EP4073460A1

EP4073460A1 - Device for controlling a shielding

Info

Publication number: EP4073460A1
Application number: EP20820946.0A
Authority: EP
Inventors: Vincent Gleize; Alexane MARGOSSIAN; Matthieu Graveleau; Mickael BOINET
Original assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Current assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Priority date: 2019-12-11
Filing date: 2020-12-10
Publication date: 2022-10-19
Also published as: CA3161064A1; US20230011664A1; WO2021116349A1; FR3104711B1; FR3104711A1

Abstract

The invention relates to a device comprising: - a shielding part (10) made of a material having a plastic deformation domain under load before breaking and an elastic deformation domain, the plastic deformation domain representing less than 1% of the elastic deformation domain, and - a deformation sensor (2) attached to the shielding part and configured to plastically deform under the effect of at least one stress applied to the shielding part and leading to a damage of the shielding part.

Description

Title: SHIELDING CONTROL DEVICE Technical area

The invention relates to a device and a method for verifying the physical condition of armor, in particular armor used for a bulletproof vest or to protect a military vehicle.

Prior art

Conventionally, a bulletproof vest comprises a protective shield made up of:

- a protective plate 1 consisting of a sandwich consisting successively of an armor plate 32, an intermediate layer 33 and a damping plate 34, called "backing", and

- an outer casing 30 enveloping the protective plate (Figure 3).

The armor plate is glued to the middle layer, which in turn is glued to the damper plate. The envelope can also be glued to the protective plate.

The shielding plate is conventionally made of a ceramic material, typically of alumina, SiC or B C.

The intermediate layer is a textile, typically made of a material chosen from polyethylenes PE, in particular ultra high density polyethylenes (UHMWPE), glass or carbon fibers, aramids, and metals such as aluminum, titanium or their alloys and steel.

Damping plate 34 is of a ductile material, typically - of a fibrous material consisting mainly of polyethylene fibers, for example Tensylon ™, Dyneema®, or Spectra ™, aramid fibers, for example Twaron ™, or Kevlar®, fiberglass, or

- in a metal, for example steel or an aluminum alloy.

The envelope is conventionally made of a fabric, for example of glass or carbon fibers. It can in particular be made from a material chosen from polyethylenes PE, in particular ultra high density polyethylenes (UHMPE), aramids, in particular Kevlar®, metals such as aluminum or even steel, in particular in cases of non-personal protection.

The glue may for example be based on polyurethane or epoxy polymers. In the service position, that is, when the bulletproof vest is worn, the cushioning plate extends from the wearer's side of the bulletproof vest. The shock caused by a projectile therefore first hits the armor plate, then the damper plate.

To check the good condition of the protective plate, the general appearance of the casing is conventionally examined. The signs of possible damage to the armor plate are indeed often very difficult to detect. In a fragile material such as that which conventionally constitutes the armor plate, the fragile rupture, or “catastrophic rupture”, can indeed result from the multiplication of microcracks which are difficult to detect. It is therefore possible that the wearer is not properly protected.

There is therefore a need for a more reliable method for monitoring the condition of a bulletproof vest, and more generally of a fragile piece of armor, without having to resort to complex investigation techniques such as x-rays for example. .

An aim of the invention is to respond, at least partially, to this need.

Disclosure of the invention Summary of the invention

The invention provides a device comprising a shielding piece and a deformation sensor fixed to the shielding piece, the deformation sensor being configured to deform plastically under the effect of at least one stress applied to the shielding piece. shielding and leading to damage to the shielding piece, preferably under the effect of a minimum damaging stress on the shielding piece, i.e. under the effect of the smallest stress applied to shielding piece and leading to damage to the shielding piece.

Note that the stresses refer to the shielding piece, while the strain refers to the strain sensor.

As will be seen in more detail in the remainder of the description, the deformation sensor therefore deforms in a plastic manner under the effect of a stress which has led to damage to the shielding part, without breaking the deformation sensor or of the shielding piece. When one ceases to apply this stress, the deformation sensor therefore retains a residual deformation which makes it possible to identify that the shielding piece has undergone said stress. This physical storage of the occurrence of the damage constraint is particularly advantageous because it allows discontinuous monitoring over time and great autonomy for the shielding part. Unlike a damage check performed using conventional strain gauges, it is not necessary to continuously measure the strain of the strain sensor.

The strain sensor is preferably configured to deform under the effect of a stress applied to the armor piece, elastically when the applied stress Ca is less than or equal to a threshold stress Cs, and plastically when the applied stress is greater than the threshold stress, the threshold stress being such that Cs <Ce _mm and, preferably (Ce _mm - Cs) / Cs <20%,

This _min being the minimum damaging stress of the shielding piece, that is to say the smallest stress applied leading to damage to the shielding piece.

As will be seen in more detail in the remainder of the description, the deformation sensor therefore deforms elastically when the stress applied to the shielding part is low and far from the minimum damage stress, that is to say - typically say in the absence of impact on the shielding piece. When we stop applying the constraint, the device therefore reverts to its initial geometry.

However, the threshold stress, which corresponds to the plastic limit of the strain sensor, is less than or equal to the minimum damage stress Ce _m , „. One, preferably any stress applied to the shielding piece and which constitutes a damaging stress, that is to say greater than the minimum damaging stress, therefore produces a plastic deformation of the deformation sensor. The deformation sensor thus keeps a trace of the application of a damage stress.

Of course, this implies that the strain sensor is functional when this stress greater than the minimum damage stress has been applied to the shielding piece. In other words, the ultimate limit, which marks the end of the plastic strain range of the strain sensor, is not reached until the piece of shielding is damaged.

In addition, the measurement of the plastic deformation advantageously makes it possible to evaluate the extent of the damaging stress, and therefore of the damage to the shielding part. To prevent the strain sensor from deforming plastically while the shielding piece has not undergone any damage stress, it is preferable that the threshold stress is as close as possible to the minimum damage stress.

