Overview

The Basics of Fretting

Fretting is a type of surface wear resulting from micro welding that occurs under very small amplitude between two contacting surfaces. This wear mechanism is commonly observed in mechanical systems with components that are subjected to vibrations or repeated loading, such as the mating surfaces of bolted and press-fit joints.

Fretting can be defined as a loss of material that occurs between tight-fitting or mating surfaces that are subject to vibrational movements (such as riveted, other fastened joints and electrical connections). Material loss is from a combination of abrasive and oxidative wear. The oscillatory movement of the two surfaces creates the formation of oxide films that are then abraded away by oxidized wear debris. The affected surfaces sometimes look as if they were deformed mechanically, so this wear is sometimes called false brinelling. It is also referred to as fretting corrosion, friction oxidation, chafing fatigue, and wear oxidation.

Combating fretting wear often requires a thorough understanding of the system design, application, and function. Some variables may include:

Material Properties: The ductility, hardness, and fatigue resistance of the materials involved play a significant role in determining their susceptibility to fretting. Materials with low hardness or poor fatigue resistance tend to be more prone to this wear mechanism.
Surface Roughness: The roughness of the contacting surfaces can affect the real area of contact, the interaction between asperities, and the stress distribution, influencing the extent of fretting wear.
Contact Pressure and Oscillation Amplitude: Insufficient contact pressures in mechanically fastened joints and small excessive vibration can lead to increased fretting at the contacting surfaces.
Lubrication and Environment: The presence of lubricants can reduce fretting by minimizing direct contact between the surfaces and by providing a protective film. The environment, including humidity, temperature, and the presence of contaminants, can also impact the wear process.

To minimize the occurrence and severity of fretting in mechanical systems, various strategies should be employed, including:

Design for Vibration Reduction: Optimize the design of components and assemblies to reduce vibrations, minimize relative motion, and evenly distribute contact pressure, thereby mitigating fretting. Increase the interference in press fit assemblies or increase the clamp load of bolted joints to prevent relative motion from occurring.
Surface Finishing: Improve the surface finish of components through processes such as nitriding or shot peening. Nitriding heat treatments produce a white layer that can minimize fretting potential. Shot peening can add some surface texture to smooth components as well as impact beneficial residual compressive stresses, reducing the risk of subsequent fatigue failures.
Monitoring: Regularly inspect mechanical systems to identify and address signs of early wear to prevent premature failures. Use non-metallic pads or shims between components to reduce direct impact between the two metal surfaces.
Functional Coatings: Use metallic coatings with high wear resistance, such as chrome, to reduce the risk of fretting.

Armoloy's Solution to Fretting Wear

Armoloy offers multiple metal surface treatments with varying levels of protection from the common causes of fretting wear. Offering both broad-spectrum and industry-specific applications, our protective metallic coatings add significant value through increased performance and decreased revenue losses from unplanned maintenance and downtime.

Our protective coatings ensure a thin, precise coat that won’t impact production, but will improve surface hardness and prevent environmental defects. Beyond increasing wear life, Armoloy tailors our metallic coatings based on the specific requirements of your application and industry.

Fretting wear poses a significant challenge in diverse mechanical systems, demanding a thorough understanding and strategic implementation of countermeasures. Gaining insights into its description, key variables, and mitigation steps will help address the challenges posed by fretting wear more effectively. By employing tailored strategies, engineers can minimize the adverse impact of fretting wear, leading not only to reduced maintenance costs but also to enhanced system efficiency and prolonged component life. Ultimately, the comprehensive understanding and management of fretting wear contributes to the development of more robust, reliable, and durable mechanical systems across various applications and industries.

Beyond the Lab: Metal Failures in Narrative Form

Other Metal Failure Modes

Other common metal failures include:

Fretting wear can also result from, or be a precursor to, other potential metal failures

Eliminate fretting wear from your operations. Meet our group of curious, innovative engineers and learn how we can help improve your industry with science-based solutions.

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Fretting Wear