ShellMITC4 stress calculation

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jorson
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Joined: Mon Aug 10, 2020 6:01 pm

ShellMITC4 stress calculation

Post by jorson » Mon Aug 10, 2020 6:18 pm

Hi everyone, I am using the ShellMITC4 shell element , the stress result of the element including 32 parameters, which is the (F11, F22, F12, M11, M22, M13, V12, V13) at the four gauss integration points, I want to know how to calculate the stresses (S11, S22, S33, S12, S13) at the gauss integration points.
Can anyone help me? Thank you !

mhscott
Posts: 506
Joined: Tue Jul 06, 2004 3:38 pm
Location: Corvallis, Oregon USA
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Re: ShellMITC4 stress calculation

Post by mhscott » Wed Aug 19, 2020 6:46 am

It depends on which section model you're using. If it's ElasticMembranePlateSection, then you can't get the stress directly. If it's PlateFiber, then you can use a recorder with something like "recorder Element .... material 1 fiber 3 stress"
The number after material should be from 1 to 4 (Gauss points)
The number after fiber should be from 1 to 5 (there are five fibers through the thickness of the PlateFiber section)

johnnyontheweb
Posts: 43
Joined: Sat Oct 08, 2011 6:28 am

Re: ShellMITC4 stress calculation

Post by johnnyontheweb » Sun Nov 22, 2020 7:51 am

Hello,
I read here that one can use:

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recorder Element -file ele1gp1forces.out -time -ele 1 material 1 forces
to get results in this order:

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 [Time Nxx, Nyy, Nxy, Mxx, Myy, Mxy, Vxz, Vyz]
If I use ShellMITC4 and PlateFiber, like this:

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nDMaterial ElasticIsotropic 3 210000 0.3
nDMaterial PlateFiber 2 3
section PlateFiber 1 2 0.01
# shell elements
element ShellMITC4 1  10001 10145 10147 10146 1
...
I have all results as zero for:

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recorder Element -file ele1gp1forces.out -time -ele 1 material 1 forces
since "material 1" is misleading I suppose...

I have 24 results (6 forces/moments by 4 GPs) for:

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recorder Element -file ele1gp1forces.out -time -ele 1 forces
I cannot still obtain the generalized shell forces Nxx, Nyy, Nxy, Mxx, Myy, Mxy, Vxz, Vyz.
How the recorder should be written in order to get such forces per unit lenght? They should be 8 x 4GPs.
To clarify, I'm not looking for single-fiber stresses. Thanks in advance

johnnyontheweb
Posts: 43
Joined: Sat Oct 08, 2011 6:28 am

Re: ShellMITC4 stress calculation

Post by johnnyontheweb » Tue Nov 24, 2020 7:38 am

I think I found the point - theElement->strain was always zero, due to the fact that

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algorithm Linear
does not set any trial strain on the element.
I used this because at this stage my model is linear, anyway I turned into

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algorithm Newton
and now I have forces.

mhscott
Posts: 506
Joined: Tue Jul 06, 2004 3:38 pm
Location: Corvallis, Oregon USA
Contact:

Re: ShellMITC4 stress calculation

Post by mhscott » Tue Nov 24, 2020 7:42 pm

Yeah, even with a linear model, it's still always a good idea to use the Newton algorithm.

Same kind of thing happens with member loads on force-based beam-column elements where you need the second iteration for the loads to have an effect.

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