US20130263727A1

US20130263727A1 - Multi-Functional Hybrid Panel For Blast and Impact Mitigation and Method of Manufacture

Info

Publication number: US20130263727A1
Application number: US13/640,259
Authority: US
Inventors: Mark R. O'Masta; Haydn N.G. Wadley
Original assignee: University of Virginia Patent Foundation
Current assignee: University of Virginia Patent Foundation
Priority date: 2010-04-07
Filing date: 2011-04-07
Publication date: 2013-10-10
Also published as: WO2012003026A2; WO2012003026A3

Abstract

This invention relates to a multifunctional structure for mitigating the effects of explosions and impeding the penetration of projectiles that is also highly effective at supporting structural (i.e. static) loads. By wrapping a tile in multiple layers of high-performance fabric, upon impact by a projectile additional tensile forces are created, aiding in the deceleration of the projectile. With added layers the tensile forces aiding projectile deceleration increase, resulting in a ballistic panel for use in multifunctional structural/armor systems having a lighter weight and greater stopping power than conventional armor systems in addition to functioning as part of a structure for supporting static loads.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM FOR PRIORITY

This application claims the benefit of U.S. Provisional Application No. 61/321,612 entitled “Ballistic Response of Aluminum and Alumina Cellular Structures” filed on Apr. 7, 2010. The Applicants of the provisional application are Mark R. O'Masta and Haydn N. G. Wadley. This non-provisional application further claims the benefit of U.S. Provisional Application No. 61/356,231 entitled “Ballistic Response of Aluminum and Alumina Cellular Structures” filed on Jun. 18, 2010. The Applicants of the provisional application are Mark R. O'Masta and Haydn N. G. Wadley. The above provisional applications are hereby incorporated by reference herein in their entireties.

GOVERNMENT FUNDING

This invention was made with government support under Grant No. N00014-07-1-0764 awarded by the United States Office of Naval Research. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to hybrid structures incorporating a multiplicity of materials and topological design that are able to support structural loads while effectively impeding the penetration of projectiles and mitigating the distributed impulse of a nearby explosion. More particularly, this invention relates to methods and systems that use a combination of high performance metals shaped in the form of sandwich panels, ceramic tiles and prismatic structures and high-tensile strength fibers mitigate the impulse loadings due to a nearby explosion and or high velocity projectiles.
2. Description of Related Art
The evolution of armor systems has been transformed by the invention and development of high-tensile strength fibers. Early armor systems relied on solid high strength metallic plates to defeat projectile impacts and resist the impulsive loadings of a nearby explosion. These plates need to be thick and are therefore heavy when used to provide adequate protection against modern weaponry. Metals used in these applications include various grades of steels, aluminum, magnesium and titanium alloys. Ceramic-based armors have been combined with metals to develop “composite” armors which are extremely hard and generally of lighter weight than all metal solutions. Composite armors that exploit ceramic materials such as alumina, boron carbide, silicon carbide, and titanium diboride, can all provide a much lighter mass solution to the defeat of a projectile, especially those that very hard and designed to penetrate conventional metal systems. Unfortunately, these ceramic-armors often crack while dissipating the energy of an explosion or a ballistic impact, thereby weakening the armor against subsequent impacts in the same region.
Modern armor uses a combination of metals, ceramics and ballistic fiber-based fabrics or fiber reinforced composites to further improve the resistance to projectile impact. High-performance fabrics have a strength-to-weight ratio several times higher than steel. One of the most popular fabrics is composed of para-aramid fibers (Kevlar® by DuPont and Twaron® by Teijin Aramid), however, other commonly used high-performance fabrics are composed of ultra-high molecular-weight polyethylene (Spectra® by Honeywell and Dyneema® by DSM), polyamides (Nylon® by DuPont), PBO (Zylon® by Toyobo), M5®, (DuPont) and carbon (IM series by Hexcel and T series by Toray) fibers. A fabric hit by a projectile can rapidly slow or decelerate the projectile by acting as a web of high tensile fibers, pulling on the projectile and forcing a rapid deceleration. When layered with ceramics and/or hard metals, such fabrics can not only provide a stopping measure for projectiles, but also helps retain the original shape of the armor components.
Layering in conventional ceramic and hard metal armor systems can often be covered by a spall shield—a layer of a polymer fiber fabric or composite usually positioned at the rear of the armor to catch material ejected from the armor during an impact event. The spall shield helps prevent the ejection of high velocity fragments of either the ceramic layer or the projectile after projectile contact.
One solution creates a large aramid fabric compressed between plastic sheets and secured in place to the surrounding structure, such as a vest or panel wall. Another solution encapsulates a ceramic structure in organic compounds, then creates a backing structure of Kevlar® or Dyneema® (see U.S. Pat. No. 7,478,579). Both solutions can help maintain the form of impacted ceramics. However, while these ceramic armor systems offer a significant advantage over previous armor systems in maintaining the shape of ceramic components, there exists a need for armor systems capable of stopping projectiles of even greater velocities, while maintaining the shapes of ceramic components and a low weight. It is further important to recognize that none of these solutions is designed to carry structural load or mitigate the effects of a nearby explosion and their ballistic integrity can be seriously diminished when exposed to explosive loadings or severe nearby impacts.

