US3773427A

US3773427A - Stress-free rod and eyelet assembly for plastic-to-metal interfaces

Info

Publication number: US3773427A
Application number: US00210423A
Authority: US
Inventors: G Lucey
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1971-12-21
Filing date: 1971-12-21
Publication date: 1973-11-20
Anticipated expiration: 1990-11-20

Abstract

Artillery fuze radomes are ordinarily made from thermoplastics. The major drawbacks from thermoplastics is their inherent tendency to stress-crack. This invention provides a valid means of avoiding stress-cracking in military hardware that involves a metal-to-plastic joint. This means is to use a stress-free assembly comprising a stress-free rod joint designed for low setback and spin projectiles. Stress free attachment is accomplished by moulding a hole larger than the joint in the plastic radome. An eyelet with an inner diameter smaller than the rod and an outer diameter smaller than the hole in the plastic is fastened into the hole. Lips at the periphery of each end of an eyelet secure the eyelet in place in the hole in the plastic radome. When the rod is forced into the eyelet the outer diameter expands, however the moulded hole in the plastic is sufficiently oversized such that binding by the eyelet is prevented. Several rods are forced into eyelets and inserted into grooves in the fuze body thereby securing the nose cone to the fuze. The assembly developed by these pieces is stress-free because the rod-eyelet assembly is free to rotate in the hole.

Description

United States Patent [191 Luccy, Jr.

[ NOV. 20, 1973 STRESS-FREE ROD AND EYELET ASSEMBLY FOR PLASTIC-TO-METAL INTERFACES [75] Inventor: George K. Lucey, .112, Silver Spring,

Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

22 Filed: Dec. 21, 1971 21 Appl. No.: 210,423

Primary Examiner-Andrew V. Kundrat Attorney-Harry M. Saragovitz et al.

[57] ABSTRACT Artillery fuze radomes are ordinarily made from thermoplastics. The major drawbacks from thermoplastics is their inherent tendency to stress-crack. This invention provides a valid means of avoiding stress-cracking in military hardware that involves a metal-to-plastic joint. This means is to use a stress-free assembly comprising a stress-free rod joint designed for low setback and spin projectiles. Stress free attachment is accomplished by moulding a hole larger than the joint in the plastic radome. An eyelet with an inner diameter smaller than the rod and an outer diameter smaller than the hole in the plastic is fastened into the hole. Lips at the periphery of each end of an eyelet secure the eyelet in place in the hole in the plastic radome. When the rod is forced into the eyelet the outer diameter expands, however the moulded hole in the plastic is sufficiently oversized such that binding by the eyelet is prevented. Several rods are forced into eyelets and inserted into grooves in the fuze body thereby securing the nose cone to the fuze. The assembly developed by these pieces is stress-free because the rod-eyelet assembly is free to rotate in the hole.

10 Claims, 2 Drawing Figures STRESS-FREE ROD AND EYELET ASSEMBLY FOR PLASTIC-TO-METAL INTERFACES RIGHTS OF THE GOVERNMENT The invention described herein may be manufactured, used, and licensed by or for the United States Government for governmental purposes without the payment to the inventor of any royalty thereon.

BACKGROUND OF THE INVENTION This invention relates generally to artillery fuze radomes and more particularly to the interface between a. plastic fuze radome and its associated metal fuze body. Artillery fuze radomes are ordinarily made from thermoplastics, which have desirable electrical and mechanical properties, are inexpensive, and are amendable to mass production. The major disadvantage to thermoplastics is their inherent tendency to stresscrack. This means that when the plastic is placed in a state of tensile or shear stress, it will eventually crack even though the stress level may be considerably below the rated strength of the material. A common method in artillery fuzing of joining a plastic radome to the metal fuze body is by crimping a portion of the metal body over a portion of the plastic radome. It has been found that this procedure places the plastic radome in a state of stress, thus exposing the finished product to the aforesaid stress-cracking tendencies. Different plastics take varying times to stress-crack, and a common military requirement is that the material survive storage for a period of years. If cracks do develop during storage, the mechanical integrity of a fuze is lowered, and the chances of early fuze functions is increased when the projectile is fired into rain, snow or clouds.

It has been suggested that if the proper data were available in the literature, then the nose cone could be designed to avoid cracking for the required 20 years. However, the data are usually unavailable and the practice of designers has been to disregard the potential of stress-cracking. This danger is reduced somewhat by using glass fiber filled plastics which have recently become available, but the true sensitivity of these materials to stress-cracking is not known.

Accordingly, the primary object of the present invention is to provide a means for adjoining a plastic radome to a metal body in a stress-free attachment and thus permanently avoid any stress-cracking tendency.

Another object of the present invention is to provide a new and novel rod-eyelet assembly for providing a stress-free interface and junction between a plastic member and a metal body by means of a modification of present parts available today.

It is yet another object of this invention to provide a new and novel rod-eyelet assembly for providing a stress-free rod joint for low setback and spin projectiles.

It is also an additional object of this invention to provide a new and novel rod-eyelet assembly for providing a stress-free rod joint for plastic-to-metal interfaces which will allow the rotation of a plastic nose cone at- ,tached by said assembly to a metal fuze body for setting point-detonation action.

"It is yet a further additional object of this invention to provide a new and novel rod-eyelet assembly for providing a stress-free rod joint for plastic-to-metal interfaces which will not allow dislodging of a plastic radome attached with said assembly by axial motion along the principle axis of the projectile.

Still another additional object of this invention is to provide a new and novel rod-eyelet assembly for providing a stress-free rivet joint for plastic-to-metal inter faces in which said rod-eyelet assembly is free to rotate thus evidencing absence of stress.

