ARMOUR

RELATED APPLICATIONS

This application claims priority from Australian provisional patent application no. 2013901435 filed on 24 Apr. 2013, the contents of which are incorporated by reference.

TECHNICAL FIELD

The invention relates to armour. More specifically, the invention relates to an armour material, composite armour systems, armour plates and structures including such armour.

BACKGROUND

Armour is commonly used in military and civil applications to protect an underlying object such as a structure or person from an incoming projectile. Armour may be in the form of armour plates which are located on or incorporated within the structure such as a vehicle or located within clothing worn by the person.

Various configurations of armour plates have been proposed for redirecting an incoming projectile and absorbing the energy associated with the projectile. One such configuration is a composite armour plate which includes a composite matrix material supported by a backing plate. The composite matrix material includes a layer or multiple layers of hard ceramic spheres set in a polyurethane foam material.

When impacted by a projectile the hard ceramic spheres deflect the projectile and also undergo limited movement within the polyurethane foam material. This movement results in some of the kinetic energy of the projectile being transferred to the composite matrix. Accordingly, the energy of the projectile is at least partially dissipated within the composite matrix which assists to protect the underlying object from the projectile.

A disadvantage of the above described armour plate configuration is that during the impact of the projectile there is limited interaction between the hard ceramic spheres, the polyurethane foam material and the backing plate. As such, the effectiveness of the armour plate configuration to dissipate, absorb and redirect energy of the projectile is limited.

The below described invention seeks to improve or overcome one or more of the above identified disadvantages and/or at least provide a useful alternative to known composite armour plates.

The reference in this specification to any known matter or any prior publication is not, and should not be taken to be, an acknowledgment or admission or suggestion that the known matter or prior art publication forms part of the common general knowledge in the field to which this specification relates.

SUMMARY

In accordance with a first aspect there is provided, an impact absorbing material or armour including an impact absorption layer supported by a backing, the impact absorption layer including a plurality of substantially rigid macroscopic particles arranged in a spaced relationship relative to one another and a matrix interposed between the macroscopic particles, wherein the matrix is impregnated with substantially rigid microscopic particles.

In accordance with a second aspect, there is provided an impact absorbing material or armour for dissipating energy associated with an impacting projectile, the armour including an impact absorption layer supported by a backing, the impact absorption layer including a plurality of macroscopic particles and a plurality of microscopic particles which are substantially encapsulated by an at least partially flexible matrix, the microscopic particles and macroscopic particles being arranged to interact with one another such that when at least one of the macroscopic particles is moved during an impact, the movement is at least partially transferred to the microscopic particles thereby assisting to dissipate the impact energy.

In an aspect, the microscopic particles are spherical.

In an aspect, the microscopic particles have a diameter in the range of 5 nm to 1 mm.

In an aspect, the microscopic particles are formed from a ceramic material.

In an aspect, the ceramic materials include at least one of glass, silicon, fumed silica, alumina and kaolin clay.

In an aspect, the matrix is composed of between about 10% and 100% microscopic particles.

In an aspect, the matrix includes a polymer material impregnated with the microscopic particles.

In an aspect, the polymer material is at least one of a flexible or semi-flexible polymer adapted to retain the macroscopic particles and the microscopic particles.

In an aspect, the polymer material is at least one of flexible epoxy resin, polyethylene, polypropylene and silicon rubber.

In an aspect, the macroscopic particles are spherical.

In an aspect, the diameter of the macroscopic particles is between about 1 mm and 100 mm.

In an aspect, the spacing between the macroscopic particles is between about 0.5 mm and 20 mm.

In an aspect, multiple layers of macroscopic particles are provided, each layer being spaced apart from one another and being substantially encapsulated by the matrix.

In an aspect, the size of the macroscopic particles in each layer is substantially similar.

In an aspect, the sizes of the macroscopic particles in adjacent layers are of a different size.

In an aspect, an outermost layer of the macroscopic particles is partially exposed from the matrix.

In an aspect, the backing includes side walls thereby bounding the impact absorption layer.

In an aspect, the backing is formed from at least one of a highly resilient material and a semi-flexible polymer.

In an aspect, the backing is formed as a composite panel including a polymer material sandwiched between substantially rigid or semi-flexible sheets.

