Using Failure Rate Functions to Drive Early Design Decisions

We have good requirements for the reliability of our design. We also have a preliminary design with ideas of how we're going to manufacture it. Is our design idea good enough? Are there things we should do to improve its performance and reliability?

For a physical product, there are three general stages in its life cycle. In many cases the failure rates of physical products can be represented by a reliability bathtub curve. This curve is really a plot of a hazard rate function, also known as a failure rate function. We talk about data collection in the early design phase, what types of failures are typical for each phase, and design decisions we may make to improve our reliability, based on the failure rate function we plot for our system.

Reliability Bathtub Curve
Bathtub_curve.jpg: Wyattsderivative work: McSush, Public domain, via Wikimedia Commons

Reliability Engineers can help with the early phases of a design in many ways. One of those ways is by analyzing the hazard rate, or failure rate, of our design choices. We can start to estimate the reliability of our system early in the design process. This gives us a sense of our design. Is it going to meet the reliability requirements we have? If it doesn't look good, the failure rate model could indicate ways that we can improve reliability including production, design, and maintenance options.

Visit my other podcast blog about HALT (highly accelerated life testing): HALT! Watch out for that weakest link. – Quality During Design


Ebeling, Charles E. An Introduction to Reliability and Maintainability Engineering. Waveland Press, Inc, 2005, pp. 149-151.

Benbow, Donald W. and Hugh W. Broome. The Certified Reliability Engineering Handbook, 2nd ed. ASQ Quality Press, 2013, pp. 26-29.

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