BRIEF DESCRIPTION OF THE DRAWINGS The specific nature of the invention as well as other objects, aspects, uses, and advantages thereof will clearly appear from the following description and from the accompanying drawings in which:

FIG. 1 is an illustration of a rod-eyelet assembly joining a plastic-to-metal interface in the form of a plastic nose cone joined to a metal fuze body by plurality of such assemblies.

FIG. 2 is a cross-section of an embodiment of a rodeyelet assembly joining a plastic member to a metal fuze body taken along the central axis of the fuze.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a plastic nose cone 10 that has been mounted and fixed onto a fuze body 14 and is representative of this new and novel assembly for joining plastic-to-metal bodies. It should be noted that the eyelet portion of the assembly illustrated in this figure is not crimped onto the plastic of the radome. It was found and that the crimping action set up stresses in the nose cone by virtue of lips 20 permanently deforming that portion of the plastic radome under or within the lips. The residual stresses with the type of attachment in which the eyelet l I is crimped onto the plastic material member are low, but over a long time period, tend to stress-crack the plastic. This event requires the future repair of stockpile fuzes, an expensive procedure.

In FIG. 2 and embodiment of a plastic-to-metal interface joined by this new rod-eyelet assembly is show which in essence is an eyelet 11 inserted into a hole within a plastic radome 10, said hole having a diameter larger than the outer diameter of the eyelet 11 yet smaller than the outer diameter of lips 20 at the periphery thereof and at each end of the eyelet 11. These lips 20 hold the eyelet within hole 16. Rod 12 is inserted into the aperture in said eyelet 11 and said rod 12 being larger in diameter than the opening or aperture within eyelet 11 expands said eyelet diameter and is thus held in place by interference of said interference between eyelet 11 and rod 12.

The rod 12 is configured such that the portion being inserted into groove 15 is smaller than the portion that interferes with the inner diameter of eyelet 11. This tapering permits the rod 12 to be substantially inserted through the eyelet 11 before being rigidly held by said eyelet 11. In the type assembly shown in FIG. 1 several rod-eyelet assemblies are used around the periphery of the radome 10.

Another possible embodiment is to put grooves or ridges into a portion of the rod 112 which interferes with eyelet Ill.

To make this new and novel assembly a cylindrical eyelet 11 is inserted into the aperture 16 in the plastic radome 10. A tool is used to crimp the ends of the eyelet 11 extending on either side of the plastic nose cone 10 downward toward the plastic radome 10. This crimping and stressing of the eyelet 11 is applied only to the eyelet 11 and the eyelet 11 is not permitted to be crimped onto the plastic radome 10. Thus a cylindrical eyelet 11 is held within the aperture 16 in the radome by crimped lips 20 at each end of the cylindrical eyelet 11. This eyelet 11 fits loosely in the aperture 16 and is held in place by the dilation of the inner portion of the eyelet 11 by the rod 12. The rod 12 is not permitted to interfere with the groove 15 in the fuze body 14. Once the rod 12 is inserted into the eyelet 11 and groove 15, the rod-eyelet assembly may be rotated in place. Thus the rod 12 is free to rotate in the groove 15 and around the metal fuze body 14 and the eyelet 11 rotates with the rod 12 in the aperture in the plastic radome 10. Rotation of this rod-eyelet assembly indicates that no stresses are exerted by the lips of the eyelet 11 nor by the expansion of the inner portion of the eyelet 11 toward the inner portion of the aperture 16 in the plastic nose cone. Also, rotation of the rod 12 extending into the groove in the metal fuze body 14 indicates that no stresses are present at the interface between the rod 12 and the metal fuze body 14. Consequently, when an opening in the metal fuze body 14 comprises a groove 15 around the periphery of said fuze body 14 then the plastic radome 10 is free to rotate around said body 14.

The inventor wishes it to be understood that he does not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art thereof.

What is claimed is:

1. A stress-free assembly for joining plastic-to-metal comprising a cylindrical member, an eyelet having an aperture in which said cylindrical member is securely held, a plastic member having a hole therein in which said eyelet is loosely held, said hole having a diameter larger than the diameter of said eyelet, and a metal body juxtaposed to said plastic member and having an opening therein having a diameter larger than the diameter of said cylindrical member and into which said cylindrical member extends.

2. The stress-free assembly of claim 1 wherein said eyelet comprises lips disposed at each end thereof, said lips loosely holding said eyelet in said hole.

3. The stress-free assembly of claim 2 wherein said cylindrical member is held in place by the interference of said eyelet.

4. The stress-free assembly of claim 3 wherein said eyelet is free to rotate in said hole.

5. The stress-free assembly of claim 4 wherein said cylindrical member with said eyelet attached is free to rotate in said opening.

6. The stress-free assembly of claim 5 wherein said plastic member comprises a radome and said metal body comprises a fuze body and wherein said assembly joins said radome to said fuze body.

7. The assembly of claim 6 wherein said opening of said metal body comprises a groove around the periphery of said body, and wherein said radome rotates freely around said fuze body, said groove providing a guide.

8. The stress-free assembly of claim 7 wherein said cylindrical member has a diameter larger than the inner diameter of said eyelet aperture and wherein said cylindrical member and eyelet has an outer diameter less than the diameter of said hole in the plastic member.

9. A plurality of the assemblies of claim 8 each having said cylindrical member inserted into said groove to prevent removal of said radome by axial forces.

10. The assembly of claim 9 wherein said groove comprises means for rotation of said radome for setting point detonation action of said fuze.