In an aspect, the plurality of macroscopic particles are arranged in a regular grid and held substantially in place by the matrix.

In accordance with a third aspect there is provided, a material, a structure, a vehicle or clothing including an impact absorbing material or armour as defined above.

BRIEF DESCRIPTION OF THE FIGURES

The invention is described, by way of non-limiting example only, by reference to the accompanying figures, in which;

FIG. 1 is a side cross sectional view illustrating an example of an armour material or armour system including an impact absorption layer supported by a backing, in this example, the impact absorption layer includes two layers of macroscopic particles retained within a matrix;

FIG. 2 is a top view illustrating the example of the armour shown in FIG. 1, the hatched macroscopic particles being the outer or front layer;

FIG. 3
a is a perspective view illustrating an example form of a backing of the armour;

FIG. 3
b is a side view illustrating the backing of FIG. 3a in a partially deformed state;

FIG. 4 is a side cross sectional view of the armour system showing an impacting projectile, the arrows indicating the expected energy transfer patterns of macroscopic particles within an impact absorption layer of the armour system;

FIG. 5 is a top view of the armour system shown in FIG. 4, the arrows indicating energy transfer patterns of macroscopic particles within an impact absorption layer of the armour;

FIG. 6 is a partial side view of two interacting macroscopic particles and showing the microscopic particles of the matrix between the macroscopic particles, the lines which join the microscopic particles are shown to represent the interaction of the microspheres as instantaneous force chains;

FIG. 7
a illustrates a model illustrating the interaction of two macroscopic particles and the microscopic particles of the matrix between the macroscopic particles;

FIG. 7
b illustrates a further model illustrating the interaction shown in FIG. 7a, with plates (representing the macroscopic particles and/or backing) and linkages between the plates (representing the microscopic particles and polymer of the matrix), the linkages being shown as individual lever segments joined by flexible elbows to represent the instantaneous force chain interactions;

FIG. 8
a illustrates a simplified model used in example System 1;

FIG. 8
b illustrates a simplified model used in example System 2;

FIG. 9 provides a table including material properties of the NSL-8 material;

FIG. 10
a provides a graph of the resultant force on the backing plate of System 1 as shown in FIG. 8a; and

FIG. 10
b provides a graph of the resultant force on the backing plate of System 2 as shown in FIG. 8b.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, there is shown an impact or energy absorbing material or armour system 10, referred to hereafter as “armour”, for protecting an underlying object from a ballistic projectile.

The armour 10 including an impact absorption layer 12 supported by a backing 14. The backing 14 includes bounding walls or sides 15 so as to form a recess 17 in which the impact absorption layer 12 is located and substantially housed. The bounding walls 15 contain and protect the impact absorption layer 12. The impact absorption layer 12 is arranged to face the direction of a potential incoming projectile and the backing 14 is generally located toward, abutted against or incorporated within an object to be protected such as a person, a vehicle or the like.

The impact absorption layer 12 includes a plurality of substantially rigid macroscopic particles 16 arranged in a spaced relationship relative to one another and a matrix material 18 interposed between the macroscopic particles 16. The matrix material 18 is impregnated with substantially rigid microscopic particles 20 such that the microscopic particles 20 are distributed throughout the matrix material 18 and are located between and around the macroscopic particles 16.

In this example, the macroscopic particles 16 are shown as being regularly-shaped, more specifically, spherical in shape. The diameter of the macroscopic particles 16 may be in the range of about 1 mm to 100 mm, and in some examples, in the range of about 4 mm to 20 mm The size of the macroscopic particles 16 will be dictated by the physical size of the incoming projectiles likely to be encountered by the armour 10. For example, larger projectiles will dictate larger macroscopic particles 16 to aid in energy absorption.

The macroscopic particles 16 will be constructed of a hard, impact resistant material which typically would be a ceramic such as silicon nitride. The macroscopic particles 16 may be spherical ceramic ball bearings.

The macroscopic particles 16 may be provided in layers in which each layer has a plurality of the macroscopic particles 16 in a generally planar alignment with one another and the backing 14. Typically, there would be more than one layer of macroscopic particles 16 to facilitate absorption and redirection of impact energy. However, a single layer may also be used in the simplest example of the armour 10.

