US2737918A - Monolithic metal structure - Google Patents

Description

March 13, 1956 A. A. BAGSAR 2,737,918

MONOLITHIC METAL STRUCTURE Original Filed March 15, 1951 Y TW Fig, 4

INVENTOR. AARON B. BAGSAR ZMW/ I/MJZQ ATTORNEY United States P O MONOLITHIC METAL STRUCTURE Aaron B. Bagsar, deceased, Drexel Hill, Pa., assiguor to.

Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey 3 Claims. (Cl. 114---79) The development of fusion welding has resulted in its successful application to various monolithic steel constructions. An early application was to structures such as pressure vessels, after which the shipbuilding industry adopted this method of construction as a substitute for the riveted type of construction throughout the greater part of the length of the hull and deck. The welding method has also been applied to a certain extent to bridges and other massive structures.

The known advantages of the welded over the riveted construction include: considerable weightand materialsaving effected by eliminating lapped seams; appreciably stronger seams obtained by welding, since the riveted construction requires drilling or punching through the structural members; no maintenance problems involved similar to riveted seams, such as leaks occurring through rivet holes due to corrosion or excessive flexing, etc.; obtaining a flush job, thereby simplifying internal drainage and painting problems and obtaining a stream-line construction, thereby reducing frictional loss.

However, in certain all-welded constructions of this type, certain difliculties have developed that 'were not foreseen and which in some cases have had serious consequences, such difiiculties being characteristic of those monolithic steel structures which are subject to multiaxial and severe stresses. For example, in ship construction serious fractures were encountered, because a normally ductile steel would exhibit a brittle fracture in a welded ship, due to complexity of the stresses imposed by construction and by the service conditions, these fractures mostly occurring in the plates and not in the Weld itself. In order to minimize these difiiculties it was later proposed to insert in certain critical sections riveted seams in order to break up the continuity of the plates in the Welded structures and also to obtain a certain amount of flexing, the purpose being to at least arrest the extent of cracking. In one of such constructions, which has actually been applied to ships, there is formed in the deck and in the top side of a ship a series of longitudinal ly extending aligning slots cut entirely through the metal plating of the shell, the slots being covered with a metal strap which is riveted to the plating along both sides of the slot. It has also been proposed to add" numerous structural members to the ships structure, mainly internally, in order to relieve the welded shell of the ship from excessive stresses, with the object of thereby preventing cracking of the hull and decking. The above remedies have distinct limitations and disadvantages. They may reduce, but do not eliminate, the danger of losing a ship by fracturing of the hull.

Insertion of riveted seams in critical sections of the ship is distinctly objectionable, since riveting requires drilling of the main shell at these sections in order to install rivets, thereby seriously reducing the strength of the section. This modification is also objectionable for the reason that most of the stresses are thrown onto these riveted seams, because the remainder of the shell and decking is continuous by virtue of the fact that the 2,737,918 Patented Mar. 13, 1956 plates are welded together and do not therefore flex as much as the riveted joint. Still another objection to this expedientis that the rivets in these insertions leak badly after a short service; which may be due to the excessive flexing and stressing that are induced in these seams, since the remainder of the shell is welded and continuous. These stresses are therefore more severe than in a wholly riveted shell, since in the latter such stresses are more evenly distributed over a number of riveted joints.

The insertion of independent members in the ship to stiffen the ships structure is also objectionable because of the difficulty of installing the sections in such a manner and with such rigidity as to make these additional sections share proportionately the stress simultaneously with the remaining members of the ships structure. In the circumstances, the hull fails first before the stress is transmitted to these additional stifieners, or in other cases the stiifeners fail first and transmit the stress to the ships shell, thereby rendering the stifleners ineifective.

The construction in which the deck or hull is provided with a series of longitudinally extending aligning slots covered by a metal strip riveted to the plating along both sides of the slots is open to most, if not all, of the objections above listed. These slots seriously weaken the body of thehull, most of the stresses are thrown onto the riveted metal strap, and leakage through the slots and under the'strap is so unavoidable that the construction was applied to the hull only at the top side of the hull adjacent the gunwale. Obviously this construction did not provide against the extension of any crack starting on one side of the hull from spreading all the way to the other side.

