How did the

sink? Recent engineering evidence suggests that the unsinkable ship experienced a hull failure at the surface and Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/120/08/54/6381729/me-1998-aug1.pdf by guest on 30 September 2021 broke into pieces before it went down. By Dan Deitz, Executive Editor

HEN OUR BOAT had rowed about half a mile matic-event in their lives, disagreed on one major point, from the vessel, the Titanic-which was illu­ and it has remained a mystery for more than 80 years: Did W minated from stem to -was perfectly the Titanic break apart at the surface or sink intact? stationary, like some fantastic piece of stage scenery," re­ Although all the officers testified that the ship sank in­ called Pierre Marechal, a French aviator and a surviving tact, some survivors and crew testified to a hull failure at first-class passenger of the ill-fated liner. "Presently, the the surface. Even during the American and British in­ gigantic ship began to sink by the bows ... suddenly the quiries into the disaster, few questions focused on the lights went out, and an immense clamor filled the air. structural aspects of the ship. Despite survivors' testi­ Little by little, the Titanic settled down ... and sank with­ monies, it was concluded that the ship sank intact. out noise .. . In the final spasm the stern of the leviathan stood in the air and then the vessel finally disappeared." EVIDENCE FROM THE DEPTH S Elmer Z . Taylor, who watched from No. 5, The mystery arose again when the wreck .of the Titanic close enough to the Titanic to observe its final demise, was discovered in 1985 and the hull was found in two would later write, "The cracking sound, quite audible pieces. Many theories were developed as to how the ship a quarter of a mile away, was due, in my opinion, to broke apart during the sinking process, and research was tearing of the ship's plates apart, or that part of the hull begun to determine how this could have happened. The below the expansion joints, thus breaking the back at a speculation intensified further when the wreck site was point almost midway the length of the ship." revisited in 1986 and a third 17.4-meter section from the "At that time the band was playing a ragtime tune," re­ midship region of the ship was found. membered Harold Sydney Bride, the surviving wireless To help solve this mystery, the Discovery Channel, in operator of the TitaniC. "I saw a collapsible boat on deck developing its award-winning " Titanic: Anatomy of a ... I went to help when a big wave swept it off, carrying Disaster" television documentary, approached Gibbs & me with it. The boat was overturned and I was beneath Cox, Inc., one of the oldest naval architecture and ma­ it, but I managed to get clear. I swam with all my might rine engineering firms in the world. Gibbs & Cox and I suppose I was 150 feet away when the Titanic, with agreed to perform a stress analysis to help determine the her quarter sticking straight up, began to settle." possibility of hull fracture at the surface. "The orchestra belonging to the first cabin assembled With funding provided jointly by the Discovery Chan­ on deck as the liner was going down and played 'Nearer nel and the Society of Naval Architects and Marine En­ My God to Thee.' By that time," as Miss C. Bounnell, gineers, Gibbs & Cox conducted a basic study of the first-class survivor, relived the night, "most of the breakup of RMS Titanic using linear finite-element­ lifeboats were some distance away and only a faint sound analysis (FEA) software. This study was done in conjunc­ of the strains of the hynm could be heard. As we pulled tion with materials testing of the Titanic steel by the Uni­ away from the ship, we noticed that she was hog-backed, versity of Missouri-Rolla, with advice from Prof. H .P. showing she was already breaking in two." Leighly Jr. , Dr. Timothy Foecke, and Dr. Harold Reem­ Four survivors with firsthand knowledge, remembering snyder of the Bethlehem Steel Corp.'s Homer Research probably the most important-certainly the most trau- Laboratory in Bethlehem, Pa.

