TARGE170 Element Description

TARGE170 is used to represent various 3-D "target" surfaces for the associated contact elements (CONTA173, CONTA174, CONTA175, CONTA176, and CONTA177). The contact elements themselves overlay the solid, shell, or line elements describing the boundary of a deformable body and are potentially in contact with the target surface, defined by TARGE170.

You can impose translational or rotational displacement, temperature, voltage, magnetic potential, pore pressure, and concentration on the target segment element. You can also impose forces and moments on target elements. See TARGE170 in the Mechanical APDL Theory Reference for more details about this element. To represent 2-D target surfaces, use TARGE169, a 2-D target segment element.

For rigid target surfaces, these elements can easily model complex target shapes. For flexible targets, these elements will overlay the solid, shell, or line elements describing the boundary of the deformable target body.

Figure 170.1:  TARGE170 Geometry

TARGE170 Input Data

The target surface is modeled through a set of target segments. Typically, several target segments make up one target surface.

Figure 170.2: TARGE170 Segment Types shows the available segment types for TARGE170. The general 3-D surface segments (3-node and 6-node triangles, and 4-node and 8-node quadrilaterals) and the primitive segments (cylinder, cone, and sphere) can be paired with 3-D surface-to-surface contact elements, CONTA173 and CONTA174, the 3-D node-to-surface contact element, CONTA175, and the 3-D line-to-surface contact element, CONTA177. The line segments (2-node line and 3-node parabola) can be paired with the 3-D line-to-line contact element, CONTA176, and the 3-D line-to-surface element, CONTA177, to model 3-D beam-to-beam contact.

For any target surface definition, the node ordering of the target segment element is critical for proper detection of contact. For the general 3-D surface segments (triangle and quadrilateral segment types), the nodes must be ordered so that the outward normal to the target surface is defined by the right hand rule (see Figure 170.2: TARGE170 Segment Types). Therefore, for the surface target segments, the outward normal by the right hand rule is consistent to the external normal. For 3-D line segments (straight line and parabolic line), the nodes must be entered in a sequence that defines a continuous line. For a rigid cylinder, cone, or sphere, contact must occur on the outside of the elements; internal contacting of these segments is not allowed.

Pair-Based Contact versus General Contact

There are two methods to define a contact interaction: the pair-based contact definition and the general contact definition. Both contact definitions can exist in the same model. TARGE170 can be used in either type of contact definition.

Pair-Based Contact

In a pair-based contact definition, the 3-D contact elements (CONTA173 through CONTA177) are associated with 3-D target segment elements (TARGE170) via a shared real constant set. The program looks for contact interaction only between surfaces with the same real constant set ID (which is greater than zero). The material ID associated with the contact element is used to specify interaction properties (such as friction coefficient) defined by MP or TB commands.

The target surface can be either rigid or deformable. For rigid-flexible contact, the rigid surface must be represented by a target surface. For flexible-flexible contact, one of the deformable surfaces must be overlayed by a target surface. See Designating Contact and Target Surfaces in the Contact Technology Guide for more information.

Each target surface can be associated with only one contact surface, and vice-versa. However, several contact elements could make up the contact surface and therefore come in contact with the same target surface. Likewise, several target elements could make up the target surface and thus come in contact with the same contact surface. For either the target or contact surfaces, you can put many elements in a single target or contact surface, or you can localize the contact and target surfaces by splitting the large surfaces into smaller target and contact surfaces, each of which contain fewer elements.

If a contact surface may contact more than one target surface, you must define duplicate contact surfaces that share the same geometry but relate to separate targets, that is, that have separate real constant set numbers.

General Contact

In a general contact definition, the general contact surfaces are generated automatically by the GCGEN command based on physical parts and geometric shapes in the model. The program overlays contact surface elements (CONTA174) on 3-D deformable bodies (on both lower- and higher-order elements) and 3-D contact line elements (CONTA177) on 3-D beams, on feature edges of 3-D deformable bodies, and on perimeter edges of shell structures. The general contact definition may also contain target elements (TARGE170) overlaid on the surfaces of standalone rigid bodies and lower-order contact surface elements (CONTA173) overlaid on 3-D deformable bodies.

The GCGEN command automatically assigns section IDs and element type IDs for each general contact surface. As a result, each general contact surface consists of contact or target elements that are easily identified by a unique section ID number. The real constant ID and material ID are always set to zero for contact and target elements in the general contact definition.

