Learning Forum

[RDurocher]

I'm trying to run a explicit dynamic study of a composite material impact test, but I'm running into issues with it. I've been following this previous post (/forum/forums/topic/running-an-explicit-dynamics-simulation-on-a-composite-plate/) as a guide and have everything (I believe) setup the same way, but keep running into an error that says "Only Linear and rigid equations of state are valid for shells". I'm not sure exactly what I need to fix in order to get it to run.

[Wenlong]

Hi,

Which Equation of State are you using in the Engineering Data?

As the error suggests, don't use nonlinear EOS, such as ideal law of gas, for shell. Pick linear ones, such as bulk or shear modulus. 

Regards,

Wenlong

 

[RDurocher]

Hi Wenlong,

How would I go about changing the EOS to shear modulus? I have tried suppressing the Orthotropic Elasticity before, but it does then asks me to input a different EOS, which I'm not sure how to do. (I'm fairly new to Ansys and am still learning how to modify the engineering data).

 

 

 

 

 

[Wenlong]

Hi Rdurocher,

So in Engineering Data, select "Equation of State" to the left. There you can see options like "Ideal gas law", etc, in which bulk modulus and shear modulus are linear and can be used for shell. 

For more information about EOS, you can refer to this page and its following pages in the Ansys Online Help: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/exd_ag/ds_ex_mat_bkgrd.html.

You can also see in the following pages that some EOS cannot be used for shell (https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/exd_ag/ds_ex_mat_idealgas.html)

Regards,

Wenlong

================ Note ====================

If you have trouble opening the links I attached, please see the first useful link below

 

 

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Useful Links

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• How to access Ansys Online Help Document


• How to show full resolution image


• How to use Google to search within Ansys Student Community

 

[RDurocher]

Hi Wenlong,

 

Thanks for sharing those links. I did not know that I those were available.

I was able to add in an EOS for the material, but when I run the solver I am still getting an error claiming that it requires an EOS. But in my material properties, I have defined the EOS with a shear modulus.

I was wondering if you've experienced this error or know what I might be missing.

 

 

[Wenlong]

HI,

You probably only defined shear modulus without bulk modulus. You need to define both to make your material model complete. In fact, defining shear and bulk modulus from EOS is equivalent to defining isotropic elasticity, as shown below. 

Regards,

Wenlong

 

[RDurocher]

 Hi Wenlong,

I added the bulk modulus and got the LDPE working, but now it seems like I'm having issues with my Prepreg now.

I am now getting an error saying that the Prepreg requires a stiffness properties, either isotropic elasticity or an equation of state. But this doesn't make sense to me as carbon fiber is an an-isotropic material. 

Do you have any suggestion on how to fix this? I've attached an image of my current carbon materials.

Thanks,

 

 

[Wenlong]

Please unsupress the orthotropic elasticity in Prepreg and try again. 

Regards,

Wenlong

 

[RDurocher]

Hi Wenlong,

I have done so, but when running it again it has the original error of "Only Linear and Rigid Equations of state are valid for shells".

[Wenlong]

Hi RDurocher,

I see. Then please try to assign orthotopic material through ACP(Pre). In this way, you can first create a composite ply then import the ply into Explicit Dynamics. If you are not familiar with ACP, below is an image about the steps (things you need to define) in ACP (Pre), you can right click on each item and insert stuff. 

After you define a laminate in ACP, you can export the shell to Explicit Dynamics, like shown below:

Sorry I didn't realize you are trying to define an orthotopic material before. It occurred to me as well that orthotopic material doesn't work directly in Explicit for shell but through ACP it works. The benefit of ACP is you can define exactly the orientation of the material direction, and even multiply plies to create a composite (in my example I only created one layer of ply). 

I also found others facing the same issue, please see this post and jj77's reply:/forum/forums/topic/explicit-dynamics-87/

Regards,

Wenlong