WO2012063271A2

WO2012063271A2 - Antiballistic element

Info

Publication number: WO2012063271A2
Application number: PCT/IT2010/000449
Authority: WO
Inventors: Massimiliano Valle
Original assignee: Petroceramics S.P.A.
Priority date: 2010-11-10
Filing date: 2010-11-10
Publication date: 2012-05-18
Also published as: EP2638354A2; WO2012063271A3

Abstract

It is illustrated an antiballistic element (1) comprising: a fragmented outer layer (2) comprising at least one antiballistic material of the ceramic type; a continuous inner layer (3) comprising at least one carbo-ceramic material reinforced with fibres; in which the fragmented outer layer (2) and the continuous inner layer (3) are integral and in which the fragmentation of the outer layer (2) is obtained by thermal cracking.

Description

DESCRIPTION

"Antiballistic element"

The present invention relates to an antiballistic element, a process for the manufacture thereof and an article comprising such an antiballistic element.

In particular, the present invention relates to an antiballistic element for protecting people or objects, capable of withstanding multi-hit attacks.

It is known to use ceramic materials to produce antiballistic devices or garments, i.e. which are capable of withstanding a mechanical load that acts in a punctiform manner.

Such materials are able to absorb large amounts of energy and, at the same time, have a low specific weight with respect to the metallic materials used previously, with obvious advantages.

However, even a ceramic material with good properties of absorbing a single-hit attack, i.e. the hit of a projectile or a different punctiform hit, is damaged after the first hit.

This causes substantial problems since, in the great majority of cases, attacks are multi-hit attacks . Therefore,^' it is necessary for antiballistic materials to withstand multi-hit attacks, i.e. 'consecutive and close one to the other hits caused by a series of projectiles.

In order to avoid this problem, ceramic materials formed from a plurality of small-sized units have been disclosed. In this way, when the first projectile hits the material, it damages only the unit hit thereby since the fracture generated by such a projectile in such a unit finds it difficult to propagate to the adjacent units. Therefore, the material has greater resistance to multi-hit attacks.

Materials of this type are known for example from WO 91/07632, US 6,532,857.

However, such known materials, in order to reach the desired efficiency, have a high weight per unit surface, with obvious transportation and mounting drawbacks .

A further drawback of such known materials is related to their manufacture process. As a matter of fact, in order to manufacture a material comprising a plurality of units it is necessary to produce a plurality of units and to assemble them accurately with manufacture processes that result time-consuming and expensive. An alternative process provides the production of a continuous material that, in a subsequent step, is machined so as to form a plurality of units therefrom. However, also this solution is time-consuming and complex.

Patent EP 1536199 discloses an antiballistic material comprising a continuous surface arranged on the side that faces the attack and a segmented surface arranged on the opposite side.

In such a material, being the continuous surface the first surface hit by the projectile, it is damaged after the first attack. Therefore, although the projectile subsequently hits the , segmented surface, the material is in any case compromised after the first attack.

The object of the present invention is therefore to provide an antiballistic element that is effective from the point of view of resistance to multi-hit attacks, light, not bulky and inexpensive.

A further object of the present invention is to provide a process for manufacturing an antiballistic element that is simple, cost-effective and that achieves the manufacture of an element that is effective from a ballistic point of view.

These and other objects are achieved by means of an antiballist^'ic element comprising:

a fragmented outer layer comprising at least one antiballistic material of the ceramic type;

a continuous inner layer comprising at least one carbo-ceramic material reinforced with fibres ;

in which the fragmented outer layer and the continuous inner layer are integral and in which the fragmentation of the outer layer is obtained by thermal cracking.

In the present context, the terms "outer" and "inner" refer to the assembled element, i.e. to the element once it has been mounted on an article. Therefore, the outer layer indicates the outer layer with respect to the article and the inner layer indicates the inner layer with respect to the article .

