Figure 10.10: Interface Layer Mesh with Degenerated Wedge Elements
10.6. Solution Procedure and Result Output.
Gasket material behavior is highly nonlinear. The full Newton-Raphson solution procedure (the standard
ANSYS nonlinear method) is the default method for performing this type of analysis. Other solution
procedures for gasket solutions are not recommended.
As with most nonlinear problems, convergence behavior of a gasket joint analysis depends on the
problem type. ANSYS provides a comprehensive solution hierarchy; therefore, it is best to use the default
solution options unless you are certain about the benefits of any changes.
Some special considerations for solving a gasket problem are as follows:
- By default, a zero stress cap is enforced on the gasket. When the element goes into tension, it loses its
stiffness and sometimes causes numerical instability. - It is always a good practice to place the lower and upper limit on the time step size (DELTIM or NSUBST).
Start with a small time step, then subsequently ramp it up. This practice ensures that all modes and beha-
viors of interest are accurat ely included. - When modeling gasket interfaces as sliding contact, it is usually necessary to include adequate gasket
transverse shear stiffness. By default, the gasket elements account for a small transverse shear stiffness.
You can modify the transverse shear stiffness if needed (TB,GASKET,,,,TSS) command. For better solution
stability, use nodal contact detection. - When modeling gasket interfaces via a matching mesh method (that is, with coincident nodes), it is better
to exclude transverse shear stiffness to avoid unnecessary in-plane interaction between the gasket and
mating components.
Like any other type of nonlinear analysis, the ANSYS program performs a series of linear approximations
with corrections. A convergence failure can indicat e a physical instability in the structure, or it can
merely be the result of some numerical problem in the finite element model. The program printout
gives you continuous feedback on the progress of these approximations and corrections. ( The printout
either appears directly on your screen, is captured on Jobname.OUT, or is written to some other file
[/OUTPUT].) You can examine some of this same information in POST1, using the PRITER command,
or in POST26, using the SOLU and PRVAR commands. Understand the iteration history of your analysis
before you accept the results. In particular, do not dismiss any program error or warning statements
without fully understanding their meaning. A typical output listing with gasket nonlinearity only is
shown in Typical Gasket Solution Output Listing (p. 332). When other types of nonlinearity such as contact
or materials are included, additional information will be printed out.
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationSolution Procedure and Result Output