CONTACT: Defining Contact Surfaces

PEN_CHECK Runs the penetration checker for contacts.

The penetration checker detects initial penetrations and crossed edges. It displays them graphically and also generates "null beams" on the crossed edges to identify them during external remeshing. Its use is summarised below.

The functions currently available have their standard meanings. (See Standard Keyword Top Level Menu Options)

Only is a function for dispalying contact contents, and is described below.

Ansys LS-DYNA has an optional _TITLE suffix to the * CONTACT_<type> keyword that is enabled if this is defined.

Optional data...

Defining data on optional *CONTACT cards A, B, C, D & E

All contact types may have additional data for optional cards A, B, C, D & E in Ansys LS-DYNA.

The exact options available will depend upon the contact type, for example the Airbag thickness vs time loadcurve is not valid for the (eroding) contact type used in this example.

The red [ ?-LC ] symbol on this panel is used to denote the fact that a loadcurve value is implied in this context if a negative number is input, whereas zero or a positive number is a simple constant. Pressing this button will give a selection menu of possible loadcurves.

(A green [ ?LC ] means that a positive value implies a loadcurve.)

When you have completed entries on this panel ==> MAIN PANEL returns you to the master panel shown above.

_<type> data... Special data input for this contact surface type.

A few contact surface types have mandatory <type> data cards. If this is the case the [_<type>_data...] button on the main panel will be live.

In this example the _ERODING_... contact type requires the extra data shown here; but other contact types will require different data.

As with the optional data cards, ==> MAIN PANEL will return you to the main contact input panel.

_THERMAL data... Special input for thermal contact types.

Where a contact surface type supports the _THERMAL or _THERMAL_FRICTION qualifier, and this is turned on, the _THERMAL data... button may be used to enter the thermal parameters.

As with the other optional card panels the ==>MAIN PANEL button will return you to the master contact definition panel.

KEYWORD Using the generic keyword editor to process contacts

The reason for this is that all *CONTACT definitions occupy at least three rows of data, some use four, and if extra keyword suffices are added then more lines may be used. Adding all five optional cards makes each keyword entry very tall, and most optional fields are not used, so the keyword editor would show many lines - mostly full of zeros - for only one or two contacts if these were always shown.

Therefore, for each contact, you must choose how many optional cards are to be "live" by setting the pseudo-suffix " Opt A-E ".

When the keyword editor is started each contact definition will have this suffix initialised to the current status, determined by scanning optional cards A to E for non-zero values or parameter usages, and will be preset accordingly.

If you want to add data to later rows, not currently active, you will first need to change this suffix to the appropriate setting, just like changing any other keyword suffix, whereupon the relevant rows will be shown in the editor.

This pseudo-suffix is purely an artifice in the keyword editor, the suffix will not be shown on the *CONTACT card when the deck is written to a keyword file.

RECURSIVE_COPY Controlling the extent of a copy operation for segment based contacts.

If "recursive" copying is used then any segment sets, (and thus their associated segments), in the subject contacts are duplicated; and the newly created contacts will reference these duplicates. Without "recursive" copying the new contacts will reference the same segment sets as the old ones. This is illustrated in the examples below, using the same 3 contacts:

With RECURSIVE_COPY selected.

In the left box recursive copying has picked up segment sets and their constituent segment.

In the right box, without recursive copying, only the contact definitions are copied.

Note that for contacts recursive copying only affects segment sets and their segments. A contact defined by parts, elements or nodes will not attempt to copy these in the "recursive" case.

LIST Summarise the contents of contacts

LIST allows the user to select any or all contacts and to list a summary of their attributes to the screen.

A listing shows contact number, title and type, plus the total in each model. A typical listing is shown here.

RENUMBER

Raises the standard renumbering panel for contacts in the chosen model, allowing you to renumber some or all of them. To renumber a single contact it may be easier to MODIFY it and update its label.

