OHSU metallurgist uses her microscope to form a riveting theory
Jennifer Hooper McCarty likes to think she's a nuts-and-bolts, brass-tacks kind of woman. Not the type to find herself treading water in the middle of a riveting international controversy.
But McCarty, a metallurgist who works at the Oregon Health and Science University Office of Technology and Research Collaborations office, has raised the Titanic. Well, not exactly. What she's done is raise the discussion over what sank the Titanic to a new level.
McCarty has discovered that it probably wasn't really the iceberg after all, but thousands of rivets made on the cheap that led to the accelerated sinking of the world's largest ship in 1912.
McCarty's research has generated much more interest since three weeks ago, when a National Geographic Channel special, 'Seconds From Disaster,' showed McCarty and her co-author of an upcoming book, Tim Foecke of the National Institute of Standards and Technology, re-creating an experiment that illustrated how the Titanic's rivets popped their heads after the Titanic met up with the iceberg in the North Atlantic.
Those subgrade rivets, McCarty believes, turned what really wasn't that hard of a blow from the iceberg into a disaster that cost more than 1,500 people their lives.
Seven years ago McCarty was working at the Smithsonian Institution studying the development of Korean ceramic. That's what she likes to do - study historical materials. And that's when the Discovery Channel called to invite her to join a scientific team intent on assessing if metallurgy played a role in the Titanic's sinking. But it wasn't rivets the team was planning to study.
Seven years ago, steel was thought to be the culprit. 'For a long time - and people still believe this - that the steel was brittle and it shattered like glass when it hit the iceberg and that's why the Titanic sank,' McCarty says. But that thinking was based on the idea that the Titanic smashed into the iceberg, McCarty says.
McCarty sees herself as more than a metallurgist, or materials scientist, as the field currently is called. What she does is forensics analysis, so she doesn't just study metal - she studies the history of the metal.
In the Titanic's case, that meant studying testimony from survivors of the ship's one and only voyage. 'The survivors of the Titanic, many of them didn't feel the collision,' McCarty says. 'Some of them felt a little jostling. None of them really says: 'Wow, it hit really hard, and I fell to the ground.' '
The type of collision was important because it would determine what type of test McCarty would conduct on the hull plates the team retrieved from the Titanic. Previous research, McCarty says, had used a process called a Charpy test on the Titanic's plates to determine how much straight-on energy was required to break them.
But if the Titanic suffered more of a glancing blow, a different test, called a slow bend test, would better duplicate the stress the Titanic's materials unsuccessfully withstood in the collision. Foecke conducted the slow bend test and discovered the steel was not that brittle and probably did not break up in the collision.
McCarty and Foecke started thinking about another explanation, and they had a suspect. 'If you know something about disaster and structural detail,' McCarty says, 'a lot of time the rivets are a weak point.'
A rush job?
McCarty headed back to the historical records. She discovered that wrought-iron rivets, which are generally weaker than steel rivets, had been used in the Titanic's bow and stern. And she discovered something else: The Titanic's shipbuilders had been under pressure to get the job done quickly.
Shipyard archives revealed that the yard was short of employees, especially competent riveters, McCarty says. The Titanic's sister ship, the Olympic, had been launched first, suffered damage in a collision, and was brought back to the yard.
It all spells pressure, and stress, on both workers and materials. 'So they're building the largest man-made moving object in the world,' McCarty says. 'Just about the time they're going to finish the Titanic, the Olympic has to come in for repairs. They're trying to finish the Titanic on time, but they have to pull people off the Titanic to work on the Olympic.
'They've got a lot of materials they've got to put together. A lot of steel and a lot of iron. They were in a frantic situation trying to fix one ship and get the Titanic finished with 3 million rivets.'
So the shipbuilders started going to lesser-known forges in search of iron, and quality control may have been bypassed, McCarty theorizes.
Back in the lab, McCarty had 48 rivets that had been retrieved from the Titanic. She broke off pieces of metal and took nearly 30,000 pictures of the metal under her microscope, then used a computer program to analyze the composition of each rivet.
What McCarty learned was that the wrought-iron rivets had been diluted with too much slag, a smelting byproduct. A 2 percent or 3 percent slag content was standard for wrought iron 100 years ago. But the Titanic's rivets had slag concentrations up to 9 percent on average. And some portions of the rivets had slag concentrations of up to 40 percent. The excess slag produced weak spots in the rivets.
Which led to the recent National Geographic television special, which opted for the dramatic by having McCarty test her weak-rivet theory on camera. Steel plates and wrought-iron rivets were made and joined to the same specifications as the Titanic's. A slow bend test was performed, and the rivets started popping their heads at 9,000 pounds of load, about half the load that properly made rivets could withstand.
'Zipper effect' idea catches on
McCarty calls the on-camera experience the 'make it or break it moment' for her theory. She had been talking about weak rivets at scientific conferences around the world for the past several years. Now, she says, Titanic experts are beginning to accept that her theory, well, holds water.
The Titanic's rivets, not its steel plates, were the weak points. 'A few bad ones when you're under collision,' McCarty says. 'One might pop and that puts the load on the next one, and then you end up with this little zipper effect.'
The result, McCarty says, was a ship sinking much faster than it should have. The Titanic might still have sunk after the collision if the rivets were all steel, or purer iron, but not as quickly. The hull plates might have held long enough for people to remain on board the ship until help arrived. As it was, the Titanic sank in just over two hours.