WO2017042528A1

WO2017042528A1 - System and method for detecting damage to armour

Info

Publication number: WO2017042528A1
Application number: PCT/GB2016/052299
Authority: WO
Inventors: Paul Martin; Aled Trefor CATHERALL
Original assignee: Plextek Services Limited
Priority date: 2015-09-09
Filing date: 2016-07-27
Publication date: 2017-03-16
Also published as: GB201804446D0; GB201515962D0; GB2556827A; GB2556827B

Abstract

A mechanical-force sensor (202) is arranged to sense a mechanical force in armour (201). The mechanical-force sensor (202) outputs an output signal corresponding to the detected mechanical force in the armour (201). Circuitry is arranged to receive output signals output by the mechanical-force sensor (202) and to process the received output signals to determine whether damage to the armour (201) may have occurred.

Description

SYSTEM AND METHOD FOR DETECTING DAMAGE TO ARMOUR

Technical Field

The present invention relates to a system and a method for detecting damage to armour.

Background

Soldiers, military platforms, such as vehicles and buildings and the like, and other items or objects, whether mobile or fixed, may be equipped with armour to protect against for example ballistic threats. Modern ballistic armour is often composed of an outer layer of ceramic or similar material, backed by a layer of reinforced plastics or composite matter (e.g. Kevlar®). There may also be additional layers on both front and back, such as plastics coatings and foam to provide weather protection and protection against impacts with hard objects. Such layered structures are generally significantly lighter than a sheet of steel that would offer the same level of ballistic protection.

Although much lighter than metals such as steel, ceramic-based armour suffers from the problem that its ceramic component is extremely brittle. Soldiers wearing ceramic armour, can, in the course of their duties, cause the ceramic component of their armour to fracture without realising it. Examples of soldier activity which may cause armour to fracture include diving onto hard ground for cover, bumping into walls and other hard structures, and even simply removing their armour and placing it on the ground. Similarly, vehicle-mounted ceramic armour can become damaged during routine operations, for example impact against hard structures such as walls and trees. Armour will also be damaged when struck by a ballistic projectile such as a bullet or a shell from a gun. For body worn armour, the wearer is usually aware of a strike from a ballistic projectile and will infer that the armour is likely to be damaged. However, the occupants of an armoured military vehicle are not always aware of a strike by a ballistic projectile from an enemy combatant due to the noise inside the vehicle exceeding the noise due to the impact of the ballistic projectile or because the vehicle may not be crewed at the time of impact. Once ceramic armour, whether body worn or vehicle mounted or otherwise, is found to contain a fracture, it is usually deemed failed and is considered unserviceable. This is regardless of how small the fracture is since no reliable metric exists for armour performance as a function of crack location, crack size and impact location. Furthermore, small hairline cracks can, over time, propagate into much larger cracks with very little force being required.

A recurring problem with ceramic-based armour is that it is not straightforward to determine the integrity of the ceramic, particularly during a military operation. As described above, body worn ceramic armour is usually sandwiched between an outer layer of protective foam or plastics and an inner layer of composite material. This usually prevents simple visual inspection of the surface of the ceramic materials to identify cracks. Notwithstanding this, even if the surface of the armour is exposed to enable visual inspection, surface fractures are not always easily detected, as they can often be hairline fractures of only a few microns in width and a few millimetres in length.

Known methods to inspect ceramic structures include ultrasonic inspection, infrared and laser thermography and x-ray imaging. However, these techniques require specialised equipment and facilities or specialised technical skills. Further, not all of these techniques can be used when the ceramic armour is sandwiched between other materials.

US2013/0043888A1 discloses a wireless damage detector for ceramic armor plates. A conductive coil connected to a conductive trace circuit is embedded within the ceramic material. A separate "interrogator" coil inductively couples with the conductive coil in the ceramic material. When the ceramic cracks, a break in the conductive trace circuit occurs, which can be sensed by use of the interrogator coil to reveal the presence of the crack. This concept, however, requires the conductive coil and conductive trace circuit to be integrated as part of the ceramic fabrication process and thus does not lend itself to retrofitting to existing armour. WO2006/019820A2 similarly relies on cracks in ceramic armour being detected by electrically detecting breaks in electrically conductive pathways integrated into the ceramic armour, such breaks causing the electrical resistance of the conductive pathways to rise which can be detected. The conductive circuitry can be adhered to the surface of the ceramic armour. Although this supports retrofitting, it is limited to only detecting cracks which propagate through to the surface of the armour. Hairline cracks forming within the bulk of the ceramic which do not cause appreciable strain to the conductive pathway on the surface of the armour will not result in the breaking of conductive pathways and thus will not be detected. Summary