54 AUGUST 1998 M EC H AN ICAL ENG I NEE R.I NG Important to the analysis effort was accurate weight and ry. In the 1960s, engineers started to analyze the stresses buoyancy data for the ship at the time it struck the ice­ in ship hulls using finite-element modeling (FEM). As a berg, and then later while it was sinking. These data were pioneer of FEA technology, MSC has been in the fore­ provided via a recent study of the ship's breakup undertak­ front of dramatically improving this technique to take en for another technical paper, "The 'Titanic and Lusitania, advantage of advances in computer technology. A Final Forensic Analysis," published in a 1996 issue of A full-ship model was graphically constructed, employ­ Marine Technology. The study provided the loading in­ ing a modern approach similar to that used for U.S. Navy formation needed to take "snapshots" of the ship's state of destroyers and today. Loadings for the model stress during the sinking process. Tests conducted on the were developed based on one flooding scenario from the steel recovered from the wreck site were performed at the paper, "The ," by Chris Hackett University of Missouri and the National Institute of Stan­ and John C. Bedford. dards and Technology in Gaithersburg, Md. The results The corresponding weight and buoyancy curves, devel­ from these metallurgical tests of Titanic steel and rivets oped by Arthur Sandiford and William H. Garzke, Jr., Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/120/08/54/6381729/me-1998-aug1.pdf by guest on 30 September 2021 were also input as data for the finite element analysis. were used to model the critical flooding conditions be­ Gibbs & Cox engineers selected MSC/ NASTRAN, lieved to represent the hull loading just prior to hull frac­ from the MacNeal-Schwendler Corp. in Los Angeles, to ture. Since the flooding process took place over several perform the analysis. FEMAP engineering-analysis hours, a quasi-static analysis was considered appropriate. modeling and visualization software from Enterprise The initial modeling effort focused on the determination Software Products in Exton, Pa. , was used to perform of the location and magnitude of high-stress regions that the pre- and postprocessing of the analyses. Gibbs & Cox developed in the hull while she remained on the surface. had been using MSC/ NASTRAN for approximately Engineers determined that stress levels in the midsec­ five years. According to David Wood, the firm's struc­ tion of the ship were at least up to the yield strength of tures department manager, MSC worked closely with his the steel just prior to sinking. When considered alone, team during the development of MSC / NASTRAN stresses at these levels do not indisputably imply cata­ Version 70 to provide the special program solutions strophic failure. Additional analyses, focusing on proba­ needed for use in their industry. ble locations of initial hull fracture, are required to indi­ Engineers analyzed the stresses in the Titanic as the cate that the ship sustained possible catastrophic failure at flooding progressed within the region, using mod­ the surface and began to break apart. ern FEA techniques that simply were not available until Significant stresses were developed in the vicinity of the the 1960s, and certainly were not known to the structur­ two expansion joints, and in the inner bottom of the ship al designers of the ship in the first decades of the centu- between the forward end of Boiler Room No. 1 and the

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Z 2: < ~ ~ 0:> '" ~ c u :0, "­ => '"fE '"~ British and U.S. investigations of the Titanic tragedy have resulted in greater lifeboat capacity, improved subdivision of ships, and the creation of an ice patrol.

MECHANICAL ENG I NEER.ING AUGUST 1998 55 aft end of the Reciprocating Engine Room. Structural William Garzke, staff naval architect at Gibbs & Cox, discontinuities, such as expansion joints, result in stress­ points out that, had the liner been elevated at 90 degrees, concentration development. Typically, stress concentra­ the huge boilers would have been ripped from their tion levels are three to four times that of free-field stress­ moorings, which was not the case. He suggests that the es. While these structural discontinuities have not yet stern section likely rose from the surface to at least 20 de­ been thoroughly investigated, it is believed that stresses grees but not more than 35 degrees, as it filled with wa­ developed at these locations were significantly higher ter or was dragged down by the bow section. than the material yield stress. Chief Baker Charlie Joughin, who was at the ensign staff at the stern end, later testified that it was like rid­ THE DEATH OF A SHIP ing an elevator down to the water. With the absence of At 2: 17 a.m., according to the various investigations after suction forces, he was able to swim away without even the disaster, the Titanic began to go under, her lights wetting his hair, so swift was the stern's demise.

