US20140224107A1

US20140224107A1 - Advanced armor laminate structure

Info

Publication number: US20140224107A1
Application number: US14/093,715
Authority: US
Inventors: Zhiyong Xia; Brad M. Ward; Morgana M. Trexler
Original assignee: Johns Hopkins University
Current assignee: Johns Hopkins University
Priority date: 2012-12-03
Filing date: 2013-12-02
Publication date: 2014-08-14

Abstract

A transparent armor laminate apparatus includes a hard disrupter layer having a substantially planar surface of transparent material configured to erode a ballistic projectile responsive to impact from the projectile, and an absorber configured proximate to the disrupter layer. The absorber includes a first absorber layer and a second absorber layer. The first and second absorber layers may be disposed proximate to each other to define an interface. The first absorber layer may include molecules substantially aligned in a mixture to form a first polymer chain orientation having a first angle relative to the interface and the second absorber layer may include molecules substantially aligned in a mixture to form a second polymer chain orientation having a second angle relative to the interface. A discontinuity exists between the first angle and the second angle or between the first polymer chain orientation and the second polymer chain orientation at the interface.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 61/732,583 filed on Dec. 3, 2012, the entire contents of which are hereby incorporated herein by reference.

TECHNICAL FIELD

Example embodiments generally relate to armor systems and, more particularly, relate to a laminate structure for use in an armor system.

BACKGROUND

There are many different applications for which transparent armor systems are useful. As an example, vehicles capable of carrying valuable personnel or payloads may advantageously be outfitted with armor systems. In situations where the armor is employed on vehicles or other devices through which optical viewing is preferred, it may also be desirable to provide portions of the armor system that are transparent. When transparent portions of armor systems are to be employed, optical clarity and ballistic performance may be desirable characteristics. However, thickness and weight of such materials, which might otherwise preferably be kept low, may sometimes increase as the optical clarity and ballistic performance characteristics are improved. Accordingly, designers may generally need to sacrifice clarity or ballistic performance if they face constraints on weight and/or thickness.

BRIEF SUMMARY OF SOME EXAMPLES

Accordingly, some example embodiments may enable the provision of an armor system that is capable of providing improved ballistic performance without requiring a typical level of corresponding increase in weight or thickness of the material used. For example, some embodiments may enable improved ballistic performance in transparent armors by improving ballistic energy dissipation over a given areal density while reducing the thickness of an absorber layer relatively significantly. Thus, for a given weight, dramatically improved ballistic energy dissipation may be achieved or, for example, for a given ballistic energy dissipation characteristic, a lighter weight may be achieved.
In one example embodiment, a transparent armor laminate apparatus is provided. The apparatus may include a hard disrupter layer having a substantially planar surface of transparent material configured to erode, break up or destroy a ballistic projectile responsive to impact from the ballistic projectile, and an absorber configured proximate to the hard disrupter layer. The absorber may include a first absorber layer and a second absorber layer. The first absorber layer and the second absorber layer may be disposed proximate to each other to define an interface therebetween. The first absorber layer may include molecules substantially aligned in a mixture to form a first polymer chain orientation having a first angle relative to the interface and the second absorber layer may include molecules substantially aligned in a mixture to form a second polymer chain orientation having a second angle relative to the interface. A discontinuity may be provided between the first angle and the second angle or between the first polymer chain orientation and the second polymer chain orientation at the interface.
In another example embodiment, a method of providing a transparent armor is provided. The method may include providing a hard disrupter layer that may include a substantially planar surface of transparent material configured to erode or destroy a ballistic projectile responsive to impact from the ballistic projectile, and disposing an absorber proximate to the hard disrupter layer. The absorber may include a first absorber layer and a second absorber layer. The first absorber layer and the second absorber layer may be disposed proximate to each other to define an interface therebetween. The first absorber layer may include molecules substantially aligned in a mixture to form a first polymer chain orientation having a first angle relative to the interface. The second absorber layer comprises molecules substantially aligned in a mixture to form a second polymer chain orientation having a second angle relative to the interface. A discontinuity exists between the first angle and the second angle or between the first polymer chain orientation and the second polymer chain orientation at the interface.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described some example embodiments of the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 illustrates a perspective view of various layers that may be employed to provide the armor system of an example embodiment;

