Description: A true surface-to-surface formulation has been added for finite-sliding contact in ABAQUS/Standard, similar to the surface-to-surface formulations introduced for small-sliding contact and mesh tie constraints in Version 6.5. In contrast to the existing node-to-surface approach, the surface-to-surface approach does not lead to stress oscillations at a contact interface, even for mismatched meshes. In addition, the surface-to-surface approach accounts for surface thicknesses and offsets. The finite-sliding, surface-to-surface formulation has inherent smoothing characteristics that sometimes lead to better convergence behavior than with finite-sliding, node-to-surface contact. It is particularly well-suited to simulations involving contact near corners. The penalty constraint enforcement method (see “Penalty method for contact enforcement in ABAQUS/Standard,” Section 11.1) is used by default for this new formulation.

The node-to-surface formulation remains the default, but you are encouraged to use the surface-to-surface formulation. In some cases the surface-to-surface approach can result in significantly increased computational cost; see “Defining contact pairs in ABAQUS/Standard,” Section 29.2.1 of the ABAQUS Analysis User's Manual, for further discussion of computational cost and a comparison of characteristics of the various contact formulations. Additional contact formulation details are discussed in “Contact formulation for ABAQUS/Standard contact pairs,” Section 29.2.2 of the ABAQUS Analysis User's Manual.

Converting a preexisting model that uses a traditional node-to-surface contact formulation to use a surface-to-surface formulation involves a very simple change to the model definition, although additional changes to the model may be required for a successful analysis. The differences in computed penetrations with the different contact formulations can sometimes fundamentally affect results. This is due to the surface-to-surface formulation considering contact conditions in an average sense over a finite region, whereas the node-to-surface formulation only considers contact conditions at slave nodes. Figure 11–1 shows a case in which the two contact formulations behave fundamentally differently due to the different approaches to computing penetrations. Both formulations converge to the same behavior as the mesh is refined. Various aspects of preexisting models, such as the friction coefficient or the pressure-overclosure relationship, may have been inadvertently “tuned” to the behavior that occurs with the node-to-surface formulation. Be aware of this possibility when converting models to the new contact formulation. See “Common difficulties associated with contact modeling in ABAQUS/Standard,” Section 29.2.11 of the ABAQUS Analysis User's Manual, for further discussion.

Interaction module: 
   InteractionCreate: Surface-to-surface contact (Standard): Sliding formulation: 
   Finite sliding: Constraint enforcement method: Surface to surface
   InteractionCreate: Self-contact (Standard): Constraint enforcement method: 
   Surface to surface