In this example, two layers are shown, a first or outer layer 22 of macroscopic particles 16 and a second or inner layer 24 of macroscopic particles 16. However, the armour 10 may include any number of layers, for example, another example of the armour system may include 5 layers.

The macroscopic particles 16 are also positioned and sized in such a way as to minimise the likelihood of a projectile directly encountering the backing plate 14 or matrix 18 without coming into contact with the macroscopic particles 16.

Accordingly, each layer of macroscopic particles 16 may be geometrically offset or staggered relative one another. This provides an increased plan form surface area covered by the macroscopic particles 16 as may be best appreciated from FIG. 2.

Each of the macroscopic particles 16 in the outer layer 22 are spaced apart by distance “A” from the neighbouring macroscopic particles 16. Likewise, each of the macroscopic particles 16 in the inner layer 24 are spaced apart by distance “B” from the neighbouring macroscopic particles 16.

The macroscopic particles 16 in each of the outer layer 22 and the inner layer 24 are also spaced apart by distance “C”. In this example, the distances “A, B, C” are shown to be the same. However, each of these distances may be varied. The distances “A, B, C” may each be in the range of about 0.5 mm to 20 mm, and in some examples, in the range of about 0.5 mm to 2 mm Accordingly, each of the layers 22, 24 includes macroscopic particles 16 arrange in a predetermined and regular arrangement or grid defined by the distances “A, B, C”.

The macroscopic particles 16 in each individual layer may be of similar size. However, adjacent layers may include macroscopic particles 16 of differing sizes. For example, the inner layer 24 may include macroscopic particles 16 having a diameter of 8 mm and the outer layer 22 may include macroscopic particles 16 having a diameter of 4 mm.

In this example, the outer layer 22 of macroscopic particles 16 may be partially exposed to aid in physical deformation of a softer incoming projectile. In another example of this material system, the outer layer 22 of macroscopic particles 16 may also be covered by a cover or bounding plate (not shown) to prevent damage or loss of the outer layer 22 of macroscopic particles 16 due to disintegration under repeated impact. The bounding plate may be made of a lightweight plastic or a metallic sheet. A material that may be employed in the bounding plate may be a polycarbonate plastic.

In this example, the matrix 18 includes a polymer material 26 and the microscopic particles 20 are impregnated within and distributed within the polymer material 26 of the matrix 18. The polymer 26 may be flexible or semi-flexible polymer or a similar material with elastomeric binding properties.

The polymer 26 may be a tough polymer having a Young's modulus which can vary from 0.001 GPa to 2 GPa. In some examples, the polymer material 26 may include or be entirely composed of at least one of flexible epoxy resin, polyethylene, polypropylene or silicon rubber. In some examples, the polymer may be rubberised material.

The macroscopic particles 16 are set within the matrix 18 such that the matrix fills all of the gaps between and substantially encapsulates the macroscopic particles 16. Accordingly, each of the layers 22, 24 are spaced apart from one another and are substantially encapsulated by the matrix 18. The matrix 18 may also be utilised to bond the macroscopic particles 16 to the backing 14.

In some examples, each of the layers 22, 24 may be formed independently as single-macrosphere layers or sheets which can then be glued together (while maintaining the correct orientation of macrospheres 16 from layer to layer). The layer of macrospheres may be held in place by structures within a flat mold (not shown) and the matrix 18, (which may be provided in the form of an NSL-8 material as described below with reference to FIG. 9) may be poured or injected into the mold forming one layer when cured. To obtain a multi-layer grid or regular grid of macrospheres, individual sheets may be glued together, for example, using the NSL-8 material.

Alternatively, two or more layers of macrospheres can be held in the correct grid arrangement by a mold (not shown) and the matrix 18, which may in some examples be the NSL-8 material, may be injected into the mold under pressure forming one continuous, multi-layer sheet. These sheets of macrospheres may then be glued on to the backing plate 14.

The matrix 18 includes a high volume of the microscopic particles 20. In some example, the volume of the matrix 18 occupied by the microscopic particles 20 may vary from about 10% to 100%, and in other examples, the volume occupied by the microscopic particles 20 may vary from 10% to 60%. The size of the microscopic particles 20 may vary from 5 nm to 1 mm microscopic particles 20 may be regularly shaped particles, more specifically, spheres such as glass or silicon microspheres or nanospheres. The microscopic particles 20 may take the form of other regularly shaped objects such as microscopic plates, for example, kaolin clay platelets.

