Special Types of Contact Problems
Interference Fit
Interference fits can be analyzed using contact modeling. This is necessary if you are interested in checking the connection with respect to, for example, slipping or local stresses.
There are two possible approaches for modeling interference fits, both equally valid:
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The actual geometry of the two parts before assembly is modeled. In this case, there will be some overlap between the two domains.
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A nominal geometry in which the contacting boundaries have the same location is created. In this case, the overlap is described as part of the contact modeling.
An imported CAD geometry can use either of these approaches, depending of the strategy used during the geometry creation. Often, the geometrical parts are modeled as nominal, and instead equipped by tolerance information that describe the amount of interference.
True Geometry
With a true geometry, you can often immediately solve the contact problem. Sometimes convergence problems may, however, appear, in particular if the material model is nonlinear. The cause is often that the initial overlap is too far from the final solution.
To deal with such a problem, add an offset in the settings for the Contact node. The offset should be defined by a parameter, so that the boundaries of the two domains are barely in contact in the initial state. Now, the offset can be reduced to zero step-by-step, using an auxiliary sweep in the solver.
Nominal Geometry
When working with a nominal geometry, you always need to add an offset in the Contact node. The offset equals the size of the interference. If needed for convergence reasons, ramp up the offset using an auxiliary sweep in the solver.
Interference Fit Connection in a Mountain Bike Fork: Application Library path Structural_Mechanics_Module/Contact_and_Friction/mountain_bike_fork
Self-Contact
To model self-contact, include the same boundaries in both the source and destination selections of the Contact Pair definition. This will cause the boundaries to act as both source and destination in the contact search and mapping. For mechanical contact, this results in a unbiased (or symmetric) contact formulation, as the contact conditions are formulated on both sides of the contact pair. Note that a source is not allowed to partially intersect the destination when used for mechanical contact.
This technique to model self-contact means that some of the considerations discussed in this chapter regarding contact modeling do not apply. For example, instead of the recommendations in Meshing for Contact Analysis, it is recommended to use a uniform mesh element size along the contacting boundaries. Self-contact is a case where it might be necessary to increase the quadrature order used in the weak equations, see Quadrature Settings.
For examples of self-contact problems, see
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Self-Contact of a Loaded Spring: Application Library path Structural_Mechanics_Module/Contact_and_Friction/loaded_spring_contact.
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Contact Analysis of a Rubber Boot Seal: Application Library path Nonlinear_Structural_Materials_Module/Hyperelasticity/rubber_boot_seal.