Preferably, (Cemm Cs) / Cs <10%, preferably (Ce _m m - Cs) / Cs 5%, preferably (Ce _m m Cs) / Cs 1%.

Preferably, the minimum damaging stress is the stress from which the shielding piece begins to microcrack.

The stress can be a mechanical stress, in particular resulting from a mechanical shock to the shielding piece.

Preferably, the strain sensor is configured so as not to be destroyed by the application of any stress on the shielding piece which does not lead to the rupture of this piece. In other words, the deformation sensor remains operational as long as the stress applied to the shielding piece does not lead to the rupture of the shielding piece.

In one embodiment, which is not preferred, the strain sensor is destroyed before the shielding piece. The stress applied to the shielding piece which defines the upper limit of the plastic deformation domain of the deformation sensor, that is to say the breaking stress of the deformation sensor, is called Cr _c. The deformation sensor is therefore configured to deform in a plastic manner, under the effect of a stress applied to the shielding part, when the stress applied is greater than the threshold stress and less than the breaking stress O _c leading to to a rupture of the deformation sensor. In order for the deformation sensor to remain functional when the minimum damage stress Ce _{m m has} been applied to the shielding part, it is then necessary that Ce _m m Cr _c .

In an embodiment which is not preferred, Cs ³ Ce _min . The strain sensor can then be used to detect only damage to the shielding piece that goes beyond the smallest damage.

A device according to the invention may also include one or more of the following optional characteristics:

the shielding piece is made of a ceramic material and / or of a glass and / or of a glass-ceramic and / or of a ceramic matrix composite (CMC) and / or of a ceramic-metal composite;

- the deformation sensor has a property, preferably an impedance, preferably an acoustic and / or electrical impedance, preferably at least one resistor electrical, variable as a function of its geometry, and in particular variable as a function of said applied stress Ca;

- the deformation sensor forms an electrically conductive circuit, closed on itself and devoid of any source of electrical energy;

- the deformation sensor comprises, or even consists of a sensor matrix, preferably polymeric, and electrically conductive particles, preferably carbon particles, preferably carbon nanotubes, distributed in the sensor matrix;

- the set of electrically conductive particles constitute a conductive network of which an electrical property, preferably the impedance, preferably the electrical resistance, preferably exclusively the electrical resistance, is a function of an arrangement of the conductive particles constituting the conductive network, said arrangement being “modifiable” in that, under the effect of a stress applied to the fragile part, the arrangement of the conductive particles of the conductive network is modified so that there results a modification of said electrical property of the network driver;

- the sensor matrix is in the form of a layer or several superimposed layers;

- the applied stress is a mechanical shock;

- the sensor matrix is made of a ceramic material;

- the sensor matrix is fixed on a support;

- the support is attached to an interfacing layer, preferably so as to constitute a patch;

- the interfacing layer is fixed to the shielding piece, the interfacing layer being configured to deform under the effect of the stress Ca applied to the shielding piece, elastically when the applied stress Ca is lower or equal to the threshold stress Cs, and in a plastic manner when the applied stress Ca is greater than the threshold stress Cs.

- The interfacing layer is an "interfacing" glue, preferably chosen from thermosetting polymer glues, preferably chosen from polyurethane glues and / or epoxy glues, or even is a geopolymer-based glue;

the interfacing layer has a thickness less than 2 mm, preferably less than 1 mm, preferably between 0.1 and 1 mm; the interfacing layer preferably extends so as to cover the entire surface of the support, in particular of the patch support, facing the shielding part;

- the deformation sensor comprises a patch of the type described in WO2017 / 009256, and an interfacing glue, by means of which the patch is glued to the shielding piece;

- the device comprises a second part, for example a damping plate, and the deformation sensor is attached to the shielding part and to said second part;

- the second piece is a bulletproof vest cushioning plate or an intermediate layer extending between a bulletproof vest cushioning plate and the armor piece;

the device is a device for protection against military projectiles, and in particular against bullets, preferably intended for the protection of a vehicle, in particular of a military vehicle, or of a person, preferably chosen from among a bulletproof vest and a helmet, the armor piece preferably being in the form of a plate.

The invention also provides a method for monitoring the physical state of a shielding part, said method comprising the following steps:

1) at an initial moment, fixing a deformation sensor on the shielding part so as to constitute a device according to the invention;

2) calibration of the device so as to determine a relationship between said physical state and a property of the strain sensor;

3) at an updated time, measuring said property and, from said relationship, determining said physical state at the updated time.

Step 3) can be repeated, two successive updated instants being for example separated by more than 1 minute, 1 hour, a day, or a week, and / or less than 6 months or less than 1 month.

A method of the invention may also include one or more of the following optional characteristics:

- said property is an impedance, preferably a resistance;

- Said physical state relates to the presence of microcracks;

- in step 3), said property is measured without contact with said deformation sensor;

- in step 3), depending on said measurement of said property:

a mechanical shock undergone, before step 3), by the shielding piece, for example during transport of said shielding piece, is detected, and / or an amplitude of said shock is measured mechanical and / or a location of the area of application of said mechanical shock is determined; and or

- a thermomechanical stress undergone, before step 3), by the shielding piece is detected and / or an amplitude of said thermomechanical stress is measured and / or a location of the application zone of said thermomechanical stress is determined;

- A failure of the deformation sensor is detected; and or

- A disassembly of the shielding piece is detected with another piece to which it is attached, the deformation sensor being sandwiched between the shielding piece and said other piece.

The invention also relates to a kit, in particular for implementing a monitoring method according to the invention, said kit comprising a device according to the invention and a measuring device suitable for measuring, preferably without contact, said property in step 3).

Definitions

We call "plate", a part whose width is greater than five times the thickness.

