PROBLEM WITH STRESS ANALYSIS ON STEEL PLATE

[samstreet101]

I'm designing a steel plate which will be used a restraint over the end of a steel duct which is embedded in concrete. The duct will be filled with expanding foam which will create an internal pressure which is thought to be approximately 4 bar (0.4 MPa). The steel plate is 420mm in diameter and 10mm thick. The diameter of the duct is 295mm and thus the area of the plate that the pressure acts on is 68349mm^2. The plate will be fixed into the concrete by 4x M20 bolts (equally spaced on a PCD 350mm diameter). Below is a picture showing the set up if I haven't described it well.

When I simulate this in Inventor 2014 Professional, I get results which seem very high, although they could be correct. I constrained the plate in the 4 bolt holes only in the Z direction (the same direction as the central axis of the plate and duct) as I think in reality the plate would be able to move in the other two directions. I applied the load as a force (27.34 kN) in one simulation and as a pressure (0.4 MPa) in another simulation. Same result each time: 432 MPa around the bolt holes and 78 MPa in the centre of the plate. See image below:

Can anyone verify these results to check and see if I've set it up wrong as if these results are correct, this will be problematic for the design.

File is attached.

Kind regards,

Sam

[GSE_Dan_A]

Using your part, I split face the plate where the heads of the bolts would be and used that as my Fixed Constraint.  My max stress (using either a Force or Pressure) was 211.2 MPa (see attached Screen Shot).  By fixing each split face seperately, you can determine the force required for each bolt to hold the plate in place. 

[samstreet101]

Would you mind telling me exactly how you got that result? Only I can't seem to acheive that. My first attempt (using your split faces method - assuming a 30mm diameter bolt head for an M20 bolt) gave me a result of 279 MPa but as I refined the mesh finer and finer I ended up with a result of 768 MPa. This was with a load of 27.34 kN applied to the opposite face as I did in my previous model and I constrained the bolt head faces (not edges) completely fixed. See images:

I then did the same thing but only fixing those faces in the Z direction, allowing them to float in the X and Y directions (not sure if that's realistic or not) and got a result of 429 MPa (mesh refined to size of 0.01 and an angle of 30 degrees).  Images below:

Could you tell me exactly how you set your model up? What size bolt heads did you assume? Were the faces fixed or the outside or inside edge? Were they totally fixed or just in one direction? What load did you apply and to where? And did you refine the mesh?

Thanks,

Sam