Thesis on Fretting Wear

[gearcutter]

Here's a link to a thesis from 2006 on the fretting phenomenon in aerospace applications.
The work concentrates on spline type applications using materials which have been case hardened using a nitriding process.
An excellent source of information for spline design, lubrication, material and heat treatment processes.

'Fretting Wear Studies of Aeroengine Materials' by Hian Ping Soh -

http://etheses.nottingham.ac.uk/3177/1/435992.pdf

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[tbuelna]

gearcutter-

I could not access the document from the link you provided, but I would be very interested in taking a look at it.

The topic of fretting wear in case hardened splines used for aircraft power transmission applications is of particular interest to me, since my work involves designing these types of high-performance spline joints. However, based on my own personal experience, the most important considerations when designing a reliable high-performance spline joint are proper lube oil flows, and applying the correct amount of tooth flank geometry modifications for things like lead correction and crowning.

There are trade-offs with regards to nitrided or carburized case hardened splines. Splined shafts that use nitriding will have less heat treat distortion, and should require less stock removal during finish grind operations. But the nitrided case thickness is also much thinner. Carburized splines will have a much thicker case, but they will also experience more distortion during heat treat, and will require more stock removal during finish grind operations.

 

[gearcutter]

tbuelna -

From within Firefox; I have just checked the document's direct link by clicking on it directly from my OP and the document started downloading just fine.
For some reason, however, copy and pasting the link into a browser causes a server error.

Here's a link to a page showing the document's abstract along with an option to download the thesis. I've checked that it works in IE, Chrome and Firefox -

http://etheses.nottingham.ac.uk/3177/

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[tbuelna]

gearcutter-

Thanks for the reply. I was able to download the paper. However, at 231 pages it will likely take some time to read through!

As a gearhead, you've got to love a guy that chooses spline fretting as the topic of his PhD thesis.

 

[Exacture]

Hello all,

The reason these people get involved in this matter is down to the geographic location of Rolls-Royce Aero engines in Derby, UK, relative to Nottingham University. You will see C. McFarlane referenced as well as A. Olver. Colin McFarlane is ex-Rolls Royce and Andy Olver had a close relationship with what is now AgustaWestland Helicopters. Indeed, I saw Colin in AgustaWestland this week. It is a small world. Splines are a critical feature in the fundamental design of aerospace assemblies as you know. Get the pcd wrong and you are either carrying an overweight assembly or have a complete liability on your hands.

I am as impressed as tbuelna and gearcutter with the dedication and application to the parameters of spline durability but it is still Dudley and Buckingham who held the key to effective design. It is the length of engagement for any particular angle of misalignment vs the pitch diameter. Plot the PV function for L, D and theta (misalignment). There is an optimal point. Control the clearances and fits (and hence the angle of misalignment) and then you can optimise for the lowest weight aero solution. The treatment and material choice is secondary without regard to the fundamental controls. You cannot make a silk purse from a sow's ear...

Best regards to all

 

[tbuelna]

Exacture,

I have done some design of rotorcraft transmission splined input shafts that mated to Rolls-Royce turboshaft engines. The engine OEMs (like R-R) provide very detailed requirements for the input shaft splines. The input shaft must usually be able to accommodate some misalignment between the engine and gearbox, due to dynamic loads and/or thermal expansion. The input shaft typically has a crowned external spline at each end with a major diameter fit.

These hardened splines are typically designed for a simple contact stress limit of around 15ksi or less, just as Dudley suggested many years ago. It is accepted that these splines will always experience some contact fretting wear. So the most important part of the spline design is ensuring the spline has a continuous flow of oil through it to flush out the debris generated from the contact fretting.