Products: ABAQUS/Standard ABAQUS/CAE
In ABAQUS/Standard there are three approaches to account for the relative motion of the two surfaces forming a contact pair in mechanical contact simulations:
finite sliding, which is the most general and allows any arbitrary motion of the surfaces (see “Finite-sliding interaction between deformable bodies,” Section 5.1.2 of the ABAQUS Theory Manual, and “Finite-sliding interaction between a deformable and a rigid body,” Section 5.1.3 of the ABAQUS Theory Manual);
small sliding, which assumes that although two bodies may undergo large motions, there will be relatively little sliding of one surface along the other (see “Small-sliding interaction between bodies,” Section 5.1.1 of the ABAQUS Theory Manual); or
infinitesimal sliding and rotation, which assumes that both the relative motion of the surfaces and the absolute motion of the contacting bodies are small.
The finite-sliding formulation allows for arbitrary separation, sliding, and rotation of the surfaces. ABAQUS/Standard uses this formulation by default.
| Input File Usage: | *CONTACT PAIR, INTERACTION=interaction_property_name |
| ABAQUS/CAE Usage: | Interaction module: interaction editor: Sliding formulation: Finite sliding |
The following input defines finite-sliding contact between the surfaces ASURF and BSURF, shown in Figure 21.2.2–1, with ASURF acting as the slave surface:
*SURFACE, NAME=ASURF ESETA, *SURFACE, NAME=BSURF ESETB, *CONTACT PAIR, INTERACTION=PAIR1 ASURF, BSURF *SURFACE INTERACTION, NAME=PAIR1
In the example shown in Figure 21.2.2–1 slave node 101 may come into contact anywhere along the master surface BSURF. While in contact, it is constrained to slide along BSURF, irrespective of the orientation and deformation of this surface. This behavior is possible because ABAQUS/Standard tracks the position of node 101 relative to the master surface BSURF as the bodies deform. Figure 21.2.2–2 shows the possible evolution of the contact between node 101 and its master surface BSURF. Node 101 is in contact with the element face with end nodes 201 and 202 at time 
. The load transfer at this time occurs between node 101 and nodes 201 and 202 only. Later on, at time 
, node 101 may find itself in contact with the element face with end nodes 501 and 502. Then the load transfer will occur between node 101 and nodes 501 and 502.
The finite-sliding contact formulation requires that master surfaces have unique surface normals at all points. Convergence problems can result if master surfaces that do not have smooth surface normals are used in finite-sliding contact analyses; slave nodes tend to get “stuck” at points where the master surface normals are discontinuous. ABAQUS/Standard automatically smoothes the surface normals of element-based master surfaces (see below) used in finite-sliding contact simulations, including those modeled with slide lines. You are expected to create smooth analytical rigid surfaces (see “Defining analytical rigid surfaces,” Section 2.3.4).
To model a master surface with corners in two dimensions (fold lines in three dimensions), break the surface into multiple surfaces. This technique prevents ABAQUS/Standard from smoothing out the corners or fold lines and allows ABAQUS/Standard to introduce constraints associated with each surface if a slave node is in contact with an interior corner or fold in the master surface.
The following input defines finite-sliding contact between the slave surface ASURF and a master surface with a corner as shown in Figure 21.2.2–3:
*CONTACT PAIR, INTERACTION=PAIR1 ASURF, BSURFA ASURF, BSURFB
For finite-sliding simulations with planar or axisymmetric deformable master surfaces, ABAQUS/Standard will smooth any discontinuous transitions between two first-order element faces with parabolic curves. Discontinuous transitions between two second-order element faces are smoothed with cubic curves connecting two points located on the element's faces. This smoothing is shown in Figure 21.2.2–4 for first-order elements (linear segments) and in Figure 21.2.2–5 for second-order elements (parabolic segments). For finite-sliding simulations with three-dimensional deformable master surfaces and rigid master surfaces using rigid elements, ABAQUS/Standard will smooth any discontinuous surface normal transitions between the master surface facets.
You can control the degree of smoothing of the master surface in surface-based contact simulations or in analyses using slide lines and contact elements by specifying a fraction 
. The default value of is 0.2.
