Projectile using shape-memory alloy to improve impact energy transfer

A projectile having an active component of shape-memory alloy that will not distort the projectile's shape or balance during launch or flight but which will alter the projectile shape upon impact to increase energy transfer efficiency against targets is disclosed.

BACKGROUND OF THE INVENTION 
The present invention relates to projectiles and, more particularly, to 
means to improve the impact energy transfer efficiency of projectiles. 
Projectiles in the form of conventional bullets remain intact upon striking 
a soft target to cause substantially a single wound tract. While 
conventional bullets may expand or tumble after impacting the soft target 
to increase lethality of the bullet, frequently the bullet will start its 
expanding or tumbling action only after much of the target has been 
penetrated. Prior art methods for improving impact energy transfer 
efficiency and thus bullet lethality generally involve alteration of the 
external configuration of the bullet, i.e., hollow-point, off-center 
punch, spoon nose and the like. 
U.S. Pat. Nos. 3,173,371, 3,861,314 and 4,338,862 disclose various attempts 
to alter the performance of a projectile by altering its external 
configuration to promote instability upon impact or by altering the 
internal configuration of the projectile with passive elements such as a 
disc or a low density filler material. Unfortunately, none of prior art 
devices provides a projectile having positive means to improve the impact 
energy transfer of the projectile. 
SUMMARY OF THE INVENTION 
The purpose of the instant invention is to provide a projectile having 
improved impact energy transfer. To accomplish this purpose there is 
provided positive means that will not distort the projectile's shape or 
balance during launch or flight but which will cause the projectile to 
change shape immediately upon impact in order to increase its energy 
transfer efficiency against targets. In the case of soft targets this is 
accomplished by deforming the projectile, thus increasing instability upon 
impact in order to cause tumbling, or by increasing the projectile's 
diameter thus increasing its frictional resistance. In the case of hard 
targets, this is accomplished by deforming the projectile, thus increasing 
the penetration capability of the projectile. In general, a projectile is 
provided in accordance with the instant invention wherein the projectile 
is of shape-memory alloy or having a deforming means of shape-memory alloy 
which is capable of altering the geometric shape of the projectile upon 
impact to improve the impact energy transfer of the projectile. 
Accordingly, an aspect of the instant invention provides a projectile, 
comprising: 
a core; and 
deforming means of shape-memory alloy in operative contact with said core, 
said means capable of altering the geometric shape of said core upon 
impact of the projectile to improve the impact energy transfer of the 
projectile. 
Another aspect of the invention provides a projectile of shape-memory 
alloy, said projectile capable of altering in geometric shape upon impact 
of the projectile to improve the impact energy transfer of the projectile. 
Yet another aspect of the invention provides a device of shape-memory alloy 
wherein said device contains voids, said voids capable of enhancing the 
speed of recovery of said device by rapidly generating heat due to 
collapse of the voids when the device is subjected to shock.

DETAILED DESCRIPTION OF THE INVENTION 
Projectiles of the instant invention may be made entirely from shape-memory 
alloy or may utilize a deforming means of shape-memory alloy which is 
capable of altering the geometric shape of the projectile upon impact to 
improve the impact energy transfer of the projectile. It is understood 
that the entire projectile can be made from shape-memory alloy and thus 
the entire projectile comprises the deforming means within the intended 
meaning of deforming means. This deforming means is a positive means which 
will not distort the projectile's shape during launch or flight but which 
will cause the projectile to change shape immediately upon impact. The 
deforming means is preferably and economically used in combination with a 
core material which is a heavy material such as lead. It is within the 
scope of the invention to make the core itself entirely from shape-memory 
alloy. The core material can be unjacketed or fully or partially encased 
within a metal jacket. Several embodiments of the instant invention having 
deforming means of shape-memory alloy are discussed hereinafter at length. 
Materials, both organic and metallic, possessing shape-memory, are well 
known. An article made from such materials can be deformed from an 
original, heat-stable configuration to a second, heat-unstable 
configuration. The article is said to have shape-memory for the reason 
that upon application of heat alone it can be caused to revert, or attempt 
to revert, from its heat unstable configuration to its original 
heat-stable configuration, i.e., it "remembers" its original shape. 
Metallic alloys of this type are hereinafter defined as shape-memory 
alloys. 
