HOW DID the TITANIC sink?? Part 2

This article is based on a paper, "Titanic, The Anatomy of a Disaster, A Report from the Marine Forensic Panel,"presented at the 1997 annual meeting of the Society of Naval Architects and Marine Engineers, that documents the work of William H. Garzke, Jr. and David Wood, Gibbs & Cox, Inc.; David K. Brown, RCNC; Paul K. Matthias, Polaris Imaging; Dr. Roy Cullimore, University of Regina; David Livingstone, Harland & Wolff; Prof. H.P. Leighly, Jr., University of Missouri-Rolla; Dr. Timothy Foecke, National Institute of Standards and Technology; and Arthur Sandiford, Consultant. Eyewitness accounts are from various sources, including the official transcripts of the 1912 U.S. Senate investigation.
The Death of a Ship
At 2:17 a.m., according to the various investigations after the disaster, the Titanic began to go under, her lights blazing in the cold of the sub-Arctic night and with more than 1,500 people still on board. With a rumbling, crashing noise, the bow of the ship sank deeper into the water and the stern rose into the air.
Believing that the Titanic was invincible, many passengers were willing to board lifeboats only after the bow began to sink below the water's surface.
The stern section remained motionless and high out of the water for 30 seconds or more. The hull fracture was described as the sound of breaking chinaware, but as it continued, it was like a loud roar. A minute later, her lights flickered and then went out.
Then, at 2:20 a.m., the stern settled back into the water. Following a series of explosions, the submerged forward section began to pull away from the stern. As the forward section began its long descent, it drew the stern almost vertical again. Once this began, Titanic picked up speed as she sank below the surface of the pond-still waters of the North Atlantic. Some of the survivors on the stern stated that it was almost perpendicular as it slid silently and with hardly a ripple beneath the surface. William Garzke, staff naval architect at Gibbs & Cox, points out that, had the liner been elevated at 90 degrees, the huge boilers would have been ripped from their moorings, which was not the case. He suggests that the stern section likely rose from the surface to at least 20 degrees but not more than 35 degrees, as it filled with water or was dragged down by the bow section.
Chief Baker Charlie Joughin, who was at the ensign staff at the stern end, later testified that it was like riding an elevator down to the water. With the absence of suction forces, he was able to swim away without even wetting his hair, so swift was the stern's demise.
The failure of the main hull girder of the Titanic was the final phase of her sinking process. This began between 2:00 and 2:15 a.m., starting somewhere between stacks Nos. 2 and 4. The FEA results indicate that the plate failures might have started around the second expansion joint, or just behind it.
Stresses in the hull were increasing as the bow flooding continued and the stern rose from the water. Detailed examination of survivor testimony and underwater surveys has confirmed that the forward expansion joint was opened up while the ship was still on the surface, suggesting the significant stresses induced by the flooding of the forward part of the hull. An FEA review of the stresses in this area confirms that the nominal hull stresses were well above the material yield stress.
Most probably, significant stress developed in the way of the second expansion joint, between its root and the deck structure below it. As the flooding progressed aftward, the hull girder was strained beyond its design limitations, and the local stresses around this expansion joint soon reached the ultimate strength of the material. It is thought that, in the end, a critical structural failure in the hull or deck plates occurred in the area around the second expansion joint.