For planar or axisymmetric deformable master surfaces, 
, where 
and 
are the lengths of the element facets that join at the surface node and 
(see Figure 21.2.2–4 and Figure 21.2.2–5).
and 
from the node at which the discontinuity exists; this smoothed segment will be used in the contact calculations. Thus, the contact surface will differ from the faceted element geometry. Smoothing affects only segments where the normal to the deformable master surface is discontinuous at the node joining two elements: it does not affect the two segments adjacent to the midside nodes on second-order element faces.For three-dimensional deformable master surfaces and rigid master surfaces using rigid elements, is defined as a fraction of the dimension of a facet as shown in Figure 21.2.2–6.
| Input File Usage: | Use the following option for surface-based contact simulations: |
*CONTACT PAIR, INTERACTION=interaction_property_name, SMOOTH=f Use the following option when using slide lines and contact elements: *SLIDE LINE, ELSET=name, SMOOTH=f |
| ABAQUS/CAE Usage: | You cannot control the degree of smoothing in ABAQUS/CAE; the default value of f=0.2 is always used. |
When a two-dimensional or axisymmetric deformable master surface ends at a symmetry plane, ABAQUS/Standard will smooth and calculate the proper surface normals and tangent planes of the end segment if the boundary condition at the symmetry end is specified with the symmetry “type” boundary XSYMM or YSYMM. This smoothing procedure is accomplished by reflecting the end segment about the symmetry plane and constructing either a parabolic or a cubic segment between the end segment and the reflected segment. Thus, the contact surface may differ from the faceted element geometry near the end. ABAQUS/Standard will automatically adjust the surface normal and tangent planes at 
of an axisymmetric master surface regardless of whether a symmetry boundary condition is defined.
Finite-sliding simulations usually include nonlinear geometric effects because such simulations generally involve large deformations and large rotations. However, it is also possible to use the finite-sliding formulation in a geometrically linear analysis (see “Geometric nonlinearity” in “General and linear perturbation procedures,” Section 6.1.2). The load transfer paths between the surfaces and the contact direction are updated in finite-sliding, geometrically linear analysis. This capability is useful for analyzing finite sliding between two stiff bodies that do not undergo large rotations.
Contact constraints produce unsymmetric terms when three-dimensional faceted surfaces come in contact. These terms have a strong effect on the convergence rate in regions on the master surfaces with large discontinuities in surface normals between facets. In such cases you should use the unsymmetric solution scheme for the step (see “Procedures: overview,” Section 6.1.1).
For a large class of contact problems the general tracking of the finite-sliding formulation is unnecessary, even though geometric nonlinearity must be considered. ABAQUS/Standard provides a small-sliding contact formulation for such problems. This formulation assumes that the surfaces may undergo arbitrarily large rotations but that a slave node will interact with the same local area of the master surface throughout the analysis.
You must specify that a large-displacement formulation should be used for the step in which the small-sliding contact formulation should be used.
In a small-sliding analysis every slave node interacts with its own local tangent plane on the master surface (see Figure 21.2.2–7). The slave node is constrained not to penetrate this local tangent plane. Each local tangent plane, which is a line in two dimensions, is defined by an anchor point, 
, on the master surface and an orientation vector at the anchor point (see Figure 21.2.2–7).
Having a local tangent plane for each slave node means that for the small-sliding formulation ABAQUS/Standard does not have to monitor slave nodes for possible contact along the entire master surface. Therefore, small-sliding contact is less expensive computationally than finite-sliding contact. The cost savings are most dramatic in three-dimensional contact problems. In addition, the small-sliding formulation does not require master surfaces to be smooth. Consequently, the automatic smoothing of master surfaces is disabled when small sliding is assumed.
