This invention relates to a fibre blend for ballistic protective fabrics for use in ballistic vests for use in the military and police and security services.

Background to the invention

Ballistic fabrics are usually composed of polyaramid fibres and the fabrics formed from these fibres are used in layers to provide bullet proof vests.

Synthetic fibres (like Kevlar, ballistic nylon, Twaron, Spectra and Zylon) have been commercially developed specifically for incorporation into light-weight protective products because of their very high tensile strength and low extensibility.

Essentially, all current commercial fabrics offering ballistic protection at NIJ Level III

A, are made from such pure synthetic yarns.

Stopping high-velocity projectiles by ballistic panels made from multiple layers of high-strength (synthetic-based) protective fabric is an extremely complex process. Many different influences determine how energy is lost at each stage of deceleration.

The polyaramid fibres are low friction materials and high speed projectiles can displace the fibres and yarns laterally. For the same reason these fabrics are less effective when wet and are not recommended for use in wet environments. Because the fabrics are heavy and are not breathable they cannot be worn for extended periods of time.

USA patent 5958804 discloses the use of flattened multi filament yarns of high strength filaments which include polyaramids.

USA patent 6668868 discloses a puncture resistant fabric composed of two types of fibres which may include polyaramids with cellulosic and polyester fabrics. Recent patents to ballistic fabrics look to different weave structures using essentially the same fibre material.

USA patent 7101818 discloses a polyaramid fabric entangled with non woven fibres using needle felting.

Blends of other fibres with polyaramids have been suggested for resistance to fire. USA application 2004/0001978 discloses a molten metal resistant fabric consisting of a blend of polyaramid, wool and flame retardant viscose.

Blends have also been proposed for cut resistant (as opposed to ballistic resistance) fabrics. New Zealand Crown research have developed a fabric blending wool with a liquid crystal polyester fibre

USA patent 6254988 by Du Pont blends cotton nylon and polyaramid fibres for a comfortable cut resistant fabric USA patent 6861378 discloses a ballistic fabric utilizing two yarns one of which is an aramid. The aramid fibres are not woven but are overlaid uni-axial, warp and weft wise and held together by an interwoven fabric of lowr tex yarns which are intended to maintain stable positioning of the aramid yarns.

It is an object of this invention to provide a high quality ballistic fabric that is able to be used in wet environments and is more comfortable to wear.

Brief Description of the invention

To this end the present invention provides a ballistic fabric composed of 80to 65 % of polyaramid fibres interwoven with 20 to 35% of animal or other natural fibres. The preferred animal fibre is wool and the preferred blend is 25% wool with 75% polyaramid fibres. It is preferred that the wool is not shrink proofed. The preferred polyaramid is Kevlar.

Three major modes of failure have been identified for ballistic fabrics that are subjected to impact from projectiles. From an analysis of these modes, it is recognised that the stopping-power of typical protective fabrics can be improved if mid-micron wool fibre is incorporated into the weave structure. The addition of wool, or other natural fibres, can also provide benefits in terms of ballistic performance, cost, wearer comfort, breathability and flame protection. If wool fibres are used, the strength of the fabric can be further enhanced if the wool is felted to further consolidate the weave.

Animal fibres other than wool also work and their effectiveness, depends on their specific properties such as fibre diameter and regain (= moisture absorbing) properties.

Cotton fibres are also suitable even though they are shorter, plant fibres with different diameters and regain properties.

The aramid (Kevlar or similar) is the primary energy-absorbing medium. The weaker wool (or similar natural) fibres play a complementary role without degrading the primary ballistic performance of the underlying basic aramid weave.. if the proportion of natural fibre rises too high, the ballistic performance will suffer because there will be (relatively) insufficient aramid. Insufficient natural fibre will not lock the weave effectively and will not adequately absorb moisture to make a sufficient difference to the wet properties of the fabric. If the type of natural fibres is changed (e.g., to cotton) then the blend proportions may have to be altered to account for their different regain properties.

The "filament thickness" and their number/yarn refers only the synthetic (aramid) component and such aramid yarns are selected and woven specific to the perceived threat. There are a range of aramid-based protective fabrics on the commercial market with different pick and end densities, and so the proportion of the natural fibres included in such fabrics would primarily be determined by this underlying fundamental aramid weave.

The purpose of the natural fibre, such as wool, is not to replace the synthetic as the primary energy-absorbent impact material. The natural fibre component fulfils a number of complementary functions:

1) To restrict the lateral separation of the synthetic yarns as the projectile tries to squeeze its way between yarns (or filaments) that it can not directly break.

2) To increase the frictional interaction at yarn intersections by forcing the filaments at cross-overs into tighter contact, and so increase the tensile forces needed to deform the fabric in the direction of the trajectory, and so restrict the effects of the recoil and interactions between closely-spaced layers.

3) To increase the forces needed to pull yarns out of the weave by increasing the frictional contact of filaments along yarns by randomly binding adjacent yarns and filaments together along their lengths. This longitudinal friction force, that restricts yarn pull-in/out, is in addition to that provided by the intersecting yarns, the lateral tensioning of which is the source of their frictional interaction.

