Five contact models are available: node-to-node, node-to-surface, surface-to-surface, line-to-line, and line-to-surface. Each type of model uses a different set of contact elements and is appropriate for specific types of problems as shown in the following table:
Table 1.1: Contact Support
| Note-to- Node | Node-to- Surface | Surface-to-Surface | Line-to- Line | Line-to- Surface | ||
|---|---|---|---|---|---|---|
| Contact Element No. | 178 | 175 | 172 | 174 | 177 | 177 |
| Target Element No. | -- | 169, 170 | 169 | 170 | 170 | 170 |
| 2D | Y | Y | Y | -- | -- | -- |
| 3D | Y | Y | -- | Y | Y | Y |
| Sliding | small | large | large | large | large | large |
| Cylindrical Gap | Y | -- | -- | -- | -- | -- |
| Spherical Gap | Y | -- | -- | -- | -- | -- |
| Pure Lagrange Multiplier | Y | Y | Y | Y | Y | Y |
| Augmented Lagrange Multiplier | Y | Y | Y | Y | Y | Y |
| Lagrange Multiplier on Normal and Penalty on Tangent | Y | Y | Y | Y | Y | Y |
| Internal Multipoint Constraint (MPC) | -- | Y | Y | Y | Y | Y |
| Contact Stiffness | semi-auto | semi-auto | semi-auto | semi-auto | semi-auto | semi-auto |
| Auto-meshing Tools for Pair-Based Contact | EINTF | ESURF | ESURF | ESURF | ESURF | ESURF |
| Auto-meshing Tools for General Contact | -- | GCGEN | GCGEN | GCGEN | GCGEN | GCGEN |
| Lower-Order | Y | Y | Y | Y | Y | Y |
| Higher-Order | -- | Y (2D only) | Y | Y | Y | Y |
| Rigid-Flexible | Y | Y | Y | Y | Y | Y |
| Flexible-Flexible | Y | Y | Y | Y | Y | Y |
| Thermal Contact | Y | Y | Y | Y | -- | -- |
| Electric Contact | Y | Y | Y | Y | -- | -- |
| Magnetic Contact | -- | Y | Y | Y | -- | -- |
| Pore Fluid Contact | -- | Y | Y | Y | -- | -- |
| Diffusion Contact | -- | Y | Y | Y | -- | -- |
To model a contact problem, you first must identify the parts to be analyzed for their possible interaction. If one of the interactions is at a point, the corresponding component of your model is a node. If one of the interactions is at a surface, the corresponding component of your model is an element: either a beam, shell, or solid element. The finite element model recognizes possible contact pairs by the presence of specific contact elements. These contact elements are overlaid on the parts of the model that are being analyzed for interaction. The various contact elements, and procedures for using them, are described in this guide.
An overview of the contact elements and their capabilities follows. For detailed information on any of these elements, refer to the Element Reference and the Mechanical APDL Theory Reference.
Support is available for both rigid-to-flexible and flexible-to-flexible surface-to-surface contact elements. These contact elements use a target surface and a contact surface to form a contact pair.
To create a contact pair, assign the same real constant number to both the target and contact elements. You can find more details on defining these elements and their shared real constant sets in Surface-to-Surface Contact (Pair-Based).
These surface-to-surface elements are well-suited for applications such as interference fit assembly contact or entry contact, forging, and deep-drawing problems. The surface-to-surface contact elements have several advantages over the node-to-node element CONTA175. These elements:
Support lower and higher order elements on the contact and target surfaces (in other words, corner-noded or midside-noded elements).
Provide better contact results needed for typical engineering purposes, such as normal pressure and friction stress contour plots.
Have no restrictions on the shape of the target surface. Surface discontinuities can be physical or due to mesh discretization.
Allow modeling of fluid pressure penetration loads.
Using these elements for a rigid target surface, you can model straight and curved surfaces in 2D and 3D, often using simple geometric shapes such as circles, parabolas, spheres, cones, and cylinders. More complex rigid forms or general deformable forms can be modeled using special preprocessing techniques (see Defining the Target Surface for more information).
Surface-to-surface contact elements are not well-suited for point-to-point, point-to-surface, edge-to-surface, or 3D line-to-line contact applications, such as pipe whip or snap-fit assemblies. You should use the node-to-surface, node-to-node, or line-to-line elements in these cases. You also can use surface-to-surface contact elements for most contact regions and use a few node-to-surface contact elements near contact corners.
The surface-to-surface contact elements only support general static and transient analyses, buckling, harmonic, modal or spectrum analyses, or substructure analyses.
CONTA175 is a node-to-surface contact element. It supports large sliding, large deformation, and different meshes between the contacting components. Contact occurs when the element penetrates one of the target segment elements (TARGE169, TARGE170) on a specified target surface. CONTA175 is typically used to model point-to-surface contact applications, such as the corners of snap-fit parts sliding along the mating surface.
You can also use CONTA175 to model surface-to-surface contact, if the contacting surface is defined by a group of nodes and multiple elements are generated. The surfaces can be either rigid or deformable. An example of this type of contact problem is a wire inserted into a slot.
Unlike the node-to-node contact elements, you do not need to know the exact location of the contacting area beforehand, nor do the contacting components need to have a compatible mesh. Large deformation and large relative sliding are allowed, although this capability can also model small sliding.
CONTA175 does not support 3D higher-order elements on the contact surface side. The element can fail if the target surface is severely discontinuous. No contour plots are available for contact results.
The contact line element, CONTA177, is typically used to model 3D beam-to-beam contact (crossing beams or beams that are parallel to each other) or a pipe sliding inside another pipe. Some practical applications are woven fabric and tennis racquet strings.
CONTA177 can be attached to 3D beam or pipe elements and supports both low-order and higher-order elements on the contact surface. The target surface is modeled with 3D line segments (TARGE170 straight line or parabolic line elements). This element supports large sliding and large displacement applications. For more information on how to use CONTA177, see 3D Beam-to-Beam Contact (Pair-Based).
The contact line element, CONTA177, can be used to model a 3D beam or shell edge contacting solid or shell elements. It can also be used to model 3D edge-to-edge contact.
CONTA177 supports both low-order and higher-order elements on the contact surface. The target surface is modeled with 3D target segment elements (TARGE170). This element is also suitable for large sliding and large displacement applications. For more information on how to use CONTA177, see Line-to-Surface Contact (Pair-Based).
Node-to-node contact elements, CONTA178, are typically used to model point-to-point contact applications. To use node-to-node contact elements, you need to know the location of contact beforehand. These types of contact problems usually involve small relative sliding between contacting surfaces (even in the case of geometric nonlinearities). An example of a node-to-node contact application is the traditional pipe whip model, where the contact point is always located between the pipe tip and the restraint.
Node-to-node contact elements can also be used to solve a surface-to-surface problem if the nodes of the two surfaces line up, the relative sliding deformation is negligible, and deflections (rotations) of the two surfaces remain small. These are typically problems with faceted and simple geometry. An interference fit problem is an example of a surface-to-surface problem where the use of node-to-node contact may be sufficient.
Another use of node-to-node contact elements is in extremely precise analysis of surface stresses, such as in turbine blade analysis.
In addition to unidirectional contact behavior, CONTA178 offers a cylindrical gap option to model contact between two parallel pipes with small relative sliding. (For large sliding applications, see 3D Line-to-Line Contact.) The two pipes can be adjacent to one another, or one pipe can be inside of another hollow pipe. Also, CONTA178 can model contact between two rigid spheres. This can be either two adjacent spheres or one sphere inside of a hollow sphere.