The program looks for contact interaction among all surfaces and within each surface. You can further control contact interactions between specific surfaces that could potentially be in contact by using the GCDEF command. The material ID and real constant ID input on GCDEF identify interface properties (defined by MP or TB commands) and contact control parameters (defined by the R command) for a specific contact interaction. Unlike a pair-based contact definition, the contact and target elements in the general contact definition are not associated with these material and real constant ID numbers.

Considerations for Rigid Target Surfaces

Each target segment of a rigid surface is a single element with a specific shape, or segment type. The program supports eleven 3-D segment types, as described in Table 170.1: TARGE170 3-D Segment Types, Target Shape Codes, and Nodes. The segment types are defined by several nodes and a target shape code (TSHAP) which indicates the geometry (shape) of the element. The segment location is determined by the nodes.

Some segment types require radii as part of their definition. For pair-based contact, the segment radii are specified by real constants (R1 and R2). For a general contact definition, the radii are specified by section data (the SECTYPE,,CONTACT,RADIUS command with radii entered on the SECDATA command).

Table 170.1:  TARGE170 3-D Segment Types, Target Shape Codes, and Nodes

TSHAP	Segment Type	Nodes (DOF)[1]	R1	R2
TRIA	3-node triangle	1st - 3rd nodes are corner points (UX, UY, UZ) (TEMP) (VOLT) (MAG)	None	None
QUAD	4-node quadrilateral	1st - 4th nodes are corner points (UX, UY, UZ) (TEMP) (VOLT) (MAG)	None	None
TRI6	6-node triangle	1st - 3rd nodes are corner points, 4th - 6th are midside nodes (UX, UY, UZ) (TEMP) (VOLT) (MAG)	None	None
QUA8	8-node quadrilateral	1st - 4th nodes are corner points, 5th - 8th are midside nodes (UX, UY, UZ) (TEMP) (VOLT) (MAG)	None	None
LINE	2-node straight line[2]	1st - 2nd nodes are line end points (UX, UY, UZ)	Target Radius[4]	Contact Radius[5]
PARA	3-node parabola[2]	1st - 2nd nodes are line end points, 3rd is a midside node (UX, UY, UZ)	Target Radius[4]	Contact Radius[5]
CYLI	Cylinder[2][7]	1st - 2nd nodes are axial end points (UX, UY, UZ) (TEMP) (VOLT) (MAG)	Radius	None
CONE	Cone[2][7]	1st - 2nd nodes are axial end points (UX, UY, UZ) (TEMP) (VOLT) (MAG)	Radius at node 1	Radius at node 2
SPHE	Sphere[2][7]	Sphere center point (UX, UY, UZ) (TEMP) (VOLT) (MAG)	Radius	None
PILO	Pilot node[3]	1st point: (UX, UY, UZ, ROTX, ROTY, ROTZ) (TEMP) (VOLT) (MAG)	None	None
POINT	Point[6]	1st point: (UX, UY, UZ)	None	None

1. The DOF available depends on the setting of KEYOPT(1) of the associated contact element. Refer to the element documentation for CONTA173, CONTA174, or CONTA175 for more details.

2. When using the direct generation modeling method to create this target segment, specify the required radius values (define the real constant set for pair-based contact; or define the RADIUS section data for general contact) before creating the element

3. Only pilot nodes have rotational degrees of freedom (ROTX, ROTY, ROTZ).

4. When TARGE170 is paired with the CONTA176 line-to-line contact element, input the target radius as a negative value to model internal 3-D beam-to-beam contact (a beam sliding inside a hollow beam); input a positive value to model external 3-D beam-to-beam contact. When TARGE170 is paired with the CONTA177 line-to-surface element, input a positive target radius for both external and internal beam-to-beam contact.

5. Input a positive contact radius for all types of 3-D beam-to-beam contact.

6. Rigid surface node. This segment type is only used to apply boundary conditions to rigid target surfaces.

7. The surface projection contact method (KEYOPT(4) = 3 on the contact element) does not support primitive target segments.

Figure 170.2: TARGE170 Segment Types shows the 3-D segment shapes.

