The Development of Armor-piercing Shells Part 3

From the above table it will be noted that the R.P.M. are exceedingly high in some cases. Upon the impact of a sh.e.l.l with armor-plate the physical phenomena occur instantaneously and the resultant forces are so great that it is impossible to mechanically record their action. A study of the stresses in the sh.e.l.l can, however, be made on a theoretical basis.

In the first place, if the projectile were twenty calibres in length and of a material offering less resistance to torsional stress than steel and rotated at the high velocities indicated we would find that upon impact the torsion would be plainly evident as per the following:

a.s.sume a projectile A of length twenty calibres, about to penetrate an armor-plate B of thickness sufficient to prevent complete penetration by the sh.e.l.l in question.

[Ill.u.s.tration: Fig. 27]

The tendency of the impact is to stop the rotation of the projectile, owing to the friction between the surfaces in contact, but owing to the length of the projectile the point receives this r.e.t.a.r.ding influence before it can be transmitted throughout the body of the sh.e.l.l to its base. The consequent result is that the head will finally come to a stop while the base is still rotating, however slightly that may be.

Theoretically considering the projectile to be composed of a series of discs a line drawn parallel to the major axis, while at rest, would be represented by the line _cd_. Upon impact, however, the rotative force tends to create a twisting couple with the result that each disc will tend to slide on its preceding disc, so that by the time these twisting couples have been transmitted to the base of the sh.e.l.l the original line _cd_ will have taken some such position as _de_.

The objection to the present method of forging sh.e.l.ls is as a result, the grain or fibre of the metal lies parallel with the major axis of the forging, the forging process causing an elongation of the ingot and the metal grain following the direction of elongation. Consequently any flaws occurring in the material will extend parallel to the grain or major axis. If a flaw remains undiscovered in a finished projectile--as is sometimes the case--the projectile is not only weakened thereby, but the element of weakness lies in such a direction that the compression forces and counterforces produce very much the same results as would a wedge driven into a niche, i.e. the separation of adjacent material.

The author is in possession of a sh.e.l.l in which a longitudinal flaw was revealed in the ogive by the cutting away of a longitudinal quarter section, Fig. 28.

[Ill.u.s.tration: Fig. 28. Armor-Piercing Sh.e.l.l. Showing position of flaw.]

There are, therefore, two great forces with which to contend in the design of projectiles, to one of which, compression, has been given the greatest attention because of its recognized tendency to cause the base of the sh.e.l.l to crowd upon the head and cause the sh.e.l.l to break up about the ogive. The other force, torsion, seems not to have been considered prior to the present instance, at any rate so far as the author has been able to ascertain, not because thought to be unimportant, but because of oversight or failure on the part of investigators to take into consideration in this instance, an element of reaction commonly considered in mechanical engineering practice, as in shafting for vessels and for power transmission in shops, etc.

The writer maintains that immediately upon impact the metal in a sh.e.l.l a.s.sumes a state of physical unrest, due to stresses similar to those in a propeller shaft when in motion, except that in the former case the intensity of the compression stresses greatly exceed those in the latter. Because a sh.e.l.l is only 3-1/2 calibres in length is no criterion that the same stresses do not exist there as would exist in the theoretical projectile considered of twenty calibres, or one of even more exaggerated proportions--there would be merely a difference in the _intensity_ of these stresses.

In a projectile making one complete revolution about its major axis in every twenty-five calibres flight, any one elementary unit area or ma.s.s in that sh.e.l.l likewise makes one complete revolution in the same distance of travel, and the path traversed by that unit area or ma.s.s is that of a spiral of radius equal to the distance of that unit area or ma.s.s from the major axis of the sh.e.l.l, the diameter of which spiral would be the diameter of the sh.e.l.l in question--and the pitch twenty-five calibres--if said unit area were on the surface of the body of the sh.e.l.l.

Upon impact the tendency of this unit area would be to continue its flight along the continuation of that spiral or along the line _ed_ of our theoretical sh.e.l.l of twenty calibres. The result would be for each disc element theoretically considered to crowd upon the next corresponding disc element and these two upon the third corresponding disc element etc., such crowding taking place along the line _ed_.

Therefore the projectile must be designed not only to penetrate, as well as to withstand the great compressional stresses upon the advancing head of the sh.e.l.l but the body of the sh.e.l.l must be so designed as to give a maximum of integrity. The torsional stresses act along _ed_, and in order to resist these stresses the sh.e.l.l must be so designed that the resisting ability will be increased along that line, re-acting along _de_.

This the author advocates by means of a "twist forging," in which the grain of the metal will lie co-incident with the lines of the torsional stresses, and by the introduction of spiral ribs lying co-incident also with the lines of the torsional stresses and the grain of the "twist forging" manufactured by a process indicated in the patent herewith appended. By the introduction of the spiral ribs it will be seen that each disc is reinforced to withstand the tendency of the disc behind to crowd upon it and that by means of a properly designed sh.e.l.l of this type the whole energy of the sh.e.l.l can be better transmitted to the point of impact by means of the spiral ribs and twisted grain.