FIG. 2 illustrates a chart showing several samples and the corresponding improvement in cross linking density in accordance with an example embodiment;

FIG. 3 illustrates the change in strain for the different samples as a function of temperature in accordance with an example embodiment;

FIG. 4 illustrates the B-relaxation for the same samples in accordance with an example embodiment;

FIG. 5 illustrates a chart of specific volume versus temperature to illustrate how a free volume may be selected based on control of a glass transition temperature in accordance with an example embodiment; and

FIG. 6 illustrates a method of providing a transparent armor in accordance with an example embodiment.

DETAILED DESCRIPTION

Some example embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all example embodiments are shown. Indeed, the examples described and pictured herein should not be construed as being limiting as to the scope, applicability or configuration of the present disclosure. Rather, these example embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout. As used herein, operable coupling should be understood to relate to direct or indirect connection that, in either case, enables functional interconnection of components that are operably coupled to each other.
Some example embodiments may provide armor designers to achieve an equal amount of ballistic performance with reduced material thickness and overall armor weight. Thus, for example, windshields and side windows for tankers, trucks, or other ground vehicles may be provided with less weight. Similarly, canopies, windshields, blast shields, lookdown windows, sensor protectors and other such uses on air vehicles such as helicopters, anti-tank aircraft, fixed wing aircraft and/or the like, may be provided with less contribution to overall vehicle weight or with less thickness. Riot visors, face shields, body shields, explosive ordinance disposal equipment and/or the like may also be improved with example embodiments.
FIG. 1 illustrates a perspective view of various layers that may be employed to provide the armor system of an example embodiment. In this regard, FIG. 1 illustrates a transparent armor laminate 100 that includes a hard disrupter layer 110 and an absorber 120. The hard disrupter layer 110 may be a substrate, plate, pane or other planar or semi-planar piece of material that is substantially rigid and transparent. Glass and ceramic are some examples of materials that may be used to form the hard disrupter layer 110. A thickness of the hard disrupter layer 110 in some embodiments may be selected to be about ⅜ inch to about 4 inches. However, thicker or thinner embodiments may also be used in some embodiments. The armor laminate 100 of the example embodiment of FIG. 1 may be employed in window panes or other transparent window-like materials for use in connection with, for example, any of the devices, vehicles or apparatuses listed above.
In an example embodiment, the hard disrupter layer 110 forms a rigid or hard layer of material that is capable of eroding, destroying or otherwise breaking up a ballistic projectile 130 that may encounter the hard disrupter layer 110. The ballistic projectile 130 may be a bullet, shell, ball, shrapnel, fragment of any of the preceding, or other projectile. When the ballistic projectile 130 encounters the hard disrupter layer 110, the ballistic projectile 130 may impact the hard disrupter layer 110 and become deformed, degraded, eroded, destroyed or otherwise modified in shape as the kinetic energy of the ballistic projectile 130 is absorbed by the armor laminate 100 as a whole. The hard disrupter layer 110 may be expected to deform, crack, split, or otherwise be penetrated to at least some degree as the energy from the ballistic projectile 130 is absorbed to stop the ballistic projectile 130.
While the energy from the ballistic projectile 130 is converted to other forms of energy and/or is transferred to the armor laminate 100, cracks and deformation from the hard disrupter layer 110 may begin to propagate toward the absorber 120. The absorber 120 may therefore be configured to absorb the energy further and prevent fragments from damaging people or structures and/or mitigate passage of potentially damaging energy to the people or structures protected by the armor laminate 100. The absorber 120 may be configured adjacent to the hard disrupter layer 110 over all or a majority of the area of the hard disrupter layer 110. Thus, the absorber 120 may be configured also as a substrate, plate, pane or other planar or semi-planar piece of material that is substantially transparent. However, the absorber 120 of an example embodiment may be less rigid and, in some cases, a softer material than the hard disrupter layer 110 (e.g., a soft plastic or other polymer layer).
In some embodiments, the absorber 120 may be joined to the hard disrupter layer 110 via an adhesive. The adhesive may be an aliphatic or aromatic polyurethane. In some embodiments, the adhesive may be polyvinyl butyral, silicone, hot melt adhesive, acrylics, or polyester. Other embodiments may employ other adhesives as well.