The term “stress” is understood to mean a stress exerted on a piece of shielding, for example a mechanical stress such as a shock, thermal or thermomechanical, a chemical or corrosion stress, a force or a moment of force. A stress can have a temporary or permanent effect on the piece of shielding. By extension, the term “stress” is used to describe the intensity of this stress with respect to the surface of the part concerned. The Ca, Cs and Ce _min stresses are applied in the same way to the shielding piece. For example, if the constraint is a mechanical action, this action is applied to the same place of the armor piece, following the same direction, only the intensity of this action being possibly different for Oa, Os and Cemin.

The "physical state" of a piece of shielding can be, for example, "damaged state" or "intact state". It can also be more specific. For example, it may be "slightly damaged condition", "moderately damaged condition" or "severely damaged condition".

"Damage" to a piece of armor is an irreversible consequence of applying stress to the piece of armor. The damage can in particular result in microcracks.

Any stress producing damage is called a “damaging stress”. The damage stress which has the lowest intensity is called “minimum damage stress”.

By "property" of a deformation sensor is meant a characteristic of this variable sensor as a function of the geometry of said sensor. Conventionally, the property of the sensor, for example its impedance, can be measured electrically.

Unless stated otherwise, "resistance" is electrical resistance, measured in Ohms.

When the deformation sensor breaks, it is conventionally not considered to be deformed in a plastic manner.

The term “brittle” is understood to mean a material whose plastic deformation domain under load before rupture represents less than 1% of the elastic deformation domain, preferably is substantially zero. In other words, the width of the range of stresses leading to plastic deformation without rupture represents less than 1% of the width of the range of stresses leading to elastic deformation.

A material can be composite or monolithic depending on whether or not it contains fibers. In particular, it can be a “Ceramic Matrix Composite”, or “CMC”, that is to say a product composed of fibers linked together by a ceramic matrix.

For a monolithic material, the load applied to measure the deformability is typically a compressive load. In the case of a ceramic composite, for example a CMC, the load is applied in tension, the elongation then being measured in the direction of the fibers.

The term “ceramic material” is understood to mean any non-metallic and non-organic material. Diamond, graphite, graphene, a carbide and a cermet are considered here as ceramic materials.

“Behave”, “present” or “understand” must be interpreted in a broad, non-limiting manner.

Brief description of the drawings

Other characteristics and advantages of the invention will become apparent on reading the detailed description which follows and on examining the appended drawing in which

- Figure 1 [Fig 1] schematically illustrates a kit according to the invention comprising a device according to the invention according to a first embodiment; - Figure 2 [Fig 2] schematically illustrates a device according to the invention according to a second embodiment;

- Figure 3 [Fig 3] shows schematically, in cross section, a ballistic protection shield of the prior art;

- Figure 4 [Fig 4] shows schematically, in cross section, various ballistic protection shields according to the invention;

- Figure 5 [Fig 5] shows the results of different tests with different ballistic protection shields according to the invention;

- Figure 6 [Fig 6] shows different devices according to the invention for evaluating the location of the impact impact zone on the piece of shielding;

- Figure 7 [Fig 7] schematically illustrates the operation of a device according to the invention;

- Figure 8 [Fig 8] schematically illustrates a device according to the invention used to detect a relative movement between two parts.

In the various figures, identical references are used to designate identical or similar members.

detailed description

Device

A device according to the invention of the type shown in Figure 1 comprises a deformation sensor 2 and a shielding part 10, on which the deformation sensor is fixed.

The deformation sensor can be placed at the heart and / or on the surface of the shielding part.

Preferably, the deformation sensor is arranged so as not to be subjected directly to the stresses applied to the armor piece, and in particular so as not to directly receive the projectiles capable of being launched on the armor piece in service. .

However, the deformation sensor must be arranged so that it is deformed under the effect of the stresses applied to the shielding piece. Arrangement on the most vulnerable parts of the shielding piece, for example corners and ridges, may be satisfactory.

Armor piece

The shielding piece 10 is made of a fragile material, preferably of a ceramic material, preferably of alumina, SiC or B C. The shielding piece 10 may have a mass greater than 500 g, preferably greater than 1 kg and / or less than 100 kg, less than 50 kg, less than 10 kg, or even less than 5 kg.

The shielding piece 10 can have any shape, determined as a function of the intended application. The shielding piece 10 may in particular have the shape of a plate, for example the shape of a plate having a length greater than 20 cm and / or less than 50 cm, a width greater than 10 cm and / or less than 30 cm and a thickness greater than 5 mm, preferably greater than 10 mm, and / or less than 2 cm.

The shape of the surface to which the deformation sensor is attached is not limiting. It can be smooth or rough, have through holes or be continuous, optionally have cavities or bosses, be developable or not, be flat or not. Preferably, this surface is flat.

Strain sensor

A deformation sensor 2 is a sensor capable of providing electrical information as a function of its geometry. The geometry of the deformation sensor can in particular result from its crushing, its stretching, its bending or its setting in rotation.

The deformation sensor 2 preferably comprises a sensor matrix 4 in which are dispersed electrically conductive particles, or “nanofillers” 6, as illustrated in FIG. 2. The sensor matrix thus loaded with conductive particles exhibits a different electrical behavior in function of its geometry.

The nanofillers 6 can be nanofillers described in WO2017 / 009256. The nanofillers can be carbon particles, preferably carbon nanotubes.

The concentration of the nanofillers in the sensor matrix is preferably determined so that, under the effect of a stress exerted on the shielding piece, the sensor matrix is deformed, which modifies the number and / or the quality of the contacts between the nanofillers, and therefore modifies the impedance, and in particular the electrical resistivity of the sensor matrix.

The change in impedance depends on the concentration and shape of the nanofillers. Simple measurements of the resistance as a function of the deformation, for a powder of nanofillers, make it possible to determine a concentration of nanofillers suitable for the intended application.

More precisely, the deformation sensor 2 exhibits elastic behavior as long as the stress applied Ca on the shielding part is less than a “threshold” stress Sc. Beyond the threshold stress, it deforms plastically. After the application of a stress Ca lower than the threshold stress Sc and the return to rest (absence of applied stress), the strain sensor therefore regains its initial geometry as long as the threshold stress has not been reached or outdated.

