Beam deformation and Stress Field plots

Dear all,
Please let me know how to plot the stress field for a model of beam. I have gone through the example beam-3D available in the examples. What changes can I make to plot the stress field?

Could you please write down mathematically what you want to plot exactly?

The variational form is as follows:
āˆ«ļøšœ†āˆ‡.š‘¢āˆ‡.š‘£ + 2šœ‡šœ–(u) : šœ–(v) š‘‘š‘„ āˆ’āˆ«ļøvš‘“ š‘‘š‘„ = 0;
and the expression that I want to plot is:
Stress=E*(du/dx), where E is a constant.

Vh stress = E * dx(u);

It worked well.
Thanks a lot.