In addition, other regularly shaped objects may be introduced into the matrix 18 to increase its physical integrity and aid in energy dissipation. These objects may take the form of short fibres. An example of the armour 10 may also contain short aramid, carbon or glass fibres within the matrix 18.

The backing 14 is the final component of the armour 10 to encounter incoming impact energy or force. The backing 14 is constructed of materials which provide a high degree of resistance to impact. The material employed in the backing 14 must be capable of momentary deformation and recovery under impact.

Accordingly, the backing 14 may be in the form of a backing plate constructed of a material with high toughness and resistance to impact damage. The backing 14 may be constructed of high-density plastic such as polycarbonate plastic, steel, aluminium or titanium. The backing 14 may be constructed of a single, uniform plate of material such as a composite plate of fibre cloth set in a rigid or flexible binder or may take the form of a composite sandwich of plastic or metal plates and sheets of fibre cloth set in a polymer binder as is further detailed in FIGS. 3a and 3b.

Referring to FIGS. 3a and 3b, the backing 14 may also be constructed as a composite sandwich including one or more layers of microscopic tubes 32 (otherwise know as microtubes or nanotubes) sandwiched between the sheets or plates 30 and 31. The microscopic tubes 32 may be air-filled or filled with a fluid.

The plates 30, 31 may be formed from plastic such as polycarbonate sheets or metal and the small tubes 32 are set between the plates 30, 31 under pressure. These tubes 32 may take the form of glass-fibre tubes or carbon nanotubes set in a binding adhesive between the plates 30, 31. As an alternative to the tubes 32, the backing 14 may incorporate aramid fibre sheets set in a binding adhesive between the plates 30, 31.

Referring more specifically to FIG. 3b, arrow “D” illustrates the momentary deformation of the surface plate 30 which may occur when a projectile impacts the armour 10. The deformation of the surface plate 30 is communicated to the tubes 32 which in turn deform in response to the movement of the surface plate 30.

In this example, the deformation of the surface plate 30 is not directly experienced by the lower plate 31 or other parts of the backing 14 which can be a source of backing plate critical failure. The deformation of the hollow tubes 32 causes compression and movement of air or fluid within the tubes 32 which consumes a percentage of the incoming energy associated with the impacting projectile. The tubes 32 also experience a recovery force due to their elastic nature and this is communicated to the front plate 30 which assists the shape recovery of the front plate 30.

In yet another example form, the backing 14 may be constructed of a semi-flexible elastomeric material or as a segmented or reticulated arrangement of rigid metal or plastic plates. The flexible backing in combination with the flexible impact absorption layer 12 provides a flexible example of the armour 10.

Turning now to the function of the above described impact absorbing armour material or armour system 10, it may be appreciated that the armour 10 includes a combination of rigid and flexible components that work together as a system to absorb, dissipate or redirect the energy associated with an incoming ballistic projectile.

Referring to FIGS. 4 and 5, the armour 10 is shown with an impacting projectile 40 normal to the armour 10 surface. The arrows “E” shown in the Figures provide indicative representations of the pathways of energy and force dissipation likely to be encountered during impact of the projectile.

During such an impact, the macroscopic particles 16 are initially impacted by the projectile 40 and undergo constrained movement within the flexible or semi-flexible matrix 18. The backing 14 supports and contains the macroscopic particles 16 and the flexible matrix 18. The backing 14 provides a final impacting structure to stop the projectile 40.

Accordingly, it may be appreciated that the armour 10 provides three main components which function together as a system for absorbing, dissipating or redirecting the energy associated with the incoming ballistic projectile 40. The three main components are: the macroscopic particles 16, the flexible or semi-flexible matrix 18 and the backing 14.

Turning firstly to the function of the macroscopic particles 16, the hardness of the macroscopic particles 16 act to deform the relatively soft metallic projectile due to the velocity and kinetic energy of the impact. This primary deformation of the projectile increases its surface area thus decreases its penetrative potential. Due to the increased surface area of the deformed projectile, the likelihood of it encountering and interacting with more macroscopic particles 16 is increased.

