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# What is contact damping? When do I need to use contact damping?

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## What is contact damping in Abaqus? | Abaqus contact damping

In Abaqus, contact damping refers to a numerical technique used to control and stabilize contact interactions between surfaces or bodies in a simulation. It helps mitigate instabilities, oscillations, or chatter that may occur due to rapid changes in contact forces or contact conditions.

During contact simulations, the contact forces between surfaces or bodies can undergo rapid changes, especially when there are large relative displacements, high strain rates, or significant material nonlinearities. These rapid changes can lead to numerical instabilities or oscillations, affecting the accuracy and convergence of the analysis.

To address this issue, Abaqus provides the option to introduce contact damping. Contact damping involves adding a damping force or resistance to the contact interface, which helps dampen the high-frequency oscillations and stabilize the contact behavior.

By applying contact damping, Abaqus dissipates energy from the system and reduces the likelihood of unstable or oscillatory contact forces. This helps maintain stability and convergence during contact simulations, particularly in cases where the contact conditions are rapidly changing or highly nonlinear.

Contact damping in Abaqus is a viscous damping force that acts between two contacting surfaces. It can be used to damp relative motions between the surfaces, which can help to improve the convergence of the analysis and reduce spurious oscillations.

Contact damping is defined in the *CONTACT PROPERTY definition. The damping coefficient can be specified as a proportionality constant with units of pressure divided by velocity, or as a unitless fraction of critical damping.

Contact damping is applied in both ABAQUS/Standard and ABAQUS/Explicit. In ABAQUS/Standard, the damping coefficient is applied independent of the open/close state of the contact. In ABAQUS/Explicit, the damping coefficient is only applied when the surfaces are in contact.

Contact damping can be used in a variety of problems, such as:

• Contact problems with large amounts of friction
• Post-buckling problems
• Problems with large deformations
• Problems with material softening
• Problems with multiple load steps that involve significant changes in the stiffness of the model

Contact damping is not always necessary, but it can be helpful in cases where convergence problems or spurious oscillations are observed.

Here are some tips for using contact damping:

• Start with a small damping coefficient and increase it gradually as needed.
• Monitor the contact forces and relative displacements between the surfaces. The damping coefficient should be large enough to damp out any spurious oscillations, but not so large that it prevents the surfaces from contacting or separating properly.
• Be aware that too much contact damping can cause non-physical behavior or even non-convergence.

The contact damping defines viscous damping between two interacted surfaces. You can use this option in the ABAQUS/Standard to damp the surface relative motions during separation or approach. In the ABAQUS/Explicit, it will damp oscillations in softened or penalty contact.

You can use this option when you have convergence issues caused by sudden contact constraints changes like buckling problems containing contact or in some snap-through.

This option is available through GUI and input file (see Figures 1and 2).

Figure 1: Contact damping through GUI, right figure is about depend on the step which method need to be used

Figure 2: Contact damping through the input file, the damping coefficients depend on the problem

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