US2729184A - A monolithic metal shell structure - Google Patents

Description

Jan. 3, 1956 A. B. BAGSAR MONOLITHIC METAL SHELL STRUCTURE 3 Sheets-Sheet 2 Filed March 15, 1951 INVEN TOR. d AARON B. BAGS/4f? ATTORNEYS.

FIG. /2.

Jan. 3, 1956 A. B. BAGSAR 2,729,184

MONOLITHIC METAL SHELL STRUCTURE Filed March 15, 1 951 :5 Sheets-Sheet :5

INVENTOR. AARON B. BAGSAR ATTORNEYS t 2,729,184 A MONOLITHIC METAL SHELL STRUCTURE Application March 15, 1951, Serial No. 215,803 Claims. (Cl. 114-79) The development of fusion welding has resulted inits 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 weight and 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 diificulties 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 difficulties 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 longitudinally 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 disad vantages. 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 theplates are i United States Patent 0 2,729,184 Patented Jan. 3, 1%56 welded together and do not therefore flex as much as the riveted joint. Still another objection to this expedient is 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 stiflen the ships structure is also objectionable because of the difliculty 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 stiifeners, or in other cases the stitfeners fail first and transmit the stress to the ships shell, thereby rendering the stiifeners ineffective.

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. i

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 seam 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.

While the description is directed to the application of the invention to the hull and deck of a ship, the invention is not necessarily limited to such application except in those claims in which that limitation is expressed, but may be applicable to other structures in which cracks may develop and, if not arrested, would spread to an extent that would cause serious damage or possible destruction. It may be added that in any all-welded construction there are inevitable imperfections. Cracks are liable to start at some locus of imperfection, which acts as 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.

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 com prising conventional plates or sections edge welded one to another and specialplates or sections that may be either in one embodiment inserted between conventional plates and edge-welded thereto or in another embodiment applied to one or both faces of conventional plates and welded thereto, and in which, in the first embodiment, all the plates are imperforate and in which, in the second embodiment, the conventional plates are imperforate while the special plates may or may notbe imperforate. In all embodiments the special plates, welded to the conventional plates, are provided with holes (which may be of different shapes including slots or grooves). These holes in all instances extend from an exposed face of the special section, those holes in imperforate sections terminating short of the opposite face of the section, each hole presenting at least one edge, namely, a line of junction between the face of the plate and the intersecting side wall of the hole at one end which is free of metal applied by fusion welding and which is, throughout the specification, designated an unfusededge, such unfused edges extending transverse to the general direction in which cracks tend to spread. In the case of the hull or deck of a ship, the general direction of such a progressive crack is across the ship. When, therefore, my invention is applied to a ship, a construction embodying my invention presents unfused edges extending longitudinally of the ship. Such unfused edges are so distributed along differentlongitudinally extending lines as to avoid the possibility ofany crack not encountering one of them. When such unfused edges are thus encountered the extension of the crack is arrested.

The invention is capable of many different embodiments a number of which are shown in the drawings, in which- Figs. 2 to 5, inclusive, are sectional views of as many different embodiments of the invention.

Fig. 6 is a view, similar to Fig. 5, but illustrating the desired relation between thickness of plate, hole depth, hole diameter and pitch dimension.

Fig. 7 is a perspective view, partly in section, of'the embodiment shown in Fig. 1.

Fig. dis a perspective view, partly broken away, of another embodiment of the invention. Fig. 9 is a plan view of the construction of Fig. 8.

Figs. 10, 11 and 12 are plan views of other modifications.

Fig. 13 is a plan view illustrating part of the area of the shell of a ship showing a multiplicity of conventional and special sections welded one to another to form an integral shell structure, together with several different arrangements of the special sections relative to each other and to the conventional sections.

Fig. 14 may be taken to be a plan view of a part 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. 15 is a plan view of part of a regular or conventional plate to which is applied a special reinforcing or lap plate provided with holes of different shape.

Fig. 16 is a cross-sectional view of a special plate interposed between two regular or conventional plates in which the holes extend entirely through the special plate but are entirely filled by rivets, bolts or set screws.

