EP3069097B1

EP3069097B1 - Antiballistic garment

Info

Publication number: EP3069097B1
Application number: EP14812630.3A
Authority: EP
Inventors: Massimiliano Valle; Umberto LOSA
Original assignee: Petroceramics SpA
Current assignee: Petroceramics SpA
Priority date: 2013-11-14
Filing date: 2014-11-14
Publication date: 2018-05-02
Anticipated expiration: 2034-11-14
Also published as: ITBS20130166A1; EP3069097A1; WO2015071866A1

Description

FIELD OF APPLICATION

The present invention relates to an antiballistic garment.
In particular, the present invention relates to an antiballistic garment able to withstand multiple attacks.

BACKGROUND ART

Antiballistic garments are known, and in particular antiballistic jackets, provided with one or more antiballistic protection plates made of ceramic materials able to withstand a mechanical load which 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 compared to the metal materials used before, with obvious advantages.
However, even a ceramic material with good properties to absorb a single attack, or the impact of a projectile or other punctiform impact, is damaged after the first impact. This involves considerable problems in that, in the great majority of cases, the attacks are of multiple type.
Therefore, it is necessary that the antiballistic materials withstand multiple attacks, or consecutive and close shocks caused by a series of projectiles.
To overcome this problem, ceramic materials have been disclosed having various compositions and variously structured, formed by a plurality of units of small size. In this way, when the first projectile strikes the material, it only damages the unit impacted thereby since the fracture generated by such a projectile in such a unit propagates with difficulty to the adjacent units. Therefore, the material has greater resistance to multiple attacks. Materials of this type are known for example from WO 91/07632 and from US 6,532,857 . EP0287918 A1 discloses a chemically bonded ceramic armour material.
However, such known materials, in order to achieve the desired efficiency, have a high weight per surface unit, with obvious drawbacks of transport and assembly, and are therefore not adapted to be used on antiballistic garments, and in particular on antiballistic jackets.
Given the limitations mentioned above, therefore, in the field of antiballistic protections there is still the need for antiballistic garments, and in particular antiballistic jackets, which combine low weight and adequate antiballistic properties in terms of ability to withstand multiple attacks.

DISCLOSURE OF THE INVENTION

Such a need is met by an antiballistic garment according to claim 1.
In particular, such a need is met by an antiballistic garment comprising at least one antiballistic protection plate which in turn comprises at least one layer of ceramic material.
The ceramic material is of the composite type.
Said at least one layer of ceramic material is internally reinforced with a metal net which forms at least one layer.
The metal net is of stretch type with a three-dimensional structure.
In particular, the metal net has a thickness of 0.1 to 6 mm and preferably of 0.5 to 1 mm. The thickness is indicated with letter S in Figure 2.
In particular, the metal net has a mesh size of 3 to 30 mm and preferably of 5 to 10 mm. The mesh size is indicated with letter D in Figure 2.
Preferably, the metal net occupies from 1% to 10% by volume of the composite ceramic body.
According to a particular embodiment of the invention, the metal net is coated on the surface with a layer of an oxide and/or a carbide, preferably obtained by anodization, plasma spray method or painting.
