Archive

Archive Of The Category "Reliability Analysis"
Designing Accelerated Life Tests

Designing Accelerated Life Tests

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 as well as common pitfalls I have witnessed. …

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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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It’s Not Really That Clean Cut

It’s Not Really That Clean Cut

Adam / July 27, 2017

This is the bathtub curve we are often shown.

This is what a real bathtub curve looks like.

A real bathtub curve would capture all the different types of failure modes, represented by each of these lines.  We typically talk about a failure mode being placed in one of the three categories, Quality (infant Mortality), Use stress, or Wear-out.  But in fact any specific type of failure mode may have driving factors in multiple categories.  The same failure mode may have a sensitivity…

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Software Design For Reliability

Software Design For Reliability

Adam / July 19, 2017

With all the complaints you hear about products rebooting and software crashing, do companies really practice Software Reliability? In fact, there are some companies that do, but they are mostly in the industries that require products to have high availability, such as telecom, defense, and space, or safety-averse industries, such as medical and industrial plant operation. Most other industries don’t pay as much attention to it. The best method to increase Software Reliability without significant increases to schedules or budgets is to use a Software Design for Reliability (SDFR) approach.  These are the key steps. Read More

Selecting the wrong ALT model

Selecting the wrong ALT model

Adam / June 27, 2017

Many product programs ( actually all) are on a tight schedule.  When Accelerated Life Testing (ALT) get’s it’s place in the process it is another mouth to feed.  ALT is not a short process.  Each round of testing typically takes weeks, and the results may drive design changes that prescribe additional testing.  It is common to want to get the ALT process going as quickly as possible.  In this haste the primary wear-out failure modes and it’s driving stresses are confidently stated, a model is created, and the test is started.

This seems insane to me. The resource and schedule hit…

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