Radioss Model Error

Hi Abhinav,

I tried running the model and it seems fine. But I doubt on the material type.

For all the parts you have assigned the same material. For honeycomb structure you can try modelling with honeycomb material (/MAT/LAW28), where this material is fully compressible and you can easily find the energy absorbed.

We have a similar tutorial https://altairuniversity.com/learning-library/modeling-and-analysis-of-honeycomb-impact-attenuator/ , please go through the same.

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Hey George,

Yeah the material is supposed to be honeycomb for that. I just wished to run to see if the connections are working properly and the model runs. The material card for Honeycomb requires a lot of data ( like the curves and E in z direction) which I dont have at the moment. I have to do sometime experimental trials to find out these information and then could give it in the material card.

I will check out the tutorial and maybe run my model with tutorial data just to see if model runs fine.

Thanks for your help.

Kind Regards

Abhinav

I would wish to know one thing, i read somewhere that the MAT/LAW28 Honeycomb is used in case of solid elements modelling . Would it be fine also with the shell modelling which is in my case.

Thanks.

Hi Abhinav,

/MAT/LAW28 is compatible with solid elements only. 

And which material card should i use for my modell with shell to represent the honeycomb?

Hi Abhinav,

Unfortunately the honeycomb material cards (/MAT/LAW28, /MAT/LAW50 and /MAT/LAW68) are not compatible with shell elements.

But /MAT/LAW50 can be used with thick shell.

Hello George,

The polyamid paper Honeycomb Core has a thickness of just .051 mm which is really small compared to its other dimensions. In reference to your previous message concerning thick shell and Mat/law50 does it mean that i modell this core with solid elements? 

Hi Abhinav,

Normally crushable honeycomb can be modeled with solid element and materials LAW28, 50 or 68 are assigned or the other possibility is, each cell can be meshed with shell elements and model with any elasto-plastic material.

Hello George,

Thanks for your last reply.. It did work out with isotropic properties.

NOw i have the results, but the stress strain plot looks very strange. could you maybe help me out or explian why is it like this.

I am sending the file per dropbox to you.

Looking forward to your reply.

With Regards

Abhinav

Hi Abhinav,

Let me know the unis consistency you have followed in your model. Also share a pic of your stress- strain curve.

Hello George,

The units are MPa, kg, mm , s.

Could you explain me how to create a crosss section in the structure to have results on these sections? SInce, when i plot the graph it gives me individual nodes to choose from and every node has different stress- strain graph.

With Regards,

Abhinav

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

Apart from that how can i see the unit system being used in the radioss?

Hi Abhinav,

I'm attaching a snapshot showing normal unit consistency followed for FE analysis. Please go through and ensure the values are correct.

The user has to ensure that the unit system followed is correct, there is no other ways to check the unit consistency.

You can create a set for these elements and recall the same set in cross section panel. Resulting forces acting on these sections will be stored in the Time History file. and for that create an output block for this section. I recommend you to go through RD-T: 3540 Front Impact Bumper Model tutorial in Help menu where we have shown creating sections.

Hey George,

thanks for the tutroial, it helped me out a lot with cross section creation.

I wish to ask you how to creat a force vs displacement plot? I made a cross section at the fixed bottom and simulated it . Although i dont exactly know how to plot the force vs displacemnt out of it. What i get is FZZ vs Time or Resultant Force vs Time. The structure is imposed with a displacement of 12mm and has a thickness of 14 mm. Simulation runs for .12 sec.

Looking forward to your suggestion how to go about it. The end result I wish to have is to extract this force vs displacement in excel and tzhen create a stress vs strain.

Would appreciate your help in this regard.

Thanks in advance.

With Regards

Abhinav

 i came across one more method, that is to create TH/ Node and define the REACZ for it but then I get individual nodes, I want the total reaction force at the fixed location of cross section. Cross plot option as well I dont find on the tabs.

Hi Abhinav,

For the section you define, create an output block for this section (/TH/SECTIO) and you can plot the forces in HyperGraph using the time history (T01) file.

Force vs displacement curve you can plot using Cross plot option in HyperGraph. 

In HyperGraph, go to File>>Load>>Preference File and select Vehicle Safety Tools and click on Load. From the Math menu select Two Curves and select Cross plot option.

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

Hello George,

Thanks for your reply.

How to export the force vs time values to excel? since i want to try in excel as well to create force vs displacement and then to create stress vs strain plot.

 I tried doing through export option in hypergraph but getting the eroor mentioned above for force vs time plot..

