Products: ABAQUS/Standard ABAQUS/CAE
Removal and reactivation of contact pairs in ABAQUS/Standard:
can be used to simulate complicated forming processes where multiple tools need to interact with the workpiece at different stages in the analysis;
can result in significant computational savings by eliminating unnecessary contact searches and updates of surface orientations during the simulation;
can be performed in mechanical, coupled temperature-displacement, coupled pore pressure-displacement, coupled thermal-electrical, or heat transfer simulations;
cannot be performed with “tied” contact pairs; and
cannot define new contact pairs.
Removal of contact pairs is a useful technique for uncoupling components of an assembly until they should be brought together (such as tooling in manufacturing process simulations). Significant computational expense may be saved by removing a contact pair and introducing it at the proper time, thus eliminating the need to monitor the contact conditions except when they are relevant.
| Input File Usage: | *MODEL CHANGE, TYPE=CONTACT PAIR, REMOVE slave_surface, master_surface |
Repeat the data line as needed. |
| ABAQUS/CAE Usage: | Interaction module: interaction manager: select interaction, Deactivate |
If the surfaces are in contact when a contact pair is removed, ABAQUS/Standard stores the corresponding contact forces (or heat fluxes if thermal interactions are present, or electrical currents if it is a coupled-thermal electrical analysis) for every node on each surface. ABAQUS/Standard automatically ramps these forces (or heat fluxes or electrical currents) linearly down to zero magnitude during the removal step. ABAQUS/Standard always removes the contact constraints for mechanical surface interactions instantaneously.
Care must be taken in removing contact pairs in transient procedures. In transient heat transfer or fully coupled temperature-displacement analysis if the fluxes are high and the step is long, this ramping down may have the effect of cooling down or heating up the rest of the body. In dynamic analysis if the forces are high and the step is long, kinetic energy can be imparted to the remaining portion of the model. This problem can be avoided by removing the contact pairs in a very short transient step prior to the rest of the analysis. This step can be done in a single increment.
A contact pair with mechanical contact interactions can be deactivated during an analysis by assigning a very large allowable contact interference to the contact pairs (see “Modeling contact interference fits in ABAQUS/Standard,” Section 29.2.4). This method has the disadvantage of not reducing the computational cost of the analysis because the contact algorithm will still calculate the contact conditions for the contact pair in each increment.
All contact pairs that will be used in a simulation must be created at the start of the analysis; they cannot be created once the simulation has begun. However, contact pairs can be created, removed at the start of the analysis in the first step, and then reactivated at a later point during the simulation.
In ABAQUS/CAE you can create contact pairs in any step. If a contact pair is created in a step other than the initial step, ABAQUS/CAE automatically deactivates the contact pair in the initial step and reactivates it in the step in which you created it.
| Input File Usage: | *MODEL CHANGE, TYPE=CONTACT PAIR, ADD slave_surface, master_surface |
Repeat the data line as needed. |
| ABAQUS/CAE Usage: | User-specified reactivation of contact pairs is not supported in ABAQUS/CAE. |
When a contact pair is reactivated, the contact constraint becomes active immediately. In mechanical simulations it is possible for the surfaces of a contact pair to move such that they become overclosed while the contact pair is inactive. If this overclosure is too severe when the contact pair is reactivated, ABAQUS/Standard may encounter convergence problems as it tries to enforce the suddenly activated contact constraint. To avoid such problems, you can specify a permissible interference value, v, for the contact pair that is larger than the overclosure for the contact pair. ABAQUS/Standard will ramp v down to zero during the step. For details on specifying allowable interferences, see “Modeling contact interference fits in ABAQUS/Standard,” Section 29.2.4.