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Contact overview

Automatic vs. Non-automatic:

Automatic contacts are recommended for most explicit simulations. Non-automatic contacts (in which contact orientation is important) are sometimes used for metal forming simulations where the geometries are very straightforward and contact surface orientation can be reliably established before the simulation is conducted. Non-automatic contacts are generally recommended for implicit simulations.

Contact types:

Type 13 contact *CONTACT_AUTOMATIC_SINGLE_SURFACE is a single surface contact (no master surface is defined) that always considers shell thickness and has no orientation. Thus it's necessary that shell surfaces be modeled with at least a small gap between them. To avoid initial penetrations, the gap should be no less than the average thickness of the two shells potentially in contact. No gap is necessary between solid elements. The contact searching algorithm for type 13 contact is more complex than for type 3 *CONTACT_SURFACE_TO_SURFACE or a3 *CONTACT_AUTOMATIC_SURFACE_TO_SURFACE, i.e., type 13 can handle situations such as shell edge to surface, and to some extent, beam to shell surface. As with any single surface contact type, resultant forces are not directly retrievable in the RCFORC file; one must define a *CONTACT_FORCE_TRANSDUCER_PENALTY in order to retrieve the contact forces. The article What is the difference between CONTACT_AUTOMATIC_SINGLE_SURFACE and CONTACT_AUTOMATIC_GENERAL ? provides additional information on *CONTACT_AUTOMATIC_SINGLE_SURFACE and contrasts it to *CONTACT_AUTOMATIC_GENERAL.

Type 3 contact *CONTACT_SURFACE_TO_SURFACE is a surface-to-surface (two-way) contact where shell thickness consideration can either be turned on or off either in *CONTACT or *CONTROL_CONTACT (*CONTACT_ has priority). The orientation of the contact segments is important with this contact type as the shell only looks in one direction for potential contact. In a two-way contact such *CONTACT_SURFACE_TO_SURFACE, nodes on the slave side are first checked for penetration thru the master surface and then master nodes are checked for penetration thru the slave surface. The exception is this approach is when segment-based contact is invoked by setting SOFT=2. Type a3 Contact type a3 has no orientation (a shell looks for potential contact from either side of the shell midplane) and always considers shell thickness, so in this regard, it's quite similar to a type 13 contact. Table 6.1 in the 950 Keyword User's Manual lists the maximum penetration d that defines when a penetrating node is released from contact consideration. This distance d is different for a type 3 contact than for a type 13 contact.

Some notes on contact parameters:

SOFT

SOFT is the first parameter on Optional Card A of *CONTACT_ The default value of SOFT is 0. SOFT=1 is more or less the same as SOFT=0 EXCEPT in the way the contact stiffness is determined. SOFT=2 is a radical departure from SOFT=0, both in the way contact stiffness is determined but also in the manner that the search for penetration is conducted. SOFT=2 invokes what is called "segment-based contact". For notes regarding contact with SOFT= 1 and 2, see the article SOFT option .

IGNORE

At any point during the simulation, if a node is suddenly found to be below the surface (say, it was moving very fast and wasn't detected before penetration), the old style (IGNORE=0) algorithm just moves the node to the master surface without applying any forces (we term this "shooting node logic"). If the shooting node logic is turned off (SNLOG=1), then you get large forces suddenly appearing, and negative contact energy. If IGNORE is set to 1 then the shooting node logic flag SNLOG has no affect. Rather the amount of sudden penetration is noted and compensated for by adjusting the contact thickness locally. So at any time during the simulation, if a sudden penetration is detected, the program doesn't apply any large forces nor are any nodes moved. Contact forces, however, will resist FURTHER penetration.

jpd 12/2002 revised 4/2003 revised 9/2003 auto vs. non-auto