Contact Interfaces

Warning ID 94 and Warning ID 477.

Where, $l_{\min }$ is the minimum main element edge length.

WARNING ID :           94
** WARNING IN INTERFACE GAP
DESCRIPTION :  
   -- INTERFACE ID : x
   -- INTERFACE TITLE : xxx
   INPUT GAPmin xxx > (MINIMUM MAIN ELEMENT EDGE LENGTH) / 2
   FOR SELF CONTACT, ARTIFICIAL STIFFENING CAN OCCUR IF AN ELEMENT IS COMPRESSED
   TO PREVENT THIS WARNING, DEFINE GAPmin < xxx
  POSSIBLE IMPACT NUMBER:        xxx  (<=           2 *NSN)

The Gap_min: will be calculated, if it is not defined in the model.

This warning is important for self-impacting interfaces and can be ignored if the interface is not self-imp-impacting. Figure 1 shows an element with edge length, $L$ , and a self-impacting interface where the $Gap=\frac{L}{2}$ . If this element is compressed more than 50%, the red node enters the gap of the neighboring element and a self-contact is then detected which is not physical. This leads to over-stiffening of the structure and non-physical behavior.

Figure 1.

Therefore, it is recommended to define $Ga{p}_{\min }<\frac{l_{\min }}{2}$ .

If $Ga{p}_{\min }>L$ , a self-contact will be detected which generates contact forces from the beginning of the computation. Such a situation can be accepted if it is local enough, but not if it is a frequent situation over the self-impacting interface. It is possible to find the source of this message by using a pre-processor and selecting the elements through size criteria.

WARNING ID :          477
** WARNING IN INTERFACE GAP
DESCRIPTION :  
   -- INTERFACE ID : x
   -- INTERFACE TITLE : xxx
   MAXIMUM VARIABLE GAP xxx > (MINIMUM MAIN ELEMENT EDGE LENGTH)/2
   FOR SELF CONTACTS WHERE THE VARIABLE GAP IS LARGE AND THE ELEMENT EDGE LENGTH IS SMALL
   ARTIFICIAL STIFFENING CAN OCCUR DURING ELEMENT COMPRESSION
SOLUTION :     
TO PREVENT THIS ISSUE, USE Igap=3 TO AUTOMATICALLY REDUCE THE GAP BASED ON ELEMENT SIZE
  POSSIBLE IMPACT NUMBER:        xxx  (<=           1 *NSN)

This warning message is like the constant contact gap warning except in this case the maximum variable gap for the entire contact is used in the check, $\max (Ga{p}_{variable})>\frac{l_{\min }}{2}$ . This warning is not as precise because it is very possible that the maximum variable contact Gap is in a different location then the minimum element length and therefore no problem exists in the model.

and the warning message will no longer be output.

Infinite domain detected.

This message can be written during the simulation in the Engine output file.

Such an error message may appear during sorting of contact interfaces when the distance between some nodes of the model becomes infinite.

One has to look at the model behavior to understand why some node coordinates are infinite. One common explanation is "flying" nodes after failure of elements belonging to interface surfaces. In this case using I_del =2 in contact interfaces should fix this problem.

Parameter Bumult.

To detect the secondary nodes and main segments which are in contact, a spatial sort is necessary. Even if using high performance sort algorithms, a full sort at each cycle would not be a fast enough solution. So during sorting, impacts within some security distance up to the gap are retained.

The frequency of interface sorting, that is to say the security distance up to the GAP for storing the candidates to the impact, relies on the parameter Bumult.

It is recommended to not change its value (which is by default 0.20), since it has been determined in order to optimize the performances, based upon our experience.

Recommended tied contact option Spot_flag.

For tied contact /INTER/TYPE2, Spot_flag=27 should be used for tied contact involving solid elements. Spot_flag=28 should be used with tied contact involving shells. Both of these tied contacts use the kinematic method, but will automatically switch to penalty formulation if kinematic conditions are already defined on a secondary node of the tied contact.