This video tests 2 by 4 beams with various defects and evaluates their strength. The evaluation is based on the flow analogy which is grounded in potential theory. Potential theory is not commonly used anymore in structural engineering but it still holds a lot of weight and insight into the behavior of continuous materials.

References:
[1] G. Beer, I. Smith and C. Duenser, The Boundary Element Method with Programming, New York: SpringerVerlag/Wien, 2008.
[2] O. M. Faltinsen, Sea Loads on Ships and Offshore Structures, Cambridge: Cambridge University, 1990.
[3] W. C. Young and R. G. Budynas, Roark's Formulas for Stress and Strain, New York: McGrawHill Companies, Inc., 2002.
[4] Y. Cengel and J. M. Cimbala, Fluid Mechanics Fundamentals and Applications, New York: McGrawHill Companies, Inc., 2014.