What is the Finite Element Method (FEM)?

In mathematics, partial differential equations (PDEs) can be solved either analytically (exact, continuous) or numerically (approximation, discrete).

Illustrating the position of FEM in the overall picture for solving PDEs

Finite element method (FEM) is a numerical method for solving PDEs. FEM is usually applied to solve for PDEs in continuum mechanics for solid mechanics problems.

Two other popular methods are the finite difference and finite volume methods (FDM FVM), which are frequently used to solve problems in fluid mechanics.

Partial Differential Equations in Continuum Mechanics

Continuum mechanics studies the mechanical behaviour of a material that has been mathematically idealised using partial differential equations (PDEs). Hence, continuum mechanics solves PDEs to understand material behaviours.

Why use idealisation?
It is not economic to fully describe material behaviours over a large range of conditions. Instead, the mathematical expression is idealised such that material behaviour is only represented for a reasonable range of loading conditions. See examples.

How to mathematically idealise/ model a material?
In continuum mechanics, materials are modelled using PDEs. These are equations assembled from (1) physical laws that are universal and (2) constitutive equations that are material specific.

PDEs in continuum mechanics = physical laws + constitutive equations

Examples of PDEs

• Navier equation
• Wave equation as special case of Navier equation
• Heat equation
• Laplace's equation as special case of heat equation
• Navier-Stokes equations