BRIEF SUMMARY OF THE INVENTION

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The features and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth herein.
An armor system for decelerating a projectile is disclosed. In one aspect, the system is formed of a number of tile or prismatic structures arranged in a grid structure. A tile is wrapped in multiple layers of a high-performance fabric from multiple directions. The tiles preferably are designed as anti-projectile tiles, and can be metallic, ceramic, or a metal-ceramic composite. An example of a metal-ceramic hybrid is a metallic frame with ceramic inserts. After selection of the tile, it is continuously wrapped in multiple layers of fabrics such as Kevlar®, Twaron®, Dyneema®, Spectra®, Zylon®, M5®, Nylon® and IM- or T-series carbon fibers. The invention specifically calls for a single sheet used for the wrapping so as to minimize free ends to sheet.
In another aspect, consolidation of the wrapped tile occurs, finishing the wrapped tile into a compact tile without loose fabrics. The method of consolidation varies according to the fabric and/or tile used, but may include hot pressing or autoclave processing. These hot presses or autoclaves can ensure any adhesive/resin sets properly, and creates a compact confined product. Further aspects can include implementation of the wrapped tile into an overall armor design, including additional structures for maintaining armor shape after projectile impact. These additional structures can include a spall shield, a lattice structure for holding tiles, blast absorbing panels and a back panel. All of these structures can further aid in projectile deceleration. A key aspect of the invention is the use of space behind the fabric wrapped the or prism layer. This is created by ledges on through-thickness webs onto which the fabric wrapped tiles/prismatic ballistic packages are placed. This behind armor space is used to enable the fabric free motion during a ballistic stopping event and to allow the vertical webs to buckle during a blast event. The design of the through-thickness webs can be optimized to facilitate construction of a sandwich panel in which the webs establish a wide gap between the faces. In this way the panels exhibit high bend resistance under static and blast loads and are highly effective at mitigating the penetration of projectiles.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and other advantages and features of the invention can be obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only exemplary embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

FIG. 1 illustrates an exemplary embodiment of wrapping a tile in fabrics, with a consolidated view;

FIGS. 2A through 2C are cross-sectional views of an exemplary tile before being wrapped with aramid fabric, after being wrapped with aramid fabric, and after being impacted by a projectile;

FIG. 3 illustrates an exemplary lattice structure;

FIG. 4 illustrates an exemplary lattice structure being populated with sandwich panels and a back panel;

FIG. 5 illustrates an exemplary lattice structure being populated with sandwich panels, a back panel, a spall shield, and tiles wrapped in fabric;

FIG. 6 illustrates an exemplary method claim for producing one possible embodiment.

