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Input File Usage: *SURFACE PROPERTY ASSIGNMENT, PROPERTY=FEATURE EDGE CRITERIA surface, ALL EDGES
Abaqus/CAE Usage: Interaction module: Create Interaction: General contact (Explicit): Surface Properties: Feature edge criteria assignments: Edit: Select the surface, click the arrows to transfer the surface to the list of feature assignments, and enter ALL in the Feature Edge Criteria column.
Specifying that all feature edges should be deactivated
You can choose to deactivate all feature edges (including perimeter edges) in the general contact domain. This option does not deactivate “contact edges” associated with beam and truss elements.
Input File Usage: *SURFACE PROPERTY ASSIGNMENT, PROPERTY=FEATURE EDGE CRITERIA surface, NO FEATURE EDGES
If the surface name is omitted, a default surface that encompasses the entire general contact domain is assumed.
Abaqus/CAE Usage: Interaction module: Create Interaction: General contact (Explicit): Surface Properties: Feature edge criteria assignments: Edit:
Select the surface, click the arrows to transfer the surface to the list of feature assignments, and enter NONE in the Feature Edge Criteria column.
Specifying a cutoff feature angle
If you specify a cutoff feature angle as the feature edge criteria, perimeter edges and geometric edges with feature angles greater than or equal to the specified angle are activated in the general contact domain. As described previously, you can activate additional feature edges if needed.
Input File Usage: *SURFACE PROPERTY ASSIGNMENT, PROPERTY=FEATURE EDGE CRITERIA surface, feature_angle_value
If the surface name is omitted, a default surface that encompasses the entire general contact domain is assumed.
Abaqus/CAE Usage: Interaction module: Create Interaction: General contact (Explicit): Surface Properties: Feature edge criteria assignments: Edit:
Select surface, click the arrows to transfer surface to list of feature assignments, and enter a value for the cutoff feature angle (in degrees) in the Feature Edge Criteria column.
Example: assigning different feature edge criteria to different regions
You can assign a different feature edge criteria to different regions of the general contact domain. For example, Table 36.4.2–3 and Table 36.4.2–4 show the input that could be used to specify that none of
the feature edges of surf1, only perimeter edges of surf2, and perimeter edges and feature edges of surf3 with a feature angle greater than 30° should be considered for edge-to-edge contact.
Table 36.4.2–3 Feature edge criteria example: input file.
| Input File Syntax |
| surf1, NO FEATURE EDGES |
| surf2, PERIMETER EDGES |
| surf3, 30 |
Table 36.4.2–4 Feature edge criteria example: Abaqus/CAE.
| Abaqus/CAE Syntax |
| Surface: surf1, Feature Edge Criteria: NONE |
| Surface: surf2, Feature Edge Criteria: PERIMETER |
| Surface: surf3, Feature Edge Criteria: 30 |
Primary and secondary feature edges
To cut down on the computational cost in certain situations, it may be desirable to identify a limited number of feature edges on a surface (presumably at locations where there are sharp gradients in the surface normals) as “primary” feature edges. A more relaxed criterion can be used to denote certain other edges on the surface as “secondary” feature edges. If secondary feature edges are specified in addition to primary feature edges, Abaqus/Explicit enforces edge-to-edge contact between primary feature edges and between primary feature edges and secondary feature edges only. Edge-to-edge contact is not enforced between secondary feature edges. This ensures that interpenetrations are avoided at locations where there are “true” edges in the model, without the need to activate primary feature edges at locations where the gradients in the surface normals are only moderate. A judicious choice of criteria for selecting primary and secondary feature edges can lead to significant savings in computational costs.
Secondary feature edges can be selected for a surface by specifying a secondary feature edge criterion in addition to the criterion used to select the primary feature edges for that surface. If the secondary feature edge criterion is omitted, only primary feature edges are activated for the surface. Allowable criteria for secondary feature edges are:
• all edges that have not been selected as primary feature edges;
• all picked edges that have not been selected as primary feature edges;
• all perimeter edges that have not been selected as primary feature edges; and
• all edges with a feature angle greater than a specified cutoff angle value that have not been selected as primary feature edges.
The allowable values for the secondary feature edge criterion permit possible combinations of criteria for primary feature edges and secondary feature edges, shown in Table 36.4.2–5.
