The CONTA177 description is the same as for CONTA174 - 3D 8-Node Surface-to-Surface Contact except that it is a 3D line contact element.

Four different scenarios can be modeled by CONTA177:

Use KEYOPT(3) = 0 or 1 for the first three scenarios (internal contact and parallel beams). In these cases, the contact condition is only checked at contact nodes.

Use KEYOPT(3) = 3 or 4 for the fourth scenario (beams that cross). In these cases, the contact condition is checked along the entire length of the beams. The beams with circular cross-sections are assumed to come in contact in a point-wise manner.

Use KEYOPT(3) = 2 for all scenarios. The contact condition is only checked at contact nodes for the first three scenarios, and on an intersection along the beams for the fourth scenario. The program reports contact pressure (contact traction-based model).

Figure 13.29: Beam Sliding Inside a Hollow Beam

Figure 13.30: Parallel Beams in Contact

Figure 13.31: Crossing Beams in Contact

Contact is detected when two circular beams touch or overlap each other. The non-penetration condition for beams with a circular cross section can be defined as follows.

For internal contact:

and for external contact:

where g is the gap distance; r_c and r_t are the radii of the cross sections of the beams on the contact and target sides, respectively; and d is the minimal distance between the two beams which also determines the contact normal direction (see Figure 13.31: Crossing Beams in Contact). Contact occurs for negative values of g.

The contact model can be either contact force-based (KEYOPT(3) = 0 or 4) or contact traction-based (KEYOPT(3) = 1, 2, or 3). For the contact traction-based model, the program determines the area (based on the underlying beam element length and the contact radius, R2) associated with the contact node.

In order to satisfy contact compatibility, forces are developed in a direction normal (n-direction) to the target that will tend to reduce the penetration to an acceptable numerical level. In addition to normal contact forces, friction forces are developed in directions that are tangent to the target plane.

(13–296)

where:

(13–297)

where:

FT = tangential contact force

KT = tangential contact stiffness (input as FKT on R command)

uT = contact slip distance

For orthotropic friction, μ_eq is computed using the expression:

(13–298)

where: