# Gap-dependent scale factor The scale factor $s _ { g a p }$ controls contact stabilization as a function of the local separation distance between surfaces. By default, this factor is unity for zero gap distance and is zero when the gap distance is greater than or equal to a characteristic surface dimension. You can control the gap distance at which $s _ { g a p }$ becomes zero. Specifying a large value for this threshold distance is not recommended because of the tendency to increase solution cost per iteration (due to increased connectivity) as the threshold distance increases. Input File Usage: \*CONTACT STABILIZATION, RANGE=distance Abaqus/CAE Usage: Interaction module: Interaction→Contact Stabilization→Create: Zero stabilization distance: Specify: distance # Hierarchy of contact stabilization definitions The interface discussed above is the recommended method for specifying contact stabilization for general contact; however, contact stabilization can be introduced for general contact interactions in two other ways. The order of precedence in cases of overlap is as follows: • First priority is given to the contact stabilization assignment options discussed in this section. • Second priority is given to the contact stabilization assignment options discussed in “Automatic stabilization of rigid body motions in contact problems” in “Adjusting contact controls in Abaqus/Standard,” Section 36.3.6. • Third priority is given to the default contact stabilization discussed in “Contact at a single point” in “Common difficulties associated with contact modeling in Abaqus/Standard,” Section 39.1.2. # 36.2.6 NUMERICAL CONTROLS FOR GENERAL CONTACT IN Abaqus/Standard Products: Abaqus/Standard Abaqus/CAE # References • “Defining general contact interactions in Abaqus/Standard,” Section 36.2.1 • \*CONTACT • \*CONTACT FORMULATION • \*CONTACT CONTROLS • “Specifying master-slave assignments for general contact,” Section 15.13.6 of the Abaqus/CAE User’s Guide, in the HTML version of this guide # Overview Numerical controls associated with the general contact algorithm in Abaqus/Standard: • should not be modified from their default settings for the majority of problems; • can be used for problems where the default settings do not provide cost-effective solutions; • can be used to control the master-slave roles and the sliding formulation; and • in some cases can be applied selectively to particular regions within a general contact domain. # Contact formulation The general contact algorithm uses the finite-sliding, surface-to-surface contact formulation, which is discussed in “Contact formulations in Abaqus/Standard,” Section 38.1.1. Other contact formulations are not available for general contact in Abaqus/Standard. # Constraint enforcement method The general contact algorithm uses a penalty method to enforce active contact constraints by default. Other constraint enforcement methods can be specified as part of the surface interaction (i.e., contact property) definition, as discussed in “Contact constraint enforcement methods in Abaqus/Standard,” Section 38.1.2. Assignment of contact properties to general contact interactions is discussed in “Contact properties for general contact in Abaqus/Standard,” Section 36.2.3. # Numerical controls for friction Numerical controls associated with friction are discussed in “Frictional behavior,” Section 37.1.5. # Beam-to-beam contact Activation of beam-to-beam contact is discussed in “Defining general contact interactions in Abaqus/Standard,” Section 36.2.1. # Master and slave roles The surface-to-surface contact formulation used by general contact generates individual contact constraints using a master-slave approach, as discussed in “Contact formulations in Abaqus/Standard,” Section 38.1.1. Abaqus/Standard assigns default pure master-slave roles for contact involving disconnected bodies within the general contact domain. Internal surfaces are generated automatically using the naming convention General\_Contact\_Faces\_k, where k corresponds to an automatically assigned component number. By default, the lowered-number component surfaces will act as master surfaces to the higher-numbered component surfaces. You can determine the default pure master-slave roles by viewing the automatically generated internal surfaces in the Visualization module of Abaqus/CAE (see Chapter 78, “Using display groups to display subsets of your model,” of the Abaqus/CAE User’s Guide). Self-contact within a body is treated with balanced master-slave contact by default, with each surface node acting as a master node in some constraints and as a slave node in other constraints. For example, if the general contact domain spans three disconnected bodies, the following three internal “component-surfaces” for general contact are created automatically: • General\_Contact\_Faces\_1 • General\_Contact\_Faces\_2 • General\_Contact\_Faces\_3 By default, the first surface listed acts as a master to the other two, and General\_Contact\_Faces\_2 acts as a master to General\_Contact\_Faces\_3. Self-contact within each of these three surfaces is modeled with balanced master-slave contact by default. # Specifying non-default master-slave roles You can override the default master-slave roles by specifying pure master-slave roles or by specifying that balanced master-slave contact should be used. The default master-slave treatment works well in most cases. Keep the following points in mind when modifying the master-slave assignments, in addition to other factors discussed in this section: • Do not use the internally generated component surfaces when assigning alternative master-slave roles (instead, use surface names that you define). • The master-slave role assignments are part of the model definition and cannot be modified from step to step. • The guidelines for assigning pure master-slave roles for contact pairs discussed in “Defining contact between two separate surfaces” in “Defining contact pairs in Abaqus/Standard,” Section 36.3.1, are also applicable for situations in which you reassign pure master-slave roles for general contact. • The limitations of balanced (symmetric) master-slave contact pairs discussed in “Using symmetric master-slave contact pairs to improve contact modeling” in “Defining contact pairs in Abaqus/Standard,” Section 36.3.1, are also applicable for situations in which you reassign balanced master-slave contact for general contact. Balanced master-slave contact can result in reduced robustness due to the increased number of constraints and the possibility of overconstraints.

