How to adjust for Volumetric Locking affects?

kirstenbraunkirstenbraun Member
edited November 16 in Structures

Hello all,

I am currently busy with developing a 3D model of a tyre in ANSYS Mechanical.

MODEL DETAILS

The following are the connections. The frictional contact has a friction coefficient of 0.64 which is the frictional coefficient between rubber (tyre tread) and stainless steel (road).

A. The origin of the model sits at [x, y, z] = [0, 0, 0]mm and is at the center of the tyre:

B. To ensure that the tyre rim is treated as static the displacement [x, y, z] = [0, 0, 0]mm as follows is applied to the faces of the sidewalls which come in contact with the rim:

C. The internal pressure as said before is applied to the internal surface of the tyre. The image below is a section of the tyre, just so you can see on which surfaces the pressure is applied to.

D. And a remote displacement is applied to the road surface along the tyre-road interface:

As I have the vertial force-displacement curve of the experimentally tested tyre I can input the vertical displacement value and thoguh using a force reaction probe and a deformation probe I can collect the vertical force and displacement that my model experiences.

The force reaction probe:

where the "Coordinate System" is as follows:

The defomration probe then sits at the same point as the force reaction probe:

SIMULATION RESULTS

At the moment I am trying to match my models results to existing experimental data of Vertical Force versus Vertical Displacement. Below are the results showing the simulation results for a 2Bar and 0.8Bar (0 camber angle) case in pink dotted lines, and the existing data in the four different coloured solid lines representing cases with the variable veriations in inflation pressure and camber angle.

FINDINGS AND MODEL ADJUSTMENTS

As you can see the model approximates the behaviour of the 2Bar ad 0.8Bar, 0 camber case very well up to a point, thereafter the relationhsip unrealisticly increases. I have tried the following to try reduce this affect but nothing has worked:

  1. Changed the integration method to Reduced to adjust for shear locking - minor differences found in the results
  2. Changed the integration method to Full to adjust for possible Hourglass mode - minor differences found in the results
  3. Visually checked for the Hourglass mode (which is seen as staggered lines in the total deformation result) - not present in the result and thus concluded that it is not present
  4. Refined the mesh - simualtion time was dramaticlly high and in the end wasnt able to solve completely
  5. Alter the material properties of the rubber parts of the tyre - the model no longer was able to match the existing experimental data as well as before
  6. Changed the Bonded contacts between two objects which have relative motion between them to Frictional Contacts - minor differences found in the results
  7. Changed the displacement defined as B above (the [x, y, z] = [0, 0, 0] of the rim to a remote displacement as well as a cylindrical support - the remote displacement simualtion did not solve and the cylindrical support could not be applied as the rim geometry is not a cylinder itself and was not able to select apropriate faces for the support.

QUESTION

I still believe that my model is still subjected to volumetric locking affects. According to the paper found here: http://engineeringdesignanalysis.blogspot.com/2011/03/volumetric-locking-in-finite-elements.html, the follwoing alterations can be made to reduce the volumetric locking affect.

1] Use Reduced Integration: It has fewer volumetric constrains [THIS DID NOT SOLVE THE PROBELM]

2] Use of Selective Reduced Integration: It treats the volumetric and deviatoric parts of stiffness matrix separately.

3] Use of B-Bar method: Similar to selective reduced integration. But instead of separating volume integral into two parts, the definition of strain is modified.

4] Use of Hybrid Elements: They work by including the hydrostatic stress distribution as an additional unknown variable, which must be computed at the same time as the displacement field. This allows the stiff terms to be removed from the system of finite element equations.

5] Reduced Integration with Hourglass Control: Artificial stiffness is added to the element which constrains the hourglass mode.

My question is: Are the model adjuestments (2 - 5 above) possible in ANSYS, and if so how?

I am not sure what else I can do to try reduce the stiffining affect which occurs in my results. Any recommendations would be greatly appreciated.

Thank you

Answers

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