In an example embodiment, the absorber 120 may include a first absorber layer 140 and a second absorber layer 150. The first absorber layer 140 and the second absorber layer 150 may be disposed proximate to each other to define an interface 160 therebetween. The interface 160 may be the planar or semi-planar contact area between the first absorber layer 140 and the second absorber layer 150, and may be used as a reference relative to structures provided in the respective absorber layers 140/150. In some embodiments, the interface 160 may be defined by or include an adhesive provided therein in order to bind the first and second absorber layers 140 and 150.
In this regard, the first and second absorber layers 140 and 150 may each be comprised of polymer layers that have tailored polymer chain orientations and/or angles provided therein. For example, the molecules employed to form the first and second absorber layers 140 and 150 may be molecules that have relatively elongated profiles in which the long ends of the molecules can be aligned to form long chains that extend substantially parallel to each other through respective ones of the first and second absorber layers 140 and 150. The free or empty space between the polymer chains (i.e., the space that is not occupied by polymer molecules) may define a free volume that may be controllable as described in greater detail below.
In an example embodiment, the first absorber layer 140 may include molecules substantially aligned in a mixture to form a series of polymer chains 142 that are positioned according to a first polymer chain orientation having a first angle relative to the interface 160. The first angle may generally be represented as the angle between the direction of extension of the series of polymer chains 142 and the interface 160. Meanwhile, the second absorber layer 150 may include molecules substantially aligned in a mixture to form a series of polymer chains 152 that are positioned according to a second polymer chain orientation having a second angle relative to the interface 160. The polymer chains may be formed of material that is relatively strong, but is also clear or transparent. In some cases, the molecules may have a size that is smaller than the wavelength of visible light.
When the hard disrupter layer 110 stops or otherwise encounters the ballistic projectile 130, cracks that may compromise the integrity of the armor laminate 100 may propagate from the hard disrupter layer 110 toward the interface between the hard disrupter layer 110 and the first absorber layer 140. In embodiments where an adhesive is placed in this location, some mitigation of crack propagation may be provided by the adhesive (e.g., based on a thickness of the adhesive). However, the energy transmitted from the hard disrupter layer 110 to the first absorber layer 140 may tend to initiate cracks in the first absorber layer 140. To the extent that any such crack is formed, it may be expected that the cracks would tend to propagate along the free space between adjacent chains. If the energy transferred to the first absorber layer 140 is sufficient to cause crack propagation through the entire width of the first absorber layer 140, the crack may attempt to cross the interface 160 and propagate through to the second absorber layer 150 as well. However, the interface 160 may be arranged such that a discontinuity may be provided between a characteristic of each of the first and second absorber layers 140 and 150 at the interface 160.
In some embodiments, the characteristic may be a characteristic that may impact crack propagation between the first and second absorber layers 140 and 150. As an example, a discontinuity may be provided at the interface 160 between the first angle and the second angle or between the first polymer chain orientation and the second polymer chain orientation. In the context of these characteristics, it should be appreciated that, in reference to the example of FIG. 1, the first angle and the second angle may represent the angle of the longitudinal direction of extension of the series polymer chains (142 and 152) relative to the interface 160 (which in this example lies in the x-y plane. Meanwhile, the first polymer chain orientation and the second polymer chain orientation may be determined based on a direction from tail to head of the polymer chains (with the tail representing a bottom most portion of the chain and the head representing the top most (i.e., closest to the hard disrupter layer 110) portion of the chain) relative to the x-z plane.