According to the invention, the strain sensor begins to deform plastically before the applied stress Ca on the armor plate reaches the minimum damage stress Ce _m , „. In other words, Cs <Ce _m , _n . In the event of application of a stress Ca greater than or equal to the minimum damage stress Ce _m , „, the deformation sensor therefore deforms plastically, and thus retains a“ physical memory ”of this application. As described below, the property measured in step 3) therefore makes it possible to detect, by means of the calibration curve, that such a stress has been applied, and therefore that the shielding piece is damaged.

The threshold stress Cs should not however be too far from the minimum damage stress. Indeed, any exceeding of the threshold stress by the applied stress leads to an irreversible degradation of the deformation sensor. This is why (Ce _m in - Cs) / Cs must be less than 20%, preferably as low as possible.

The tolerance (Ce _m in - Cs) / Cs however depends on the intended application. In particular, if Ce _mm is different from Cs, the plastic deformation of the deformation sensor begins before the shielding piece is damaged. Thus, the strain sensor can be used to physically record the occurrence of stresses which do not damage the shielding part, for example stresses which announce damaging stresses, or more generally occurrences of stresses which do not damage the shielding part. 'did not leave any marks on the piece of armor. The deformation sensor thus makes it possible, for example, to follow an aging of the shielding part which is not not visible on the shielding part. In one embodiment, (Cemin - Cs) / Cs> 5%, (Cemin - Cs) / CS> 10%, (Cemin - Cs) / Cs> 15%.

In one embodiment, the sensor matrix is of a polymeric material, particularly if the shielding piece is intended for use at a temperature below 200 ° C.

In one embodiment, the sensor matrix is made of a thermoplastic or thermosetting material, in particular a material described in WO2017 / 009256.

In one embodiment, the sensor matrix is made of a ceramic material, particularly if the shielding piece is intended for use at a temperature above 200 ° C. Of preferably, the sensor matrix is made of a ceramic material resistant to a temperature of 1500 ° C.

The strain sensor can be fabricated in situ. The sensor matrix is then preferably directly in contact with the shielding piece:

In one embodiment, a precursor liquid of the sensor matrix loaded with nanofillers (that is to say allowing, after curing, to obtain said matrix) is applied to the shielding piece, then cured, preferably by drying, to form the sensor matrix loaded with nanofillers. The precursor liquid can be deposited on the shielding piece by any means, for example manually, in particular with a glue gun, or in an automated manner. All known methods for depositing a liquid can be used.

The deformation sensor can be further manufactured by depositing on the shielding part a precursor film of a ceramic matrix loaded with nanofillers, then by sintering this film at 1000 ° C under a neutral atmosphere.

The deformation sensor can also be manufactured before being attached to the shielding piece:

The deformation sensor may in particular have the shape of a thin sintered plate consisting of a ceramic matrix loaded with nanofillers and which is bonded with a refractory glue to the piece of shielding before use.

In an alternative embodiment, the deformation sensor has the shape of a patch, that is to say comprises a thin support 8, preferably having a thickness less than 5 mm, preferably less than 2 mm, of preferably less than 1 mm, for example a strip or a sheet, which can be fixed to the shielding part and which carries the sensor matrix 4 containing the nanofillers 6 (FIG. 2).

The support 8 may have a surface area greater than 10 mm by 10 mm and a thickness less than 1 mm, or even less than 500 micrometers.

One side of the backing can be coated with an adhesive to be easily attached to the shielding piece.

WO2017 / 009256 describes a deformation sensor which is preferably in the form of a patch. However, the patch of WO2017 / 009256 is recommended to follow the deformation of fabrics such as boat sails or to anticipate the breakage of blades, wind turbine masts, wings, sections of planes, masts, floats. , sailboat hydrofoils, chassis or car bodies. In these applications, the part to which the patch is attached is not classically not fragile. The patch can advantageously follow and measure the deformations of this part. But tests have shown that the patch described in WO2017 / 009256 is not suitable for monitoring damage to fragile parts. Its behavior remains elastic until the breakage of the shielding piece.

This patch, or, in general, any patch whose behavior remains elastic until the shielding part breaks, can however be used by fixing the support on an interfacing layer 9 exhibiting a plastic deformation on approach. breakage of the shielding piece. The interfacing layer is then fixed to the shielding piece (figure 2).

The assembly consisting of the patch 4-6-8 and the interfacing layer 9 then forms a deformation sensor 2 suitable for the invention.

The interfacing layer 9 may in particular be an adhesive comprising a thermosetting, thermoplastic or crosslinkable elastomer polymer. Preferably, when the polymer is thermosetting, its degree of crosslinking is greater than 75%, or even greater than 90%. Preferably, when the polymer is thermoplastic, its degree of crystallinity varies from 0% to 80%. More preferably, the adhesive comprises more than 50% by weight of polymer (s) (polyurethane, epoxy), or even of geopolymer (s).

The thickness of the interfacing layer 9 disposed between the patch and the shielding piece is preferably constant, preferably greater than 0.1 mm and / or less than 2 mm, preferably less than 1.5 mm. Preferably, the interfacing layer is spread over the entire surface of the patch which rests on the shielding piece.

The nature of the interfacing layer 9 is adapted to the behavior of the shielding part. Advantageously, the same patch can thus be used for different pieces of shielding, by modifying only the interfacing layer 9.

Preferably, the interfacing layer 9 has a “deformation-tensile stress” curve close to that of the shielding part, at least in the temperature range in which it is intended to use the shielding part, and of preferably from room temperature. The interfacing layer therefore deforms in the same way as the shielding piece.

Of course, the interfacing layer is chosen so as not to break before the damage to the shielding piece begins.

