Patent Description:
Composite structures typically comprise a matrix reinforced with fibers wherein the fibers are embedded in the matrix. Composite structures are typically designed to transmit loads along the length of the fibers. Loads from one fiber may be transferred to another fiber in the same layer or to fibers in an adjacent layer by passing through the matrix material. However, the matrix is typically weaker than the fibers such that when a sufficiently high load is transmitted from one fiber to another fiber across the matrix, the matrix will fail. The failure of the matrix allows the fibers to move within the composite structure.

During a ballistic event wherein a composite panel is impacted by a projectile, the ability of the fibers to move within the matrix may affect the ballistic performance of the composite panel. For example, the ability of the fibers in the matrix to move may affect the resistance of the composite panel to penetration by the projectile. For transparent composite panels, movement of the fibers relative to the matrix may also affect the optical performance of the composite panel. In this regard, movement of the fibers relative to the matrix during a ballistic event may affect the size of the area having reduced optical performance as a result of impact by the projectile.

As can be seen, there exists a need in the art for a composite structure wherein the movement of the fibers in the matrix may be controlled such that the ballistic performance and the optical performance of the composite structure may be improved.

<CIT>, according to its abstract states "A composite material, comprising long or cut fibers of variable longitudinal cross-sectional geometry, is new.

<CIT>, according to its abstract states "The present invention provides thickened fabrics and reinforcements for use as a spacer or reinforcement for a matrix system. The fabric includes in a first embodiment a woven fabric comprising weft and warp yarns containing glass fibers. A portion of the weft yarns are undulated into a sinusoidal path forming a generally "C" shaped bridge between adjacent warp yarns which results in an increased thickness for the fabric. The fabric is coated with a polymeric resin or bonding agent, for substantially binding the weft yarns in the undulated condition. This invention also includes methods for making such fabric by increasing the thickness of a woven or non-woven material by such methods as applying tension to warp yarns having opposite twists during weaving operations, or using unbalanced yarns, for example.

<CIT>, according to its abstract, states "Fibers, continuous or discontinuous, and bars having optimized geometries for use in the reinforcement of cement, ceramic and polymeric based matrices are claimed. The geometries are designed to increase the ratio of surface area available for bond between the fiber and the matrix to the cross-sectional area of fiber. In the case of a continuous reinforcement comprised of a single fiber or a bar made out of a bundle of fibers, such as is the case in reinforced and prestressed concrete, increasing the surface area available for bond leads to a decrease in crack width, development length, and transfer length. The fibers or bars are also configured to be amenable for twisting or to have spiral like deformations along their longitudinal axis to further develop the mechanical component of bond between the fibers and the matrix. Additional methods of mechanical bond enhancement, such as crimping and/or addition of anchorages, such as hooked ends, paddles, buttons, etc.. , can be applied to the claimed fibers to further improve their bond characteristics.

The invention, to which this European patent relates, is defined by the appended claims.

The above-described needs associated with composite articles are specifically addressed and alleviated by the present disclosure which, according to claim <NUM>, provides a composite article having a matrix and fibers embedded in the matrix. Each one of the fibers has a fiber length and a fiber geometry. The fiber geometry varies along the fiber length. The fiber geometry has a cross-sectional shape having a transverse axis, the transverse axis has an orientation, the orientation of the transverse axis twists back-and-forth along the fiber length, and the fiber geometry has a constant cross-sectional area along the fiber length.

According to claim <NUM>, disclosed is a method of manufacturing a composite article. The method includes the step of providingfibers each having a fiber length and a fiber geometry. The method further includes the step of varying the fiber geometry along the fiber length, wherein the fiber geometry has a cross-sectional shape having a transverse axis, wherein the transverse axis has an orientation, wherein the orientation of the transverse axis twist back-and-forth along the fiber length, and wherein the fiber geometry has a constant cross-sectional area along the fiber length. The method additionally includes the step of embedding the fibers in a matrix.

Also disclosed is a method of loading a composite article such as composite panel of a vehicle. The method may include providing the composite article as a plurality of fibers embedded in a matrix wherein each one of the fibers has a fiber length and a fiber geometry and wherein the fiber geometry may vary along the fiber length. The method may include placing the composite article in a first state comprising a static loading condition. The method may also include placing the composite article in a second state comprising a dynamic loading condition.

