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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Posted by: Hari (ch_hari_prasad@indiatimes.com )
Date posted: Sat Mar 8 0:24:41 US/Eastern 2003
Subject: Physical significance of Weibull Shape and scale paramenters
Message:
Someone can you help me please...... When statistically speaking shape decides the shape of the distribution(Whether it is normal,exponential,skewed distribution,etc....),Scale parameter decides the 63%of population fail with in that time.... When you convert this statical problem to physical problem(Practicle problem),On what properties this parameters depends........So in brief... What is the physical significance of Weibull shape and scale parameter?


Reply:

Subject: Weibull Parameters
Reply Posted by: Jorge Romeu (jromeu@alionscience.com )
Organization: RAC
Date Posted: Tue Mar 11 10:03:31 US/Eastern 2003
Message:
we can observe how, when the shape parameter is less than unit, values (e.g. lives) tend to be largely very small (early failures) then taper out as lives increase. If the shape parameter is unit, then the failures occur at random and the distribution is Exponential. If the shape is larger than unit, values (lives) tend to cluster around an (interior) value called Mode (wear out). In equality of other circumstances, the scale parameter  acts as a multiplier that extends the range of values (e.g. lives). Of course, the scale parameter is also the characteristic life, which comprises approximately 63% of the cases (63.2 % of all lives fail by this time). We provide, below, some bibliographical references for further reading. References: 1. Weibull Analysis; Dodson, B. ASQ Press. 1994 2. Reliability and Life Testing Handbook. Kececioglu., D. Prentice Hall, NJ. 1994. 3. Methods for Statistical Analysis of Reliability and Life Data. Mann, N., R. Schafer and N. Singpurwalla. John Wiley. NY. 1974. 4. Reliability Statistics I: Random Variables and Distributions. Romeu, J. L. RAC Journal. http://rac.alionscience.com/pdf/3q2001.pdf 5. A Practical Guide to Statistical Analysis of Material Property Data. Romeu, J. L. and C. Grethlein. AMPTIAC. 2000. 6. Empirical Assessment of Weibull Distribution Assumptions. Romeu, J. L. RAC START. Volume 10, Number3. http://rac.alionscience.com/pdf/WEIBULL.pdf


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