| Input File Usage: | Use both of the following options: |
*CONTACT PAIR, INTERACTION=interaction_property_name, SMALL SLIDING … *STEP, NLGEOM For example, the following options define small-sliding contact between the two bodies shown in Figure 21.2.2–1: *SURFACE, NAME=ASURF ESETA, *SURFACE, NAME=BSURF ESETB, *CONTACT PAIR, INTERACTION=PAIR1, SMALL SLIDING ASURF, BSURF *SURFACE INTERACTION, NAME=PAIR1 … *STEP, NLGEOM |
| ABAQUS/CAE Usage: | Interaction module: interaction editor: Sliding formulation: Small sliding |
Step module: step editor: Nlgeom: On |
ABAQUS/Standard can use one of two approaches in the small-sliding contact formulation: the “node-to-surface” approach or the “surface-to-surface” approach. The default approach is the node-to-surface approach. The surface-to-surface approach optimizes stress accuracy for a given surface pairing and allows shell and membrane thicknesses to be considered in the contact calculations. The improved stress accuracy with the surface-to-surface approach is realized only if the slave surface is element based. The surface-to-surface approach generally involves more master nodes per constraint and, therefore, can increase solution cost. In most applications the extra cost is fairly small, but the cost can become significant in some cases. The following factors (especially in combination) can lead to the surface-to-surface approach being quite costly:
A large fraction of nodes in the model involved in contact
The master surface being more refined than the slave surface
Multiple layers of shells involved in contact, such that the master surface of one contact pair acts as the slave surface of another contact pair
| Input File Usage: | Use the following option to choose the default node-to-surface approach: |
*CONTACT PAIR, INTERACTION=interaction_property_name, SMALL SLIDING, TYPE=NODE TO SURFACE Use the following option to choose the surface-to-surface approach: *CONTACT PAIR, INTERACTION=interaction_property_name, SMALL SLIDING, TYPE=SURFACE TO SURFACE |
| ABAQUS/CAE Usage: | Interaction module: interaction editor: Sliding formulation: Small sliding: Constraint enforcement method: Node to surface or Surface to surface |
Contact pairs that use the surface-to-surface approach account for initial shell and membrane thicknesses by default; whereas contact pairs that use the node-to-surface approach will not account for surface thickness. Accounting for element thicknesses in contact calculations is generally desirable, but you can avoid having thickness considered with the surface-to-surface approach.
| Input File Usage: | Use the following option to ignore shell and membrane thicknesses: |
*CONTACT PAIR, INTERACTION=interaction_property_name, SMALL SLIDING, TYPE=SURFACE TO SURFACE, NO THICKNESS |
| ABAQUS/CAE Usage: | Interaction module: interaction editor: Sliding formulation: Small sliding: Constraint enforcement method: Surface to surface: toggle off Include shell/membrane element thickness |
Consider the case of a shell pinched between two rigid surfaces, as shown in Figure 21.2.2–8. In this example contact pairs using the surface-to-surface small-sliding formulation are defined between the top surface of the shell and the top rigid surface and between the bottom surface of the shell and the bottom rigid surface. The augmented Lagrangian constraint enforcement method (see “Contact pressure-overclosure relationships,” Section 22.1.2) should be used to avoid overconstraining slave nodes in this example. The following input could be used:
*SURFACE, NAME=TOP_RIG_SURF TOP_RIG_ELS, *SURFACE, NAME=SHELL_TOP_SURF SHELL_ELS,SPOS *SURFACE, NAME=SHELL_BOT_SURF SHELL_ELS,SNEG *SURFACE, NAME=BOT_RIG_SURF BOT_RIG_ELS, *CONTACT PAIR, INTERACTION=INTER_AL, SMALL SLIDING, TYPE=SURFACE TO SURFACE SHELL_TOP_SURF, TOP_RIG_SURF SHELL_BOT_SURF, BOT_RIG_SURF *SURFACE INTERACTION, NAME=INTER_AL *SURFACE BEHAVIOR, AUGMENTED LAGRANGE
For the node-to-surface approach ABAQUS/Standard chooses the anchor point of a slave node's local tangent plane such that the vector from the anchor point to the slave node coincides with the normal vector from the master surface. The anchor point is chosen before the analysis starts using the initial configuration of the model. This algorithm requires that the master surface have a smoothly varying normal vector 
, where 
is any point on the master surface.
The first step in defining is to construct the unit normal vectors at each node of the master surface. ABAQUS/Standard forms these nodal normals by averaging the normals of the element faces making up the master surface; only the element faces in the surface definition will contribute to the nodal normals and, thus, to . ABAQUS/Standard uses the initial nodal coordinates to compute these normals.