In the example shown in FIG. 1, the first angle and the second angle may each be about 40 degrees. However, the first polymer chain orientation and the second polymer chain orientation may be 180 degrees apart from each other. This provides a discontinuity at the interface 160 of about 80 degrees in angular difference as a crack attempts to propagate across the interface 160. The relatively high amount of change in the alignments of the polymer chains at the interface 160 that is caused by the discontinuity makes it more difficult for a crack to propagate across the interface 160. The provision of an adhesive (e.g., similar to the adhesives described above) at the interface 160 may further facilitate arresting of crack propagation. In such examples in which an adhesive is employed, the thickness of the adhesive and the material properties of the adhesive employed may further impact the characteristics of the armor laminate 100 relative to arresting of crack propagation. In some embodiments, a thickness of the adhesive layer placed between the first absorber layer 140 and the second absorber layer 150 may be about 40 mils to about 60 mils.
In an example embodiment, the discontinuity provided by the interface 160 could therefore include any or all of the inclusion of the adhesive having a given thickness, the provision of different first and second angles, and/or the provision of different orientations for the polymer chains. In some example, the first and second angles may generally be selected to have a value of between about 20° and about 40°. However, other angles may be utilized in connection with other structures and other example embodiments. The ability to alter angles and orientations means that some embodiments could have the same first and second angles, but different orientations. Meanwhile, other embodiments could employ different first and second angles and the same orientations. Still other embodiments could employ different first and second angles and different orientations.
In some cases, a thickness of the first absorber layer 140 and the second absorber layer 150 may also be altered in order to impact the effectiveness of the armor laminate 100. Thus, for example, if the thickness of the first absorber layer 140 is selected to have a value L, the thickness of the second absorber layer 150 may be selected to have a desired ratio relative to the thickness L. In some embodiments, for example, the thickness of the second absorber layer 150 may be selected to have the value L, 2L, 0.5L, 1.5L, or any other suitable value. In some embodiments, the value of L may fall within a range of about ½ inch to 1 inch, or within a range of about ¼ inch to about 1¾ inch.
In some cases, thermoplastic plastics may be formed of melted polymer chains that are then cooled via a relatively slow cooling process. However, to increase production times, a faster cooling process may be preferred. Using a fast cooling process may tend to create voids (or free volume) between the chains. Example embodiments may utilize or control this free volume in order to alter the properties of the resulting materials. Furthermore, in some cases the alignment of the long chain molecules of the first and second absorber layers 140 and 150 may be produced using equal channel angular extrusion (ECAE), which may incorporate the deformation of the material being produced (e.g., Poly(methyl methacrylate) (PMMA)) by forcing the material through an angled channel to introduce a relatively high deformation strain without reducing the cross sectional area of the material. By using EACE, for example, a selected angle may be provided for the chains relative to the interface 160, and/or a selected orientation of the chains may be achieved. Meanwhile, the PMMA, oriented by ECAE, may still have excellent optical clarity.
It should also be appreciated that a high ballistic impact resistance may be achieved through the use of a high molecular entanglement density with a high β-relaxation. In this regard, FIG. 2 illustrates a chart showing several samples and the corresponding improvement in cross linking density. FIG. 3 illustrates the change in strain for the different samples as a function of temperature, and FIG. 4 illustrates the β-relaxation for the same samples.
FIG. 5 illustrates a chart of specific volume versus temperature to illustrate how a free volume may be selected based on control of a glass transition temperature in accordance with an example embodiment. Example embodiments may therefore control or improve the quasi-static and high strain impact fracture toughness in polymers by adjusting the free volume in the polymeric materials. Due to the relatively wide range of molecular weight (Mw) distribution in polymers, there may be a distribution of free spaces. In the liquid state, the free volume of the polymer may be large enough for the polymer chains to move relatively easily. The chains may also change in conformational states. As shown in FIG. 5, when temperature drops below a glass transition temperature (Tg), the free volume will begin to shrink and limit the long-range cooperative micro Brownian motions. Therefore, the free volume below Tg may be considerably smaller than the free volume above Tg. At temperatures greater than Tg, the free volume increases at a much faster rate than at temperatures below Tg. The high free volume makes the polymer chains able to compensate for relatively large amounts of impact deformation without causing any damage to the material. In other words, having a high free volume may result in a relatively high impact toughness. The free volume (Vf) at temperatures above Tg may be expressed as:
Vf=Vf*+(T−Tg)dVf/dT (1)
Dividing both sides of equation (1) leads to:
f _T≧Tg =f _g+(T−Tg)α_f
where f_gis a free volume fraction at Tg, and is about 0.025 in this example. α_fmay represent the volumetric thermal expansion coefficient, and can be measured by thermal mechanical analysis. The free volume can be modified by a number of techniques. In this regard, for example, 1) the free volume may be modified via the control of molecular orientation, or 2) the free volume can be modified by effective control over the glass transition temperature with respect to the glass transition. In some cases, the effective free volume in the polymer may be controlled via a simple shear induced molecular orientation. The controlled molecular orientation may decrease the specific gravity of the polymer at room temperature (i.e., higher free volume). The increase in free volume may increase the dissipation of mechanical energy upon impact. However, too high of a free volume increase may result in materials that are too weak. Accordingly, although an increase in free volume is desirable, the increase must be maintained at relatively low levels to avoid too much weakening of the material. In some embodiments, the free volume may be maintained within a range of about 2% to about 10% of the material volume.
Accordingly, rather than using thick heavy parts for improving ballistic resistance, example embodiments may utilize controlled molecular orientations in adjacent layers for effectively improving the ballistic resistance of the material. In some cases, the improvement of the free volume in the polymer portions may further enhance ballistic resistance. In this regard, a higher free volume along with increased mechanical properties may greatly improve the impact of energy dissipation and therefore improve the ballistic resistance of the material.
FIG. 6 illustrates a method of providing a transparent armor. The method may include providing a hard disrupter layer that may include a substantially planar surface of transparent material configured to erode or destroy a ballistic projectile responsive to impact from the ballistic projectile at operation 300. The method may further include disposing an absorber proximate to the hard disrupter layer at operation 310. The absorber may include a first absorber layer and a second absorber layer. The first absorber layer and the second absorber layer may be disposed proximate to each other to define an interface therebetween. The first absorber layer may include molecules substantially aligned in a mixture to form a first polymer chain orientation having a first angle relative to the interface. The second absorber layer comprises molecules substantially aligned in a mixture to form a second polymer chain orientation having a second angle relative to the interface. A discontinuity exists between the first angle and the second angle or between the first polymer chain orientation and the second polymer chain orientation at the interface.
Example embodiments may therefore provide a relatively light, but effective armor that is transparent. By utilizing such armor to provide shielding that is transparent, a lighter weight vehicle, or other device that requires at least a portion of visible armor thereon, may be provided with still a high level of ballistic resistance. Alternatively, improved ballistic performance may be achieved for the same weight parameters. With less weight taken up by the transparent portions of the device, for example, more of a weight allotment may be dedicated to other systems or devices that improve the performance of vehicles or devices that may employ example embodiments.
Many modifications and other embodiments of the example embodiments of the invention set forth herein will come to mind to one skilled in the art to which these example embodiments of the invention pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the example embodiments of the invention are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe exemplary embodiments in the context of certain exemplary combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. In cases where advantages, benefits or solutions to problems are described herein, it should be appreciated that such advantages, benefits and/or solutions may be applicable to some example embodiments, but not necessarily all example embodiments. Thus, any advantages, benefits or solutions described herein should not be thought of as being critical, required or essential to all embodiments or to that which is claimed herein. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