According to a first aspect of the present invention, there is provided a system for detecting damage to armour, the system comprising:

armour;

a mechanical-force sensor arranged to sense a mechanical force in the armour and to output an output signal corresponding to the detected mechanical force; and circuitry arranged to receive output signals output by the mechanical-force sensor and to process the received output signals to determine whether damage to the armour may have occurred. The term "force" is to be understood broadly in this context, and includes for example stress, pressure, shock and load.

In an embodiment, the circuity is arranged to determine that damage to the armour may have occurred when the output signal received by the circuitry indicates that the mechanical force exceeded a predetermined threshold value.

In an embodiment, the sensor is provided by at least one accelerometer. Other sensor(s) may be used in some applications. In an embodiment, the mechanical-force sensor is attached to or integrated with the armour. In an embodiment, the system comprises a display for displaying an indication that damage to the armour may have occurred. In an embodiment, the display is provided as a separate component that is arranged to be selectively connected to and disconnected from the circuitry. In an embodiment, the circuity is arranged to latch when it has been determined that damage to the armour may have occurred, and the display is arranged to interrogate the circuitry to determine whether it has latched.

In an embodiment, the armour comprises plural armour plates, and comprising a respective mechanical-force sensor provided for at least two of said armour plates.

According to a second aspect of the present invention, there is provided a method of detecting damage to armour, the method comprising:

a mechanical-force sensor sensing a mechanical force in the armour and outputting an output signal corresponding to the detected mechanical force; and

using circuitry, processing output signals output by the mechanical-force sensor to determine whether damage to the armour may have occurred.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 shows schematically how peak acceleration varies with impact energy; Figure 2 shows a first example of modelled results from impact testing;

Figure 3 shows a second example of modelled results from impact testing;

Figure 4 shows schematically an example of apparatus according to an embodiment of the present invention; Figures 5 to 7 show schematically examples of sensor units and displays of embodiments of the present invention; and,

Figure 8 shows schematically another example of apparatus according to an embodiment of the present invention.

Detailed Description

When an impactor strikes the surface of armour, including in particular ceramic armour, it generates stress waves or Shockwaves which propagate through the bulk of the ceramic and along the surface of the ceramic. If the impact is sufficiently severe, the ceramic will fracture. The formation of the fracture generates stress waves which are in addition to those generated by the impact itself. The amplitude of the fracture- induced Shockwaves is often significantly greater than the Shockwave associated with the impact itself (particularly for marginal impacts which are just sufficient to cause fracture).

In one example of an embodiment of the present invention, a mechanical-force sensor is arranged to sense a mechanical force in the armour and to output an output signal corresponding to the detected mechanical force. The "mechanical force" may be, or may correspond to, the stress waves or Shockwaves that are generated by the impact itself and/or the stress waves or Shockwaves that are generated in the case that a fracture forms. Circuitry is arranged to receive output signals output by the mechanical-force sensor and to process the received output signals to determine whether damage to the armour may have occurred. The use of a mechanical-force sensor to sense a mechanical force in the armour, rather than use of inductive coils or breaks in electrically conductive pathways or other non-mechanical techniques as in the prior art, overcomes the problems discussed in the introduction above. As noted above, the term "force" is to be understood broadly in this context, and includes for example stress, pressure, shock and load. The mechanical-force sensor may be provided by for example at least one accelerometer. Some other suitable sensor capable of measuring stress, pressure, shock or load could be used instead. It may be noted that in practice Shockwaves of this type are typically short duration events, typically lasting less than lms or so. Accordingly, the mechanical-force sensor that is used is preferably able to resolve such short duration events to ensure accuracy and fidelity.