To choose an interfacing layer, you can glue so-called patches on shielding pieces with different adhesives, to constitute identical test devices, then choose the one that allows the strain sensor to maintain elastic behavior up to stresses as close as possible to the minimum damage stress, then to adopt a plastic behavior beyond the minimum damage stress.

A person skilled in the art knows how to modify the yield strength of an adhesive. In general, the behavior of an adhesive can be modified by adjusting its composition, for example by modifying its quantity of organic materials (thermosetting polymers, thermoplastics or crosslinking elastomers), accelerating agents, retarders or thinners. It is also possible to load it, in particular with an elastomeric filler or one consisting of polymer or mineral fibers.

Preferably, the deformation of the deformation sensor 2 is guided by the deformation of the sensor matrix 4 and / or by the deformation of the interfacing layer 9. In other words, the deformation sensor deforms elastically or plastically depending on whether the sensor matrix and / or the interfacing layer deforms elastically or plastically, respectively.

Preferably, whether the deformation sensor is manufactured in situ or not, it has an electrical property which varies as a function of its geometry, for example of its elongation.

Preferably, the deformation sensor is passive, that is to say that it does not include any energy source. The deformation sensor can in particular form an electrically conductive circuit closed on itself, preferably shaped to be readable by magnetic induction.

More preferably, the deformation sensor comprises connection terminals 18 which are provided to facilitate the connection of a measuring device 16.

An electrically resistive strain sensor advantageously allows real-time measurement, in a simple manner, by measuring resistance alone (or, equivalently, electrical resistivity).

The deformation sensor is not, however, necessarily a sensor of which an electrical property is measured. In one embodiment, the deformation sensor comprises “micropiezos” exhibiting a variable acoustic impedance as a function of the geometry of the sensor. This type of sensor, of the “SAW” type, in English “surface acoustic wave”, requires the application of a stress, for example in the form of mechanical energy, in order to make the shielding part vibrate, then the measurement of attenuation of the acoustic signal in the shielding room. The surface of the shielding piece 10 on which the deformation sensor 2 is fixed can be any surface of the shielding piece 10, provided that, in service, it is subjected to the mechanical stresses capable of degrading the shielding piece.

Preferably, the attachment surface of the strain sensor represents more than 10%, preferably more than 30%, preferably more than 50% of the impact surface Si of the armor piece, that is to say of the surface capable of receiving the projectiles 36 in the service position.

In the particular embodiment where the armor piece is an armor plate of a bulletproof vest, the deformation sensor 2 may be disposed within the material of the envelope, as shown in FIG. 4A, between the The shell and the impact surface of the armor plate 32, as shown in Figure 4B, between the armor plate 32 and the intermediate layer 33, as shown in Figure 4C, preferably in the intermediate layer 33 as shown in Figure 4D, or between the intermediate layer 33 and the damping plate 34, as shown in Figure 4E.

Preferably, the deformation sensor is integrated in the glue fixing the intermediate layer 33 to the armor plate 32 and / or in the glue fixing the intermediate layer 33 to the damping plate 34 and / or in the glue fixing the 'casing 30 to the armor plate 32 and / or in the glue securing the casing 30 to the cushioning plate 34.

Said adhesive can in particular constitute an interfacing layer with a patch or constitute a said matrix, as described above.

Kit

A kit according to the invention comprises a device according to the invention and a measuring device 16 suitable for measuring the property in step 3), for example by means of cables connecting it to connection terminals 18 of the deformation sensor ( figure 1 ). Preferably, the measuring apparatus 16 is adapted to measure the non-contact property.

The measuring apparatus 16 is also connected to an analysis apparatus 22, that is to say an apparatus conventionally comprising a processor, a computer memory and a software configured to determine, from the measured property, a state. of the shielding piece.

The measuring apparatus 16 can be physically integrated into the analysis apparatus. Process

The manufacturing process follows directly from the above description.

In step 1), a deformation sensor 2 is fixed on a piece of shielding 10, so as to constitute a device according to the invention, for example of the type shown in Figure 2.

In step 2), the device is calibrated, that is to say a relation is determined, which can be represented in the form of a calibration curve 24, providing, for each possible response of the sensor of deformation 2, information on the physical state of the shielding piece, and in particular on the damage, and preferably information on the amplitude of the damage.

The calibration is preferably carried out at a reference instant prior to the first commissioning of the device according to the invention.

Preferably, the calibration is carried out on test devices identical to the device according to the invention and which each are subject to a particular constraint. The possible damage to the shielding piece is then observed. Preferably, the possible damage is measured, preferably without contact, preferably by means of x-rays, ultrasound or a resonance method.

For example, by applying stresses of increasing intensity, we thus detect the minimum damage stress beyond which any stress leads to damage to the shielding piece, as well as the corresponding response of the strain sensor.

The inventors have found that very little damage, eg, microcracking, leads to measurable strain of the strain sensor. In the region of the calibration curve corresponding to a plastic deformation of the deformation sensor, it is therefore advantageously possible to establish a relationship between a measurement of said property and the magnitude of the damage.

In step 3), at the updated instant and with the measuring device 16, the strain sensor 2 is interrogated to measure a property whose value depends on the geometry of the strain sensor.

The time interval between the calibration instant and the updated instant may be greater than one week, two weeks, one month, two months and / or less than one year, or six months.

Step 3) can be carried out at regular intervals. If said property is an electrical resistance of the sensor matrix loaded with nanocharges, the two cables of the measuring device 16, conventionally an ohmmeter, are conventionally connected to the connection terminals 18 (FIG. 1).

The connection of the measuring device to the connection terminals can be deactivated, which is particularly useful when the screening of the shielding part is carried out on an ad hoc basis. It can be non-deactivatable, that is to say permanent, in particular when the control is substantially continuous.

In a preferred embodiment, the measurement of said property is carried out without contact with the deformation sensor. In particular, the property can be an inductance, which can be conventionally measured at a distance.

