High Youngs Modulus material

[Tuckabag]

I am trying to locate a material (possibly unobtanium!) with a high Youngs Modulus and low density.
Ideally we are looking at a Youngs Modulus of ~200GPa and a density of <4,000kg/m3, however we have a little wriggle room on either.

Any bright ideas as I have come up empty. Closest I can find is CFRP materials which aren't ideal for this application (long shaft with dynamic sealing on OD).

Thanks.

 

[EdStainless]

You are asking for a specific stiffness that is huge, double that of steel or Al alloys.
The only such materials that I know of are technical ceramics, or maybe Beryllium? (just kidding, but it meets the requirements)
Why not CFRP? You can have inlays of say 17-4PH tube in the seal areas.

This shaft is a tube correct? What size?
What strength do you need?
What about corrosion resistance? Temperature limits?

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P.E. Metallurgy, Plymouth Tube

 

[Tuckabag]

I know, we are asking a lot arent we!
316SS gives us the required elasticity, however the additional mass gives us grief in the calculations we are required to follow for this application (PTC19.3-2016). Whereas say T6061 is great with regards to mass, but the reduced Youngs Modulus kills us.

CFRP may be doable, I can get around the issue of product contact inside the tube with a tube in tube design to isolate the product going up the tube from the tube itself. I've never worked with CFRP before so unsure of if we can maintain tight enough tolerances/finishes for o-ring sealing at high pressures (up to 24,820kPa). We also need a piston in the middle and threads at each end for attaching other components..... it just gets more and more complex!

Correct, shaft is a tube. OD is approx. 40mm and overall length would be around 1,600mm (we could possible halve that by making the shaft 2 part).

I forgot to mention that the dynamic sealing on the OD is reciprocating, so the shaft needs to slide in/out of a process pipeline. Therefore the OD would need to be suitable as a sealing surface.

Yield strength required of around 205MPa. I haven't played with that number as 316SS pass the bending moment calcs so it is possible we could use a lower yield material.

Corrosion not really an issue as pretty inert process.

Upper Temp limit of around +60deg C.

 

[Tmoose]

Does the entire thing have to slide into something else ? If not I'd boost the diameter beyond sealing region and use something from Home Depot.

"we could possible halve that by making the shaft 2 part." .
The lack of pictures etc has me wondering how that could be, and thus wandering down shadowy halls thinking a center support is then required, but struggling with why that is not possible with a one piece shaft.

 

[Tuckabag]

The probe shaft slides through a mounting flange into a process pipeline. We need to seal around the OD of the probe to contain process pressure. So we cant increase the probe OD beyond around 40mm as we are limited by the nozzle ID.
There is a piston halfway along the shaft which uses hydraulic force to drive the probe into the process line under pressure. Hence we can make the probe shaft in two halves as the hydraulic end of the shaft is not subject to the process flowing atream and subsequent bending moment force and shedding frequencies.

 

[BrianPetersen]

Why does it need such an exceptional Youngs modulus? Nothing you've described so far explains why that would be the case.

Why does it need such low density? Nothing you've described so far explains why that would be the case.

 

[WKTaylor]

What are Your REAL loads and stiffness requirements?

Low or high speed shaft inertia affects and/or shaft torsion loads... including acceleration/deceleration? Any other mix of random or harmonic vibrations? Is 'fatigue' an issue?

Some metal matrix composites... including ceramic-fiber reinforced extrusions... have a tremendous increase in stiffness and a substantial increase in strength with a subtle decrease in density... at substantial increase in cost and other processing factors.

Perhaps a hybrid shaft made from a 'mix' of CF-epoxy-tape [torque] and Boron-epoxy-tape [bending] would come closer to a solution.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[EdStainless]

Or stick with a PH stainless and make it thinner and stronger. You will only loose a little stiffness by thinning the wall and you can shed a lot of weight.

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P.E. Metallurgy, Plymouth Tube

 

[MintJulep]

"We have this great design. It just needs a material that doesn't exist and tolerances that can't be achieved to work."

Step back. Start over.

The way you are going now is unlikely to work.

 

[Tuckabag]

Thanks for the feedback so far.

I realise that the material I am looking for most likely does not exist, I just wanted to throw it out there and see if there was something that I have overlooked.......

This application is brownfields work, so we are constrained by existing equipment and the clients insistence on meeting certain design standards.
Basically we are constrained by the following :
1)

Maximum OD of 40mm (due to process standoff nozzle ID)​

2)

Probe minimum length is fixed due to needing to be inserted through a process DBB, the standoff nozzle and then protrude into the pipe ID​

3)

Probe must be able to be retracted from the pipeline whilst under process pressure to enable maintenance​

4)

The probe design must have a Fs/Fn ratio of <0.4 as defined by calculations in PTC19.3-2016.​

Point 4 is the kicker, due to the limit on the probe OD, the fixed minimum insertion length and the defined process conditions from the client, the only other variables we can change to try and get the design to pass the calcs is the probe material Youngs Modulus and Density.

Hence my original question so I could research these materials (if they actually existed, which I suspected they did not). I wasn't expecting miracles.