Advantageously, the variation in the fiber geometry may enhance the mechanical coupling between the fibers and the matrix. The variation in the fiber geometry may also enhance the mechanical coupling between adjacent fibers. The mechanical coupling provided by the variation in the fiber geometry may provide a means to control fiber movement relative to the matrix. The mechanical coupling may also provide a means to control fiber slippage or movement of immediately adjacent fibers.

Controlling the slippage of the fibers may provide a means to control the portions of the fiber lengths of the fibers that are involved in an impact event. By controlling the length of the fibers involved in an impact event, the energy-absorbing capability of the fibers may be improved which may improve the ballistic performance and/or the optical performance of the composite article in response to impact by a projectile.

The features, functions and advantages that have been discussed can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings below.

These and other features of the present disclosure will become more apparent upon reference to the drawings wherein like numerals refer to like parts throughout and wherein:.

Referring now to the drawings wherein the showings are for purposes of illustrating preferred and various embodiments of the disclosure, shown in <FIG> is a composite article <NUM>. The composite article <NUM> may be fabricated as a fiber-reinforced composite panel <NUM> comprising a matrix <NUM> and a plurality of fibers <NUM> embedded within the matrix <NUM>. Advantageously, the fibers <NUM> are provided with fiber geometry <NUM> that varies along the length of the fibers <NUM>. The variation in fiber geometry <NUM> along the fiber length <NUM> of the fibers <NUM> may facilitate mechanical coupling between the fibers <NUM> and the matrix <NUM> (e.g., fiber-matrix coupling). The variation in fiber geometry <NUM> along the fiber length <NUM> of the fibers <NUM> may also facilitate mechanical coupling between adjacent fibers <NUM> (e.g., fiber-to-fiber coupling) in the same layer <NUM> and/or between fibers <NUM> in different layers <NUM>.

The fiber-matrix mechanical coupling may provide a means to control the movement or slippage of the fibers <NUM> relative to the matrix <NUM>. The fiber-to-fiber mechanical coupling may provide a means to control fiber-to-fiber movement or slippage. By varying the fiber geometry <NUM> along the length of the fibers <NUM>, the portion of the fiber length <NUM> that is involved in an impact event may be controlled. Advantageously, varying the fiber geometry <NUM> along the fiber length <NUM> may improve the ability to decelerate a projectile impacting or entering the composite article <NUM>.

The amount of slippage between the fibers <NUM> and the matrix <NUM> may also provide a means to control the failure of the fibers <NUM> as a function of distance or penetration of a projectile through the composite article <NUM>. In this regard, the present disclosure advantageously provides the technical effect of controlling or selectively increasing the portion of the length of each fiber <NUM> that is involved in a ballistic event such that the tensile strain in each fiber <NUM> may be distributed through a relatively longer length of the fiber <NUM>. By controlling (e.g., increasing) the portion of the length of the fibers <NUM> that are involved in a ballistic event, the total amount of energy absorbed by the fibers <NUM> during an impact event may be controlled (e.g., increased). In this regard, the tensile loads in the fibers <NUM> can be controlled as a means to prevent premature breakage of the fiber <NUM> upon the fibers <NUM> reaching the ultimate strain value.

Furthermore, by selectively varying the fiber geometry <NUM> along the fiber length <NUM>, relative movement of the fibers <NUM> can be controlled as a means to control the amount of time that the fibers are involved in a ballistic impact event which may correlate to an increase in the amount of time that the fibers <NUM> have for decelerating a projectile and increasing the amount of projectile energy that may be absorbed by the fibers <NUM>. The control of the slippage of the fibers <NUM> relative to the matrix <NUM> and relative to one another may also be affected or improved by forming the fibers <NUM> from materials having an appropriate ultimate strain value and/or an appropriate strain rate response as described in greater detail below. In this regard, the fibers <NUM> may be formed from materials having an ultimate strain that prevents failure of the fibers <NUM> while also resisting or preventing penetration of the composite article <NUM> by a projectile.

In <FIG>, shown is the composite article <NUM> having articles surfaces <NUM>. The composite article <NUM> is formed as a composite panel <NUM> having panel surfaces <NUM> and including a plurality of the fibers <NUM> embedded within a matrix <NUM>. The fibers <NUM> may function as structural reinforcement for the matrix <NUM> and may improve the mechanical and ballistic performance of the composite article <NUM>. In this regard, the fibers <NUM> may provide structural reinforcing to tailor the specific stiffness of the composite article <NUM> as a result of the enhanced tensile strength and targeted modulus of elasticity (e.g., stiffness) of the fibers <NUM>. In the present disclosure, properties such as strength, strain, and stiffness are described in terms of dynamic or high strain rate properties.

