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Equivalent stress in shock response calculation

Hello,

 

I'm performing a shock response calculation in Sol103 Response Simulation (NX9). I am calculating the stress components and the equivalent stress (von Mises) using the CQC method.

Does anybody know according to which calculation process the equivalent stress is evaluated? I looked for some theoretical background in the help, but I couldn't find any equations. For example, does NX combine the scalar values of the equivalent stress similar to the stress components?

 

Thank you,

Diana

7 REPLIES

Re: Equivalent stress in shock response calculation

Diana,

 

I'm doing some ghost writing here for one of our developers. For von Mises related CQC computations, the von Mises values are first computed from the components, then the CQC calculation is performed. It does not do CQC calculations on individual components, then generate von Mises from the CQC results from the components.

 

Regards,

Mark 

 

Mark Lamping

Simulation Product Management

Product Engineering Software

 

Siemens Industry Sector

Siemens Product Lifecycle Management Software Inc.

mark.lamping@siemens.com

Re: Equivalent stress in shock response calculation

Mark,

 

thanks for your response. Just to make sure that I have understood correctly, the CQC calculation is performed with the scalar values of the von Mises stresses, not with the tensors, right?

 

I have another question. Is there a recommended procedure in NX to combine the equivalent stresses from a shock response analysis with the results from a static analysis? I could add up the scalar values of the equivalent stresses, but this would be quite conservative...

 

Regards,

 

Diana

Solution
Solution
Accepted by topic author eea
‎08-26-2015 04:32 AM

Re: Equivalent stress in shock response calculation

Diana,

 

You understood my reply correctly.

 

It is possible to combine the shock response von Mises stress with a linear statics von Mises stress in NX using the Combine Results command. The attached picture shows the outcome of that. The top left result is the combined result from those on the right (shock response and linear statics). I simply added the two stress components together.

 

Whether or not this is too conservative is beyond me. Can you suggest another combination method? If so, then I can try to determine a way to do it in NX.

 

Regards,

Mark

Re: Equivalent stress in shock response calculation

Mark,

 

your suggestion of the result combination was one solution I thought about.

The other one was to generate the equivalent stress from the CQC results of the components and then combine the tensors. This should be less conservative but it might be that the results are too optimistic.

My problem is, which combination should I choose to get realistic results possible.

 

Regards,

Diana

 

Re: Equivalent stress in shock response calculation

[ Edited ]

Hi Diana,

We typically RSS the results, which NX Combine would let you do...

Re: Equivalent stress in shock response calculation

Hi,

 

thank you for the hint. Could you please explain me what you mean with RSS the results?

Re: Equivalent stress in shock response calculation

RSS refers to "square root of the sum of the squares". I asked one of our Nastran/response experts about this and he felt that the original approach was the way to go. He also suggested that you search the web/literature for any design guidelines particular to your industry and analysis needs. There may be something out there already that outlines accepted practices.

 

The RSS suggestion is going to give you a more conservative value too, so that may be even better for you.

 

Regards,

Mark