Figure 21.2.2–7 shows the nodal unit normals for a master surface, the anchor point , and the local tangent plane associated with slave node 103. ABAQUS/Standard uses the nodal unit normals 
and 
, along with the shape functions of the element containing the two nodes, to construct on the 2–3 element face. ABAQUS/Standard chooses the anchor point of the local tangent plane for node 103 so that 
passes through node 103. is the contact direction for slave node 103 and defines the orientation of the local tangent plane. In this example, as in many cases, the local tangent plane is only an approximation of the actual mesh geometry.
Sometimes the master surface normal and the local tangent plane that ABAQUS/Standard calculates are not suitable for the desired analysis. The most common situation where unsuitable surface normals are calculated occurs when a curved master surface ends at a symmetry plane and the boundary conditions have been specified in direct format rather than in symmetry “type” format (XSYMM, YSYMM, or ZSYMM—see “Boundary conditions,” Section 19.3.1). In this case, the correct normals should be in the symmetry plane; however, because the surface facets that abut the symmetry plane usually form an angle with the plane, the normal will project away from the symmetry plane. The effect of this behavior can be that a slave node does not have a normal from the master surface pass through it (the slave node is said not to “intersect” the master surface). No contact constraints will be enforced for such slave nodes.
A message is printed in the data (.dat) file whenever a slave node does not intersect its master surface. By specifying the proper symmetry “type” boundary condition, ABAQUS/Standard will calculate the correct normal and local tangent planes along the symmetry planes of the master surface.
If the unit normals of the master surface and the local tangent planes calculated by ABAQUS/Standard are unsuitable and it is not feasible to apply symmetry “type” boundary conditions, several other methods are available for modifying them. One method is to add or remove some of the element faces making up the master surface. However, this method can influence only the surface normals near the perimeter of the master surface.
The other method is to modify the nodal normals on the master surface by defining user-specified normals (see “Normal definitions at nodes,” Section 2.1.4). This method is especially useful in providing a more accurate representation of the surface geometry. Figure 21.2.2–9 shows two concentric cylinders that contact each other; the inner cylinder is chosen as the master surface CSURF.
Figure 21.2.2–9 Master surface normal at node 1 in a small-sliding model of concentric cylinders. With the default 
slave node 100 will never contact CSURF.
If a half-symmetry model is used, the default master surface normal at the symmetry plane will cause problems. As shown in Figure 21.2.2–9, the nodal normal does not point along the symmetry plane, which means that slave node 100 will never intersect the master surface. In a small-sliding problem if a slave node fails to intersect the master surface at the start of the analysis, it will be free to penetrate the master surface because no local tangent plane will be formed. ABAQUS/Standard provides the initial contact status—open, overclosed, or “no intersection”—in the data file for every slave node in the model. Use this information to confirm that the necessary tangent planes for a model have been found.
In situations such as that shown in Figure 21.2.2–9, define a YSYMM “type” boundary condition at node 1 to specify the symmetry plane. The master normal at the node on the symmetry plane will be modified to lie along the symmetry plane, allowing slave node 100 to see the master surface CSURF.
In situations where a symmetry “type” boundary condition cannot be specified, define a user-specified normal (1.00E+00, 0.00E+00, 0.00E+00) at node 1 on the master surface CSURF to correct the problem. This method will also allow slave node 100 to see the master surface.
The modification to CSURF's normal at node 1, which makes CSURF a better approximation of the actual surface, is shown in Figure 21.2.2–10.
The algorithm to establish the anchor point location for the surface-to-surface approach is more complex in most respects than the algorithm for the node-to-surface approach; however, it does not make use of master surface nodal normals. Details of the surface-to-surface approach are proprietary. The anchor point location typically does not depend significantly on whether the node-to-surface or surface-to-surface approach is used. You cannot control the anchor point location for the surface-to-surface approach.
The local tangent plane is always orthogonal to the contact direction. By default, the contact direction is taken as an averaged normal of the master surface at the anchor point. For the node-to-surface approach this is the interpolated normal, , as shown in Figure 21.2.2–7. For the surface-to-surface approach a more complicated averaging is performed to determine the default contact direction. (By default, with the surface-to-surface approach the default contact direction for slave nodes on a symmetry plane will be normal to the symmetry plane if symmetry “type” boundary conditions are specified.) You can override the default contact direction to specify a direction with a spatially varying clearance or overclosure definition (see “Specifying the surface normal for the contact calculations” in “Adjusting initial surface positions and specifying initial clearances in ABAQUS/Standard contact pairs,” Section 21.2.3).