blazing in the cold of the sub-Arctic night and with The failure of the main hull girder of the Titanic was Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/120/08/54/6381729/me-1998-aug1.pdf by guest on 30 September 2021 more than 1,500 people still on board. With a rumbling, the final phase of her sinking process. T his began be­ crashing noise, the bow of the ship sank deeper into the tween 2:00 and 2:15 a.m., starting somewhere between water and the stern rose into the air. stacks Nos. 2 and 4. The FEA results indicate that the T he stern section remained motionless and high out of plate failures might have started around the second ex­ the water for 30 seconds or more. T he hull fracture was pansion joint, or j ust behind it. described as the sound of breaking chinaware, but as it Stresses in the hull were increasing as the bow flooding continued, it was like a loud roar. A minute later, her continued and the stern rose from the water. Detailed lights flickered and then went out. examination of survivor testimony and underwater sur­ Then, at 2:20 a.m., the stern settled back into the wa­ veys has confirmed that the forward expansion joint was ter. Following a series of explosions, the submerged for­ opened up while the ship was still on the surface, sug­ ward section began to pull away from the stern. As the gesting the significant stresses induced by the flooding of forward section began its long descent, it drew the stern the forward part of the hull. An FEA review of the stress­ almost vertical again. Once this began, Titanic picked up es in this area confirms that the nominal hull stresses speed as she sank below the surface of the pond-still wa­ were well above the material yield stress. ters of the North Atlantic. Some of the survivors on the Most probably, significant stress developed in the way stern stated that it was almost perpendicular as it slid of the second expansion joint, between its root and the silently and with hardly a ripple beneath the surface. deck structure below it. As the flooding progressed aft-

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.

56 AUG U ST 1998 ME C HA N IC AL ENG INEERI NG ward, the hull girder was strained beyond its design limi­ When this happened, the unsupported length of the in­ tations, and the local stresses around this expansion joint ner bottom suddenly grew to 165 feet, encompassing soon reached the ultimate strength of the material. It is Boiler Rooms Nos. 1 and 2, as well as the Reciprocating thought that, in the end, a critical structural failure in the Engine Room. This condition allowed deformation of hull or deck plates occurred in the area around the sec­ the inner bottom structure to extend up further into the ond expansion joint. ship's machinery spaces, while the deck structure failures Once localized fracture began in the way of this joint, continued. It is believed that this compression of the hull additional plate failures and associated fracturing likely girder brought about the failure of the side shell plates, radiated out from this joint, toward both port and star­ and also freed equipment inside the ship, such as the board. The decks, however, with their finer grain struc­ boilers in Boiler Room No. 1, from its foundations. ture, were most likely able to deform well into the plas­ It cannot be established with any certainty what hap­ tic range of the material before failing in ductile tears. It pened to the ship during its descent to the seabed. How­ is speculated, however, that the side shell plates suffered ever, what is now known is that once the Titanic disap­ Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/120/08/54/6381729/me-1998-aug1.pdf by guest on 30 September 2021 brittle fracture due to their coarser grain structure and peared below the ocean's surface, it broke into three manganese sulfide inclusions. This type of failure is evi­ pieces. The depth where these events occurred cannot be dent on the wreck today. estimated with any precision. The buoyancy of the stern Free field stresses, already at the yield point of the ma­ piece also appears to have resisted the downward pull of terial, may have