topic Re: Contact: Orthotropic Friction - Different Friction for Different Directions in Simulation Mechanical Forums (Read-Only)

Contact: Orthotropic Friction - Different Friction for Different Directions

Anonymous — Tue, 09 Aug 2016 19:30:52 GMT

Hello,

I was wondering if there is a way with Autodesk Simulation 2017 to simulate different friction coeficients for each direction.

I know that ANSYS has this functionality as it is shown below.

Even if there isn`t the functionality, do you think I could simulate this somehow?

I actually though about using in one of the part's material an Orthotropic material in which the Young Modulus would be near 0 for the direction I want the friction to be neglected - but still the surface gets reaction forces in that direction.

Any ideas?

Thank you very much.

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4.16.2. Orthotropic Friction

The orthotropic friction model uses two different coefficients of friction in two principal directions (see Frictional Model in the Mechanical APDL Theory Reference for details). It is applicable only to 3-D contact and is available for current-technology contact elements.

Issue the TB,FRIC command with TBOPT = ORTHO or EORTHO to define orthotropic friction, and specify the coefficients of friction, MU1 and MU2, on the TBDATA command.

To define a coefficient of friction that is dependent on temperature, time, normal pressure, sliding distance, or sliding relative velocity, use the TBFIELD command. Suitable combinations of up to two fields can be used to define dependency, for example, sliding relative velocity and normal pressure as shown below:

TB,FRIC,1,,,ORTHO   ! Activate orthotropic friction model
TBFIELD,SLRV,10.0    ! Define first value of sliding relative velocity
TBFIELD,NPRE,200.0   ! Define first value of normal pressure
TBDATA,1,MU1,MU2     ! Define coefficients of friction
TBFIELD,NPRE,250.0   ! Define second value of normal pressure
TBDATA,1,MU1,MU2     ! Define coefficients of friction
TBFIELD,SLRV,20.0    ! Define second value of sliding relative velocity
TBFIELD,NPRE,150.0   ! Define first value of normal pressure
TBDATA,1,MU1,MU2     ! Define coefficients of friction
TBFIELD,NPRE,300.0   ! Define second value of normal pressure
TBDATA,1,MU1,MU2     ! Define coefficients of friction

See Understanding Field Variables for more information on the interpolation scheme used for field-dependent material properties defined using TBFIELD.

The two options TBOPT = ORTHO and EORTHO differ only when the frictional coefficients are defined as a function of sliding distance or sliding velocity. The difference occurs in the way the coefficients are interpolated. For TBOPT = ORTHO, the friction coefficient in each direction is a function of sliding distance or velocity in that direction only. For TBOPT = EORTHO, the friction coefficient in each direction depends upon the magnitude of total sliding or total velocity, thus causing sliding in one direction to affect the friction coefficients in both directions.

To define a coefficient of friction that is dependent on temperature only, use the TBTEMP command as shown below:

TB,FRIC,1,2,,ORTHO	  ! Activate orthotropic friction model
TBTEMP,100.0         ! Define first temperature
TBDATA,1,MU1,MU2     ! Define coefficients of friction at temp 100.0
TBTEMP,200.0         ! Define second temperature
TBDATA,1,MU1,MU2     ! Define coefficients of friction at temp 200.0

Note that if the coefficient of friction is defined as a function of temperature, the program always uses the contact surface temperature as the primary variable (not the average temperature from the contact and target surfaces).

Re: Contact: Orthotropic Friction - Different Friction for Different Directions

marwan_azzam — Wed, 10 Aug 2016 12:29:08 GMT

Hello,

The quick answer is no, friction coefficient is the same in all directions.

What is it that you're trying to model? Perhaps it can be done in another way.

Re: Contact: Orthotropic Friction - Different Friction for Different Directions

John_Holtz — Wed, 10 Aug 2016 12:32:37 GMT

Hi scudelari,

I'm curious what you are trying to model. Is the friction really different in the different directions, or is friction just an approximation of something mechanical?

Perhaps we will have some ideas after understanding what you are trying to model, but the only thought that comes to mind is to use the "results-based load curve" (see the page "Define Load Curves" in the documentation) and change the "friction force" based on the velocity (that is, direction of motion). Since this works with loads that you apply to the model, it requires that you know the magnitude of the friction force and assume that it is uniform over the surface area.

Re: Contact: Orthotropic Friction - Different Friction for Different Directions

Anonymous — Wed, 10 Aug 2016 12:46:10 GMT

Hello to you two!

What I wanted to model is shown below. It is the idealization of the rotation around itself of a crawler crane. And I just want to prove the existence of horizontal pressure on the ground due to the friction of the crane's track sliding on the ground.

The Green part is the soil with large rigidity.

The tracks are linked on the center with movement blocked (except vertically).

The vertical pressure is applied in a slope from 0 to 1 seconds.

The horizontal loads you see underneath are applied from 1 to 5 (they are 0 from 0s to 1s the beginning of the analysis).

There is contact setup between the soil and the tracks, with friction.

The thing is that, in this case, the tracks will simply move on the ground (rotate around the sprockets) on the longitudinal sense. And I want them to move in this direction.

But, since the horizontal loads are towards different directions, and since the center is locked in horizontal movement, the tracks will rotate. And this is the effect I want to capture - the friction loads existing in the ground due to the polar sliding of the tracks.

thanks for your assistance!