The measurement M performed by the deformation sensor, or “updated property”, is then analyzed by the analysis device 22, connected to the measuring device 16, in order to provide information on the possible damage to the part. shielding. More specifically, the analysis apparatus uses the calibration curve 24 to determine information on the damage E of the shielding piece.

Preferably, if the updated property is within the range that corresponds to the applied stresses leading to elastic deformation of the strain sensor, the condition of the shielding piece is considered "satisfactory". Otherwise, that is, if the updated property is within the range that corresponds to the applied stresses leading to plastic deformation of the strain sensor, the condition of the shielding piece is considered "unsatisfactory". In the latter case, the calibration curve makes it possible to assess the level of damage. The condition of the shielding piece can then be described, for example, as "weakly cracked", "moderately cracked" and "heavily cracked", depending on the updated property value.

Depending on the condition of the shielding piece thus determined, it is possible to identify the type of fault in the shielding piece and / or to decide whether the shielding piece remains usable or whether it should be replaced and / or to plan maintenance operations.

In one embodiment, the physical states determined according to the invention are statistically processed, for example by means of artificial intelligence algorithms, so as to improve decision making.

Examples of applications and non-limiting tests FIG. 7 illustrates the deformation e of a piece of shielding (solid line) and of the deformation sensor (dashed line) as a function of the stress Ca applied to the piece of shielding.

C _rM denotes the breaking stress of the armor piece and e _GM denotes the maximum strain, corresponding to the rupture of the armor piece. It is considered that the end of the elastic deformation domain and the start of the plastic deformation domain of the shielding part are defined by Ce _min , the stresses greater than or equal to Ce _min leading to damage to the shielding part.

Cr _c designates the stress applied to the shielding piece and which leads to the rupture of the sensor. (In practice, the rupture of the shielding piece can lead to the rupture of the sensor). e _G o designates the maximum deformation of the sensor, corresponding to its rupture (assuming that the rupture of the shielding piece has not damaged the sensor).

Cs denotes the threshold stress, the deformation of the strain sensor being elastic or plastic depending on whether the stress applied to the shielding piece is less than or greater than or equal to Cs, respectively. s _s denotes the strain of the strain sensor when the threshold stress is applied.

The parts of the curves which correspond to plastic deformations are in bold.

It is noted that, preferably, the plastic deformation of the shielding part only occurs when the deformation sensor itself undergoes a plastic deformation. Any damage to the shielding part is then memorized by the deformation sensor.

The minimum damaging stress of the shielding piece Cemin is less than the stress Cr _c applied to the shielding piece and which leads to the rupture of the deformation sensor.

Preferably, however, the plastic deformation of the deformation sensor begins while the shielding piece is still in elastic deformation. The deformation sensor can thus memorize a high stress which, however, has not led to damage to the shielding part.

Preferably, the plastic deformation domain of the deformation sensor ends after the shielding piece has broken. The deformation sensor can thus memorize any stress which has led to damage to the shielding part.

Figure 7 illustrates how the deformation sensor reacts under the application of an increasing stress Ca applied to the shielding piece: It first deforms elastically, until a threshold stress Cs is applied to the shielding part (thin dashed line, until the deformation e _s ), then plastically.

In particular, the deformation of the strain sensor is plastic when the stress applied to the armor piece reaches Ce, ™ and the armor piece begins to degrade. This plastic deformation of the deformation sensor makes it possible, if the stress ceases, to keep a trace that stresses leading to damage to the shielding part have been reached.

If the stress continues to increase, it causes plastic deformation of the shielding piece, in addition to plastic deformation of the strain sensor. It reaches for example the constraint Ci, corresponding to the strain £ i. When the stress then decreases to zero, this plastic deformation results in a residual deformation e ₂ of the deformation sensor, which thus stores the application of the maximum stress Ci applied to the shielding part.

The arrow illustrates the deformation of the strain sensor when the stress ceases after reaching Ci, greater than Ce _min , and shows that the plasticity of the strain sensor has memorized the damage to the shielding piece.

If the stress continues to increase, it reaches Cr _M and the piece of armor breaks.

Cr _c designates the stress applied to the piece of shielding and which would lead to the rupture of the deformation sensor if the piece of shielding were not broken. (In practice, the rupture of the shielding piece generally leads to the rupture of the deformation sensor).

Detection of the occurrence of constraints and evaluation of the amplitude of said constraints

Three QRS resistive deformation sensors, in the form of patches supplied by the company Sense-In, were glued, using a two-component epoxy resin supplied by Elantas under the reference ElanTech AS89.1 / AW89.2, on the rear faces of respective armor pieces, in the form of square plates with sides 200 mm, in silicon carbide, 7.5 mm thick. Each time, the strain sensor was placed 45mm from one edge of the plate and 25mm from an adjacent edge.

An aramid textile intermediate layer was then bonded to each said rear face with an epoxy resin.

A damping plate made of a thermoplastic composite was finally glued to each said intermediate layer, so as to constitute three protective plates of a first series. of examples. Each protective plate was then introduced into an aramid textile envelope which was closed so as to enclose the protective plate and constitute a protective shield, as shown in FIG. 4C.

Different constraints have been applied to the different protective shields:

The first protective shield was projected by a paper ball of approximately 2 g, launched at approximately 10 m / s in the center of the front face of the said shield and perpendicular to the said impact face. The second protective shield was projected by a steel ball of approximately 30 g, launched at approximately 50 m / s in the center of the front face of the said shield and perpendicular to the said impact face. The third protective shield, weighing 50 kg, was dropped from a height of 50 cm in the center of the front face of said shield and perpendicular to said impact face.

The resistance of the strain sensor was measured continuously using a wire-connected HBM MX840A acquisition system.

Figure 5 shows the relative variations in resistance (Ar%) noted for the first, second, and third protective shields (5A, 5B and 5C, respectively) over time, in seconds.

The artifact corresponds each time to the application of the constraint (fleeting shock).

