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Stress analysis contacts

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Message 1 of 8
joshcrews
1516 Views, 7 Replies

Stress analysis contacts

I am trying to simulate the following:

 

I have an 8" OD/5.523" ID steel tube. A 5.5" OD/4.957"ID tube is placed inside.  The 8" and 5.5" tubes are placed over a 4.9375"OD shaft.  So basically you have a hollow shaft attached to a drive shaft, with a filler tube placed between them to fill the gap.  Two 1-1/2" UNC bolts are placed in matching1.531" diameter holes in every component (thru bolted) with a nut.  Tightening the nut will tend to flatten the pipes, taking up the clearance between then and creating a contact pressure on the drive shaft.  I have having trouble getting all of the contacts correct since the components are not in contact at the beginning of the simulation due to the radial clearances.

 

Two axial bolt loads of 129,000 lbs will be placed on the tubes.  I have used a sliding/no separation contact between the bolt and nut.  Then I put a fixed constraint on the bottom face of the nut (not in contact with the tube) and put a 129,000 force on the top of each bolt head to simulate the axial load created by the bolt preload.  What type of contact should I use betweent the tubes that have radial clearance?

 

I have attached the tubes and drive shaft.  The 1-1/2" bolts and nuts (both heavy hex) were found in the library.

7 REPLIES 7
Message 2 of 8
JDMather
in reply to: joshcrews


@joshcrews wrote:
 I have having trouble getting all of the contacts correct since the components are not in contact at the beginning of the simulation due to the radial clearances.

 

You can set the max clearance to be automatically converted.  Or change contact yourself after autocreation.

 

... put a 129,000 force on the top of each bolt head to simulate the axial load created by the bolt preload. 

 

This doesn't sound right. but I haven't looked at the files yet (attach the assembl AND attach the fasteners - if you put a load on a fastener - will need that fastener)

 


 


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Message 3 of 8
joshcrews
in reply to: JDMather

I have attached the assembly files.  The bolts are preloaded to 70% of yield.  They are 1-1/2" diameter, Grade 5 bolts with stress area = 1.406 sq in.  The axial load generated is about 127,000 pounds.  You will see the bolts in the assembly, but I have them excluded in the stress analysis and have added loads directly to the outer tube to simulate the effects of the bolt preload.  I basically want to see if the bolt load on the outside tube will create a contact pressure on the drive shaft.

Message 4 of 8
JDMather
in reply to: joshcrews

The 8 in tube is set to Generic material in the analysis?


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Message 5 of 8
joshcrews
in reply to: JDMather

Sorry,

 

         I made up the drive shaft real quick to isolate the area in question. It is steel.  I have attached it.  The FEA files keep getting kicked back due to size.  What I ended up doing is just placing a load on the edge of the thru-hole with a  magnitude of 127,000#.  I placed another equal load on the other edge (where the nut would be) of equal magnitude. I placed a fixed constrain on the opposide end of the 8" tube so the model would run. I am interested in the y-displacement (flattening) and contact pressures between tubes.

 

Thanks again for your help.

Message 6 of 8
JDMather
in reply to: joshcrews


@joshcrews wrote:
  Two 1-1/2" UNC bolts are placed in matching1.531" diameter holes in every component (thru bolted) with a nut. 

Wouldn't it be the heads of the bolts and nuts that apply the clamping force?
Create flats on the cylinder where the high stress at tangent line between clamping faces of the fasteners and the cylinder would flatten the cylinder.  Apply the clamping force tothe planar faces.
Can you attach image of the fasteners in the assembly (I am interested particularly in the washers or true clamping faces of the fasteners).

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Message 7 of 8
joshcrews
in reply to: joshcrews

I went ahead and added flats on the 8" tube and applied the loads to the flats to simulate the bolt loads.  The actual design simply has 2 bolts placed thru the holes and a nut on the other side.  No washers.  Long story short, my group was asked to look into this connection (original) versus another design.

 

The question no becomes: what type of contact do I use between the tubes?  They have a clearance before starting the stress analysis. Basically, I want to know if the bolts can generate enough load to compress the 8" pipe such that it compresses the 5.5" pipe onto the drive shaft.

Message 8 of 8
swalton
in reply to: joshcrews

Have you checked to see if the bolt load will compress the 8" pipe enough to hit the 5.5" pipe at all?  Run the outer pipe by itself and check the deflection.  If you are .011" clear on a radius and the tube only moves .005" on a radius, you won't transfer any load onto the inner tube.

 

I would try seperation contacts as a start.  I might make use the split tool to make a few small regions on each pipe and cofine my seperation contacts to those regions. 

Steve Walton
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