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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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Original Message:

Posted by: sastri
Date posted: Thu Aug 8 12:07:52 US/Eastern 2002
Subject: dormant storage life
Message:
I am looking for models and accelerated test methods that would enable me to predict the preformance of electronic and mechanical parts placed in a relatively stable environment. The subsystems have to perform after being dormant for a long time.


Reply:

Subject: Accelerated Testing
Reply Posted by: B.W.Dudley (bdudley@alionscience.com )
Organization: RAC
Date Posted: Thu Aug 8 14:09:11 US/Eastern 2002
Message:
This is a repeat of the November 20,2000 accelerated test answer. There are no magic analytical models that accurately estimate the life of complex assemblies. Each life analytical model describes physical change mechanisms associated with specific material characteristics. The first step in constructing accelerated tests is to define the failure mechanisms in terms of the materials used in the product to be tested. The next step is to determine the environmental parameters the product will be exposed when operating and when not operating or stored. Based on the failure mechanisms most likely to limit the life of the product, one can choose a test or tests that will accelerate that failure mechanism. Some of the models that can be considered are: Miner's Rule for accumulated fatigue, Arrhenius Temperature test for accelerated temperature and chemical aging effects, Peck's Model for temperature and humidity combined effects, Coffin-Manson non-linear mechanical fatigue damage model and Eyring/Black/Kenney models for temperature and voltage acceleration. In the 2001 Reliability and Maintainability Symposium, Pantelis Vassiliou and Adamantios Mettas presented a complete tutorial on "Understanding Accelerated Life-Testing Analysis" that is worth reviewing as they developed a presentation on the problems and pitfalls of accelerated testing. Inaddition to the tutorial, J.D. Seager of the IBM corporation published a paper on " A Method to Predict an Average Activation Energy for Subassemblies" (IEEE, Transactions on Reliability, Vol. #37, No.5, 1988) that could be considered in the search for a single test value. This approach uses a combination process to average the expected component activation energies. In any event, the only tried and true method is to perform multiple high stress experimental tests to determine the real activation energy for the product using plots of the data.


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