■ In other words, the outer layer is the one hit first, whereas the inner layer is hit afterwards, i.e. it receives the residual impact.

- In the present context by "fragmented layer" it is meant a layer comprising a plurality of units, of regular or irregular shape, having the same or different dimensions as one another. Said units^' are delimited by fractures caused by thermal cracking that extend substantially over the entire thickness of the layer. Of course, it is possible to provide also less deep fractures, i.e. fractures that extend partially into the thickness of the layer. These help in achieving the final object.

In the present context the term "integral", used with reference to the two layers, indicates that such layers are . joined to form a single piece.

Thanks to the presence of a fragmented outer layer it is possible to obtain a material that withstands multi-hit attacks. As a matter of fact, the first projectile damages a single unit and does not propagate to the adjacent units, for which reason the antiballistic element is not entirely damaged after the first attack.

The presence of an outer layer made from ceramic material and an inner layer made from carbo-ceramic material reinforced with fibres, achieves an element with excellent properties of resistance to impacts and with low weight per unit surface.

Thanks to the fragmentation obtained by thermal cracking it is possible to obtain such an element with a rapid, simple and cost-effective manufacturing process. In accordance with a preferred embodiment of the invention, the interface surface between the fragmented outer layer and the continuous inner layer has concavities and/or convexities.

In other words, the interface between the two layers is not flat. This means that the impact wave that propagates in the material following an attack goes back weakened, for which reason the decompression due to the return of the wave, which often causes the break of the material, is reduced.

Advantageously, said antiballistic material of the ceramic type has_, a density of between 2.3 and 6.5 g/cm³, preferably between 2.3 and 3.3 g/cm³ and said carbo-ceramic material reinforced with fibres has a density of between 1.8 and 2.5 g/cm³, preferably between 2.1 and 2.4 g/cm³.

In this way it is possible to obtain low-weight antiballistic elements.

Preferably, the fibres of said fibre-reinforced carbo-ceramic material are pre-oriented fibres. In this way it is possible to optimise the properties of the material achieving properties of tensile strength along a specific direction.

Even more preferably, such fibres can be woven fibres or else short fibres pre-oriented in the plane in a known way^'.

Advantageously, the fragmented outer layer has a thickness of between 3.8 and 25 mm, more preferably between 4 and 10 mm and the continuous inner layer has a thickness of between 3.8 and 25 mm, more preferably between 4 and 10 mm. In this way it is possible to obtain an antiballistic element with an optimal strength/thickness ratio.

In accordance with preferred embodiments, the fragmented outer layer has a plurality of units, each delimited by one or more fractures caused by thermal cracking. The surface of each of such units is between 0.5 and 25 cm² and more preferably between 1 and 10 cm².

In accordance with a second aspect thereof, the invention concerns an article comprising such an antiballistic element, which achieves the same advantages, i.e. high resistance to multi-hit attacks, low weight, low manufacture costs.

In accordance ^' with a third aspect thereof, the invention concerns a process for manufacturing an antiballistic element comprising the following steps: a. providing components of an outer layer, among which at least one antiballistic material of the ceramic type, and components of an inner layer, among which at least one carbo-ceramic material reinforced with fibres;

b. shaping and moulding the outer layer and the inner layer;

c. assembling the inner layer with the outer layer so as to form an assembled element;

d. pyrolysis of the assembled element;

e. infiltration of the pyrolysed element;

f. cooling of the infiltrated element so as to obtain the fragmentation of the outer layer by thermal cracking.

Such a process allows to solve the aforementioned problems related to the assembly or to the formation of a plurality of units.

Therefore, it allows obtaining a simple, rapid and low-cost manufacturing process that achieves the manufacture of an effective antiballistic element with low weight per unit surface.

