Johns Hopkins Magazine -- June 1999
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JUNE 1999

S C I E N C E    &    T E C H N O L O G Y

A riveting probe of Titanic's hull... looking at atoms with new resolution... the wheels on the bus go bumpety-bump...

Tim Weihs (top) and student Bill Closkey examine a section of a Titanic rivet.
Photo by Louis Rosenstock
Titanic's riveting quandary

She was more than half as long as the Empire State Building is tall, weighed 46,000 tons, and could travel at a speed of 23 knots. The Titanic was the largest moving object of her day. But in Tim Weihs's Hopkins laboratory, this mighty ship is reduced to a microscopic fiber.

The materials scientist is investigating tiny fibers of iron silicate in the wrought iron rivets used to hold together the steel plates of the Titanic's hull.

For several years, researchers have pondered the series of mechanical failures that occurred after the Titanic hit an iceberg in the Atlantic and sank on the night of April 14-15, 1912. One topic of debate: What gave first? Did the steel plates in the hull crack and fracture, as some sonar evidence suggests? Or did the connecting rivets snap or fracture, leaving the steel plates to peel open at the seams?

Tim Foecke, a metallurgist at the National Institute of Standards and Technology, proposed that the rivets were the weak link, and invited Weihs to pursue this line of inquiry. So last summer, Weihs accompanied a team of 40 on an expedition to the icy waters 400 miles southeast of Newfoundland, where the ship is still submerged. Their journey was featured recently in a Discovery channel special program.

On the research vessel at the site of the wreck, Weihs examined several of the rivets that were retrieved, and brought several back to Homewood for further investigation.

In his office, Weihs rises from a chair to retrieve one of these rivets from a filing cabinet. Hefty enough to make a nice paperweight, the rivet is pitted and pockmarked, but those holes are only battle scars from 87 years of corrosion, says Weihs. Only when Weihs examines rivets like this one under an optical microscope does he see what he and Foecke believe compromised the rivets' integrity: long, spindly particles of iron silicate-- known as slag in the iron business.

All wrought iron is a combination of soft iron and the glass-like iron silicate particles, explains Weihs. But not all slag is the same. When slag is thoroughly mixed into iron, it forms spherical particles. "If slag is not broken up and mixed in well, it can take on the shape of long fibers," Weihs says.

The iron foundries that manufactured the rivets were not necessarily negligent. "The process back then involved guys with rakes," who laboriously mixed the slag into the molten iron. "There was no quality control," says Weihs. The quality of the iron might have been adequate by historical standards.

Further studies of the ship's hull have borne out Weihs's findings. The plates in the hull did split at several seams, rather than suffering internal fractures.

Today, manufacturers generally weld rather than rivet ship hulls. "So we're not going to learn how to build better ships from this research," adds Weihs. "But we're gaining some useful historical lessons.

"The creation of new technology can breed over-confidence," he muses. Just before it crashed on its maiden voyage, the Titanic was traveling at top speed in the dark through ice-strewn waters, racing to cross the Atlantic in seven days or less. But the ship did not carry enough lifeboats to hold all passengers. "Not even the hand of God could sink this ship," a crewman reportedly told a passenger. "Technology is not always as superior as we think," says Weihs. --Melissa Hendricks

Dave Veblen and Kevin Hemker (pictured at right) can now zoom in on atomic geometry
Photo by Keith Weller
Journey to view an atom

At Hopkins, viewing an atom requires some fastidious preparation. The journey begins in the lobby of Homewood's Olin Hall, home to the Department of Earth and Planetary Sciences. Down two flights of stairs sits a windowless room, which houses a new high-resolution transmission electron microscope.

Before entering the room, visitors must change into special clean shoes and stamp their feet on a sticky rubber mat to remove stray dirt. Special controls maintain a constant level of humidity and a never-wavering temperature of 72 degrees F. Filters cleanse the air of even the tiniest motes of dust. Silence is mandatory, and heavy gray acoustical curtains line the walls. Sound waves, dust, temperature fluctuations--all could alter the microscope's resolution. And even jossling the instrument a hair's breath is like the span of an ocean in an atom's world.

