Stress Functions - Morera Stress Functions

The Morera stress functions are defined by assuming that the Beltrami stress tensor tensor is restricted to be of the form

\Phi_{ij}=
\begin{bmatrix}
0&C&B\\
C&0&A\\
B&A&0
\end{bmatrix}

The solution to the elastostatic problem now consists of finding the three stress functions which give a stress tensor which obeys the Beltrami-Michell compatibility equations. Substituting the expressions for the stress into the Beltrami-Michell equations yields the expression of the elastostatic problem in terms of the stress functions:

\sigma_x
= -2\frac{\partial^2 A}{\partial y \partial z} \sigma_{yz}
=-\frac{\partial^2 A}{\partial x^2} +\frac{\partial^2 B}{\partial y \partial x} +\frac{\partial^2 C}{\partial z \partial x}
\sigma_y
= -2\frac{\partial^2 B}{\partial z \partial x} \sigma_{zx}
=-\frac{\partial^2 B}{\partial y^2} +\frac{\partial^2 C}{\partial z \partial y} +\frac{\partial^2 A}{\partial x \partial y}
\sigma_z
= -2\frac{\partial^2 C}{\partial x \partial y} \sigma_{xy}
=-\frac{\partial^2 C}{\partial z^2} +\frac{\partial^2 A}{\partial x \partial z} +\frac{\partial^2 B}{\partial y \partial z}

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