In order to better understand the invention and appreciate its advantages, hereafter a description of some non-limiting example embodiments of the antiballistic element and of the process of the invention will be provided, with reference to the attached figures, in which:

figure 1 is a cross section view of an antiballistic element according to a first embodiment of the invention;

figure 2 is a cross section view of an antiballistic element according to a second embodiment of the invention;

figure 3 is a ^" cross section view of an antiballistic element according to a third embodiment of the invention;

figure 4 is a cross section view of an antiballistic element according to a fourth embodiment of the invention;

figure 5 is a cross section view of an antiballistic element according to a fifth embodiment obtained through a preferred embodiment of the manufacturing process of the invention; and

figure 6 shows a perspective view of an antiballistic element according to the invention, after it has been hit by a projectile .

With reference to figures 1-5, an antiballistic element according to the present invention is wholly indicated with reference number 1.

The antiballistic element 1 substantially forms the rejecting portion of an antiballistic module. The latter generally comprises a rejecting portion, an absorbing portion and a filling portion.

Although ^' the antiballistic element 1 constitutes the rejecting portion, it also helps the absorbing and containment functions .

The antiballistic element 1 according to the invention comprises a fragmented outer layer 2 that in turn comprises at least one antiballistic material of the ceramic type.

The fragmented outer layer 2 has a plurality of units 5, each delimited by one or more fractures caused by thermal cracking. The dimensions of each of said units 5 are comprised between 0.5 and 25 cm and preferably between 1 and 10 cm².

The partial fractures, i.e. those having a lower depth than the depth of the outer layer 2, although helping in making the antiballistic element 1 effective, are not considered fractures in the meaning given thereto in the present context.

The fragmented outer layer 2 performs the function of withstanding the impact of the projectile and of preventing the breaking caused by the projectile from propagating from one unit 5 to the adjacent units 5.

The antiballistic material of the ceramic type may be of any known type.

Examples of antiballistic ceramic materials are: aluminium oxide, zirconium oxide, boron carbide, silicon nitride, silicon carbide, infiltrated silicon carbides, infiltrated boron carbides.

According to the present invention, the antiballistic material of the ceramic type preferably has a density of between 2.3 and 6.5 g/cm³, more preferably between 2.3 and 3.3 g/cm³.

According to preferred embodiments of the invention, such an antiballistic material of the ceramic type comprises infiltrated silicon carbide and/or infiltrated boron carbide.

More preferably it comprises silicon carbide and/or boron carbide infiltrated with metallic silicon or silicon carbide and/or boron carbide infiltrated with silicon and aluminium or silicon carbide and/or boron carbide infiltrated with silicon and iron or silicon carbide and/or boron carbide infiltrated with silicon and copper.

In the case in which the antiballistic material of the ceramic type comprises silicon carbide infiltrated with -metallic silicon, it has a density of between 2.90 and 3.15 g/cm³.

In the case in which the antiballistic material of the ceramic type comprises silicon carbide infiltrated with silicon and aluminium or else silicon carbide infiltrated with silicon and copper, its density is comprised between 2.90 and 3.5 g/cm³.

In the case in which the antiballistic material of the ceramic type comprises boron carbide infiltrated with metallic silicon, its density is comprised between 2.4 and 2.8 g/cm³.

In such cases, the antiballistic material of the ceramic type has a hardness of between 20 and 40 GPa measured according to the Vickers scale (HV 500g) , a modulus of rupture (MOR) of between 220 and 330 MPa, and a modulus of elasticity (MOE) of between 180 and 280 GPa.

The antiballistic element 1 according to the present invention also comprises a continuous inner layer 3, i.e. not having discontinuities, i.e. substantially monolithic. The inner layer 3 comprises at least one carbo-ceramic material reinforced with fibres .

Said inner layer 3 has the function of absorbing the residual energy of the impact caused by the projectile on the outer layer 2. Therefore, as stated earlier, the antiballistic element 1, although performing the function of a rejecting portion of an antiballistic ^'module, also helps the function of an absorbing portion.

The fibre-reinforced carbo-ceramic material may be of any known type.