In <FIG>, shown is an exploded illustration of the composite article <NUM> or composite panel <NUM> of <FIG> and illustrating a plurality of layers <NUM>. In each one of the layers <NUM>, the fibers <NUM> are positioned in side-by-side <NUM> arrangement. Each fiber <NUM> has a fiber length <NUM> and a longitudinal axis <NUM>. The fiber geometry <NUM> of the fibers <NUM> in each layer <NUM> may vary along the fiber length <NUM>. The fiber geometry <NUM> may comprise the cross-sectional area <NUM> and the cross-sectional shape <NUM>, either one of which or both of which may vary along the fiber length <NUM>. The fibers <NUM> in each layer <NUM> may be generally aligned with one another wherein the longitudinal axes <NUM> of the fibers <NUM> in a given layer <NUM> are generally parallel. However, in any of the embodiments disclosed herein, the fibers <NUM> may be incorporated into woven lamina (not shown) in a matrix and are not limited to alignment in side-by-side relation to one another in a layer or substantially parallel relation to one another in a layer. Furthermore, any of the fiber <NUM> embodiments disclosed herein may be implemented in a fabric (not shown) without a matrix and wherein fiber-to-fiber coupling may provide advantages regarding penetration resistance of the fabric by a projectile in a manner similar to that which is described herein.

In an embodiment, the longitudinal axes <NUM> of the fibers <NUM> in one layer <NUM> may be oriented at an angle relative to the longitudinal axes <NUM> of the fibers <NUM> in an immediately adjacent one of the layers <NUM>. For example, <FIG> illustrates the longitudinal axes <NUM> of the fibers <NUM> in one layer <NUM> being oriented perpendicularly relative to the longitudinal axes <NUM> of the fibers <NUM> in the layers <NUM> immediately adjacent thereto. However, the longitudinal axes <NUM> of the fibers <NUM> of adjacent ones of the layers <NUM> may be oriented at any angle relative to one another depending on the desired ply stack up of the composite article <NUM>.

<FIG> is an enlarged view of a portion of the composite article <NUM> of <FIG> and illustrating several layers <NUM>. Each one of the layers <NUM> includes fibers <NUM> having fiber geometry <NUM> that varies along the fiber length <NUM>. As indicated above, the layers <NUM> may include fibers <NUM> oriented in any direction relative to the fibers <NUM> of an immediately adjacent layer <NUM>. For example, <FIG> illustrates a cross-ply configuration wherein the fibers <NUM> of one layer <NUM> are oriented perpendicularly relative to the fibers <NUM> of the immediately adjacent layer <NUM>. It should be noted that <FIG> is an illustration of a non-limiting embodiment of the composite article <NUM> and is not to be construed as limiting alternative arrangements of the fibers <NUM> within the matrix <NUM>. For example, the fibers <NUM> in the layers <NUM> may be oriented in perpendicular orientation relative to the fibers <NUM> in other layers <NUM> as illustrated in <FIG> or the fibers <NUM> may be oriented in non-perpendicular orientation (e.g., <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>°, etc.).

<FIG> is a top view of a layer <NUM> of fibers <NUM> showing the variation in fiber geometry <NUM> along the fiber length <NUM> of the fibers <NUM>. The fiber geometry <NUM> of a fiber <NUM> may be characterized by the cross-sectional area <NUM> (<FIG>) of the fiber <NUM> at a given location along the fiber length <NUM> and/or by the cross-sectional shape of the fiber <NUM> at a given location along the fiber length <NUM>. However, the fiber geometry <NUM> may be characterized by additional parameters including, but not limited to, the shape of the transition between a first portion <NUM> of the fiber <NUM> and a second portion <NUM> of the fiber <NUM>. For example, the fiber geometry <NUM> may be characterized by a rounded or smoothly-radiused transition between first portions <NUM> and second portions <NUM> as shown in <FIG>. Alternatively, the geometry may be characterized by relatively sharper or more abrupt transitions between first portions <NUM> and second portions <NUM> as shown in the embodiment of <FIG> and described below.

