Load Shoulder Pressure Stress Calculations (Sketch Attached)

[506818]

I'm in the process of designing a part which must be submerged down to 2000m (200 bar/20 MPa/ 2900 psi). A sketch of the part has been attached. The outer housing will be titanium and the inner part aluminium. I've carried out the calcs for the outer part to withstand the external pressure, but am stuck a little with the internal part.

My understanding of the stresses acting on this part are:
- Compressive stress on the load shoulder
- Shear stress acting across at roughly a 45° angle (assuming this angle and not a straight line across)

Both these stresses at present are below the material yield (quick bonus question: I'm assuming that the shear stress for aluminium is 60% of the yield - is this a correct assumption?). I'm thinking I can't just leave it here and that I should be working out principal stresses and max shear stresses etc. Can anyone provide guidance on this? Is this required? What should I be looking for (Mohr's circle to calculate P1/P2/shear max, Rankine's theory, von Mises etc.).

 

[hydtools]

I would add stress concentration in the shoulder corner to your concerns.

Ted

 

[chicopee]

Is the part under cyclic loading?

 

[506818]

Good point with the stress concentration, there will be a blend rad at that point.

No, can assume it will be under static pressure (cycles involve removing from water and redeploying once a day max). What are the concerns with cyclic loading other than fatigue?

 

[506818]

Bumping this a touch - any other ideas?

 

[chicopee]

From the drawing only, I see that the shoulder contact may not be enough and that you could extrude either the Al or Titanium at the shoulder given enough force. Explore that situation. Also if the shoulder has a sharp corner as shown, the material could score.

 

[506818]

Thanks.

You're correct, extrusion is the problem I'm trying to eliminate. It's the way to calculate the dimensions required to prevent extrusion is where I'm struggling.

The corner will have a rad to reduce stress concentrations.