Edge-to-edge contact

Most contact types do not check for edge-to-edge penetrations as the search entails only nodal penetration through a segment. This may be adequate in many cases; however, in some unique shell contact conditions, the treatment of edge-to-edge contact becomes very important.

There are several ways to handle edge-to-edge contact; the merits/demerits of each one of these methods are discussed below.

*CONTACT_AUTOMATIC_GENERAL excluding Interior Edges

By default, *CONTACT_AUTOMATIC_GENERAL considers only exterior edges in its edge-to-edge treatment as indicated by Figure 1. An exterior edge is defined as belonging to only a single element or segment whereas interior edges are shared by two or more elements or segments. The entire length of each exterior edge, as opposed to only the nodes along the edge, is checked for contact. As with other penalty-based contact types, SOFT=1 can be activated to effectively treat contact of dissimilar materials.

*CONTACT_AUTOMATIC_GENERAL including Interior Edges

Edge-to-edge contact which includes consideration of interior edges may be invoked in one of two ways. One method takes advantage of the beam-to-beam contact capability of *CONTACT_AUTOMATIC_GENERAL. This labor-intensive approach involves creating null beam elements (*ELEMENT_BEAM, *MAT_NULL) approximately 1 mm in diameter (elform=1, ts1=ts2=1,2mm, tt1=tt2=0 in *SECTION_BEAM) along every interior edge wished to be considered for edge-to-edge contact and including these null beams in a separate *AUTOMATIC_GENERAL contact. This is illustrated in Figure 2. The elastic constants in *MAT_NULL are used in determining the contact stiffness so reasonable values should be given. Null beams do not provide any structural stiffness.

A preferred alternative to the null beam approach, available in version 960, is to invoke the interior edge option by using *CONTACT_AUTOMATIC_GENERAL_INTERIOR. A certain cost penalty is associated with this option.

*CONTACT_SINGLE_EDGE

This contact type treats edge-to-edge contact but, unlike the other options above, it treats only edge-toedge contact. This contact type is defined via a part ID, part set ID, or a node set on the slave side. The master side is omitted.

figure 9_1

Figure 1 Interior and Exterior Shell Edges

figure 9_2

Figure 2 Null Beams to treat edge-to-edge treatment

sb 2001