In <FIG>, the fiber geometry <NUM> may vary in a periodic <NUM> manner along the fiber length <NUM>. In this regard, the fiber <NUM> may include a series of the second portions <NUM> that may be distributed in a substantially uniform manner with substantially uniform spacing between the second portions <NUM>. Each pair of second portions <NUM> may be separated by a first portion <NUM>. The periodic <NUM> arrangement of fiber geometry <NUM> may comprise a substantially similar and repeating fiber geometry <NUM> along the fiber length <NUM>. Although the present disclosure describes fiber geometry <NUM> that varies in a periodic <NUM> manner along the fiber length <NUM>, fibers <NUM> may be provided having fiber geometry <NUM> that varies in a semi-periodic <NUM> (<FIG>) manner. For example, the fiber geometry <NUM> may vary with progressively larger or smaller distances between adjacent pairs of second portions <NUM> such as a progressive or gradual increase or decrease in spacing between the second portions <NUM> of a fiber <NUM>. In addition, the fiber geometry <NUM> may vary in repeated patterns (e.g., <FIG>) along any portion of the fiber length <NUM> of a fiber <NUM>. The fiber geometry <NUM> may also be arranged in a non-periodic or random (not shown) manner along the fiber length <NUM>.

In <FIG>, each fiber <NUM> is shown as being substantially similarly configured. The fibers <NUM> each have side surfaces <NUM> and are arranged such that a gap <NUM> is formed between adjacent fibers <NUM>. Each one of the gaps <NUM> may be substantially filled with matrix <NUM> material when the fibers <NUM> are embedded within the matrix <NUM>. The variation in fiber geometry <NUM> along the fiber length <NUM> of the fibers <NUM> may improve mechanical coupling of the fibers <NUM> with the matrix <NUM>. In addition, as shown in <FIG>, the fibers <NUM> may be arranged such that the second portions <NUM> of the fibers <NUM> are at least partially nested <NUM> with the first portions <NUM> of adjacent fibers <NUM>. Advantageously, the at least partially nested relation of the fibers <NUM> may improve mechanical coupling of the fibers <NUM> (e.g., fiber-to-fiber coupling). As indicated above, mechanical coupling of the fibers <NUM> may reduce fiber-to-fiber slippage or movement which may provide a means to control the portion of the fiber length <NUM> that is involved in a ballistic event. In this regard, reduced fiber-to-fiber slippage may result in the involvement of a greater quantity of fibers <NUM> in a ballistic event. Increasing the quantity of fibers <NUM> involved in a ballistic event may increase the collective energy-absorbing capability of the fibers <NUM> which may improve the ballistic performance of the composite article <NUM> and/or the post-impact optical performance of the composite article <NUM> as described above.

Referring to <FIG>, shown is a top view of one of the fibers <NUM> of <FIG>. In the embodiment shown, the variation in fiber geometry <NUM> comprises first portions <NUM> and second portions <NUM> alternating in a periodic <NUM> manner along the fiber length <NUM>. Although shown as having a generally symmetrical configuration relative to the longitudinal axis <NUM>, it is contemplated that the fiber geometry <NUM> may be provided having an asymmetrical configuration (not shown) wherein the configuration of the fiber <NUM> on one side of the longitudinal axis <NUM> is different than the configuration of the fiber <NUM> on an opposite side of the longitudinal axis <NUM>. The fiber <NUM> has a fiber width <NUM> which may be defined as the largest width of the fiber <NUM> at any location along the fiber length <NUM>. In any of the fiber embodiments disclosed herein, the fiber geometry as illustrated may or may not be exaggerated for clarity.

<FIG> is a side view of the fiber <NUM> of <FIG>. The fiber <NUM> may be provided in a generally flat configuration wherein the fiber <NUM> has an upper surface <NUM> and a lower surface <NUM> which are generally parallel to one another and which may define a fiber thickness <NUM> that may be generally constant along the fiber length <NUM>. The fiber thickness <NUM> of a fiber <NUM> may be defined as being measured perpendicularly relative to the fiber width <NUM>. The fiber <NUM> may be provided in an embodiment wherein the fiber <NUM> upper surface <NUM> and lower surface <NUM> are oriented in non-parallel relation to one another.

