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Stress Range linear combine

I can't seem to figure out how to get the Model-->Output-->Process-->Linear Combination to give me what I want.  


I would like to subtract one stress vector from another to get the stress range for fatigue calculations.   Any pointers?    /    -    \   =   <--

                                               /            \

Once I have that I would like to look at the max absolute principle stress of the combined top an bottom sheets.


Thanks, RB


Re: Stress Range linear combine



You can use the Model / Output / Calculate command to create a new output vector containing your desired data. This equation will give you the absolute value of the Top X and Bottom X substraction:

1/Select output sets to process

2/Enter this equation

3/Select elements to process


Seif Eddine Naffoussi, Stress Engineer

Re: Stress Range linear combine

Select Elemental Data

Seif Eddine Naffoussi, Stress Engineer

Re: Stress Range linear combine

Merci Monsiour Naffoussi.   Ca me donne des ideas.


It is close to what I am looking for, but not quite. 


Ideally, I would like to subtract the Case 2 tensor from the Case 1 tensor.   Then extract the max(abs()) of the top and bottom maximum and minimum principle stresses.  I do not want to subtract the top from the bottom, they are different. 


Would it be better to do a linear combine (Case1 + -1*Case2) and then calculate the max(abs())?


Thanks, Richard

Re: Stress Range linear combine

Hi Richard,


The equation was for example.

For the substraction between two different output sets you can indeed use the Model/Output/Process and play with the scale factor. when the scale factor is left to 1 then Femap will do a summation of the two cases you select and will create a newest one which will contain the output vectors checked. Once the new output set is created you can use the Model/Ouput/Calculate and create a new results for ABS(outputvector).


Give it a try and keep me informed if it works for you.


Seif Eddine Naffoussi, Stress Engineer
Accepted by topic author AllTrans
‎08-28-2015 02:02 PM

Re: Stress Range linear combine

Ok, I finally got back to this and figured out how to get what I wanted.  We'll call this the Absolute-Max-Top-Bottom-Major-Minor-Principle-Stress-Range Finder.


Step 1 - Find difference between load sets

    Model-->Output-->Process-->Linear Combination

    Set Scale Factor to 1 and select first set then…

    Set Scale Factor to 1 and select second set …This will create a third set that calculates the  

    difference from 1 set to the next…or the range


Step 2 - Find Max abs of minor and major principle stresses for both top and bottom shell





Hopefully, someone will find this useful.