Generally, fibre-reinforced carbo-ceramic materials are obtained by:

carbonising a mixture comprising resin, in liquid or powder form, graphite, preferably in powder, and filaments or bundles of filaments of carbon fibres;

densifying the resulting porous structure with silicon infiltration, thus obtaining a structure or matrix comprising carbon, silicon and silicon carbide.

Examples of carbo-ceramic materials reinforced with fibres of the known type are: silicon carbide reinforced with fibres of the same material, silicon carbide reinforced with carbon fibres.

The fibre-reinforced carbo-ceramic material, according to preferred embodiments of the invention, comprises woven fibres, or short fibres, mixed with carbon powders, silicon powders, silicon carbide powders and/or with liquid or powdered binders, such as phenolic or epoxy resins. Such components forming the fibre-reinforced carbo-ceramic material are processed according to the prior art, for which reason they will not be described any further.

Preferably, the carbo-ceramic material reinforced with fibres has a density of between 1.8 and 2.5 g/cm³, a modulus of rupture ( OR) of between 40 and 120 MPa and a modulus of elasticity (MOE) of between 15 and _.50 GPa.

More preferably, it has a density of between 2.3 and 2.4 g/cm³, a modulus of rupture (MOR) of between 50 and 70 MPa and a modulus of elasticity (MOE) of between 20 and 35 GPa.

Alternatively, it has a density of between .2.1 and 2.3 g/cm³, a modulus of rupture (MOR) of between 75 and 110 MPa and a modulus of elasticity (MOE) of between 25 and 40 GPa.

Preferably, the fibres of said carbo-ceramic material reinforced with fibres are pre-oriented fibres .

According to the present invention, the fragmented outer layer 2 and the continuous inner layer 3 are integral, i.e., at the end of the manufacturing process of the antiballistic element 1, they are joined. to form a single piece.

In particular, an entire surface of the outer layer 2 is joined with an entire surface of the inner layer 3, so as^' to form a single piece.

Such joining surfaces form the interface surface 4 between the outer layer 2 and the inner layer 3.

According to the first two embodiments of the present invention, respectively shown in figures 1 and 2, said interface surface 4 is a substantially flat surface, for which reason its cross section is a straight line.

In accordance with the third, fourth and fifth embodiment, respectively shown in figures 3, 4 and 5, said interface surface 4 has concavities and/or convexities .

In particular, in the third and fourth embodiments, shown in figures 3 and 4, said interface surface 4 has a cross section substantially of the broken line type. On the other hand, in the fifth embodiment, shown in figure 5, said interface surface 4, has a cross section substantially of the curved line type.

As shown hereafter, it is possible to give the interface- 4 the desired geometry, by suitably varying the steps of the manufacturing process. .

According to the present invention, the fragmentation of- the outer layer 2 is obtained by thermal cracking, as we will see hereafter. In accordance with preferred embodiments, said fragmented outer layer 2 has a thickness of between 3.8 and 25 mm, more preferably between 4 and 10 mm and said continuous inner layer 3 has a thickness of between 3.8 and 25 mm, more preferably between 4 and 10 mm.

Analogously, it is possible to obtain the desired thicknesses, by suitably varying the conditions in which the steps of the manufacturing process of the antiballistic element 1 are carried out .

The present invention also concerns an article comprising at least one antiballistic element 1 as previously described.

Said article may be an item of clothing, or a vehicle or another article aimed at protecting people or objects.

Said article may be made through assembly of the antiballistic element 1 in a known way. For example, the antiballistic element 1 may be associated with a containing portion made from kevlar fibres and with an absorbing portion comprising resins to form an antiballistic module that is mounted on the final article.

Alternatively, it is possible to associate many antiballistic elements 1, assembling them one on top of the other, so as to obtain an antiballistic module in which an outer layer 2 and inner layer 3 repeatedly alternate.

A process for manufacturing an antiballistic element 1, according to the present invention will now be described.