<FIG> is a cross section of the first portion <NUM> of the fiber <NUM> of <FIG>. The fiber geometry <NUM> (<FIG>) has a cross-sectional area <NUM> and a cross-sectional shape <NUM> (<FIG>). In <FIG>, the first portion <NUM> of the fiber <NUM> has a first cross-sectional area 38a and a first cross-sectional shape 40a comprising a rectangular shape. The rectangular cross-sectional shape has a short transverse axis <NUM> and a long transverse axis <NUM>. <FIG> illustrates the second portion <NUM> (<FIG>) having a second cross-sectional area 38b and a second cross-sectional shape 40b which may be similar to the rectangular first cross-sectional shape 40a. In this regard, <FIG> represent an embodiment of a fiber <NUM> (<FIG>) wherein the cross-sectional area <NUM> is variable along the fiber length <NUM> and the cross-sectional shape <NUM> is substantially constant (e.g., rectangular) along the fiber length <NUM> (<FIG>). The change in cross-sectional area <NUM> along the fiber length <NUM> of the fiber <NUM> of <FIG> is the result of an increase in the aspect ratio of the rectangular cross-sectional shape <NUM> along the long transverse axis <NUM>. The embodiment of the fiber <NUM> illustrated in <FIG> may facilitate fiber-to-fiber mechanical coupling within an in-plane direction (e.g., within a layer).

Referring to <FIG>, shown it is a top view of one of the fibers <NUM> in an alternative embodiment wherein the fiber <NUM> includes alternating first and second portions <NUM>, <NUM>. The second portions <NUM> may include an opening <NUM> such as a hole or a slot extending at least partially or completely through the fiber <NUM>. Advantageously, the second portions <NUM> of the fiber <NUM> may be configured such that the cross-sectional shape of the fiber <NUM> in the first portion <NUM> may vary along the fiber length <NUM> relative to the cross-sectional shape of the fiber <NUM> in the second portion <NUM>. In addition, in the embodiment shown in <FIG>, the cross-sectional area of the fiber <NUM> in the second portion <NUM> may be substantially equivalent to the cross-sectional area of the fiber <NUM> in the first portion <NUM>. The load-carrying capability (e.g., tensile load) of the fiber <NUM> may be limited to the load-carrying capability of the smallest cross-sectional area at any point along the length of the fiber <NUM>. In <FIG>, the smallest cross-sectional area of the fiber <NUM> may be located in the first portion <NUM>. By limiting the cross-sectional area of the second portion <NUM> to be substantially equivalent to the cross-sectional area of the first portion <NUM>, any weight penalty associated with enlarged cross-sectional areas of the fiber <NUM> may be minimized.

<FIG> is a side view of the fiber <NUM> of <FIG>. The fiber <NUM> may be provided in a generally flat configuration as described above for the fiber <NUM> embodiment of <FIG>. In this regard, the fiber <NUM> shown in <FIG> may have a fiber thickness <NUM> that may be generally constant along the fiber length <NUM>. However, the fiber <NUM> may be provided in an embodiment wherein the fiber <NUM> has a non-constant thickness.

<FIG> is a cross section of the first portion <NUM> of the fiber <NUM> of <FIG>. The fiber geometry <NUM> at the first portion <NUM> comprises a first cross-sectional shape 40a represented by the cross-hatched rectangle and which encloses the first cross-sectional area 38a. <FIG> shows the second portion <NUM> having a second cross-sectional area 38b and a second cross-sectional shape 40b. The second cross-sectional shape 40b comprises the generally rectangular shape of the fiber <NUM> divided by the opening <NUM> between the two cross-hatched areas. The second cross-sectional shape 40b of the second portion <NUM> comprises the collective area of the pair of cross-hatched areas. The collective area of the pair of cross-hatched areas in <FIG> may be substantially equivalent to the cross-hatched area shown in <FIG>. In this regard, <FIG> illustrate one of many fiber embodiments that may be configured wherein the cross-sectional area <NUM> of the fiber <NUM> is substantially constant along the fiber length <NUM> (<FIG>) and the cross-sectional shape <NUM> is variable along the fiber length <NUM>.

Referring to <FIG>, shown is an embodiment of a fiber <NUM> having fiber geometry <NUM> that varies along the fiber length <NUM>. The fiber geometry <NUM> is comprised of a series of first portions <NUM> and second portions <NUM> that alternate relative to one another. The first portions <NUM> and second portions <NUM> are shown as being arranged in a periodic <NUM> manner along the fiber length <NUM>. However, as indicated above, the fiber geometry <NUM> may be arranged in a semi-periodic <NUM> manner as shown in <FIG> and described below. The fiber geometry <NUM> may also be arranged to vary in a non-periodic manner.

