US3516670A - Polyethylene target with waffle-type rigidifying structure - Google Patents

Description

June 23, 1970 v, F, DAGQSTINO ETAL 3,516,670

POLYETHYLENE TARGET WITH WAFFLE--TYPE RIGIDIFYING STRUCTURE Filed May 25, 1968 2 Sheets-Sheet 1 Tic 1E: TiE'ILA- 1 N VENTORS June 23, 1970 v. F. D'AGOSTINQ E AL POLYETHYLENE TARGET WITH WAFFLE-TYPE RIGIDIFYING STRUCTURE Filed May 23, 1968 2 Sheets-Sheet 2 I N VEN TORS Vmcayr F fi/flwsmyo @M/P 59 6/9 United States Patent 3,516,670 POLYETHYLENE TARGET WITH WAFFLE-TYPE RIGIDIFYING STRUCTURE Vincent F. DAgostiuo and Philip Brielf, Huntington Station, N.Y., assignors to RAI Research Corporation, Long Island City, N.Y., a corporation of New York Filed May 23, 1968, Ser. No. 731,391 Int. Cl. A631) 63/04 US. Cl. 273-102.2 7 Claims ABSTRACT OF THE DISCLOSURE A gunnery training target made of a rigid, weatherresistant, shaped sheet of polyethylene. The polyethylene is molded or treated to provide a member which produces small diameter holes when punctured by low caliber projectiles. These holes may also be partially sealed by heat treating the polyethylene. Alternating vertical and horizontal protrusions and indentations form a wafile-type structure on the target to impart rigidity thereto. The target may also be made to look like an aggressor soldier by coloring it drab green as a soldiers uniform, cutting it in the shape of a silhouette of a soldier, or by using a vinyl decal bearing the likeness of a soldier. The target may have its lower edge clamped to a reset device which allows the rigid target to transmit a bullets energy thereto to lower the target. 'In a short predetermined time the target is raised.

BACKGROUND Target combinations, such as the 1.1.8. Army Trainfire Mechanism M3 1A1, to enable military trainees to improve their proficiency at small arms fire, have been used for many years. These devices include an automatic reset feature, i.e. when a bullet strikes the target a microswitch sensitive to vibrations detects the hit and lowers the target, indicating to the shooter and instructor that the hit has indeed been accomplished. In a short predetermined period of time, the reset device will reerect the target, readying it for the next shot. These reset devices are also commonly equipped with a mechanism for counting the number of hits, and registering it in a conveniently visible place. The most frequently used type of target has been a simple fiat board, cut in the shape of a silhouette of an enemy soldier. These targets have usually been made of fiberboard comprising a high percentage of :kraft and jute fibers blended with a laminating adhesive.

Fiberboard has shown many market disadvantages in this application. This material is particularly deficient in performance characteristics under moist conditions, since it tends to absorb a significant amount of water. This has two serious disadvantages. First, the additional water causes an undesirable weight gain in the target material itself, and this puts an undue stress upon the reset mechanism, and often causes such reset mechanisms to fail entirely. Secondly, the absorption of water into the fiberboard causes the silhouette target to acquire an undesirable degree of flexibility. When a target of this nature is unduly flexible, a bullet striking it does not cause its kinetic energy to be transmitted to a sufiicient degree to the reset mechanism. This means that the microswitch which serves to activate the reset device does not always receive the proper stimulus and will fail to register hits upon the target.

Workers in this art have endeavored to provide the fiberboard material with a resin or plastic coating which Patented June 23, 1970 ice serves to keep out unwanted moisture from the material itself. This works adequately if the target is not fired upon. However, when the target absorbs a number of hits, the holes made by bullets striking the fiberboard expose its uncoated inner surfaces. Thus, the moisture absorption problem is not satisfactorily alleviated in this way.

Another related disadvantage is also apparent. The fiberboard material, upon impact, tends to splinter or fragment, leaving holes which are actually larger in diameter than the bullets which cause them. This obviously causes rapid disintegration of the target under fire, and seriously limits its ability to absorb successfully a large number of hits.

It is desirable that a target for field practice or small arms fire be as lifelike as possible. The reason for this is that a soldier or trainee upon using the present targets, may acquire a high degree of proficiency and ability to hit a silhouette made of fiberboard, but may, in combat circumstances remain unable to fire upon a man. A more lifelike target for use during training accustoms the fighting men to firing upon the human form, increasing their efiiciency and effectiveness.

THE INVENTION This invention is directed to targets comprising a polyethylene structure. The polyethylene is molded or treated to provide a puncture resistant target which, when pierced by small-arms fire, results in a hole smaller than the diameter of the piercing projectile. The holes in the targets may be partially closed by subjecting the polyethylene member to a heat treatment.

The polyethylene material has the decided advantage of being virtually unaffected by water; it therefore retains its rigidity indefinitely. The material may be fabricated with sufficient rigidity to transmit to a reset device a substantial part of the kinetic energy imparted by a bullet striking the target. The target is clamped at its lower edge to the reset device. The ability of this target to transmit the bullets energy to the reset device is not critically dependent upon the point of the target at which the bullet strikes. Thus, much greater accuracy in counting the number of hits is obtained by the use of this invention.

In addition to increased rigidity, the plastic material used in this invention does not disintegrate rapidly upon the absorption of a large number of bullet hits. In fact, the hole left in the material by the striking projectile is generally smaller in diameter than the projectile which caused the hit. This plastic material can also be healed by heating it to substantially close bullet holes and subsequently cooling the material. Thus, targets made in the manner described in the invention can be reused. The target of this invention has been shown to be capable of absorbing approximately five to ten times the number of hits that can be absorbed successfully by a conventional target, and still transmit a striking projectiles energy successfully to the reset device.

This invention will be described in greater detail in conjunction with the following figures.

FIGS. 1A and 1B are front views of embodiments of the present invention.

FIGS. 2 and 3 are sectional views thru FIGS. 1A and 1B, respectively.

FIG. 4 shows the combination of a target member and an automatic reset target mechanism.

Targets manufactured according to this invention can be made in fiat or curved pieces. The fiat structure is made from sheets of polyethylene 10, as in FIGS. 1A

and 2. The weight of the target can be altered to meet specifications by changing, within limits, the thickness of this plastic sheeting. The design of member comprises at least one reinforcing rib 12 around the periphery of the target. If the target is to be made by extrusion additional reinforcing ribs 14 are incorporated into the design to provide the necessary rigidity. A rigid structure is necessary for two reasons: to transmit the force of projectile impact upon the target to the microswitch actuator at the base of the target; and to prevent whipping when the target is moved between the vertical and horizontal positions, since such whipping might actuate the microswitch. To reduce the possibility of whipping and to accommodate the limitations of the presently available reset mechanisms, the weight of the target must be kept below about three pounds. For this reason the reinforcing ribs are in effect channels in the target having the same wall thickness as the remainder of the target.

An improved design, which can be made by vacuum or pressure forming, injection, or rotational molding, or cold or hot stamping, is the wafile structure in conjunction with the reinforcing rib. The waffie structure comprises alternating indentations 16 and protrusions 18 running horizontally and vertically. This design does not increase the weight of the target and provides a sound structural member that can withstand repeated impacts. This design also reduces buckling or curling of edges of the structure toward the firing line, which would otherwise occur during use of the target.

In an alternate embodiment, member 10 can be curved about a vertical axis, with the concave shape facing toward the trainee on the firing line. This sectional shell is illustrated as 10 in FIGS. 1B and 3. The shell structure provides increased rigidity and reduces the whipping and buckling tendency even without reinforcing ribs or channels. In addition the shell structure provides greater realism and is responsive to flanking fire.

For added lifelike qualities the target can be colored in such a way that it resembles an aggressor soldier. The most successful way found of coloring the frontal piece is to manufacture it from plastic which is initially produced in a drab green, to resemble an enemy soldiers uniform. Facial and other skin features may be added by coating the facial and hand areas heavily with an organosol colored in skin tones. Alternatively realism can be imparted to the target by applying to it a decal, such as a vinyl decal 20, which bears the likeness of an aggressor soldier.

The combination of the target member 22 of this invention and a conventional automatic reset mechanism 24, is shown in FIG. 4.

The polyethylene useful as a target or as a backboard is fabricated to meet three main structural requirements: lightweight; rigid and puncture-resistant. These three requirements are uniquely met by the polyethylene used in the present invention. The latter noted requirement is of particular significance. It may be defined as the ability of the structure to yield a hole of smaller diameter than that of a projectile which passes through it.

Irradiated polyethylene or high density polyethylene (about .94.96 g./cc.) are the preferred materials from which the targets should be fabricated. They absorb less than .Ol% by weight of water, proved excellent in ability to activate the microswitch, and were comparatively low in cost. The polyethylene targets are resistant to temperatures over a wide range, such as from -40 F. to 160 F.

Firing tests conducted with these polyethylenes mounted in the target holder and fired upon with .30 caliber ammunition gave hole sizes which were .187" to .195". In an experiment, a sheet of 60 mil thickness polyethylene mounted in the target holder was actuated by four successive shots. Two holes were found in the 4 target sheet and the larger of these passed two bullets in addition to the original hole making hit. The diameter of this larger hole was 0.225". The polyethylene target board (.060 inch thick) was able to accurately register 1800 rounds of .30 caliber fire while a standard fiberboard target failed within 400 rounds.

In addition to these surprising target characteristics, bullet holes in polyethylene could be closed by heating the polyethylene to C. to 145 C., preferably C. to C. This phenomenon of hole closure is due to the fact that the bullet deformed plastic has internal stresses which are released when the plastic is heated. Such heating has reduced bullet holes from an 0.190" diameter to .055". This effect occurs in both the irradiated polyethylene and the high density molded polyethylene. By this method pierced targets are made reusable.

The irradiated polyethylene given a 15 megarad dose from a C0 source provides an addititonal advantage. The cross-linking induced by the radiation provides the plastic with a permanent tendency to return to its initial shape which would exist even if internal stresses were relieved by annealing the plastic in a bullet deformed condition.

When linear polyethylene is irradiated to a sufficient degree, from 2 to 25 Mrads, it forms a substantial number of crosslinks in its molecular structure. This crosslinking gives to the plastic material a high degree of memory. That is, the irradiated plastic has the ability after deformation to resume its original shape. This characteristic is of consequence since it enables this material, after being pierced by a bullet passing through it, to substantially close these holes upon heat treatment to about 140 C. This quality substantially lengthens the life of the target, enabling it to be healed of deformations and penetrations. Thus, the target of this invention can be reused by taking advantage of these healing powers.

A comparison with other materials shows the surprising advantages of the polyethylene used in the present invention. On evaluating polyvinyl chloride sheet material, a consideration of its density (approximately 1.34) and the area of the target 671 in. shows that a target of 60 mil thickness will weigh 2 lbs. When a sample of this material was fired at, the material shattered leaving a hole which was several times the diameter of the .30 caliber bullet. A rigid vinyl which could provide adequate rigidity in a thinner section, would not provide satisfactory bullet characteristics.

A copolymer of ethylene and vinyl acetate, which is low in density (.92.95 g./cm. was evaluated under fire and found to give holes of 0.15" diameter. However, there is a fundamental difference bet-ween a bullet hole in polyethylene and one in an ethylene-vinyl acetate sheet. In polyethylene the plastic in the path of the bullet is displaced and forms a crater around the bullet holes. In the ethylene-vinyl acetate copolymer the material which was in the holed spot had been removed from the sheet by the piercing projectile.

Phenolic laminates were of a brittle nature and their tendency to shatter made them unusable for target members.

The uses of pressed board, paper laminates, and plastic impregnated paper were also unsuccessful. Samples were evaluated by soaking them in solvent solutions of wax or resin, including polyethylene and vinyl chloride solutions; after drying, the composites were evaluated for water absorption and structural characteristics. Although significant reduction in water absorption was effected, the targets were not as weather resistant as the polyethylene targets of the present invention, and detrimental changes in physical properties which occurred in conjunction with the treatments resulted in products which were not suitable as target boards.

A summary evaluation of the characteristics of the conventional cardboard target currently used verses an improved polyethylene target of this invention (FIG. 2, high density) is shown below.

Depending on weather conditions.

The polyethylene target members are unaffected by water immersion and can be obtained in grades suitable for outdoor exposure. Its rigidity and bullet hole characteristics are uniquely suited for target application. Other plastic sheet materials evaluated (vinyls, ethylenevinyl acetate and modified cellulosics) were not suitable. The effect of bullet penetration upon the plastics tested suggest that the elasticity, tensile strength, and modulus of flexure of polyethylene contributed to the unusual type of deformation effected by bullets. Thus, a reusable target has been constructed which is light in weight without sacrificing rigidity, will not become undesirably flexible by absorbing moisture, is capable of absorbing an enormous number of bullet hits without disintegration, and is further able to faithfully transmit the energy of a bullet striking hit to the vibration sensitive microswitch of the reset device.

This invention has been described interms of specific embodiments set forth in detail. Alternative embodiments will be apparent to those skilled in the art in view of this disclosure, and accordingly such modifications are to be contemplated within the spirit of the invention as disclosed and claimed herein.

What is claimed is:

1. In a gunnery training target combination having a target member in operative contact with a retract and return automatic mechanism, the improvement which comprises a polyethylene target member of sufficient rigidity to transmit the force of impacts upon it to actuate the automatic mechanism and which, when pierced by a low caliber projectile, produces a hole with a diameter smaller than that of the piercing projectile, wherein said target member is formed with a series of horizontal and vertical protrusions and indentations comprising "'affie-type structure.

2. The combination of claim 1 wherein said target member has vertical reinforcing ribs.

3. The combination of claim 1 wherein said polyethylene is crosslinked by irradiation.

4. The combination of claim 1 wherein said polyethylene is of high density.

5. The combination of claim 1 wherein said polyethylene is crosslinked by radiation of a dosage of from 2 to 25 megarads.

6. A target member having a silhouette the size and shape of the outline of the head and body of a man adapted for use in an automatic retract and return mechanism, made of polyethylene of sufiicient rigidity to transmit the force of impacts upon it to actuate the automatic mechanism and which, when pierced by a low caliber projectile, produces a hole with a diameter smaller than that of the piercing projectile, and having formed therein a series of horizontal and vertical protrusions and indentations which constitute a waffle-type structure to impart rigidity to said target.

7. The target member of claim 6 made of high density polyethylene.

References Cited UNITED STATES PATENTS 2,5 35 ,280 12/ 1951 Gartrell. 2,819,084 1/1958 Brown et a1. 2,819,085 1/1958 Brown et a1. 2,858,247 10/1958 De Swart 161-131 3,004,735 10/1961 Kinard. 3,004,763 10/ 1961 Knapp. 3,029,077 4/ 1962 Benkoe. 3,034,788 5/ 1962 Cauble. 3,158,372 11/1964 Ohlund et a1. 3,215,933 11/ 1965 Scanlon. 3,222,596 12/1965 Meyer et al. 3,233,904 2/ 1966 Gillam et a1. 3,330,561 7/1967 Kandel. 3,353,827 11/1967 Dun. 3,401,939 9/1968 La Mura.

RICHARD C. PINKHAM, Primary Examiner T. ZACK, Assistant Examiner US. Cl. X.R.

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