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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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Reliability Engineering is More Than Tools

Reliability Engineering is More Than Tools

Reliability engineering is a blend of disciplines from material science to asset management. We use problem-solving, design, maintenance, and statistical tools on a regular basis, yet that is not the only thing we do.

Having met a few engineers that define their role as a reliability engineer as conducting HALT or FMEA only, strikes me as to what most believe we do, or should do, as a reliability engineer. It is true that someone may specialize by choice or chance on one tool, yet even then is that all they do?

I don’t think so.

[Read more…]

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OC Curve with Binomial Method

OC Curve with Binomial Method

The operating characteristic curve is useful to understand the capability of a lot sampling plan. It depicts a graphical relationship between the unknown lot’s defect rate and the probability of the specific sampling plan to accept the lot. Ideally, we want a sampling plan the correctly accepts good lots and rejects bad lots. [Read more…]

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Sources of Variation

Sources of Variation

We have statistics to describe the variation that occurs in our world. Statistics is the language of variation.

If each of your produced products were identical in every way to all products produced, with no variability, we wouldn’t be concerned with the effect of variation on the performance and reliability of our designs.

Yet, variation does happen and we have a range of tools to identify and minimize the naturally occurring variation. [Read more…]

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Fault Tree Analysis 8 Step Process

Fault Tree Analysis 8 Step Process

Fault Tree Analysis (FTA) provides a means to logically and graphically display the paths to failure for a system or component. One way to manage a complex system is to start with a  reliability block diagram (RBD). Then create a fault tree for each block in the RBD.

Whether a single block or a top level fault for a system the basic process to create a fault tree follows a basic pattern. [Read more…]

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Benefits of Fault Tree Analysis

Benefits of Fault Tree Analysis

Is a logical, graphical diagram that organizes the possible element failures and combination of failures that lead to the top level fault being studied.

The converse, the success tree analysis, starts with the successful operation of a system, for example, and examines in a logical, graphical manner all the elements and combinations that have to work successfully.

With every product, there are numerous ways it can fail. Some more likely and possible than others. The FTA permits a team to think through and organize the sequences or patterns of faults that have to occur to cause a specific top level fault. The top level fault may be a specific type of failure, say the car will not start. Or it may be focused on a serious safety related failure, such as the starter motor overheats starting a fire. [Read more…]

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How to Break into Reliability Engineering

How to Break into Reliability Engineering

I’ve recently received a couple of notes from individuals looking at starting a career in reliability engineering. One is a student looking at a career path, another a working engineer with an interesting in reliability.

Both asked how to land a position given no reliability engineering experience.

Hum, I don’t know anyone that had reliability engineering experience before they got started working in reliability engineering. Not counting taking apart the family toaster and trying to repair it before Mom got home as a kid.

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When to Make a Reliability Prediction

When to Make a Reliability Prediction

The easy answer is very often. Each time you want to know how long a product will operate. The accompanying question on how well the estimate will match actual performance makes the real answer more difficult.

We regularly and intuitively do reliability predictions all the time. When starting a car at the beginning of a trip, we estimate the ability of the vehicle to complete the journey. When we purchase a phone, we expect it to operate for at least two years (your expectations may differ).

During the design process, we may have formal or informal useful life expectations. It is not knowing if our decisions related to the design will fulfill the lifetime expectations that leads to the desire to know how well the resulting system will operate. We also may need to estimate warranty or maintenance costs, thus knowing what is likely to fail becomes important.

In general, knowing how long something will operate without failure provides the feedback we need to create a viable system that meets our business and customer reliability expectations.

In short, we do reliability predictions regularly to gauge is we are making good decisions. [Read more…]

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When to Do FMEA

When to Do FMEA

Failure modes and effect analysis is a tool to identify potential failures and prioritize based on severity, occurrence, and detection. I like to describe FMEA as an organized brainstorm. You probably have some experience with FMEA.

In some industries, there is a high expectation or mandate to do an FMEA study. In some industries FMEA maybe just another tool to consider using during various stages of the product or asset lifecycle.

In my opinion, FMEA should be a part of your project plan when it is likely to add value.

Value in the sense that the organization will receive an adequate benefit based on the investment to conduct the FMEA study. [Read more…]

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Optimizing Maintenance

Optimizing Maintenance

One of the considerations when planning maintenance is the timing of the replacement of parts of the system. In some cases it makes sense to wait for the item to fail, sometimes, it makes sense to place it on an interval or set an amount of operating time, and yet in others, we can measure indicators that a replacement is necessary.

In order to make these decisions, we need data.

According to O’Connor and Kleyner (Practical Reliability Engineering, 5th Ed.), we need specific information for each part. The following list outlines the recommended information. [Read more…]

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When to Conduct HALT

When to Conduct HALT

HALT (highly accelerated life testing) is a method to reveal product weaknesses. Design prototypes experience the step-stress application of relevant stresses until failures appear.

The intent is to find design or process related weaknesses early in the design process thus providing time to economically address the issue. Using a build-test-fix approach does improve a product’s robustness and reliability.

Being a useful tool, should you conduct HALT on every project? It seems that revealing weaknesses is certainly useful. [Read more…]

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Expectation and Moment Generating Functions

Expectation and Moment Generating Functions

In statistics and reliability, we use distributions to describe time to failure patterns. The four functions commonly used in reliability engineering include

  • The probability density function
  • The cumulative distribution function
  • The reliability function
  • The hazard function

We often use terms like, mean, variance, skewness, and kurtosis to describe distributions (along with shape, scale, and location). The mean is defined as the use of a moment generating function. First though let’s first back up to the concept of center of gravity (cog) from mechanics. [Read more…]