It has been found that, in many cases and for many materials and configurations or arrangements, the difference in peak amplitude between the stress waves produced from an impact whose severity is just below that required to cause fracture and that which is just above that required to cause fracture is significant, for example typically by a factor of 5 or more in peak acceleration. This is the case even when the formed fractures are hairline in width and a few millimetres in length. Figure 1 shows schematically an example of how peak acceleration, as measured by an accelerometer on the surface of an armour plate, varies with impact energy (as measured by a drop height). As can be seen, at low impact energies, the measured peak acceleration increases roughly in proportion to the impact energy (see the range represented by a drop height of 5 cm to around 30 cm in Figure 1). However, at a certain threshold impact energy, fractures form and there is a step change in peak acceleration (see the step change occurring between drop heights of 30 cm and 35 cm in Figure 1).

It is therefore possible for many cases to define a reliable threshold level for peak force or acceleration below which it is likely that no fracture has occurred and above which a fracture is likely to have occurred. In measurements we have conducted on a particular type of ceramic armour we find that a threshold of lOOg in peak acceleration in the in-plane directions and 200g in the out-of-plane directions works well. For different constructions, different values for the threshold may be required to provide the necessary performance.

For many cases, depending on for example the materials and configurations or arrangements that are used, the threshold level for peak force or acceleration may be such that it is certain or at least practically certain that no fracture has occurred if the peak force or acceleration is below that threshold, and, correspondingly, certain or at least practically certain that a fracture has occurred if the peak force or acceleration is above that threshold. However, there may be cases where the difference in peak amplitude between the stress waves produced from an impact whose severity is just below that required to cause fracture and that which is just above that required to cause fracture is small or only marginal. This may be the case with some ceramic materials for example. There may even be occasions in such cases where the peak amplitude following an impact whose severity is just below that required to cause fracture is greater than the peak amplitude following an impact whose severity is above that required to cause fracture. In such instances, an amplitude threshold cannot be used as an indicator that no fracture is certain to have occurred if the peak force or acceleration is below that threshold and, correspondingly, cannot be used as an indicator that a fracture is certain to have occurred if the peak force or acceleration is above that threshold. In such cases, a threshold will indicate a fracture has occurred with a certain probability.

This is illustrated by way of example in Figures 2 and 3.

In particular, Figure 2 shows an example of modelled results from impact testing on a material in which there is a large difference between the peak amplitude of an impact that results in a fracture and the peak amplitude of an impact that does not result in a fracture. In a case such as this, if the peak amplitude of the impact is above the threshold, it can fairly be said that a fracture has almost certainly occurred, and, correspondingly, if the peak amplitude of the impact is below the threshold, it can fairly be said that a fracture has almost certainly not occurred.

Figure 3 on the other hand shows an example of modelled results from impact testing on a material in which the difference is small, or the levels overlap. In this example, a threshold of lOOg would be successful in detecting nine out of ten impacts which resulted in the formation of a fracture (i.e. there is a 90% true positive rate). However, such a threshold would also incorrectly predict the formation of cracks in three separate impact events (i.e. 25% false positive rate). Increasing or decreasing the threshold will have the effect of adjusting the rate of true positives and false positives. In most instances it is envisaged that a threshold would be chosen to ensure that the true positive rate is as close as possible to 100% and a moderate false positive rate would be tolerated.

In another example of an embodiment of the present invention, a mechanical- force sensor is arranged to sense a mechanical force in the armour and to output an output signal corresponding to the detected mechanical force. Again, the "mechanical force" may be, or may correspond to, the stress waves or Shockwaves that are generated by the impact itself and/or the stress waves or Shockwaves that are generated in the case that a fracture forms. Circuitry is arranged to receive output signals output by the mechanical-force sensor and to process the received output signals to determine whether damage to the armour may have occurred. As noted above, the term "force" is to be understood broadly in this context, and includes for example stress, pressure, shock and load. The mechanical-force sensor may be provided by for example at least one accelerometer. Some other suitable sensor capable of measuring stress, pressure, shock or load could be used instead. In this example, the circuity is arranged to determine that damage to the armour may have occurred when the output signal received by the circuitry indicates that the mechanical force exceeded a predetermined threshold value. In some examples, the sensor is able to detect the formation of cracks anywhere within the bulk or on the surface of the armour.