As shown in <FIG>, the fiber <NUM> has a first cross-sectional area 38a and a first cross-sectional shape 40a comprising a circular shape and representing a first portion <NUM> of the fiber <NUM> (<FIG> illustrates a second portion <NUM> (<FIG>) of the fiber <NUM> having a second cross-sectional area 38b and a second cross-sectional shape 40b also comprising a circular shape. <FIG> illustrate a fiber <NUM> embodiment having a varying cross-sectional area <NUM> (<FIG>) along the fiber length <NUM> (<FIG>) and a substantially constant cross-sectional shape <NUM> along the fiber length <NUM>. The change in cross-sectional area <NUM> in <FIG> may be the result of a radially-uniform increase or enlargement in the size of the circular cross-sectional shape <NUM>.

In an embodiment, the second portions <NUM> (<FIG>) of the fiber <NUM> may have a second cross-sectional area 38b (<FIG>) that is no more than approximately <NUM> percent larger than the first cross-sectional area 38a (<FIG>) of the first portions <NUM> (<FIG>). However, the fiber <NUM> may be provided in embodiments wherein the second portions <NUM> have a second cross-sectional area 38b that is greater than approximately <NUM> percent of the first cross-sectional area 38a of the first portions <NUM>. In the present disclosure, the second cross-sectional area 38b of each second portion <NUM> encompasses, circumscribes, or otherwise includes the first cross-sectional area 38a of the first portion <NUM> or the fiber core <NUM> (<FIG>). As indicated above, the load-carrying capability (e.g., tensile load) of the fiber <NUM> is defined by the load-carrying capability of the smallest cross-sectional of the fiber <NUM> which may be located at the first portion <NUM>. By limiting the size of the second portions <NUM>, the weight penalty and/or economic penalty associated with the non load-carrying portion of the fiber <NUM> may be minimized.

Advantageously, the fiber <NUM> embodiment illustrated in <FIG> may facilitate fiber-to-fiber mechanical coupling within an in-plane direction (e.g., within a layer) and also fiber-to-fiber mechanical coupling within an out-of-plane direction (e.g., between layers). Although not shown, out-of-plane mechanical coupling of fibers <NUM> may be facilitated by nesting engagement of the second portions <NUM> of the fibers <NUM> in one layer <NUM> with first portions <NUM> of the fibers <NUM> in the layers <NUM> immediately adjacent thereto.

Referring to <FIG>, shown is a top view of an embodiment of a fiber <NUM> having a serpentine shape <NUM>. The fiber <NUM> may have a cross-sectional area <NUM> that may be offset relative to the longitudinal axis <NUM> at different locations <NUM> along the fiber length <NUM>. In an embodiment, the fiber <NUM> may have a fiber width <NUM> that is generally constant along the fiber length <NUM> although the fiber <NUM> may be provided with a fiber width <NUM> that is generally variable along the fiber length <NUM>. As shown in <FIG>, the fiber <NUM> has upper and lower surfaces <NUM>, <NUM> which are generally parallel to one another and defining a fiber thickness <NUM> that may be generally constant. However, as was indicated above, the fiber <NUM> may be provided in an embodiment wherein one or more of the fiber surfaces <NUM> are oriented in non-parallel relation to one another. In an embodiment, a plurality of the fibers <NUM> shown in <FIG> may be arranged in side-by-side arrangement (not shown) to form a layer wherein offsets <NUM> of the fibers <NUM> may be at least partially nested with one another to provide fiber-to-fiber coupling.

<FIG> is a sectional view of the fiber <NUM> (<FIG>) illustrating a rectangular cross-sectional area <NUM> of the fiber <NUM>. The cross-sectional area <NUM> defines an area centroid <NUM> which may be offset <NUM> on one side or both sides of the longitudinal axis <NUM> (<FIG>) of the fiber <NUM>. <FIG> is a further sectional view of the fiber <NUM> illustrating the rectangular cross-sectional area <NUM> of the fiber <NUM> having an area centroid <NUM> that is offset <NUM> on one side of the longitudinal axis <NUM> relative to the offset <NUM> of the area centroid <NUM> shown in <FIG>. The fiber <NUM> in <FIG> has a substantially constant cross-sectional area <NUM> and a substantially constant cross-sectional shape <NUM> (<FIG>) along the fiber length <NUM>. Although the offset <NUM> is periodic <NUM> (<FIG>) along the fiber length <NUM> on alternating sides of the longitudinal axis <NUM>, the offset <NUM> on opposite sides of the longitudinal axis <NUM> may be semi-periodic or non-periodic as described above. Furthermore, the offset <NUM> is not limited to being offset <NUM> in a single direction such as along the long transverse axis <NUM> as shown in <FIG> but may be offset <NUM> in one or more of a variety of different directions including in a short transverse axis <NUM> direction, or in any one of a variety of different directions.

