To achieve the "element death" effect, the program does not actually remove "killed" elements. Instead, it deactivates them by multiplying their stiffness (or conductivity, or other analogous quantity) by a severe reduction factor (ESTIF). This factor is set to 1.0E-6 by default, but can be given other values. (For more information, see Apply Loads and Obtain the Solution.)

Element loads associated with deactivated elements are zeroed out of the load vector, however, they still appear in element-load lists. Similarly, mass, damping, specific heat, and other such effects are set to zero for deactivated elements. The mass and energy of deactivated elements are not included in the summations over the model. An element's strain is also set to zero as soon as that element is killed.

In like manner, when elements are "born," they are not actually added to the model; they are simply reactivated. You must create all elements, including those to be born in later stages of your analysis, while in PREP7. You cannot create new elements in SOLUTION. To "add" an element, you first deactivate it, then reactivate it at the proper load step.

When an element is reactivated, its stiffness, mass, element loads, etc. return to their full original values. Elements are reactivated with no record of strain history (or heat storage, etc.); that is, a reactivated element is generally strain-free. Initial strain defined as a real constant, however, is not be affected by birth and death operations.

Unless large-deformation effects are activated (NLGEOM,ON), some element types will be reactivated in their originally specified geometric configuration. (Large-deformation effects should be included to obtain meaningful results.)

Thermal strains are computed for newly-activated elements based on the current load step temperature and the reference temperature. Thus, newborn elements with thermal loads may not be stress-free as intended. The material property REFT can be used instead of the global TREF to specify material-dependent reference temperatures, allowing you to specify the activation temperature as a stress-free temperature.