Among the metallic alloys, the ability to display shape-memory is a result 
of the fact that the alloy undergoes a reversible transformation from an 
austenitic state to a martensitic state with a change in temperature. This 
transformation is sometimes referred to as a thermoelastic martensitic 
transformation. An article made from such an alloy is easily deformed from 
its original configuration to a new configuration when cooled to a 
temperature below which the alloy is transferred from the austenitic state 
to the martensitic state. 
The temperature at which this transformation begins is usually referred to 
as M.sub.s and the temperature at which it finishes is M.sub.f. When an 
article thus deformed is warmed to a temperature at which the alloy starts 
to revert back to austenite, referred to as A.sub.s (A.sub.f being the 
temperature at which the transformation is complete), the deformed object 
will begin to return to its original configuration. Also, the alloy is 
considerably stronger in its austenitic state than in its martensitic 
state. The deforming means of the instant invention may be fabricated from 
nickel-titanium shape-memory alloys which are well known to those skilled 
in the art, and, for example, are described in U.S. Pat. No. 3,351,463, 
which is incorporated herein by reference. Other literature describing the 
processing and characteristics of suitable compositions includes an 
article by Dr. William J. Buehler, the principal developer of the 
material, and William B. Cross, entitled "55 Nitinol-Unique Alloy Wire", 
which appeared in the June, 1969 issue of Wire Journal. A description of 
the materials and certain of the properties also may be found in the 
brochure entitled "Nitinol Characterization Studies" dated September, 
1969. This document, identified as N-69-36367, or NASA CR-1433, is 
available from the Clearinghouse for Scientific and Technical Information, 
Springfield, Virginia, 22151. All of these publications are incorporated 
herein by reference. These binary shape-memory alloys are commercially 
available from a number of suppliers, one of which is Raychem Corporation 
in Menlo Park, California. 
Other examples of shape-memory alloys are disclosed in U.S. Pat. Nos. 
3,012,882, 3,174,851, 3,558,369, and 3,672,879, the disclosures of which 
are incorporated herein by reference. As made clear in these patents, 
these alloys undergo a transition between an austenitic state and a 
martensitic state at certain temperatures. When they are deformed while in 
the martensitic state, they will retain this deformation while maintaining 
this state but revert to their original configuration when they are heated 
to a temperature at which they transform to their austenitic state. 
A significant part of the instant invention is the use of voids in the 
portions made of shape-memory alloy. This aspect of the invention is 
useful in all embodiments of the invention and in any device where 
extremely rapid recovery is desired. 
Specifically, it is within the scope of the invention to utilize components 
of shape-memory alloy having voids therein. This may be accomplished by 
the known technique of powdered metallurgy wherein small particle grains 
of shape-memory alloy are held under temperature and pressure and, in 
essence, are sintered together. The desired porosity is accomplished by 
varying the size of the particles and the pressures applied. Other methods 
of creating voids are well known in the art, for example, the mixing of 
another material with the particles of shape-memory alloy to obtain the 
desired voids. 
The provision of voids enhances the speed of recovery of the component. In 
the application of a projectile, or a deforming means for a projectile the 
voids are useful to rapidly generate heat upon impact due to the collapse 
of the voids being shocked. 
A projectile transfers energy to the object it strikes by means of momentum 
transfer through shock waves. However, at impact a shock wave is also 
transmitted into the projectile. This shock wave in the projectile 
generates heat and pressure in the projectile. The instant invention 
utilizes the shock wave generated within the projectile to trigger the 
deforming means of shape-memory alloy. Specifically, the heat and pressure 
generated by the shock wave elevate the temperature of the alloy to the 
austenitic temperature discussed earlier. In several of the embodiments of 
the instant invention the deforming means of shape-memory alloy is located 
in the nose portion of the projectile. In these embodiments no shape 
change would occur during launch or flight. At impact, the heat and 
pressure associated with the shock wave in the projectile would cause the 
shape-memory alloy deforming means to alter the shape of the deforming 
means instantaneously and thus the shape of the projectile. It is within 
the scope of the invention to optimize the shape change for each type of 
projectile in order to provide improved impact energy transfer to the 
target. Shape changes such as diameter increase to increase resistance and 
point deformation to cause tumbling are examples. 
The impact of a projectile upon a material has been studied experimentally 
and analytically at several centers, principally, the Material Technology 
Laboratory, the Ballistics Research Laboratory and Washington State 
University. Others include the Los Alamos National Laboratory and the 
Lawrence Livermore National Laboratory. A book which is incorporated 
herein by reference on the subject is "High Velocity Impact Phenomena", 
Academic Press, Inc., N.Y., (1970), edited by R. Kinslow, Library of 
Congress Catalog Card Number: 71-91425. 
