## *MODEL CHANGE

Keyword type: step

With this option one can activate or deactivate elements and contact pairs. Furthermore, one can turn the mechanical strain in existing elements into residual strain at the start of a new step.

One can deactivate or activate any element which has been defined in the model section of the input deck. Before the first step all elements are by default activated. There is one required parameter TYPE=ELEMENT and there are two mutually exclusive parameters ADD and REMOVE. One- and two-dimensional elements which are expanded in CalculiX (such as plane stress or shell elements) cannot be removed in the first step (to circumvent this restriction a dummy first step doing nothing can be inserted). The ADD parameter can be complemented by the modifiers STRAIN FREE or WITH STRAIN (ADD=STRAIN FREE and ADD=WITH STRAIN, respectivily). If ADD=STRAIN FREE is selected the strains at the time of adding the element, if any, are modified by artificial initial strains such that the resulting stress tensor is zero. In that sense the elements are stress free rather than strain free. With ADD=WITH STRAIN the strains at the time of activation are not modified. Default is STRAIN FREE.

To activate or deactivate contact between two surfaces, contact must have been defined between these surfaces using a *CONTACT PAIR card before the first step. By default all contact pairs are activated before the first step. There is one required parameter TYPE=CONTACT PAIR and there are two mutually exclusive parameters ADD and REMOVE.

Finally, one can turn the mechanical strain from the end of the last step into a residual strain by using the parameter MECHSTRAINTORESIDUAL. If no new loading is applied in the actual step this will result in zero stress provided the force equilibrium is still satisfied. This is for instance the case when the loading purely consists of prescribed displacements. No elements are added or deleted.

First line:

• *MODEL CHANGE
• enter the required parameter TYPE=CONTACT PAIR or TYPE=ELEMENT and one of the mutually exclusive parameters ADD and REMOVE.

Following line for TYPE=ELEMENT:

• List of elements and/or sets of elements to be activated or deactivated (maximum 16 entries per line).

Repeat this line if needed

Following line for TYPE=CONTACT PAIR:

• Name of the slave surface (can be nodal or element face based).
• Name of the master surface (must be based on element faces).

Only one such line is allowed; repeat *MODEL CHANGE if several contact pairs are to be modified.

Example:

*MODEL CHANGE,TYPE=CONTACT PAIR,REMOVE
dep,ind


deactivates contact between the surfaces dep and ind.

Example files: modelchel,modelchel2