Table 36.4.2–5 Valid combinations of primary feature edge and secondary feature edge criteria.
| Primary Feature Edge Criterion | Secondary Feature Edge Criterion |
| No feature edges | All remaining edges, picked edges, perimeter edges, cutoff angle |
| All edges | Any criterion specified for secondary feature edges will be ignored |
| Picked edges | All remaining edges, perimeter edges, cutoff angle |
| Perimeter edges | All remaining edges, picked edges, cutoff angle |
| Cutoff angle | All remaining edges, picked edges, perimeter edges, cutoff angle |
Specifying all remaining edges as secondary feature edges
You can specify that all edges belonging to the surface that have not been selected as primary feature edges become secondary feature edges.
Input File Usage: *SURFACE PROPERTY ASSIGNMENT, PROPERTY=FEATUREEDGE CRITERIA
surface, primary feature edge criterion, ALL REMAINING EDGES
If the surface name is omitted, a default surface that encompasses the entire general contact domain is assumed.
Abaqus/CAE Usage: Secondary feature edges are not supported in Abaqus/CAE.
Specifying picked edges as secondary feature edges
You can specify that all picked edges of the surface that have not already been selected as primary feature edges become secondary feature edges.
Input File Usage: *SURFACE PROPERTY ASSIGNMENT, PROPERTY=FEATUREEDGE CRITERIA
surface, primary feature edge criterion, PICKED EDGES
If the surface name is omitted, a default surface that encompasses the entire general contact domain is assumed.
Abaqus/CAE Usage: Secondary feature edges are not supported in Abaqus/CAE.
Specifying perimeter edges as secondary feature edges
You can specify that all perimeter edges of the surface that have not already been selected as primary feature edges become secondary feature edges.
| Input File Usage: | *SURFACE PROPERTY ASSIGNMENT, PROPERTY=FEATURE EDGE CRITERIASurface, primary feature edge criterion, PERIMETER EDGESIf the surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. |
Abaqus/CAE Usage: Secondary feature edges are not supported in Abaqus/CAE.
Specifying a cutoff feature angle for secondary feature edges
You can specify that edges on the surface with a feature angle greater than the specified value that have not been selected as primary feature edges become secondary feature edges. If an angle value has also been specified for primary feature edges, the angle value specified for secondary feature edges must be smaller than the value specified for primary edges.
| Input File Usage: | *SURFACE PROPERTY ASSIGNMENT, PROPERTY=FEATURE EDGE CRITERIASurface, primary feature edge criterion, feature_angle_valueIf the surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. |
Abaqus/CAE Usage: Secondary feature edges are not supported in Abaqus/CAE.
Specifying that edges are activated only as secondary feature edges
For a particular surface you may not want to activate any primary feature edges; instead, you might want to activate all or some edges on the surface as secondary feature edges (to enforce contact between these secondary feature edges and primary feature edges on another surface in the model). In that case you can specify that no feature edges should be activated as the primary feature edge criterion for the surface, while using any criterion of choice for the secondary feature edges.
| Input File Usage: | *SURFACE PROPERTY ASSIGNMENT, PROPERTY=FEATURE EDGE CRITERIASurface, NO FEATURE EDGES, secondary feature edge criterionIf the surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. |
Abaqus/CAE Usage: Secondary feature edges are not supported in Abaqus/CAE.
Surface geometry correction
By default, contact calculations are based on unsmoothed, faceted representations of the finite element surfaces in a general contact domain. Discrepancies between the true surface geometry and the faceted
surface geometry may result in significant noise in the solution. Optional contact smoothing techniques simulate a more realistic representation of curved surfaces in the contact calculations. These techniques allow a discretized surface with discontinuous surface normals to more closely approximate the behavior of a smooth surface during an analysis. Improvements to results with the surface correction include more accurate contact stresses and less solution noise upon relative sliding between contact surfaces.
Contact smoothing can be specified for surfaces in a general contact domain using a surface property assignment. A single surface property assignment specifies all of the surfaces to be smoothed, as well as the appropriate geometry correction method for each surface. Three geometry correction methods can be employed:
• The circumferential smoothing method is applicable to surfaces approximating a portion of a surface of revolution.
• The spherical smoothing method is applicable to surfaces approximating a portion of a sphere.
• The toroidal smoothing method is applicable to surfaces approximating a portion of a torus (i.e., a circular arc revolved about an axis).
