History of Bueckner’s principle?

I am hoping someone has some historical knowledge of some
interesting mechanics, or just an interest to discuss it. A superposition principle is widely used to solve crack problems, with illustrations like these:

http://ars.sciencedirect.com/content/image/1-s2.0-S0142112308002211-gr1.jpg

http://ars.els-cdn.com/content/image/1-s2.0-S0142112399000778-gr2.gif

Bueckner proved this principle in 1958 [1] but never published a figure
similar to those we see. He did explain it in text, such as “….. Any [elastic]
crack or notch problem can be reduced to one where the external load appears in
the form of tractions distributed over the faces of the crack.[2]” The first drawing similar to
the modern ones that I could find that was attributed to Bueckner was by
Barenblatt in 1962 [3]. Paul Paris’ landmark 1961 paper
on fatigue crack growth [node/7705]
shows a similar figure that he credits to some report he wrote at Boeing in
1957 [4]

Anybody have any more history of this principle? I would not
be surprised if it was used well before Bueckner proved it. Any earlier
published figures that show the principle? Does anyone have Paris’ 1957 report?

[1] Bueckner, H., 1958, "The propagation of cracks and the energy of elastic
deformation," Transactions of the American Society of Mechanical
Engineers, 80, pp. 1225-1230.

[2] Bueckner, H. F., 1973, "Field singularities and related integral
representations," Mechanics of Fracture G. C. Sih, ed., pp. 239-314.

[3] Barenblatt, G. I., 1962, "The Mathematical Theory of Equilibrium Cracks in
Brittle Fracture," Advances in Applied Mechanics, H. L. Dryden, T. v.
Kármán, G. Kuerti, F. H. v. d. Dungen, and L. Howarth, eds., Elsevier, pp.
55-129.

[4] P. C. Paris,
"The Mechanics of Fracture Propagation and Solutions to Fracture
Arrestor Problems," Document No. D2- 2195, Boeing Co., 1957.