How to apply Initial Stress 1

[ZohrehA]

Hi dear expertise,

Does any one knows how can I apply a uniform initial stress to a part.
I know predefined field, but there I have to define every 6 component of the stress that I don't have them. I only have a single number indicating the effective stress.

 

[FEA way]

Check the documentation chapter Prescribed Conditions --> Initial Condition Types --> Defining Initial Stresses. All stress tensor components have to be provided unless you are defining elevation-dependent (geostatic) initial stresses where effective stress is used.

 

[ZohrehA]

Dear FEA way,

Thanks for your reply.
I have read the documentation, but as I said I have not the stress component, since I have calculate stress from strain (stress=E*Strain).
What is elevation-dependent (geostatic) stress? Can I use it instead?

 

[FEA way]

Can you describe the details of your workflow - what you already did and what you want to do ? Maybe there are other ways to achieve your goal. Geostatic stress is meant for soil analyses.

 

[ZohrehA]

Yes sure.
I want to validate the results of experiments about distortion of Strips (70*20*3 mm).
I need defining initial stress to defining stress induced by great blasting (before the main process: cold spray coating).
I have calculated the stress induced by grit blast by using distortion of the strips.
I mean that I measured the distortion of strips, then changing it to curvature and calculating the stress by using some formula.

I need some way to make stress inside the part. Dosen't matter how.
If it was a bie-metal it was possible to do that, by defining different initial temperature for two part. But in my case it is only one part, since it is before coating (just after great blasting)

 

[FEA way]

It would be best to simulate the first stage (grit blasting), even by just applying prescribed displacement to the part. Then you would have a complete stress field for use in subsequent cold spray coating analysis.

 

[ZohrehA]

But how can I apply displacement without applying force or stress? As you know I don't know the exact force even. I only have the mean stress of the entire component (part)!

 

[FEA way]

Apply enforced (non-zero) displacement boundary condition instead of force. For example, consider a simple bar in compression. Instead of applying force to its end, you could also enforce its displacement and obtain the reaction force so do something opposite than usual approach.

 

[ZohrehA]

I have measured the distortion by an Almen Gage (measuring the arc high). So you mean that I consider that number as the displacement of the arc direction and apply it to one node on arc direction (in the middle of top surface) and leave the edge of the specimen free (no fixing and boundary condition on the edge). Yes?
Is it ok to apply displacement only to one node on tope of the surface exactly in the middle or I have to apply it to all node of a line from bottom to top surface in the middle?

 

[FEA way]

Actually, it might be better to use some rigid indenter (with a geometry corresponding to the shape of the desired deflection) and apply enforced displacement to its reference point. I would also search the literature for descriptions of simulations of similar processes.

 

[ZohrehA]

Ok, Thanks for your idea.
I will, try it.