# What is the difference between non-linear elastic simulation and linear elastic simulation with plasticity?

I'm learning how to do Finite Element calculations using Comsol Multiphysics.

In Comsol, Linear Elastic Material and Nonlinear Elastic Material are available as material models:

Using Linear Elastic Material, you can add Plasticity, and define Initial yield stress as well as the tangent modulus:

I'm wondering, if we have plasticity, doesn't that make our material model immediately nonlinear? Plasticity implies change in the elastic modulus, and being able to define separate Young's modulus and tangent modulus produces a nonlinear stress-strain curve.

What is the difference between defining Linear Elastic as material model and then adding plasticity, versus using a Non-linear material model?

I did a simple cantilever calculation with point load at the tip (right edge):

Taking the stress at a cross section along the beam shows the stress gradient change around 30MPa:

• The answer to your question: "I'm wondering, if we have plasticity, doesn't that make our material model immediately nonlinear?" is yes (assuming the stresses are high enough to cause yielding of the material) Jul 14, 2022 at 18:23

• Geometrical nonlinearities appear when stains are not negligible ($$\epsilon \gg 1$$ does not hold). This implies that the definition of strains is no longer linear and include a second-order term. You found also have that displacements are also not negligible, implying that the original and deformed configurations do not coincidence. You need to pick your measures of strain and stresses (Cauchy stress is no longer used).