Title:

Reducing the Variability and Cost of Determining the Coefficient of Friction of Various Lubricants

The Navy requires accurate fastener preloading for many of its fastened applications to protect the safety of the vessel and its personnel, and to ensure proper operation of various components. The preload is based on many properties including fastener materials, fastener geometries, and the coefficient of friction (COF) between mating surfaces. The COF is a critical value in determining the torque-load relationship of a fastener and is dependent on the contact surface area and the materials in contact, the condition and finish of the contact surfaces, and any lubricant applied in these contact areas. Due to the large amount of variables in a joint, the COF of any particular lubricant must be determined empirically via a time and resource intensive testing regime that tests over 250 individual fastener assemblies. For the Navy, the lubricants that currently have known COF values are expensive, difficult to procure, or lack other favorable properties such as washout resistance or the ability to be used in a diver-safe environment. Portsmouth Naval Shipyard (PNS) has tasked me with optimizing their existing procedure to require less time and resources, and to improve the process to make it safer and more efficient.

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