Patent Application
20080248707
The invention relates in general to armorings, in particular armorings against high dynamic impulsive loads based on glass materials or glass-ceramic materials.
Armorings are generally built up as a laminar structure having a hard material and a substrate or backing. Amide fiber fabrics, steel nettings or else steel plates, for example, come into use as substrate. Such armorings are used, for example, for personal protection, for example for a bulletproof vest or for protection of objects such as vehicles and flying apparatuses. It is important in all these fields of use that the armorings do not become excessively heavy being of high strength.
U.S. Pat. No. 4,473,653 A discloses armoring having a lithium-aluminosilicate glass ceramic, and its production. It is also known to protect flying apparatuses such as, for example, helicopters by means of borocarbide-containing armorings. In general, use is made for this purpose of a ceramic that contains aluminum oxide (Al2O3), silicon carbide (SiC), borocarbide (B4C) and titanium boride (TiB2). These materials are relatively light, but are also very expensive owing to the complicated production. Armorings made from ceramic composite material are also disclosed in U.S. Pat. No. 5,763,813 A.
In the case of the multiply used ceramic materials for antiballistic armorings, for example armorings against high dynamic impulsive loads such as upon the striking of projectiles, there is the general problem that ceramic still has a certain porosity. The pores can in this case constitute weak points that favor the propagation of cracks upon the striking of a projectile. Particularly in the case of ceramic composite materials, the problem also arises, furthermore, that the ceramic matrix frequently does not perfectly enclose the further phase such as, for example, embedded fibers, since the ceramic material cannot flow upon sintering. Increased porosities can therefore occur precisely with ceramic materials. In addition, many ceramic materials suitable for armorings exhibit high weight. Thus, the density of aluminum oxide ceramic is approximately 4 g/cm3.
It is therefore the object of the invention to provide armoring against high dynamic impulsive loads, for example against bombardment, that is lightweight and exhibits a denser microstructure that is improved as against ceramic composite materials. This object is already defined in a surprisingly simple way by the subject matter of the independent claims. Advantageous refinements and developments of the invention are specified in the respective dependent claims.
The invention consequently provides a preferably plate-shaped armoring or armor against high dynamic impulsive loads that comprises a composite material having at least two phases, the first phase forming a matrix for the second phase, and the first phase being a glass or a glass ceramic, and the second phase being embedded and distributed in the form of particles and/or fibers in the matrix formed by the material of the first phase. Such armoring is produced by mixing fibers and/or particles with pulverulent material that forms glass or glass ceramic, and the mixture is heated such that there is formed from the material that forms glass or glass ceramic a flowable glass or glass-ceramic phase that fills in interspaces between the fibers and/or particles such that after being cooled the fibers and/or particles are embedded and distributed in the solidified glass or glass-ceramic phase.
By contrast with conventional ceramic armorings, this offers the advantage that interspaces between the fibers and/or particles of the at least one further phase of the composite can be substantially more effectively filled in, owing to the flowability of the material forming glass or glass ceramic, than in the case of sintering a ceramic. The inventive process can also be denoted as liquid-phase sintering, since the glass or glass ceramic is at least semifluid during its crystallization. Consequently, dense filling is effected with a low fraction of pores between the fibers and/or particles of the second phase. It is possible in this case to achieve a density of the composite material of above 99% of the theoretical density of a nonporous body with the components used. A substantial advantage of the invention is, furthermore, that with the glass or glass-ceramic composites described the density of the material can nevertheless be kept to below 3.5 g/cm3, even when use is made of steel particles or steel fibers in the glass or glass-ceramic matrix. If particles or fibers other than steel fibers, for example steel particles, are used, the density of the material can be reduced even substantially further. Consequently, the material is superior to many ceramic armorings in view of its low weight.
A better connection of the two phases, that is to say between the fibers/particles and the glass or glass-ceramic matrix, is achieved, in particular, by the denser microstructure. A high fracture toughness against high dynamic mechanical loads such as occurs upon being struck by a projectile is thereby achieved. The common feature of all the developments of the invention described below is, inter alia, that the armor material is built up additively from its individual components.