. It is known that riveted seams are not as susceptible to crack propagation as welded ships of monolithic type, and that cracks may be arrested in these riveted seams, although failure of riveted seams themselves by cracking is not altogether uncommon. It is believed that the virtue of the riveted scam in this respect over the welded construction is attributable to the fact that no excessive stress concentrations are possible because of the relative flexibility of the riveted seam, and also to the inherent geometry of the riveted seam in which the adjoining plates are not made integral with each other, as in welding, but are held together mechanically by rivets and butt straps or by the lapping arrangement. I

There may be structures other than the hull or deck of a ship in which similar defects exist and to which, in the opinion .of some engineers, fusion welding would be inapplicable, notwithstanding its recognized advantages, and which could not be satisfactorily remediable by any of the above specified expedients that break up a focal point, from which cracks may start, and unless some means is provided to. arrest them, these cracks will spread very rapidly, often almost instantly, and assume serious proportions. In the case of a ship a single crack may wholly incapacitate it or even cause it to break into sections.

r The object of my invention is to arrest the extension of shearing or tearing fractures of local origin while avoiding the limitations and disadvantages of both the riveted and welded construction and of the expedients heretofore adopted having the same object. The invention contemplates the maintenance of an all-welded construction comprising conventional plate sections x edge-welded one to another to form an impervious monolithic shell and special plates or sections applied to one or both faces of conventional plates. The term conventional plates should be understood as meaning plates of usually uniform thickness such as are usually employed in ships hull and deck construction, the plates being in lateral alignment and, in the so-called all-welded type of construction mentioned at the introductory part of this description, secured together solely by edge welding to form a monolithic shell. Where, in this description, conventional plates or conventional sections are mentioned, it will be understood that my invention contemplates no necessary departure from pre-existing constructions. Where the term special plates or special sections is employed, they are to be understood as plates applied to one or both surfaces of the shell formed by the known conventional sections and having the specific construction illustrated in the drawings and hereinafter in detail described. The longitudinal direction of extension of the special plates is transverse to the general direction in which such cracks spread. Certain of such special plates are spaced apart along saidgeneral direction and are in parallel relationship. Such special plates are secured to the shell solely by edge welding, the welds being applied along the end edges of a plate and along one only of the two longitudinal edges thereof. The longitudinal unwelded (or unfused) edges of certain of said plates so spaced apart and in parallel relationship face in opposite directions, as, for example, toward each other, as shown in Fig. 3, and are so located that any line extending in said general direction intersects a plurality of the last specified special plates. Of the last specified special plates each is effective to arrest a crack extending in one general direction but not in the opposite general direction, but the specified arrangement of such last specified special plates insures that one or the other of such plates will be efiective to arrest the extension of the crack.

In the case of the hull of a ship the general direction of such a progressive crack is across the ship. When, therefore, these special plates, arranged along different longitudinal lines, present unwelded (or unfused) edges facing toward opposite top sides of the hull, any progressing crack will encounter at least one of such unwelded edges. The arrest of crack extension is thus insured.

These special plates should be applied at or near the top side of the hull, preferably in the midship part of the hull, where the stresses are likely to be the greatest. The construction also permits application of the plates to the submergible part of the hull, as otherwise a crack present near one of the top sides or gunwale of the hull might extend entirely across the hull. So far as concerns stress distribution at the top or on the bottom of a ships hull, this is variable and is influenced by the loading conditions. If the ship is loaded the bottom is more stressed than the top, while if unloaded or partly loaded the reverse may be true. So both top and bottom should be protected from crack propagation. To insure not only the arrest of a crack but its arrest before it has proceeded any considerable distance, the special plates are preferably along a number of parallel lines at various distances between the two top sides of the hull, so that no crack, wherever it originates, can proceed for but a minor part of the width of the hull.

Particular embodiments of the invention will give a better understanding of the invention. Certain of such embodiments are illustrated in the drawings, in which- Fig. 1 may be taken to be a plan view of the deck of a ship or an inverted plan view of the hull of a ship showing the application thereto of several embodiments of the invention.

