-Dependent Performance Failure rates = # of Failures observed sum of test times or cycles Average Life =sum of test times or cycles# of Failures observedSystem Reliability System in series exists only if its functioning depends on that of ALL its parts Rs = r1 . r2 . r3 . . . . .rn Rs = reliability of series system ri = reliability of component i n = number of parts in systemSystem Reliability Parallel System in able to function if at least one of its components is functioning Rp = 1- (1-r1) . (1-r2 ). . . .(1- rn) Rp = reliability of parallel systemRedundant Systems Reliability Backup/spare components used if primary comp. fails Rb = r1 + rb (1- r1) Rb =reliability of backup systemr1 =reliability of primary comp.rb =reliability of backup comp.Reliability Programs The entire system The humans in the system Maintenance of the system Simplicity Redundant & fail-safe featuresReliability Programs Manufacturing methods and purchasing requirements Maintenance of complete product or system performance records