For each surface, you must specify the appropriate geometry correction method and either the approximate axis of revolution (for circumferential or toroidal smoothing) or the approximate spherical center (for spherical smoothing). For toroidal smoothing, you must also specify the distance of the center of the circular arc from the axis of revolution, and the line joining point \mathrm { ( X _ { a } , Y _ { a } , Z _ { a } ) } and the center of the circular arc should be perpendicular to the axis of revolution.
Input File Usage: Use the following option to apply a geometric correction:
*SURFACE PROPERTY ASSIGNMENT, PROPERTY=GEOMETRICCORRECTION
data lines to define smoothing regions (see below)
Use the following data line to apply circumferential smoothing to a surface with an axis of symmetry passing through points ( \mathrm { X } _ { \mathrm { a } } , \mathrm { Y } _ { \mathrm { a } } , \mathrm { Z } _ { \mathrm { a } } ) and ( \mathrm { X } _ { \mathrm { b } } , \mathrm { Y } _ { \mathrm { b } } , \mathrm { Z } _ { \mathrm { b } } ) { \mathrm { : } } :
surface, CIRCUMFERENTIAL, X _ { a } , Y _ { a } , Z _ { a } , X _ { b } , Y _ { b } , Z _ { b }
Use the following data line to apply spherical smoothing to a surface with a spherical center at point ( \mathrm { X } _ { \mathrm { a } } , \mathrm { Y } _ { \mathrm { a } } , \mathrm { Z } _ { \mathrm { a } } ) :
surface, SPHERICAL, X _ { a } , Y _ { a } , Z _ { a }
Use the following data line to apply toroidal smoothing to a surface with an axis of symmetry passing through points ( \mathrm { X } _ { \mathrm { a } } , \mathrm { Y } _ { \mathrm { a } } , \mathrm { Z } _ { \mathrm { a } } ) and ( X _ { \mathrm { b } } , \ : \mathrm { Y _ { \mathrm { b } } , Z _ { \mathrm { b } } ) } with the center of the revolved circular arc at a distance R from the axis of symmetry:
surface, TOROIDAL, X _ { a } , Y _ { a } , Z _ { a } , X _ { b } , Y _ { b } , Z _ { b } , R
Repeat the data lines as many times as necessary to define the appropriate geometry corrections for all surfaces in the contact domain.
Abaqus/CAE Usage:
Contact surface smoothing can be applied only to native geometry models in Abaqus/CAE. Abaqus/CAE can automatically detect all circumferential, spherical, and toroidal surfaces in the general contact domain that can be smoothed and apply the appropriate smoothing.
Use the following option to enable automatic surface smoothing of a model:
Interaction module: Create Interaction: General contact (Explicit): Surface Properties: Surface smoothing assignments: Edit: toggle on Automatically assign smoothing for geometric faces
Use the following option to manually apply smoothing to a surface:
Interaction module: Create Interaction: General contact (Explicit): Surface Properties: Surface smoothing assignments: Edit: Select the surface, click the arrows to transfer the surface to the list of smoothing assignments.
In the Smoothing Option column, select REVOLUTION to apply circumferential smoothing, select SPHERICAL to apply spherical smoothing, select TOROIDAL to apply toroidal smoothing, or select NONE to prevent smoothing of the surface.
Considerations for geometric correction
The contact smoothing technique assumes that the initial locations of the surface nodes lie on the true initial surface geometry, with the exception of midedge nodes of C3D10M elements. This smoothing technique remains effective even if the midedge nodes of C3D10M elements do not lie on the true initial geometry (models meshed using Abaqus/CAE always have midedge nodes placed on the true initial geometry, but this may not be the case with other meshing preprocessors).
The effects of contact smoothing tend to be most significant for analyses involving small deformation, and the smoothing technique works well for cases involving large relative motion between the surfaces. For analyses with large deformation this smoothing technique typically has an insignificant effect on the solution. However, in some cases—especially where the underlying elements can fail—the smoothing can degrade the solution accuracy after large deformation.