Fig. 2 is a plan view of one of the special plates.

Figs. 3 and 4 are plan views of two of such special plates so arranged as to present opposing unwelded (or unfused). edges.

Fig. 5 is a sectional view showing the application of special plates to opposite sides of the conventional base shell.

Fig. 2, as just stated, is a plan view of one of the special plates hereinbefore described. It comprises a plate a, which may be of any length which by welds b, c and d are secured to the monolithic shell. One edge e is unwelded (or unfused). Any crack proceeding in the direction of the arrow and encountering the plate a at any point along the length of the plate will be arrested. Such a plate cannot, however, be relied upon to arrest a crack proceeding in the opposite direction. One way of insuring the arrest of a crack proceeding in either direction is to provide a pair of such special plates with their unwelded edges facing in opposite directions, e. g. toward each other, as illustrated. Any crack or fracture in the monolithic shell that reaches one of the plates a will progress until it reaches the space between the plates, at which the crack will have its notch angle suddenly increased to the radius being likewise increased, thereby arresting further extension of the crack.

In Fig. 4 the plates of the pair are spaced apart as in Fig. 3, and the space is filled with a plug of plaster or cement p and the weld 1 may extend entirely around the outer periphery of the pair of plates.

It should be understood that a plurality of pairs of special plates like that shown in Figs. 3 and 4 should be located along diiferent longitudinal lines so that no crack can progress far before encountering such a pair. Further, no pair of special plates need extend throughout the length of the hull or throughout that part of the length of the hull desired to be protected, provided pairs of plates arranged along difierent longitudinal lines are so staggered that any transversely progressing crack will certainly encounter one or more of the pairs of special plates.

In Fig. l, which may be considered to be a plan view of the deck of a ship, or a plan view of the hull of a ship looking from beneath, several of many possible arrangements of special plates are shown. Thus along one longitudinal line is arranged a pair of plates like that shown in Fig. 3. Along another parallel longitudinal line is arranged a pair of plates like that shown in Fig. 4. Along two other parallel longitudinal lines are applied special plates like that shown in Fig. 2 but spaced apart transversely at relatively greater distances.

All these difierent described embodiments of the invention (and other embodiments that will suggest themselves to those skilled in the art) may be applied to a single hull or deck, or other structure requiring similar protection against crack extension. Thus 3A illustrates one application of the structure disclosed in Fig. 3. 2A, 2A illustrate applications of Fig. 2, which is a duplication of 3A except that the two plates are spaced apart a greater distance. 4A illustrates an application of the united plates shown in Fig. 4. 2B, 2B, 2B, 2B show the same arrangement as 2A, 2A, except that the single plates do not extend throughout the length of the hull or deck or that part thereof requiring arrest of crack extension, but are shorter plates in staggered relation.

Any crack extending in either transverse direction, at whatever point the crack originates, is bound to encounter an unwelded (or unfused) edge and be thus prevented from further spreading.

From a practical, and economical, standpoint, however, it is preferable to utilize only one embodiment of the invention as applied to a single hull or deck, say, for example, a number of the embodiments designated 3A arranged along difierent parallel longitudinal lines and spaced apart.

The invention does not require the use of bolts or rivets to efieet adherence of the special plates to the monolithic shell, bolts or rivets being in fact objectionable for reasons hereinbefore fully explained. The welds, therefore, should be of sufiicient thickness to insure such adherence. Such thickness, measured in the direction of the thickness of the special plates, should approximate the thickness of the plates so that the edge of the weld should extend to, or nearly to, the corner between the edge of the plate and its exposed face.

This application is a division of an application filed by me March 15, 1951, Serial No. 215,803, now Patent 2,729,184, issued January 3, 1956.

