Long Rod Extension System Utilizing Shape Memory Alloy

This invention relates generally to the packaging of long rod components prior to use thereof in a dimensionally extended condition.

The reshaping of deformable components for use-on-demand, is generally well known in various arts, including ballistic missile or projectile installations as disclosed for example in U.S. Pat. Nos. 4,704,968, 4,964,341 and 4,979,443 to Davis, Jr., Hebert and Rittel et al., respectively. The Davis, Jr. patent furthermore discloses the concept of deforming and reshaping a component made of a shape memory alloy in a projectile installation. As to the prior art availability of shape memory alloys having different properties dependent on alloy composition factors, including pseudoelasticity properties at room temperatures and lows, U.S. Pat. No. 4,894,100 to Yamauchi et al. is relevant. Such pseudoelasticity property of a shape memory alloy is based on its martensitic transition induced by stress applied thereto, and subsequent phase transformation to the austenitic state without heating by release of the stress according to the Yamauchi et al. patent, which does not however relate to or suggest use of shape memory alloy properties for prepackaging of components made from such alloys so as to improve performance involving the reshaping of the packaged components. While the Davis, Jr. patent does teach the use of a shape memory alloy to improve target penetration, such teaching is limited to reshaping the projectile in accordance with thermoelastic properties dependent on temperature conditions resulting from heat generated by target impact.

It is therefore an important object of the present invention to provide an arrangement and method for reshaping shape memory alloy components to and from a compact packaged condition, dependent exclusively on the pseudoelastic and/or superelastic property of the alloy under a wide range of operating temperatures.

It is a further object of the invention in accordance with the foregoing object to functionally improve performance of shape memory alloy components in projectiles, such as the penetration of targets by long rod penetrators, without reliance on the effects of target impact including heating to provide a rise in temperature according to the Davis, Jr. patent aforementioned herein.

In accordance with the present invention, the composition of shape memory alloy material, such as Nitinol, is selected to display the desired pseudoelastic and/or superelastic properties under a wide range of operating temperatures in a martensite/austenite condition of an elongated rod deformed into a coil or serpentine shape for storage or packaging purposes prior to use of the rod while undergoing shape recovery. The packaged rod retains its coiled or serpentine shape under deformation stress by physical constraint, which is selectively removed to induce pseudoelastic and/or superelastic change reflected by shape recovery extension into elongated rod shape.

The elongated rod may be utilized as a target penetrator associated with a projectile within which the rod is packaged and stored in coiled condition prior to launch under physical constraint retaining the deformation stress therein. Such constraint is removed before impact during flight of the projectile from its launch site toward the target.

A more complete appreciation of the invention and many of its attendant advantages will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

FIG. 1A is a side section view through a shape memory component under constraint in a packaged storage condition, in accordance with one embodiment of the invention;

FIGS. 1B and 1C are side section views of the shape memory component of FIG. 1A in different phases of elongation following constraint release;

FIG. 2A is a partial side view of a shape memory component under constraint in a packaged condition, in accordance with another embodiment of the invention;

FIG. 2B is a partial section view taken substantially through a plane indicated by section line 2B--2B in FIG. 2A;

FIG. 3 is a block diagram depicting the method associated with the present invention;

FIG. 4 is a side section view through a portion of a long rod penetrator type of projectile within which the present invention is installed;

FIG. 5 is a transverse section view taken substantially through a plane indicated by section line 5--5 in FIG. 4;

FIG. 6 is a partial section view taken substantially through a plane indicated by section line 6--6 in FIG. 4; and

FIG. 7 is a partial side section view corresponding to that of FIG. 5, showing projection of the long rod penetrator from the projectile prior to target impact.

Referring now to the drawing in detail, FIG. 1A illustrates a shape memory alloy component in a packaged condition according to one embodiment of the invention, in the form of a closely wound helical coil generally referred to by reference numeral 10. The coil 10 is formed from a rod 12 made of shape memory alloy, such as Nitinol, having a nickel/titanium atomic composition ratio of 50.5% to 49.5% (1.002). The rod 12 in such embodiment has a 0.1 inch diameter and a linear length of 35 inches and is helically wound at room temperature on a mandrel of 11/8 inch diameter, to thereby substantially deform it into coil 10 having an axial length of 1 inch.

The shape memory alloy composition of the rod 12 was chosen to assure that it is in a totally austenitic state before it is deformed into its helical coil shape at or below room temperature. The deformation of the rod 12 into the shape of coil 10 was then induced under stress to effect its phase transformation to the martensitic state by an accompanying increase in temperature in accordance with the prior art as aforementioned herein. The stress is however applied to rod 12 in accordance with the present invention within permissible strain limits of 8% to 10%, in order to avoid permanent deformation while producing the phase transformation of the shape memory alloy to its martensitic state.

FIG. 1A shows the coil 10 axially retained between end caps 14 and 16 of a stress retention device generally referred to by reference numeral 18. In such illustrated embodiment, the device 18 also has a pivoted section 20 releasably retained in engagement with end cap 16 by means of a selectively releasable latch mechanism 22. Accordingly, upon release of the latch 22 as shown in FIG. 1B, deformation stress in the coiled rod 12 is relieved as axial expansion of the coil 10 occurs until complete shape recovery of the rod 12 is attained as shown in FIG. 1C. Such shape recovery of the rod 12 is achieved pseudoelastically in a very short period of time, such as 44 milliseconds, upon removal of the physical constraint of the caps 14 and 16 which had maintained the coil 10 under stress. In the full recovery condition of rod 12, as shown in FIG. 1C, its shape memory alloy material is restored to the austenitic state at room temperature.

