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Fatigue Failure Analysis Case Studies


Expert Witness: Materials Engineering Solutions, LLC
Fatigue fracture can occur in many components such as fasteners and tubular pole structures. In this paper, fatigue failure mechanisms have been described and the application of the principles for failure analysis for each case will be presented. Cyclic loading at stresses above the fatigue limit of the material can initiate cracks at the surface or at internal defects.

Introduction

Metal characteristics can be changed due to the application of cyclic stress or strain and it can lead to the formation of cracks and eventual failure. The term fatigue has become a widely acceptable word in engineering material science for describing a particular mode of failure. Fatigue crack phenomena in metals are initiated by nucleation in at the nano and micro-scales, leading to macroscopic crack growth and propagation, and ultimately to complete failure of a component or structure.

Significant damage and the failure of machinery, welded structures, moving vehicles, and various mechanical systems can occur under fluctuating loads, and it requires a better understanding of the mechanisms of fatigue damage formation for planning strategies in engineering design, materials selection, and manufacturing processes to improve performance,
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extend fatigue life, and enhance safety of products.

The combination of elevated temperatures or corrosive environments with variable loads intensifies fatigue damage. More complex fatigue damage formation has been observed in situations of mechanical contact between component surfaces in conjunction with repeated loads in rotating sliding systems. Selection of an appropriate mitigation process requires understanding the fatigue damage mechanisms in materials and the fundamentals of engineering mechanics.

Evaluation of Fatigue Fracture

The early stages of failure analysis include the collection of background information and the selection of appropriate samples for laboratory testing. Additional steps should include site inspection, a timeline history of the failure, material specifications, review of maintenance and repair records, number of past failures for the same component and any material substitutions made.

A visual examination of the failed part or structure, as well as non-destructive testing of the component, with extensive photographic documentation should be performed first. The failed parts selected for laboratory testing and analysis should be
carefully stored or protected during transport to prevent any damage to the fracture surfaces from humidity, dust, and dirt.



AUTHOR: Mehrooz Zamanzadeh, Edward Larkin and Reza Mirshams

Copyright Materials Engineering Solutions, LLC

Disclaimer: While every effort has been made to ensure the accuracy of this publication, it is not intended to provide legal advice as individual situations will differ and should be discussed with an expert and/or lawyer.For specific technical or legal advice on the information provided and related topics, please contact the author.

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