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Constance Tipper and fracture mechanics

June 4, 2002

A public radio commentary

Every time I ride in a jet, I look out the window and watch the wing. When I see it's still there, I say a silence thanks to Constance Tipper. We take for granted that in our high tech world, things like airplane wings, car axles and buildings stay together, but it hasn't always been this way; that they now stay together is largely because of Constance Tipper. Tipper was born at end of the 19th century and followed a career path unusual at the time for a women. She earned degrees in the sciences, then settled in at Cambridge university to study something that seemed very esoteric. She wanted to know exactly how the arrangement of the atoms in a metal affected its strength and durability. In her lab day after day, she used a special microscope to examine the structure of the metal, then studied how it broke. She did this quietly for nearly thirty years, until she was called to aid her country in its battle with Germany.

The German U-boats were sinking British ships at a rapid rate. Ship builders responded by developed an innovative way to make metal ships. Instead of riveting the slabs of metal, which was time consuming, they simply welded the pieces together. Using this new method they were able to produce a 10,000 ton ship in just forty-two days. During the war the shipyard produced nearly five thousand of these vessels, called Liberty Ships.

Although at first a welcome aid to the war effort, these ships soon became a liability. As they carried crucial supplies across the North Atlantic on the icy Archangel run, the keel of the ship would suddenly crack, as if it had turned to glass. This crack would propagate around the hull until the ship broke in two and foundered at sea.

This called into question whether the rapid welding method should be used. Perhaps, they thought, they should return to the older, slower riveting method. It was at this point that Constance Tipper entered the picture.

The British government appointed a committee to investigate the cause, with Tipper as the technical expert. Tipper, who'd investigated the failure of metals for years, pointed out that the ships fell apart in icy conditions. She acquired pieces of the failed ships, then returned to her lab and showed that under these icy conditions the steel rapidly became brittle, and could then snap like a dry twig. Her work revealed to the ship makers that the fault lay not in the welding, but in the steel. She showed them how to test the steel to ensure the stability of the ships.

With this work Tipper opened up a field called fracture mechanics. Its still used by engineers today to develop wings that don't fall off and car axles that stay attached. So, today as the mechanical world around you doesn't fall apart, give thanks to Constance Tipper.

Copyright 2002 William S. Hammack Enterprises