According to a first particular embodiment of the invention, the metal net forms a single layer inside said at least one layer of composite ceramic material.
Preferably, the metal net has a coefficient of thermal expansion greater than that of the composite ceramic material.
In particular, said at least one layer of composite ceramic material 3 has a thickness of between 5 mm and 15 mm. The thickness of the ceramic body is indicated with letter H in Figure 2.
According to a preferred embodiment, the composite ceramic material comprises a vitreous matrix in which ceramic particles are dispersed.
Preferably, the ceramic particles dispersed in the vitreous matrix are composed of ceramic oxides, preferably selected from the group consisting of silicates, aluminium silicates and oxides of aluminium, zirconium, chromium, iron and titanium.
Preferably, the composite ceramic material comprises a vitreous matrix consisting of a glass having a sodium-potassium, sodium or boric composition.
According to a particularly preferred embodiment, the composite ceramic material with ceramic particles dispersed in a vitreous matrix has the composition and structure of a vitrified porcelain stoneware.
In particular, the composite ceramic material with ceramic particles dispersed in a vitreous matrix has the composition and structure of a vitrified porcelain stoneware, enriched with alumina powders, preferably by a percentage by weight of not more than 20%.
Preferably, the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a density of 2.1 to 2.6 g/cm³.
Preferably, the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a coefficient of thermal expansion α of 5 to 9 K^-1 10^-6.
Preferably, the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a hardness of 7 to 20 Gpa measured on the Vickers scale (HV 500g).
Preferably, the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a modulus of rupture (MOR) of 40 to 60 MPa.
Preferably, the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a modulus of elasticity (MOE) of 25 to 40 GPa.
According to a particularly preferred embodiment, the composite ceramic material has the composition and structure of a porcelain stoneware, preferably with a thermal expansion coefficient α of between 5 and 9 K^-1 10^-6, and even more preferably equal to 7 K^-1 10^-6, and the stretch type metal net with three-dimensional structure is made of stainless steel AISI 430, preferably having a thermal expansion coefficient α equal to 12 K^-1 10^-6 at 20-600 °C.
According to a particular embodiment, said at least one antiballistic protection plate comprises a first layer of fibrous material associated to the layer of composite ceramic material on the side thereof facing towards the outside of the garment.
In particular, said at least one antiballistic protection plate may comprise a second layer of fibrous material associated to the layer of composite ceramic material on the side thereof facing towards the inside of the garment.
Preferably, said first and/or second fibrous layer is a structure composed of fibres selected from the group consisting of UHMW (Ultra-High Molecular Weight) polyethylene, aramide, copolyaramide, polybenzoxazole, polybenzothiazole, liquid crystal, glass and carbon.
Preferably, said first and/or second fibrous layer is impregnated with polymers selected from the group consisting of thermoplastic, thermosetting, elastomeric, viscous or viscous-elastic polymers.
According to an alternative embodiment, the composite ceramic material is a non-oxide ceramic material made of one or more compounds selected from the group consisting of silicon carbide, boron carbide and silicon nitride.