In accordance with a first step a, components of an outer layer 2, among which at least one antiballistic material of the ceramic type, and components of an inner layer 3, among which at least one carbo-ceramic material reinforced with fibres, are provided.

Subsequently a step b of shaping and moulding the outer layer 2 and the inner layer 3 is carried out. Said step may be carried out in different ways.

In accordance with a first embodiment of the process of the invention, step b comprises two independent shaping and moulding steps, one for each layer. In this way it is possible to optimise the shaping and moulding conditions based on the specific requirements of each layer.

In such a case, after step b a step c of assembling the . inner layer 3 with the outer layer 2 is carried out, so as to form an assembled element. It may be carried out through simple juxtaposition of the two layers, or by juxtaposition and gluing of the two layers.

The binder can be a ceramic slurry, or other type of glue suitable for such a use.

Alternatively, said step c may be carried out through gluing of a containment receptacle onto one of the two layers, preferably onto the inner layer 3, and subsequent insertion of the other layer into said rec^'eptacle .

Alternatively, it is possible to provide that in shaping and moulding step b , one of the two layers is provided with a containment receptacle and, in the subsequent step c the other layer is inserted into said containment receptacle.

In accordance with . a second embodiment of the invention, step b comprises a step bl of shaping and moulding the outer layer 2 or the inner layer 3 and a subsequent step b2 of shaping and moulding the layer not yet moulded onto the layer already moulded.

In other words, the outer layer 2 is moulded, preferably through hot mould pressing with phenolic or epoxy resin, and then the inner layer 3 is moulded directly onto the moulded outer layer 2, preferably- through the same technology. Otherwise/ the inner layer 3 is moulded, preferably through hot mould pressing with phenolic or epoxy resin, and then the outer layer 2 is moulded directly onto the moulded inner layer 3, preferably through the same technology.

Alternatively, step bl comprises moulding the inner layer 3 and step b2 comprises pouring a slurry, or other suitable binder, of an antiballistic material of the ceramic type onto the moulded inner layer 3.

In this case, it is possible to provide that step bl comprises moulding an inner layer 3 provided with containment receptacles for receiving the slurry of an antiballistic material of the ceramic type in the subsequent step b2.

By using said manufacturing processes it is possible to obtain the antiballistic elements 1 shown in figures 1 and 2.

As described above, the antiballistic material of the ceramic type may be of any known type, but preferably it comprises infiltrated silicon carbide and/or infiltrated boron carbide and it preferably has a density of between 2.3 and 3.3 g/cm³.

Preferred examples of fibre-reinforced carbo- ceramic materials are: silicon carbide reinforced with fibres of the same material, silicon carbide reinforced with carbon fibres. They preferably have a density of between 2 and 2.5 g/cm³.

By varying the thickness of the layers it is possible to obtain antiballistic elements 1 with different properties and _. therefore to adapt the antiballistic element 1 to the specific use for which it is intended.

In particular, by increasing the thickness of the outer layer 2, it is possible to obtain an antiballistic element 1 that is hard, with high mechanical strength and low number of units 5. On the other hand, by increasing the thickness of the inner layer 3, it is possible to obtain an antiballistic element 1 that is light and has a large number of units 5.

According to a particularly preferred embodiment of the invention, it is possible to provide, between step bl and step b2, a step of shaping the surface of the moulded layer. Such a step has the function of obtaining a desired geometry of the interface surface 4 between outer layer 2 and inner layer 3.

Preferably, said shaping step comprises forming concavities and/or convexities on interface surface 4, or in any case a non-flat interface surface 4, so as to weaken the return impact wave.

By using such a manufacturing process it is possible to obtain the antiballistic elements 1 shown in figures 3 and 4.

In accordance with a third embodiment of the invention, shaping and moulding step b comprises the simultaneous co-moulding of the inner layer 3 with the outer layer 2 in a single mould.

By carrying out such a process, the antiballistic element 1 shown in figure 5 is obtained.