A stress analysis suggests that the Titanic's hull girder stresses exceeded the yield point of the steel.Once localized fracture began in the way of this joint, additional plate failures and associated fracturing likely radiated out from this joint, toward both port and starboard. The decks, however, with their finer grain structure, were most likely able to deform well into the plastic range of the material before failing in ductile tears. It is speculated, however, that the side shell plates suffered brittle fracture due to their coarser grain structure and manganese sulfide inclusions. This type of failure is evident on the wreck today.
Free field stresses, already at the yield point of the material, may have been increased by a factor of two to four in areas of structural discontinuities, such as large openings or those with small radii, or doubler plate edges. Fractures typically spread in random chaotic paths, following weaknesses in the plate and microcracks already present around rivet holes.
Assuming that the hull girder failed at the surface, then as Boiler Room No. 4 filled with water, the stern rose farther out of the water, resulting in some 76 meters of unsupported hull, which sharply increased the hull girder stresses, in turn accelerating the fracturing of the steel plates. The angle of trim grew to a maximum of 15 to 20 degrees, further increasing the stresses in the hull and deck plating near the aft expansion joint. The stresses continued to build in this area of the ship, where there were large openings for a main access, the machinery casing for the Reciprocating Engine Room, the uptakes and intakes for the boilers, the ash pit door on the port side of Boiler Room No. 1, and the turbine engine casing. As the hull girder continued to fail, the bow was first to begin its plunge toward the seabed.
As the bow and stern sections continued to separate, there were some local buckling failures in the inner bottom and bottom structure. This is what caused the stern section to settle back toward the water's surface as the decks began to fail and the side shell fractured into many small plate sections. The MSC/NASTRAN finite element analysis indicates that the stresses in the region of Boiler Room No. 1 and the Reciprocating Engine Room were elevated.
An additional stress analysis, based on classical beam theory, indicates that the hull girder stresses exceeded the yield point of the steel. When the bow and stern began to separate, the two main transverse bulkheads bounding Boiler Room No. 1 collapsed as they were compressed by the downward movement of the deck structures. The decks, in turn, failed because of the lack of bulkhead support.
When this happened, the unsupported length of the inner bottom suddenly grew to 165 feet, encompassing Boiler Rooms Nos. 1 and 2, as well as the Reciprocating Engine Room. This condition allowed deformation of the inner bottom structure to extend up further into the ship's machinery spaces, while the deck structure failures continued. It is believed that this compression of the hull girder brought about the failure of the side shell plates, and also freed equipment inside the ship, such as the boilers in Boiler Room No. 1, from its foundations.
It cannot be established with any certainty what happened to the ship during its descent to the seabed. However, what is now known is that once the Titanic disappeared below the ocean's surface, it broke into three pieces. The depth where these events occurred cannot be estimated with any precision. The buoyancy of the stern piece also appears to have resisted the downward pull of the bow. The extent of damage evident in the stern wreck implies that the bow section may have pulled the stern section quickly below the water's surface, resulting in structural implosions that caused significant damage. Structural failures ultimately led to the separation of the bow portion, followed by the third or double bottom piece. It is interesting to note that the bow section did not suffer damage similar to that in the stern section. This was likely due to the gradual flooding of the bow section, and its stability during the descent to the bottom. It rests upright on the bottom with little apparent damage directly attributable to impact with the seabed.
The analysis supports some witnesses' testimony that the ship likely began to fracture at the surface, and that the fracture was completed at some unknown depth below the water's surface. The resulting stress levels in the strength deck below the root of the second expansion joint (aft), and in the inner bottom structure directly below, were very high because of the unusual flooding occurring in the forward half of the ship. These patterns of stress support the argument that initial hull failure likely occurred at the surface. Additional work is being performed to investigate this further.
These findings mirror the testimony of Seaman Edward John Buley at the U.S. Senate hearings. Stating that as the bow continued to slip below the surface, "She went down as far as the after funnel, and then there was a little roar, as though the engines had rushed forward, and she snapped in two, and the bow part went down and the afterpart came up and stayed up five minutes before it went down ... It was horizontal at first, and then went down."
In response to what he meant by "snapped in two,"and how he knew this, Buley testified, "She parted in two ... Because we could see the afterpart afloat, and there was no forepart to it. I think she must have parted where the bunkers were. She parted at the last, because the afterpart of her settled out of the water horizontally after the other part went down. First of all, you could see her propellers and everything. Her rudder was clear out of the water. You could hear the rush of the machinery, and she parted in two, and the afterpart settled down again, and we thought the afterpart would float altogether. She uprighted herself for about five minutes, and then tipped over and disappeared ... You could see she went in two, because we were quite near to her and could see her quite plainly."
RMS Titanic, the largest ship of its day, was built in Belfast, Ireland, and was said to be "unsinkable,"a belief so strong that it was to have tragic consequences. Having confidence in the ship's "unsinkability,"many passengers chose to remain on board. The first lifeboats to leave were only half, or one-third full.
The fallacy of the claim itself became tragically apparent during the ship's maiden voyage. Just three hours after it collided with an iceberg, the majestic Titanic vanished beneath the cold waters of the North Atlantic. This ill-founded confidence led to the ignoring of at least 14 warnings of hazardous ice fields, six of which were received on the day of the disaster.
Equipped with only 20 lifeboats, the Titanic went down with the loss of 1,523 passengers and crew. This incredible disaster led to a number of investigations in Great Britain and the United States that resulted in sweeping changes in maritime safety law and ship construction.
The demise of the mighty Titanic was swift, sure, and terrible. Whatever could have gone wrong, did. The engineering marvel that heralded the beginning of the age of technology also displayed, all too clearly, its vulnerability and limits—as well as the need for prudence and safety.
"The analyses, and future analyses we hope to make employing both MSC/NASTRAN and MSC/DYTRAN, help us make critical design decisions about future marine structural features, such as deck openings and expansions joints."Wood said.
"Today, we're changing the way we design ships. In the past, nominal load conditions were averaged. Today, we design for the ultimate stress levels and strength,"says Robert Sielski, senior staff engineer at Gibbs & Cox. "MSC/NASTRAN helps us evaluate and design for increased survivability."

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