6061 T6 fatigue in high stress application?

[GTMule]

I'm working on a project, designing some pieces to a race car. The car is a design with a fully stressed engine, and therefore, the engine mounts essentially hold the car together. My question is, for a part that's taking the vibration of the engine and road, as well as the off and on loading of a race car going around a circut (don't forget, this mount is connecting the two halves of the car) is 6061 T6 a good idea? I'm a little worried that it'l be a bit brittle, and fatigue rather quickly. Any thoughts on this would be much appreciated.

Thanks,
Charles Boulware

 

[mloew]

GTMule,

Some questions for you to consider: What are the loads, stresses, etc. in this component? What is the geometry? How will you be analyzing the component?

Aluminum components can be used quite successfully in fatigue prone applications, but you need to know the answers to the above questions, as a start. Best regards,

Matthew Ian Loew

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora

 

[GregLocock]

Effectively your engine becomes a chassis component. People do build chassis spaceframes out of 6061 T6. Therefore you are in with half a chance. As Matthew says, designing aluminium parts for fatigue is much more complex than steel parts, as there is no endurance limit.

Fatigue modelling is also a black art - it has to be a time history simulation, not spectral, unless the inputs are dominated by one frequency.

Luckily in this case you can get close - the primary stresses will be due to the suspension inputs, probably at around 5 Hz. Decide how much track time you will want for a life, look at s/n curves for 6061T6, estimate your stresses, et voila, a predicted life. The bad news is that you could easily be out by a factor of 10.

Cheers

Greg Locock