In the case of co-moulding, step b is preferably preceded by a step of distributing the materials inside the mould so as to obtain, in the subsequent step b, an interface surface 4 between the outer layer 2 and the inner layer 3 with a desired geometry.

In other words, by suitably distributing the first material, preferably in powder form, of the two materials that will form the outer layer 2 and the inner layer 3, it is possible to obtain different geometries of the interface surface 4 and thus different properties of the antiballistic element 1.

In this way it is possible to obtain antiballistic elements 1 in which the development Of the section of the interface surface 4 is similar to the developments shown in figures 3 and 4.

In the second embodiment of the invention, i.e. in the embodiment that comprises carrying out the two consecutive steps bl and b2, and in the third embodiment of the invention, i.e. in the embodiment that comprises the co-moulding, assembly step c results to be carried out during shaping and moulding step b.

After the shaping and moulding step b, once an assembled element has been obtained through step c, consecutive to or simultaneous with step b, a step d of pyrolysis of the assembled element is carried out.

It is carried out at a temperature preferably between 600°C and 1300°C.

In accordance with preferred embodiments, pyrolysis step d is carried out in a furnace with inert atmosphere.

It is particularly preferred for the pyrolysis to be carried out in nitrogen at about 900°C, or other temperature suitable for decomposing the resins used as binders.

The process of the invention then comprises a step e of infiltration, i.e. of insertion of a binding material between the two layers.

It is preferably carried out with metallic silicon or with metallic silicon and aluminium or with metallic silicon and copper.

During such a step the two assembled layers become integral by brazing. In other words, the infiltrated metallic silicon acts as a link between the two layers.

According to a preferred embodiment, said infiltration step is carried out evenly, i.e. the material is infiltrated in an even and not localised manner.

In this case, an antiballistic element 1 is obtained having a gradual variation of the concentration of boron carbide along the thickness of the outer layer 2. In particular, the concentration of boron carbide in the outer layer 2 decreases as the interface surface 4 is approached.

An outer layer 2 is obtained with a substantially absent concentration of boron carbide at the interface surface 4, which increases moving towards the opposite surface.

This gradual variation of concentration of boron carbide is obtained by allowing the boron carbide of the outer layer 2 near to the interface surface 4 to react with the infiltration metallic silicon, evenly distributed over, the entire surface. The step of infiltration with metallic silicon is carried out in a suitable furnace at a temperature of between 1400°C and 2300°C and at a pressure comprised between deep vacuum and 800 mbar.

Since it is a known process, the infiltration process will not be described any further.

According to the present invention, the process for manufacturing an antiballistic element 1 comprises carrying out a cooling step f.

It has the purpose of causing a fragmentation of the outer layer 2 by thermal cracking, i.e. exploiting the different thermal expansion coefficients a of the two materials that forms respectively the outer layer 2 and the inner layer 3.

In other words, the outer layer 2, having a higher thermal expansion coefficient a than the thermal expansion coefficient a of the inner layer 3, contracts more. Therefore, the lesser contraction of the inner layer 3 leads to a deformation of the element 1 that results in . the fragmentation of the outer layer 2.

This results in the formation of a plurality of units 5, each delimited by one or more fractures.

Step f is carried out at a temperature that depends on the characteristics of the materials used, however it is preferably carried out at a temperature of between 600°C and 1400°C.

The number of fractures generated in said step f, and therefore the number of units 5 and the dimensions of each unit 5, depends on the thicknesses of the two layers and on the difference between the thermal expansion coefficients a of the materials used, as will be seen more clearly in the following examples .

It is therefore possible to control the fragmentation of the outer layer 2 and therefore the properties of the antiballistic element 1 that it forms .

The cooling step f is then followed by a step g of removing possible excess silicon through pressurised sand.

