In general, curved contact and target surfaces can be well approximated by contact and target elements when the mesh is sufficiently refined. However, in certain circumstances this is not the case. For example, when the underlying elements do not have midside nodes or when the midside nodes of quadratic elements do not lie exactly on the initial curved geometry because a third party mesh generator was used. Therefore, in some contact applications, using a faceted surface in place of the true curved geometry can significantly affect the accuracy of contact stresses.

To avoid this problem, you can use an optional geometric correction for circular segments and for spherical and revolute (cylindrical) surfaces via SECTYPE and SECDATA section commands (see Surface Smoothing). Geometry correction is available for surface-to-surface contact elements (TARGE169, TARGE170, CONTA172, and CONTA174).

All types of geometry correction for contact (that is, contact section sub-types on the SECTYPE command) are available for general contact surfaces, including the bolt-thread geometry correction. See Geometry Correction for Contact and Target Surfaces for details.

Input a section ID or a node component name on the SECTYPE command to identify the general contact surface that needs correction. For example, to apply a cylindrical geometry correction to a specific surface whose section ID can be represented by a pre-defined node component, use the following command:

SECTYPE,ComponentName,CONTACT,CYLINDER
SECDATA,X1,Y1,Z1,X2,Y2,Z2

An extension can be added to the component name to limit the scope of the section IDs used from the node component, as described in Specifying General Contact Interactions Between Nodal Components. The labels ALL_EDGE, ALL_FACE, ALL_TOP, and ALL_BOT can also be input on the SECTYPE command to identify the general contact surface. (See the GCDEF command for details of the meaning of each label.)

Equivalent Radius for Beam-to-Beam and Edge-to-Edge Contact

To model 3D beam-to-beam contact and edge-to-edge contact (CONTA177 element), the program assumes two cylinders are coming into contact. The equivalent radius of the assumed cylindrical surface is defined via SECTYPE and SECDATA commands:

SECTYPE,SECID,CONTACT,RADIUS   ! Set Type = CONTACT and Subtype = RADIUS for user-defined contact radius
SECDATA,VAL1,VAL2,VAL3         ! VAL1 and VAL2 are radius values; VAL3 is a flag

where:

If the radius is not defined, the program determines a corresponding radius for each CONTA177 contact element based on the geometry of the underlying element.

This same SECTYPE and SECDATA input format is used to define the radius of a TARGE170 rigid target element that represents a beam (a line or parabola) in a general contact definition. However, for the TARGE170 element, the program cannot determine a corresponding radius if one is not supplied because there is no underlying element. Therefore, you must explicitly input the target radius for all TARGE170 target segments.

Radius (or Radii) of Primitive Rigid Target Segments

Some primitive rigid target segments require a radius (or radii) to be input as part of their definition. These include the 2D circle segment (TARGE169 element) and the 3D cylinder, sphere, and cone segment types (TARGE170 element). The radius or radii associated with the rigid target geometry are defined via SECTYPE and SECDATA commands, as follows:

SECTYPE,SECID,CONTACT,RADIUS   ! Set Type = CONTACT and Subtype = RADIUS 
SECDATA,VAL1,VAL1              ! Enter radius values R1 and R2

where VAL1 and VAL2 are the radius values required for the target geometry being defined (see the TARGE169 and TARGE170 descriptions for specific geometry details).