Referring to <FIG>, shown is a top view of an embodiment of a fiber <NUM> having a series of substantially equally-sized and configured protuberances <NUM> formed along the fiber length <NUM>. The protuberances <NUM> are shown as being generally centered along the longitudinal axis <NUM>. However, the protuberances <NUM> may be provided in any location relative to the longitudinal axis <NUM>. Although the fiber <NUM> is shown as having side surfaces <NUM> that are generally straight, the fiber <NUM> may be provided in any shape such as in a serpentine shape <NUM> as shown in <FIG> or in any other shape, without limitation.

<FIG> is a side view of the fiber <NUM> of <FIG> showing a fiber thickness <NUM> that is generally constant along the fiber length <NUM>. The protuberances <NUM> are shown as extending from both the upper surface <NUM> and the lower surface <NUM> of the fiber <NUM> in an alternating manner. However, the protuberances <NUM> may be formed on a single one of the upper and lower surfaces <NUM>, <NUM>. Alternatively, the protuberances <NUM> may be formed on the upper and lower surface <NUM>, <NUM> in a non alternating pattern (not shown). In the embodiment shown, the protuberances <NUM> are each shown as optionally including a hollow portion R4 which may be open to an exterior of the fiber <NUM> such that the protuberances <NUM> may have holes to reduce the overall weight of the composite article <NUM> (<FIG>) containing the fibers <NUM>.

<FIG> is a sectional view of the fiber <NUM> taken along a portion of the fiber <NUM> between a pair of protuberances <NUM>. As indicated by the crosshatched area, the fiber geometry <NUM> has a first cross-sectional area 38a defined by a first cross-sectional shape 40a formed as a rectangle. <FIG> is a sectional view of the fiber <NUM> passing through one of the protuberances <NUM>. The fiber geometry <NUM> at the noted location has a second cross-sectional area 38b and a second cross-sectional shape 40b formed in the shape of an arch. The second cross-sectional area 38b may be larger than the first cross-sectional area 38a (<FIG>). The protuberances <NUM> may facilitate mechanical coupling with the matrix <NUM> (<FIG>). In addition, although not shown, the protuberances <NUM> in one layer <NUM> of fibers <NUM> may be sized and configured to nest within the hollow portions R4 (<FIG>) of the protuberances <NUM> in fiber <NUM> of an immediately adjacent layer <NUM> (<FIG>). Such nesting of the protuberances <NUM> may facilitate fiber-to-fiber mechanical coupling in an out-of-plane direction (e.g., between layers <NUM>) which may facilitate an increase in the quantity of fibers <NUM> involved in a ballistic event.

<FIG> is a top view of an embodiment of a fiber <NUM> having a series of relatively large protuberances <NUM> and relatively small protuberances <NUM> formed along the fiber length <NUM>. <FIG> is a side view of the fiber <NUM> showing the relatively large protuberances <NUM> formed on the upper surface <NUM> and the relatively small protuberances <NUM> formed on the lower surface <NUM>. <FIG> is a sectional view of the fiber <NUM> passing through one of the relatively small protuberances <NUM> wherein the crosshatched area represents a first cross-sectional area 38a formed in the shape of an arch. <FIG> is a sectional view of the fiber <NUM> passing through one of the relatively large protuberances <NUM> wherein the crosshatched area represents a second cross-sectional area 38b also formed in the shape of an arch. By providing the fiber <NUM> with different sized protuberances on the upper surface <NUM> and lower surface <NUM>, different levels of mechanical coupling may be provided with the matrix <NUM> and/or with other fibers <NUM>.

