Guidelines for handling contact in simulations
It's not uncommon to analyze a mechanism in which components initially touch or later come into contact.
Simulation software automates most of the setup and control of contact analyses, but still lets users customize default settings as needed.
Apply necessary loads and constraints. Although it may seem realistic to "leave parts free to fly around" and come into contact, contact analyses are often greatly simplified by partially restraining parts. Take a pin that passes through a yoke and clevis, for example. Applying constraints prevents the pin from rotating and thereby reduces chattering.
Run the analysis. Most processors generate messages on the status of contact analysis during a solution. Problems, such as slow convergence, can be spotted, letting the user stop the analysis, adjust parameters, and restart.
Review results. When two smooth surfaces contact, they create a relatively smooth stress contour. However, nonsmooth surfaces with a coarse mesh produce less uniform stress contours. In such cases, users must refine or modify the mesh and analyze the model again. No single set of contact-parameter values provides an accurate solution for all models. Many problems solve without difficulty using automatic and default settings, while some models benefit from changes to controlling parameters. Hence, you must understand the purpose of each parameter to determine a proper set of values for the given problem.
When encountering convergence problems or poor results from a contact analysis, carefully check the geometry, mesh, material properties and all contact parameters. As with all CAE analyses, simplify where possible.
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What to adjust when looking for contact Contact stiffness is calculated from the geometry and material properties of the parts in the contact pair. A custom value can be specified. It will be adjusted based on contact status, such as penetration or none, to provide improved accuracy and convergence. Contact tolerance is the distance between any two nodes on surfaces that may contact. The software applies a contact stiffness when the two nodes are within the tolerance. Contact interaction distance tells the software to consider contact calculations when two surfaces are closer than this value. Maximum penetration distance tells the software not to calculate surface contact when a point on a secondary surface is farther away than this value. Maximum initial distance is an initial distance between elements. When greater than this value, contact is not created. It limits the amount of checking the software must do for contact and thus speeds the analysis. Extend contact element sides can specify the length for extending contact-element boundaries. It's used to resolve incorrect penetration. |
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