What is claimed is:

1. A transparent armor laminate apparatus comprising:

a hard disrupter layer comprising a substantially planar surface of transparent material configured to erode, break up, or destroy a ballistic projectile responsive to impact from the ballistic projectile; and

an absorber configured proximate to the hard disrupter layer, the absorber comprising a first absorber layer and a second absorber layer, the first absorber layer and the second absorber layer being disposed proximate to each other to define an interface therebetween,

wherein the first absorber layer comprises molecules substantially aligned in a mixture to form a first polymer chain orientation having a first angle relative to the interface,

wherein the second absorber layer comprises molecules substantially aligned in a mixture to form a second polymer chain orientation having a second angle relative to the interface, and

wherein a discontinuity exists between the first angle and the second angle or between the first polymer chain orientation and the second polymer chain orientation at the interface.

2. The apparatus of claim 1, wherein polymer chains of each of the first and second absorber layers are defined via equal channel angular extrusion.

3. The apparatus of claim 1, wherein a thickness of the first absorber layer is the same as a thickness of the second absorber layer.

4. The apparatus of claim 1, wherein a thickness of the first absorber layer is different than a thickness of the second absorber layer.

5. The apparatus of claim 1, wherein the first angle is the same as the second angle, and wherein the first polymer chain orientation is different than the second polymer chain orientation.

6. The apparatus of claim 1, wherein the first polymer chain orientation is the same as the second polymer chain orientation, and wherein the first angle is different than the second angle.

7. The apparatus of claim 1, wherein the first angle is different than the second angle, and wherein the first polymer chain orientation is different than the second polymer chain orientation.

8. The apparatus of claim 1, wherein an adhesive layer is provided between the first absorber layer and the second absorber layer.

9. The apparatus of claim 1, wherein an adhesive layer is provided between the first absorber layer and the hard disrupter layer.

10. The apparatus of claim 1, wherein the first angle and the second angle are between about 20° and about 40°.

11. The apparatus of claim 1, wherein a thickness of the hard disrupter layer is about ⅜ inch to about ⅝ inch, and wherein a thickness of the absorber is about ¼ inch to about ¾ inch.

12. The apparatus of claim 11, wherein an adhesive layer is provided either or both of between the first absorber layer and the hard disrupter layer and between the first absorber layer and the second absorber layer, and wherein a thickness of the adhesive layer is about 40 mils to about 60 mils.

13. The apparatus of claim 1, wherein the first absorber layer and the second absorber layer each have a free volume defined by a free space between adjacent polymer chains, and wherein the free volume in each of the first absorber layer and the second absorber layer is defined within a range of about 2% to about 10%.

14. The apparatus of claim 13, wherein the free volume is set via shear induced molecular orientation.

15. The apparatus of claim 13, wherein the hard disrupter is glass and wherein the free volume is set via control of a glass transition temperature of the glass.

16. The apparatus of claim 1, wherein the hard disrupter is glass.

17. The apparatus of claim 1, wherein the hard disrupter is ceramic.

18. The apparatus of claim 1, wherein an adhesive layer is provided either or both of between the first absorber layer and the hard disrupter layer and between the first absorber layer and the second absorber layer, and wherein a material used to provide the adhesive layer comprises an aliphatic or aromatic polyurethane.

19. The apparatus of claim 1, wherein an adhesive layer is provided either or both of between the first absorber layer and the hard disrupter layer and between the first absorber layer and the second absorber layer, and wherein a material used to provide the adhesive layer comprises polyvinyl butyral, silicon, or polyester.

20. A method of providing a transparent armor comprising:

providing a hard disrupter layer comprising a substantially planar surface of transparent material configured to erode or destroy a ballistic projectile responsive to impact from the ballistic projectile; and

disposing an absorber proximate to the hard disrupter layer, the absorber comprising a first absorber layer and a second absorber layer, the first absorber layer and the second absorber layer being disposed proximate to each other to define an interface therebetween,