Once the contact direction is defined, the orientation of the local tangent plane with respect to the master surface facet remains fixed. Because the small-sliding formulation considers nonlinear geometric effects, ABAQUS/Standard continuously updates the orientation of . Hence, ABAQUS/Standard also updates the local tangent plane to account for the rotation and, assuming that the master surface is deformable, the deformation of the master surface. The position of the anchor point relative to the surrounding nodes on the master surface facet does not change as the master surface deforms.
In a small-sliding analysis the slave node can transfer load only to a limited number of nodes on the master surface. These nodes on the master surface are chosen based on their proximity to the slave node's anchor point. The magnitude of load transferred to each master surface node is weighted by its proximity to the slave node when the slave node contacts the local tangent plane. For example, in Figure 21.2.2–7 node 103 transmits load to both nodes 2 and 3 on the master surface if the node-to-surface approach is used (if the surface-to-surface approach is used, load may be transmitted to additional nearby master nodes). Thus, if node 103 contacts the local tangent plane, a larger share of the force would be transmitted to the master surface node, 2 or 3, closer to the slave node.
When the anchor point corresponds to a node on the master surface, as is the case with slave node 104 and master surface node 3 in Figure 21.2.2–7, the transmitted load for the node-to-surface approach is shared by the node at and all of the master surface nodes that share an adjacent surface facet with that node (additional master nodes may take part in the load transfer for the surface-to-surface approach). In Figure 21.2.2–7 the three master surface nodes sharing the force transmitted by slave node 104 are nodes 2, 3, and 4.
As a slave node slides along its local tangent plane, ABAQUS/Standard updates the distribution of load transferred by a given slave node to its associated master surface nodes. However, no additional master surface nodes are ever added to the original list of nodes associated with a given slave node. The slave node will continue to transmit load to the original list of master surface nodes, regardless of the distance slid by the slave node along its contact plane. Figure 21.2.2–11 shows the potential problem that arises if small sliding is used but the relative tangential motion of the surfaces is not “small.” It shows the possible evolution of contact between slave node 101 in Figure 21.2.2–1 and its master surface BSURF. Using the unit normal vectors 
and 
, the anchor point is found for slave node 101; for the purposes of this example, assume that it lies at the midpoint of the 201–202 face. With this location of the local tangent plane for node 101 is parallel with the 201–202 face. The load transfer always occurs between node 101 and nodes 201 and 202, no matter how far node 101 slides along the local tangent plane. Therefore, if node 101 moves as shown in Figure 21.2.2–11, it will continue to transmit load to nodes 201 and 202 when, in fact, it really slid off the mesh forming the master surface BSURF.
A contact pair in a small-sliding contact simulation should not grossly violate any of the assumptions or limitations outlined above. Adhere to the following guidelines:
Slave nodes should slide less than an element length from their corresponding anchor point and still be contacting their local tangent plane. If the master surface is highly curved, the slave nodes should slide only a fraction of an element length. The accumulated slip at a slave node (CSLIP) can provide a good estimate of how far a slave node has moved.
The local tangent planes formed by ABAQUS/Standard should be a good approximation of the mesh geometry; if necessary, define a user-specified normal (“Normal definitions at nodes,” Section 2.1.4) to improve the smoothly varying master surface normal, .
The rotation and deformation of the master surface should not cause the local tangent planes to become a poor representation of the master surface during the course of the analysis.
The basic guidelines given in “Defining contact pairs in ABAQUS/Standard,” Section 21.2.1, should still be followed in a small-sliding simulation—the slave surface should be the more refined surface or the surface on the more deformable body. However, in a small-sliding simulation more thought must be given when defining the master surface. With small-sliding contact each slave node views the master surface as a flat surface, which can be significantly different than the true shape of the surface, even in the local region near the anchor point. In some cases the local tangent planes provide a good local approximation to the master surface in the initial configuration, but deformation and rotation of the master surface can reorient the local tangent planes such that they become a poor representation of the master surface. Figure 21.2.2–12 shows an example where distortion of the master surface results in such a situation. This problem can be minimized to some extent by using a more refined mesh on the master surface, thus providing more element faces to control the motion of the tangent planes. Excessive mesh refinement should not be necessary since only small sliding should occur.