As mentioned, the mechanical-force sensor may be provided by one or more accelerometers. The electronics circuitry analyses the output of the accelerometer(s) or other sensor(s) and records if the output of one or more of the accelerometers exceeds a threshold value associated with the formation of a crack in the ceramic. Other sensors capable of measuring stress, pressure, shock or load could be used instead of accelerometers. In an example, the sensor change of state is (electronically) latched and the new state (i.e. indicating for example that a crack in the armour has been (possibly) detected) is indicated on an electronic display which may be either integrated into the sensor or a separate device which can be connected to the sensor wirelessly or via a wired connection. The sensor and associated electronics circuitry for the sensor may be provided as a single module. Plural sensor modules, each with a sensor and associated electronics circuitry for the sensor, may be provided for the armour. The or each sensor or sensor module may be attached to the front face of the armour, to the side or to the rear. As noted above, the armour may be for example a layered ceramic armour having an outer layer of ceramic or similar material, backed by a layer of reinforced plastics or composite matter (e.g. Kevlar®), optionally with additional layers on both front and back, such as plastics coatings and foam to provide weather protection and protection against impacts with hard objects. In such a case, the or each sensor or sensor module may be provided between the ceramic layer and the reinforced plastics or composite backing. The advantage of attaching the sensor or sensor module to the front face or side of the ceramic armour is that the sensor or the sensor module can in many instances be retro-fitted to existing armour. The advantage of emplacing the sensor or the sensor module between the ceramic and composite backing is that the sensor or the sensor module itself is protected from accidental damage.

A display may be provided to interface with the sensor module/circuitry in order to provide a visual indication of whether or not the sensor module has detected an acceleration exceeding the threshold value. The display can be incorporated into a unit which also contains the sensor module and permanently connected to it. As an alternative, the display could be a discrete item, separate from the sensor module/circuitry, and connect to the sensor module/circuitry via a wired or wireless link. A single display can be connected to a multiplicity of sensor units (via either a wired or wireless link) and display the status of each sensor unit. The display may be provided with or connected to display electronics circuitry. It is preferred that the sensor electronics circuitry provides a latching function and that the display electronics circuitry interrogates the sensor electronics circuitry to determine whether the sensor electronics circuitry has latched, which indicates that a crack in the armour may have occurred, and provides an appropriate indication on the display for the user. The display and the associated display electronics circuitry may be provided in some examples as a display module or unit. Referring to Figure 4 of the drawings, in a first embodiment a unit 202 comprising a sensor module and a display module is attached to a piece of ceramic armour 201. Typical ceramics which may be used include AI2O3 (aluminium oxide or alumina), SiC (silicon carbide), S13N4 (silicon nitride) and B₄C (boron carbide). Other materials in addition to or instead of ceramics, may be used. The armour 201 in this case is in the form of a plate, though other shapes and configurations may be used. The armour may be for example personal armour, which is worn on the body of a user, or vehicle or building armour, etc. Figure 5 provides a more detailed view of an example of a sensor unit 301. The unit 301 contains a sensor module (not shown in Figure 5) which contains one or more accelerometers or other sensor(s) and electronic circuitry to read the output of the accelerometers and record when the output exceeds a threshold value associated with crack formation. This process is optionally continuously active from point of manufacture, whilst a power source is present, such that there is a continuous function of the detection of crack formation. A display module (not shown in Figure 5), which includes a display and the associated display electronics circuitry, contained within the sensor unit 301 interrogates the sensor module and provides an indication to a user whether or not acceleration exceeding the threshold value has been recorded via a display, optionally by learning whether the sensor electronics circuitry has latched, as discussed above. The display may be or include for example two light emitting diodes 302, 303 on the outside of the sensor unit 301, and/or some other display technology, such as an alphanumeric display which can be used to provide additional information such as the number of times the threshold was exceeded since the last read, the level of force detected, etc.) The display module is controlled via a switch 304.

Figure 6 shows schematically a more detailed view of another example of a sensor unit 405. An accelerometer module 401 contains one or more accelerometers or other sensor(s) and an electronics module 402 which analyses the output of the accelerometer module 401 and records whether or not a threshold value of acceleration has been exceeded. As described above, this measurement process may be continuous. A display module 403, which includes a display and the associated display electronics circuitry, interfaces with the electronics module 402 to indicate whether or not a threshold value of acceleration has been exceeded. The interface is controlled by a switch 404 which is accessible to a user from outside the casing of the unit 405. The switch 404 could, for example, be a simple push button to facilitate a "push-to-test" application.

