Nonlinear analysis settings for a bending test

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  • Last Post 17 July 2019
Jonathan974 posted this 16 July 2019

Hi everybody,

I finally managed to model my 4 points bending test as I wanted i.e with frictionless contacts for the supports of my sandwich beam but my goal would be to have a non-linear force-displacement curve output (polynomial curve, it is what I obtain by experiments) however by solving the problem with the large displacement option active I just get a straight curve...

My question would be: what settings do I need to activate to get the desired result?  I've tried to deal with Newton-Raphson option but I'm not sure about what I am doing,

 

Thanks a lot, J.

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peteroznewman posted this 16 July 2019

Does your experimental 4-point bending test take the beam past the elastic range and cause a failure?  What type of failure occurs, does the core fail in shear or does the adhesive bond between the core and the face sheet fail?

For whichever failure mode occurred in the experiment, you have to include that failure behavior in the simulation.

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Jonathan974 posted this 17 July 2019

Hi,

So yes I took the beam past to the elastic range and it causes a core failure, so I look option on ACP and I found the Composite Failure Tool, do I need to add nonlinear properties on core and face sheets I use ( that I don't have), or just the composite tool is enough to get the curve I want ?

Furthermore I've found this post you've made : https://studentcommunity.ansys.com/thread/i-want-to-see-the-failure/ but I guess this is not appropriate here because of composites ?

Thanks a lot J.

jj77 posted this 17 July 2019

There are specific damage initiation criteria and evolution law capabilities for composites in Ansys that you can use for this.

 

See this tutorial on how to use that to model damage in composites:

 

 

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Jonathan974 posted this 17 July 2019

Hi,

Thanks for answering,

I looked at the tutorial and this tutorial and I guess this is not really appropriate for my case because to use damage initiation criteria and evolution law capabilities I need to add orthotropic strain/stress limit for tension and compression and this is not my case ..

Actually, I would like to add a sandwich failure criteria on my core ( core failure) to get then the same vertical displacement that i get by experiments(polynomial) instead of a linear one,

 

I've found this topic but the link for Sandwich failure is not working .. https://www.sharcnet.ca/Software/Ansys/17.0/en-us/help/acp_ug/acp_failure_analysis.html

Thanks in advance J.

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peteroznewman posted this 17 July 2019

Any documentation you can find on that site can also be found in your current version of ANSYS Help.

What is the core material in your case?  Do you have core shear test data from a test like this.

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jj77 posted this 17 July 2019

There is something in ACP called core failure but that is a failure criteria (does only tell you if it has failed). Never used this so I can not comment on it. See the proper documentaion in your help manual (not the internet). 

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v193/acp_ug/Core_Failure.html

 

Even though these are anisotropic damage initiation and evolution laws one can just set all the directions the same and you get isotropy which you might have.

 

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Jonathan974 posted this 17 July 2019

 Thank you both for answers,

Here are results I obtain with Large deflection option ON,

Core is a honeycomb core and I have the 9 coefficients of the stiffness matrix (E,G,nu) I furthermore added a type ply : Honeycomb core. even for face sheets I have the 9 coefficients of the orthotropic elastic materials.

Does it exist a bending strength limit I can add to make the blue curve like the orange one  ? I am a bit lost I admit

Thanks for help !

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