UNDERSTANDING NONLINEAR ANALYSIS
Finite element analysis (FEA) has become a practical tool in design engineering, with CAD software now equipped with built-in capabilities. Historically, engineers were hesitant to use nonlinear analysis due to its complex problem formulation and long solution time. However, nonlinear FEA software interfaces with CAD and has become easier to use.
Differences between Linear and Nonlinear Analysis
- Stiffness is a property of a part or assembly that characterizes its response to the applied load.
- Three primary factors affect stiffness: shape, material, and part support.
- Linear analysis assumes that neither the shape nor material properties change during the deformation process, simplifying problem formulation and solution.
- Nonlinear analysis requires engineers to abandon the assumption of constant stiffness, as stiffness changes during the deformation process.
Understanding Different Types of Nonlinear Behavior
- Nonlinear analyses can be classified based on the principal origin of nonlinearity.
- Some analyses may have to account for more than one type of nonlinearity due to the inability to point out a single cause of nonlinear behavior in many problems.
Nonlinear Analysis in Part Stiffness Changes
- Nonlinear analysis is necessary when part stiffness changes under operating conditions.
- Geometric nonlinearity refers to changes in stiffness due to shape changes.
- Large visible deformations can cause changes in stiffness.
- Nonlinear geometry analysis is recommended for deformations larger than 1/20th of the part's largest dimension.
- Pressure vessel under high pressure undergoes drastic shape change, requiring analysis of geometric nonlinearity with nonconservative (or following) loading.
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