Assigning elements in Mesh and Material property.

[Souhardya Roy]

"3520 linear quadrilateral elements of type R3D4 were used to mesh the upper and lower rigid plates. The deformable foam model with dimensions of 10*10*10 mm was meshed using 8000 linear hexahedral C3D8R components. Isotropic and elastoplastic foam compressive behavior was assumed." This is an excerpt from a study paper that I'm trying to validate. I'm having difficulty assigning elements in meshing as mentioned in the text. Also, please advise me on the material properties and parameter values I should utilise for closed cell foams?

 

[FEA way]

What problems do hou have with meshing ?

For material properties you should search the research papers. There are different kinds of foams and different approaches to their modeling.

 

[Souhardya Roy]

Yeah, I figured out material category of my foam. It falls under the crushable foam part. I assigned the following (attached as png files) values for the foam based on chatGPT and research papers. But I am getting the following error:

"*crushable foam requires the use of *elastic,type=iso*
*crushable foam requires the use of *crushable foam hardening
6250 elements have been defined with zero hour glass stiffness. You may use *hourglass stiffness or change the element type. The elements have been identified in element set ErrElemZeroHourGlassStiffness.
6250 elements are missing elastic property reference. The elements have been identified in element set ErrElemMissingElasticPropRef.
Porous elasticity must have a nonzero (positive) tensile limit when used with *foam,hardening=exponential
Analysis Input File Processor exited with an error."

What should I do next? Please guide. All the units are in ton, mm, Mpa. And I have used tie constraint as interaction between the surfaces.

 

[FEA way]

You have to add elasticity (Young’s modulus and Poisson’s ratio) as well.

 

[Souhardya Roy]

I did it. Gave E=16MPa and meu=0.33. Now it's giving the following error : The uniaxial plastic strain at first yield must be zero

*CRUSHABLE FOAM PLASTICITY YIELD SURFACE CANNOT BE CONSTRUCTED DUE TO BAD INPUT PROPERTIES: k = 3.0000 kt = 2.0000

Analysis Input File Processor exited with an error. There is a problem with the Compressive yield stress ratio and hydrostatic yield stress ratio.

 

[Souhardya Roy]

I changed the values of the compressive yield stress and the uniaxial plastic strain to 2 and 1.5 respectively. And the second error got resolved. Now the error is : "The uniaxial plastic strain at first yield must be zero
Analysis Input File Processor exited with an error."
How to make the uniaxial plastic strain at first yield zero?

 

[FEA way]

This refers to crushable foam hardening definition. The first value of plastic strain in the table must be 0.

 

[Souhardya Roy]

How will I get the subsequent values?

 

[FEA way]

Look for some research papers, that’s pretty much the only way (apart from the documentation examples) if you don’t perform physical tests and want to use physically accurate values.