The rituals are worth the fuss, says mechanical engineer Kevin Hemker. "We're really getting down to where we can probe the atomic level. We can magnify 5,000 to 5 million times," he says.

The state-of-the-art microscope works by firing a powerful beam of electrons at a sample. The beam penetrates the sample and lands on a phosphorescent screen, producing a glowing image that shows the precise geometric arrangement of the specimen's atoms.

The $1.3 million microscope, one of just two dozen in the country, was recently purchased with funding from the National Science Foundation and the W.M. Keck Foundation. It is is overseen by Hemker and Dave Veblen, professor of Earth and planetary sciences. But it is available to those researchers throughout the university who wish to probe the interior of metals, alloys, crystals, thin films, and other materials.

Scientists have been imaging materials in the atomic-size ballpark for a decade or so, but this latest generation of microscope is degrees more powerful--plus it features analytical tools for studying the chemistry and geometry of a material's atoms. Unlike an older transmission electron microscope, which sits just next door, the new instrument offers a 20-fold improvement in chemical analysis.

Hemker will use it to study how various materials behave under stress, such as corrosive forces, high temperatures, or the impact of a missile. This information could help scientists develop improved materials for aviation and defense.

Veblen will be studying where heavy metals--such as uranium, mercury, and chromium--found in manufacturing and nuclear waste, bind to minerals in the soil. Such studies provide answers to how long toxic materials remain in soil before they are washed away. "We hope to resolve single atoms of uranium on a substrate," comments Veblen.

Two dozen other scientists across a wide span of disciplines are planning to use the microscope. Among them are nanostructures researchers who are creating a range of new thin films and alloys. The microscope, says Hemker, "provides the eyes for them to see what they make." --MH

Illustration by Bonnie Matthews
A safer ride to school?

Children riding on school buses could be protected from injury by technology long used in amusement parks: lap bars. Two Hopkins engineering students are devising a padded lap bar restraint as part of their Engineering Design Projects course.

While fatalities on school buses are rare, the severity of injuries when buses roll or fall into ravines can be devastating. In the 1993-94 school year, for example, there were 400,000 school buses on the roads in the U.S., federal statistics show; 10 students were killed and 11,000 sustained injuries--mostly head injuries from minor traffic accidents.

"There is an obligation to keep children safe, considering how many buses and how many miles these children are traveling," says Andy Lincoln, assistant scientist at Public Health's Center for Injury Research and Policy, which is co-sponsoring the project with the Applied Physics Laboratory.

Says project co-designer William Thompson, 22, a Hopkins senior in mechanical engineering: "We looked at a security camera tape of a bus just going over a wooden bridge and the kids bounced up and hit the ceiling of the bus. There's currently nothing in most school buses for side impact or rollover crashes, where severe injuries take place."

Shoulder belts are impractical in most buses, and lap belts can cause abdominal injuries. Another problem: "Seat belts are sometimes used to hit other kids," Lincoln says. "They can sit right next to the class nerd and whap him upside the head."

In their preliminary research, Thompson and classmate Stephen Pantano, 22, found that most school buses use what's called "compartmentalization": "They put a lot of padding on the seats," Pantano said.

But that doesn't prevent children from becoming projectiles in the event of a major crash. So Pantano and Thompson have designed a padded lap bar, similar to the one found on some roller coasters. "Children would reach forward, grab it and pull it down like buckling a seat belt," explains Pantano. "It would not be automatic because in a crash electronics could fail."

Under their proposed design, the bar would be mounted on the floor next to the seats. The device could be retrofitted to existing buses. A prototype, funded by $5,500 from the School of Public Health, is being constructed and tested on campus using a mock-up of a bus with donated seats. If successful, the lap bar restraint could be adopted by local school districts; already the National Highway Traffic Safety Administration has made inquiries.

One problem still to be overcome: Most school bus aisles are only 14 inches wide, and the lap bar mechanism could take up to four inches alongside each seat, leaving a too-narrow walkway: "There's not a lot of room to work with," Pantano says. "If you go into a school bus, it's not as big as you remember it." --Joanne P. Cavanaugh