The difference between the infinitesimal-sliding and small-sliding formulations is that the infinitesimal-sliding formulation ignores nonlinear geometric effects. To specify the infinitesimal-sliding formulation, you choose the small-sliding contact formulation and a small-displacement formulation for the analysis step.
Infinitesimal sliding assumes that both the relative motions of the surfaces and the absolute motions of the model remain small. The orientations of the local tangent planes are not updated, and the load transfer paths and the weightings assigned to each master surface node remain constant during an infinitesimal-sliding simulation.
| Input File Usage: | Use both of the following options: |
*CONTACT PAIR, INTERACTION=interaction_property_name, SMALL SLIDING … *STEP |
| ABAQUS/CAE Usage: | Interaction module: interaction editor: Sliding formulation: Small sliding |
Step module: step editor: Nlgeom: Off |
ABAQUS/Standard calculates the initial orientation of the two slip directions by default. However, if the default slip directions are not convenient to prescribe an anisotropic friction model or to view contact output, you can define the slip directions. These slip directions will rotate with the contact pair in a geometrically nonlinear analysis.
By default, ABAQUS/Standard determines the initial orientation of the two slip directions, 
and 
, using the conventions discussed below. Exceptions to these conventions arise when slave surfaces are generated from three-dimensional beam, truss, or pipe elements and used in finite-sliding contact or when surfaces are created on CGAX elements or MGAX elements. In the case of slave surfaces attached to three-dimensional beam-type elements and used in finite-sliding contact, the first and second slip directions are always defined along the length of the beam and transverse to the beam, respectively. For surfaces on generalized axisymmetric bodies, the first slip direction at any point on the surface is always tangent to the surface in the local 
–
plane. The second slip direction is orthogonal to this plane in the local circumferential direction.
Finite sliding: The default initial orientations of the two slip directions are calculated at each node on the slave surface based on the negative normal at that node, using the standard convention for calculating surface tangents (see “Conventions,” Section 1.2.2). For the node-based slave surface the initial slip directions coincide with the global 
- and 
-axes with the normal being along the -axis. The negative normal is then aligned with the master surface normal, changing the slip directions accordingly.
Small sliding: The default initial orientations of the two slip directions are calculated at each point on the master surface based on the master surface normal, using the standard convention for calculating surface tangents.
Finite sliding: The default slip direction, , is tangential to the cross-section used to generate the analytical rigid surface. The default slip direction, , is computed such that and , together with the normal to the rigid surface, form an orthogonal coordinate system at every point on the surface.
Small sliding: Small sliding uses the same convention for establishing the default initial slip directions as finite sliding.
Alternatively, you can define the slip directions by associating an orientation definition (see “Orientations,” Section 2.2.5) with a contact pair surface, with the exception of finite-sliding contact between a deformable slave surface and an analytical rigid surface. You can assign an orientation only to one surface of a contact pair. The surface on which an orientation can be defined is the same surface on which the default orientation would be calculated (see the conventions given previously). For example, an orientation can be defined only on the slave surface in deformable vs. deformable finite-sliding contact. If a second orientation is also given, an error message is issued. An orientation that is defined on a slave surface of a contact pair that is generated from three-dimensional truss-type elements or from a list of nodes without rotational degree of freedoms will not be rotated if the slave surface undergoes finite motion. In this case a warning message is issued during input processing.
| Input File Usage: | *CONTACT PAIR, INTERACTION=interaction_property_name slave surface name, master surface name, orientation for slave surface slave surface name, master surface name, , orientation for master surface |
| ABAQUS/CAE Usage: | You cannot define alternative slip directions for contact pairs in ABAQUS/CAE. |
For geometrically nonlinear analysis the tangential slip directions of a contact pair rotate with the surface on which these directions were initially calculated or redefined using an orientation definition as described above. These rotated tangential slip directions are further rotated to ensure that the normal vector, computed using the cross product of the rotated tangential slip directions, corresponds to the normal vector on the master surface when the slave node comes into contact.
