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Chapter 13: Element Birth and Death

If material is added to or removed from a system, certain elements in your model may become come into existence or cease to exist. In such cases, you can use element birth and death options to activate or deactivate selected elements, respectively.

The element birth and death feature is useful for analyzing excavation (as in mining and tunneling), staged construction (as in shored bridge erection), sequential assembly (as in fabrication of layered computer chips), and many other applications in which you can easily identify activated or deactivated elements by their known locations.

The birth and death feature is available in the ANSYS Multiphysics, ANSYS Mechanical, and ANSYS Structural products.

The following additional element birth and death topics are available:

13.1.Elements Supporting Birth and Death

13.2.Understanding Element Birth and Death

13.3.Element Birth and Death Usage Hints

13.4.Using Birth and Death

13.5.Where to Find Examples

13.1. Elements Supporting Birth and Death

If an element supports birth and death, it is indicated in the “Special Features” section of the documentation for that element.

User-defined elements can also be given the birth and death capability.

In some circumstances, an element's birth and death status depend upon a program-calculated quantity, such as temperature, stress, and strain. You can issue commands such as ETABLE and ESEL to determine the value of such quantities in selected elements, and to change the status (melted, solidified, ruptured, etc.) of those elements accordingly. This capability is useful for modeling effects due to phase changes (as in welding processes, when structurally inactive molten material solidifies and becomes structurally active), failure-surface propagation, and other analysis-dependent element changes.

13.2. Understanding Element Birth and Death

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 (p. 333).)

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.

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