White Rose University Consortium logo
University of Leeds logo University of Sheffield logo York University logo

Frictional Behaviour of Coated Self-locking Aerospace Fasteners

Tronci, Giuseppe (2017) Frictional Behaviour of Coated Self-locking Aerospace Fasteners. PhD thesis, University of Sheffield.

[img] Text
Thesis_Final_Corrected.pdf
Restricted until May 2019.

Request a copy

Abstract

Nuts and bolts used in aero-engines are manufactured from heat-resistant super-alloys. These materials have a high CoF, and frequently seizure occurs. In order to prevent this, a silver coating is applied to the nut threads, providing a low friction boundary at the interface. Additionally, a radial crimp is applied to the nut, in order to provide a self-locking feature preventing vibration self-loosening. In this study, the CoF of the thread contact will be investigated both during initial joint assembly, and after thermal ageing. Additionally, a finite element model will be employed to investigate the contact mechanics as a consequence of the crimp. The low CoF observed during initial assembly was found to be a consequence of shear flow of the silver coating, with an approximate doubling of this value once the coating aged. Areas of silver removal were found to be coincident with areas of high contact pressure in the joint, attributable to the crimp feature. Additionally, new alternatives coating were tested in order to identify a replacement for the electroplated silver. Through a series of analyses, similarly done for the silver coating, from a list of 19 different thin films and paints, the list is reduced to three possible films, Chromium, Titanium and Nickel-Titanium. Finally, through the FEA approach, a new self-locking design was developed, with an axial deformation instead of the radial crimp typically used. Thereafter, few nuts were manufactured, tested and compared to the elliptical, demonstrating it is a promising design with respect to the contact pressure distribution and silver removal.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Mechanical Engineering (Sheffield)
Depositing User: Mr Giuseppe Tronci
Date Deposited: 26 May 2017 14:15
Last Modified: 26 May 2017 14:15
URI: http://etheses.whiterose.ac.uk/id/eprint/17374

Actions (repository staff only: login required)