[ANSYS Meshing] Small mesh error: Zero or negative volume for elements. [Explicit dynamics]

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September 14, 2017, 20:19
Small mesh error: Zero or negative volume for elements. [Explicit dynamics]
#1
New Member

matin
Join Date: Nov 2014
Posts: 4
Rep Power: 11
Hello everyone,

I’m getting “Zero or negative volume for element” error, while trying to create a very simple mesh in ANSYS 17.2, using workbench. I’m using the explicit dynamics module to simulate the high velocity impact of a micro-particle on an aluminum plate at velocities up to 10 kms-1. The simulation velocities are in the range of 1 to 10 kms-1. The micro-spherical projectile is steel and the diameter varies from 1 to 10 micrometer. The geometry is very simple, the steel projectile impacts a very thin rectangular aluminum plate, 50 micrometer in thickness. In order to save computational time, as can be seen in the attachment, the target and the projectile are modeled as quarter models by invoking symmetric boundary conditions. I’m interested to study the deformation of the plate and the penetration of the particle into it. The simulation nicely works when I have 20 divisions in each direction, however, I believe some of my results don’t make sense. When I try to further increase the number of divisions to 30 in each direction, I get the following error before even the simulation starts:

Generating External Faces ...... please wait
Zero or negative volume for element 1240 ( 2 )
Zero or negative volume for element 14739 ( 13501 )
Zero or negative volume for element 1242 ( 4 )
Zero or negative volume for element 1243 ( 5 )
Zero or negative volume for element 1245 ( 7 )
Zero or negative volume for element 1246 ( 8 )
Zero or negative volume for element 1247 ( 9 )
Zero or negative volume for element 1248 ( 10 )
Zero or negative volume for element 1249 ( 11 )
Zero or negative volume for element 1250 ( 12 )
Finished model setup with errors...

All the negative and zero volume elements are in the plate. I found the mentioned elements using their corresponding ids, and I don’t think the error is associated with the mesh structure, as it is a very simple hex mesh. I thought maybe some other factors are influencing my case. Maybe the explicit dynamics analysis does not support systems with micron dimensions, which I don’t have enough information about it. Another reason might be the minimum step time which is calculated based on the sound speed and is proportional to the smallest element characteristic dimension. I’m not sure how to control the step time in explicit dynamics, as it has been recommended to let the program take control over it. So, I have no clue at this moment how to overcome this problem and get rid of this error!
I greatly appreciate any help or advice regarding my problem.
Thank you.
Matin
Attached Images
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