Foam modelling issu...
 
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Foam modelling issues  

 

anuragdogra
(@anuragdogra)
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October 2, 2020 7:01 am  

I am trying to model high-velocity impact of a structure by applying foam material in the front to reduce damage. Most of the literature suggests two types of young' modulus: i) The Youngs modulus of foam specimen tested (for PUR - 79 MPA) ii) The young modulus of the material itself (for PUR-1300-1600 MPA). I am using the foam specimen young modulus i.e. case i) but my model is not working properly. (Material cards used: i) MAT_57_low_density_foam ii)Add Erosion to avoid negative volume error)

Questions: Am I using the correct value of the youngs modulus?

If someone can look into my model and recommend something, that would be great. ( I am using a highly concentrated mass on thin shell element plate attached behind the foam colliding a steel plate at 250 knots). The file is attached below.

This topic was modified 2 months ago by anuragdogra

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Negative Volume
(@negativevolume)
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October 2, 2020 5:23 pm  

Hi @anuragdogra

What do you mean by "specimen tested" vs "material itself". I'm not sure what the difference in the material tested is between the two young's modulus values that you provided. 


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anuragdogra
(@anuragdogra)
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October 2, 2020 5:43 pm  

By specimen tested I mean the 'foam block' made by using polyurethane for testing and the material itself means a 'chunk of Polyurethane' tested to measure polyurethane properties (not including the air cavities as they exist in the foam just a solid chunk of polyurethane material)

If this does not make clear what I am trying to say, I will share with you the papers which I am referring to.

Thanks!:)  


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Negative Volume
(@negativevolume)
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October 2, 2020 6:18 pm  

@anuragdogra okay that makes sense. You were correct to use the modulus from the specimen. I’ll take a look a little further and get back to you. 


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anuragdogra
(@anuragdogra)
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October 2, 2020 6:23 pm  

Great, thanks!


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anuragdogra
(@anuragdogra)
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October 8, 2020 3:22 pm  

Hey, did you had time to look at my model? I am still stuck on it.


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Negative Volume
(@negativevolume)
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October 12, 2020 10:07 pm  

@anuragdogra To start, you need an *Hourglass control for the foam. I would suggest using IHQ=6 and QM=0.5 - 1.0. You are probably seeing instabilities in the foam because of this. Additionally, I think it's a little odd that the modulus of the specimen and material are so different. I also think that I mis-spoke, you should use the modulus of whatever is the most raw material property, which I believe is the higher value according to what you described. In most cases, you want to define the material within LS-Dyna to represent the physical material without any effects caused from things like geometry and air bubbles etc. 


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anuragdogra
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October 12, 2020 10:27 pm  

@negativevolume I will check it out. Thanks!


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