4) To improve the moisture and temperature regulation within and through the ballistic fabric and so improve wearability and comfort.

5) To provide additional protection against flame and the melting of synthetics onto the skin.

The fabric design utilizing the blend of this invention is preferably a square-sett hopsack weave. The yarns are preferably aramid of approximately 100 tex and the wool is preferably wool of approximately 35 tex.. Preferably the weft sett of the base aramid fabric is approximately 10 - 15 p/cm and the associated warp sett is also approximately 10 - 15 e/cm.

In developing the current invention, attention has been focussed on adding wool to Kevlar or ballistic nylon. Analysis of the factors involved in achieving the positive performance results for these wool/synthetic blends have indicated that other cellulosic or protein fibres, particularly those with moisture-management capabilities, also have the potential to positively benefit the ballistic and comfort performance of protective fabrics woven from pure synthetics.

Detailed Description of the invention

Preferred embodiments of the invention are described with reference to the drawings in which

Figure 1 illustrates the yarn pull-in effects of impacts at different locations on a ballistic panel; Figure 2 illustrates a typical wool/Kevlar blend hopsack design according to this invention;

Figure 3 illustrates a test apparatus that applies lateral tension to fabric samples for yarn pull-out tests;

Figure 4 illustrate typical warp-yarn pull-out profiles for pure ballistic nylon fabric (lower) and felted wool-ballistic nylon blend fabric (upper);

Figure 5 illustrates comparative yarn-pull fabric samples after extraction of eight weft yarns from the warp - pure ballistic nylon Control fabric (left) and wool/ballistic nylon blend fabric (right);

Figure 6 illustrates comparative eight-yarn pull-out force profiles for three felted wool/ballistic nylon blend fabrics against an equivalent pure ballistic nylon Control fabric having a maximum peak at 2000 N;

Figure 7 illustrates Tear Strength tests on dry, pure Kevlar Control fabric, weft;

Figure 8 illustrates Tear Strength tests on dry, un-felted wool/Kevlar fabric, weft;

Figure 9 illustrates Tear Strength tests on dry, pure Kevlar Control fabric, warp; Figure 10 illustrates Tear Strength tests on dry, un-felted wool/Kevlar fabric, warp;

Figure 11 illustrates the strike face of a typical target panel showing sewn lines and location of impacts under NIJ Level IHA; Figure 12 illustrates a Control ballistic test under NIJ Level HIA with 10 layers of

Kevlar 704 fabric and 26 layers of Kevlar 363 fabric;

Figure 13 illustrates a ballistic test under NIJ Level IUA with 10 layers of Kevlar plus

26 layers of un-felted wool/Kevlar blend fabric; Figure 14 illustrates a ballistic test under NIJ Level HIA with 10 layers of Kevlar plus

26 layers of felted wool/Kevlar blend fabric;

Figure 15 illustrates a ballistic test under NIJ Level IHA with 10 layers of Kevlar plus

18 layers of un-felted wool/Kevlar blend fabric;

Figure 16 illustrates the strike face for Panel #1 (wet test) showing sewn lines and location of impacts;

Figure 17 illustrates the strike face for Panel #2 (wet test) showing sewn lines and location of impacts;

Figure 18 illustrates a wet ballistic test under NIJ Level HA with 20 layers of un-felted wool/Kevlar blend fabric; Figure 19 illustrates a wet ballistic test under NIJ Level IHA with 10 layers of Kevlar plus 26 layers of un-felted wool/Kevlar blend fabric.

Stopping high-velocity projectiles by ballistic panels made from multiple layers of high-strength (synthetic-based) protective fabric is an extremely complex process. Many different influences determine how energy is lost at each stage of deceleration. The justification for blending wool into pure-synthetic fabrics arises from considering the different contributions to energy absorption from each failure mode at successive layers in a ballistic panel. When a high-speed projectile hits the first fabric layer in a multi-layered stack, the first layer suffers tensile failure caused when a longitudinal strain wave, exceeding the extensibility limit (2 - 3% for Kevlar), propagates along the yarn filaments at the speed of sound. This speed is determined by the density and Young's Modulus of the synthetic. The modulus for aramid fibres is strongly strain-rate dependent, so at very high impact velocities, aramid fibres may appear much stronger than at low velocities, with a complementary reduction in extensibility. Yarn filaments fail by near-instantaneous tensile extension. Very high localised strains may even cause premature stress failure if any surface roughness, blemishes or micro-cracks exist that can act as sites for failure initiation. Surface integrity is particularly important for those filaments forming the outer layer of a bundle in a yarn. The accompanying transverse wave from a high-speed impact is slower to propagate. Catastrophic yarn failure occurs before the strain energy of the transverse wave can be absorbed, so the entry hole is neat and round. The propagation of this transverse wave forms a square pyramidal shape of gross fabric distortion in the direction of the trajectory, the corners of which align with the warp and weft. This distortion strains those principal yarns not directly in contact with the tip of the projectile, and also causes their intersecting cross-yarns to be strained. Even without yarn slippage at these intersections, the result of these mutual strains in the direction of the trajectory must result in a separation of adjacent yarns - the "net" structure of the weave must open up

