Nonlinear elements display an abrupt change in stiffness when they experience a change in status. For example, when a cable goes slack, its stiffness suddenly drops to zero. When two separate bodies come into contact, their overall stiffness changes drastically. These and other status-dependent stiffness changes can be modeled by using nonlinear elements (described below), by applying birth and death options to applicable elements (see the Advanced Analysis Guide), or by changing material properties (MPCHG). Some of the nonlinear element features described below are only available in certain products. See the Element Reference for details.
Sometimes, an element's status changes between "existent" and "nonexistent." The birth and death options (EKILL, EALIVE, ESTIF) can be used to deactivate or reactivate selected elements in such cases. The birth and death feature is discussed in detail in Element Birth and Death in the Advanced Analysis Guide.