DETAILED DESCRIPTION

Various embodiments of the invention are discussed in detail below. While specific implementations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without parting from the scope and spirit of the invention. Having specified that alternative embodiments exist and those discussed here are illustrative only, the disclosure turns to a general discussion of the invention.
Disclosed is an improved form of projectile armor, with methods of manufacture and implementation. Units of high-performance fabric are wrapped around a ballistic tile. Exemplary aramid fabrics are woven or layered from Kevlar®, Twaron®, Dyneema®, Spectra®, Zylon®, M5C), Nylon® and IM- or T-series carbon fibers, which all have high-tensile strength to weight ratios several times greater than steel. The number of fabric layers wrapped around a ballistic the can vary, though in a preferred embodiment application of the fabric is continuous and positioned such that the fabric envelopes the entire ballistic tile. As used herein, the term “high-performance fabric” shall refer to any such fabric that is suitable for use as anti-ballistic material.
The number of units or rolls of fabric can vary. In most embodiments, the number of rolls used equals the number of sets of parallel sides. For example, a square has 2 sets of parallel sides, and thus uses two rolls. A hexagon would use 3 rolls, an octagon 4, and so on. Generally these separate rolls of fabric will be applied such that fabric covers the entire ballistic tile, though on occasion there may be incentive to expose a piece of the panel or have certain sections of the panel less wrapped than other sections. In one embodiment, the rolls will be applied sequentially, each roll forming a layer until all the rolls have formed layers, and repeating this sequential process until wrapping completes. In another embodiment, one roll wraps around the tile until complete, followed by a second roll, and so on until all rolls have been used.
After completion of wrapping, the wrapped tile becomes consolidated and used as anti-projectile armor. Consolidation can be performed using hot presses to remove any additional air in the fabric layering and seal the layers together. Consolidation can also be performed using autoclaves, which can cure any interior adhesives used, such as those used for adhering ceramics to metal tile frames or for adhering fabric layers to one another. One purpose of consolidation is to make a smooth, compact, finished product which can be used without likelihood of unraveling.
An exemplary advantage of wrapping tile in fabric is that upon impact of a projectile, the fibers of the fabric receive tension from larger surface areas created by material in the interior of the tile. This increased surface area creates additional stopping power, particularly when the projectile fragments. Under normal circumstances, a projectile with sufficient kinetic energy will, upon entering a ceramic, crack and push the ceramic in a distal direction and angles to the distal direction from the projectile. The tremendous kinetic energy also creates a void in the wake of a projectile expanding, referred to as “mushrooming,” of the ceramic and creating greater tension in the fibers. The fragmented and dispersed load from the originally intact projectile involves a larger amount of the fabric wrapping. The large volume of fabric is all under tension absorbing tensile strain energy and pushing back against the expanding fragmented debris. As the projectile pushes matter into the “exit side” of the tile, the tension will continue to increase, pulling back on extruding tile portions and resulting in rapid deceleration and dissipation of kinetic energy. Testing shows that implementing such a system can result in dramatically increasing the velocity a tile can absorb without projectile escape. Other exemplary advantages can include a reduction in weight, an increase in flexibility, and an increased ability to retain tile or ceramic pieces after impact deformation.
Exemplary implementations may include a wrapped tile being placed within a cavity of a vest for use as individual body armor, or a wrapped tile being placed into a lattice with other anti-projectile measures, such as a spall shield, a composite back panel, or a blast mitigation layer. An implementation with a lattice could, in some instances, be too bulky for use in an individual's body armor, but could be implemented into building or vehicular systems. The disclosure now turns to FIG. 1.
FIG. 1 illustrates an exemplary embodiment 100. The ballistic tile 102 shown will be wrapped in aramid fabric 104 a, 104 b. The ballistic tile can be of any material desirable to promote deceleration of projectiles, such as metal plates, ceramic tiles, or composite tiles. For example, the ballistic tile 102 depicts an Aluminum 6061-T6 frame with Alumina (Al₂O₃) ceramic inserts, but can be replaced with a steel plate, or a purely ceramic material. In particular the tile 102 can be made of at least one of aluminum, steel, magnesium, titanium, boron carbide, silicon carbide, aluminum oxide and cermets (metal matrix composites).