In Figs. 1 and 7 a special reinforcing or lap plate b is applied to one face of one of the regular or conventional plates 11 of a mainly or wholly welded ship hull or ship deck, comprising a multitude of plates welded edge to edge to form a monolithic shell structure. The special plate b is secured to the conventional plate a by welding, as shown at d. A number of holes 0 are formed in the plate b said holes extending, preferably but not necessarily, from face to face, and being preferably irregularly distributed, as shown in Fig. 7. While such irregularity need not be a random one, as shown in Fig. 7, it is undesirable that the holes should be formed in straight rows measured in any direction, although any regular arrangements that would not afford straight line paths clearing all holes is not necessarily inferior to a random arrangement. It will be understood that cross-sections through actual structures like those illustrated in Fig. 1 and the remaining figures are not likely to exhibit the regular holespacing shown therein, but are more likely to exhibit holes irregularly spaced apart at varying distances dependent upon the line on which the section is taken.

In Fig. 13 is shown a multitude of shell sections joined by edge-welding to form part of a large area of a united shell structure such as the hull or deck of a ship. Some of the plates shown are conventional plates at and others x are special plates, which are illustrated as composed of plates like the conventional plates to which are applied orificed lap platesas shown in Fig. 1. However, the special plates x may be like, for example, any of those shown in Figs. 1 to 9. All the plates are edge-welded to adjacent plates. No special arrangement is required so long as any spreading crack meets an edge, not fused to the shell, that will arrest its further spread. If the conventional plate is provided with circular holes, a substantial length of the arc of the circular edge surrounding a hole will extend transverse to the path that the crack takes and will stop its further extension. The general direction of such path is shown by the arrow.

in the arrangement shown at the left side of Fig. 13 there are two adjacent rows of special plates extending longtitudinally of the ship. At the center of the figure is shown a single row of special plates, which will suffice to stop a crack, since the holes are distributed along different lines transverse to the path of a crack, one at least of such holes being in any path the crack may take. All the protective plates of a row need not be special plates, but some of the plates or" a row may be conventional plates and others special plates, as shown at the right of the figure.

These illustrative arrangements of special plates are merely typical. Other arrangements will suggest themselves. Eut a plurality of such arrangements should extend, more or less widely spaced apart transversely, longitudinally along the hull, and preferably also along the deck, so that a crack will be arrested before it has spread any considerable distance.

Fig. 2 shows special plates b, b, each like that of Fig. 1, applied to opposite faces of one of the conventional plates (1.

In Fig. 3, the plate a, to which a special plate b, is welded, is like one of the regular or conventional plates except that it is dished in to receive the plate b, in the pocket thus formed, the outer face of the plate b being flush with the face of the plate a. The plate b is provided, like plate b, with similar holes c.

In Figs. 4 and 5 a special plate 1 is interposed between two regular or conventional plates e, e, in edge to edge relation and welded thereto in the usual manner. The special plate 1'', like the special sections above described, is preferably, but not necessarily, of greater thickness than the conventional plate e and is provided with holes g that do not extend entirely through the plate. Preferably, but not necessarily, these holes open on opposite faces of the plate, each set of holes preferably being irregularly distributed and being offset relatively to the holes formed in the other face.

While in the embodiments shown in Figs. 1, 2 and 3, the perforated lap plate b or b having the holes 0 may overlap a plurality of base plates, it is preferred to apply each lap plate to a single base plate so that the special sections may be formed before they are welded in position.

The holes 0, g may be of many different forms in transverse section, such as circular, oval, or polygonal.

Fig. 15 is a plan view of a regular or conventional plate a to which is applied a special reinforcing or lap plate b provided with holes c of polygonal shape and holes (2 of oval shape. To simplify the illustration, a shortplate is shown containing only a single row of holes, although it will be understood that such holes, polygonal or oval, would preferably be provided in a plate of greater area and distributed in the manner shown in Figs. 7 or 13.

The greater the diameter of the holes, the more nearly absolute insurance exists against .the extension of a crack beyond any hole in its path, since the greater the diameter of the hole the greater the sudden increase in the radius of the crack and in the notch angle. But the holes should not have a diameter so great, and should not be spaced apart at such small distances, as to seriously weaken the perforated section. I have found, for example, that if the diameter of a circular hole is about one-half the total thickness of the special section, or if the radius measured to the curve connecting adjacent fiat sides of a polygonal hole is about one-quarter the total thickness of the special section, such holes are adequate to arrest, or substantially resist, crack extension.

