Rigid body-mass

[MadEng]

Hello Sir,

I am new to Abaqus, so please help me.

I am using a 3D discrete Rigid body to apply pressure on a 3D deformable body. i will use abaqus explicit dynamic. This Rigid body is fixed in the horizontal direction and can move only in the vertical direction.

In abaqus Explicit dynamic, i need to define a mass for the Rigid body.

in interaction module>> special>> point mass/inertia>> mass

How can i determine the mass of that rigid body? is it the density times the volume?

And if i assume that it is made of steel so the mass will be (the volume * density of steel)?

Please correct me if i am wrong.

Thank you so much.

 

[CrazyMan]

Hi,

You can define density in property stage.

 

[MadEng]

To define a density i need to assign section, however Rigid body does not accept assigning a section.

 

[burningDiesel]

add mass to the reference point

 

[MadEng]

Hello CrazyMan,

I define the density by editing KeyWords for the model:
*Rigid Body, ref node=RF-2, elset=RB-2, position=CENTER OF MASS, Density = 5.12

and after adding the density i got this error message:

The rigid bodies with the reference nodes contained in node set ErrNodeRefNodeNoMass have no mass associated with them and some degrees of freedom of the reference node are not restrained. Either mass must be defined or all of the translational degrees of freedom must be constrained. See the status file for further details.

I am wondering why Abaqus does not calcuate the mass from the dimensions and the input density. Does it mean i need to define the mass also?

Could you please help me.
Thanks

 

[akabarten]

Hi,

Density option in *RIGID BODY keyword affect only rigid elements (R3D3, R3D4).
If you are using those elements you are missing thickness value in *RIGID BODY keyword.

**
*Rigid Body, ref node=RF-2, elset=RB-2, position=CENTER OF MASS, Density = 5.12
 1.0
**

If you are using continuum elements like tetra, penta, hexa,
you need to define standard solid section with a material and next switch those elements into rigid body.
You can use elastic material since it is the easiest to define.

**
*SOLID SECTION, ELSET=RB-2, MATERIAL=steel
*MATERIAL, NAME=steel
*DENSITY
7.85e-09
*ELASTIC
210.0e+03, 0.3
**
*RIGID BODY, REF NODE=RF-2, ELSET=RB-2
**

In this case density from the material will be used to calculate mass of the rigid body.

Regards,
Bartosz

 

[MadEng]

Thank you very much Bartoz.

Let me ask you one last question.
So if i use R3D3 or R3D4, i have to define [thickness], Correct?
Or i can use continum element and then change the section to rigid body.

Thanks

 

[akabarten]

Hi,

So if i use R3D3 or R3D4, i have to define [thickness], Correct?

Yes, if you do not have thickness Abaqus can calculate only area not volume.

For continuum elements (C3D6, C3D8, ...) you need to use *SOLID SECTION + *MATERIAL (with density) + *RIGID BODY.
For shell elements (S3, S4, ...) you need to use *SHELL SECTION (with thickness) + *MATERIAL (with density) + *RIGID BODY.
For rigid elements (R3D3, R3D4) you need to use *RIGID BODY (with density and thickness).

Regards,
Bartosz

 

[MadEng]

Thank you so much.