The fabrics 104 a, 104 b are shown in rolls, but can be any shape which allows the fabric to be continuously distributed when wrapping the ballistic tile 102. Because the ballistic tile 102 shown has four sides it has two sets of parallel sides: top and bottom, left and right. This results in two units of aramid fabric 104 a, 104 b to be used for wrapping the tile. If, however, one desired a tile with a hexagonal shape, three units could be used—one for each set of parallel edges. In another aspect, one could use four units or rolls of fabric on a square tile, one starting on each unique edge of the tile. Both the shape of the tile and the number of units of aramid fabric can be modified to the particular situation desired by a user.
Having discussed the ballistic tile 102 and the general nature of the fabrics 104 a, 104 b, the fibers 104 a, 104 b wrap around the ballistic tile 102. Wrapping occurs sequentially, as indicated by the arrows 106. In this example a first roll 104 a would be wrapped around tile 102 in a first direction, followed by a second roll 104 b wrapping around the tile 102 in a second direction perpendicular to the first direction. Each application of a roll 104 a, 104 b applies a single layer of fabric around the tile. This process continues until a desired number of layers has been applied to the tile. In a preferred embodiment, each roll of fabric applied to a square tile as shown in FIG. 1 would be applied eleven times, resulting in twenty-two total layers of aramid fabric around the tile.
Upon completion of the wrapping consolidation begins. A consolidated wrapped tile 112 of multiple layers will then have dimensions 108, 110 which can be used for calculation purposes when implementing the consolidated tile into projectile armor systems. The consolidated tile 112 shown has markers for the corners. In certain embodiments corner pieces may be used for locking the tile into place. In other embodiments, the corners may be rounded and smooth. Here, corner pieces are shown to mark the edges of the consolidated units, aiding in distinguishing separate tiles when combined with other anti-projectile technology.
FIGS. 2 a-2 c illustrate an exemplary side view of a composite ceramic tile before being wrapped 2 a, after being wrapped but pre-impact 2 b, and after impact 2 c. As in FIG. 1, the composite ceramic tile has a metal frame 202 and ceramic inserts 204. FIG. 2 b shows the composite ceramic the wrapped in fabrics 206. The number of layers may vary from that shown according to user needs.
FIG. 2 c shows this same exemplary wrapped composite ceramic the after impact from a projectile 216. The projectile impacted and entered the wrapped the at a location 208. As the projectile entered the wrapped tile, kinetic energy was dispersed such that matter not in the projectile's trajectory was pushed away, resulting in mushrooming 210. The mushrooming pushes back on the wrapped fabrics, increasing the overall tension of the fabrics. As the projectile continues through the tile, it pushes matter into the fabric layers on the “exit side” of the wrapped tile. This creates additional tension in the fabrics resulting in a hoop stress 212 and 214 circulating the tile 112. If, as in this example drawing, the projectile lacked sufficient kinetic energy to emerge from the wrapped tile, the fabrics on the exit side of the will remain intact. In this case one may find the projectile 216, or its shattered pieces within the deformed tile. If the kinetic energy were sufficient the wrapped fabrics may also break. In considering the tension forces resisting against or pulling on the projectile as it impacts the wrapped tile, one must not forget that the tensile forces come from all sides as a consequence of fabric wrapping in multiple directions, not just those shown in the figures.
In one possible implementation of a wrapped anti-ballistic tile as disclosed, the wrapped the fits into existing armor or body armor systems. Another possible implementation places the wrapped tile into a honeycomb lattice structure, as illustrated in FIG. 3. The lattice structure 300 can be made of any material suitable for this purpose, such as metal, plastic, ceramic, or otherwise. The lattice 300 contains specific segments for population by armor components. A top segment 302 exists for affixing spall shielding or other armor plating sufficient to hold other components in and prevent ricochets. A first level 304 exists for insertion of the wrapped tiles, a second level 306 receives a blast mitigation layer, and a bottom segment 308 receives an interior spall shield. Other implementations of the wrapped tile in an armor system may add or remove any additional layers. For example, the use of multiple layers of wrapped tiles or the creation of an air gap layer are both possible embodiments. In addition, the lattice structure 300 shown need not be based on square openings, and a multilayered lattice could have offset tile locations from layer to layer.
FIG. 4 illustrates a lattice structure system 400 for a multifunctional panel similar to that shown in FIG. 3 being populated with components in accordance with a method of manufacture of a multifunctional hybrid panel according to the invention. The lattice structure 402 can be composed of various materials. In a lower level 408 a blast mitigation tile 404 slides into place in the lattice 402, where it can be locked into place by screws, nails, adhesive, or other suitable means for locking tiles into place, forming a fixed tile 406. The blast mitigation tile 404 can be formed of any material suitable for absorbing and dispersing energy from blast or explosion events. An interior view 414 of these blast mitigation tiles 404 shows that they can, in certain embodiments, be sandwich panels. To the bottom of these panels 410 a final layer 412, or interior spall shield, can be attached, aiding in retaining impacted materials and providing a final layer of projectile defense as a solid piece of armor 416.