For low-friction filaments like Kevlar, there may also be yarn slippage at intersections. The remote yarn strain, and the slippage at intersections, both absorb kinetic energy. Warp and weft yarns may be strained to the point of (remote) failure even when they are not physically impinged by the projectile. Even if they do not fail, they may be strained beyond their elastic limits so that after the fabric relaxes, a permanent distortion in the formerly planar fabric surface will result. Some failure characteristics in the first few layers depend on the shape of the tip of the projectile.

Two effects are evident. For a pointed nose, the projectile can physically slip between adjacent yarns (or filaments) by displacing them laterally. This is more likely if the angle of incidence is not 90° to the fabric. Thus, there may be considerable variability in the modes of energy absorption. A projectile with a blunt nose can cut straight through a fabric because of the extremely high localised stresses imposed on the fabric by the sharp corners.

Heat generation and the temperature of the projectile prior to and during the impacts with the fabric layers may reduce the ballistic performance of the impacted fabrics by softening, melting or charring them. This may assume importance for synthetics such as polyethylene. Impacts with successive fabric layers cause the temperature of the projectile to rise due to the friction between the nose and the impacted yarn filaments, and the internal heat generated by the mushrooming of the nose as it decelerates. The frontal shape of the projectile is important when considering subsequent frictional energy losses at each layer, and modes of energy loss become complex at each subsequent impact.

The deflection of the weave along the trajectory path may be fairly localised in the first few layers of the panel because strain failure will occur before the transverse wave can fully propagate. As the projectile slows and distorts, the transverse energy wave may have sufficient time to propagate radially from the impact point to reach the boundaries of the fabric sample before the projectile breaks through to the next layer. The transverse energy wave can now be reflected from the edges of the fabric layer. The far-field boundary conditions that depend on the sample size, the distance of the impact from each edge, and how the edges of the fabric layers are constrained), will determine the form of any reflection, recoil, and associated energy losses.

One problem with fabric distortion along the trajectory path is that it may reach a considerable depth before full penetration takes place and the fabric layer recoils. For a ballistic vest, this may lead to it being classed as a "failure" due to blunt trauma.

As a mushrooming projectile advances through a fabric stack, the mode of failure at each layer changes as the projectile decelerates. The increasing frontal area means that more and more (principal) yarns are directly impacted, to be stretched and broken, or laterally displaced. As cross yarns slide over each other due to transverse strains, some yarns in the weave are pulled along their lengths. This "yarn pull-in/out" is a major mode of energy dissipation at lower impact speeds. For yarn pull-in/out, the projectile does not possess sufficient kinetic energy to immediately cut through the yarns. As the yarns rise in tension, a transverse wave is set up which strains the cross yarns so they start to slide past each other. The principal yarns, in direct contact with the projectile, start to straighten, stretch, and begin to be pulled into the developing impact hole. The principal yarns then interchange their weave crimp with their cross yarns, and this interchange progresses radially from the impact point toward the edges of the fabric. If the projectile has sufficient energy, the principal yarns eventually fail in tension, and the projectile slips through the hole so created, laterally displacing some unbroken adjacent yarns as it goes. If the kinetic energy is lower, these principal yarns will be pulled in along their length toward the impact point from the periphery to form a "cross" shape of longitudinally displaced yarns. Yarn pull-in toward the impact point, leads to high levels of energy dissipation.

Energy dissipation in the yarn pull-in/out mechanism depends on at least three important parameters: 1 ) The yarn-to-yarn surface friction of the filaments

2) The lateral tension that is applied to the intersecting yarns in the fabric, perpendicular to the principal yarns being pulled out. This tension - related to the edge constraints in the panel - increases the yarn-to-yarn friction at intersections and so increases the force needed to extract yarns, 3) The number of yarn intersections that contribute to the total frictional force that must be applied to pull out the yarns. For a ballistic panel, this is directly related to the fabric sett and the proximity of the impact to the edge of the panel.

The location of the impact point (Figure 1) on a ballistic panel is important if it has close proximity to an edge or a corner because significant yarn pull-in can occur even if the projectile ultimately pierces the layer. Substantial fabric distortion occurs as the principal yarns slide through the fabric. The number of yarns so displaced will depend on the diameter and shape of the mushroomed projectile at that layer, the proximity of the projectile to the fabric edge, and any edge constraints applied to the layers forming the panel. A projectile, centrally impacting a fabric sample, will try to un-crimp the principal yarns and then pull them in equally from all sides. Friction from crossovers prevents yarn pull-in if samples are large enough. A projectile impacting toward one edge will unequally pull in yarns from all sides. For a large sample, friction from crossovers preferentially allows significant yarn pull-in from one side. Incorporating wool in the weave reduces yarn pull-in and increases energy dissipation. A projectile impacting toward one corner of a sample preferentially allows yarn pull-in from two sides. Incorporating wool in the weave reduces yarn pull-in and increases energy dissipation.

