Mass density

[AleksaBgd94]

Hi everyone,

which value of mass density should I adopt for steel material?

Everything in my model is defined in mm and N.

I assume that mass density should be in N/mm3 because everything is defined in N and mm, so I calculated the value for mass density of 76.982e-6 N/mm3.

Is there a mistake here?

Thanks

 

[FEA way]

When you use SI(mm) unit system then density should be given in tonne/mm^3. Check Abaqus consistent units tables available in the internet for more information.

 

[StefCon]

Hi,
I think it should be tonne/mm^3. Could 7.6982E-09 tonne/mm^3 be correct?

If the model is fast to solve you could always check the reaction force and compare to expected reaction force.

 

[Erik Panos Kostson]

This is a good link:

https://www.dynasupport.com/howtos/general/consistent-units

 

[AleksaBgd94]

Thank you very much!

I understand it now.

 

[rothers]

I'm not an Abaqus user but shouldn't mass density units be NS^2/mm^4 ?

 

[AleksaBgd94]

The only problem now is that the job is running very slow... Do you have any tips how to solve that problem?

 

[AleksaBgd94]

Yes, rothers. That's correct, it was my mistake.

 

[rothers]

In which case should it be 7.6982e-9 NS^2/mm4 ? (assuming you've used 7698.2 kg/m3 for density).

I like to remember 1 NS^2/mm4 = 1000 kg/mm^3

 

[AleksaBgd94]

It is 7.6982e-9 Ns^2/mm^4 if I use mm as a unit for length and N as a unit for force.

Since 1 N = kgm/s^2 then kg = Ns^2/m or kg=Ns^2/(1000mm).

Mass density which is 7698.2 kg/m3 is 7698.2 Ns^2/1000mm/m^3 = 7.6982 Ns^2/mm/(1000mm)^3 and that is 7.6982e-09 Ns^2/mm^4 or 7.6982e-09 ton/mm^3 because 1 ton = Ns^2/mm. This is why we use ton/mm^3 with N and mm.