Young's Modulus limit?

Submitted by Joel Martis on Tue, 08/04/2015 - 15:26

Hi all.
I'm pouring steel pellets into a container. When I set the young's modulus to 2.1 e11 , the pellets seem to go right through the wall, which I have created using fix wall/gran ( i.e. fix xwalls1 all wall/gran model hertz tangential history primitive type 1 xplane -0.1 limitForce 'on' ).
The pellets don't go through the wall if I lower the young's modulus to around 2.1 e9
Can someone explain why this is happening?

Thanks

Joel Martis

Forums:

Joel Martis | Wed, 08/05/2015 - 12:09

Lowering the timestep did the trick!

Regards,

Joel

Joel Martis
Bachelor of Technology in Mechanical Engineering (Senior Year)
Indian Institute of Technology Madras

ckloss's picture

ckloss | Wed, 08/05/2015 - 23:02

Hi Joe,

1e11 is much higher than needed for most purposed. Usually 5e7 Pa does the trick

Christoph

Joel Martis | Thu, 08/06/2015 - 11:46

I'm trying to simulate steel pellets falling into a container. Shouldn't the young's modulus be close to 200 GPa?

Joel Martis
Bachelor of Technology in Mechanical Engineering (Senior Year)
Indian Institute of Technology Madras

ckloss's picture

ckloss | Mon, 08/24/2015 - 10:57

The Young's modulus can be decreased in DEM - that's what most people do to make simulations run faster.

Best wishes
Christoph

JoshuaP | Tue, 09/01/2015 - 11:02

Hi Christoph,

using lower youngs modulus just works under low stress states? Because I'm trying to load a bulk of particles with 600 kPa and it makes a large difference if I use 1e8 or 4e8 for youngs modulus.

regards
Joshua

ckloss's picture

ckloss | Mon, 09/07/2015 - 14:55

Hi Joshua,

that's clear - if particles get compressed using a standard DEM formulations the assumptions of this standard DEM get violated

Best wishes
Christoph

JoshuaP | Tue, 09/08/2015 - 09:19

Hi Christoph,

I'm not sure what you mean. I can not use LIGGGHTS for simulation of compression tests? I mean there are many papers of uniaxial and triaxial compression tests using DEM codes. Or are assumptions just violated if particles get compressed to much?

kind regards
Joshua

ckloss's picture

ckloss | Thu, 09/24/2015 - 09:38

Hi Joshua,

maybe I was not clear enough - you for sure can simulate compression tests. But standard models will not work for high compressions, e.g. if you compact a loose soil sample by factor 2. Standard DEM models assume the overlaps is small compared to the particle size and contacts are independant from each other. Both assumptions get violated for high compressions

Christoph

RAJ KASHYAP's picture

RAJ KASHYAP | Fri, 09/25/2015 - 11:42

I am using young modulus in the range of e11 using cgs system.But till e7 youngs modulus all is ok .But after that the program slow to large extent.I also play around the time step.
Is thier any limit in liggghts about youngs modulus.

Raj Kashyap