Example

In terms of final fabric weight, yarn tex and weave sett, the design of the wool-blend ballistic fabrics herein described was broadly based on existing commercially available ballistic fabrics such as Kevlar A363. The properties of the pure Kevlar yarns woven into the commercial A363 fabric are set out in Table I and the characteristics of the finished fabric are set out in Table II.

TABLE I Yarn T964C Keylar 129 used in Keylar Fabric A363

After extensive research trials in which singles and two-fold woollen yarns (-35 tex) were blended with multifilament ballistic nylon or Kevlar yarns, several blended fabrics was developed. A typical hopsack design is shown in Figure 2. The wool must be introduced as yarn at the weaving stage. Intimate fibre blends of wool and synthetics during yarn formation are not practicable due to the great dissimilarity in fibre properties. The wool cannot be incorporated into existing pure synthetic ballistic fabrics because the base synthetic weave must not be damaged.

The wool and synthetic may be inserted as parallel yarns into the warp and weft of a square sett plain hopsack weave.

A commercial mill produced several styles of wool/Kevlar blend fabric at 300 p/min.

The 93 tex Kevlar base weave was woven at 11 e/cm x 11 p/cm, with a two-fold 35 tex wool yarn inserted as a parallel input to give a hopsack design in the warp. In the weft, several types of pick insertion were used to produce different woven structures.

In the "semi-hopsack" design, the adjacent wool and Kevlar picks were inserted alternately and the pick density of the primary Kevlar yarn was reduced as a result, as indicated in Table III. The effects of felting the wool yarns in the fabrics, with the associated weave consolidation can also be seen by the changes in pick and end densities and fabric weights.

TABLE III

Some blended and pure Kevlar fabrics subjected to ballistic testing under NIJ Level IMA.

Yarn Pull-in/out Tests Energy dissipation occurs when a projectile pulls in unbroken principal yarns from the weave structure toward the impact point. The ease with which yarns can be pulled out of a woven sample gives a measure of how well the yarns are held in place by the frictional interactions between the warp and weft intersections. Factors influencing this pull-in/out force include the: • style of weave,

• coefficient of surface friction of the yarns and their constituent fibres,

• the number of yarns to be extracted

• pick and end density,

• size of the sample, • lateral tension applied perpendicular to the direction of the yarns being pulled out,

• speed of withdrawal of the yarns,

• effect of inter-fibre and inter-yarn bonding mechanisms, especially at yarn intersections,

• whether the edges have been sewn or otherwise bonded.

Increasing energy dissipation by yarn pull-in is important near the edges or corners of a ballistic panel where the number of restraining cross-yarns are fewer or shorter. Incorporating wool in the weave increases the interaction forces during yarn pull-in, so dissipating more energy.

The yarn pull-in/out test in Figure 3 shows a sample mounted in a frame in a laboratory tensile testing machine. The fabric sample is cut and mounted so as to define an active test area of 100 mm x 100 mm. The lower jaw clamps the bottom of the sample, and a fixed lateral tension is applied to the sides. Eight centrally located yarns are clamped in the top jaw and are cut just above the bottom jaw to define a frictional interaction length of 100 mm. These eight yarns are then withdrawn vertically from the sample at 50 mm/min.

Figure 4 clearly shows the benefits of the wool component when eight warp yarns are extracted from the weft for a felted wool/ballistic-nylon blend fabric (upper curve) compared with its pure ballistic-nylon Control (lower curve). The energy absorbed by the wool-blend is greater by a factor of ~3. The peak force is greater by a factor of ~2, and is maintained for an extra withdrawal distance (~6 mm) before the characteristic sawtooth failure profile sets in. This indicates that the wool locks the weave together and prevents cross yarns from releasing prematurely. Figure 5 shows that compared with that of the pure synthetic Control fabric (left), the residual failure zone for the wool-blend fabric (right) is restricted only to the very edge of the sample. The different shapes of the failure zones show how the synthetic yarns along an edge can be easily unravelled without the wool constraint. For the pure ballistic-nylon fabric, the failure zone where cross yarns have been pulled out, extends considerably further in toward the middle of the sample. This indicates that the synthetic yarns can easily be displaced laterally and intersectional friction is low. The force that restrains the lateral displacement and longitudinal pull-out is increased when the wool is present, especially if the wool has been felted into the base weave.

