on Product Reliability

A listing in reverse chronological order of articles by:

Kirk Grey — Accelerated Reliability series

Les Warrington — Achieving the Benefits of Reliability series

Adam Bahret — Apex Ridge series

Michael Pfeifer — Metals Engineering and Product Reliability series

Fred Schenkelberg — Musings on Reliability and Maintenance series

Arthur Hart — Reliability Engineering Insights series

Chris Jackson — Reliability in Emerging Technology series

by Fred Schenkelberg 1 Comment

Product Reliability and Customer Service

After 30 minutes of being on hold, I wasn’t sure what to expect from customer service for a product reliability issue. The scratchy soundtrack didn’t foretell a great experience either.

Once connected to a company representative, we resolved the issue quickly and satisfactorily. Unfortunately, that was a pleasant surprise. All too often, the frequently repeated “Your call is important to us.” (an Amazon affiliate link) just isn’t true, in my experience.

Did you know that customer service can add significant value to an organization, especially when product reliability doesn’t meet customers’ expectations? Besides providing the team with valuable product reliability performance information for past products, the service team can improve customer loyalty.

Failure Mode and Mechanism

In a previous article I discussed the degradation of materials due to exposure to stressors (use conditions) and how to identify stressors. Cracks form and grow in axles and shafts due to cyclic stress, steel screws corrode when exposed to water, some plastics become brittle when exposed to sunlight, and coatings on surfaces can wear away. When too much degradation occurs, components and joints fail, leading to product failure.

Things to consider during design

If you’re someone who likes to design reliable products, you must think about the stressors and their effects. When designing a product, we must identify the following things [Read more…]

by Fred Schenkelberg 2 Comments

Writing and Accendo Reliability

While I’m not much of a New Year’s Resolution guy, I guess I’ve set a resolution. I need to restart writing weekly articles for Accendo Reliability.

The thing is, I struggle to write. Plenty of other interests and tasks keep me away from the keyboard. Yet, as I explained to a few new authors how writing and posting on Accendo Reliability is a good thing, I realized I have been putting off hitting the keyboard again.

Over the past few weeks, I’ve explained to those interested in writing articles about the virtuous circle created by having many authors contribute articles, which increases interest, engagement, and traffic to those articles, which further increases the reach of those articles. Of course, this is just one reason, and there are others, plus plenty of hurdles to overcome.

Fatigue

Fatigue is a common degradation and failure mechanism. It involves localized, permanent damage to metals exposed to cyclic stress. The stress can be uniaxial, bending, or torsional resulting from a variety of sources including an applied force, vibration, acceleration and deceleration, and differences in thermal expansion between mating components exposed to heating and cooling cycles. Localized means the damage is confined to a small portion of a component or joint.

[Read more…]

by John Kreucher Leave a Comment

ALT Design using Damage Bins

The Arrhenius Equation is widely used and accepted by reliability and validation engineers from many industries to develop accelerated life tests (ALT) for thermal aging environments.

The general form of the equation describes the reaction rate of a process as a function of temperature (K), the Boltzmann constant (8.617E-5 eV/K) and two empirical factors. It can be written as:

Why Stainless Steel is Corrosion Resistant

Stainless steel is known for its corrosion resistance in many environments, with different alloys having different levels of corrosion resistance. Also, stainless steels are available with a wide range of strengths. Understanding the reasons for the corrosion resistance is helpful for selecting alloys based on the required strength and environment to which the steel will be exposed.

Thinking small

Fatigue cracks that originate at inclusions. Stainless steel intergranular corrosion due to chromium carbide precipitates. Low steel toughness because martensite not tempered enough. Low aluminum strength because of excessive grain boundary precipitation. Orange peel due to large grains.

These are examples of how problems with a metal’s microstructure lead to reliability and performance problems. Of course, there are thousands of examples of microstructures that lead to good reliability and good performance.

One hurdle to understanding metallurgy is being able to think small – very small. Less than a millimeter. Less than a micron. And sometimes on the scale of atoms.

