`Egyptian obelisk engineering mystery (Al Bakun / Wendell Wilkenning fracture analysis)`

Wendell Wilkening's MIT doctoral thesis under Backofen on the brittle fracture of granite. Used to introduce microcracking at crack tips as the mechanism explaining why Egyptian obelisks survived lifting.

[Tom holds up a fracture toughness specimen made of granite.] This is a fracture toughness specimen made out of granite. This was part of Wendell Wilkening's doctoral thesis. He was finishing up his doctoral thesis here when I started, the week I was starting as an assistant professor. Wink — we call him Wink — was studying the fracture of granite because Professor Backofen, who had taught me mechanics when I was a sophomore, was curious about how they raised the Egyptian obelisks. You know, these things that look like the Washington Monument. Everyone had assumed they cut the stone in the horizontal position, it's all one stone, and they just lifted it up. But if you did the fracture mechanics that people understood in 1970, it should have broken under its own weight. Such a brittle material — as you lifted it up, it should have fractured.