As the projectile encounters an increasing number of macroscopic particles 16, the mass of the impact system increases, thereby decreasing the velocity and hence the kinetic energy of the projectile 40.

During such an impact there is also interaction between the adjacent macroscopic particles 16 and between macroscopic particles 16 and the backing 14. As a projectile strikes the energy absorption layer 12, the projectile 40 makes physical contact with one or more macroscopic particles 16. These macroscopic particles 16 react to the impact with constrained motion within the matrix 18. The energy of the impact is thus spread laterally throughout the energy absorption layer 12 as well as towards the backing 14 as more and more macroscopic particles 16 move in response to the impact.

Due to the arrangement of the layers of the macroscopic particles 16, the macroscopic particles 16 directed toward the backing 14 are predominantly at an angle to the backing surface less than 90 degrees. It is also noted that due to the physical properties chosen for the backing 14, impact at less than 90 degrees is far more likely to cause a deflection of the incoming energy or force thus minimising the likelihood of penetration.

Turning now to the second main component of the armour 10, the matrix 18. There are two mechanisms of energy dissipation within the matrix 18.

The first mechanism of the matrix 18 relates to the conservation of momentum whereby an impulse of energy caused by an impact event has the effect of producing a shock-wave that travels through a medium and causes damage to that medium. As the shock wave travels through the matrix 18, the shock wave encounters more and more microscopic particles 20 which are located within the matrix 18.

The microscopic particles 20 are forced into constrained motion within the polymer material 26 of the matrix 18. This motion of the microscopic particles 20 incorporates their mass, momentum and inertia into the system of impact. This has the effect of dampening the motion and absorbing the energy of the shock wave in motion and heat.

The second mechanism of the matrix 18, relates to the inertia linkage for the microscopic particles 20 as is shown in FIG. 6 also referred to as instantaneous force chains. In this Figure, the left hand macroscopic particle 16 undergoes an initial impulse in direction “F” of the right hand macroscopic particle 16.

The matrix 18, more specifically, the microscopic particles 20 located within the polymer material 26, provide elastic linkages or “pathways” also referred to as instantaneous force chains, shown as “H” to transfer energy between the microscopic particles 20 and ultimately the macroscopic particles 16. The matrix 18 absorbs at least a portion of the energy associated with the initial impulse such that the right hand macroscopic particle 16 undergoes a reduced impulse relative to the left hand macroscopic particle 16 in direction “G”.

Accordingly, the energy dissipation in the matrix 18 includes: instantaneous force chain interactions between adjacent microscopic particles 20; redistribution of vectors into a random cloud or mass of the microscopic particles 20; and the mass of the microscopic particles 20 which undergo constrained movement to dissipate energy via heat.

Referring to FIG. 7a, due to the inertia of the microscopic particles 20 within the matrix 18, a rapid impulse of energy is less likely to cause them to slide past one another. A rapidly applied force will take the path of least resistance which is directly through instantaneous force chains between which can spread out in all directions from the point of impulse.

These instantaneous force chains, indicated with the letter “J” in FIG. 7a, dissipate the energy or force throughout the matrix 18 allowing the matrix 18 to encounter a greater area or amount of the macroscopic particles 16, the backing 14 and the bounding sides 15 of the backing 14.

Referring to 7b, an analogy may be drawn wherein the matrix 18, in particular the interaction of the microscopic particles 20 within the polymer 26, are considered to behave as a multitude of small, interconnected inflexible levers 50 linked by flexible elbows 52. The levers 50 and elbows 52 providing an analogous linkage between impact receiving structures which in this example include plates 54, 56 and 58.

If the impulse is a rapid short event and the levers 50 inhibit the elbows 52 from rotating, more of the impulse is transferred from plate 54 to plates 56 and 58. However, if the impulse is a slower, longer duration event, the inertia of the levers 50 can be overcome and the levers 50 will merely rotate about the elbows 52 which results in very little of the impulse being transferred from the plate 54 to plates 56 and 58.

As may be appreciated from the FIG. 7b, the initial impulse is spread over a larger surface area. In this example, two plates 56, 58 are affected by the impulse received by the first plate 54 which dissipates and propagates the force to a larger area.

The third major component for energy dissipation is provided by the backing 14. The backing 14, in particular the materials and construction selected for the backing 14 as has been described above, are adapted to momentarily deform under stress and recover without critical failure.