EXAMPLES

EXAMPLE 1

An outer layer 2 made from silicon carbide having

—6 ^—1 a thermal expansion coefficient a equal to 3x10 K and dimensions equal to 90x90x4mm was moulded. Afterwards, over said outer layer 2, a shaped plate of fibre-reinforced carbo-ceramic material forming the inner layer 3, having a thermal expansion coefficient a equal to 1.5xl0^"6K^_1 and dimensions of 90x90x7mm was ^'moulded. The thus obtained element was subjected to pyrolysis in nitrogen atmosphere at about 900°C for 120 minutes. The pyrolysed element was subjected to infiltration with metallic silicon at 1550° in vacuum furnace for 90 minutes. The element was cooled to room temperature.

The outer layer 2 fragmented by thermal cracking thus leading to the formation of about 50-80 units 5, each having a surface of between 0.5 and 2 cm².

EXAMPLE 2

An outer layer 2 made from silicon carbide having a thermal expansion coefficient a equal to 3xlO^"6K^_1 and dimensions equal to 90x90x7mm was moulded. Subsequently, over said outer layer 2, a shaped plate of fibre-reinforced carbo-ceramic material forming the inner layer 3, having a thermal expansion coefficient a equal to 1.5χ10^~6Κ^-1 and dimensions of 90x90x4mm was moulded. The thus obtained element was subjected to the same conditions as example 1.

The outer layer 2 was fragmented by thermal cracking thus leading to the formation of about 25-50 units 5, each having a surface of between 1 and 5 cm².

By firing a projectile with an energy of 4000 J at 920 m/s at the thus obtained antiballistic element 1, the antiballistic element 1 shown in figure 6 is obtained.

From such a figure 6 it can be seen that the antiballistic element 1 is not entirely damaged by the first impact, but only locally.

The antiballistic element 1 therefore achieves to contain the damage due to the first impact in a small area of the antiballistic element 1 itself.

This demonstrates how such an antiballistic element 1 allows to make antiballistic modules suitable for withstanding multi-hit attacks. As a matter of fact, the impact following the first hits intact portions of the antiballistic element 1.

EXAMPLE 3

An outer layer 2 made from zirconia having a thermal expansion coefficient a equal to 6xlO^~6K^_1 and dimensions equal to 90x90x7mm was moulded. Subsequently, over said outer layer 2, a shaped plate of fibre-reinforced carbo-ceramic material forming the inner layer 3, having a thermal expansion coefficient a equal to 1.5xlO^"6K^_1 and dimensions ..of 90x90x4mm was moulded. The thus obtained element was subjected to the same conditions as example 1.

The outer layer 2 was fragmented by thermal cracking thus leading to the formation of about 40-60 units 5, each having a surface of between 1 and 3 cm².

CONCLUSIONS

Comparing example 1 with example 2, it can be seen how by increasing the thickness of the outer layer 2 and decreasing the thickness of the inner layer 3, all the remaining conditions being equal, the number of units 5 decreases and the dimensions of such units 5 increase.

Comparing example 2 with example 3, it can be seen how, by increasing the difference between the thermal expansion coefficients a of the two layers, all the remaining conditions being equal, the number of units 5 increases and the dimensions of such, units 5 decrease.

In the above description and in the following claims, all of the numerical sizes indicating quantities, parameters, percentages, and so on should be taken to be preceded in all circumstances by the term "about" unless indicated otherwise. Moreover, all of the ranges of numerical sizes include all the possible combinations of maximum and minimum numerical values and all the possible intermediate ranges, in addition to those specifically indicated in the text. Of course, the man skilled in the art may bring further modifications and variants to the antiballistic element and to the process for the manufacture thereof according to the present invention, in order to satisfy contingent and specific requirements, all of which are in any case covered by the scope of protection of the present invention.