When you request contact constraint information from the analysis input file processor (see “Controlling the amount of analysis input file processor information written to the data file” in “Output,” Section 4.1.1), ABAQUS/Standard provides a table for each infinitesimal-sliding or small-sliding contact pair in the data (.dat) file showing the master nodes associated with each slave node, so that you can check them. Each row of the table lists a slave node and the master nodes to which the slave node transfers load when in contact with the master surface. The number of nodes in the table indicates whether or not the anchor point for a slave node lies on an element face or at a node.
For example, in the output shown below for a two-dimensional model, slave node 2 has an anchor point at master surface node 101 because it interacts with three master surface nodes. Slave node 1 has an anchor point between nodes 100 and 101. This table also provides a list of slave nodes that did not find an intersection with the master surface. This is important because these nodes can penetrate the master surface since they have no local tangent plane.
The contact element number associated with each slave node is also given in this table. ABAQUS/Standard generates this number automatically. Because the element is not user-defined and does not appear in the input file, it can be difficult to locate it if an error or warning message refers to the contact element number. This table provides the information specifying the location of this internally generated contact element in the model.
SMALL SLIDING NON-RIGID AX ELEMENT(S)
INTERNALLY GENERATED FOR SLAVE BLANK AND MASTER SPHERE
WITH SURFACE INTERACTION INF1
ELEMENT SLAVE MASTER
NUMBER NODE(S) NODE(S)
46 1 101 100
47 2 102 101 100
50 9 NO INTERSECTION
***WARNING: 1 SLAVE NODES FOUND NO INTERSECTION WITH A MASTER
SURFACEIn a finite-sliding simulation a similar table is given for every contact pair providing the internally generated contact element number for every facet or node on the slave surface. Because the slave nodes can interact with any portion of the master surface, ABAQUS/Standard gives no information about which slave nodes interact with which portions of the master surface.
By default, no contact constraint output to the data file is provided.
| Input File Usage: | *PREPRINT, CONTACT=YES |
| ABAQUS/CAE Usage: | Job module: job editor: General: Preprocessor Printout: Print contact constraint data |
ABAQUS/Standard provides the relative tangential motion (slip) of the two surfaces at each slave node as output. In two-dimensional models a slave node can slide along only the master surface in the plane of the model. The tangent to the master surface in the plane of a two-dimensional model is the first slip direction. ABAQUS/Standard defines the orientation of this tangent by the cross product of the vector into the plane of the model (0., 0., 1.0) and the master surface normal vector. This tangent is the first slip direction of the surface, . The accumulated incremental relative displacement of a slave surface node in this direction is CSLIP1, where the incremental relative displacement is along the current -direction; the -direction may change during the motion.
In a three-dimensional model there are two orthogonal slip directions, and , for each contact pair. These two directions together with the relevant surface normal form an orthogonal coordinate system at every point on the surface. The output variables for the accumulated incremental relative motions along the first and second slip directions are CSLIP1 and CSLIP2, respectively. The incremental relative motions are measured in the current - and -directions, which may change during the motion.
You can request that the relative motions of surfaces be written as output for an analysis to the data, results, or output database file. See “Defining contact pairs in ABAQUS/Standard,” Section 21.2.1, for an example.
ABAQUS/Standard defines the incremental relative motion (slip) for a slave node as the scalar product of the incremental relative nodal displacement vector, 
, and a slip direction, or , associated with the node. The incremental relative nodal displacement vector measures the motion of the slave node relative to the motion of the master surface. Details about the calculation of this quantity can be found in “Small-sliding interaction between bodies,” Section 5.1.1 of the ABAQUS Theory Manual; “Finite-sliding interaction between deformable bodies,” Section 5.1.2 of the ABAQUS Theory Manual; and “Finite-sliding interaction between a deformable and a rigid body,” Section 5.1.3 of the ABAQUS Theory Manual. The sums of all such incremental slips during the analysis are reported as CSLIP1 and CSLIP2. The incremental slip is accumulated only when the slave node is contacting the master surface. In small- or finite-sliding problems the orientation of the slip directions is updated continually to account for the motion of the surfaces.