X-ray analysis using a HI-SCAN 6046si type detection device supplied by Smiths Detection did not reveal any visible defects on the armor piece of the first shield. The stress was too low to lead to plastic strain of the strain sensor. FIG. 5A however shows the great sensitivity of the deformation sensor.

A naked eye observation of the armor piece of the second protection shield did not reveal any signs of cracking. However, damage was detectable by X-ray measurement, with a crack 15 mm in length. Figure 5B shows that the resistance after stress application (projection of the steel ball) is different from the resistance before stress application. The deformation sensor thus advantageously kept track of the occurrence of the projection of the steel ball. It can also detect damage not visible to the naked eye.

A naked eye observation of the armor piece of the third protection shield revealed significant cracking. Figure 5C shows that the resistance after application of the stress (drop) is significantly different from the resistance before the stress is applied. The deformation sensor thus kept a trace of the occurrence of the fall.

These tests show that the deformation sensor advantageously makes it possible to memorize the occurrence of light shocks on the armor plate, for example undergone during the transport of the protective shield, or of shocks which have led to invisible damage without recourse to rays. X. Furthermore, the measurement of the resistance does not require observation of the shielding piece, and in particular its extraction from the casing, provided that access to the connection terminals is possible.

The constraints Ce _m in and Cs were determined as follows:

Representative samples of the series are subjected to increasing Ca stresses, resulting from the projection of a projectile in the center of the front face of the sample, perpendicular to said front face.

The stress Ca depends on the mass m of the projectile, on the impact surface S of the projectile on the front face, and on the acceleration A measured on the front face of the part. It is calculated as follows \ Ca = mx A / S, Ca being expressed in MPa, m in Kg, A in m / s ² and S in mm ² .

The mass of the projectile is determined using a precision milligram scale.

The impact surface is measured using a ruler on the part after impact and corresponds to the mark left by the projectile on the aramid textile envelope. When this is not visible, before the projection stage, the envelope is marked with graduations so as to precisely determine (to the nearest mm) the impact surface using a fast camera.

Acceleration is measured by an accelerometer consisting of a cell glued to the front face, or "impact face", of the sample. This is glued at a distance of 100 mm from the point of impact.

After applying a stress, the sample is analyzed with X-rays.

The minimum damage to stress in this _m was estimated by the Ca strain from which a defect at least equal to 2 mm is detected by X-ray radiography

The threshold stress Cs was determined by reading the variation in electrical resistance of the deformation sensor, such as the constraint from which the variation in electrical resistance is no longer reversible while the part is not damaged after checking with X-rays, that is to say from which the strain sensor no longer returns to its initial dimensions before application of the stress. The Ce, ™ / Cs ratio was evaluated at 1.1 in the context of the example of a shield device as described above, with a square plate of 200 mm side, in silicon carbide, 7.5 mm d. 'thickness.

Detection of the failure of a deformation sensor

The measurement made in step c) allows the detection of the failure of the deformation sensor. In particular, if a strain sensor does not provide a property consistent with that (s) of one or more other strain sensors, preferably also disposed on the shielding piece, it can be considered to be faulty. For example, the electrical resistance of a strain sensor can be compared to that of a sensor attached to it.

The failure of a strain sensor can also be detected by monitoring the evolution of the property it provides at various updated times.

Detection, measurement and localization of stresses, in particular mechanical shocks

The magnitude of the plastic deformation of the strain sensor depends on the magnitude of the shock suffered, which in turn depends on the distance between the strain sensor and the area of application of the shock on the piece of armor.

Knowing the position of several strain sensors on the piece of armor and the updated properties they provide thus makes it possible to assess the position of the shock application zone, or "point of impact".

It also makes it possible to determine a distribution of the stresses undergone by the shielding part.

For example, in the embodiment of Figure 6A, with the assumption that the four strain sensors 6 ₁ , 6 ₂ , 63 and 64 are identical and evenly spaced, if the updated properties, e.g. updated resistances, measured for the strain sensors 6 ₁ and 6 ₂ are equal and that the updated property of the strain sensor 63 is lower than that of the strain sensors 6 ₁ and 6 ₂ , and greater than that of the strain sensor 64, we can consider that the point of impact (represented by a cross) is on a line (represented in broken lines) halfway between the deformation sensors 6 ₁ and 6 ₂ .

With an assembly like that of FIG. 6B, it is possible, by comparing the updated resistances of the four deformation sensors, to determine the position of the point of impact even more precisely. For example, if the updated properties of the four sensors of deformation 6 ₁ , 6 ₂ , 6 ₃ and 6 ₄ are identical, the point of impact is at the center of the rectangle defined by these deformation sensors.

In the embodiment of FIG. 6C, the deformation sensor has the form of a substantially closed loop, but remaining open. Several updated properties can be measured on several sections of the deformation sensor, for example between points Pi and P ₂ , between points P ₃ and P ₄ , between points P ₅ and Re, and between points P ₇ and Pg. As with the embodiments of FIGS. 6A and 6B, a comparison of these updated properties makes it possible to determine the position of the point of impact.

In these embodiments, to assess the location of an impact point, a comparison of the updated properties with properties measured prior to the updated time is not necessary.

Preferably, the effect of a stress on a strain sensor is analyzed as a function of the conditions of application of the strain and of the position and shape of the strain sensor.

Preferably, a model is established to determine the effect of a predetermined stress on the property of a strain sensor, depending on the position of the strain sensor relative to the point of application of the strain. Preferably, such a model is established by modifying the stress each time, for example by modifying its amplitude.

Simple test campaigns thus make it possible to establish a relationship between a property measured with a strain sensor and the position and / or the nature of the stress. This relationship then allows, in service, to interpret the updated property of a strain sensor similar to the strain sensor tested.

For example, if the tests show that the property measured following a predetermined mechanical shock evolves linearly with the distance from the point of impact, a simple measurement of this property after the piece of armor has received a shock makes it possible to define the zone on which this shock was applied.

