Dear Hiba,

In Abaqus, there is no unit definition for input and output parameters (every thing is relative). In other word, the unit of your output parameter is dependent on the unit of your input parameters.

As an example, consider a simple linear elastic case. For such a problem, you need elastic modulus and Poisson's ratio as input parameters. Assume that elastic modulus is E = 5 GPa (5,000,000,000 N / m2) and Poisson's ratio is v =0.3. If you pick meter as the unit of length and Newton as the unit of force, then your input parameters would be:

E = 5,000,000,000

v = 0.3

Consequently, your output parameters will have the following units:

displacement  => meter (m)

reaction force => newton (N)

If you pick micro-meter as the unit of length and milli-Newton as the unit of force, then your input parameters would be:

E = 5

v = 0.3

Consequently, your output parameters will have the following units:

displacement  => micro-meter (um)

reaction force => milli-newton (mN)

If you pick milli-meter as the unit of length and Newton as the unit of force, then your input parameters would be:

E = 5,000

v = 0.3

Consequently, your output parameters will have the following units:

displacement  => milli-meter (mm)

reaction force => newton (N)

Note that as Poisson's ratio is a dimensionless parameter, it will be always the same.

Best regards,

Farid Alisafaei

Hi Hiba,

Since your length is specified in mm and density in kg/mm3, It makes sense to use modulus of elasticity in N/mm2.  Or you convert and specify your length in m and density in kg/m3, then you can specify modulus of elasticity in MPa which is nothing but 106 N/m2.

Dear Hiba,

In Abaqus, there is no unit definition for input and output parameters (every thing is relative). In other word, the unit of your output parameter is dependent on the unit of your input parameters.

As an example, consider a simple linear elastic case. For such a problem, you need elastic modulus and Poisson's ratio as input parameters. Assume that elastic modulus is E = 5 GPa (5,000,000,000 N / m2) and Poisson's ratio is v =0.3. If you pick meter as the unit of length and Newton as the unit of force, then your input parameters would be:

E = 5,000,000,000

v = 0.3

Consequently, your output parameters will have the following units:

displacement  => meter (m)

reaction force => newton (N)

If you pick micro-meter as the unit of length and milli-Newton as the unit of force, then your input parameters would be:

E = 5

v = 0.3

Consequently, your output parameters will have the following units:

displacement  => micro-meter (um)

reaction force => milli-newton (mN)

If you pick milli-meter as the unit of length and Newton as the unit of force, then your input parameters would be:

E = 5,000

v = 0.3

Consequently, your output parameters will have the following units:

displacement  => milli-meter (mm)

reaction force => newton (N)

Note that as Poisson's ratio is a dimensionless parameter, it will be always the same.

Best regards,

Farid Alisafaei

What you need is consistency of units. So, as Rajeev says, since you use mm in other units then you should stay with mm and so use N/mm2

If you mix units then

However, be aware that if you use N, mm and kg, you time unit will change:

1N = 1m kg/s² = 1mm kg/ (new unit)²

so your new unit time will contain an awkward sqrt(1000). This may be of no concern if you have no time-dependent quantities, but if you have, it will make for a terrible mess...

It might be better to use mN as force unit or to switch to a unit system of mm, g, ms.

Thanks a lot for all your responses , it is very helpful for me but could you Mr.Martin Baeker correct me if I am wrong ..so if I have E=1500 MPa I have to use E=1500000 mN/mm2 to avoid that terrible mess since I have a time -dependent quantities ....

Sincerely,

Dear Hiba,

I always recommend  to introduce all the dimensions in mm and forces in N

Then what you will have is stress in (N/mm2)=(N/(m*1000)2)(1,000,000*N/m2)=1,000,000*Pa=MPa

But it is very important to introduce mass in tones (1000 kg) and density as Tones/mm3 because F=ma >>> N=mass*mm/s2 >>>mass=N*s2/mm.We already know that N=kg* m/s2. Therefore mass=(kg*m/s2)*s2/mm=1000kg. 

By using these units you don't need to be worried about your numbers.

@Hiba

As I said, that's one possibility. The other is to switch to mm, g, ms, which again gives you Newton and MPA for forces and stresses. Or you can use the system recommended by Nariman (which is however a bit awkward if you have things like heat capacity).

The important thing in my opinion is to be able to check a system of units on your own - sooner or later you'll encounter some quantity which has a weird dimension (like MPa sqrt(m) in fracture mechanics).

Hi Mr. Martin Baeker

If my input units in abaqus 6.14 are as follow

Density = kg/mm^3

Young,s Modulus = Gpa

Length =mm

Time = mili_second

Mass= Kg

Force = KN

Gravity = Kg/sec^2

Energy = KN-mm

Stress = Gpa

1: are they all correct?

2: what are the output units for each of them please mention each one?

Chekc for yourself, this is simple math, really.

Hi dear researcher

If you are using dimension in mm, you have to consider the stress as MPa. Then, your force will be in N. Please refer to consistent units in Abaqus.

Warmest Regards

Vahid

Hi Hiba,

I believe this photo can help you. You can chose the system you like.

The units of Abaqus are specified by you and this is a nice approach allowing a lot of flexibility. Abaqus assumes you use consistent units. It does not matter which units you use, as they match with each other.