Behavior normal to the surfaces

The distance separating two surfaces is called the clearance. The contact constraint is applied in Abaqus when the clearance between two surfaces becomes zero. There is no limit in the contact formulation on the magnitude of contact pressure that can be transmitted between the surfaces. The surfaces separate when the contact pressure between them becomes zero or negative, and the constraint is removed. This behavior, referred to as “hard” contact, is the default contact behavior in Abaqus and is summarized in the contact pressure-clearance relationship shown in Figure 1.

Figure 1. Contact pressure-clearance relationship for “hard” contact.

By default, “hard” contact is directly enforced when using contact pairs in Abaqus/Standard. The dramatic change in contact pressure that occurs when a contact condition changes from “open” (a positive clearance) to “closed” (clearance equal to zero) sometimes makes it difficult to complete contact simulations in Abaqus/Standard; the same is not true for Abaqus/Explicit since iteration is not required for explicit methods. Alternative enforcement methods (e.g., penalty) are available for contact pairs, as discussed in Contact constraint enforcement methods in Abaqus/Standard. Penalty enforcement of the contact constraints is the only option available for general contact. Other sources of information include Common difficulties associated with contact modeling in Abaqus/Standard, Common difficulties associated with contact modeling using contact pairs in Abaqus/Explicit, the “Modeling Contact with Abaqus/Standard” lecture notes, and the “Advanced Topics: Abaqus/Explicit” lecture notes.