Furthermore, should any flaws be present in the ingot, their size would be reduced by the twisting, as are the s.p.a.ces between the strands of a rope when twisted in the proper direction for so doing. Also, with a flaw in a finished projectile, and lying in a spiral direction the result of the compression stresses would be to jump across the flaw or to decrease the gap instead of acting wedgelike along the flaw causing it to open as before mentioned. Finally, an increase in integrity means an increase in penetrability, or in the percentage of complete penetration, with the ultimate necessity of increasing the thickness of armor-plate to successfully exclude the improved armor-piercing sh.e.l.l.

No. 863,248. PATENTED AUG. 13, 1907.

C. DE ZAFRA.

PROJECTILE.

APPLICATION FILED DEC. 10, 1906.

[Ill.u.s.tration: FIG. 1.]

[Ill.u.s.tration: FIG. 2.]

[Ill.u.s.tration: FIG. 3.]

[Ill.u.s.tration: Witnesses [Names are illegible]

Carlos de Zafra Inventor

By his Attorney Hensey Gough

United States Patent Office

CARLOS DE ZAFRA, OF NEW YORK, N.Y.

Projectile

No. 863,248

SPECIFICATION OF LETTERS PATENT. Patented Aug. 13, 1907.

Application filed December 10, 1906, Serial No. 347,055

_To all whom it may concern:_

Be it known that I, CARLOS DE ZAFRA, a citizen of the United States, residing at New York city, county of New York, and State of New York, have invented certain new and useful Improvements in Projectiles, of which the following is a specification.

My invention, relates to an improved form of explosive sh.e.l.l or other projectile, and more particularly to those projectiles which are reinforced by longitudinal ribs.

It further relates to a method whereby such a projectile may be made.

The object of my invention is to provide a sh.e.l.l having a maximum strength or perforating power, together with a maximum capacity for an explosive charge, and the invention consists in forming the projectile with the fibers or grain of the metal running in a spiral direction from the base of the sh.e.l.l to the top thereof, and in reinforcing the interior of the sh.e.l.l with ribs which shall run in the same direction, starting at the base of the projectile and ending at the top end of the inner chamber.

In the drawings, Figure 1 is a side view of a projectile, the grain or fiber of which is indicated by dotted lines. Fig. 2 is a longitudinal section showing the interior ribs. Fig. 3 is a transverse section on the line 3--3, Fig. 2.

While the tendency to rupture is very much lessened by the use of straight longitudinal ribs on the interior of sh.e.l.ls and projectiles of various kinds, yet such a straight longitudinal rib is itself liable to a sheering and disruptive stress along transverse lines when the projectile strikes, due to the rotative inertia of the projectile in its flight.

The aim of my invention is to provide ribs which will be coincident with the rotative travel of the sh.e.l.l so that when the point of the projectile enters an armor plate, the stress of this sudden stoppage of rotation will be taken up along the fiber or grain of the sh.e.l.l and by the spiral ribs therein. Thus the sheering tendency of the metal in the walls of the sh.e.l.l is greatly reduced and greater strength is given to resist the tendency of the rear end of the sh.e.l.l to twist off, due to the rotatory course when the head of the sh.e.l.l is embedded in an armor plate.

Like letters in the figures designate like parts.

A represents the sh.e.l.l, and B the fuse, B' being the rotating band which is secured on the sh.e.l.l near the base in the usual way. The hollow portion of the sh.e.l.l consists of a chamber C extending from the base to the forward end of the sh.e.l.l. The walls of this chamber are provided with the ribs D extending from the base to the point of the chamber in a spiral direction. In the drawings, I have shown the pitch of this spiral as one quarter turn in the length of the chamber, but it is to be understood that I may use a greater or less pitch without departing in any way from my invention.

I have shown a pitch of one quarter turn particularly for purposes of ill.u.s.tration, as if a greater pitch had been used the section Fig. 2 would not have shown any one rib entirely.

As will be seen by Fig. 1, the grain or fiber of the metal is also twisted spirally in accordance with the pitch of the ribs D, in this case a quarter turn from the rear end of the projectile to its point.

In order to manufacture a projectile of this character I have devised the following method which I deem preferable, though I do not wish to limit myself thereto. This consists first in casting an ingot from which the solid forging is to be produced. Previous to, during or after the process of forging, the ingot is twisted in a torsion apparatus, one end of the ingot being held fixed while the other end is being rotated by any suitable rotative gripping mechanism through an arc of the number of degrees desired. This will result in what I term a "twist forging" in which the grain or fiber will lie in any predetermined or desired spiral direction or pitch. The spiral ribs which are to lie in the direction preferably parallel to the grain or fiber of the metal may now be formed by the boring process similar to that employed in the rifling of modern artillery.

My projectile might also be formed by forming the sh.e.l.l with the ribs running longitudinally there along in a direct line from front to rear and with the fiber of the metal also running in a direct line parallel with the ribs. The projectile might then be reheated for forging and while being forged the rear could be held in any suitable gripping device and the forward end be rotated, as before explained. Thus the fiber of the sh.e.l.l and the interior ribs will both be given the spiral twist desired.

It will be seen that with either of these processes the fiber of the sh.e.l.l and the spiral ribs lie parallel to each other and are most perfectly formed to resist the shock of impact, the reaction of which will be along the line coincident with the resultant of the angular or rotative and the trajectoral velocities, which line will lie parallel with the spiral ribs, the pitch of such fiber and ribs having been predetermined by suitable calculation.

The above described methods while not claimed herein are to form the subject-matter of a separate application.