In Fig. 6 I have indicated specific preferred relations between thickness of plate z, hole depth v, hole diameter y and pitch dimension w, in which y: /2 X preferred minimum v= /s preferred minimum w=-/ X preferred maximum These approximate dimensions are distinctly preferred, but no hard and fast rule dictates holes of absolutely definite size spaced definite distances apart.

The holes in the special lap plate, as shown in Figs. 1, 2 and 3, or in a special section like those shown in Figs. 4 and 5, may contain rivets, bolts, or set screws; or they may be filled with cement, plastic or other convenient material which, after hardening or setting, effectively fill the holes and avoid open pockets that would be likely to cause corrosion, erosion or other objectionable irregularities, as shown at h, Fig. 1. If rivets are applied, they should preferably be countersunk, to obtain a flush surface, before the plate is installed. If the holes are filled as above described it would permit the holes to be drilled entirely through a special section.

In Fig. 16 is shown a special plate 11 having holes extending entirely through the plate but filled, one with a rivet v, another with a bolt w, and a third with a set screw y. it is preferred, however, not to extend the holes entirely through the plate, but only partly through, as shown in Figs. 4 and 5. This avoids the expense required to fill the holes as described and more nearly insures that the plate will be impervious to leakage.

It would be theoretically possible for a crack that extends in the general direction hereinbefore described to zigzag around the holes in a special section. But this is extremely unlikely, because the strength of the section is reduced by the holes and the crack will tend to proceed through the weakest part of the structure and not through the strongest.

Figs. 8 and 9 disclose a modification in which the holes take the form of grooves or slots 0 whose longitudinal direction of extension is transverse to the general direction of any fracture that may develop. These grooves or slots may be arranged in longitudinal rows, each row comprising a series of aligning, spaced apart, grooves or slots in staggered relation to the grooves or slots of the next adjacent row or rows; each groove or slot in any row being at least as long as, and preferably slightly longer than, the transversely opposing solid part of the plate 6 grooves or slots may contain a plug or filling h of cement or plaster, as shown in Fig. 1.

As shown in Figs. 8 and 9, these grooves or slots 0 are formed in special plates that are applied to convenseparating two aligning grooves in the next adjacentrow or rows. However, no two grooves need necessarily align longitudinally so long as the longitudinal extensions of the slots are along different longitudinal lines and provided that there is more or less overlapping of slots extending in different longitudinal lines. Any fracture thatmay develop will be certain to encounter a groove or slot and thus have its notch angle suddenly increase to 180; thereby arresting further extension ofthe crack. In this modification it is permissible to provide a single long narrow plate, as shown in Fig. 9, or a plurality of such plates, the same extending lengthwise of the ship and applied to the hull or deck or both. Fig. 1 serves to illustrate a cross-section on the line 1-1 of Fig. 9. These tional plates edge-welded together as in ordinary monolithic steel constructions. They may be applied to one or both faces of the monolithic shell, Fig. 2 representing a cross-section through such a construction. Or certain plates of the monolithic shell may be dished and the slotted or grooved plates may be applied to the shallow recess thus formed, Fig. 3 representing a cr0ss-section through such a construction. Or certain plates of the monolithic shell may be made in part of special thickness and grooved in opposite faces, Fig. 4 representing a cross-section through such a construction. Or special plates may be interposed between, and edge-welded to, regular plates, and such special inserted plates may be grooved or slotted, Fig. 5 representing a cross-section through such a construction.

The same resistance to crack or fracture extension may be effected by applying pairs of plates r to the monolithic shell and by spacing apart the plates of a pair and welding the plates to the shell along three edges but not along the opposing spaced apart edges of the two plates, as shown in plan view in Fig. 10. The elongated space between the plates of a pair is the equivalent of a slot formed in a single plate. monolithic shell that reaches one of the plates r will progress until it reaches the space between the plates, at which space (the plates not being fused to the shell, as by Welding) the crack will have its notch angle suddenly increased to the radius being likewise increased; thereby arresting further extension of the crack, just as in the case of a slotted or grooved single special plate.

