The following guidelines apply to analyses using the element birth and death capability:
Constraint equations (CE, CEINTF, etc.) cannot be applied to inactive degrees of freedom. Inactive degrees of freedom occur when a node has no active ("alive") elements attached to it.
You can model stress-relieving operations (such as annealing) by deactivating and then reactivating elements.
In nonlinear analyses, be careful not to deactivate or reactivate elements in such a way as to create singularities (such as sharp re-entrant corners in a structural analysis) or sudden large changes in stiffness. Such situations are likely to cause convergence difficulties.
Killing contact/target elements or their underlying elements will cause the status of the contact pair to change to far field contact (open and not near contact), even for bonded contact. You may need to kill both the contact/target elements and their underlying elements to reestablish the pre-death contact status when the elements are later reactivated.
The full Newton-Raphson option with adaptive descent activated (NROPT,FULL,,ON) often yields good results in analyses employing element birth and death.
You can retrieve a parameter whose value will indicate the status (active or inactive) of an element (*GET,Par,ELEM, n, ATTR, LIVE) This parameter could be used in APDL logical branching (*IF, etc.) or in other applications for which you need to monitor the birth-and-death status of an element.
Since a Multiframe restart will recreate the database using the *.rdb file, the elements selected in /POST1 can not be killed in a multiframe restart.
The load-step file method (LSWRITE) for solving multiple load steps cannot be used with the birth-death option, because it will not write the status of deactivated or reactivated elements to the load step file. Birth and death analyses having multiple load steps must therefore be performed using a series of explicit SOLVE commands.
You might be tempted to deactivate or reactivate elements by changing their material properties via the MPCHG command.
You must proceed cautiously if you attempt such a procedure. The safeguards and restrictions applying to "killed" elements do not apply to elements that have had their material properties changed in the solution phase of the analysis. (Element forces will not be automatically zeroed out; nor will strains, mass, specific heat, etc.) Many problems can result from careless use of the MPCHG command. For example, if you reduce an element's stiffness to almost zero, but retain its mass, it could result in a singularity if subjected to acceleration or inertial effects.
One application of the MPCHG command would be in modeling construction sequences in which the strain history of a "born" element is maintained. Using MPCHG in such cases will enable you to capture the initial strain experienced by elements as they are fitted into the displaced nodal configuration.