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Archive Of The Category "Reliability Analysis"
Physics of Failure vs:  Chemistry of Failure

Physics of Failure vs: Chemistry of Failure

Adam / December 15, 2017

The term “Physics of Failure” is used when referring to the underlying mechanism that has driven a failure mode.  I have issue with the words “Physics” in this phrase as a “catch all.”  This implies we are only working with physical or kinematic interactions when studying product wear-out. Wear-out failures are rooted in chemistry as well.  Most electronic failures are chemistry based.   If a failure can be tracked back to a material property change, dielectrics, brittleness, transformation (oxidation), strength loss based on property change without fatigue, we have a chemistry…

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Is this the same as that?

Is this the same as that?

Adam / November 23, 2017

A common tool for comparing if two populations are the same is the “student t-test.”  This is often used in reliability, and science, if we want to investigate if a factor has caused a change in a respnse.

A population was assembled in location “A”.  Another population was assembled in location “B”.  Population “A” has an average defect rate of 4%.  Population “B” has an average defect rate of 5.5%. Does the location of assembly affect defect rate?  That’s just a big argument unless we can project the statistical likelihood that what we have measured is not just an overlap…

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Language is The Tragedy of Reliability

Language is The Tragedy of Reliability

Adam / November 08, 2017

I was teaching a class on Reliability 101 a few years ago and it turned out to be one of those great classes where debate and discussion would just pop up all over the place.  I frequently start my classes with “If I end up being the only one speaking today I am going to take that as an indication of complete failure in having engaged you in this material.”  So I was loving that this group were starting to debate each other on the material we were covering.  I wasn’t even in some of the conversations.  This rich…

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Designing Accelerated Life Tests (ALT)

Designing Accelerated Life Tests (ALT)

Adam / October 04, 2017

I just returned from the IEEE ASQ Accelerated Stress Test and Reliability Conference, held this year in Austin, Texas.  It’s always been a great conference. There is such a good comradery and sharing of knowledge when a large group comes together on such a specific topic. I meet a lot of great people from many different industries, all with great experience to share.   We shared as much over dinner as we did in presentations, just with more colorful language. I presented a paper on considerations when designing an accelerated stress test (ALT) as well as common pitfalls I have…

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Confidence and “Confidence”

Confidence and “Confidence”

Adam / September 27, 2017

Confidence is used in reliability to give a probabilistic value to the likelihood that a taken measurement will represent a full population.  It is determined by measuring a sample size and then using a selected statistical distribution table to translate to a likelihood. Emotional confidence is how one feels about making a decision based on known information at a specific point in time.   Similar but different. But it is important to connect them.  This is why.

Unless we are running the production equivalent product in the actual user, or perfectly simulated environment we are including assumptions.  This means that any…

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Is It Faster to Demonstrate Component Reliability at the System Level?

Is It Faster to Demonstrate Component Reliability at the System Level?

Adam / September 05, 2017

Here is a common situation that is considered when reliability testing is being planned. Let’s use letters to designate depth in a product component structure. The top level product is level “A” and a component in top sub assembly is “B”. A sub assembly, of a sub assembly, of a sub assembly, is at level “D”.  So is it more efficient to test the component at level “E” or at level “B”?

Question: Is it more efficient to test the component at level “E” or at level “B” to demonstrate it’s individual goal?

An allocation model is used to derive goals…

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Mission profile

Mission profile

Adam / August 15, 2017

Mission profiles are fundamental to any reliability prediction being valid.  Without clearly defined environmental and use profiles there will be a long chain of inaccuracy that accumulates into significant errors within a product. 

This is what occurs at the following stages, or tools, if the mission profile or environment profile changes after its completion.

  • DFMEA: Failure modes may be excluded.  Critical failure modes may be ranked low for occurrence and not be addressed
  • DOE:  Stresses may not be included in the matrix.  Resulting singular and interaction failure modes will not be discovered in advance.
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