Fig. 11 represents a slight modification of Fig. 10. The plates of the pair are spaced apart as in Fig. 10, a plug h of plaster or cement may fill this space (this may be done also in the construction of Fig. 10) and the weld d may extend entirely around the outer peripheryof the pair of plates.

A simplified embodiment of the broad invention, applicable to certain monolithic shells, is shown in Fig. 12. A single special plate t is applied to the monolithic shell and welded to the shell around one longitudinal edge and the two end edges but not along one longitudinal edge. This afiords a discontinuity in the otherwise completely integral shell. Any crack spreading in a direction transverse to the longitudinal direction or extension of the special plate t and in the direction of the arrow, Fig. 12, will have its notch angle suddenly increased to 180, and the radius is likewise increased, when the crack reaches the edge of the special plate that is not welded to the shell.

It will be understood that the pairs of plates shown in Figs. 10 and 11 or the single plates shown in Fig. 12

will be so located along different longitudinal lines and so staggered that any transversely progressing crack will encounter one of the pair of plates r, or one of theplates t. Special illustration is unnecessary, since this described arrangement of the plates is the same as that shown in Figs. 8 and 9 as applied to elongated grooves. Alternatively a single elongated pair of plates r, or a single elongated plate I, or a plurality of either, may extend along the monolithic shell for a distance equal to the width of the'zone in which development or extension of cracks may be apprehended. In Fig. 14, 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, each of the crack arresters shown in Figs. 10, 11 and 12 is shown as extending longitudinally of the axis of the ship, within, and from one end to the other of, the area desired to be protected from crack extension. The distribution may be, however, for example, like that of the grooves in Figs. 8 and 9.

Where the construction shown in Fig. 12 is adopted,

Any crack or fracture in the the special plate will be effective to resist the extension of a crack only if the crack develops in one transverse direction,.namely, toward the edge of the plate that is not fused to the shell. Therefore, such plates should be so distributed that any crack'progressing within the vulnerable zone, in either of two opposite directions transverse to the longitudinal extension of the plates, will encounter at least one plate whose unfused edge faces toward the crack.

Where in the claims holes are specified it is to be understood that they comprehend holes of any contour including elongated holes which in the description are s ecifically called grooves or slots.

It will be understood, also, that the term special section, when specified in the claims, includes an interposed section, as shown in Figs. 4 and 5, as well as the combination of a regular or conventional section to which is applied a special plate, as shown in Figs. 1, 2, 3, 8 and 9.

The constructions shown in all the figures have the feature in common that the special sections are welded to the main shell but are of such configuration as to present edges not fused with the shell, such edges facing in the direction in which, in the monolithic shell, any crack or fracture developing therein will extend and that such edges are of such total width that any crack within the zone within which such crack is adapted to extend will in its extension encounter such an edge to thereby suddenly increase the radius of the notch at the base of the crack to thereby resist further extension of the crack. In the figures shown on sheet 1 these edges are formed by those concavities of the holes which intersect any line that may be drawn in the direction first specified within the zone in which cracking is liable to develop and progress. In the embodiments shown in Figs. 8 and 9, these edges are formed by the longitudinal walls of the elongated holes.

In Figs. 10, 11 and 12 these edges are formed by the walls of the plates that bound those longitudinally extending sides thereof that are not fused to the monolithic shell. Such edges, however, formed, afford such discontinuity in an otherwise integral structure as is required to resist or arrest crack extension.

The many embodiments of the invention herein de scribed and shown in the accompanying drawings are not exhaustive of all possible specific constructions and will suggest to those skilled inthe art other modifications that will be equally effective to accomplish the object of the invention.

This application is a continuation-in-part of applications filed by me January 25, 1947, Serial No. 724,392,

andJuly 31, 1947, Serial No. 765,007, both of which i,"

became abandoned. I

There is not herein claimed the specific construction illustrated in Figs. 10, ll, 12, 14 and 16, the same being the subject matter of a divisional application filed July 30, 1954,Ser. No. 446,853.

