Session 11

MEEG 481 / MEEG 681
Computer Solution of Engineering Problems
Computer Session 11

Nonlinear Analysis of a 2-D Rubber Seal

In this session we will simulate large deformation (stresses and deflections) of a rubber seal and its contact process with a trunk door when being pushed in. The complex shape of the seal also leads to rubber-rubber surface contact.

The purpose of the analysis is to examine the stresses and deflections created within the rubber
during the closing of a door. The seal is made of a rubber material and therefore is modeled using hyperelestic material properties. Since the trunk door is much stiffer than rubber seal, the trunk door will be modeled as a rigid body. Additionally, the rubber seal will come in contact with itself. This contact must be taken
into accout explicitly, otherwise the seal will pass through itself.

New features

Hyper-elastic material using Mooney-Rivlin model
Rigid-elastic body contact
Elastic-elastic body contact
Multiple domains (rubber seal vs trunk door)

Steps in a contact analysis:

The basic steps for performing a typical surface-to-surface contact analysis are listed below:
(See Structural Analysis Guide, Section 9.4. Performing a Surface-to-Surface Contact Analysis. GUI: Modeling > Create > Contact Pair > Contact Wizard )

Create the model geometry and mesh.
Identify the contact pairs.
Designate contact and target surfaces.
Define the target surface.
Define the contact surface.
Set the element key options and real constants.
Define/control the motion of the target surface (rigid-to-flexible only).
Apply necessary boundary conditions.
Define solution options and load steps.
Solve the contact problem.
Review the results.

Designating contact and target surfaces:

Contact emelents are constrained against penetrating the target surface. However, the target elements can penetrate through the contact surface.

For rigid-to-flexible contact, the designation is obvious: the target surface is always the rigid surface and the contact surface is always the deformable surface.

For felxible-to-flexible contact, the guidelines are:

If a convex surface is expected come into contact with a flat or concave surface, the flat/concave surface should be the target surface.
If one surface has a fine surface mesh and, in comparison, the other has a coarse mesh, the fine mesh should be the contact surface and the coarse mesh should be the target surface.
If one surface is stiffer than the other, the softer surface should be the contact surface.

Pre-processing notes:

The ANSYS input file used in Spring 2002.

The model creation consists of six phases.

The different phases are:

PHASE I: Creating the Geometry for the rubber seal and the trunk beam
PHASE II: Define material and element properties for these finite elements
PHASE III: Creating the finite element mesh for the rubber seal and rigid body
PHASE IV : Modelling the Trunk to Seal Contact (rigid-elastic contact). Note that a pilot node (node 10000) is introduced to model the trunk movement. A "pilot node" is really an element with one node, whose motion governs the motion of the entire target surface (trunk). You can think of a pilot node as a handle for the rigid target surface. Forces/moments or rotations/displacements for the entire target surface can be prescribed on just the pilot node. The pilot node can be one of the nodes on the target element or a node at any arbitrary location. If you define a pilot node, ANSYS checks for boundary conditions only on the pilot node and ignores any constraints on other nodes.
PHASE V: Modelling the Seal to Seal contact (elastic-elastic contact),
Three pairs in total. For each pair, the target surface and contact surface are identical.
PHASE VI: Apply loads and boundary conditions to the model

The ANSYS log files:
Seal-MR.part1 (Phase I - III),
Seal-MR.part2 (Phase IV: Create contact pairs: Trunk to Seal),
Seal-MR.part3 (Phase V: Create contact pairs: Seal-to-Seal self contacts within the hole, Seal to Seal-support contacts (2 pairs)),
Seal-MR.part4 (Phase VI) ,
are made to give you essentially step-by-step instructions. Solution substeps:


 SOLUTION HISTORY INFORMATION FOR JOB: seal.mntr

======================== 2001 ===========================================================
 ANSYS RELEASE  5.6             .2      17:34:47    04/30/2001

 LOAD SUB-  NO.   NO.  TOTL   INCREMENT    TOTAL       VARIAB 1    VARIAB 2    VARIAB 3
 STEP STEP  ATTMP ITER ITER   TIME/LFACT   TIME/LFACT  MONITOR     MONITOR     MONITOR
                                                       CPU         MxDs        MxPl

