How to overcome from element penetration LS-Dyna
Nikesh Kumar Ojha
James Kennedy
Dear Nikesh,
Addition notes on contact.
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Following notes taken from this link:
http://www.dynasupport.com/tutorial/ls-dyna-users-guide/contact-modeling-in-ls-dyna
Contact modeling in LS-DYNA
Contact treatment forms an integral part of many large-deformation problems.
Accurate modeling of contact interfaces between bodies is crucial to the prediction
capability of the finite element simulations. LS-DYNA offers a large number of
contact types. Some types are for specific applications, and others are suitable for
more general use. Many of the older contact types are rarely used but are still re-
tained to enable older models to run as they did in the past. Users are faced with
numerous choices in modeling contact. This document is designed to provide an
overview of contact treatment in LS-DYNA and to serve as a guide for choosing
appropriate contact types and parameters.
How Contact Works
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. A search for penetrations, using any of a number of
different algorithms, is made every time step. 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. Unless otherwise stated, the contacts
discussed here are penalty-based contacts as opposed to constraint-based contacts.
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.
Though sometimes it is convenient and effective to define a single contact that will
handle any potential contact situation in a model (for example, *CONTACT_AUTO-
MATIC_SINGLE_SURFACE), it is permissible to define any number of contacts in
a single model. 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. 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. In the following sections (see above link),
contact types are first discussed with recommendations regarding their application.
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You first must make a decision as to which contact type might best represent the
numerical simulations you wish to attempt.
Links discussing crash analysis in LS-DYNA:
Bala, S., and Day, J., "General Guidelines for Crash Analysis in LS-DYNA", Livermore
Software Technology Corporation, Livermore, California, November, 2006.
http://ftp.lstc.com/anonymous/outgoing/jday/faq/guidelines.ppt
http://blog2.d3view.com/wp-content/uploads/2006/11/Crash_Guidelines.pdf\
Kessler, D., "Workshop: Best Practice in Crash Analysis and LS-DYNA Tools", 13th
German LS-DYNA Forum, Bamberg, Germany, October, 2014.
Once you have chosen your contact option, then you can choose which set of input
parameters (usually segments, parts, part sets, nodes or boxes volumes) for identifying
the contacting object that will work best or most efficient for your model (full options
given here):
*CONTACT_xxxx
SSID - Slave segment set ID, node set ID, part set ID, part ID, or shell element set ID,
see *SET_SEGMENT, *SET_NODE_OPTION, *PART, *SET_PART or *SET_SHELL_
OPTION. For ERODING_SINGLE_SURFACE and ERODING_SURFACE_TO_
SURFACE contact types, use either a part ID or a part set ID. For ERODING_NODES_
TO_SURFACE contact, use a node set which includes all nodes that may be exposed to
contact as element erosion occurs.
EQ.0: Includes all parts in the case of single surface contact types.
MSID - Master segment set ID, node set ID, part set ID, part ID, or shell element set ID..
EQ.0: Master side is not applicable for single surface contact types.
SSTYP - ID type of SSID:
EQ.0: segment set ID for surface-to-surface contact,
EQ.1: shell element set ID for surface-to-surface contact,
EQ.2: part set ID,
EQ.3: part ID,
EQ.4: node set ID for nodes-to-surface contact,
EQ.5: include all (SSID is ignored),
EQ.6: part set ID for exempted parts. All non-exempted parts are included in the contact.
For AUTOMATIC_BEAMS_TO_SURFACE contact, either a part set ID or a part ID can
be specified.
MSTYP - ID type of MSID:
EQ.0: segment set ID,
EQ.1: shell element set ID,
EQ.2: part set ID,
EQ.3: part ID.
EQ.4: node set ID (for eroding force transducer only. See Remark 3),
EQ.5: include all (MSID is ignored).
EQ.6: part set ID for exempted parts. All non-exempted parts are included in the contact.
SBOXID - Include in contact definition only those slave nodes/segments within box
SBOXID (corresponding to BOXID in *DEFINE_BOX), or if SBOXID is negative, only
those slave nodes/segments within contact volume |SBOXID| (corresponding to CVID in
*DEFINE_CONTACT_VOLUME). SBOXID can be used only if SSTYP is set to 2 or 3,
i.e., SSID is a part ID or part set ID. SBOXID is not available for_ERODING contact
options.
MBOXID - Include in contact definition only those master segments within box MBOXID
(corresponding to BOXID in *DEFINE_BOX), or if MBOXID is negative, only those
master segments within contact volume |MBOXID| (corresponding to CVID in *DEFINE_
CONTACT_VOLUME). MBOXID can be used only if MSTYP is set to 2 or 3, i.e., MSID
is a part ID or part set ID. MBOXID is not available for_ERODING contact options
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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.
I recommend that you use the newer "automatic" option. Please consider the placement
of your shell mid-surface when using this newer contact.
Automatic contact types in LS-DYNA are identifiable by the occurrence of the word
AUTOMATIC in the *CONTACT command. The contact search algorithms employed
by automatic contacts make them better-suited than older contact types to handling
disjoint meshes. 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'. 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. We sometimes refer to this off-
setting of the contact surfaces from shell mid-planes as considering shell thickness offsets.
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Bala, S., "Contact Modeling in LS-DYNA - Parts 1, 2, 3, and 4", Livermore Software
Technology Corporation, Livermore, California, August, 2001.
http://blog2.d3view.com/wp-content/uploads/2007/10/contact_modeling_in_ls-dyna_parts1-4.pdf
Bala, S., "Contact Modeling in LS-DYNA", Livermore Software Technology Corporation,
Livermore, California, August, 2001.
http://www.dynasupport.com/tutorial/contact-modeling-in-ls-dyna
Please see latest Theory Manual, Section 29 Contact-Impact Algorithm
"LS-DYNA Theory Manual", LS-DYNA Dev/Revision 8903, Livermore Software
Technology Corporation, Livermore, California, August, 2017.
http://ftp.lstc.com/anonymous/outgoing/jday/manuals/DRAFT_Theory.pdf
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Connection/interfacing of different parts has many different influences and considerations.
Presentations on the available contacts:
Stelzmann, U., "Robuste und Effiziente Kontaktmodellierung in LS-DYNA: Wie gut sind die neuen
Optionen?", 30th CADFEM Users' Meeting, Kassel, Germany, October, 2012.
http://www1.beuth-hochschule.de/~kleinsch/Expl_FEM/2012_Explizit_Kontakte_UM.pdf
Karajan, N., Graf, T., and Andrade, F., "Workshop: Kontakte in LS-DYNA", 13th German LS-DYNA
Forum, Bamberg, Germany, October, 2014.
https://www.youtube.com/watch?v=KgvYHbMObso
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For most cases I usually try to use SOFT=2; however, there are many instances
where I am required to use SOFT=1 due to different contacting material stiffnesses.
The default, SOFT=0, usually works well for simple contact geometry involving similar
stiffness materials.
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If you are only addressing contact without element failure and penetration, I would
suggest trying *CONTACT_AUTOMATIC_SURFACE_TO_SURFACE with soft=1.
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Eroding contact types are recommended whenever solid elements involved in the contact
definition are subject to erosion (element deletion) due to material failure criteria. These
eroding contacts contain logic which allow the contact surface to be updated as exterior
elements are deleted.
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Sincerely,
James M. Kennedy
KBS2 Inc.
February 16, 2022
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