Effects of geometric correction
The impact of contact surface smoothing can be demonstrated by a simple model of contact between concentric cylinders with a small clearance between them. With a matched mesh as shown in Figure 36.4.2–7 there are no initial overclosures; therefore, there are no initial strain-free initial displacement adjustments. However, if the inner cylinder is rotated, the cylinders develop stresses (see Figure 36.4.2–8) as contact is detected due to the linear faceted representation of the master surface. This behavior is improved when the circumferential smoothing technique is applied to the contacting surfaces of the two cylinders.
natural_image
Circular diagram with grid pattern, no text or symbols present
Figure 36.4.2–7 Concentric cylinders with matched mesh.
heatmap
| S, Misses (Avg: 75%) | Value |
|---|---|
| +8.165e+02 | +8.165e+02 |
| +7.487e+02 | +7.487e+02 |
| +6.809e+02 | +6.809e+02 |
| +6.131e+02 | +6.131e+02 |
| +5.453e+02 | +5.453e+02 |
| +4.875e+02 | +4.875e+02 |
| +4.097e+02 | +4.097e+02 |
| +3.419e+02 | +3.419e+02 |
| +2.741e+02 | +2.741e+02 |
| +2.063e+02 | +2.063e+02 |
| +1.385e+02 | +1.385e+02 |
| +7.071e+01 | +7.071e+01 |
| +2.905e+00 | +2.905e+00 |
Figure 36.4.2–8 Stesses as cylinder rotates.
36.4.3 ASSIGNING CONTACT PROPERTIES FOR GENERAL CONTACT IN Abaqus/Explicit
Products: Abaqus/Explicit Abaqus/CAE
References
• “Defining general contact interactions in Abaqus/Explicit,” Section 36.4.1
• “Mechanical contact properties: overview,” Section 37.1.1
• “Contact pressure-overclosure relationships,” Section 37.1.2
• “Contact damping,” Section 37.1.3
• “Frictional behavior,” Section 37.1.5
• *CONTACT
• *CONTACT PROPERTY ASSIGNMENT
• *SURFACE INTERACTION
• “Specifying and modifying contact property assignments for general contact,” Section 15.13.2 of the Abaqus/CAE User’s Guide, in the HTML version of this guide
Overview
Contact properties:
• define the mechanical surface interaction models that govern the behavior of surfaces when they are in contact; and
• can be applied selectively to particular regions within a general contact domain.
Assigning contact properties
The default contact property model in Abaqus/Explicit assumes “hard” contact in the normal direction, no friction, no thermal interactions, etc. You can assign a nondefault contact property definition (surface interaction) to specified regions of the general contact domain.
Contact property assignments propagate through all analysis steps in which the general contact interaction is active.
The surface names used to specify the regions where nondefault contact properties should be assigned do not have to correspond to the surface names used to specify the general contact domain. In many cases the contact interaction will be defined for a large domain, while nondefault contact properties will be assigned to a subset of this domain. Any contact property assignments for regions that fall outside of the general contact domain will be ignored. The last assignment will take precedence if the specified regions overlap.
Input File Usage: *CONTACT PROPERTY ASSIGNMENT
surface_1, surface_2, interaction_property_name
This option must be used in conjunction with the *CONTACT option. It should appear at most once per step; the data line can be repeated as often as necessary to assign contact properties to different regions.
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 or is the same as the first surface name, contact between the first surface and itself is assumed. Keep in mind that surfaces can be defined to span multiple unattached bodies, so self-contact is not limited to contact of a single body with itself. If the interaction property name is omitted, the unnamed set of default contact properties in Abaqus/Explicit is assumed. If an interaction property name is specified, it must also appear as the value of the NAME parameter on a *SURFACE INTERACTION option in the model portion of the input file.
Abaqus/CAE Usage: Interaction module: Create Interaction: General contact (Explicit): Contact Properties:
Individual property assignments: Edit: select the surfaces and the contact property in the columns on the left, and click the arrows in the middle to transfer them to the list of contact property assignments
or
Global property assignment: interaction_property_name
In Abaqus/CAE you must assign a contact property definition to every general contact interaction; Abaqus/CAE does not assume a default contact interaction property.
Example
The following contact property assignments are specified below for the first step in a general contact analysis:
• a global assignment of contProp1 to the entire general contact domain;
• a local assignment of contProp2 to self-contact for surf1;
• a local assignment of the default Abaqus contact property to contact between surf2 and surf3; and
• a local assignment of contProp3 to contact between the entire contact domain and surf4.
*SURFACE INTERACTION, NAME=contProp1
*FRICTION
0.1
*SURFACE INTERACTION, NAME=contProp2
*FRICTION
0.15
*SURFACE INTERACTION, NAME=contProp3
*FRICTION
0.20