[Read more…]

by John Kreucher Leave a Comment

Test Reliability Targets and Expected Field Reliability

An example of an automotive validation test reliability target is R97C50. In this case, the objective of the validation effort would be to demonstrate at one life on test, with 50% confidence, that the product has a reliability of 97% or better.

Does this mean that a field failure rate of 3% can be expected?

[Read more…]

by John Kreucher Leave a Comment

Validation Testing – Right Parts on the Right Tests

As you begin design validation (DV) and product validation (PV) testing you are entering the more formal phase of a test program. Usually, you are working to internal and/or customer test specs with timelines that are critical and little margin for error. If you’ve conducted adequate design verification testing and given your parts a chance to fail on test exposures that are similar to those your product will see in the field, you have reason to expect to be successful in validation [see previous article outlining accelerated test methods: Expect to Pass Validation].

Residual Stresses in Metals

When designing components consider fatigue or stress corrosion cracking. It’s important to be cognizant of the residual stresses in the component. Understanding residual pressure and its sources is important when making decisions about a component’s shape, features, alloy, and fabrication process.

Fatigue and stress corrosion cracking require the presence of tensile stresses on a component. When residual presures are tensile they add to the applied tensile pressure, reducing the life of a component. In fact, components sometimes fail due to stress corrosion cracking when residual stress is the only source of tensile stress.

[Read more…]

by John Kreucher Leave a Comment

Expect to Pass Validation using Accelerated Tests

Product Validation Testing is a critical and expensive endeavor. The part build process must align with the latest prototype process (for Design Validation (DV)) or production process (for Product Validation (PV)) and be fully documented for posterity. Depending on the product and application, the validation test plan consists of a battery of tests, some of which are lengthy – often six months or more. Because of this, DV and PV test plans are invariably on the critical path for a customer program. Test failures that require fixing the design and repeating DV or PV jeopardize project timing and company profits. Further, they jeopardize the customer program along with your company’s reputation.

Steel Hydrogen Embrittlement

One failure mechanism that I’m frequently asked about is hydrogen embrittlement of carbon and low-alloy steel. So, in this article I’ll discuss that topic.

Hydrogen embrittlement is the result of the absorption of hydrogen by susceptible metals resulting in the loss of ductility and reduction of load bearing capability. Sustained stress on an embrittled material can result in cracking and fracture at stresses less than the metal’s yield strength.

Product Reliability: Selection and Control

In a recent Accendo podcast, Chris Jackson and Fred Schenkelberg discussed who is responsible for producing a reliable product, which included designers and suppliers. I’m going to weigh in.

The reliability of any product depends on the reliability of the individual components and joints within the product. That is, the ability of the components and joints to withstand exposure to stressors without degrading to the point that they fail, resulting in the product no longer performing as required. Stressors, which include corrosion conditions, fatigue, and wear, were discussed in an earlier article.

Whether individual components and joints have the reliability required boils down to two basic aspects of engineering – selection and control. The appropriate form (i.e. shape, dimensions, features) and materials for components and joints must be selected during product design. Then, systems must be put in place to control fabrication of components and joints, ensuring their form and materials are as specified. This will enable the components and joints to consistently meet performance and reliability requirements.

So, who’s responsible for this selection and control?

Designing Components for Strength and Fatigue

Metal strength and fracture toughness are important mechanical properties for components exposed to fatigue conditions and components with stress concentrations. Optimization of the two properties through alloy selection and component fabrication must be considered when designing components for these situations.

For structural components, strength and fracture toughness are two important mechanical properties. Yield strength is the stress a metal can withstand before deforming. Tensile strength is the maximum stress a metal can support before starting to fracture. Fracture toughness is the energy required to cause a material that contains a crack to fracture.

Example of Using Failure Analysis to Improve Reliability

Here’s an example of how a metallurgical failure analysis led to identification of the root cause of a failure, and to identification of the corrective actions needed to prevent the failures from recurring.

Failure analysis

As I discussed in my previous article, metallurgical failure analysis can be used to improve product reliability. The information from failure analysis of a failed component is used to determine the root cause of the failure. Once the root cause is identified, the failure analysis data and findings is used to help identify the corrective measures required to prevent the failure from recurring.

[Read more…]