In order to produce the inventive multiphase armorings, the components are mixed and the mixture is subjected to heat treatment. Specifically, there are many different ways of producing multiphase materials containing glass or glass ceramic. One preferred possibility is to produce the armoring by hot isostatic pressing of the mixture. The pressure exerted on the mixture during hot isostatic pressing assists the flow of the vitreous material. In a development of this embodiment of the invention, a portion of the mixture can be subjected to a dry pressing process. The pressed shaped body can then be finished by hot isostatic pressing in a further fabrication step. Alternatively, it is also possible to produce as preliminary product a preliminary body of the mixture, or a prepreg, and for the preliminary body subsequently to be uniaxially hot pressed.
In each case, a preliminary body can firstly be produced from the mixture by cold isostatic pressing and subsequently be sintered by heating, for example, in a hot isostatic fashion or under uniaxial hot pressing, or else without pressure. In the case of cold isostatic pressing, pressures of at least 500 atmospheres, preferably at least 200 atmospheres, are preferably exerted in the press on the mixture, in order to obtain as dense a microstructure as possible even before the sintering.
As further phases of the composite that are mixed with the material forming glass or glass ceramic in order to produce the armoring, particular consideration is given to the following materials:
carbon fibers, hard fibers, such as fibers made from SiC (silicon carbide), Si3N4 (silicon nitride), Al2O3 (aluminum oxide), ZrO2 (zirconium oxide), boron nitride, and/or mullite as main components, appropriately with admixtures of Si, Ti, Zr, Al, O, C, N, for example fibers of the sialon type (Si, Al, O, N), glass fibers, metal fibers, such as, in particular, steel fibers, metal particles, hard particles, such as, in particular, particles made from the above-named materials of hard fibers. The above-named materials can also be combined with one another with particular advantage.
Carbon fibers and silicon carbide fibers or particles have comparatively low coefficients of thermal expansion. In order to reduce internal stresses in the material between the fibers and/or particles and the surrounding matrix, it is particularly in the case of such materials of the second phase that it is favorable to use a glass or glass-ceramic matrix with a low linear coefficient of thermal expansion, preferably less than 10*10−6/K.
The goal and core of the invention is to set the multiphase nature suitably so as to attain a high fracture toughness and thus, finally, a resistance to bombardment, and/or a high resistance to high dynamic mechanical loads. If metal particles and/or metal fibers are embedded, this is achieved by alternating ductile and brittle components. In the case of fiber-reinforced glasses and glass ceramics, the high fracture toughness against high dynamic loads is achieved by a pull-out effect that absorbs energy strongly. Relevant elementary mechanisms in the composite are, for example, crack deflection, crack branching, crack stoppage and energy dissipation. Additionally, because of the different speeds of sound in the individual materials of the composite material, scattering and dispersion of the shockwave produced during striking occur, and so the shockwave is weakened.
Particularly suitable as particles are metal chips, preferably with dimensions of up to a length of 1 cm. These metal chips can absorb large quantities of kinetic energy by deformation. In the case of fibers as component of the second phase, smaller dimensions are preferred instead of wires. In particular, fibers with diameters of less than 0.2 millimeters can be used. The thin fibers can thus be admixed in a larger number. This is advantageous in order to effect a distribution of the forces in a large number of different directions.
The fibers can be short, long and endless fibers. The fibers can be embedded in ordered or unordered fashion. There are, in turn, various possibilities for ordered fiber arrangements with nonmetallic fibers such as, for example, woven, knitted or nonwoven fabrics. For example, it is possible to use crossply fabrics (0°/90° fabrics) or fabrics with fiber angles of 0°/45°/90°/135°.
Glass ceramics are generally distinguished by high base values of the elasticity module, and are therefore very well suited to armoring against high dynamic impulsive loads. However, it emerges that glass ceramics in crystallized form generally can be sintered only with difficulty, or even no longer, in particular when use is made of the inventive liquid phase sintering process, in the case of which the material forming glass ceramic is intended to be liquid at least for a time.
However, this can be solved in a development of the invention by virtue of the fact that powder of a starting glass for glass ceramic is used as material forming glass ceramic, and a ceramizing of the starting glass takes place during the heating of the mixture. Consequently, in this case the starting glass, which is also denoted as green glass, is firstly formed as the mixture is heated. This green glass can then flow into the interstices between the particles and/or fibers of the second phase before complete ceramization takes place. As the composite material is being produced, the temperature is preferably controlled such that at least partial ceramization of the green glass takes place during heating of the mixture, for example under isostatic or uniaxial pressing.