Claims

Antiballistic element (1) comprising:

- a fragmented outer layer (2) comprising at least one antiballistic material of the ceramic type;

a continuous inner layer (3) comprising at least one carbo-ceramic material reinforced with fibres;

wherein the fragmented outer layer (2) and the continuous inner layer (3) are integral and wherein the fragmentation of the outer layer (2) is obtained by thermal cracking. Antiballistic element (1) according to claim 1, wherein the interface surface (4) between the fragmented outer layer (2) and the continuous inner layer (3) has concavities and/or convexitie-s .

Antiballistic element (1) according to claim 1 or 2, wherein said antiballistic material of the ceramic type has a density of between 2.3 and 6.5 g/cm³ and said carbo-ceramic material reinforced with fibres has a density of between 1.8 and 2.5 g/cm³.

Antiballistic element (1) according to any one of the previous claims, wherein said antiballistic material of the ceramic type has a hardness of between 20 and 40 GPa measured according to the Vickers scale (HV 500g) .

Antiballistic element (1) according to any one of the previous claims, wherein said antiballistic material of the ceramic type has a modulus of rupture (MOR) of between 220 and 330 MPa.

Antiballistic element (1) according to any one of the previous claims, wherein said carbo- ceramic material reinforced with fibres has a modulus of rupture (MOR) of between 40 and 120 MPa.

Antiballistic element (1) according to any one of the previous claims, wherein said antiballistic material of the ceramic type has a modulus of elasticity (MOE) of between 180 and 280 GPa.

Antiballistic element (1)^■ according to any one of the previous claims, wherein said carbo- ceramic material reinforced with fibres has a modulus of elasticity (MOE) of between 15 and 50 GPa.

Antiballistic element (1) according to any one of the previous claims, wherein said antiballistic material of the ceramic type comprises one or more from the following materials: infiltrated silicon carbide, infiltrated boron carbide.

Antiballistic element (1) according to any one of the previous claims, wherein said carbo-ceramic material reinforced with fibres comprises woven fibres, or short fibres, mixed with carbon powder, silicon powder, silicon carbide powder and/or with liquid or powdered binders.

Antiballistic element (1) according to any one of the previous claims, wherein said fragmented outer layer (2) has a thickness of between 3.8 and 25 mm and said continuous inner layer (3) has a thickness of between 3.8 and 25 mm.

Antiballistic element (1) according to any one of the previous claims, wherein the fragmented outer layer (2) has a plurality of units (5), each delimited by one or more fractures caused by thermal cracking, the dimensions of which are between 0.5 and 25

Article comprising at least one antiballistic element (1) according to any one of claims 1- 12.

14. Process for manufacturing an antiballistic element (1) comprising the following steps: a. providing components of an outer layer

(2) , among which at least one antiballistic material of the ceramic type, and components of an inner layer

(3) , among which at least one carbo- ceramic material reinforced with fibres; b. shaping and moulding the outer layer (2) and the inner layer (3) ;

c. assembling the inner layer (3) with the outer layer (2) so as to form an assembled element;

d. pyrolysis of the assembled element;

e. infiltration of the pyrolysed element;

f . cooling the infiltrated element so as to obtain the fragmentation of the outer layer (2) by thermal cracking.

15. Process according to claim 14, wherein moulding step b comprises the following sub- steps in sequence:

bl. moulding the outer layer (2) or the inner layer (3) ; b2. moulding the layer not yet moulded on the already moulded layer.

16. Process according to claim 15, wherein step b2 is preceded by a step of shaping the surface of the moulded layer.

17. Process according to claim 14, wherein moulding step b comprises the co-moulding of the inner layer (3). with the outer layer (2) .

18. Process according to claim 17 wherein step b is preceded by a step of distributing the materials inside the mould so as to obtain, in the subsequent step b, an interface surface (4) between ^' the outer layer (2) and the inner layer (3) with a desired geometry.

19. Process according to any one of claims 14-18, wherein infiltration step e is carried out with metallic silicon or with metallic silicon and aluminium or with metallic silicon and copper.

20. Process according to claim 19, wherein the infiltration is carried out evenly over the entire interface surface (4) .