This example is modeled as a plane strain problem.
The moving and static mating parts are considered to be rigid. The seal bead is modeled as a hyperelastic material.
The seal is chemically bonded (zero applied displacement) to the static rigid mating part, as shown in Figure 2.2: Schematic of Finite-Element Static Elastomeric Seal Assembly with Dimensions.
The pressurization gap is the location for the fluid insertion. The moving rigid mating part moves downward, reducing the 0.02-inch gap to a 0.002-inch gap, at which an extrusion may form.
The notch indicates the region where self-contact in the seal bead is expected to occur.
Three load steps are applied to secure the seal:
The top of the seal is compressed first by moving the rigid part downward by 0.018 inches, leaving a small gap of 0.002 inches at the top (TIME = 0 - 1 s). This load step simulates the first phase of the seal assembly where the rigid mating parts come together to form the seal gland which the seal bead must eventually fill.
The temperature of the seal is increased from the current room temperature (72° F) to 302° F (TIME = 1 - 2 s).
This load step simulates the thermal loading phase, where the seal is allowed to expand laterally, filling most of the clearance gaps.
A uniform pressure of 4000 PSI is applied in the pressurization gap (to all open status contact elements), effectively pressurizing the seal (TIME = 2 - 3 s). This is the pressure exerted by the sealing fluid in the pressurization gap.
This load step simulates the injection of the fluid, which pressurizes the seal laterally. The seal fills all clearance gaps and possibly creates some material extrusion.
The nonlinear sparse solver is used for the solution. A static analysis is required when geometric nonlinearity is present (NLGEOM,ON).
The seal bead is modeled by PLANE182 plane strain (KEYOPT(3) = 2) elements. The elements have full integration with B-Bar formulation (KEYOPT(1) = 0). Mixed u-P formulation (KEYOPT(6) = 1) is specified to counter any chance of volumetric locking (which can occur at high strains).
The contact elements are modeled with CONTA172 with augmented Lagrangian formulation (KEYOPT(2) = 0). The stiffness updates of the contact elements are done at each iteration, based on the mean stress of the underlying solid element (KEYOPT(10) = 0).
The target elements are modeled with TARGE169 elements.
The fixed mating part is chemically bonded to the seal bead, as shown in Figure 2.2: Schematic of Finite-Element Static Elastomeric Seal Assembly with Dimensions. The bonding is modeled by constraining the displacements on the seal bead in the chemically bonded boundaries (D).
The seal bead material is modeled using an Ogden hyperelastic material, as shown in this input fragment:
TB,HYPE, 1, 1, 2, OGDEN TBTEMP,0.000000 TBDATA, 1, 2.80000e+00, 7.90000e+00, -1.86000e+02, TBDATA,4,-1.85000e+00, 1.00000e-05, 0.00000e+00,
For more information about the seal bead material, see Material Properties.
In load step 3, the fluid-penetration loads are applied as a uniform element pressure in the pressurization gap (shown in Figure 2.2: Schematic of Finite-Element Static Elastomeric Seal Assembly with Dimensions). The fluid-penetration loads are applied via the following command sequences:
Specific contact elements (on which the fluid penetration loads are to be applied) are selected as follows:
esel,s,,,2166,2186 esel,a,,,2248 esel,a,,,2250,2261 esel,a,,,2556
The default fluid-penetration starting points are selected as follows:
sfe,all,2,pres,,-1
The third argument is set to 2 to allow the SFE command to specify the starting points for the fluid penetration. The argument -1 specifies that none of the selected element nodes can be considered a starting point for fluid penetration.
The fluid pressure magnitude is specified as follows:
sfe,all,1,pres,,4000
The command specifies a pressure magnitude of 4000 PSI on face 1 (the default face for 2D contact elements) of the selected elements.
The specific fluid-penetration starting points are specified as follows:
sfe,2186,2,pres,,1 sfe,2248,2,pres,,1 sfe,2556,2,pres,,1
The input specifies that the nodes of the contact elements 2186, 2248, and 2556 are starting points, as they are initially exposed to the fluid. Also, depending on the contact status (open or closed), the node can either be a fluid penetrating point (for "open" contact) or can no longer be a starting point (if contact closes).
The manual rezoning process occurs as follows:
/clear,nostart ! clear environment
/file,base ! load the database named 'base'
/solu ! enter solution processor
rezone,manual,2,10 ! start rezoning at load step 2
remesh,start ! start the remeshing
! select a group of elements which need to be refined by
splitting
ESEL,S,ELEM,,6169 ! elements 6169,6175,6182 and 6185 are
ESEL,A,ELEM,,6175 ! are selected. They may be contiguous
ESEL,A,ELEM,,6182 ! or isolated from each other
ESEL,A,ELEM,,6185
remesh,split ! split the selected elements and
! automatically create quad transitions
remesh,finish ! automatically generate BC, loads, temp
! etc on new mesh and generate new contact
! or target elements on new mesh as needed
mapsolve,500, pause ! mapping of state variables and
! residual balancing
finishIn this case, the load step selected to start rezoning is 2. Element-splitting refinement is used to increase the number of degrees of freedom in the selected region to enhance flexibility. All-quadrilateral transition elements are generated to connect the new refined mesh to the old unrefined mesh.
After every rezoning, a multiframe restart is necessary. Issuing a (RESCONTROL,DEFINE,ALL,1) command ensures that restart files are written at all substeps, which potentially enables rezoning at any substep. Issuing an (OUTRES,ALL,ALL) command ensures that the results file is written at every substep; the results at each substep are viewable from within the GUI to determine where rezoning is needed.
Vertical rezoning is used for this problem. Three nested rezonings occur at:
Load step 1, substep 20 (TIME = 0.4 s),
Load step 1, substep 50 (TIME = 0.8996 s), and
Load step 2, substep 10 (TIME = 1.145 s).