It is often said that “nature is nonlinear”! Some common everyday situations illustrate important types of nonlinear behavior: flexing a paper clip 
back and forth; stretching a rubber band to many times its original length; crushing a beer can so that it buckles; and pressing a finger against a balloon to form a dimple. The three major types of structural nonlinearities are:
- Geometric Nonlinearity (large deformation, large strain, snap-through buckling)
- Material Nonlinearity (plasticity, creep, viscoelasticity, rubber & elastomeric materials)
- Boundary Nonlinearity (contact and separation between components, follower forces)
Nonlinear Finite Element Analysis can appropriately treat all of these types of nonlinearities. In general, the complete nonlinear stiffness is comprised of three parts:
- Elastic Stiffness
- Initial Stress Stiffness
- Geometric Stiffness
Nonlinear analysis is essential in many design and manufacturing problems. Some examples include:
- Manufacturing simulations – sheet metal forming, rolling, deep-drawing, welding
- Assembly analysis – snap fits, press fits, mechanical connections
- Rubber and elastomeric material analysis
- Failure analysis – overstress, material failure, fracture, crack propagation
Most failure analysis investigations require the use of nonlinear finite element analysis.
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