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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

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

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Original Message:

Posted by: Ed
Date posted: Mon Jan 6 13:17:18 US/Eastern 2003
Subject: Wearout or random failure
The failure criteria of a device is 10% change in one parameter. Is it a wearout or random failure? Thanks.

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Subject: Wear-Out MTTF
Reply Posted by: Joe Dzekevich ( )
Organization: Raytheon RAL
Date Posted: Tue Jan 7 16:41:56 US/Eastern 2003
Ed, since it is a wear-out device, then you should treat it like you would with a fan or e-cap. For the unit, quote two numbers: a MTBF (includes all non wear-out components and the random f/r of wear-out components) and a MTTF for the wear-out. Now, if you want to combine them into one number, you then must quote it over some time period, like x days, y warranty, z mission time. Many preduction tools allow you to mix MTBF (exponential) with MTTF (Weibull), but the Weibull part needs a mission time. In effect, you are adding the Weibull f/r at time t to the exponential random failure rate. Joe Joe

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