   1     1    1     1     1   0.50000E-01 0.50000E-01  19.750     -.35000E-01 0.78886E-30
   1     2    1     1     2   0.50000E-01 0.10000      37.470     -.70000E-01 0.78886E-30
   1     3    1    11    13   0.75000E-01 0.17500      149.45     -.12250     0.78886E-30
   1     4    3     9    42   0.18750E-01 0.19375      430.70     -.13562     0.78886E-30
   1     5    1     3    45   0.18750E-01 0.21250      467.09     -.14875     0.78886E-30
   1     6    1     5    50   0.28125E-01 0.24062      522.28     -.16844     0.78886E-30
   1     7    1     7    57   0.28125E-01 0.26875      596.30     -.18813     0.78886E-30
   1     8    1     8    65   0.28125E-01 0.29688      679.88     -.20781     0.78886E-30
   1     9    1     5    70   0.42188E-01 0.33906      735.54     -.23734     0.78886E-30
   1    10    1     9    79   0.63281E-01 0.40234      832.39     -.28164     0.78886E-30
   1    11    1    11    90   0.63281E-01 0.46563      948.03     -.32594     0.78886E-30
   1    12    1    12   102   0.63281E-01 0.52891      1076.8     -.37023     0.78886E-30
   1    13    1    11   113   0.63281E-01 0.59219      1188.7     -.41453     0.78886E-30
   1    14    1     9   122   0.63281E-01 0.65547      1282.0     -.45883     0.78886E-30
   1    15    1     8   130   0.94922E-01 0.75039      1366.1     -.52527     0.78886E-30
   1    16    1    11   141   0.14238     0.89277      1478.1     -.62494     0.78886E-30
   1    17    2     8   160   0.53613E-01 0.94639      1704.6     -.66651     0.78886E-30
   1    18    1    11   171   0.53613E-01  1.0000      1822.1     -.70925     0.78886E-30

 SOLUTION HISTORY INFORMATION FOR JOB: seal.mntr

=================== 2005 ========================================================
 ANSYS RELEASE  5.7             .1      21:06:57    11/16/2005

 LOAD SUB-  NO.   NO.  TOTL   INCREMENT    TOTAL       VARIAB 1    VARIAB 2    VARIAB 3
 STEP STEP  ATTMP ITER ITER   TIME/LFACT   TIME/LFACT  MONITOR     MONITOR     MONITOR
                                                       CPU         MxDs        MxPl

   1     1    1     1     1   0.10000     0.10000      7.1750     -.70000E-01 0.78886E-30
   1     2    2     1    12   0.50000E-01 0.15000      49.823     -.10500     0.78886E-30
   1     3    2    11    33   0.25000E-01 0.17500      128.82     -.12250     0.78886E-30
   1     4    1     9    42   0.25000E-01 0.20000      164.81     -.14000     0.78886E-30
   1     5    1     5    47   0.37500E-01 0.23750      185.93     -.16625     0.78886E-30
   1     6    1    10    57   0.56250E-01 0.29375      225.15     -.20563     0.78886E-30
   1     7    1     8    65   0.56250E-01 0.35000      258.57     -.24500     0.78886E-30
   1     8    1    12    77   0.84375E-01 0.43438      307.79     -.30406     0.78886E-30
   1     9    1    15    92   0.84375E-01 0.51875      366.90     -.36313     0.78886E-30
   1    10    1    14   106   0.84375E-01 0.60313      419.83     -.42219     0.78886E-30
   1    11    1    11   117   0.84375E-01 0.68750      462.56     -.48125     0.78886E-30
   1    12    1     8   125   0.84375E-01 0.77187      494.20     -.54031     0.78886E-30
   1    13    1     9   134   0.12656     0.89844      529.71     -.62891     0.78886E-30
   1    14    2     8   155   0.50781E-01 0.94922      633.85     -.66872     0.78886E-30
   1    15    1    11   166   0.50781E-01  1.0000      676.66     -.70904     0.78886E-30

Results: Total push down = (-0.07,-0.7)

The following plots are done with following settings:
contour > nodal solution > stress - von Mises
Utility > Plot control > Symbols > surface load symbols = pressure

At 10% of push down

At 53% of push down

At 75% of push down

At 100% of push down

Reaction force on the Trunk
Reaction force on trunk is computed using: List > reaction force and by selecting the pilot node (node=10000)