Figure 6 compares the 8-yarn pull-out force for three samples of wool/ballistic-nylon fabric with an equivalent pure ballistic nylon Control fabric. The lowest profile (with a peak maximum ~ 1700 N) shows weft yarns being pulled out of the warp. Although the pick density for this sample was only 9.5 p/cm (c.f., 11 e/cm for warp), the peak force recorded was only 15 % below that for the Control fabric (which exhibited a peak maximum -2000 N). Using a sample cut from the same wool/ballistic-nylon blend fabric, the highly "sinusoidal" curve resulted when eight warp yarns were extracted from the weft. Here the majority of the sinusoidal multiple force peaks (up to ~2500 N) exceeded the peak for the ballistic-nylon Control, until a considerable length (~ 70 mm) of the eight yarns had been withdrawn from the weave. Synthetic yarns in a blended weave can be so well constrained by felting-in the wool component that they fail in tension when their sliding withdrawal is totally prevented. This is shown in the third profile where the peak force (where the eight yarns failed in tension) reached 4500 N.

Wet and Dry Tear Strength Testing

Tear Strength tests, broadly based on Standard AS 2001.2.10 (Determination of Tear Resistance of Woven Textile Fabrics by the Wing-Rip Method), were also carried out. Once beyond the initial peak in the tear strength (N), (see Figures 7 to 10), the remaining yarns tend to fail with a fairly constant force given by the Mean Tear Strength. Table IV shows:

> Both the un-felted and felted wool/Kevlar blends are stronger (by between

31.2% and 44.1%) than the equivalent pure Kevlar Controls for both wet and dry tear strength tests. > In both warp and weft directions, tear strength is reduced between dry and wet states for all three fabric styles. This strength reduction is 25.5% (weft) and 21.3% (warp) for pure Kevlar, it is 22.8% (weft) and 21.6% (warp) for the un-felted wool/Kevlar blend, but it is only 8.2% (weft) and 14.1% (warp) for the felted wool/Kevlar blend. > The un-felted wool/Kevlar blends are slightly stronger than their felted equivalents in three out of four cases. The felting process may cause damage to the fabric that reduces performance more than is gained by the weave consolidation induced by the felting-in of the wool. > When wet, the felted form of the wool-blend fabric performs relatively better than if un-felted due to the effects of the natural fibres swelling and consolidating the weave structure.

> A comparison of mean tear strengths for warp and weft in Table V show the significant improvement of the wet un-felted and felted wool/Kevlar blends over the dry pure Kevlar fabric. Even when wet, both the felted and un-felted wool/Kevlar blend fabrics are stronger to tearing than the dry pure Kevlar fabrics, by between 20.2% and 25.1%.

A 20% reduction in ballistic performance for commercial Kevlar vests, when wet out, is well recognised. To pass NIJ Level IMA requires wet testing, and a pass may require that the number of layers in a vest be increased from 32 to 36 layers, with an associated increase in weight, discomfort and cost.

Wool in a synthetic blend offers significant advantages. Wool fibres absorb up to 36% of their own weight in water without feeling wet, and the fibre diameters expand by ~ 16%. This effect tightens the weave and increases the mass that the bullet must penetrate. Although synthetic filaments may be lubricated by interstitial water, they are held more tightly in place by the grip of enveloping wool fibres and yarns. Felted wool-synthetic blend fabrics show an improved tearing performance when wet, however if un-felted wool blends can perform adequately, the removal of the felting process is a significant cost saving and simplification for fabric manufacture. TABLE IV

Percentage improvements in the Mean Tear Strengths of wool/Kevlar blends relative to the pure Kevlar controls, for dry and wet conditions.

TABLE V The percentage improvement in the Mean Tear Strengths for WET wool/Kevlar blends compared with the DRY pure Kevlar Control having weft strength (528 N) and warp strength (497 N).

Dry Ballistic Tests

Sample panels containing between 18 and 36 layers of wool/synthetic and/or pure synthetic fabric layers in various combinations were generally (dry and wet) tested according to NIJ Ballistic Standard at Level III A.

Panels were impacted by the minimum array of six shots in a set pattern from either a Luger 9 mm Full Metal Jacket - Round Nose (8.2 g at 436 m/s), or from a 44 Magnum Sem- Jacketed Hollow Point (15.6 g at 436 m/s). Extra shots were also fired close to the edges, corners and sewn lines on some panels, to evaluate the extent of yarn pull-in and the modes of energy absorption and fabric failure.

The strike face of a typical panel is shown in Figure 11 with the major area (on the right) reserved for the Standard NIJ 6-shot test to be carried out through the full panel thickness composed of varying combinations of wool-blend synthetic or pure synthetic fabrics. The smaller area (on the left) exposed a smaller number of layers to the extra shots close to the edges. Tests were initially done on dry panels (this section). The number of layers penetrated and the Back Face Signature (BFS) for four representative dry tests are summarized by the stylisations of Figures 12 to 15, and in Table Vl.

There is variability in penetration depth and BFS indentation for each of the shots in each of the panels. Bearing in mind the differing modes of energy dissipation as each layer is penetrated, the wool-blend panels performed as well as the pure aramid Control. Shots # 7 and #8 were deliberately aimed near the edge/corner of the panels, in direct contradiction to the requirements of the NIJ Standard. Only one bullet fully penetrated any panel (Shot #7 in Panel #4) and this was through only 18 layers. Clearly 18 wool-blend layers were insufficient to prevent penetration, but 26 layers could. Because the un-penetrated layers are deformed and recoil as a single unit, their number is important for limiting the BFS.