In accordance with another embodiment of the invention, a shape memory rod 12' is packaged and retained under stress in a serpentine configuration 10' as depicted in FIG. 2A. Toward that end, one end of the rod 12' is anchored by a clamp 15 to a base 18' while in its deformed serpentine shape between parallel spaced bars 14' and 16' fixed to the base. The rod is in frictional sliding contact with the bars 14' and 16' as shown in FIG. 2B with its end opposite clamp 15 in engagement with a pivoted retention element 20' pivotedly connected to a selectively releasable latch 22'. Accordingly, upon release of latch 22', deformation stress in the rod 12' is relieved as the constraint of pivoted element 20' is removed, to allow pseudoelastic shape recovery of rod 12' as hereinbefore described with respect to coil 10 in FIGS. 1A, 1B and 1C.

A shape memory component may be packaged pursuant to the present invention for installation and use in different applications. The procedure involved is summarized in the block diagram of FIG. 3, wherein block 24 denotes the selection of the shape memory alloy composition for a rod, in terms of the Ni/Ti ratio necessary to accommodate pseudoelastic and/or superelastic change in state within a desired operating temperature range such as 5.degree. C. to 65.degree. C. as denoted by block 26. After dimensional deformation of the rod into a packaged condition within the operating temperature range, as denoted by block 28, the packaged rod is placed in some installation as denoted by block 30. The rod is maintained in its installational package shape by stress retention, as denoted by block 32, until the stress is relieved by selective trigger release of the package constraint, as denoted by block 34, under operating temperature conditions. Upon removal of the retention stress, the packaged rod undergoes pseudoelastic change and transformation from the martensitic state to the austenitic state of its shape memory alloy material, involving shape recovering projection, as denoted by block 36 in FIG. 3.

FIG. 4 illustrates a projectile installation for the present invention, wherein the helical coil 10 as hereinbefore described is utilized as the dimensionally deformed rod 12 serving as a long rod penetrator having a target penetrating nose 38 at one end and a stabilizing fin 40 at the other end. The rod 12 is positioned, in its deformed package condition as coil 10 under stress, within a shell casing 42 ejected after firing of a gun from its breech causing launch of the coil 10 in the flight direction indicated by arrow 44 in FIG. 4. The coil 10 is retained in such installation under stress within a cylindrical sabot 46 from which the nose 38 of the rod projects. The sabot is formed by three arcuate sections 46a, 46b and 46c, as more clearly seen in FIG. 5, and has a nose end 48 of inwardly projecting conical shape as shown in FIG. 4. The sabot sections are maintained assembled in stress retaining relation to the coil 10 by a notched ring 50, as more clearly seen in FIG. 6, to releasably hold the coil 10 positioned in its packaged condition within the shell casing 42. Rotating bands 52, made of a material such as Nylon, are carried on the sabot 46 at opposite axial ends in sliding contact with the shell casing 42, thereby acting as a gas seal for the projectile during launch from the gun barrel.

After exit of the sabot 46 and coil 10 from the gun barrel under a high velocity during launch, the ram air pressure entering the conical end 48 of the sabot sufficiently augments the radial expansion pressure being exerted by the stress in the coil 10 on the sabot sections to cause the gas seal bands 52 and stress retention ring element 50 to rupture. The sabot sections are accordingly disassembled as coil 10 undergoes pseudoelastic shape recovery resulting in axial elongation of the rod 12 prior to target impact, as shown in FIG. 7. It should of course be appreciated that other prior art stress retention constraints and associated constraint release devices could be utilized in the foregoing coil installation described, including triggered explosive devices.

It should also be appreciated that the foregoing described projectile installation for the coil 10 will significantly improve target penetration by rod 12 of substantial length as compared to prior art long rod penetrators which were heretofore limited in length by handling and storage considerations to 12 to 18 inches for example. Such a penetrator rod has a corresponding target penetration depth (D) at hyper-velocity in accordance with the formula: ##EQU1## where L is the penetrator rod length, Pp is the density of the rod and Pt is the density of the target. Thus, an 8 foot long penetrator rod 12 that is 16 times as long as prior art penetrators when deformed into a coil 10 having a 1.5 foot packaged axial length, as shown in FIG. 4 for example, provides a four fold increase in penetration depth (D) as compared to prior art penetrators because of the pseudoelastic extension of the coil 10 into the long rod 12 as shown in FIG. 7.

As hereinbefore indicated, the present invention is not limited to projectile installations. Other applications include, but are not limited to, rapid deploying and self-erecting antenna installations for various communication purposes on battlefields, life rafts, in ski emergency kits, etc., as well as use in locations such as outer space, deserts, mountain and arctic regions. Also, the present invention is useful as an extension handle for tools, self-erecting flares, self-erecting legs for cots and prepackaged fishing rods, where linear rod type extensions are critical.

Obviously, numerous other modifications and variations of the present invention are possible in light of the foregoing teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.