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Discrepancy between LSPrepost and hand calculations -Shell element stress output

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Posts: 12
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(@mmia1)
Paid Intern
Joined: 4 months ago

Hi

I perofrmed some analysis in LSDyna. Upon checking the Von Misses stresses, I found that they do not match with the value I calculated using standard von misses stress formula as below:

image

I used fully integrated shell element (ELFORM = 16) with two integration points. I opened the elout file where I found that LSDyna wrote stress output (sigma-x, sigma-y etc) at two integration points. It basically looks like below:

image

So, when I checked any element say element 1 and plot von misses stress variation with time in LSPREPOST. I found that it does not match with what I got using elout stress values in von Misses stress formula. 

Can anyone help me in this regards?

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Negative Volume
Posts: 639
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(@negativevolume)
CEO
Joined: 5 years ago

How far off are your hand calculations from Dyna? You can try using and under-integrated shell formulation like 2 and see how that changes your results. 

Also what type of element are you using for your mesh? What's your element size? All of these things can affect your stress results pretty substantially. 

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