Material nonlinearity

This type of nonlinearity is probably the one that you are most familiar with and is covered in more depth in Materials. Most metals have a fairly linear stress–strain relationship at low strain values; but at higher strains the material yields, at which point the response becomes nonlinear and irreversible (see Figure 1).

Figure 1. Stress-strain curve for an elastic-plastic material under uniaxial tension.

Rubber materials can be approximated by a nonlinear, reversible (elastic) response (see Figure 2).

Figure 2. Stress-strain curve for a rubber-type material.

Material nonlinearity may be related to factors other than strain. Strain-rate-dependent material data and material failure are both forms of material nonlinearity. Material properties can also be a function of temperature and other predefined fields.