FIG. 5 illustrates a lattice structure panel 500 similar to the lattice structure shown in FIG. 4, now being further populated with wrapped ballistic tiles 502, 508. A wrapped tile 502 becomes placed into a space 504 on top of the blast mitigation tiles 404 inserted in FIG. 4. In one embodiment, an air gap exists between the ballistic tiles 508 and the blast mitigation tiles 404, in which the size of the air gap is related to the failure strain of the fabric in tension and the width 110 or length 108 of the tile (see FIG. 1). After insertion, a wrapped tile 508 may be secured using screws, nails, adhesive or other suitable materials. To the top of the lattice structure system 500 a spall shield 506 may be applied after insertion of all desired wrapped tiles.
The completed lattice structure panel 500 is also highly effective at supporting structural (i.e. static) loads in addition to impeding projectile penetration and mitigating blast effects of explosions. For example, the completed panel 500 may be used in the construction of an architectural structure (for example: pillars, walls, shielding, foundations or floors for buildings or pillars, wall shielding floors), a civil engineering structure (for example: road facilities such as noise resistant walls and crash barriers, road paving materials, permanent and portable aircraft landing runways, pipes, segment materials for tunnels, segment materials for underwater tunnels, tube structural materials, main beams of bridges, bridge floors, girders, cross beams of bridges, girder walls, piers, bridge substructures, towers, dikes and dams, guide ways, railroads, ocean structures such as breakwaters and wharf protection for harbor facilities, floating piers/oil excavation or production platforms, airport structures such as runways), military security/protection/defense structures; machine structures (for example: frame structures for carrying system, carrying pallets, frame structure for robots, etc.), automobile structures (for example: body, frame, doors, chassis, roof and floor, side beams, bumpers, etc.), ship structures (for example: main frame of the ship, body, deck, partition wall, wall, etc.), freight car structures (for example: body, frame, floor, wall, etc.), aircraft structure (for example: wing, main frame, body, floor, etc.), spacecraft structures (for example: body, frame, floor, wall, etc.), space station structures (for example: the main body, floor, wall, etc.), and submarine, ship or watercraft structures (for example: body, frame, etc.).
FIG. 6 illustrates an exemplary method of manufacturing a ballistic tile. First a base panel, or tile, is wrapped in fabric (602). The base panel can be metallic, ceramic, or a composite of both metals and ceramics. In one exemplary embodiment, ceramic inserts are placed with in an aluminum frame. Another embodiment could use a solid metal plate. Fabrics used to wrap the base panel can include popular fabrics such as Kevlar®, Twaron®, Dyneema®, Spectra®, Zylon®, M5®, Nylon® and IM- or T-series carbon fibers. In a preferred embodiment, the wrapping will be several layers thick, and layers alternate in different directions between multiple rolls or units of fabric. In other words, a first roll can wrap around the base panel in a first direction creating a first layer, and a second roll can wrap around the base panel in a second direction, creating a second layer. There can be additional rolls or units of fabric, applied in the same or alternative directions, in various embodiments.
Upon being wrapped in multiple layers, the wrapped panel is consolidated (604). A purpose of consolidation can be to finish the conversion of the wrapped panel into a ballistic panel. To this end, one exemplary embodiment uses heat to adhere separate layers of fabric to one another, preventing unwrapping of the panel. Another exemplary embodiment could use adhesive to cement the layers together. Certain embodiments may require autoclaves to cure resins in the fabric or with ceramic inserts into the base panel. Another purpose of consolidation can be to remove any additional air gaps in the fabric layering. Upon consolidation the newly formed ballistic tile can be implemented by means discussed earlier, or by means available to those with skill in the art.
Although the above description may contain specific details, they should not be construed as limiting the claims in any way. Other configurations of the described embodiments of the invention are part of the scope of this invention. For example, the present invention appears to apply most directly to projectile armor technologies, but could also be applied to other types of armor or construction technologies. Accordingly, the appended claims and their legal equivalents should only define the invention, rather than any specific examples given.