In the case of glass ceramics as matrix, there is also the idea, in particular, of using glass ceramics other than MAS glass ceramics (magnesium-aluminum-silicate glass ceramics). CaO—Al2O3—SiO2 glass ceramics or MgO—CaO—BaO—Al2O3—SiO2 glass ceramics are material systems suitable for the glass-ceramic matrix as against the above-named MgO—Al2O3—SiO2 glass ceramics (MAS glass ceramics).
A further glass-ceramic class particularly suitable for the invention is represented by Mg—Al-containing glass ceramics which include a spinel phase, preferably MgAl2O4-based spinels. These crystallites are distinguished by a high modulus of elasticity. Because of the crystallites with spinel structure, these glass ceramics surprisingly prove to be particularly stable against high dynamic impulsive loads in conjunction with the incorporated particles and/or fibers.
Glass ceramics such as, for example, cordierite glass ceramics that can be processed to form a very hard composite material with the admixture of hard particles. Zirconium oxide-containing particles are particularly suitable for this glass ceramic. Fibers and/or ductile components such as metal particles are particularly suitable here for the purpose of improving the fracture toughness of the admittedly hard, but also brittle material.
The maximum process temperature when heating the mixture to produce the armor material is preferably selected with the aid of the processing temperature or another suitable characteristic of the temperature-dependent profile of the viscosity of the glass used. This ensures that the glass melt can flow sufficiently well into the interstice between the other components, in particular the particles and/or fibers of the further phase. Here, 800° C. can already suffice as processing temperature for so-called low-Tg glasses (glasses with a low transformation temperature of less than 560° C.). Processing temperatures above 1200° C. are preferred for many other technical glasses. It is preferred to use as processing temperature a temperature in the case of which the viscosity is less than or equal to the Littleton point of ρ=107.6 dPas·s.
Alternatively or in addition to using glass powder for producing the mixture with the fibers and/or particles, it is also possible to use a mixture of the starting materials for a glass or a glass ceramic as material forming glass or glass ceramic, and to mix it with the fibers and/or grains. In this case, the glass is then produced upon heating the mixture to the temperature required for producing the glass. Boron acid-containing glasses such as, in particular, borosilicate glasses, are particularly suitable glasses for producing the inventive armoring, or the matrix thereof, for the incorporated fibers and/or particles. The high thermal shock resistance of borosilicate glass also turns out to be advantageous for resistance to high dynamic loads such as occur upon striking by a projectile. Borosilicate glass powder can be used as glass-forming material in order to produce such armoring. Alternatively or in addition, it is also possible to mix the starting materials for borosilicate glass with the fibers and/or particles such that the borosilicate glass forms from the starting materials upon heating of the mixture. Preferred ranges of composition of such glasses in percent by weight on an oxide basis are 70-80% by weight of SiO2, 7-13% by weight of B2O3, 4-8% by weight of alkalioxides and 2-7% by weight of Al2O3. These glasses, which also include the glasses known under the trade names of “Pyrex” and “Duran”, have a linear coefficient of thermal expansion in the range of 3-5*10 −6/K and a glass transition temperature in the range of 500° C. to 600° C.
It is also possible to use aluminosilicate glasses as matrix. Glasses are preferred here which exhibit the following composition in percent by weight on an oxide basis: 50-55% by weight of SiO2, 8-12% by weight of B2O3, 10-20% by weight of alkaline-earth oxides, and 20-25% by weight of Al2O3.
Furthermore, thought is also being given to the use of alkaline alkaline-earth silicate glass for the glass matrix of the first phase of the armoring. Preferred compositions lie in the range of 74±5% by weight of SiO2, 16±5% by weight of Na2O, 10±5% by weight of CaO. These glasses are particularly favorable in price and, inter alia, also permit the economic production of large area armorings. Again, the linear coefficient of thermal expansion is generally still lower than 10*10−6/K.
Furthermore, it is also possible to use basalt glass or a starting glass for rock wool.
If the projectile strikes the armoring, its kinetic energy is dissipated as it penetrates into the armor material. The effect of the armoring can therefore be improved by having its microstructure change in a direction along the direction from which the projectile strikes, that is to say generally in a direction perpendicular to the exposed side of the armoring. In particular, it is also advantageously possible for the density, composition or size of the fibers and/or particles to change along this direction. In this case, it is a varying particle and/or fiber density that is understood by a varying density. Thus, the armoring can be of plate-shaped design, the fibers or particles being arranged with density varying perpendicular to a lateral surface of the plate-shaped armoring.