Looking forward to your inputs.

Thanks in advance again.

Regards

Abhinav

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

i used cross plot for force vs time and displacement vs time. Why is the force value so low in force vs displacement compared to force vs time? shouldnt it stay same? 

Could you please clarify it to me?

Thanks.

Regards

Abhinav

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

I checkd displacement vs Force plot as well, with that i get the correct values.

SO something to do with the scale factor X*Y->X

Hi Abhinav,

There are multiple queries and I'll try to answer each:

How to export the force vs time values to excel?

Once the Force vs Tine curve is plotted select that window so that HyperGraph is open now and from the menu choose Export>>Curves option so that you can export in .csv format.

I tried doing through export option in hypergraph but getting the eroor mentioned above for force vs time plot..

Can you try as mentioned above and if the error pops up again please take a snapshot of it and post as from the above image I'm not able to read the error showing.

Why is the force value so low in force vs displacement compared to force vs time? shouldnt it stay same? 

Ensure you have provided the correct coordinates for the new curve.
 

CurveX (scaleX*Y-> X)  The curve whose Y-axis you want as the X-axis of the new curve 

CurveY (scaleY*Y-> Y)  The curve whose Y-axis you want as the Y-axis of the new curve

If they are chosen correctly the values will be the same.

SO something to do with the scale factor X*Y->X

If you want to scale the X or Y coordinates then you can use this option. If the same values has to be retained keep it in 1. 

Hi Abhinav,

The issue related to Force vs Disp plot was moved to our Postprocessing sub forum (HyperView/HyperGraph) and our experts will help you in resolving this. You can follow up the query at: https://forum.altairhyperworks.com/index.php?/topic/22908-force-vs-displacement-curve/

Hello George,

I am trying to do solid modeling in order to compare the results which I have got through shell modeling of the sandwich core with an imposed velocity of 1mm/sec.

Somehow I am not getting any displacements in the solid and the error % is coming as 99%.

Could you please help me out in explaining what I am doing wrong in the solid modeling and the boundary conditions.

Please find the file attached herewith.

Thanks in advance.

With Regards

Abhinav

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Secondly are there any solid modelöed crushing tutorials avaliable, which I can look at?

Hello George,

I had defined rigid bodies during solid modeling which resulted in -99.9% error. When I removed it the model did function but the values are way beyond expected.

I thought of putting a skin at top and bottom and with rigid definition on these surfaces and a  cross section at the bottom, I can get the requierd force vs displacemnt. but somehow the simulation is not running. It shows an error but cant see which error is it. The Model checker says everything to be fine.#

Could you please help me out. I would appreciate it.

In attachment you will find the file.

With Regards

Abhinav

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Hi Abhinav,

For this objective please try this modelling approach:

>. Create a rigid wall in the bottom of the solid. Please don't forget to add the slave nodes of the solid component.

>. In the top create a surface, make it rigid and apply the imposed velocity on the master node of the rigid body.

We have a similar tutorial which you can access at https://altairuniversity.com/learning-library/modeling-and-analysis-of-honeycomb-impact-attenuator/

Hello George,

I did exactly the way you said. However I am having intersection errror, which I am not able to fix. Could you check it once Please.

I have used automatic fixing tool, and then tried manually.

Thanks.

With Regards

Abhinav

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One more question even If I do it with face skin on top surface , shouldnt it function?

If I am not mistaken I wouldnt be needing contact definition as well since the face is generated out of solid model.

I tried with face skin  as well but getting 1 error about kinematic condition.

Hi,

I have made some modifications in your model and you can try this approach.

There were also some unit consistency issues in your model for the material parameters and so I changed the values. Recheck the material values and correct them accordingly.

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Hello George,

thanks for your correction.

I see that you have put rigid walls on all the sides of the cube. I wished to have the reaction force on the bottom of the cube. Slo if I remove the other rigid wall and leave it just at bottom with outblock corresponding to rigid wall, would it give the results required?

Apart from that I wish to ask why you made rigid walls on all the sides of the block? any particular reason for that? <elements move together?>

Regards

Abhinav

Hello George,

I have to model the honeycomb structure and an impactor to find out the energy absorbed. Unfortunately I am getting an error 156. I saw in one of your posts that this error occur due to the material curves. Could you check my model, if it is okay. I dont have all the values required by material card 28 like in direction 11 & 22 , and G12. WOuld it be possible to run the simulation without these curves.

Looking forward to your reply.

Thanks.

With Regards

Abhinav

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