COMPOSITE BOX

Scap97

Hi, I'm trying to create a sort of box made of composite material (Mat 25: Composite Shell; Prop: Compp). The component is shown on attached file.

When I create the laminate, HM shows me error id #197 ( REFERENCE DIRECTION IS ALMOST NORMAL TO SHELL ID=1600). This error is for only 400 elements while my component is made of almost 2000 elements.

How can I correct this error. 

Thanks

<?xml version="1.0" encoding="UTF-8"?>

Simon Križnik

Hi,

 

when assigning material orientation, make sure the direction is not perpendicular to shell elements. You have probably assigned material orientation in the height direction for the whole component, which is invalid for the elements on top (check material orientation of element 1600).  The best practice is to assign material orientation for each surface one by one.

Scap97

So your suggest is to create 6 different sets with 6 coupled systems?

Thanks for help

 

Edit:

I tried creating a ply for each surface of my box (so I created a total of 8 different set). I created also 8 systems, one for each surface and I create the laminate. 

Once I launch the solver, I obtain the same errors but this time I found 600 error messages. 

Can you please help me finding the error. Thanks

Simon Križnik

Can you share the model?

Scap97

Yes!

Thanks for help

Unable to find an attachment - read this blog

Simon Križnik

The first anisotropic direction of material could be defined with angle ϕ and global vector (Vx ,Vy ,Vz ). It is also possible to use angle ϕ and skew. In this case, x-axis of skew replaced the global vector V.

 

The orthotropy direction is set with Vx, Vy and Vz parameters in /STACK card (laminate). To override laminate direction set up ply with local skew and Def_orth=1. 

Unable to find an attachment - read this blog

Scap97

Altair Forum User said:

ϕ and global vector (Vx ,Vy ,Vz ). It is also possible to use angle ϕ and skew. In this case, x-axis of skew replaced the global vector V.

 

So what I need to do is to create plies with angle ϕ an Ioth=1 for each different surface? After I create these plies, I have to use prop #11 (Sandwich shell) or I have to use prop #1 as you do?

When I open your edit file (thanks for help!!), I found no plies and it returns to me an error due to incompability beetween Material type #2 and prop type #1.

Could you please help me also this time? Thanks

Simon Križnik

You need to define local skew and Def_orth=1 only for those plies that have an invalid orientation assigned by /STACK (in your case Vx=1, Vy=0, Vz=0 means only plies whose normal points in global x-direction has to be corrected).

 

All elements with PCOMPP prop_ID type must belong to a ply (/PLY) inside a stack (/STACK). 

Unable to find an attachment - read this blog

Scap97

Thanks for you help!! 

Now I have another problem, this time with contact interfaces (groups). Vertical surfaces pass through the ground (as it's represented in figure below). I used contact interfaces type 7 (multi usage) to connect the entire box with the ground. I can't understand while the lower parallel surface didn't show this problem while the vertical ones gives errors.

For group that involves Impactor and Box I used type 2.

Maybe Ground should be bigger than the box (now they are of the same external shape).

Thanks

<?xml version="1.0" encoding="UTF-8"?>

Simon Križnik

Without the model file, my best guess is the contact at the edges are not detected. If that is the case, define an additional type 11 or 19 contact.

 

You may find helpful Free eBook: Introduction to Explicit Analysis with Altair RADIOSS. I have recently revised the third edition which should be available in the near future.

Scap97

Thanks for help. Sorry for late reply.

If I want to create continuum shell element in black circles area should I add some RBE2 in this zone or I read about solid shell element (HSEPH or Shell16) but I don't know how to create.

What's the best configuration for creating continuity in these zones?

Thanks for help

<?xml version="1.0" encoding="UTF-8"?>

Simon Križnik

The Like button is an easy way to show appreciation for the help. /emoticons/default_wink.png' srcset='/emoticons/wink@2x.png 2x' title=';)' width='20' />

 

The common approach is to ensure node-to-node connectivity with equivalence in the edges panels (shift+F3): 

 

 I would not recommend connecting with RBE2 elements, because these connections are infinitely stiff. 

The thick shell approach might work, however they are more useful for thick shell structures with massive junctions. It may give better stress distribution and capture deformation modes more accurately but it will significantly increase the computational cost.

 

Scap97

So according to the video I have to pick connecting elements (as in picture below) and use function 'equivalence'.

I've tried doing like the video, but my node didn't highlight and the edges remain in the model. Is there something I miss?

 

 

<?xml version="1.0" encoding="UTF-8"?>

Simon Križnik

Either pick elements or components- the latter is less time consuming if proper tolerance is used.

 

If no nodes were highlighted with preview equiv it means no nodes were found within the tolerance specified. Increase tolerance until expected nodes are highlighted. 

 

The ^edges component will remain in the model unless you delete it. 

 

Share the model, if the issue persists.

Scap97

Now it's working; hoping everything goes ok.

Thanks for help!!

Another question about this: if I want to use an aluminium foam as the material for my crashbox, which material and property should I use?

 

Simon Križnik

Glad to help.

 

Try to model aluminum foam with /MAT/LAW33 (FOAM_PLAS) and any of the compatible solid properties.

This material model was used in a similar application:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.940.3859&rep=rep1&type=pdf

Scap97

I've made a simulation with this type of material as the others I made before, but, while I impose an initial velocity in the opposite direction my crashbox goes in the other way (as in figure below). There's something I miss?

I use material type 33 and prop type 6.

Thanks

<?xml version="1.0" encoding="UTF-8"?>

Simon Križnik

The initial velocity should be a negative number along the global Z direction.

 

There is a crashbox tutorial in the Radioss ebook, and here are a few videos:

 

 

Scap97

Thanks for the videos!

Yes, I used a negative velocity in the z-axys (as I did for every other simulation), but this time my crashbox goes in the wrong direction. I don't know why this time I have this error

Simon Križnik

Following these tutorials, you should be able to resolve this basic issue. 

 

Without having access to your model I can only guess.