With 44 mm being the pass/fail level for the NIJ Standard, it is clear that the two BFS failures occurred when the panel had only 26 rather than 36 layers. Although one failure was for a felted assembly of Kevlar/wool and one for an un-felted assembly, these two blend combinations also produced an impact that passed the Standard. The felted and un-felted blends may therefore be seen as performing equivalently. The three impacts through felted fabrics that penetrated ftyrfΛesf through the panel nevertheless gave relatively lower BFS values. Thus, a greater number of penetrated layers should not be viewed as a precursor to catastrophic failure by full penetration, but may be a preferred result, if the BFS is reduced. One aim of adding wool to the Kevlar is to modify the mode of yarn and fabric failure in a panel in such a way that all bullets can be prevented from penetrating, with an associated reduction in the BFS. Both of the outcomes should hopefully be achieved at a lower cost (e.g., with fewer layers), or with other benefits (e.g., improved comfort).

For wool/Kevlar blend fabrics, cross-shaped yarn-pull-in distortions are almost never seen, indicating that the presence of the wool component inhibits crimp interchange and yarn-pull as an energy-dissipating mechanism in stopping the bullet. More energy is therefore expended in tensile-breakage of the synthetic yarns. The wool also significantly inhibits the lateral displacement of adjacent Kevlar yarns. Thus all Kevlar yarns in the impact cross section are forced to substantially fail before bullet penetration to the next layer can occur. Particularly for the wool/Kevlar blend fabrics, Kevlar yarns from one layer may be substantially "trailed through" to the next and subsequent layers, even several layers beyond that at which the bullet is finally brought to rest.

So long as there are a sufficient number of layers, first to prevent penetration, and second to limit the BFS, the ballistic performance of the dry wool-blend panels appears to be equivalent to the dry pure Kevlar Control.

TABLE Vl Test 476 Panel 1 - Pure Kevlar (K)

Test 477 Panel 2 - Keylar (K) and/or Un -FeI ted (UF) Wool/Keylar WK Blend

Test 478 Panel 3 - Keylar (K) and/or Felted Wool/Keylar (WK Blend

Test 479 Panel 4 - Keylar K and/or Un -Fe I ted (UF) Wool/Keylar (WK) Blend For the wool-blend fabrics, there is almost never any indication of crimp interchange showing the typical cross-shaped pattern of yarn pull. The yarns are clearly held in place and the failure is usually seen as a neat hole, with all yarns broken and with any long trailing ends carried through to the next and subsequent layers. The highly distorted bullet may be stuck in the hole in such a way as to bind a number of layers together. The fabric closely encapsulates the bullet and there may be fibrillation and blackening of several layers beyond the one at which the bullet stopped. In addition, all bullets show a clear imprint of the fabric weave on the central part of the face and a smeared or streaked appearance of the weave imprinted around the edge of the mushroom-shaped bullet.

Wet Ballistic Tests

Table VII summarizes the assembly of the two panels and the types of bullets used to wet test under NIJ Levels HA and HIA. Figures 16 and 17 show the arrangement of the two targets and the approximate locations of the impacts.

TABLE VII

Panel #1 , shown in Figure 16, was a simple assembly of 20 layers of Kevlar/wool blend with a single line sewn across each diagonal and a rectangle sewn 250 mm x 180 mm in the middle. This panel was tested under NIJ Level HA using Luger 9 mm bullets.

Panel #2 was designed with two strike areas shown in Figure 17. Panel #2a, represented by the major (right) area of the strike face, allowed the Standard NIJ IIIA test to be carried out through the full stack of 36 layers using 44 Magnum SWC GC bullets. Panel #2b, represented by the smaller (left) area of the strike face, was exposed so that three 9mm Luger FMJ shots could be fired through the back 26 layers. These layers were made from the Kevlar/wool blend fabrics, whilst the front 10 layers were commercial Kevlar 704 fabric. All layers were sewn together with a single line across each diagonal and a square (of side ~18 cm) in the middle of the full stack of layers as shown in Figure 17. The smaller (left) area also had a single diagonal sewn line to hold these layers in place.

On Panel #2, the first test consisted of six NIJ impacts at Level HIA using 44 Magnum semi-jacketed hollow-nose bullets weighing 15.5 g. Shots #4 and #5 were incident at an angle of 30° to the normal to the strike face. Three additional shots (Shots #7 to #9) using 9 mm Luger FMJ bullets were then fired into the smaller area of the strike face, avoiding the 10 front layers. Two of these three extra shots were deliberately directed close to the corners of the panel in order to evaluate the effectiveness of the wool component in preventing the pull-in of Kevlar yarns near free (un-sewn), or minimally restrained, edges and corners.