Figure 170.2:  TARGE170 Segment Types

For simple rigid target surfaces (including line segments), you can define the target segment elements individually by direct generation. You must first specify the SHAPE argument on the TSHAP command. If the target segment requires radius values, you must also define the radius (or radii) before creating the element (specify real constants R1 and R2 for pair-based contact, or specify the RADIUS section type via SECTYPE and SECDATA commands for general contact).

For general 3-D rigid surfaces, target segment elements can be defined by area meshing (AMESH). Set KEYOPT(1) = 0 (the default) to generate low order target elements (3-node triangles and/or 4-node quadrilaterals) for rigid surfaces. Set KEYOPT(1) = 1 to generate target elements with midside nodes (6-node triangles and/or 8-node quadrilaterals).

For 3-D rigid lines, target segment elements can be defined by line meshing (LMESH). Set KEYOPT(1) = 0 (the default) to generate low order target elements (2-node straight lines). Set KEYOPT(1) = 1 to generate target elements with midside nodes (3-node parabolas).

You can also use keypoint meshing (KMESH) to generate the pilot node.

If the TARGE170 elements are created via automatic meshing (AMESH, LMESH, or KMESH commands), then the TSHAP command is ignored and the program chooses the correct shape automatically.

For rigid-to-flexible contact, by default, the program automatically fixes the structural degree of freedom for rigid target nodes if they aren't explicitly constrained (KEYOPT(2) = 0). If you wish, you can override the automatic boundary condition settings by setting KEYOPT(2) = 1 for the target elements. For flexible-to-flexible contact, no special boundary conditions treatment is performed, and the KEYOPT(2) = 0 setting should be used.

You can assign only one pilot node to an entire rigid target surface (or none if it is not needed). In a pair-based contact definition, the target element associated with the pilot node has the same real constant ID as the other target elements in the pair. In a general contact definition, the target element associated with the pilot node has the same section ID, but it has a zero real constant ID, as do the other target elements of each rigid surface in the general contact definition.

The pilot node, unlike the other segment types, is used to define the degrees of freedom for the entire target surface. This node can be any of the target surface nodes, but it does not have to be. All possible rigid motions of the target surface will be a combination of a translation and a rotation around the pilot node. The pilot node provides a convenient and powerful way to assign boundary conditions such as rotations, translations, moments, temperature, voltage, magnetic potential, pore pressure, and concentration on an entire rigid target surface. By default (KEYOPT(2) = 0), you can assign the boundary conditions only to the pilot node, eliminating the need to assign boundary conditions to individual target nodes, thus reducing the chance of errors. The program also automatically fixes the structural degrees of freedom on the pilot node if they aren't explicitly constrained.

By setting KEYOPT(2) = 1 for the target elements, you can apply boundary conditions on any rigid target nodes rather than only on the pilot node. It is your responsibility to make sure the rigid target surface is not under-constrained or over-constrained. It is still recommended that you apply all boundary conditions on the pilot node, even when KEYOPT(2) = 1.

TARGE170 Output Data

The solution output associated with the element is shown in Table 170.2: TARGE170 Element Output Definitions.

The Element Output Definitions table uses the following notation:

A colon (:) in the Name column indicates that the item can be accessed by the Component Name method (ETABLE, ESOL). The O column indicates the availability of the items in the file Jobname.OUT. The R column indicates the availability of the items in the results file.

In either the O or R columns, “Y” indicates that the item is always available, a number refers to a table footnote that describes when the item is conditionally available, and “-” indicates that the item is not available.

You can display or list the actual fluid pressure applied to the target element through several POST1 postprocessing commands, as shown below:

PLESOL,CONT,FPRS
PLNSOL,CONT,FPRS
PRESOL,CONT
PRNSOL,CONT

Note that only the FPRS (fluid penetration pressure) output item is meaningful when the PRESOL and PRNSOL commands are used for target elements.

Table 170.3: TARGE170 Item and Sequence Numbers lists output available through the ETABLE command using the Sequence Number method. See Creating an Element Table in the Basic Analysis Guide and The Item and Sequence Number Table in this reference for more information. The following notation is used in Table 170.3: TARGE170 Item and Sequence Numbers:

TARGE170 Assumptions and Restrictions

TARGE170 Product Restrictions

When used in the product(s) listed below, the stated product-specific restrictions apply to this element in addition to the general assumptions and restrictions given in the previous section.

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