Even though stress stiffening theory assumes that an element's rotations and strains are small, in some
structural systems (such as in Figure 8.8: Stress-Stiffened Beams (p. 201) (a)), the stiffening stress is only
obtainable by performing a large deflection analysis. In other systems (such as in Figure 8.8: Stress-
Stiffened Beams (p. 201) (b)), the stiffening stress is obtainable using small deflection, or linear, theory.
Figure 8.8: Stress-Stiffened Beams
(a)
P(b) F
PTo use stress stiffening in the second category of systems, you must issue PSTRES,ON (GUI path Main
Menu> Solution> Unabridged Menu> Analysis Type> Analysis Options) in your first load step.
Large strain and large deflection procedures include initial stress effects as a subset of their theory. For
most elements, initial stiffness effects are automatically included when large-deformation effects are
activated (NLGEOM,ON) (GUI path Main Menu> Solution> Analysis Type> Sol'n Control ( : Basic Tab)
or Main Menu> Solution> Unabridged Menu> Analysis Type> Analysis Options).
8.4. Modeling Material Nonlinearities
A number of material-related factors can cause your structure's stiffness to change during the course
of an analysis. Nonlinear stress-strain relationships of plastic, multilinear elastic, and hyperelastic materials
cause a structure's stiffness to change at different load levels (and, typically, at different temperatures).
Creep, viscoplasticity, and viscoelasticity give rise to nonlinearities that can be time-, rate-, temperature-
, and stress-related.Swelling induces strains that can be a function of temperature, time, neutron flux
level (or some analogous quantity), and stress. Any of these types of material properties can be incor-
porated into your analysis if you use appropriate element types. Nonlinear constitutive models (TB) are
not applicable for the ANSYS Professional program.
The following topics related to modeling material nonlinearities are available:
8.4.1. Nonlinear Materials
8.4.2. Material Model Combination Examples8.4.1. Nonlinear Materials
If a material displays nonlinear stress-strain behavior, use the TB family of commands to define the
nonlinear material property relationships in terms of a data table:TB,TBTEMP,TBDATA,TBPT,TBCOPY,
TBLIST,TBPLOT,TBDELE (Main Menu> Preprocessor> Material Props> Material Models> Structural>
Nonlinear) .The precise form of these commands varies depending on the type of nonlinear material
behavior being defined.
The various material behavior options are described briefly below. See Material Models in the Material
Reference for details about each material behavior type.
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationModeling Material Nonlinearities