Airy stress function

Definition edit

The Airy stress function ( ):

  • Scalar potential function that can be used to find the stress.
  • Satisfies equilibrium in the absence of body forces.
  • Only for two-dimensional problems (plane stress/plane strain).

Airy stress function in rectangular Cartesian coordinates edit

If the coordinate basis is rectangular Cartesian   with coordinates denoted by   then the Airy stress function   is related to the components of the Cauchy stress tensor   by


Alternatively, if we write the basis as   and the coordinates as  , then the Cauchy stress components are related to the Airy stress function by


Airy stress function in polar coordinates edit

In polar basis   with co-ordinates  , the Airy stress function is related to the components of the Cauchy stress via


Something to think about ...

Do you think the Airy stress function can be extended to three dimensions?

Stress equation of compatibility in 2-D edit

In the absence of body forces,



  • Note that the stress field is independent of material properties in the absence of body forces (or homogeneous body forces).
  • Therefore, the plane strain and plane stress solutions are the same if the boundary conditions are expressed as traction BCS.

In terms of the Airy stress function





  • The stress function   is biharmonic.
  • Any polynomial in   and   of degree less than four is biharmonic.
  • Stress fields that are derived from an Airy stress function which satisfies the biharmonic equation will satisfy equilibrium and correspond to compatible strain fields.

Some biharmonic Airy stress functions edit

In cylindrical co-ordinates, some biharmonic functions that may be used as Airy stress functions are




Displacements in terms of scalar potentials edit

If the body force is negligible, then the displacements components in 2-D can be expressed as




and   is a scalar displacement potential function that satisfies the conditions


To prove the above, you have to use the plane strain/stress constitutive relations


Note also that the plane stress/strain compatibility equations can be written as


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