The above referenced book at pages 293-417 shows the connection between 
impact velocity and the pressure rise due to the impact shock wave in a 
material. A description of the calculation of the temperature rise due to 
a shock wave is given in this reference. 
The following is a basic description understandable to a person skilled in 
the art of the method of calculating pressure and temperature rises due to 
impact shock waves. The description is meant to be illustrative. The 
previous reference gives data for most metals, common alloys, and some 
other materials, concerning the resultant pressure rises for that material 
for varying impact velocities. The data is presented numerically. The 
locus of single shock states with varying shock strengths is called the 
Hugoniot. 
To obtain the shock wave pressure for a projectile impacting an object, 
first the Hugoniot curve for the projectile is reflected (mirror image) 
and then both of the reflected projectile Hugoniot and the object Hugoniot 
are located in the pressure/projectile velocity plane. The intersection of 
the reflected projectile Hugoniot with the object Hugoniot gives the 
pressure and particle velocity upon impact. This calculation is based on 
the fact that the pressure and particle velocity of both projectile and 
object are identical at the impact interface. 
The previous reference shows how, and gives the data, to calculate the 
temperature and pressure rises that will occur in the material of a 
projectile impacting another material, at a known velocity. The impact 
pressure depends on the projectile material. The material being struck, 
and the impact velocity of the projectile. For the purpose of this patent 
the following discussion concerns only a projectile impacting soft 
material, animal tissue, plastics, etc. The results can be divided into 
two groups; the first is when the projectile impact velocity is high, 
above 2 km/s, and the second when the projectile impact velocity is below 
1 km/s. In the projectile velocity range between 1 and 2 km/s the results 
are dependent on the materials of the projectile and the object being 
struck. 
Generally, for the first group, when a metal projectile has an impact 
velocity greater than 2 km/s, the impact shock wave will be strong enough 
the produce pressure rises on the order of 50 to 100 kbar and temperature 
increases on the order of 20 to 50 degrees C. The exact increases depend 
on the materials of the projectile and the object being struck. The 
previous reference describes the methods and gives data to allow the 
pressure and temperature rises to be calculated for this first group. A 
basic premise in those calculations is that the projectile material is 
high-density, void free metal. The pressure and temperature rises for the 
first group will probably be sufficient to trigger the shape change in 
shape-memory-alloy. 
The pressure and temperature rises for the second group will be much less, 
and are not expected to be sufficient to trigger the shape change in the 
shape-memory-alloy, unless further design is done to enhance those rises. 
For example, a copper projectile impacting high-density (0.95) 
polyethelene at 1 km/s will have about a 36 kbar pressure rise and about a 
15 degree C. temperature rise. Those rises would probably be insufficient 
to trigger the shape change in shape-memory-alloy pieces in such a 
projectile. Projectiles of other high-density metals would have pressure 
and temperature rises similar to those for copper, because these metals 
have only a few percent compression at low impact velocities, especially 
when impacting soft material. Most rifle and pistol bullets have 
velocities in this range, below 1 km/s. 
A method which allows temperature increase in the projectile to be 
increased for a given impact velocity is to decrease the density of the 
material of the projectile, that is to increase the voids in the metal. 
The reason this increases the temperature rise is that the voids collapse 
under the impact shock wave. That greatly increases the plastic work done, 
and that in turn causes more heat to be generated in the metal. For the 
example used previously, changing only from no voids in the copper to 10% 
voids in the copper metal, the temperature rise due to the impact shock 
wave increases to about 62 degrees C. 
As discussed earlier, there are several methods to create voids in metals. 
One which allows a precise control of the amount of void in the metal is 
to start with metal powder that has a known particle size and hot press 
the powder to form a piece having the desired void content. 
In general summary, the instant invention provides a piece of shape-memory 
alloy in the nose of the projectile wherein no shape change would occur 
during launch or flight. At impact the temperature rise due to the shock 
wave in the projectile would cause the shape-memory alloy piece to change 
shape. The shape change would be optimized for each type of projectile in 
order to provide improved impact energy transfer to the target. Shape 
changes such as diameter increase to increase resistance, and point 
deformation to cause tumbling are examples. 
