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# Stress Range linear combine

Valued Contributor

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

5 REPLIES

# Re: Stress Range linear combine

Legend

Hi,

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

Regards,

Seifeddine Naffoussi
SafeMecha Stress Engineering

# Re: Stress Range linear combine

Legend

Select Elemental Data

Seifeddine Naffoussi
SafeMecha Stress Engineering

# Re: Stress Range linear combine

Valued Contributor

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

Legend

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.

Seifeddine Naffoussi
SafeMecha Stress Engineering

# Re: Stress Range linear combine

Valued Contributor

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

Model-->Output-->Calculate

Equation:

MAX(MAX(ABS(VEC(!case;7026;!i));ABS(VEC(!case;7027;!i)));MAX(ABS(VEC(!case;7426;!i));ABS(VEC(!case;7427;!i))))

Hopefully, someone will find this useful.