When to Use Nonlinear Analysis
Linear analysis is based on the static
and linearity assumptions and is, therefore, valid as long as these
assumption are valid. When one (or more) of these assumptions fails, linear
analysis will produce wrong predictions and nonlinear analysis must be
used to model the nonlinearities.
The linearity assumption is true if:
All the materials in the model comply with Hook's
law, that is stress is directly proportional to strain. Some materials
demonstrate such behavior only if the strains are small. As the strains
increase, the stress-strain relationships become nonlinear. Other materials
display nonlinear behavior even when the strains are small. A material
model is a mathematical simulation of the behavior of a material. A material
is said to be linear if its stress-strain relations are linear. Linear
analysis can be used to analyze models with linear materials assuming
that there are no other types of nonlinearities. Linear materials can
be isotropic, orthotropic, or anisotropic. Whenever a material in the
model demonstrates a nonlinear stress-strain behavior under the specified
loading, nonlinear analysis must be used. Nonlinear analysis offers many
types of material
models.
The induced displacements are small enough so
that you can ignore the change in the stiffness caused by loading. Nonlinear
analysis offers a large deformation option when defining the material
properties of a solid component or a shell. The stiffness matrix computations
can be recomputed at every solution step. The frequency of recalculating
the stiffness matrix is controlled by the user.
Boundary conditions do not vary
during the application of loads. Loads must be constant in magnitude,
direction, and distribution. They should not change while the model is
deforming. For example, contact problems are naturally nonlinear because
the boundary conditions change when loading contact occurs. However, linear
analysis offers an approximate solution for contact problems
where the large deformation effect is considered.
Related Topics
Guidelines
on Studies with Contact Conditions
Performing
Nonlinear Analysis
Setting
the Properties of Nonlinear Analysis
Setting
the Result Options of Nonlinear Analysis