What is claimed is:

l. A metal shell structure which it is desired to protect from the extension in either of opposite general directions of any crack which may develop within the area sought to be protected, said shell structure comprising the combination, with impervious conventional sections extending throughout such area, adjacent conventional sections being united solely by welding to form a base shell, of special sections applied to at least one face of the base shell, said special sections comprising a number of plates whose longitudinal direction of extension is transverse to said general direction and which, in such longitudinal direction of extension, are in parallel relationship and spaced apart, each of said special plates being secured to the base shell solely by edge weld fusion applied to one longitudinally extending wall of the special plate and extending substantially to the longitudinal edge of said longitudinally extending wall and applied also to the transversely extending end walls of the special plate, the remaining longitudinal wall of the special plate being free of such Weld fusion, the longitudinal fused edges of different special plates facing in opposite directions and hence the unfused edges of different plates facing in opposite directions, one set of special plates therefore adapted to arrest a crack extending in one of said general directions and the other set of special plates adapted to arrest a crack extending in the opposite direction, said special plates being so located that any line extending along said general direction intersects a plurality of plates whose unfused edges face in opposite directions.

2. The construction defined in claim 1 in which the shell is that part of the hull of a ship which it is desired to protect from transverse crack extension and in which said special plates are applied to the hull and extend longitudinally of the hull.

3. The construction defined in claim 1 in which the plates are arranged in pairs and in which the unfused edges of the two plates face toward one another.

References Cited in the file of this patent UNITED STATES PATENTS 1,290,091 Cole Jan. 7, 1919 2,393,653 Pamphilis Jan. 29, 1946 2,462,670 Pew Feb. 22, 1949 2,495,782 Smith Jan. 31, 1950

Claims (1)

1. A METAL SHELL STRUCTURE WHICH IT IS DESIRED TO PROTECT FROM THE EXTENSION IN EITHER OF OPPOSITE GENERAL DIRECTIONS OF ANY CRACK WHICH MAY DEVELOP WITHIN THE AREA SOUGHT TO BE PROTECTED, SAID SHELL STRUCTURE COMPRISING THE COMBINATION, WITH IMPERVIOUS CONVENTIONAL SECTIONS EXTENDING THROUGHOUT SUCH AREA, ADJACENT CONVENTIONAL SECTIONS BEING UNITED SOLELY BY WELDING TO FORM A BASE SHELL, OF SPECIAL SECTIONS APPLIED TO AT LEAST ONE FACE OF THE BASE SHELL, SAID SPECIAL SECTIONS COMPRISING A NUMBER OF PLATES WHOSE LONGITUDINAL DIRECTION OF EXTENSION IS TRANSVERSE TO SAID GENERAL DIRECTION AND WHICH, IN SUCH LONGITUDINAL DIRECTION OF EXTENSION, ARE IN PARALLEL RELATIONSHIP AND SPACED APART, EACH OF SAID SPECIAL PLATES BEING SECURED TO THE BASE SHELL SOLELY BY EDGE WELD FUSION APPLIED TO ONE LONGITUDINALLY EXTENDING WALL OF THE SPECIAL PLATE AND EXTENDING SUBSTANTIALLY TO THE LONGITUDINAL EDGE OF SAID LONGITUDINALLY EXTENDING WALL AND APPLIED ALSO TO THE TRANSVERSELY EXTENDING END WALLS OF THE SPECIAL PLATE, THE REMAINING LONGITUDINAL WALL OF THE SPECIAL PLATE BEING FREE OF SUCH WELD FUSION, THE LONGITUDINAL FUSED EDGES OF DIFFERENT SPECIAL PLATES FACING IN OPPOSITE DIRECTIONS AND HENCE THE UNFUSED EDGES OF DIFFERENT PLATES FACING IN OPPOSITE DIRECTIONS, ONE SET OF SPECIAL PLATES THEREFORE ADAPTED TO ARREST A CRACK EXTENDING IN ONE OF SAID GENERAL DIRECTIONS AND THE OTHER SET OF SPECIAL PLATES ADAPTED TO ARREST A CRACK EXTENDING IN THE OPPOSITE DIRECTION, SAID SPECIAL PLATES BEING SO LOCATED THAT ANY LINE EXTENDING ALONG SAID GENERAL DIRECTION INTERSECTS A PLURALITY OF PLATES WHOSE UNFUSED EDGES FACE IN OPPOSITE DIRECTIONS.

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