B urak Sal Presenter M Altun Istanbul Technical University Istanbul Turkey Motivation CALT uses 6 samples ALT uses 100 samples WHICH ONE DO YOU CHOOSE 6 samples lt 100 samples ID: 1030534
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1. Extensive Investigation of Calibrated Accelerated Life Testing (CALT) in Comparison with Classical Accelerated Life Testing (ALT)Burak Sal (Presenter), M. AltunIstanbul Technical University, Istanbul, Turkey
2. MotivationCALT uses 6 samplesALT uses 100 samplesWHICH ONE DO YOU CHOOSE ?6 samples < 100 samples Is it though?Is it though?Is it though?Is it though?What about the time that CALT has to run until the sample fails?So choosing CALT will be the best way ever!!!!What about the accuracy?
3. OUTLINEIntroduction Definition of ALT and CALTGeneral Test MechanismLife-Stress Plot of CALTPerformance Parameters Bounds RatioCalculation of Performance ParametersComparison of ALT and CALT with changing performance parametersFailure Rate ComparisonAcceleration Factor ComparisonCase StudiesThreshold Values of ALT and CALTCase StudiesCase Study - 1Case Study - 2Case Study - 3Conclusion
4. Definiton of ALT and CALTAccelerated Life Testing (ALT) and Calibrated Accelerated Life Testing (CALT) are mainly used test methods.Also Highly Accelerated Life Testing (HALT) is used before these testing methods to determine absurd stress levels.ALT uses analytical equations to determine test stress level and sample size.CALT uses profile methods for stress levels and 2 sample size for each profile. Each profile is %10 reduced version of previous level.
5. General Test Mechanism
6. Life-Stress Plot of CALTCALT’s Life-Stress plot is controversial because of few stress points are determined.
7. Performance Parameters – Bounds RatioBounds Ratio affects accuracy with failure rate and sample size.
8. Calculation of Parameters - ALTReliability, R(t)= exp(-WT/MTTF) R(t)= exp(-t/n )^β β= Beta, n= Eta, t= WT (hours) AF=exp[(Ea/k)*(1/Tfield-1/Ttest)] Ea= Activation Energy, Tfield= Field Temperature, Ttest= Test Temperature, n1 /AF= n2P1= 1-exp(-t/n1)^β, P2= 1-exp(-t/n2)^βP1 and P2 Probability of Failure values, t= Estimated Time (hours), k= Boltzmann constant
9. Calculation of Parameters - ALTBounds Ratio= Upper Limit/Lower Limit lnTp+ z*std(lnTp)= Upper Limit lnTp- z*std(lnTp)= Lower Limit Tp= Standard Deviation, z= Normal Distribution Parameter. Sample Size= (z*A*BR)^c A= Average variance coefficient, c= Distribution Parameter.Unit Test Time= (Normal Yearly Time*Warranty Time)/AFTotal Test Time= Sample Size × Unit Test Time
10. Calculation of Parameters - CALTSample Size= 6 Recommended sample size for CALT is 6, however, sample size can be increased in order to increase accuracy. Unit Test Time= (Normal Yearly Time*MTTF)/AF Total Test Time= Sample Size × Unit Test Time
11. Comparison of ALT and CALT – Failure RateWe have compared FR (%10, %1, %0.1) and accuracy levels of ALT and CALT by the changing of WT and MTTF.altaltaltcaltcaltcalt
12. Accuracy Comparison with Failure Rate levelsAccuracy Comparison FR=%10, MTTF=30 years, WT=3 Years.ALTCALT%100%97Accuracy Comparison FR=%1, MTTF=30 years, WT=3 Years.ALTCALT%100%50Accuracy Comparison FR=%0.1, MTTF=30 Years, WT=3 Years.ALTCALT%100%14Accuracy Comparison FR=%10, MTTF=30 Years, WT= 1 year.ALTCALT%100%98Accuracy Comparison FR=%1, MTTF=30 Years, WT= 1 year.ALTCALT%100%70Accuracy Comparison FR=%0.1, MTTF=30 Years, WT= 1 year.ALTCALT%100%45Accuracy Comparison FR=%10, MTTF=10 Years, WT= 1 year.ALTCALT%100%99Accuracy Comparison FR=%1, MTTF=10 Years, WT= 1 year.ALTCALT%100%84Accuracy Comparison FR=%0.1, MTTF=10 Years, WT= 1 year.ALTCALT%100%62
13. Comparison of ALT and CALT – Acceleration FactorWe have compared AF (10, 20, 30) and accuracy levels of ALT and CALT by the changing of FR.altaltaltcaltcaltcalt
14. Accuracy Comparison with Acceleration Factor levelsAccuracy Comparison FR=%10, MTTF=30 years, WT=3 Years, AF=10ALTCALT%100%97Accuracy Comparison FR=%1, MTTF=30 years, WT=3 Years. AF=10ALTCALT%100%50Accuracy Comparison FR=%0.1, MTTF=30 Years, WT=3 Years. AF=10ALTCALT%100%14Accuracy Comparison FR=%10, MTTF=30 Years, WT= 1 year, AF=20ALTCALT%100%100Accuracy Comparison FR=%1, MTTF=30 Years, WT= 1 year, AF=20ALTCALT%100%97Accuracy Comparison FR=%0.1, MTTF=30 Years, WT= 1 year, AF=20ALTCALT%100%50Accuracy Comparison FR=%10, MTTF=10 Years, WT= 1 year, AF=30ALTCALT%100%100Accuracy Comparison FR=%1, MTTF=100 Years, WT= 1 year, AF=30ALTCALT%100%98Accuracy Comparison FR=%0.1, MTTF=10 Years, WT= 1 year, AF=30ALTCALT%100%72
15. Threshold Values for ALT and CALT UsageALT and CALT can not be used under these values.TfW=10 hoursTfW=30 hoursAFALTCALT10180 hours1750 hours2090 hours900 hours3070 hours465 hoursAFALTCALT1054 hours525 hours2027 hours270 hours3021 hours140 hours
16. Case Study - 1We determined wanted input values and chose one of the test methods.Input ValuesALTCALTAF=10MTTF=30 yearsWT=3 yearsBR= 5TT= 1000 hoursTfW= 10 hoursFR=%9.5SS=11Accuracy=%9TT=1000 hoursCAN NOT BE USED. (IT IS UNDER THE THRESHOLD VALUE)
17. Case Study - 2We determined wanted input values and chose one of the test methods.Input ValuesALTCALTAF=20MTTF=30 yearsWT=3 yearsBR= 5TT= 1000 hoursTfW= 3 hoursFR=%9.5SS=20Accuracy=%100TT=652 hoursFR=%9.5SS=5Accuracy=%98TT=1000 hours
18. Case Study - 3We determined wanted input values and chose one of the test methods.Input ValuesALTCALTAF=20MTTF=30 yearsWT=3 yearsBR= 5TT= 500 hoursTfW= 3 hoursFR=%9.5SS=15Accuracy=%76TT=500 hoursFR=%9.5SS=3Accuracy=%41TT=500 hours
19. ConclusionWe show that even though CALT uses fewer sample size than ALT, its accuracy and total test time can not beat ALT in some levels.Also, we support that result with parameter calculations, graphs and case studies.Our future work will be ‘Dynamic Test Method’ which can be used with one by one sample and performance parameter will change to arrange wanted test results.
20. Thank you for listeningAny Questions?Info: salb@itu.edu.tr