Input File Usage:

Use the following option to indicate that the first surface should be considered the slave surface:*CONTACT FORMULATION, TYPE=MASTER SLAVE ROLESSurf_1, surf_2, SLAVEUse the following option to indicate that the first surface should be considered the master surface:*CONTACT FORMULATION, TYPE=MASTER SLAVE ROLESSurf_1, surf_2, MASTERIf the first surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. The second surface name must be specified.Use the following option to specify that balanced master-slave contact should be used between two surfaces:*CONTACT FORMULATION, TYPE=MASTER SLAVE ROLESSurf_1, surf_2, BALANCEDIf the first surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. If the second surface name is omitted, contact between the first surface and itself is assumed.

Abaqus/CAE Usage:

Interaction module: Create Interaction: General contact (Standard):Contact Formulation: Master-slave assignments: Edit:select the surfaces in the columns on the left, and click the arrows in the middle to transfer them to the list of master-slave assignments.In theFirst Surface Typecolumn, enter SLAVE to indicate that the first surface should be considered the slave surface, enter MASTER to indicate that the first surface should be considered the master surface, or enter BALANCED to specify that balanced master-slave contact should be used between the two surfaces.

# Automatically generated contact exclusions Abaqus/Standard automatically generates contact exclusions for the master-slave roles opposite to specified pure master-slave roles; therefore, self-contact is excluded for any regions of the two surfaces that overlap. For example, specifying that the general contact interaction between surf\_A and surf\_B should use pure master-slave contact with surf\_A considered to be the slave surface would result in exclusions being generated internally for master faces of surf\_A contacting slave faces of surf\_B; self-contact would be excluded for the region of overlap between surf\_A and surf\_B. An error message is issued if the second surface name is omitted or is the same as the first surface name since this input would result in the exclusion of self-contact for the surface. # Smoothness of contact force redistribution upon sliding You can control the smoothness of nodal contact force redistribution upon sliding. The default setting, which is generally appropriate, results in the smoothness of the nodal force redistribution being of the same order as the elements underlying the slave surface; that is, linear redistribution smoothness for linear elements, and quadratic redistribution smoothness for second-order elements. Quadratic redistribution smoothness usually tends to improve convergence behavior and improve resolution of contact stresses within regions of rapidly varying contact stresses. However, quadratic redistribution smoothness tends to increase the number of nodes involved in each constraint, which can increase the computational cost of the equation solver. Linear redistribution smoothness tends to provide better resolution of contact stresses near edges of active contact regions and, therefore, occasionally results in better convergence behavior. # Input File Usage: Use the following option to indicate that the smoothness of the contact force redistribution upon sliding should be of the same order as the elements underlying the slave surface: \*CONTACT FORMULATION, TYPE=SLIDING TRANSITIONsurf\_1, surf\_2, ELEMENT ORDER SMOOTHING If the first surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. If the second surface name is omitted, contact between the first surface and itself is assumed. Use the following option to indicate linear smoothness of the contact force redistribution upon sliding: \*CONTACT FORMULATION, TYPE=SLIDING TRANSITION surf\_1, surf\_2, LINEAR SMOOTHING If the first surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. If the second surface name is omitted, contact between the first surface and itself is assumed. Use the following option to indicate quadratic smoothness of the contact force redistribution upon sliding: \*CONTACT FORMULATION, TYPE=SLIDING TRANSITIONsurf\_1, surf\_2, QUADRATIC SMOOTHING If the first surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. If the second surface name is omitted, contact between the first surface and itself is assumed. # Additional global numerical controls for general contact Some additional numerical contact controls can be modified globally from step-to-step for general contact; you cannot specify contact controls for individual surface pairings within the general contact domain. You can apply contact stabilization to address rigid body modes that occur prior to the establishment of contact in the model, and you can adjust the tolerances used by Abaqus/Standard to determine contact penetrations and separations; both techniques are discussed in “Adjusting contact controls in Abaqus/Standard,” Section 36.3.6. # 36.3 Defining contact pairs in Abaqus/Standard • “Defining contact pairs in Abaqus/Standard,” Section 36.3.1 • “Assigning surface properties for contact pairs in Abaqus/Standard,” Section 36.3.2 • “Assigning contact properties for contact pairs in Abaqus/Standard,” Section 36.3.3 • “Modeling contact interference fits in Abaqus/Standard,” Section 36.3.4 • “Adjusting initial surface positions and specifying initial clearances in Abaqus/Standard contact pairs,” Section 36.3.5 • “Adjusting contact controls in Abaqus/Standard,” Section 36.3.6 • “Defining tied contact in Abaqus/Standard,” Section 36.3.7 • “Extending master surfaces and slide lines,” Section 36.3.8 • “Contact modeling if substructures are present,” Section 36.3.9 • “Contact modeling if asymmetric-axisymmetric elements are present,” Section 36.3.10