PEN_CHECK Checking initial penetrations and crossed edges

The contact penetration checker may be run from:

• The PEN_CHECK command in the top level menu here
• The PEN_CHECK command in any contact create/edit panel
• The main MODEL > CHECK command as part of model checking

Calling the penetration checker from the top menu panel

Summarise all Runs the checker on all contacts in turn in "summary" mode, producing a listing of penetrations and crossed edges for each one, but no details. Note - the number of penetrations may exceed the number of penetrating nodes as there may be >1 penetration on a node.

This is useful as an initial scan to look for problems meriting further attention.

Contact Tree As Summarise all but displayed as Quality check warnings on tree. This allows the user to access the detailed Pen Check for each contact directly.

-> pencheck.csv writes all qualifying (above user threshold) part vs part interactions to a .csv file.

Explicit selection from menu

Runs the checker in detailed mode on the contact selected.

By default the contact check will be performed using MPP methods with the exception of the minimum threshold for reported penetrations. PRIMER uses the minimum of the SMP threshold (calculated from element sizes) and 0.001 (the hard-wired Ansys LS-Dyna threshold). This is far more sensible for models in metre units. However, the user may over-ride this and apply their own value for MPP threshold.

Calling the penetration checker from the Create/Edit panel

The PEN_CHECK command in this context runs the checker on the current (scratch) contact definition currently being edited.

Contact penetration checking is covered in more detail in Contact Penetration Checking

Visualising contact surfaces

They are drawn in terms of the parts, elements, nodes and segments that define them. Where boxes are used to delimit contacts these are displayed if switched on in the "Associated data" section.

They may also be drawn via the SKETCH functions above.

Special display modes for contact surfaces

Since contacts are drawn in terms of the structural elements or segments that define them it would be difficult to distinguish a contact from normal structure if both were rendered in the same way. Therefore PRIMER use different forms of display to distinguish contacts from ordinary structure.

By default contacts are drawn using a technique called "stippling", as shown here, in which alternate pixels are omitted. This gives a distinctive slighty fuzzy appearance, but also allows graphics of other items behind the contact to be visible.

In this example a contact covers the whole of the dummy's head, but internal structure (beams and accelerometers) is visible through the stippled contact.

Other display modes for contacts are available in the Display Options panel.

Various degrees of stippling give different effects. It is also possible to revert to the "old" PRIMER method of drawing the contacts solid shaded with cross-hatched lines added, however this is slow to render and is not recommended.

Rather than trying to describe the effects here it is suggested that the curious try experimenting

Duplicates during input

*CONTACT cards can have the suffix _TITLE in which case they must also be given a specific label. If two or more such cards have the same label then normally PRIMER would treat this as an input error and reject the input deck.

However it transpires that Ansys LS-DYNA has some special logic to deal with this situation, meaning that duplicate contact definitions are (semi) legal:

• Before Ansys LS-DYNA R7: It issued a warning and continued to run with both contact definitions, leaving them both as having the same label. This could make post-processing confusing!
  
• From Ansys LS-DYNA R7 onwards: It also issued a warning and continued to run, but relabelled the duplicate contact to the next "highest + 1" label.

Therefore from PRIMER 13 onwards the treatment of duplicate contact cards during keyword input has been modified as follows:

• Duplicate contact cards are read silently, and the excess definitions are given temporary internal labels that prevent label clashes.
• When keyword input is complete these duplicates are listed on the screen, together with their include files and whether or not they are referenced.
• The user must then choose one of three options for dealing with them:

Warning:

Although Ansys LS-DYNA will accept this practice it is recommended that you do not use it . Not only is it a "hostage to fortune" that relies on non-standard and undocumented Ansys LS-DYNA behaviour, but also the labels ultimately assigned to contact surfaces in Ansys LS-DYNA will depend on the order in which they are read, and changing include file order will affect this.

It is strongly recommended that you either eliminate duplicate definitions, or relabel them explicitly to make them unique.

Note:

This treatment of duplicate contact definitions is not standard PRIMER behaviour, and applies only to the *CONTACT keyword.

The standard treatment of duplicate labelled keyword is controlled by the Options panel during keyword input, and is described in Options: Permit duplicate definitions.