Rezone using element-splitting refinement.

Rezoning with element splitting is essential for solving this type of problem properly. Extrusion modeling is critical for simulating accurate physical behavior of the seal. A gradual reduction of element size in the vicinity of the extrusion gap is necessary as the material flow into the gap increases over time.

Use element edge pivots to facilitate extrusion flow.

See the edge pivot shown by (c) in Figure 2.5: Deformation Profile at Load Step 1 -- Substep 20 (First Rezoning). The pivot prevents the elements at the reentrant corner from deforming too severely under compression and can, in general, improve convergence. Providing for a pivot in the starting mesh allows it to remain until the end of the analysis, as element splitting does not change mesh topology.

Perform rezoning early to minimize convergence issues during mapping.

Large stress and strain gradients are not easily equilibrated (MAPSOLVE) and can cause nonlinear convergence issues. The problem may converge better if rezoning is done early enough when the gradients have a lesser chance of occurring.

Performing rezoning too early in the analysis process, however, may be counterproductive as the mesh may not have sufficiently deformed, possibly causing the rezoned mesh itself to deform later in the analysis. It is also difficult to discern regions likely to benefit from rezoning too early in the analysis.

Minimize intersections of transition regions for overlapped meshes.

When element-splitting refinement is used for rezoning, ensure that the transition regions of overlapped rezoned meshes do not intersect to a great degree. Excessive intersections can cause badly shaped elements.

Use nesting during vertical rezoning.

If using vertical rezoning with element splitting, nesting the refinements ensures that transition regions do not overlap, resulting in better element quality. Maintain mesh gradation during the vertical rezoning process to avoid mesh distortion in large strains and to better resolve large stress/strain gradients.

The following figure shows the mesh gradation obtained from nesting the remeshing zones properly:

Figure 2.15: Mesh Gradation Created with Nested Element Splitting During Vertical Rezoning

The mesh area reduces from h to h/64 in three rezoning steps. The nesting scheme ensures that the transition zones do not overlap, and no badly shaped elements occur. Despite the presence of large strains, a remeshing strategy using only element splitting refinement does not create elements with bad aspect ratios, or skew.