What is claimed is:

1. A metal shell structure which it is desired to protect from the extension in one general direction of any crack that may develop in the shell, said shell comprising impervious conventional sections and special sections, adjacent conventional sections being at their edges united one to another by welds and each of said special sections being at their edges united to adjacent conventional sections by welds to thereby form a continuous integral struc ture extending throughout a predetermined area to be protected from such crack extension, the special secl Ii tions having a multiplicity of holes therein which open only in exposed faces of such special sections, thereby providing with the conventional sections an impervious monolithic shell, said holes in said special sections being distributed in closely spaced relationship to each other both along and transversely of said general direction so that any line extending approximately along said general direction intersects the edges of a plurality of said holes.

2. A structure as defined in claim 1 in which the holes are in the form of parallel grooves whose longitudinal extension is transverse to said general direction.

3. The construction defined in claim 2 in which the shell is the hull of a ship and in which the grooves are located in an area including that part of the hull that is intended to be protected from crack extension and in which the longitudinal direction of the grooves is along the length of the hull.

4. The construction specified in claim 3 in which the grooves are spaced apart along the width of the hull and are in such staggered relation that any line extending along said general direction intersects a plurality of said grooves.

S. A structure in accordance with claim 2 in which the grooves are spaced apart along said general direction and being in such staggered relation that any line extending along said general direction intersects a plurality of said grooves.

6. A structure as defined in claim 1 in which said special sections are applied to at least one face of said conventional sections.

7. The construction defined in claim 6 in which the shell is the hull of a ship and in which the holes are located in an area including that part of the hull that extends throughout the length of the hull that is intended to be protected from crack extension and in which any line extending across that part of the hull intersects a plurality of said holes.

8. A structure as defined in claim 1 in which said spe' cial sections are positioned between spaced apart conventional sections.

9. The construction defined in claim 8 in which the shell is the hull of a ship and in which the holes are located in an area including that part of the hull that extends throughout the length of the hull that is intended to be protected from crack extension and in which any line extending across that part of the hull intersects a plurality of said holes.

10. The construction. defined in claim 1 in which the shell is the hull of a ship and in which the holes are located in an area including that part of the hull that extends throughout the length of the hull that is intended to be protected from crack extension and in which any line extending across that part of the hull intersects a plurality of said holes.

References Cited in the file of this patent UNITED STATES PATENTS 1,290,09l Cole Jan. 7, 1919 2,366,698 Cole Jan. 9, 1945 2,393,653 Pamphilis Ian. 29, 1946 2,460,893 MacCutcheon ct al Feb. 11-349 OTHER REFERENCES The Design and Methods of Construction of Welded Steel Vessels, l5 .iuly 1945, pages 69-78, Government Printing Office, Washington, D. (3., 1947.

Claims (1)

1. A METAL SHELL STRUCTURE WHICH IT IS DESIRED TO PROTECT FROM THE EXTENSION IN ONE GENERAL DIRECTION OF ANY CRACK THAT MAY DEVELOP IN THE SHELL, SAID SHELL COMPRISING IMPERVIOUS CONVENTIONAL SECTIONS AND SPECIAL SECTIONS, ADJACENT CONVENTIONAL SECTIONS BEING AT THEIR EDGES UNITED ONE TO ANOTHER BY WELDS AND EACH OF SAID SPECIAL SECTIONS BEING AT THEIR EDGES UNITED TO ADJACENT CONVENTIONAL SECTIONS BY WELDS TO THEREBY FORM A CONTINUOUS INTEGRAL STRUCTURE EXTENDING THROUGHOUT A PREDETERMINED AREA TO BE PROTECTED FROM SUCH CRACK EXTENSION, THE SPECIAL SECTIONS HAVING A MULTIPLICITY OF HOLES THEREIN WHICH OPEN ONLY IN EXPOSED FACES OF SUCH SPECIAL SECTIONS, THEREBY PROVIDING WITH THE CONVENTIONAL SECTIONS AN IMPERVIOUS MONOLITHIC SHELL, SAID HOLES IN SAID SPECIAL SECTIONS BEING DISTRIBUTED IN CLOSELY SPACED RELATIONSHIP TO EACH OTHER BOTH ALONG AND TRANSVERSELY OF SAID GENERAL DIRECTIONS SO THAT ANY LINE EXTENDING APPROXIMATELY ALONG SAID GENERAL DIRECTION INTERSECTS THE EDGES OF A PLURALITY OF SAID HOLES.

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