been increased by a factor of two to four the bow. The extent of damage evident in the stern in areas of structural discontinuities, such as large open- wreck implies that the bow section may have pulled the A stress analysis suggests that the Titanic's hull girder stresses exceeded the yield point of the steel. ings or those with small radii, or doubler plate edges. stern section quickly below the water's surface, resulting Fractures typically spread in random chaotic paths, fol­ in structural implosions that caused significant damage. lowing weaknesses in the plate and microcracks already Structural failures ultimately led to the separation of the present around rivet holes. bow portion, followed by the third or double bottom Assuming that the hull girder failed at the surface, piece. It is interesting to note that the bow section did not then as Boiler Room No. 4 filled with water, the stern suffer damage similar to that in the stern section. This was rose farther out of the water, resulting in some 76 me­ likely due to the gradual flooding of the bow section, and ters of unsupported hull, which sharply increased the its stability during the descent to the bottom. It rests up­ hull girder stresses, in turn accelerating the fracturing of right on the bottom with little apparent damage directly the steel plates. The angle of trim grew to a maximum attributable to impact with the seabed. of 15 to 20 degrees, further increasing the stresses in the The analysis supports some witnesses' testimony that hull and deck plating near the aft expansion joint. The the ship likely began to fracture at the surface, and that stresses continued to build in this area of the ship, where the fracture was completed at some unknown depth be­ there were large openings for a main access, the machin­ low the water's surface. The resulting stress levels in the ery casing for the Reciprocating Engine Room, the u'p­ strength deck below the root of the second expansion takes and intakes for the boilers, the ash pit door on the joint (aft), and in the inner bottom structure directly be­ port side of Boiler Room No. 1, and the turbine engine low, were very high because of the unusual flooding oc­ casing. As the hull girder continued to fail, the bow was curring in the forward half of the ship. These patterns of first to begin its plunge toward the seabed. stress support the argument that initial hull failure likely As the bow and stern sections continued to separate, occurred at the surface. Additional work is being per­ there were some local buckling failures in the inner bot­ formed to investigate this further. tom and bottom structure. This is what caused the stern These findings mirror the testimony of Seaman Edward section to settle back toward the water's surface as the John Buley at the U.S. Senate hearings. Stating that as the decks began to fail and the side shell fractured into many bow continued to slip below the surface, "She went down small plate sections. The MSC/ NASTRAN finite ele­ as far as the after funnel, and then there was a little roar, as ment analysis indicates that the stresses in the region of though the engines had rushed forward, and she snapped Boiler Room No. 1 and the Reciprocating Engine in two, and the bow part went down and the afterpart Room were elevated. came up and stayed up five minutes before it went down An additional stress analysis, based on classical beam theo­ .:. It was horizontal at first, and then went down." ry, indicates that the hull girder stresses exceeded the yield In ~esponse to what he meant by "snapped in two," and point of the steel. When the bow and stern began to sepa­ how he knew this, Buley testified, "She parted in two .. . rate, the two main transverse bulkheads bounding Boiler Because we could see the afterpart afloat, and there was no Room No. 1 collapsed as they were c.ompressed by the forepart to it. I think she must have parted where the downward movement of the deck structures. The decks, in bunkers were. She parted at the last, because the afterpart turn, failed because of the lack of bulkhead support. of her settled out of the water horizontally after the other