The backing 14 represents a large surface for final energy dissipation. This large surface area is made accessible for energy dissipation by the interaction of the macroscopic particles 16 and the microscopic particles 20 set within the matrix 18.

Comparative Analysis Example

Referring now to FIGS. 8a, 8b, 9, 10a and 10b along with Equation 1 below, there is provided a simplified comparative mathematically modelled example to compare the performance of two armour systems or arrangements, System 1 and System 2.

The first armour system, System 1 as shown in FIG. 8a, is a simplified example of the reactive armour system 10 as substantially hereinbefore described and like numerals are used to denote like parts. Accordingly, System 1 includes three major elements being: the macrospheres 16a, 16b and 16c held in a regular grid but not in direct contact with each other or the backing plate; a flexible rubberised matrix 18 containing microspheres 20 and also holding the macropsheres 16a, 16b and 16c in a regular grid; and a backing plate 14.

In System 1, the diameter, D₁, of the macrospheres 16a, 16b and 16c is 10 mm, the distance, D₂, between the macrospheres is 1mm and the distance, D₃, between the outer edge of the macrospheres 16b, 16c and an edge of the model is 5 mm and the overall width, D₄, is 31 mm. The distance, D₅, is about 9.5 mm and the distance D6 is 6 mm.

System 2, is shown in FIG. 8b, and comprises only hard macrospheres 16a, 16b and 16c held in a regular grid in direct contact with each other and with the backing plate 20. Accordingly, the primary difference between System 1 and System 2, is that System 1 includes spacing between the macrospheres and the backing 14, and the matrix 18 including microspheres 20 held by a rubberised material.

In System 2, the diameter, D₁, of the macrospheres 16a, 16b and 16c is 10 mm, and the macrospheres 16b and 16c are arranged to directly abut the backing plate 14. The angle, A₁, is 40 degrees and as such the angle between the points of contact with the backing plate 14 and impact force, F₀, is 20 degrees.

Referring to FIG. 9, there is shown material data for NSL-8 which is a flexible epoxy material having microparticles that may be used as a binder material. The NSL-8 material was developed by and may be obtained from Thermal Mitigation Technologies of Louisiana, USA. In the example, the NSL-8 material is used to approximate the behaviour of the matrix material 18 in System 1. The NSL-8 material is used in this example due to the availability of the material data. However, matrix materials 18 other than the NSL-8 material may also be utilised.

General Experimental Model Approximations

Turning now to the models used to approximate and compare the backing plate impact forces (as shown in FIGS. 10a and 10b) of System 1 and System 2, a number of approximations were made in order to simplify the models and calculations. These approximations were as follows:

- 1. The armour systems were modelled only two dimensionally as a cross-section. In a three-dimensional model, force will be more effectively distributed since more macrospheres will become involved in the interaction but since this is a comparative simulation and the phenomenon will be observed in both models, this can be ignored;
- 2. In order to standardise and simplify the comparison, only 3 macrospheres and their interactions with each other and the backing plate were considered in both models. The macrospheres were arranged in a triangular “billiard ball” pattern with one macrosphere on the surface of the armour plate and two macrospheres behind it near to the backing plate;
- 3. The impulse will only be considered in an optimal position normal to the surface of the armour plate and on the central axis of the lead macrosphere. In addition, only force components normal to the backing plate will be considered in the final comparison;
- 4. A destructive impact will not be considered for the purposes of this comparison since all that is of interest in this instance is a comparison of how well each armour system distributes forces into the backing plate;
- 5. The sizes of the macrospheres in both models will be standardised to 10 mm diameter for the purposes of this comparative simulation;
- 6. In System 1, only the first impulse will be analysed and not the subsequent oscillations of the macrospheres and the microspheres which will in turn produce further force reverberations through the matrix. The reflections off the backing plate will not be considered either since all subsequent impulse forces will be smaller in magnitude than the primary impulse due to frictional energy loss;
- 7. In order to further simplify the comparative model, frictional forces and associated losses will not be taken into account;
- 8. It is assumed in this model that the hard macrospheres and backing plate are incompressible.

