Units assistance for loading of parts

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SUMMARY

The discussion focuses on unit consistency in Abaqus modeling, specifically regarding dimensions, density, and applied forces. The user initially entered dimensions in millimeters and density as 2.5 g/cm³, which should be converted to 2.5e-9 tonne/mm³ for accuracy. The correct units for applied force are Newtons (N), not pressure force, and the user was advised to maintain clarity by following international standards for unit notation. Strain is confirmed as dimensionless and does not require unit conversion.

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  • Basic principles of mechanics, including force and strain
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Corsan
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Hi all,

I am building a model in Abaqus and wondered if someone could assist with the units I need to enter.

I have built my parts using mm as the dimension, i.e. part is 10 units (mm) wide.

(To clarify this can also be entered as metres as in 10e-3, however I chose to be consistent with the mm approach).

Then for my material data I have entered my mass as 0.0025 (which was 2.5g/cc).
Youngs Modulus as 72000 and for the Plastic data I have entered my yield stress data as MPa (such as 425 with a plastic strain of 0.0090 (mm-3)).

As I wasn't consistent in using the SI measurements for mm (e-3) does this have a knock on effect for the above data?

Now for my loading of my parts can anyone clarify what I will need to enter for a 5000N load (pressure force)?

Thanks in advance
 
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Corsan: 2.5 g/cm^3 is called density, not mass. Enter your density in units of tonne/mm^3; i.e., 2.5e-9 tonne/mm^3, where 1 tonne = 1000 kg. Everything else you did currently sounds correct, except perhaps for strain. Applied force is called force, not pressure force. Pressure is in units of MPa. Enter your applied force in units of Newtons; i.e., 5000 N. In summary, use N, mm, MPa, tonne.

Strain is dimensionless. Therefore, strain does not change, regardless of the units. Therefore, I am not sure why you wrote mm^-3 after your strain value.

By the way, always leave a space between a numeric value and its following unit symbol. E.g., 5000 N, not 5000N. See the international standard for writing units[/color] (ISO 31-0[/color]). Or see any credible textbook.
 
Last edited:
nvn said:
Corsan: 2.5 g/cm^3 is called density, not mass. Enter your density in units of tonne/mm^3; i.e., 2.5e-9 tonne/mm^3, where 1 tonne = 1000 kg. Everything else you did currently sounds correct, except perhaps for strain. Applied force is called force, not pressure force. Pressure is in units of MPa. Enter your applied force in units of Newtons; i.e., 5000 N. In summary, use N, mm, MPa, tonne.

Strain is dimensionless. Therefore, strain does not change, regardless of the units. Therefore, I am not sure why you wrote mm^-3 after your strain value.

By the way, always leave a space between a numeric value and its following unit symbol. E.g., 5000 N, not 5000N. See the international standard for writing units[/color] (ISO 31-0[/color]). Or see any credible textbook.

Thank you for the response, that was exactly what I was looking for.
Appreciate the tip on units too :smile:
 

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