Patent Application
20100319523
This invention relates to the ceramic armor component field.
Ceramic armor is typically used for body armor and for the protection of different types of vehicles, such as various types of land vehicles, ships, and aircraft.
Usually, a ceramic armor is made of a ceramic tile and composite material as backing. Typically, ceramic tiles are adhesively secured to a substrate then encapsulated in an outer cover. These substrate and cover represent the backing composite material.
The ceramic armor system is then attached to a vehicle by a variety of means or merely placed in a fabric pocket, as in the case of body armor.
The function of the ceramic layer is to break the bullets while the function of the composite backing is to hold the ceramic in places during the impact and to catch the fragments produced during the impact and dissipate their mechanical energy by a plastic deformation.
A very important characteristic of ceramic component armors is their ability to defeat multiple shots within a relatively small area. The challenge in developing multi-hit ceramic composite armor is to control the damage of the armor structure after the impact in its proximity. While metal armor have inherently this characteristic, that is related to the metal ductility and ability to withstand plastic deformation, in ceramic armor components it must be addressed by an appropriate design of the armor components.
The damage produced in ceramic hard face components by projectile impact can be classified into (1) a comminution zone of highly pulverized material in the shape of a conoid under the incident projectile footprint,
(2) radial and circumferential cracks,
(3) spalling, through the thickness and lateral directions by reflected tensile pulses, and
(4) impact from comminuted fragments.
Crack propagation is arrested at the boundaries of an impacted tile if the web between the tiles in the tile array is properly designed. However, stress wave propagation can occur through the web and into the adjacent tiles and can still damage the adjacent tiles.
As far as the ceramic layer is considered, the most common approach to increase the multihit capability of a ceramic composite armor is the use of ceramic tiles mosaics. The physical separation between the tiles in the mosaic constitute a barrier to the propagation of the ceramic damage that occur during the impact. In this way the area of the ceramic strike face damaged by an impact is limited to the size of tile, or maximum to a portion of two if the impact occurs across the junction.
From the industrial point of view the drawback of this approach is the increased complexity introduced in the composite manufacturing. During the bonding of the tiles a great care must be used to avoid that an excessive gap between the tiles is introduced. While a minimum gap (0.1-0.3 mm) may be beneficial, an excessive one (0.5 mm or greater) constitute a week point of the ceramic armor to be absolutely avoided.
For the above mentioned reasons the lay-up of mosaic in the construction of composite armor on industrial scale is the most labor intensive production phase. Usually tiles are aligned manually by trained personnel. The increasing multi-hit requirements are forcing armor designer to adopt more and more mosaics based on to small ceramic, like tiles 20 mm×20 mm or 30 mm×30 mm. Using such small tiles the number of components per square meter increase very rapidly to more than 1000-2000 units.
An additional drawback of ceramic components armor based on mosaics is how to guarantee that in the finished armor every gap between the tiles in below the maximum allowed (usually 0.3/4 mm). The only possibility is to X-ray all the panel to measure the gap between the tiles. This is a significant expensive measurement.
In order to overcome the above said difficulties, it has been thought to use larger tiles with some discontinuities in their structure. These slots can involve the whole tiles thickness or only part of it and function as breaking barrier to the crack propagation during the impact phase.
In the patent requests EP 1 878 933, WO 2005114089 and GB 2377006 are described different applications of the above said solution.
Unfortunately, this finding did not reveal itself as completely satisfying since it implicates serious manufacturing problems. In fact, ceramic tiles are not easily cut because of their typical hardness.
This is the reason why in literature reference is always made to ceramic carbides the mechanical manufacturing necessity or to the complex forming processes and always regarding ceramic carbides.
Since market constantly requires strong, low-cost and easily realized armors with high multi-hit properties, it is evident the need to develop ceramic monolithic tiles that do not involve a complex mosaic structure, capable of overcoming the manufacturing problems relevant to the realization to the slots described before.
Description of ceramic monolithic tiles for composed armor, cut-out and/or through thickness channels.
It has been surprisingly noted that ceramic tiles with penetrating cylindrical channels distributed in various ways, are extremely suitable for manufacturing ceramic armors, avoiding the before mentioned production drawbacks, and offer unexpected advantages in comparison with the analogous tiles with slots, as described here below.
