Fretting Corrosion and Its Impact on Connector Performance

Fretting corrosion is one of the leading causes of connector failure and yet many still remain unaware of what it is or how it can be prevented. Fretting corrosion is the result of micromotion caused by vibration and/or thermal expansion due to heating or cooling cycles. These micromovements wear down through the metal coatings into the base material that then becomes oxidized. As this oxide layer builds up and increases, the oxide film acts as an insulator between the contacts which creates an open circuit resulting in voltage drop across the terminal and ultimately, power failure or signal loss.  

Fretting wear is one of the major forms of deterioration and electrical failure in a variety of industries, including Automotive, Aerospace, Appliance, and Consumer Electronics.  There are many well-known applications that experience fretting, including engine bearings on a diesel engine that is left idling, slot mounted server boards that are not isolated from vibration, and electrical connector harnesses in a taillight. When electrical failures occur, it can cause problems ranging from nuisance to increased warranty costs to critical safety problems.

How Does Connector Grease Prevent Fretting Corrosion?

To minimize fretting wear and keep oxidation at bay, the implementation of a connector grease is key. Connector grease has two primary benefits:  

• The grease reduces physical wear between the connecting surfaces as they undergo micromotions and fretting wear. This helps to preserve the layered coatings on the connectors, designed to prevent oxidation and minimize resistance.
• They insulate the system from the surrounding environment, preventing the build-up of insulative oxide layers which are ultimately responsible for resistance increase and signal loss.  

Optimizing Reliability with In-House Fretting Testing  

FUCHS performs a variety of tests in-house on our lubricants. A full complement of laboratory equipment enables us to complete qualification testing to ensure the design and performance requirements of your application are met. The fretting wear test apparatus designed by FUCHS monitors the fretting cycles (micromotion) of terminals until resistance increases 100 milliohms over the static baseline.  

How does it work? This custom test is based upon a magnetic linear actuator which operates using the Lorentz Force Law. This actuator produces oscillations in a frequency range of 1Hz to 1,000Hz, amplitudes of 1-200μm, and with a continuous load of 50lbs and 150lbs of peak force. To ensure accurate position control, an absolute encoder is utilized for closed loop motion control to keep the amplitude resolution within 1 μm.

With this new fretting test methodology and apparatus, we can determine the durability and reliability of our lubricants. Through the testing of lubricants to their ultimate fretting failure point, we can look forward to helping our customers design systems that are optimized with a lubricant to reduce or eliminate fretting failures. This can lead to a reduction in the warrantee and safety issues seen in many industries.