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Fatigue and Reliability Analysis with Time-Varying Stress Using the Cumulative Damage Model

Fatigue is defined as weakness in metal or other materials caused by repeated variations of mechanical stress. Fatigue cracks are caused by cycling loading. Hence, if the loading does not change (stress stays constant), then there is no fatigue problem. On the other hand, varying stresses may lead to fatigue failure even though the magnitude of the stress is not high. In metallurgic terms, the microscopic damage caused by fatigue cyclic means there is no recovery from the fatigue failure mode.


Fatigue is a statistical problem, not a deterministic one, which means that we will not be able to calculate exactly how many cycles it takes for a product to fail. But we can estimate the reliability of that particular product at a given number of cycles via life-stress relationship models used in accelerated life testing (ALT) analysis. In this article, we will talk about two methods for analyzing fatigue failure data collected under time-varying stress, and then analyze an example data set in an ALTA folio to show how we can quickly analyze fatigue data.


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ARDC Call for Papers

Take center stage and present at the Applied Reliability and Durability Conference. By presenting, you could gain insight on solutions for your organization and further your own professional development, plus you will receive complimentary registration. Presentation topics should be based on practical reliability, durability, maintainability and quality engineering practices derived from real-life experience. For more information visit


ARDC North America will take place June 26-28, 2018 in Portland, Oregon. If you wish to share the experiences that have helped shape your reliability and durability career by presenting at this event, please submit your proposal by December 15, 2017. Complete details, including the required proposal form, are available at


The ARDC Europe proposal deadline is October 27, 2017. Complete details, including the required proposal form, are available at


Seminars Offered in Washington, D.C.

You are invited to attend a two-day seminar, "Analysis Tools and Solutions for Reliability Engineers" and "The Role of Vibration in Fatigue" taking place on November 14-15 in Washington, D.C. The reliability session will showcase basic concepts and theories with hands-on examples in software applications, as well as tips and tricks on how to get the most out of ReliaSoft tools. The fatigue session is focused on practical engineering considerations for designing against vibration and fatigue, how it can help you to avoid unnecessary over-design and prevent operational failures. To learn more and register, visit:

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