As appears from
Tiles can have smooth and continuous borders or they can present (12) cavities represented by part of the channels (11) (preferably an half of total number as shown in
Channels can be simple holes or hollow tubes placed in the body of the tile, constituting an open channel on both opposite surfaces.
Channels can have circular or polygonal section (for example, square, hexagonal, triangular, pentagonal) and can be perpendicularly disposed or inclined across the tiles surfaces.
Preferably, channels internal dimensions should be between 0.5 and 5 mm. In addition, if necessary, channels could have a rectangular (FIG. 1-a), conic or biconic inner section, or be tapered off at one or the other or both ends (
The presence of channels according to this invention considerably increase the multi-hit resistance, because shock waves propagation through the tile is stopped thanks to these diffraction lines inside the material itself.
One of the most common causes of the collapse of ceramic components is the propagation of shock waves created by the impact of projectile against the armor. It is known in literature that the attenuation of the shock waves inside the ceramic parts considerably improves the ceramic armor ballistic performance. Such mitigation is usually obtained by introducing longitudinal discontinuities (U.S. Pat. No. 4,704,943 and US20090136702). While, in this invention discontinuities involve the whole thickness of tiles uniformly distributed on the surface. This characteristic sensibly increase the above said mitigation power.
In addition, the internal volume of the channels could be streamlined with materials that have an acoustic impendence, as for example alumina, zirconia, boron carbide or silicon carbide, silicon nitride, silica or mixture thereof, metals as copper, iron, steel and wolfram, different from the ceramic one, such as plastic materials (low acoustic impendence) or metallic/ceramic materials (high acoustic impendence). In so doing, it is possible to modulate the mitigation power of the shock waves according to the different threats to be arrested. In fact, because of their different impact velocity, they create wave trains different for frequency and intensity.
A further advantage of this invention is the weight reduction obtained by the presence of channels. This characteristic is very important because ballistic armors always represent a parasitic weight.
This invention involves tiles commonly made of ceramic materials such as: aluminum oxide, boron carbide, silicon carbide, glass ceramic materials, titanium diboride, or their mixtures and other similar products. They are manufactured following well known processes (using moulds or by extrusion).
In the same way, the channels related to this invention are easily realized, by extrusion or by cold pressing using moulds with punch matrixes. These are the most common forming techniques used for mass production.
Possible streamline can be easily conducted during the manufacturing process of the ballistic panel or as an intermediate phase after the ceramic tile production. While filling of channels can be made successively, after the monolithic tile production and can obtained by fusion of plastic, metal or vitreous materials.
In case of ceramic materials, channels can be filled with powder that are sintered with an additional thermal treatment.
A further producing system consists of the co-shaping of two ceramic powders or a ceramic and metal one. Recently, systems of co-injection of different ceramic materials have been set up, in order to obtain composite ceramic products.
Again, another manufacturing system consists of the filling of a mould with two powders, that are the matrix and the channels, with the second one placed upright resembling channels shape. Multiple components proportioning systems are well known and used in many technical ceramics applications.
It is important to note that tiles with channels are sensibly more homogeneous compared to the tiles with slots described in the state of the art. In fact, channels create 2-10 mm discontinuities (channels diameter 1 mm, at a distance of 2 mm from each other) while slots create discontinuities of 20-50 mm. A higher discontinuity density heightens the effects and improves the capacity of arresting of the fracture propagation.
The presence of channels permits the mechanical connection of the two parts of the ballistic inserts making the whole structure more strong and firm. While, there is no possibility to reach this purpose with tiles with slots, because such slots should not have a diameter of more than 0.5 mm.
The high discontinuity density enhances the multi-hit power, in fact near to the impact point there will always be conjunction points between the two parts of the composite panel (front and rear). This increases the ceramic confinement. It is well known in literature that the ceramic confinement improves the multi-hit characteristics.
The ceramic fragments produced in the impact will be better hold together and confined thanks to the high density of the connections.
Channels can be distributed in the ceramic body of the tiles in a casual way or according to repeated geometric drawings, such as: parallel lines equidistant or at different distances from each other. Channels can be disposed in squares, hexagons, star-like shape etc. as schematically shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| FI2009A000130 | Jun 2009 | IT | national |