MEC H AN IC AL ENG INEE R.I NG AUGUST 1998 57 Testing the Titanic's Steel

IN 1996, SEVERAL SAMPLES OF STEEL from the Titanic-a Test, used to simulate rapid loading phenomena; the test hull plate from the bow area and a plate from a major trans­ used samples oriented both parallel and perpendicular to verse bulkhead-were recovered from the wreck site and the original direction of the hull plate. The ductile-brittle subjected to metallurgical testing by Prof. H.P. Leighly at transition temperature (using 20 Ibs.-ft. for the test) was the University of Missouri-Rolla, as well as at the laborato­ found to be 20°C in one direction and 30°C in the other, ries of Bethlehem Steel and the National Institute of Stan­ compared with -15°C for a reference sample of modern A dards and Technology. Chemical testing revealed a low 36 steel-and a water temperature of -2°C on the night residual nitrogen and manganese content, and higher lev­ the ship collided with the . The Titanic steel was els of sulfur, phosphorus, and oxygen than would be per­ also shown to have approximately one-third the impact

mitted today in mild steel plates or stiffeners. This indicates strength of modern steel. Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/120/08/54/6381729/me-1998-aug1.pdf by guest on 30 September 2021 that the steel was produced by the open-hearth rather than When the Titanic samples were also examined with a the Bessemer process, most likely in an acid-lined furnace; scanning electron microscope, the grain structure of the the steel is of a type known as semi-killed, that is, partially steel was found to be very large; this coarse structure deoxidized before casting into ingots. (Other fragments of made it easier for cracks to propagate. Rivet holes were the Titanic's hull have yielded slightly different results, sug­ cold-punched, a method no longer allowed (they must now gesting a degree of variability in the chemical and, hence, be drilled), nor were they reamed to remove microcracks. the mechanical properties of the steel used in the ship.) The steel grain size; the oxygen, sulfur, and phosphorus Excess oxygen can form precipitates that can em brittle content of the steel; and the cold-punched, unreamed rivet the steel, and will also raise transition temperatures. In the holes were found to have contributed to the breakup of the absence of sufficient manganese, sulfur reacts with the Titanic, along with the steel's relatively low ductility at the iron to form iron sulfide at the grain boundaries; it can also freezing point of water. The shell plates showed signs of react with manganese, in either case creating paths of brittle fracture, though some plates demonstrated signifi­ weakness for fractures . Sulfide particles under stress can cant plasticity. nucleate microcracks, which further loading will cause to Of course, the science of metallurgy has advanced con­ coalesce into larger cracks; in fact, this was found to have siderably since the Titanic's day, and William Garzke of been the mode of failure in the shell plating of the Titanic. Gibbs and Cox and his collaborators emphasized in their Phosphorus, even in small amounts, has been found to fos­ report that "the steel used in the Titanic was the best avail­ ter the initiation of fractures. Of course, much of this met­ able in 1909-1914" when the ship was built. In fact, they allurgical information has only been learned in the years add that when 39,000 tons of water entered the bow, "no since the Titanic went down. modern ship, not even a welded one, could have withstood To determine the steel's mechanical properties, it was the forces that the Titanic experienced during her subjected to tensile testing, as well as the Charpy V-Notch breakup ." HENRY BAUMGARTNER part went down. First of all, you could see her propellers changes in maritime safety law and ship construction. and everything. Her rudder was clear out of the water. The demise of the mighty Titanic was swift, sure, and ter­ You could hear the rush of the machinery, and she parted rible. Whatever could have gone wrong, did. The engi­ in two, and the afterpart settled down again, and we neering marvel that heralded the beginning of the age of thought the afterpart would float altogether. She upright­ technology also displayed, all too clearly, its vulnerability ed herself for about five minutes, and then tipped over and and limits-as well as the need for prudence and safety. disappeared ... You could see she went in two, because we "The analyses, and future analyses we hope to make were quite near to her and could see her quite plainly." employing both MSC/ NASTRAN and MSC/ DY­ RMS Titanic, the largest ship of its day, was built in TRAN, help us make critical design decisions about fu­ , Ireland, and was said to be "unsinkable," a belief ture marine structural features, such as deck openings so strong that it was to have tragic consequences. Having and expansions joints." Wood said. confidence in the ship's "unsinkability," many passengers "Today, we're changing the way we design ships. In the chose to remain on board. The ·first lifeboats to leave past, nominal load conditions were averaged. Today, we . were only half, or one-third full. design for the ultimate stress levels and strength," says The fallacy of the claim itself became tragically appar­ Robert Sielski, se nior staff engineer at Gibbs & Cox. ent during the ship's maiden voyage. Just three hours af­ " MSC/ NASTRAN helps us evaluate and design for in­ ter it collided with an iceberg, the majestic Titanic van­ creased survivability." _ ished beneath the cold waters of the North Atlantic. This ill-founded confidence led to the ignoring of at 'Dlis article is based Oil a paper, "Titanic, n ,e A llatolllY oJ a Disaster, A Report least 14 warnings of hazardous ice fi elds, six of which Jrolll the Marille Forellsic PO/,e1," presellted at the 1997 O/IIIIIa l meeting oJ the So­ ciety of Na"al Architects alld Marille EIIgilleers, that dOCIIlllellts the work of Willialll were received on the day of the disaster. H . Carzke, Jr. and Da"id Wood, Cibbs & Cox, IlI c.; David K. BrowlI , Equipped with only 20 lifeboats, the Titanic went down RCNC; Paul K. Mat/bia s, Polaris /m agillg; Dr. Roy Culli",ore, Ull iversity oJ with the loss of 1,523 passengers and crew. This incredi­ Regilla; Da"id Li"ingstoll e, Harlalld & Wolff; Prof. H.P. Leighly, Jr. , Ulli"ersity oJ Missollri-Rolla; Dr. Timothy Foecke, Na tional Illstill/te of Standards and Tech- ble disaster led to a number of investigations in Great 1I010gy; alld Art/lllr Salldiford, COl/s llltallt . Eyewitness acco llllts are Jrolll various Britain and the United States that res ulted in sweeping sOllrces, inclllding tlte official transcripts of the 19'12 u.s. Swate in vestigation.

58 AUGUST 1998 MECHAN ICAL ENG INEERING