DESCRIPTION OF THE DRAWINGS

Further features and the advantages of the present invention will appear more clearly from the following description of preferred non-limiting embodiments thereof, in which:

Figure 1 shows an antiballistic garment according to an embodiment of the invention;
Figure 2 shows a schematic sectional view of an antiballistic protection plate according to a first embodiment of the invention;
Figure 3 shows a schematic sectional view of an antiballistic protection plate according to a second embodiment of the invention;
Figure 4 shows a schematic sectional view of an antiballistic protection plate according to a third embodiment of the invention;
Figure 5 shows a perspective view of an example of stretch net; and
Figures 6 and 7 show two photographs of a protection plate (plate A) of a ballistic element according to a first preferred embodiment of the invention, respectively before and after firing tests; and
Figures 8 and 9 show two photographs of a protection plate (plate B) of a ballistic element according to a second preferred embodiment of the invention, respectively before and after firing tests.

DETAILED DESCRIPTION

With reference to the above figures, reference numeral 1 globally denotes an antiballistic garment according to the present invention.
According to a general embodiment of the invention, shown in Figure 1, the antiballistic garment 1 comprises at least one antiballistic protection plate 2, which in turn comprises at least one layer of ceramic material 3.
In particular, as shown in Figure 1, the antiballistic garment 1 can be an antiballistic vest or jacket for the protection of an individual's upper trunk.
The ceramic material is of the composite type. Said at least one layer of ceramic material is internally reinforced with a metal net 4 which forms at least one layer.
The ceramic material cooperates synergically with the metal reinforcement net, increasing the mechanical resistance of the protection plate of the antiballistic garment, and in particular the ability to withstand multiple attacks. The metal reinforcement net has in fact the main function of putting into compression the ceramic material, of retaining the propagation of the fracture and thus it interacts synergically with the ceramic material, reducing the tendency thereof to fragmentation.
Thanks to this synergy, with the same antiballistic performance, the antiballistic garment according to the invention has a thickness lower than traditional antiballistic garments.
The metal net is of stretch type with a three-dimensional structure.
As will be resumed hereafter, it has been found experimentally that the use of a stretch type metal net significantly improves the ability of the antiballistic garment 1 to withstand attacks of the multiple type. Performances being equal, the use of a stretch metal net allows making an antiballistic garment with a protection plate having smaller thickness and thus smaller weights.
The stretch net is a continuous, seamless structure. An example of stretch net is shown in Figure 5.
In particular, the stretch net is obtained by engraving and cold moulding operations of the raw material in rolls or sheets, which give the net a three-dimensional structure. The shape of the knives impacting the sheet determines the shape and width of the mesh.
The three-dimensional structure of the stretch net, characterised by a high number of undercuts, allows a homogeneous and deep anchorage between the net and the ceramic material. It is therefore possible to obtain a very cohesive and resistant body, in which the net cannot slide with respect to the ceramic material when the ballistic element is subjected to loads, in particular pulse-type loads, such as bullet hits.
The absence of joints and especially welding gives the stretch reinforcement net a high structural uniformity which significantly contributes to the cohesion of the composite ceramic material.
The net can have any mesh geometry. Preferably, the mesh geometry is polygonal and thus provided with corners to increase the points of adhesion with the ceramic material. For example, the mesh geometry can be square, hexagonal or rhomboidal.
Advantageously, the metal net has a thickness of 0.1 to 6 mm and preferably of 0.5 to 1 mm.
Advantageously, the metal net has a mesh size of 3 to 30 mm and preferably of 5 to 10 mm. It has been verified that a mesh too large increases the fracture propagation and a mesh too small does not integrate well into the ceramic, tending to split it.
Preferably, the metal net 4 occupies from 1% to 10% by volume of the composite ceramic body.
The stretch net 4 can be made of any metal. Preferably, the metal net is made of a material selected from the group consisting of iron, stainless steel, titanium, molybdenum, aluminium, copper, brass.
It is preferable that the stretch metal net does not change its features at the temperatures of the formation process of the ceramic material in which it is inserted.
In particular, the metal net must not react by crystallising with the ceramic material.
Advantageously, according to a particular embodiment of the invention, the metal net may be coated on the surface with a layer of an oxide and/or a carbide. This coating has the function of inerting the metal net, reducing the aggressiveness of the ceramic material on the same net.
The oxide and/or carbide layer can be obtained through anodization (standard or PEO, Plasma Electrolytic Oxydation), plasma spray method or painting.
According to a first particular embodiment of the invention, schematically shown in Figure 2, the metal net 4 forms a single layer inside said at least one layer of composite ceramic material 3.