This test particularly determined the effect on the ballistic performance caused by the uptake of water, either absorbed within the fibre (wool), or held within the interstitial spaces between the fibres (wool and Kevlar). The panels were wet out under vertical sprays according to the requisite NIJ Standard. At the time of testing, for Panel #1 , the wet pickup was 4.4%, and for Panel #2 the pickup was 6.0%. The commercial Kevlar fabric had been given a water-resistance treatment as part of its normal manufacturing process, and the wool/Kevlar blend fabric was given an equivalent water-resistance treatment.

The basic results are summarized in Table VIII and in the two stylisations of Figures 18 and 19. TABLE VIII

Panel #2 - Kevlar (K) and/or Kevlar/Wool (KW) Blend - Combined Tests Levels IHA (Shots 1 - 6) and IIA (Shots 7 - 9)

Examination of Figure 18 and Panel #1 of Table VIII showed that the wet blends exhibited very good stopping power and Back Face Signature for five of the six shots under NIJ Level MA. The one failure was Shot #3, which completely penetrated the panel and lodged in the clay backing mass. Although this shot did have the highest impact velocity of the six (348.0 m/s), it fell within the prescribed limits (± 9.2 m/s) set by the Standard. Like Shot #2, which passed the test, Shot #3 had been fired close to a diagonal line of sewing.

At the layer(s) where Shots # 1 , #2 and #6 were brought to rest, the mushroomed bullets were completely trapped and well encapsulated by unbroken yarns and fibres pulled through from a number of preceding layers. Despite the wetness of the test Panel #1, there was little indication of yarn-pull as an energy dissipation mechanism except for the last one or two layers where the bullets became encapsulated by unbroken yarns. Yarns were fully broken and the trailing ends pulled through the hole, which indicated that maximum energy was dissipated breaking filaments that were firmly held in place by the crossover-friction of the weave crimp, rather than due to yarn slippage caused by the moisture-reduced surface friction that allows yarns to slip over each other.

Figure 19 shows the penetration depths and Back Face Signatures for the six bullets impacting the Kevlar and wool-blend composite Panel #2 of 36 layers. Despite the presence of water, all six shots passed the NIJ Level III A Standard, although Shot #3 was close to the 44 mm limit for the BFS.

For the second wet test on Panel #2, based on the 26 layers tested at NIJ Level Il A, all three shots (#7 to #9) clearly passed, both in terms of penetration and BFS. In this test, Shots #8 and #9 were deliberately fired toward the corners of the sample, whilst Shot #7 was placed in the central line, and 120 mm away from the nearest edge, and fairly well removed from any lines of sewing. Shot #8 was approximately 50 mm from both edges and there were no constraining lines of sewing anywhere in the vicinity. Its penetration to Layer #11 may be explained by the fact that each layer was free to react independently (and fully recoil separately) until Layer #11, after which, the remaining 15 layers acted in unison. Shot #9 was fired 90 mm away from one edge and 80 mm from the adjacent edge, but also had the apparent benefit of a constraining line of sewing.

The presence of lubricating water, especially on the filament surfaces and migrating along the interstices between the filaments, would normally increase yarn/filament slippage and the lateral separation of cross yarns. The effect of the water-resistance treatment on the fabric is to increase the tendency for the water to be shed from yarn surfaces so it is less likely to penetrate between the filaments. Wool has the advantage of being able to absorb some of this excess water (up to 36% of its own weight) before any remains as sensible water on the surface. Any excess water that is not shed from the fabric surface may therefore be absorbed by the wool. The absorbed water also swells the wool fibres so the weave is further tightened, thus locking the intersections and restricting filament movements, either along their lengths or as lateral yarn separations. Water absorbed into the wool also temporarily increases the mass of the wool-blend yarns (until it dries out) so that the heavier fabric can better absorb the energy of the impact. Ballistic Summary for Exemplified Fabric Samples

The above results show that the inclusion of wool into a square-sett base synthetic weave, in both the warp and weft, (with the option of then felting the wool to consolidate the weave), enables wool-blend samples to at least match, if not surpass, the properties of an equivalent commercial pure-synthetic ballistic fabric, especially when the fabrics are wet. Even without using the option of creating a felted finish, the addition of the wool into the weave generally causes the burst strength and yarn pull-out forces to increase significantly in dry or wet states.

In terms of ballistic performance, wool-blend fabrics perform very well, dry or wet. In wet conditions there appears to be no significant loss in performance so long as the blend fabric receives a water-resistance treatment in the same way as that routinely applied to equivalent existing pure-synthetic commercial fabrics. The wool helps to absorb any excess wetness and in doing so, tightens the fabric structure due to its diametric swelling. It temporarily adds more (beneficial) mass to the panel, and reduces the degradation of ballistic performance due to moisture lubricating the synthetic filaments.

The indicative wet ballistic tests to NIJ Levels Il A and III A (above) have shown that the ballistic wool/Kevlar blend fabric can perform at least equivalents to pure Kevlar fabrics under wet as well as dry conditions. When wet, 26 layers of the wool/Kevlar blend were shown to be sufficient to stop 9 mm FMJ Luger bullets from penetrating a panel with an acceptable BFS, but 20 layers may be insufficient. The probabilistic nature of such tests requires any new panel design to be fully assessed statistically.

