R:ReliabilityTheabilityofan itemtoperformarequiredfunction,undergivenenviromentalandoperationalconditionsandforastatedperiodoftime-lEC60050.Function oftimeFunctionofoperatingconditionWhenlookingforward(i.e.,intothefuture),theterm"reliability"without anyadditionispreferred."Based onanalyses,mynew carwill haveaveryhigh reliability”When talking about theexperienced reliability (i.e.,what happened in thepast),theterm"reliabilityperformance"maybepreferred.e.g."Mypreviouscar hadaverygoodreliabilityperformance-withvirtuallynofailures"NTNU-TrondheimNorwegian University ofScienceandTechnologywww.ntnu.edu
6 R: Reliability The ability of an item to perform a required function, under given enviromental and operational conditions and for a stated period of time‐IEC 60050. • Function of time • Function of operating condition • When looking forward (i.e., into the future), the term “reliability” without any addition is preferred. “Based on analyses, my new car will have a very high reliability” • When talking about the experienced reliability (i.e., what happened in the past), the term “reliability performance” maybe preferred. e.g. “My previous car had a very good reliability performance – with virtually no failures
Reliability vs.QualityQuality:Thetotalityoffeaturesand charactersticsof aproductorservicethat bearon itsabilitytosatisfystatedorimpliedneeds.-ISo8402QualitydenotestheconformitytospecificationsProductreliabilitycanberegardedasanextensionof qualityintothetimedomainNTNU-TrondheimNorwegian University ofScience and Technologywww.ntnu.edu
7 Reliability vs. Quality Quality: The totality of features and characterstics of a product or service that bear on its ability to satisfy stated or implied needs. – ISO 8402 • Quality denotes the conformity to specifications. • Product reliability can be regarded as an extension of quality into the time domain
8DifferentapproachesHardwarereliability-withtwoapproaches:Structural reliabilityAlsocalledthephyisicalapproachBased ontheassessment of loads and stressesMainlyapplicabletostruturalelementsSystem reliabilityAlsocalledtheactuarialapproachBased on the study of the time-to-failure of single componentsMainlyapplicabletocomponentsandsystemsSoftwarereliabilityHuman reliabilityNTNU-TrondheimNorwegian University ofScience and Technologywww.ntnu.edu
8 Different approaches Hardware reliability – with two approaches: • Structural reliability – Also called the phyisical approach – Based on the assessment of loads and stresses – Mainly applicable to strutural elements • System reliability – Also called the actuarial approach – Based on the study of the time‐to‐failure of single components – Mainly applicable to components and systems Software reliability Human reliability
0PhysicalapproachLoad distributionamqeqoud--TheitemwillfailwhenS<LRegion offailureThereliability of theitemis defined asStrength distributionR = Pr(S > L)StressNTNU - Trondheim莎Norwegian UniversityofScienceandTechnologywww.ntnu.edu
9 Physical approach The item will fail when S ൏ L The reliability of the item is defined as ܴ ൌ Pr ሺܵ ܮሻ
10Physical approachStrength distributionLoad distributiopLoad distributiorCStrensth distribolRegion offailuresStressStresTwowaysofdesignforreliabilityNTNU-Trondheim莎Norwegian UniversityofScienceand Technologywww.ntnu.edu
10 Physical approach Two ways of design for reliability