Published data concerned with impact mechanics, such as the previous 
reference, point out that the impact shock wave attenuates as it travels 
from the point of impact along the length of the projectile. No shock wave 
should be expected beyond one projectile diameter back from the nose 
portion, or point of impact. The majority of projectiles are cylindrical 
so that the front center is the projectile nose, and the intended point of 
impact. Therefore, all designs shown hereinbelow concentrate on having the 
deforming means of shape-memory alloy at the front center of the 
projectile. It is within the scope of the invention however to locate the 
deforming means at other locations within a projectile to perform a 
desired projectile shape change. 
With continued reference to the drawing, FIG. 1 illustrates a generic 
projectile shown generally at 10, preferably comprising a core 12 and a 
deforming means 14. "Generic" projectile configurations are illustrated 
and described through the specifications but it is understood that the 
instant invention is applicable to a myriad of geometric configurations 
well known to those skilled in the art. The projectile 10 is shown to be 
of conventional design having a core 12 of heavy metal such as lead which 
is optionally but conventionally encased within a jacket 16. 
The deforming means is formed of a shape-memory alloy and the deforming 
means is in operative contact with the core. In this embodiment the 
deforming means is contained within the core wherein the core has a 
longitudinal axis and the deforming means comprises a generally 
cylindrically shaped rod that is in general axial alignment with the axis. 
The shape-memory alloy has a martensitic state and an austenitic state and 
the deforming means is capable of being dimensionally deformed while the 
alloy is in its martensitic state into the cylindrically-shaped rod shown 
in the Figure. While in its martensitic state prior to impact of the 
projectile the alloy remains in its martensitic state and the deforming 
means 14 remains in column contained within the core. 
FIG. 2 illustrates the projectile 10 after impact, i.e., after the 
temperature rise due to the impact shock wave has triggered the phase 
transition in the shape-memory alloy from its martensitic state to its 
austenitic state. As seen in FIG. 2, the deforming means 14 is capable of 
recovering upon impact to its non-deformed dimension that of a bent or 
out-of-column rod. It can be seen that the out-of-column deforming means 
14 is capable of altering the geometric shape of the core 12 which will 
cause the projectile to tumble and therefore improve the impact energy 
transfer of the projectile. 
The projectile 10 has thus been shown before impact in FIG. 1 in the smooth 
and symmetric shape required for launch and flight. In FIG. 2 the 
projectile is shown after impact, after the temperature rise due to the 
impact shock wave has triggered the phase transition in the shape-memory 
alloy which then, in turn, deforms the projectile into a curved shape 
causing the projectile to tumble after impact. 
FIG. 3 illustrates a second embodiment of a generic projectile 18 having a 
core 20 and a deforming means 22 of shape-memory alloy in operative 
contact with the core 20. The projectile 18 is further provided with an 
optional skin 24. 
In this embodiment, the core 20 again has a longitudinal axis and includes 
a nose portion 26 and the deforming means 22 comprises a cap that is 
complementary to and in contact with the nose portion 26. It can be seen 
from the figure that the cap is symmetrical about the axis of the core 
with respect to the nose portion. The deforming means 22 is actually 
dimensionally deformed while in its martensitic state into this 
symmetrical configuration, a change from its martensitic state to its 
austenitic state being capable of recovering the deforming means upon 
impact to its non-deformed dimension which is illustrated in FIG. 4 
wherein the cap is capable of being asymmetrical about the axis with 
respect to the nose portion. 
FIGS. 3 and 4 therefore show a projectile 18 that before impact is in the 
smooth and symmetric shape required for launch and flight. The projectile 
is shown in FIG. 4 after impact, after the temperature rise due to the 
impact shock wave has triggered the phase transition in the shape-memory 
alloy and which then has deformed the nose portion 26 such that the point 
of the nose is not along the longitudinal axis of the core or of the 
projectile. That altered shape will cause the projectile to tumble after 
impact. 
FIG. 5 illustrates a third embodiment of the instant invention wherein a 
generic projectile shown generally at 28 comprises a core 30 and deforming 
means 32. Again, the core and deforming means may be covered by an 
optional skin 34. In this embodiment the core 30 again has a longitudinal 
axis and includes a nose portion 36 and the deforming means 32 comprises a 
cap 38 that is complementary to and in contact with the nose portion and 
further includes a generally cylindrically shaped rod 40 that is in 
general axial alignment with said axis. 
In this embodiment, the rod 40 of the deforming means 32 is deformed by 
lengthening the rod while the alloy of the deforming means is in its 
martensitic state. The deformed condition of the rod 40 is illustrated in 
FIG. 5. Upon impact and phase change of the alloy from its martensitic 
state to its austenitic state the rod 40 recovers and reduces in length to 
its original non-deformed dimension as seen in FIG. 6. 
