The contact thickness can be specified directly or scaled by the user using optional parameters in the contact definition. We sometimes refer to this offsetting of the contact surfaces from shell mid-planes as considering shell thickness offsets. Further, at the exterior edge of a shell surface, the contact surface wraps around the shell edge with a radius equal to one-half the contact thickness thus forming a continuous contact surface. In the case of shell elements, automatic contact types determine the contact surfaces by projecting normally from the shell mid-plane a distance equal to one-half the contact thickness. The contact search algorithms employed by automatic contacts make them better-suited than older contact types to handling disjoint meshes.
Automatic contact types in LS-DYNA are identifiable by the occurrence of the word AUTOMATIC in the *CONTACT command. For this reason, the automatic contact options are recommended as these contacts are non-oriented, meaning they can detect penetration coming from either side of a shell element. In crash analysis, the deformations can be very large and predetermination of where and how contact will take place may be di cult or impossible. *CONTACT_AUTOMATIC_SINGLE_SURFACE (with SOFT=2, SBOPT=3 and DEPTH=5) Type 10: *CONTACT_ONE_WAY_SURFACE_TO_SURFACE Type 9: *CONTACT_TIEBREAK_SURFACE_TO_SURFACE Type 8: *CONTACT_TIEBREAK_NODES_TO_SURFACE Type 7: *CONTACT_TIED_SHELL_EDGE_TO_SURFACE Type i26: *CONTACT_AUTOMATIC_GENERAL_INTERIOR Type 13: *CONTACT_AUTOMATIC_SINGLE_SURFACE A description of the contact parameters is then presented. In the following sections, contact types are first discussed with recommendations regarding their application. To enable flexibility for the user in modeling contact, LS-DYNA presents a number of contact types and a number of parameters that control various aspects of the contact treatment. It is generally recommended that redundant contact, i.e., two or more contacts producing forces due to the same penetration, be avoided by the user as this can lead to numerical instabilities. Though sometimes it is convenient and effective to define a single contact that will handle any potential contact situation in a model, it is permissible to define any number of contacts in a single model. Rigid bodies may be included in any penalty-based contact but in order that contact force is realistically distributed, it is recommended that the mesh defining any rigid body be as fine as that of a deformable body. Unless otherwise stated, the contacts discussed here are penalty-based contacts as opposed to constraint-based contacts. In the case of a penalty-based contact, when a penetration is found a force proportional to the penetration depth is applied to resist, and ultimately eliminate, the penetration. A search for penetrations, using any of a number of different algorithms, is made every time step. In LS-DYNA, a contact is defined by identifying (via parts, part sets, segment sets, and/or node sets) what locations are to be checked for potential penetration of a slave node through a master segment.
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