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Margin of Safety Calculation / Utilization Factor

[ Edited ]

with reference to the article from FEMAP forum: MoS Calculation in Femap .

Is something similar available in NX post-processing ?

Some time ago i started similar discussion and answer was that in NX 9 such functionality does not exist, but in future releases will be possible to do.

 

So, I do not hava access to NX 10/11 yet, but hopefully will in near future, but in the meantime ... does anyone have experience with it (if of course such or simmilar feature is available) and can get some tips/tricks how to use it or where to find the functions that can be used in such post-proccessing.

 

at this moment in NX 9 it's quite frustrating when in bigger structure, few pass of Utilization Factors calculations need to be performed separetly, when for example few different materials are used and whole assembly is simulated together.

 

Thanks

Tomek.

3 REPLIES

Re: Margin of Safety Calculation / Utilization Factor

Tomek,

 

I believe I replied to your previous question. NX 10 introduced Results Probes. This capability lets you define formulas to generate user defined results. Its math operations are built off of the NX expressions capabilities. As such it is limited to scalar expressions and scalar output (i.e. no vector or matrix math). Results Probes can produce multi-step output (i.e. transient, frequency, static subcase, etc.). Results Probes work by defining Results Variables, then using those variables in expressions (formulas) to produce output. A simple example would be the calculation of margin of safety using Von Mises stress and yield stress.

 

1. Define a results variable as VONMSTRESS

2. Define an expression for yield stress as YIELD=XXX, where XXX is some real value

3. On a solution, define a results probe with a formula such as 

 

StressMargin = 1 - VONMSTRESS/YIELD

 

4. Define the results probe to be evaluated over the entire model

5. Generate a contour plot of the stress margin

 

This will work, assuming the entire model uses the same material. You can make it work better with a function that looks up the yield stress from a given element's material. NX 10 doesn't have such a function OOTB, but SC 11 (NX 11) does. NX 9 or 10 introduced the ability to define user defined plugin functions. These are math operators, lookups, or other functions that accept input and return output used in formulas. The user user can code up such functions and use them in expresions. I asked one of our developers to do that for me in 10, then had development support the function OOTB in 11. So what would I do in SC 11? I would replace the suggestion above to define YIELD as a real value expression with the YIELD function. That function is given an element as input. It then retrieves the element's material, which next leads to the material's yield stress. That yield stress is used in the formula. Now you have something that works for a model having multiple materials, assuming the yield stress is defined on each material.

 

The attached presentation provides some results probes examples. More information can be found in the NX 10 and SC 11 online help.

 

Regards,

Mark

Re: Margin of Safety Calculation / Utilization Factor

Hello @MarkLamping

 

I digged out that old topic and are trying to check the functionality you described above.

 

In NX11 I tried to create the result probe and to return the Yield value of the material.

For Result probe it worked:

 

rods.png

 

However how to use that function in example in Reduction / Multiple Reduction ? When I use the fuction Yield there it returns some wrong value.

 

 

example: for formula

SVM / Yield (20[C])

 

reduction.png

in results I thet the Von Mises Stress, so it looks that Yield fuction returns 1 istead of the real value. Any tips / tricks how to use that function ?

 

Using an ocasion, how return the value of:

- beam / rod cross section area

- element thicknes, 

- element Youngus Modulus

- etc...

 

Are such function available in postprocessor?

 

thanks Smiley Happy !

 

Re: Margin of Safety Calculation / Utilization Factor

Tomek,

 

I will have to ask the developer(s) about the support for functions in the create results commands such as Reduction and Multiple Reduction. I am 90% certain that I asked them this question previously, and the answer was that functions are not supported by them. That's consistent with the behavior you are reporting. Please submit this question to GTAC, and if it isn't supported, the IR can be used to create an enhancement request for you.

 

Regards,

Mark