Titanic wreckage still tells a riveting tale.

Eighty-six years after the RMS Titanic scraped against an iceberg and sank to the bottom of the Atlantic Ocean, researchers are still trying to unravel the mystery of what happened on that fateful night. The iceberg sliced several long slits, each no more than an inch wide, into the side of the ship. Yet the supposedly unsinkable vessel went down after no more than 3 hours.

Now, a panel of naval engineers and scientists has concluded that the Titanic owed its rapid demise in large part to the failure of the rivets that fastened its hull together. According to a metallurgical analysis of samples retrieved from the wreckage this summer, the inconsistent quality of the wrought iron rivets weakened them, allowing the ship's steel panels to rip apart at the seams.

Tim Foecke of the National Institute of Standards and Technology (NIST) in Gaithersburg, Md., presented results of the analysis this week in Boston at a meeting of the Materials Research Society.

The panel's conclusion contradicts conventional wisdom, which holds that in the icy ocean water, the ship's steel hull turned exceptionally brittle and cracked apart. In 1991, a team of Canadian researchers tested a steel plate fragment from the ship and found that it was indeed brittle--not only when cold but even at room temperature.

"We believe that brittle steel didn't have much to do with the sinking of the Titanic," Foecke says. "[We are] willing to declare the brittle steel theory dead."

The Canadian researchers aren't convinced, though. "I would say--barring a miracle--the rivets have absolutely nothing to do with the sinking of the Titanic," says James Matthews, an engineer and materials specialist at the Defence Research Establishment-Atlantic in Halifax, Nova Scotia.

In 1996, the Marine Forensics Panel of the Society of Naval Architects and Marine Engineers began investigating the Titanic disaster. Panel chair William A. Garzke Jr., a naval architect at Gibbs & Cox in Arlington, Va., suspected that the rivets played an important role. Foecke, a panel member, then analyzed two rivets retrieved during a 1996 expedition to the wreck.

He found that the rivets contained three times the expected amount of silicate slag, an impurity that strengthens the metal at concentrations of 2 to 3 percent but tends to weaken it at higher concentrations.

Moreover, the slag ordinarily forms long fibers that run along the length of the rivets, reinforcing them. At the ends of the rivets, however, Foecke found the fibers turned to a horizontal orientation. Aligned that way, the layers of iron and slag easily peel apart.

Last August, another expedition brought back more rivets for testing. Foecke found slag problems in 14 out of 30 samples. The additional data, Foecke says, confirm the rivet theory, first published in a NIST report issued in February.

Matthews counters, "A lot of things draw interpretations, but they are not indicative of performance." He adds that the huge forces suffered by the ship when it snapped in two and hit the ocean bottom could have mangled the rivets.

To bolster their respective theories, both Foecke and Matthews cite the RMS Olympic, a ship almost identical to the Titanic that was hit by a British warship in 1911. Foecke says that rivets popped out as far as 15 feet away from the point of impact. Matthews, on the other hand, focuses on the cracks, characteristic of brittle steel fracture, that propagated through the hull.

The steel in both ships, and in ships built today, is of a poor grade, Matthews says. "There are no riveted ships anymore, yet 40 to 50 a year are lost," he reports. "Ships are sinking now for the same reason," he says--brittle fracture.

The panel now plans to explore a third ship of Titanic's design, the HMHS Britannic, which rests beneath the Aegean Sea. With more rivet samples, the researchers can get a better statistical analysis of the material, he explains.

"What sank the Titanic?" Foecke asks. "It hit an iceberg." The question is how it might have stayed afloat longer, giving time for help to arrive. Instead, more than 1,500 people perished, memorialized by the riveted steel hull that lies 12,000 feet beneath the waves.