Model Development

Taking into account the above approximations, the experimental model for System 1 was developed around the approximation of the matrix material (being a flexible epoxy or rubberised material impregnated with microspheres) behaving similarly to a granular material when impacted. This approximation has been used because granular materials approach the behaviour of a rubberised solid due to interactions between the individual particles often referred to as instantaneous force chains (as for example shown in FIGS. 7a and 7b). The approximation of the matrix material being modelled as a granular material may be considered a conservative approximation for the behaviour the actual matrix material as the flexible polymer, being a rubber like or rubberised material, may absorb further impact energy in comparison to a purely granular material.

In particular, the assumption of a loose granular material has been applied whereby the interactions between the elements, in this instance the macrospheres 16a, 16b and 16c, are modelled as instantaneous force chains or linkages between the elements. The instantaneous force chains or linkages are provided with material properties, in this example for the NSL-8 material, such as a Young's Modulus so as to a least partially account the energy transfer and distribution of such a material between the macrospheres 16a, 16b and 16c.

Accordingly, System 1 may be modelled in accordance with the following equation:

$\begin{matrix} Force Model for System 1 \partial_{zz} = \frac{F_{0}}{2 π} \frac{2 (\partial_{1} + \partial_{2}) z^{2} [\partial_{1} \partial_{2} x \cos θ_{0} + x \sin θ_{0}]}{[(\partial_{1} z^{2}) + x^{2}] [(\partial_{2} z^{2}) + x^{2}]} & Equation 1 \end{matrix}$

In the model the following variables are utilised:

$\partial_{1} = r + \frac{\sqrt{(r^{2} - t)}}{t};$

$\partial_{2} = r + \frac{\sqrt{(r^{2} - t)}}{t};$

$t = \frac{E_{x}}{E_{z}};$

$r = 0.5 E_{x} (\frac{2}{G} - \frac{V_{z}}{E_{z}} - \frac{V_{x}}{E_{x}})$

It is noted that due to the response of a granular material, Equation 1 utilises t<r²and r>0. The material and physical data properties utilised are as follows:

- E_x=0.0344 (Young's Modulus in GPA in X axis);
- E_z=0.0344 (Young's Modulus in GPA in Z axis);
- V_x=0.5 (Poisson ratio in X axis);
- V_z=0.5 (Poisson Ratio in Z axis);

$G = \frac{E_{x}}{2 (1 + V_{x})} (Shear Modulus);$

- θ=0.0 (Angle of F₀to the Z-axis which in this case is zero as the impacting force is aligned with the Z-axis);
- F₀=1 (impact force of 1 Newton).

The experimental model example for System 2, is derived from a simple vector diagram. Since the macrospheres (16a, 16b and 16c) are in direct contact with each other and the backing plate, at the instant of force application, force will be communicated directly through the macrospheres into the backing plate. There are no intervening mechanisms which might further dissipate this force. Due to the two path-ways presented by the macrosphere arrangement chosen for the model of System 2, the force is effectively split in two (aside from the small components that are lost due to being at right angles to the axis of the backing plate).

$\begin{matrix} Force Model for System 2. F_{2} = \frac{F_{o}}{2} \cos (θ); & Equation 2 \end{matrix}$

In the model the following variables are utilised:

- θ=20° (Angle between Z-axis and contact point with backing plate, as shown in FIG. 8b).
- F₀=1 (impact force of 1 Newton).

This force is expressed at the points where each of the back two macrospheres make contact with the backing plate, causing two force spikes, as is shown and further described in relation to FIG. 10b below.

System 1—Description of the Model for Force Impact:

Referring again to FIG. 8a, the impulse force will first be encountered by the primary sphere, 16a. Under this impulse force, it will generate a force distribution within the matrix 18 which is felt in part by the two back macrospheres 16b, 16c and a proportion of which is felt by the backing plate 14. The two back macrospheres 16b, 16c will in turn generate their own force distributions within the matrix 18 due to the force exerted on them by the first macrosphere 16a. These secondary force distributions will be felt along with the remnant of the first macrosphere force distribution by the backing plate 14.

