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**trilbytim****Member**- Registered: 2023-03-08
- Posts: 13

So, in trying to learn this software to model composite shells I am modelling a beam, at the moment just 1 layer thick and at the moment just loaded in tension. My first stupid mistake (not constraining rotation at the beam end) was solved on this forum, but now, I must be making another stupid mistake as I'm getting a displacement from Code Aster which is exactly 100x higher than I calculate, but I can't see the mistake.

Working in mm and N, my beam is 1000mm long x100mm wide x 1mm thick with 100N loaded in tension at the end. The stress in it is therefore 1 N/mm^2. The stiffness in the longitudinal direction I have set as 125e3 N/mm^2 for a typical unidirectional CFRP. The strain should therefore be 8e-6. Since the panel is 1000mm long, this should therefore increase in length by 8e-3mm.

However when I create a model with all those dimensions (enter 1000x100 to the geometry, 1 into the EPAIS field for shell thickness, 100 into the FORCE_ARETE field and 125000 into the El stiffness field) then it gives a maximum displacement of 8e-1. i.e. exactly 100x too big. It seems that I must be making a mistake with the units somewhere, but I can't see it. Any ideas where it is coming from?

My model is here:

https__://www.dropbox.com/s/rmut2gzn2qk0hsa/validate.hdf?dl=0

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**jacob****Member**- From: Dolní Benešov
- Registered: 2022-03-07
- Posts: 158

load0 = AFFE_CHAR_MECA(identifier='7:1',

FORCE_ARETE=_F(FX=100.0,

GROUP_MA=('loadend', )),

MODELE=model)

is actually 100 N / mm so if you want 100 N you have to enter 100 / edge length

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**trilbytim****Member**- Registered: 2023-03-08
- Posts: 13

Thank you, that explains it!

jacob wrote:

load0 = AFFE_CHAR_MECA(identifier='7:1',

FORCE_ARETE=_F(FX=100.0,

GROUP_MA=('loadend', )),

MODELE=model)

is actually 100 N / mm so if you want 100 N you have to enter 100 / edge length

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