The three-dimensional structure of the stretch net, without junctions, in fact ensures a reinforcement capacity greater than the nets traditionally used, thus allowing the use thereof in a single layer rather than in a plurality.
The use of a single layer of net is also made possible by the fact that the antiballistic element 1 according to the invention can be made with smaller thickness than the traditional solutions in vitreous matrix with ceramic powders.
There may also be alternative embodiments in which the composite ceramic body is internally reinforced by a plurality of layers of metal net, as shown schematically in Figure 2.
Preferably, said at least one layer of composite ceramic material has a thickness of between 5 mm and 15 mm.
Greater thicknesses may be provided, if it is necessary to increase the resistance capacity of the antiballistic garment. In this case, increasing the thickness of the protection plate, the ceramic body is preferably reinforced by a plurality of layers of metal net.
Preferably, the metal net has a coefficient of thermal expansion greater than that of the ceramic material with respect to all ceramic materials. In this way, the coupling between the ceramic material and metal net can generate within the composite ceramic material compressive stress states functional to the improvement of the mechanical features of the material itself. Thanks to the fact that the ceramic body has a thermal expansion coefficient lower than that of the metal net and since the ceramic material is obtained through a thermal treatment, upon cooling of the body, the metal net has a more pronounced shrinkage compared to the ceramic material. This causes on the ceramic material a compressive stress state which improves the hardness and impact resistance features.
According to a preferred embodiment, the composite ceramic material comprises a vitreous matrix in which ceramic particles are dispersed.
Preferably, the ceramic particles dispersed in the vitreous matrix are composed of ceramic oxides, preferably selected from the group consisting of silicates, aluminium silicates and oxides of aluminium, zirconium, chromium, iron and titanium.
Preferably, the composite ceramic material comprises a vitreous matrix consisting of a glass having a sodium-potassium, sodium or boric composition.
According to a preferred embodiment, the composite ceramic material with ceramic particles dispersed in a vitreous matrix has the composition and structure of a vitrified porcelain stoneware.
In particular, the vitrified porcelain stoneware comprises silicon dioxide (SiO₂) with a percentage by weight of between 66% and 72%.
In particular, the vitrified porcelain stoneware comprises alumina (Al₂O₃) with a percentage by weight of between 19% and 25%.
In particular, the vitrified porcelain stoneware comprises potassium oxide (K₂O) with a percentage by weight of between 1.5% and 2%.
In particular, the vitrified porcelain stoneware comprises sodium oxide (Na₂O) with a percentage by weight of between 3% and 5%.
In particular, the vitrified porcelain stoneware comprises a mixture of calcium oxides (CaO) and magnesium (MgO) with a percentage by weight of less than 1%.
In particular, the vitrified porcelain stoneware comprises a mixture of iron oxides (Fe₂O₃) and titanium () with a percentage by weight of less than 1%.
In particular, the vitrified porcelain stoneware comprises zirconium oxide (ZrO₂) with a percentage by weight of between 3% and 6%.
In particular, the vitrified porcelain stoneware has the following composition (percentages by weight): SiO₂ 66-72%; Al₂O₃ 19-25%; K₂O 1.5-2%; Na₂O 3-5%; CaO+MgO <1%; Fe₂O₃+TiO₂ <1%; ZrO₂ 3-6%.
According to a particularly preferred embodiment, the composite ceramic material with ceramic particles dispersed in a vitreous matrix has the composition and structure of a vitrified porcelain stoneware, enriched with alumina powders.
Preferably, the percentage by weight of alumina powders is not more than 20%.
In particular, the vitrified porcelain stoneware enriched with alumina powders comprises SiO₂ with a percentage by weight of between 53% and 60%.
In particular, the vitrified porcelain stoneware enriched with alumina powders comprises Al₂O₃ with a percentage by weight of between 34% and 42%.
In particular, the vitrified porcelain stoneware enriched with alumina powders comprises K₂O with a percentage by weight of between 1% and 2%.
In particular, the vitrified porcelain stoneware enriched with alumina powders comprises Na₂O with a percentage by weight of between 2.5% and 4%.
In particular, the vitrified porcelain stoneware enriched with alumina powders comprises CaO+MgO with a percentage by weight of less than 1%.
In particular, the vitrified porcelain stoneware enriched with alumina powders comprises Fe₂O₃+TiO₂ with a percentage by weight of less than 1%.
In particular, the vitrified porcelain stoneware enriched with alumina powders comprises ZrO₂ with a percentage by weight of between 2% and 5%.
In particular, the vitrified porcelain stoneware has the following composition (percentages by weight): SiO₂ 53-60%; Al₂O₃ 34-42%; K₂O 1-2%; Na₂O 2.5-4%; CaO+MgO <1%; Fe₂O₃+TiO₂ <1%; ZrO₂ 2-5%.
Advantageously, the composite ceramic material with ceramic particles dispersed in a vitreous matrix having the composition and structure of a vitrified porcelain stoneware, is made by powder sintering.
Preferably, the production process is by axial moulding. In particular, the operating conditions are as follows:

loading powder and net in the mould (made of metal or metal/rubber);
sintering in a reducing or oxidising atmosphere at a temperature of 800 - 1400 °C (preferably, a detaching powder is used to prevent the article from adhering to the baking plate);
optional bending in temperature of the plate using a suitably shaped support;
- quality control (size, penetrant liquids, density, ...).

Alternatively, the production process can be by casting (in pressure or not). In particular, the operating conditions are as follows:

preparation of a slurry of the powders, preferably water-based;
casting (in pressure or not) in a mould capable of absorbing water (for example, gypsum);
drying;
sintering in a reducing or oxidising atmosphere at a temperature of 800 - 1400 °C (preferably, a detaching powder is used to prevent the article from adhering to the baking plate);
optional bending in temperature of the plate using a suitably shaped support;
quality control (size, penetrant liquids, density, ...).

In both processes described above, the metal net (in a single layer or multiple layers) is arranged inside the mould. If a single layer of metal net is inserted, arranged for example halfway of the layer of composite material, the mould is loaded with the powder or the slurry to half its weight; at this point, the net is arranged and then the remainder of the powder charge or slurry. Then, the subsequent operations of forming of the ceramic body are carried out. The powder charge or slurry can also be split into unequal parts, depending on the position that the net must have within the ceramic body.
Advantageously, standard particle sizes are adopted for the powders in the production of porcelain stoneware. Preferably, the finest particle size profiles are adopted. In fact, it was found that the finer the particles the better the antiballistic properties of the composite obtained.
Preferably, the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a density of 2.1 to 2.6 g/cm³.
Preferably, the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a coefficient of thermal expansion α of 5 to 9 K^-1 10^-6.
Preferably, the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a hardness of 7 to 20 Gpa measured on the Vickers scale (HV 500g).
Preferably, the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a modulus of rupture (MOR) of 40 to 60 MPa.
Preferably, the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a modulus of elasticity (MOE) of 25 to 40 GPa.
Advantageously, the vitreous-ceramic composite has a very low porosity. Preferably, the porosity is less than 5%. Even more preferably, the porosity is less than 2%, and much more preferably less than 0.5%.
The porosity is a measure of the internal voids of a material. Typically, there are two types of porosity: open porosity and closed porosity. "Open porosity" is when there are internal pores interconnected to one another and connected to the surface; on the other hand, "closed porosity" is when there are no internal pores interconnected to one another. Generally, percentages of porosity of less than 2% give a closed porosity.
A material substantially free of open porosity does not absorb water and/or humidity. It is therefore possible to exclude the risk of corrosion attacks to any metal materials incorporated in the material.
Moreover, a low porosity improves the properties of mechanical resistance to impulsive impacts.
According to a particular embodiment, schematically shown in Figure 3, said at least one antiballistic protection plate 2 comprises a first layer of fibrous material 5 associated to the layer of composite ceramic material 3 on the side thereof facing towards the outside of the garment.
The first fibrous layer has the function of containment of the fragments.
In particular, said at least one antiballistic protection plate 2 may comprise a second layer of fibrous material 6 associated to the layer of composite ceramic material 3 on the side thereof facing towards the inside of the garment.
The function of the second fibrous layer is, in addition to the containment of the fragments, to dissipate the impact energy of the projectiles transmitted by the layer of ceramic material to reduce the effects thereof on the user, and thus the resulting trauma.
In particular, said first and/or second fibrous layer is a structure composed of fibres selected from the group consisting of UHMW (Ultra-High Molecular Weight) polyethylene, aramide, copolyaramide, polybenzoxazole, polybenzothiazole, liquid crystal, glass and carbon.
Particularly preferred is the use of UHMW polyethylene fibres, such as Dyneema® or Spectra® fibres.
Preferably, said first and/or second fibrous layer is impregnated with polymers selected from the group consisting of thermoplastic, thermosetting, elastomeric, viscous or viscous-elastic polymers. The impregnation with the above polymers imparts rigidity to the fibrous layer, increasing the capacity thereof of energy dissipation.
According to an alternative embodiment, the composite ceramic material can be a non-oxide ceramic material made of one or more compounds selected from the group consisting of silicon carbide, boron carbide and silicon nitride.
Firing tests have been conducted on antiballistic garments according to the invention in order to assess their effectiveness in terms of ability of resistance to multiple attacks. Some of these tests were carried out directly on the antiballistic protection plates with which the antiballistic garments according to the invention are provided.
The antiballistic protection plates were placed on a backing of Dynaema, packaged with a transparent stretchable film to not disperse the plate fragments after firing, and positioned on a target of plasticine. The tests were carried out by firing with a barrel gauge at a distance of 10 m projectiles caliber 7.62x51 FMJ nato ball with a speed of 830 m/s and projectiles caliber 7.62x39 with soft iron core with a speed of 730 m/s.
In particular, two plates were tested, of dimensions 250 x 300 mm made of composite ceramic material of vitrified porcelain stoneware, enriched with alumina powders. Both plates had an average thickness of about 5 mm and were provided with a stretch steel metal net with thickness of 0.8 mm and with rhomboidal meshes 16 x 8 mm. The nets had dimensions of 232 x 276 mm, a weight of 108.9 g equal to 1.70 Kg/m².
A first plate A was tested with projectiles 7.62x51 FMJ nato ball Fiocchi 9.6 g undergoing 8 shots fired at equidistant points about 100 mm from one another. Plate A had an average thickness of 5.40 mm and a weight per surface area of 13.30 Kg/m².
A second plate B was tested with projectiles 7.62x39 with soft iron core undergoing 5 shots fired at equidistant points about 100 mm from one another. Plate B had an average thickness of 5.50 mm and a weight per surface area of 13.50 Kg/m².

