Shaft torsion at cryogenic temperatures of -196C
Shaft torsion at cryogenic temperatures of -196C
(OP)
I cannot find any recommendations for materials being used as shafts in cryogenic conditions. Shear modulus / modulus of rigidity always appear to missing from the majority of materials I do search on.
Can anyone recommend any material with a shear modulus greater than 87 GPa (17-4PH)?
There appears to be a lot of information about cryogenic conditioning but very little data on the properties of material at those temperatures!
Hope someone can help.
Br
Bernard H
Can anyone recommend any material with a shear modulus greater than 87 GPa (17-4PH)?
There appears to be a lot of information about cryogenic conditioning but very little data on the properties of material at those temperatures!
Hope someone can help.
Br
Bernard H





RE: Shaft torsion at cryogenic temperatures of -196C
G = E / [2 (1 + ν)]
where
G = shear modulus
E = elastic modulus
ν = Poisson's ratio (if unknown, assume 0.3)
Thus, look for materials with high E, which means they also have high G.
For a stiff shaft, other metals to investigate include alloys of Be, Co, Mo, and W. However, your shaft will also need strength and fracture toughness, which may be missing from these materials. Good luck.
RE: Shaft torsion at cryogenic temperatures of -196C
I believe youngs modulus would also change at cryogenic temperatures and the data for these figures is limited.
Bernard
RE: Shaft torsion at cryogenic temperatures of -196C
RE: Shaft torsion at cryogenic temperatures of -196C
If on the contrary it is a matter of resistance and not of stiffness, then I suppose that the commonest choice of a stainless steel is not good (though I would give it a try): then you should turn into the field of high Nickel alloys (Hastelloy and the like).
prex
http://www.xcalcs.com
Online tools for structural design
RE: Shaft torsion at cryogenic temperatures of -196C
A cylinder in torsion will have minimum mass per unit deflection when constructed from a material with the maximum quantity G0.5/ρ, where G is shear modulus and rho is mass density. Therefore, one must find materials with high G. Your statement "Hence your parameter is fixed and you can't change it." is false.
RE: Shaft torsion at cryogenic temperatures of -196C
If you want to extend your search to other metals, then Titanium may be a choice for you: both the elastic modulus and the density are roughly half as those of steel, so your ratio improves. On the contrary Copper is not good, as the density is higher than that of steel, but the elastic modulus is halved, and even worse it goes with aluminum (low density but much lower modulus). Zirconium alloys are not very different from Titanium, just a little worse from your point of view. High Nickel alloys, that I already mentioned, are not very dissimilar from common steels, just a little worse from your perspective (similar modulus, slightly higher density).
However there is a simpler way to obtain a high torsional stiffness with minimum mass: simply use a tube instead of a solid bar!
prex
http://www.xcalcs.com
Online tools for structural design
RE: Shaft torsion at cryogenic temperatures of -196C
I believe you have received an answer to your question, but not a solution to the problem. Previous posts are correct in stating that Young's modulus does not change significantly for materials that are suitable for use at -196 C. Materials that retain sufficient ductility at cryogenic temperature so they are mechanically useful are 300 series stainless, Monel, Bronze, Titanium, Aluminum, Hastelloys, Nickel, and 17-4PH cond. H1150M or 15-5PH.
My guess is that you may have a shaft wind-up problem. Excessive torsional wind-up will not be resolved with a simple material change. You will need to increase the shaft diameter in a non critical area to increase its stiffness.
Let me know if my guess is incorrect and you need more information.
DBay
RE: Shaft torsion at cryogenic temperatures of -196C
I have to use a solid shaft because of the danger of cavities at these temperatures (we would only have to have a pin hole in a seal weld to cause untold damage), I must mention we are talking about equipment for pressure retention which could be as great as 255 Barg.
The wind up is still excessive despite the use of larger diameters in a compound shaft.
I have fixed input and output diameters, so was looking for a more rigid steel, 10% would help but there appears to be nothing greater than 17-4PH unless I go to VERY expensive materials which have even less cryogenic data than the steels!! 17-4PH is >£240 a kilo as it is.
Bernard
RE: Shaft torsion at cryogenic temperatures of -196C
If you work any material backwards I think you'll find this to be true, if not then could you pls go further?
B
RE: Shaft torsion at cryogenic temperatures of -196C
I don't understand what you mean by "youngs modulus of elasticity for TORSION". I used accepted materials properties, names, and symbols to describe elastic constants. You can see a more detailed description at:
http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/elastic_constants_G_K.cfm
I think you have a full understanding of your problem. If you need higher elastic/shear modulus, you will need to use a more expensive material which has less published data than your current material. I recommend investigating beryllium alloys - try Brush Wellman at:
http://www.brushwellman.com
RE: Shaft torsion at cryogenic temperatures of -196C
this is the same site but gives all equations for calculating E, G, k or v -
http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/calc_elastic_constants.cfm#Table
Bernard