There are two dominant methods of force dispersal through the matrix 18 which will be taken into account in this simulation. 1. Through force propagation through the flexible matrix 18 via instantaneous force chain interactions between microspheres 20 in direct contact or close enough to form instantaneous force chains. 2. Through interactions within the matrix 18 between the macrospheres 16a, 16b and 16c

The first macrosphere 16a will react with constrained movement within the flexible matrix 18 due to the unity force acting on it. i.e. It will experience an acceleration due to the impulse force (F) but will also experience a deceleration due to the resistance of the flexible matrix 18. The first macrosphere 16a will produce forces similar in magnitude and direction to the forces produced by a static force pressing down on a flexible half-solid by a submerged, inflexible sphere.

The force acting on the plane which fully intersects the two remaining macrospheres 16b, 16c will be calculated. The resultant force acting on the remaining two macrospheres 16b, 16c will become the sum of the forces contained in the plane cut that intersect the macrospheres 16b, 16c.

The remaining two macrospheres 16b, 16c will be stimulated into movement in the same way as the first macrosphere 16a and will in turn produce their own force distribution pattern in the matrix. The force felt by the two back macrospheres 16b, 16c will be subtracted from the primary force exerted by the first macrosphere 16a. Finally the resultant force distribution felt by the backing plate 14 will be the sum of the forces exerted by all the macrospheres 16a, 16b, 16c. This resultant force distribution is plotted in FIG. 10a.

System 2 Description:

Referring again to FIG. 8b, System 2 is comprised of rigid spheres 16a, 16b, 16c in contact with each other and with the backing plate 14. Accordingly, compression of the macrospheres 16a, 16b, 16c and the backing plate 20 is not considered in this model and the force distribution becomes quite simple. The incoming unity force is communicated instantaneously to the backing plate via the contact points between the macrospheres and the backing plate. The force vectors normal to the backing plate may appear in two locations at the contact points between the back two macrospheres and the backing plate. These two force “spikes” are plotted on a graph for comparison with the resultant force distribution graph produced for System 1. This resultant force distribution is plotted in FIG. 10b.

Referring now more specifically to FIG. 10a, the results demonstrate that System 1 produces a more continuous spread of force over the length of the backing plate with two peaks at the points closest to the back two macrospheres. The magnitude of the force spikes for System 1, in this example, is 0.11 N.

In comparison, and now referring additionally to FIG. 10b, it is demonstrated that System 2 produces two discrete, discontinuous force spikes at the points of contact between the macrospheres and the backing plate. In this example, the magnitude of the force spikes for System 2 is 0.45 N which is over 4 times the force produced by System 1.

Accordingly, System 1 is better able to distribute the impact force and reduce the point force load on the backing plate and as such System 1, which is representative, of the armour 10 according to the invention described herein may provide advantageous impact absorbing properties, shielding and protection in comparison to previously known systems, which may function in a similar manner to that modelled above in relation to System 2.

In the light of the above, it may be appreciated that the above described impact absorbing material provided in the form of an armour plate system provides a rigid or semi-rigid plate of any shape and size which can be deployed to protect personnel, property or vehicles which are subject to projectile attack.

The armour material or armour plate system may take a number of physical configurations and may be deployed or arranged as an armour plates or other structure having continuous, unbroken armoured surface or as a series of discrete, interlocked or segmented pieces forming a semi-flexible whole (scale armour). When formed as scale armour, the armour system may be utilised as or for producing personal body armour for use by military or law-enforcement personnel. The armour plate system described herein may be formed as a stand alone armour plate or panel, or incorporated within another structure such as a side wall of a vehicle or clothing.

Advantageously, the material and armour system described herein includes a number of interacting components or sub-systems which interact with one another to deflect, dissipate and absorb energy associated with an impacting projectile such as a bullet. As described above, these components or sub-systems include the macroscopic particles, the matrix which includes the polymer impregnated with the microscopic particles and the backing.

More specifically, when the armour system or plate is impacted the hard macroscopic particles undergo constrained motion within the matrix. During this constrained motion the microscopic particles set within the polymer of the matrix also undergo constrained motion and dissipate the impact throughout the energy absorption layer and the backing. The backing also interacts with the matrix and hence the macroscopic particles so as to absorb energy from and physically restrain or contain the energy absorption layer.

While specific examples of the invention have been described, it will be understood that the invention extends to alternative combinations of the features disclosed or evident from the disclosure provided herein.

Many and various modifications will be apparent to those skilled in the art without departing from the scope of the invention disclosed or evident from the disclosure provided herein.

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