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CRE Preparation Notes

Prep notes for ASQ Certified Reliability Engineer exam ISSN 2165-8633


The idea of the CRE Preparation Notes series is to provide you short practical tutorials on all the elements that make up the ASQ CRE body of knowledge. The articles provide introductionary material, basics, how-to’s, examples, and practical use guidance for the full range of reliability engineering concepts, terms, tools, and practices.


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You will find the most recent tutorials in reverse chronological order below. Below each article is the section and specific clause of the CRE Body of Knowledge that tutorial addresses. Click on those tags to find other articles on the same topic. To the right on the sidebar, there is a listing of the 7 major categories in the body of knowledge - it's a quick way to find groups of articles on each specific area. You can also use the search function to locate articles, podcasts, or tutorials on specific topics.

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Norris-Landzberg Solder Joint Fatigue

Norris-Landzberg Solder Joint Fatigue

Before Norris-Landzberg’s study there was the work of Coffin and Mason.

Coffin-Manson

One way to approach accelerated life testing is to use a model for the expected dominant failure mechanism. One such model is for solder joint low-cycle fatigue originally published by Coffin (1954) and Manson (1953), independently.

 

Norris-Landzberg

Norris and Landzberg proposed the plastic strain range is proportional to the thermal range of the cyclic loading (ΔT). They also modified the equation to account for effects of thermal cycling frequency (f) and the maximum temperature( T). They and other than empirically fit the parameters for the equation. [Read more…]

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Accelerated Life Testing

Accelerated Life Testing

A form of testing that reduces the time till results are known, ALT provides a means to estimate the failure rate over time of a product without resorting to normal use conditions and the associated duration.

For example, solar photovoltaic cells should operate for 25 years without failure. The product development time is less than a year for a new panel and the team wants to estimate the reliability of the cells over the 25-year duration. [Read more…]

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Reliability Modeling Options

Reliability Modeling Options

When this posts I should be just getting home from Nepal (jet lag is no place to write posts). So, this post and the next couple are homework for you. Take a look, work the problem, solve it, then show your work. Comment with why you chose your response and why you didn’t select one of the others.

From question 19 of ASQ CRE 2009 sample exam. [Read more…]

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Corrective Action Question

Corrective Action Question

When this posts I should be near 17k ft altitude without electricity or internet – hoping for the best. So, this post and the next couple are homework for you. Take a look, work the problem, solve it, then show your work. Comment with why you choose your response and why you didn’t select one of the others.

Here is question 18 from the ASQ CRE 2009 sample exam. [Read more…]

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Fault Isolation

Fault Isolation

I’m about to leave for Nepal for a month and much of it without internet. So, this post and the next couple are homework for you. Take a look, work the problem, solve it, then show your work. Comment with why you chose your response and why you didn’t select one of the others.

This is question 17 from the ASQ CRE 2009 sample exam. [Read more…]

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Reliability Math

Reliability Math

Recently a question came to me about the difference between hazard rate and failure rate. A lot of literature and reference use these two terms interchangeably. I have long thought there is a difference, and to check my understanding I asked a good friend and reliability engineering consultant Chet Haibel. He provides a slide set (below) that described the various functions we use working reliability statistics and he details out the functions when using the exponential distribution.

Please review the slides and comment or ask questions – both Chet and I will attempt to help clarify any misunderstandings. I do think the slides are excellent and will do a great job providing a review of basic reliability math and the exponential distribution.

Slide set posted with permission of Chet Haibel.

Chet’s slides

 

Related:

Using The Exponential Distribution Reliability Function (article)

Basic Statistics (article)

The Exponential Distribution (article)

 

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First Five Questions

First Five Questions

ASQ has posted sample exams for the past 10 or so years for the certifications. The CRE one is from 2009 and has questions used on previous exams. You can find a copy here or here.

This post has the first 5 questions with the answers explained. This is how I think or work through the problem to select an answer. Please comment if you have a different approach, especially if it would save time. [Read more…]

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The Paired-Comparison Hypotheses Test for Variances

The Paired-Comparison Hypotheses Test for Variances

The F-test provides a means to compare paired data variances. It is a variance hypothesis test.

If we are exploring the precision of one measuring device or another, or we are comparing assembly processes, we often want to know if the variance is different or not.
Working with data from normal distributions from two different processes or devices, we know from statistical theory that the ratio (s1)2 / (s2)2 is described by the F distribution.
There are three hypothesis test possible, basically to test if the population variances are different, or one is less than or greater than the other. The following details the three test’s null and alternative hypotheses. [Read more…]