Claims

What is claimed is:

1. A method for manufacturing a ballistic tile, comprising:

wrapping a base the in high-performance fabric, yielding a wrapped tile; and

consolidating the wrapped panel to yield the ballistic tile.

2. The method of claim 1, wherein consolidating the wrapped tile further comprises using at least one of a hot press and an autoclave.

3. The method of claim 1, wherein the base the comprises at least one of a metallic tile, a ceramic tile, and a composite tile.

4. The method of claim 3, wherein the composite tile further comprises a metallic frame with ceramic inserts.

5. The method of claim 1, wherein the fabric comprises at least one of Kevlar®, Twaron®, Dyneema®, Spectra®, Zylon®, M5®, Nylon® and IM- and T-series carbon fibers.

6. The method of claim 1, wherein wrapping the base the comprises at least two separate units of fabric wrapped in unique directions.

7. The method of claim 6, wherein the at least two separate units of fabric wrapped in unique directions alternate wrapping the base panel sequentially.

8. The method of claim 1, wherein wrapping the base panel in fabric comprises creation of multiple layers of wrapped fabric covering the base panel.

9. A ballistic tile, comprising:

a base the wrapped in at least two layers of high-performance fabric that have been consolidated, yielding a ballistic tile.

10. The ballistic the of claim 9, wherein the high-performance fabric has been previously woven or layered into a ballistic fabric.

11. The ballistic the of claim 9, the wrapped tile further comprising multiple layers of high-performance fabric.

12. The ballistic the of claim 9, wherein the base the comprises at least one of aluminum, steel, magnesium, titanium, boron carbide, silicon carbide, aluminum oxide and cermets (metal matrix composites).

13. The ballistic the of claim 9, wherein the base the comprises at least one of a metal, a ceramic, and a polymer composite.

14. A multifunctional system for resisting ballistic projectiles and/or mitigating blast effects of explosions, comprising:

a multi-tiered lattice structure with a top, a top cavity, a bottom cavity, a gap between the top cavity and the bottom cavity, and a bottom;

a blast mitigation material attached to the multi-tiered lattice structure in the bottom cavity; and

a ballistic panel wrapped in high-specific strength consolidated fabric attached to the multi-tiered lattice structure in the top cavity.

15. The system of claim 14, further comprising:

at least one of a strike plate attached to the top of the multi-tiered lattice structure and a spall shield attached to the bottom or top of the multi-tiered lattice structure.

16. The system of claim 14, wherein the ballistic panel further comprises at least one of a metal, a ceramic, and a metal-ceramic composite and fiber reinforced composites.

17. The system of claim 14, wherein the high-specific strength consolidated fabric comprises at least one of Kevlar®, Twaron®, Dyneema®, Spectra®, Zylon®, M5®, Nylon® and IM- and T-series carbon fibers.

18. The system of claim 14, wherein the ballistic panel is wrapped by at least two rolls of high-specific strength fabric, sequentially alternating layers of fabric from the at least two rolls of high-specific strength fabric.

19. The system of claim 18, wherein each of the at least two rolls of high-specific strength fabric wraps around the ballistic panel at least twice.

20. The system of claim 14, wherein the gap between the top cavity and the bottom cavity has a depth associated with a dimension of the ballistic tile, the tensile strength of the fabric and the elongation to failure of the fabric.

21. The system of claim 14, wherein the system is part of a static load bearing member of any one of:

an architectural structure, a civil engineering structure, a military security/protection/defense structure, a machine structure, an automobile structure, a ship structure, a freight car structure, an aircraft structure, a spacecraft structure, a space station structure, and a submarine, structure.