Thread: axle design guidelines

Originally Posted by 5teve

Hi Guys

does anyone know if there are any guidelines / regulations involving safety factors or Proof loads that axles / housings are required to perform to?

i know there are some brains on here so thought i would ask!

thanks

Steve

If you look at the dana axles website, they list torque ratings for their axles, both continuous and peak. I think they also list maximum axle loads.

If you were designing a vehicle, you would either consult a table like that to work out which axle you needed, or give the specs of your vehicle to your axle supplier (e.g. Dana) and get them to work out what the best option would be.

Is that what you were looking for?

If you had the specs from the axle manufacturer (including materials data such as UTS = ultimate tensile strength) you could calculate it yourself, however I doubt this is commonly done.

EDIT - if you were the person actually designing the axles, there are a several applicable SAE publications, e.g.
http://www.sae.org/technical/papers/640251

John (Bush65) is the expert in mech. eng. design on here (also Dougal) - so they can probably give more/better info.

Thanks for that

im actually looking at redesigning a section of axle, my previous experience has been within the rail industry where they specify the proof loads of equipment in the form of G. so axle mounted equipment has to be rated to twenty g according to QR. so i was looking for something similar.

i know the current axle load capacity, but this doesnt have the safety factor or proof loads included. i need to feed a figure into the FEA package to get some meaningful results but without any idea of what is expected im a bit at a loss.

Things that need to be considered are, shock loads from bumps in the road (effect on unsprung mass and on sprung mass) braking loads etc. thats why im looking for a figure!

Thanks again

Steve

I don't know what the ADR's require - probably sound engineering by the manufacturer.

Very difficult to produce a good balanced design of a complex fabrication like an axle housing by stipulating a factor of safety or proof load. For example, what failure criteria is the safety factor applied to? And as far as proof load, that is a static case.

IMHO, a rigorous fatigue analysis is required, in conjunction with the British Standard for fatigue design of welded structures (sorry can't remember the BS number and would have to look up the standard at work).

For the axle shaft, the Australian Standard for Design of Rotating Shafts is good, but a little conservative and lacks some stress raising factors for methods that can be used to reduce the stress raiser. But more important IMHO is to design the axle with attention to details that maximise the strain energy that the axle can absorb - none of which would be considered if simply designing for static torque, or stress raising factors.

Hi Steve
As its a commercial project Dana or Hardey Spicer etc sureley could offer help as they may get their gear involved.No point re-inventing the wheel if they have done the sums.Phill633 may be able to give you tech contacts as he specializes in truck parts.

Andrew

Originally Posted by Bush65

I don't know what the ADR's require - probably sound engineering by the manufacturer.

Very difficult to produce a good balanced design of a complex fabrication like an axle housing by stipulating a factor of safety or proof load. For example, what failure criteria is the safety factor applied to? And as far as proof load, that is a static case.

IMHO, a rigorous fatigue analysis is required, in conjunction with the British Standard for fatigue design of welded structures (sorry can't remember the BS number and would have to look up the standard at work).

For the axle shaft, the Australian Standard for Design of Rotating Shafts is good, but a little conservative and lacks some stress raising factors for methods that can be used to reduce the stress raiser. But more important IMHO is to design the axle with attention to details that maximise the strain energy that the axle can absorb - none of which would be considered if simply designing for static torque, or stress raising factors.

Thanks John, much appreciated. Fatigue i can deal with as there is an australian standard i think its as4100 which is what we used for the rail stuff. however this is not welded, its machined, and it also isnt a full axle housing its a modification to (cant say too much). I'm just surprised that there isn't a proof load such as the train standard which along with fatigue also states that any equipment ect must have a proof load case of XXg, which would give me something to start with. pretty much like a standard that says for vehicle type x the maximum shock loading expected to be seen for unsprung mass is XXg etc etc.

its a bit of a strange one as the axle housing isnt totally unsprung, due to the tyres acting as a spring, and the mass of the vehicle is sprung, limiting the shock loading that the axle will take from the body. oh well i could only hope for some guidelines.. i'll have to make my own load case up!

Originally Posted by LandyAndy

Hi Steve
As its a commercial project Dana or Hardey Spicer etc sureley could offer help as they may get their gear involved.No point re-inventing the wheel if they have done the sums.Phill633 may be able to give you tech contacts as he specializes in truck parts.

Andrew

Andy Thanks for the thought, but most companies are pretty hostile towards us.. dont quite know why yet! Dana have actually been helpful but thats for other stuff, as far as i know only one off shops have attempted what im trying to do in the way that im doing it, mainly as its not a very commercial thing to do, but helps us with another problem.. again i am being cryptic so sorry for that!

i may give phil a shout on some other info we are trying to get tho!

Thanks guys

Steve

Originally Posted by 5teve

Thanks John, much appreciated. Fatigue i can deal with as there is an australian standard i think its as4100 which is what we used for the rail stuff. however this is not welded, its machined, and it also isnt a full axle housing its a modification to (cant say too much). I'm just surprised that there isn't a proof load such as the train standard which along with fatigue also states that any equipment ect must have a proof load case of XXg, which would give me something to start with. pretty much like a standard that says for vehicle type x the maximum shock loading expected to be seen for unsprung mass is XXg etc etc.

its a bit of a strange one as the axle housing isnt totally unsprung, due to the tyres acting as a spring, and the mass of the vehicle is sprung, limiting the shock loading that the axle will take from the body. oh well i could only hope for some guidelines.. i'll have to make my own load case up!



Andy Thanks for the thought, but most companies are pretty hostile towards us.. dont quite know why yet! Dana have actually been helpful but thats for other stuff, as far as i know only one off shops have attempted what im trying to do in the way that im doing it, mainly as its not a very commercial thing to do, but helps us with another problem.. again i am being cryptic so sorry for that!

i may give phil a shout on some other info we are trying to get tho!

Thanks guys

Steve

AS4100 Steel Structures Code, has a section on fatigue design, but it only covers a small range of the many possible variations in a weldment.

The British Standard I mentioned is: BS7608 Code of Practice for Fatigue Design and Assessment of Steel Structures. It is the best for fatigue design.

Many diff housings from well regarded manufactures have suffered from fatigue cracking on our corrugated outback tracks. IMHO they would have easily passed any reasonable proof load. Much attention to small details is required to avoid fatigue - designing for a static load is simple in comparison.