In terms of the dissipation of impact energy in ballistic tests at NIJ Level III A (and below), in particular, the addition of wool to a pure synthetic ballistic fabric is identified as making a positive contribution to ballistic performance in the following areas. The presumption is that:

1. Wool can be strategically incorporated into a basic square sett plain weave of high-tensile (e.g., aramid) synthetic yarn. It can optionally then be felted to form interconnecting bonds through the fabric around yarns and between individual filaments that would effectively "spot weld" the structure of the synthetic-fabric layer so that lateral and longitudinal filament and yarn movements would be reduced.

2. In the first layers impacted by the projectile, when it is at its highest velocity, the presence of the wool restricts the lateral separation of the synthetic yarns forming the base weave. This means that adjacent yarns cannot open up as much laterally when the nose of the projectile impacts. There is clear evidence to show that even though the projectile will readily shear through the filaments in the principal yarns in the first few layers, it also separates some of these yarns, and squeezes between them when the fabric is stretched in the direction of impact. The hole created is generally smaller than the diameter of the projectile (dependent on the shape of the nose). The weave structure must always open up due to the transverse strains imposed, even if no frictional sliding of the intersections may occur. Additionally, the spot welding effect reduces any propensity for the intersections to slide because the friction at each intersection is increased. More principal yarns are held in place to dissipate energy rather than being shouldered aside.

3. Wool makes a positive contribution in increasing energy losses when yarn pull- in/out is the dissipation mechanism. The spot welding effect increases and better maintains the normal pressure between intersections and makes the crimp interchange more difficult. This increases the frictional force required to pull yarns in/out. One test for the effectiveness of the incorporation of wool is a yarn pull-out test. For synthetic/wool blend panels, cross-shaped yarn-pull distortions on any layers are seldom observed (and are of limited extent) even near edges or corners of panels. Even when there are lubricating effects from water, the presence of the wool component inhibits crimp interchange and yarn- pull as an energy-dissipating mechanism. This has particular application near weakly-constrained (sewn or un-sewn) corners. Instead, energy loss is optimised by the mechanism of tensile failure of the synthetic yarns. 4. The wool significantly inhibits the lateral displacement of adjacent synthetic yarns at intersections. Especially in the first few layers in a panel, penetration holes are small and neat and show little lateral displacement of yarns prior to the penetration of the projectile to the next layer. Virtually all principal synthetic yarns lying within the impact cross-section are forced to substantially fail in tension. Broken ends of the synthetic filaments from one layer may be pulled through to the next and subsequent layers, thus encapsulating the projectile by the time it is brought to rest.

5. If individual wool fibres can randomly inveigle their way between small groups of filaments, the longitudinal friction along their length would also increase. This would increase the effective bundle strength of a group of filaments subjected to high tensions and strains.

6. The increase in filament-to-filament friction, because the wool forces the filaments into closer contact, also has potential advantages if the synthetic fabric gets wet. It is known that the performance of wet ballistic panels is degraded by as much as 20% and wearers are warned not to wear vests when wet. (Only if they are dried will their former performance characteristics be restored). Wool offers two advantages.

The wool forces filaments closer together, especially if it is woven under tension. The second is that wool can absorb significant quantities of water into the fibre due to its excellent regain properties. Wool absorbs approximately 36% of its own weight in water before there is sensible wetness on the fibre surfaces.

Thus, excess surface water that can lubricate the synthetic filaments and reduce their intra-filament friction, can be removed. In changing from dry, to a state of 100% regain, wool fibres increase diameter by 16%. This in turn, may further tighten the constrictions around filament bundles.

The results of the indicative wet ballistic tests show that the presence of water does not significantly change the ballistic performance of the wool-blend fabrics relative to the dry fabrics. Thus these wool-blend fabrics, for a given application, should perform at least as well as, if not significantly better than, an equivalent commercial pure-synthetic fabric, especially when wet.

7. Under nominally "dry" environmental conditions, the presence of the wool offers the opportunity to mediate the humidity of its closely-surrounding environment, and can be used to help improve the comfort of the wearers by reducing the effects of sweating and the chance of overheating. It is recognised that for the very highest-rating ballistic vests (NIJ Levels III and IV), the problem of overheating and wearer comfort has restricted such vests to a practical wearing duration of perhaps only half an hour. Lower-level vests (e.g., NIJ Level III A and below) are intended to provide protection for extended periods for police and military personnel, with minimal discomfort and loss of efficiency.

8. Freely protruding wool fibres on the surface of the synthetic layer may also effectively separate the layers more than for pure-synthetic fabrics, and make the layered structure react more like a spaced system, where the individual performance of each layer can be maximised. For a given fabric construction, this prediction can only be checked by experiment.

Those skilled in the art will also realise that this invention may be implemented in embodiments other than those described without departing from the core teachings of this invention.