Conversely, if the position of the point of impact relative to the deformation sensor is known, it is possible to determine the intensity of the shock.

Checking an assembly

In a particularly advantageous embodiment, the deformation sensor is interposed at the interface between the shielding part and another part 20, fragile or not, as shown in FIG. 8. Attached to these two parts, the deformation sensor 2 allows advantageously to detect and / or measure the effect of stresses affecting each of the two parts.

In addition, since the deformation sensor is glued to each of the parts, it deforms under the effect of a relative displacement of one of these parts with respect to the other. It can therefore be used to detect and / or measure such a relative displacement.

As is now clear, the invention therefore provides a process which makes it possible, in a simple manner, to

- detecting the past application of a damaging stress on a piece of shielding, for example a thermomechanical or mechanical shock;

- evaluate said stress and / or said damage and / or the location of the area of application of said thermomechanical or mechanical shock.

The invention is advantageously applicable for armor parts having various geometries. In addition, it does not significantly change the size of these parts. Finally, it makes it possible to detect deformations of small amplitudes, the deformation sensor being very sensitive. It therefore allows the detection of weak signals, and therefore anticipates a catastrophic degradation of the shielding part even though the pseudo-plastic deformation zone (resulting from microcracks) of the shielding part is extremely limited.

Of course, the invention is not limited to the embodiments described and shown, provided for illustrative purposes only.

In particular, the position of the deformation sensor on the shielding piece and the number of deformation sensors are not limiting. The number of deformation sensors can in particular be adapted to the extent of the surface area of the shielding piece to be monitored.

Communication between the deformation sensor and the measuring device and / or between the measuring device and the analysis device can be carried out wired or wireless, for example by wi-fi or Bluetooth.

Claims

1. Device comprising:

- a shielding part (10) made of a material having a plastic deformation domain under load before rupture and an elastic deformation domain, the plastic deformation domain representing less than 1% of the elastic deformation domain, and

- a deformation sensor (2) attached to the armor piece and configured to deform plastically under the effect of at least one stress applied to the armor piece and leading to damage to the armor piece.

2. Device according to the immediately preceding claim, the deformation sensor being configured to deform under the effect of a stress Ca applied to the shielding piece, elastically when the applied stress Ca is less than or equal to a stress of threshold Cs, and in a plastic manner when the applied stress Ca is greater than the threshold stress Cs, the threshold stress being such that Cs <Ce min,

This _min being the minimum damage stress of the shielding piece.

3. Device according to the immediately preceding claim, wherein

(Cemin - Cs) / Cs <20%.

4. Device according to the immediately preceding claim, in which (Cemin - Cs) / Cs <10%.

A device according to any preceding claim, wherein the minimum damaging stress is the stress from which the shielding piece begins to microcrack.

6. Device according to any one of the preceding claims, in which the applied stress is a mechanical shock.

7. Device according to any one of the preceding claims, wherein the shielding piece is made of a ceramic material.

8. Device according to any one of the preceding claims, in which the deformation sensor has a variable impedance as a function of said stress Ca applied to the shielding piece.

9. Device according to any one of the preceding claims, in which the deformation sensor forms an electrically conductive circuit, closed on itself and devoid of a source of electrical energy.

10. Device according to any one of the preceding claims, wherein the deformation sensor comprises a sensor matrix (4) and a set of electrically conductive particles (6) distributed within said sensor matrix.

11. Device according to the immediately preceding claim, in which the electrically conductive particles (6) are carbon nanotubes.

12. Device according to any one of the two immediately preceding claims, in which the sensor matrix is made of a ceramic material.

13. Device according to any one of the three immediately preceding claims, in which the sensor matrix is fixed on a support (8), the support is fixed to an interfacing layer (9) and the interfacing layer is fixed. on the shielding piece (2), the interfacing layer being configured to deform under the effect of the stress Ca applied to the shielding piece, elastically when the applied stress Ca is less than or equal to the stress of threshold Cs, and in a plastic manner when the applied stress Ca is greater than the threshold stress Cs.

14. Device according to any one of the preceding claims, constituting a device for protection against military projectiles (36).

15. Device according to any one of the preceding claims, comprising a second part (20), the deformation sensor (2) being fixed to the shielding part and to said second part.

16. Device according to the preceding claim, wherein the second part is a damping plate (34) of a bulletproof vest or an intermediate layer (13) extending between a damping plate (34) of a bulletproof vest and the armor piece.

17. Device according to any one of the preceding claims, in which the deformation sensor is configured so as not to be destroyed by the application of any stress on the shielding piece which does not lead to the rupture of the shielding piece. shielding.

18. A method of monitoring the physical state of a piece of shielding, said method comprising the following steps:

1) at an initial time, fixing a deformation sensor (2) on the shielding piece (10) so as to constitute a device according to any one of the preceding claims;

2) calibrating the device so as to determine a relationship (24) between said physical state and a property of the strain sensor;

3) at an updated instant, measuring said property (M) and, from said relation (24), determining said physical state (E) at the updated instant.

19. Method according to the immediately preceding claim, in which said property is an impedance, preferably a resistance, and / or said physical state relates to the presence of microcracks.

20. The method of the immediately preceding claim, wherein, in step 3), said property is measured without contact with said deformation sensor.

21. A method according to any of the three immediately preceding claims, wherein, in step 3), based on said measure of said property:

- a mechanical shock undergone, before step 3), by the shielding piece is detected and / or an amplitude of said mechanical shock is measured and / or a location of the area of application of said mechanical shock is determined; and or

- A thermomechanical stress undergone, before step 3), by the shielding piece is detected and / or an amplitude of said thermomechanical stress is measured and / or a location of the zone of application of said thermomechanical stress is determined; and or - A failure of the deformation sensor is detected; and or

- A disassembly of the shielding part (10) with another part (20) to which it is attached is detected, the deformation sensor (2) being sandwiched between the shielding part and said other part.