A preferred volume fraction of the second phase, that is to say the volume fraction of the fibers and/or particles incorporated in the matrix, is in the range from 10 to 70% by volume.
An inventive armoring against high dynamic impulsive loads is particularly suitable for use in a personal protection device, in particular for armored garments such as armored vests, and for armoring of vehicles and flying apparatuses. A desire for low weight is common to these applications. In particular, the lightweight, but very expensive boron carbide-containing ceramic armorings can be replaced by the invention.
Furthermore, it is also possible for a number of different inventive composite materials having a glass or glass-ceramic matrix and preferably fibers and/or particles distributed in both materials to be arranged on one another in order to produce a particularly effective composite. For example, two inventive plate-shaped composite materials can be placed on one another. This can be done directly or with the aid of an intermediate material.
Virtually any desired shapes of the composite material can be produced by means of the inventive production method by means of liquid phase sintering of a mixture having a material, forming glass or glass ceramic, and fibers and/or particles.
A particular synergy effect can be produced if use is made of metal fibers and/or particles as component of the second phase. Because of their ductility, metal components not only act strongly to absorb energy, but can accelerate the production method. In this case, specifically, the mixture with the pulverulent material, which forms a glass or glass-ceramic matrix, can be heated inductively, the metal fibers and/or particles being heated by the electromagnetic field of the induction heating, and outputting the heat to the surrounding material. Since the energy is in this way input directly into the volume of the mixture, the heating can be carried out very quickly and, moreover, very homogeneously.
The invention is explained in more detail below with the aid of exemplary embodiments and with reference to the attached drawings, in which the same reference numerals refer to the same or similar parts, and in which:
As shown in
As illustrated in
The admixture of the metal particles 7 in this case enables heating to be done inductively by means of an induction coil 19 surrounding the compression mold. The electromagnetic alternating field heats the metal particles 7 directly by currents induced in the particles. The metal particles output their heat to the surrounding material such that a quick temperature compensation and homogeneous heating are achieved. Irrespective of the compression method, it is generally preferred to make use for the inductive heating of high or medium frequency currents to excite the induction coil 19 with frequencies in the range of 5 to 500 kHz.
The resulting plate-shaped composite material 2 of armoring 1 is illustrated in
The glass or glass-ceramic matrix 20 is very hard, but also brittle. The hardness of the material is further raised locally by the incorporated hard particles. These particles have a destructive effect on a striking projectile. In addition, because of their ductility, the metal particles 7 act to absorb energy and distribute the forces transferred from the projectile onto the material. Finally, the fibers 9 raise the fracture toughness with reference to the high dynamic impact loads upon the striking of the projectile.
A variant of the example shown in
Rather, the fibers 9 and/or particles 5, 7 exhibit a density varying in a direction perpendicular to an exposed side of the armoring. The exposed side, that is to say the surface which points outward in the case of the armoring and on which a projectile then strikes in the case of a bombardment, can, for example, be the side 21 in the case of the armoring 1 shown in
In addition, owing to the different density of the matrix 20 and the particles 5, 7, the ensuing shockwave is dispersed at the particles such that the shockwave strikes the rear side 22 with reduced intensity. The fibers 9, which are embedded on the rear side with a higher particle density, raise the fracture toughness there and enable the ensuing tensile loads along the rear side to be absorbed. This prevents the composite material from tearing into pieces, something which would lead to passage of the projectile.
Yet another development is illustrated in
Glass or glass-ceramic plates are otherwise generally produced by rolling, in the case of a glass ceramic by rolling a green glass plate that is subsequently ceramized. Plate-shaped bodies with flat surfaces are thereby obtained.
The textile material 37 of the vest 35 serves as substrate for plates of the composite material 2 that can, for example, be sewn in between two textile plies. The sewed-in plates, not visible from outside, of the composite material are illustrated as dashed lines in
It is evident to the person skilled in the art that the invention is not restricted to the above-described exemplary embodiments. In particular, the individual features of the exemplary embodiments can also be combined with one another in a variety of ways.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 056 209.7 | Nov 2006 | DE | national |
