Round tube loaded between 2 v blocks?

[dandersonjr]

I’m taking a measurement between 2 points on opposite sides (90° apart) of a thin wall tube after it has been loaded between 2 v blocks.
I haveone analysis setupwhere I'm using 4 loads 90° apart over a .1" wide surface region with inertia relief.
I have another analysis setup on an assembly with 2 v blocks applying a load to the tube.

Both analyses have a measure between 2 points (trying to measure deflection after load) on the tube.
The assembly Mechanica analysis results correlates with the hand calculations I have. (Second setup) .05"
The part model Mechanica analysis results are way off. (First setup) .004"

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[randyspeed]

Don,

You could use planar symmetry in your assembly model. Symmetry constraints eliminate the need for inertia relief (assuming you are using IR to prevent rigid body motion).

You can actually use planar symmetry along two planes (90 degrees to each other). That is, along the vertical (Y-Z) plane and along the horizontal (X-Z) plane. This will simplify the setup of boundary conditions for you - addressing the frustrating process of trying to constrain a floating body (elimination of rigid body motion). You will, of course, create the quarter model by defining a cut feature in the assembly. It will be an assembly model.

Contact is still required to model the load transfer between the v-blocks and tube properly.

Alternatively, you may consider modeling this as a 2-D plane strain analysis type. There is plenty of information in PTC help files for setting the 2-D plane strain models. It is still an assembly contact model, just reduced to a plane. It follows the assumption that the strains in-and-out of the plane are negligible. This may be true for the cylinder longitudinal (Z axis) direction. You could quickly and easily run a sensitivity study on the tube wall thickness, for example. 2-D analyses run so much quicker than 3-D analyses.

Good luck,

Randy Speed
President & CEO
Speed Consulting, LLC
4715 Harvest Hill Road
Dallas, Texas 75244
(214) 213 4440
(214) 853-9221 fax
www.speedconsulting.com


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