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Fred Schenkelberg — Thought Leader

Author of CRE Preparation Notes, Musings", NoMTBF, multiple books & ebooks>, co-host on Speaking of Reliability>/a>, and speaker in the Accendo Reliability Webinar Series.


This author's archive lists contributions of articles and episodes.

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The Sum of Squares Concept

The Sum of Squares Concept

The data analysis course professor tended to focus on the practical application of statistics.

Avoiding statistical theory was fine with me. Learning statistics for me was on how to solve problems, optimize designs, and understanding data.

Then one lecture started with the question, “Why do we sum squares regression analysis, ANOVA calculations, and with other statistical methods?” He paused waiting for one us to answer.

We didn’t. I feared the upcoming lecture would include arcane derivations and burdensome theoretical annotations. It didn’t. [Read more…]

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The Fundamental Set of Reliability Engineering Tools

The Fundamental Set of Reliability Engineering Tools

In a single meeting, you may need to structure a reliability model, create estimates, outline test plans, and discuss a field failure. The breadth of tools and knowledge to be effective is staggering.

No two problems, questions, situations, or industries are the same. Thus, the solutions you provide must differ as well. If you enjoy a complete set of reliability engineering tools at your disposal, you are well situated to address any question.

[Read more…]

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Bartlett’s Test for Homogeneity of Variances

Bartlett’s Test for Homogeneity of Variances

A common assumption when comparing three or more normal population means is they have similar (the same) population variances.

ANOVA and some DOE analysis results rely on the underlying data having similar variances. If this assumption is not true, the conclusions suggested by the ANOVA or DOE may be misleading.

It doesn’t take long to check. [Read more…]

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Plot Your Derating Guidelines

Plot Your Derating Guidelines

The concept of derating is similar to the mechanical engineering concept of a stress–strength analysis.

The intent is to ensure that the selected component or the mechanical design has sufficient strength to withstand the expected applied stresses.

Components operating at or near their rated values have short lives. Consequently, the general practice is to use components for materials well below their rated values to extend the operating life of the items.

This is where derating comes into play. [Read more…]

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Confidence Interval Interpretations and Misunderstandings

Confidence Interval Interpretations and Misunderstandings

Confidence intervals (CIs)provide a means to judge point estimates based on a sample from the population.

If that statement excites you, you may well have the makings of a fine statistician.

CIs are a form of internal estimate and specify a range within which a parameter may reside. CIs helps us evaluate the trustworthiness of point estimates. [Read more…]

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Tolerance Specifications Impact on Reliability

Tolerance Specifications Impact on Reliability

Mechanical drawings and electrical schematics communicate the design.

They provide information sufficient to create a product or build a system.

They provide the necessary details that allow others to construct something that originally was only imaged.

We no longer rely on a single craftsman to build a chest of drawers from concept to delivery.

Instead, they may be a team scattered across many organizations relying on the drawings.

Included on the drawings and schematics are dimensions along with tolerances. A keypad will be a specific width, plus/minus some amount. A resistor is nominally 100 ohms, yet anything between 90 and 110 ohms is fine.

Tolerances acknowledge the variability between individual components or caused during the construction process.

Tolerances also impact the reliability performance of your products.  [Read more…]

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Introduction to Derating

Introduction to Derating

Derating is the selection of components and materials according to a set of standardized safety-margin definitions.

It is used by design engineers to ensure the selected elements of the design do not experience performance problems due to overstress conditions.

Derating, like stress-strength analysis, assists the designer when selecting elements for the product or system.

The outcome is a robust design able to withstand the expected, and some of the unexpected, stress applied. [Read more…]

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Inputs to Consider When Setting Tolerances

Inputs to Consider When Setting Tolerances

Technical drawings and electrical specifications often include tolerances.

The range of values allowed for a particular aspect of the part.

Reliability engineers do not set the tolerances, yet we should both understand and influence them.

A critical element of design for reliability is the creation of a robust product.

It is not just robust in the end use, your product should also be robust to the variability that will occur during manufacturing and transportation. [Read more…]

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The Basics of Vibration and Shock

The Basics of Vibration and Shock

Did you shake a wrapped gift as a child?

Sometimes the rattling sound may indicate the hidden contents. A sweater from Grandma would make a muffled sound, while a new Lego set would rustle the many parts.

Your customers may not shake the package to guess its contents, yet your product will experience vibration and shock.

The environments of assembly, transpiration, use, maintenance, etc all include shock and vibration inputs to your product. The operation of your product may include producing vibration and shock loading across the product.

Understanding the basics of vibration and shock will assist you to design your product to operate as expected in the noisy, shaky world.

The rattling about your product experiences is just one of the many environmental and use factors. [Read more…]

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Starting a Career in Reliability Engineering

Starting a Career in Reliability Engineering

Reliability engineers all have a start.

A point zero.

The transition point from pursuing something else, or nothing at all, then we begin our journey as a reliability engineering professional.

Getting started can be difficult and at times overwhelming.

Then you find Accendo Reliability and there is a lot of great content, maybe too much. So, this short article has the intent to create a starting point for you.

Plus, for those well along in their career, a request.

What is your advice to those just starting their career? My plan is to gather the advice from this community and assembly a start here guide just for those just starting their career.

Leave a comment below with your words of wisdom.  [Read more…]

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Introduction to Thermal Cycling Life Testing

Introduction to Thermal Cycling Life Testing

Materials expand or contract with temperature change. Water expands as it freezes, whereas steel contracts as it cools.

This motion can limit the life of your system.

Materials and mechanical engineers include the expected motion into their designs, well the better engineers do.

Even centuries ago, craftsmen used expansion slots or features when attaching wooden table tops to their frames.

The motion due to temperature change will occur and has the potential to create immense strain within your product. [Read more…]

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5 Ways You Know a Reliability Program is Working

5 Ways You Know a Reliability Program is Working

When your reliability program is working well, it may be difficult to recognize the benefits incurred.

Likewise, when the program is not working, it is obvious.

As you work to improve your program, keep in mind you may need to include elements to ensure your efforts remain visible.

I don’t mean staging field issues that you can solve quickly, rather that you are able to show the impact you and your program make to the organization. [Read more…]