Researchers have discovered that the builder of the Titanic struggled for years to obtain enough good rivets and riveters and ultimately settled on faulty materials that doomed the ship, which sank 96 years ago Tuesday.

The builders own archives, two scientists say, harbor evidence of a deadly mix of low quality rivets and lofty ambition as the builder labored to construct the three biggest ships in the world at once the Titanic and two sisters, the Olympic and the Britannic.

For a decade, the scientists have argued that the storied liner went down fast after hitting an iceberg because the ships builder used substandard rivets that popped their heads and let tons of icy seawater rush in. More than 1,500 people died.

When the safety of the rivets was first questioned 10 years ago, the builder ignored the accusation and said it did not have an archivist who could address the issue.

Now, historians say new evidence uncovered in the archive of the builder, Harland and Wolff, in Belfast, Northern Ireland, settles the argument and finally solves the riddle of one of the most famous sinkings of all time. The company says the findings are deeply flawed.

Each of the great ships under construction required three million rivets that acted like glue to hold everything together. In a new book, the scientists say the shortages peaked during the Titanics construction.

The board was in crisis mode, one of the authors, Jennifer Hooper McCarty, who studied the archives, said in an interview. It was constant stress. Every meeting it was, Theres problems with the rivets and we need to hire more people.

Apart from the archives, the team gleaned clues from 48 rivets recovered from the hulk of the Titanic, modern tests and computer simulations. They also compared metal from the Titanic with other metals from the same era, and looked at documentation about what engineers and shipbuilders of that era considered state of the art.

The scientists say the troubles began when its ambitious building plans forced Harland and Wolff to reach beyond its usual suppliers of rivet iron and include smaller forges, as disclosed in company and British government papers. Small forges tended to have less skill and experience.

Adding to the problem, in buying iron for the Titanics rivets, the company ordered No. 3 bar, known as best not No. 4, known as best-best, the scientists found. Shipbuilders of the day typically used No. 4 iron for anchors, chains and rivets, they discovered.

So the liner, whose name was meant to be synonymous with opulence, in at least one instance relied on cheaper materials.

Many of the rivets studied by the scientists recovered from the Titanics resting place two miles down in the North Atlantic by divers over two decades were found to be riddled with high concentrations of slag. A glassy residue of smelting, slag can make rivets brittle and prone to fracture.

Some material the company bought was not rivet quality, said the other author of the book, Timothy Foecke of the National Institute of Standards and Technology, a federal agency in Gaithersburg, Md.

The company also faced shortages of skilled riveters, the archives showed. Dr. McCarty said that for a half year, from late 1911 to April 1912, when the Titanic set sail, the companys board discussed the problem at every meeting. For instance, on Oct. 28, 1911, Lord William Pirrie, the companys chairman, expressed concern over the lack of riveters and called for new hiring efforts.

In their research, the scientists, who are metallurgists, found that good riveting took great skill. The iron had to be heated to a precise cherry red color and beaten by the right combination of hammer blows. Mediocre work could hide problems.

Hand riveting was tricky, said Dr. McCarty, whose doctoral thesis at Johns Hopkins University analyzed the Titanics rivets.

Steel beckoned as a solution. Shipbuilders of the day were moving from iron to steel rivets, which were stronger. And machines could install them, improving workmanship.

The rival Cunard line, the scientists found, had switched to steel rivets years before, using them, for instance, throughout the Lusitania.

The scientists discovered that Harland and Wolff also used steel rivets but only on the Titanics central hull, where stresses were expected to be greatest. Iron rivets were chosen for the stern and bow.