Mechanical APDL Structural Analysis Guide

8.7. Performing a Nonlinear Transient Analysis

8.8. Example Input for a Nonlinear Transient Analysis

8.9. Restarts

8.10. Using Nonlinear (Changing-Status) Elements

8.11. Unstable Structures

8.12. Guidelines for Nonlinear Analysis

8.13. Example Nonlinear Analysis (GUI Method)

8.14. Example Nonlinear Analysis (Command or Batch Method)

8.15. Where to Find Other Examples

8.1. Causes of Nonlinear Behavior

Nonlinear structural behavior arises from a number of causes, which can be grouped into these principal
categories:

• Changing status


• Geometric nonlinearities


• Material nonlinearities

8.1.1. Changing Status (Including Contact)

Many common structural features exhibit nonlinear behavior that is status-dependent. For example, a
tension-only cable is either slack or taut; a roller support is either in contact or not in contact. Status
changes might be directly related to load (as in the case of the cable), or they might be determined by
some external cause.

Situations in which contact occurs are common to many different nonlinear applications. Contact forms
a distinctive and important subset to the category of changing-status nonlinearities.

See the Contact Technology Guide for detailed information about performing contact analyses.

8.1.2. Geometric Nonlinearities

If a structure experiences large deformations, its changing geometric configuration can cause the
structure to respond nonlinearly. An example would be the fishing rod shown in Figure 8.2: A Fishing
Rod Demonstrates Geometric Nonlinearity (p. 194). Geometric nonlinearity is characterized by "large"
displacements and/or rotations.

Figure 8.2: A Fishing Rod Demonstrates Geometric Nonlinearity

A B

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Nonlinear Structural Analysis