The table below shows the results of the firing tests.

shot	plate	average H	Kg/m2	projectile	speed in m/s	result	trauma mm	Back	notes
a	A	5.40	13.30	7.62x51 FMJ nato ball Fiocchi 9.6 g	819	retained	not meas.	Dynaema 11 Kg/m2	plate intact
b					831	retained	not meas.
c					824	retained	not meas.
d					835	retained	not meas.
e					824	retained	not meas.
f					828	retained	not meas.
g					826	retained	not meas.
h					824	retained	not meas.
a	B	5.50	13.50	7.62x39 soft iron core	738	retained	28	Dynaema 13 Kg/m2	plate intact
b					797	retained	32
c					817	retained	30
d					831	retained	36
e					852	retained	39

Figures 6 and 7 show two photographs of the protection plate A respectively before and after the firing tests; Figure 7 shows with letters a-h the points of impact of the shots fired.
Figures 8 and 9 show two photographs of the protection plate A respectively before and after the firing tests; Figure 9 shows with letters a-e the points of impact of the shots fired.
The tests provided excellent results. In fact, the plates blocked all the shots without breaking, resulting damaged only around the points of impact of the projectiles.
The normal approval tests require that the plate remains intact for 3-5 shots. In the case of plate A, the shots were 8; in the case of plate B, the shots were 5.
The stretch metal net, although not well incorporated or slightly melted, is able to retain the fracture of the plate after the first shot. The plate remains intact with small diameter holes. This allows the plate to withstand and stop many shots even very close together, preventing any trauma in the case of plate A with shots 7.62x51 FMJ nato ball 9.6 g or maintaining a constant trauma in the case of plate B.
Both plates managed to retain shots with very high speeds and - consequently - very high energy with projectiles 7.62x51 FMJ nato ball and with projectiles 7.62x39 with soft iron core. In the latter case (plate B), the projectiles are not able to drill holes in the plate even with a speed of 850 m/s. The standard is 730 m/s.
According to a particularly preferred embodiment of the invention, said at least one layer of the antiballistic protection plate is made of composite ceramic material with the composition and structure of a vitrified porcelain stoneware, preferably having a thermal expansion coefficient α of between 5 and 9 K^-1 10^-6, and even more preferably equal to 7 K^-1 10^-6. In particular, the vitrified porcelain stoneware has a composition according to one of the alternatives described above and is produced according to one of the two methods defined above. Said at least one layer of composite ceramic material of vitrified porcelain stoneware is internally reinforced by a stretch type metal net with three-dimensional structure, arranged to form at least one layer inside the ceramic material. The net is made of steel AISI 430 (ferritic stainless steel), preferably having a thermal expansion coefficient α equal to 12 K^-1 10^-6 at 20-600 °C.
Experimentally, the combination of ceramic composite material of vitrified porcelain stoneware and stretch type metal net of steel AISI 430 (ferritic stainless steel) gave surprising results in terms of the ability of resistance to multiple attacks.
At the end of the ballistic resistance tests, the test plates made according to this combination (vitrified porcelain stoneware - net of steel AISI 430) showed significantly less marked and extensive fracture conditions than the comparison plates, as proof of the superior properties of antiballistic protection. In particular, the comparison was made with plates made of the same composite ceramic material, but in which the reinforcement net was made with the following steels:

a. AISI 304 stainless steel with chromium and nickel, austenitic, with thermal expansion coefficient α equal to 18.5 K^-1 10^-6 at 20-600 °C;
b. C 346 stainless steel with thermal expansion coefficient α equal to 15 K^-1 10^-6 at 20-600 °C;
c. 452/C stainless steel with thermal expansion coefficient α equal to 19 K^-1 10^-6 at 20-600 °C.