With reference to FIG. 5 the projectile 28 is shown before impact in the 
smooth and symmetric shape required for launch and flight. In FIG. 6 the 
projectile is shown after impact, after the temperature rise due to the 
impact shock wave has triggered the phase transformation in the 
shape-memory alloy of the deforming means which then broadened the nose 
portion 36 and pulled the nose portion closer to the projectile base, 
which has, in turn, forced the core 30 to flow radially outward, thus 
causing the projectile diameter to increase. The altered shape of FIG. 6 
improves the impact energy transfer of the projectile. 
All of the aforementioned projectiles have been illustrated as having a 
generic projectile shape and as having a core of malleable metal as well 
as an optional skin. It is understood that it is within the scope of the 
invention to form the projectile into other known projectile 
configurations with or without a skin and further, to form a projectile 
wherein the deforming means comprises the core with or without a skin, 
i.e., where the entire projectile is made from shape-memory alloy. 
FIG. 7 illustrates a further embodiment of the instant invention wherein a 
generic cutting projectile shown generally at 42 having a core 44 having a 
longitudinal axis and including a cutting head 46. The projectile 42 
includes a deforming means 48 that is contained within the cutting head 
and in general axial alignment with the axis. A change of the alloy of the 
deforming means from its deformed martensitic state as seen in FIG. 7 to 
its austenitic state as seen in FIG. 8 being capable of radially expanded 
the cutting head 46 with respect to the axis, increasing the cross-section 
of the cutting head. 
FIG. 7 therefore shows the projectile before impact in the smooth and 
symmetric shape again required for launch and flight. In FIG. 8 the 
projectile is shown after impact, after the temperature rise due to the 
impact shock wave has triggered the phase transition in the shape-memory 
alloy of the deforming means which has then separated the cutting head of 
the projectile into two or more sections which open outward at the point 
of the projectile, both increasing the projectile's cross-section and 
exposing more cutting edge. The expanded shape will cause the projectile 
to have increased lethality after impact. 
FIG. 9 illustrates a fifth embodiment of the instant invention wherein an 
armor-penetrating projectile shown generally at 50 comprises a core 52, a 
skin 54 surrounding the core 52 and a deforming means 56 positioned 
between the core 52 and the skin 54. In this embodiment, the core 52 has a 
longitudinal axis and the deforming means 56 has been radially expanded 
while the alloy is in its martensitic state to the configuration 
illustrated in FIG. 9. Upon impact, the deforming means goes through 
transition from its martensitic state to its austenitic state and is 
capable of radially compressing the core 52 about the longitudinal axis to 
improve the armor penetration characteristics of the projectile. 
FIG. 9 thus illustrates the projectile before impact in the smooth and 
symmetric shape required for launch and flight. FIG. 10 illustrates the 
projectile after impact, after the temperature rise due to the impact 
shock wave has triggered the phase transition in the shape-memory alloy 
wherein the deforming means 56 has recovered to a reduced diameter at the 
front of the projectile to improve the armor-penetration characteristics 
of the projectile. 
FIGS. 11 and 12 illustrate a generic soft nosed projectile wherein the 
deforming means 58 is positioned in the nose of the core 60. The core 60 
is preferably partially jacketed by skin 62. As seen in FIG. 12, upon 
impact the core 60 is "mushroomed" out by the deforming means 58 which 
recovers to a larger diameter as it is driven deeper within the core 60 by 
the impact. 
FIG. 11 also illustrates another aspect of the invention which is 
applicable to all embodiments of the invention. Multiple elements 58', 
58", 58"', and 58"" are shown in phantom. These elements are also of 
shape-memory alloy. The elements may be made from different shape-memory 
alloys, may have different degrees of recovery and may have different void 
contents-all to improve projectile energy transfer. 
FIG. 13 illustrates the general concept of making the entire projectile 64 
from shape-memory alloy as described earlier herein. This figure also 
illustrates the concept of fabricating the projectile 64 from shape-memory 
alloy material containing voids. It is understood that any of the 
embodiments discussed heretofore may also be fabricated from shape-memory 
alloy containing voids. 
While the preferred embodiments of the present invention have been 
described, it should be understood that various changes, adaptations and 
modifications may be made therein without departing from the spirit of the 
invention and the scope of the appended claims.