Referring to Figure 7, in another embodiment, a sensor unit 501 containing at least a sensor module (not shown in Figure 7) is attached to the ceramic or other armour (not shown in Figure 7). The unit 501 in this example includes a port 502 to enable a separate display module unit 507 to interface via a wired connector 503. The display module unit 507 includes a display and the associated display electronics circuitry. The display module unit 507 interrogates the sensor module and indicates whether or not acceleration exceeding the threshold value has been recorded via a display (e.g. via two light emitting diodes 504, 505 on the outside of the sensor unit 501, and/or via some other display as discussed further above). The display unit is controlled via a switch 506.

Referring to Figure 8, in this example each of a plurality of discrete armour plates 601 is equipped with a respective sensor unit containing a sensor module 602. The sensor units communicate with a display unit 603 via either a wired or wireless link. The display unit 603 could be for example a separate hand held device, such as a tablet computer, "smart phone", etc., or a fixed display unit within a vehicle on which the armour plates 601 are mounted. The display unit 603 displays the status of each of the armour plates 601, in this case by a graphical representation of panels 604 corresponding to the armour plates 601, by indicating which sensor units have detected an acceleration event above the threshold associated with crack formation. For example, as indicated by dark shading in the display unit 603 shown in Figure 8, a threshold has been exceeded for one of the armour plates 601. It will be understood that the processor or processing system or circuitry referred to herein may in practice be provided by a single chip or integrated circuit or plural chips or integrated circuits, optionally provided as a chipset, an application- specific integrated circuit (ASIC), field-programmable gate array (FPGA), digital signal processor (DSP), etc. The chip or chips may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry, which are configurable so as to operate in accordance with the exemplary embodiments. In this regard, the exemplary embodiments may be implemented at least in part by computer software stored in (non-transitory) memory and executable by the processor, or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware).

The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

1. A system for detecting damage to armour, the system comprising:

armour;

a mechanical-force sensor arranged to sense a mechanical force in the armour and to output an output signal corresponding to the detected mechanical force; and circuitry arranged to receive output signals output by the mechanical-force sensor and to process the received output signals to determine whether damage to the armour may have occurred.

2. A system according to claim 1, wherein the circuity is arranged to determine that damage to the armour may have occurred when the output signal received by the circuitry indicates that the mechanical force exceeded a predetermined threshold value.

3. A system according to claim 1 or claim 2, wherein the sensor is provided by at least one accelerometer.

4. A system according to any of claims 1 to 3, wherein the mechanical-force sensor is attached to or integrated with the armour.

5. A system according to any of claims 1 to 4, comprising a display for displaying an indication that damage to the armour may have occurred.

6. A system according to claim 5, wherein the display is provided as a separate component that is arranged to be selectively connected to and disconnected from the circuitry.

7. A system according to claim 5 or claim 6, wherein the circuity is arranged to latch when it has been determined that damage to the armour may have occurred, and the display is arranged to interrogate the circuitry to determine whether it has latched.

8. A system according to any of claims 1 to 7, wherein the armour comprises plural armour plates, and comprising a respective mechanical-force sensor provided for at least two of said armour plates.

9. A method of detecting damage to armour, the method comprising:

10. A method according to claim 9, wherein the circuity determines that damage to the armour may have occurred when the output signal received by the circuitry indicates that the mechanical force exceeded a predetermined threshold value.

11. A method according to claim 9 or claim 10, wherein the sensor is provided by at least one accelerometer.

12. A method according to any of claims 9 to 12, wherein the mechanical-force sensor is attached to or integrated with the armour.

13. A method according to any of claims 9 to 12, comprising a display displaying an indication that damage to the armour may have occurred.

14. A method according to claim 13, wherein the display is provided as a separate component that is arranged to be selectively connected to and disconnected from the circuitry.

15. A method according to claim 13 or claim 14, the circuity latches when it has been determined that damage to the armour may have occurred, and the display interrogates the circuitry to determine whether it has latched.

16. A method according to any of claims 9 to 15, wherein the armour comprises plural armour plates, and a respective mechanical-force sensor is provided for at least two of said armour plates.