To explain these experimental results, the following technical explanation was given, to which we do not intend, however, to necessarily bind. The composite ceramic material of vitrified porcelain stoneware per se already has a good resistance to compression. The association with a metal net is designed to enhance the compressive strength. For this purpose, the metal must have a higher coefficient of expansion than the ceramic material. The experimental results seem to point out that to significantly improve the impact resistance, and thus the properties of antiballistic protection, it is necessary to use a steel with an expansion coefficient only slightly higher than that of the ceramic material. The difference should not be too sharp, otherwise you may get the opposite effect. If the expansion coefficient of the net greatly exceeds that of the vitrified porcelain stoneware, the ceramic material could "crack". The coefficient of steel should also not be too close to that of ceramic, otherwise the mechanical properties required to withstand the stresses caused by the projectiles are not achieved. With this reading, the stainless steel AISI 430 seems to be the steel that provides the best dilatometric agreement with the vitrified porcelain stoneware and thus, the more marked reduction of the residual stresses in the ceramic-net assembly at the end of the production process, which in particular provides for the baking of the material.
In particular, in the test example with the use of a metal net of stainless steel AISI 304, an uneven vitrification (ceramization) occurred between the two different materials, probably due to a too high coefficient of expansion of the steel used.
The invention allows several advantages to be achieved, some of them already described.
The antiballistic garments according to the invention are able to offer a capacity of resistance to attacks of multiple type comparable to that of traditional antiballistic garments, but with lower thickness. This is essentially linked to the fact that the integration into the ceramic material of the reinforcement net determines a lower tendency to fracturing under impulsive hits.
Therefore, antiballistic performances being equal, the antiballistic elements according to the invention have lower weights.
The invention is therefore able to meet the need in the field to have antiballistic garments, and in particular antiballistic jackets, which combine low weight and adequate antiballistic properties in terms of ability to withstand multiple attacks.
The use of a stretch metal net without junctions and welding significantly reduces the risk that internal defects are generated within the protection plate which are not immediately identifiable and potentially capable of reducing the antiballistic properties. This increases the reliability of the antiballistic garment.
The absence of welds increases the degree of structural homogeneity of the metal net, reducing the risk of uncontrolled deformation or in any case not homogeneous during the thermal treatment of the ceramic body. The risk of generating in the ceramic body unwanted stress conditions, which could adversely affect the behaviour of the composite ceramic body, is also reduced.
The absence of welds reduces the possibility of formation of cracks in the ceramic material. This positively affects the shock absorption capacity by the composite ceramic body, as well as the effectiveness of the reinforcement provided by the metal nets themselves.
Finally, the absence of welding spots exposes the metal of the net to a lower risk of reactivity with the ceramic material during the manufacturing process. This significantly improves the effectiveness of intervention of the metal nets.
The invention thus conceived thus achieves the intended purposes.
A man skilled in the art may make several changes and adjustments to the antiballistic garment described above in order to meet specific and incidental needs, all falling within the scope of protection defined in the following claims.

Claims

Antiballistic garment comprising at least one antiballistic protection plate (2) comprising at least one layer of ceramic material (3), wherein said ceramic material is of the composite type, said at least one layer being internally reinforced by metal net (4) which forms at least one layer, characterised in that said metal net is of the stretch type with a three-dimensional structure.
Antiballistic garment according to claim 1, wherein said net has a thickness of 0.1 to 6 mm and preferably of 0.5 to 1 mm.
Antiballistic garment according to claim 1 or 2, wherein said metal net has a mesh size of 3 to 30 mm and preferably 5 to 10 mm.
Antiballistic garment according to claim 1, 2 or 3, wherein said metal net occupies from 1% o 10% in volume of the composite ceramic body.
Antiballistic garment according to one or more of the previous claims, wherein said metal net is coated on the surface with a layer of an oxide and/or a carbide, preferably obtained by anodization, plasma spray method or painting.
Antiballistic garment according to one or more of the previous claims, wherein said metal net forms a single layer inside said at least one layer of composite ceramic material.
Antiballistic garment according to one or more of the previous claims, wherein said metal net has a coefficient of thermal expansion greater than that of said composite ceramic material.
Antiballistic garment according to one or more of the previous claims, wherein said at least one layer of composite ceramic material has a thickness of 5 mm to 15 mm.
Antiballistic garment according to one or more of the previous claims, wherein the composite ceramic material comprises a vitreous matrix in which ceramic particles are dispersed.
Antiballistic garment according to claim 9, wherein said ceramic particles are composed of ceramic oxides, preferably selected from the group consisting of silicates, aluminium silicates and oxides of aluminium, zirconium, chromium, iron and titanium.
Antiballistic garment according to claim 9 or 10, wherein the composite ceramic material comprises a vitreous matrix consisting of a glass having a sodium-potassium, sodium or boric composition.
Antiballistic garment according to one or more of the claims from 9 to 11, wherein the composite ceramic material has the composition and structure of vitrified porcelain stoneware.
Antiballistic garment according to claim 12, wherein the composite ceramic material has the composition and structure of a vitrified porcelain stoneware, enriched with alumina powders, preferably by a percentage by weight of not more than 20%.
Antiballistic garment according to claim 12 or 13, wherein the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a density of 2.1 to 2.6 g/cm³.
Antiballistic garment according to claim 12, 13 or 14, wherein the vitreous-ceramic composite consisting of vitrified porcelain stoneware has a coefficient of thermal expansion α of 5 to 9 K^-1 10^-6, and preferably equal to 7 K^-1 10^-6.