<FIG> illustrate an embodiment of a fiber <NUM> formed in a helix shape <NUM>. The fiber geometry <NUM> has a cross-sectional shape <NUM> having a long transverse axis <NUM>. The orientation of the long transverse axis <NUM> of the cross-sectional shape <NUM> varies along the fiber length <NUM> when the fiber <NUM> is viewed along a direction parallel to the fiber length <NUM>. In the embodiment shown, the cross-sectional area <NUM> and/or the cross-sectional shape <NUM> of the fiber <NUM> may be substantially constant along the fiber length <NUM>. However, the fiber <NUM> may be provided in an embodiment wherein the cross-sectional area <NUM> and/or the cross-sectional shape <NUM> may vary (not shown) along the fiber length <NUM>. In the embodiment shown, the orientation of the long transverse axis <NUM> changes in a continuous direction such as a clockwise direction or a counterclockwise direction, depending upon the direction along which the fiber <NUM> is viewed. The fiber <NUM> is shown as having a helix shape <NUM> wherein the orientation of the long transverse axis <NUM> changes at a constant rate along the fiber length <NUM>. However, the fiber <NUM> may be configured such that the orientation of the long transverse axis <NUM> changes at a variable or random rate. The orientation of the long transverse axis <NUM> may also alternate back-and-forth (<FIG>) along the fiber length <NUM> and is not limited to changing in a constant clockwise (or counterclockwise) direction of a helix shape <NUM>.

<FIG> illustrates an embodiment of the fiber <NUM> formed in a back-and-forth twisting shape <NUM>. The fiber geometry <NUM> has a cross-sectional shape <NUM> that has a long transverse axis <NUM> (<FIG>) for which the orientation twists back-and-forth along the fiber length <NUM> (<FIG>) when the fiber <NUM> is viewed along a direction parallel to the fiber length <NUM>. For example, in the embodiment shown, the transverse axis <NUM> twists back-and-forth approximately <NUM> degrees along the fiber length <NUM>. However, the fiber <NUM> may be configured such that the transverse axis <NUM> twists back-and-forth by any angular amount. The fiber <NUM> embodiments in <FIG>, examples not in accordance with the invention to which this European patent relates, may have a substantially constant cross-sectional area <NUM> along the fiber length <NUM>. The fiber <NUM> embodiments in <FIG> have a substantially constant cross-sectional area <NUM> along the fiber length <NUM>. Advantageously, because the load-carrying capability of a fiber is generally defined by the load-carrying capability of the smallest cross-sectional area at any point along the length of a fiber, the substantially constant cross-sectional area <NUM> of the fiber <NUM> embodiments of <FIG> minimizes any weight penalties otherwise associated with fibers having enlarged cross-sectional areas along the fiber length.

<FIG> is a top view of an embodiment of a fiber <NUM> having a cross-sectional shape <NUM> that is substantially constant along the fiber length <NUM> and a cross-sectional area <NUM> that varies along the fiber length <NUM>. The fiber <NUM> is shown as having generally periodic <NUM> variations in fiber geometry <NUM> in the form of periodic <NUM> changes in cross-sectional shape <NUM> and cross-sectional area <NUM> along the fiber length <NUM>. However, as indicated above, the fiber <NUM> may be configured such that the changes in the cross-sectional shape <NUM> and cross-sectional area <NUM> are semi-periodic or non-periodic. <FIG> is a side view of the fiber <NUM> illustrating changes in fiber geometry <NUM> along the fiber length <NUM>. <FIG> is a sectional view of the fiber <NUM> having a first cross-sectional area 38a and a first cross-sectional shape 40a that is generally rectangular. <FIG> is a sectional view of the fiber <NUM> taken at a location along the fiber length having a second cross-sectional area 38b and a second cross-sectional shape 40b that is generally square. The first cross-sectional area 38a and the second cross-sectional area 38b may be substantially equivalent in the embodiment shown. However, as was indicated above, the cross-sectional area <NUM> may be variable along the fiber length <NUM>.

Referring to <FIG>, shown is a top view of a fiber <NUM> comprised of a first material <NUM> and a second material <NUM>. In an embodiment, the first material <NUM> of the fiber <NUM> may be included in a first portion <NUM> of the fiber <NUM>. The first portion <NUM> of the fiber <NUM> may comprise the fiber core <NUM> and which may extend along the longitudinal axis <NUM> of the fiber <NUM>. The second material <NUM> of the fiber <NUM> may be included in one or more second portions <NUM> of the fiber <NUM>. In an embodiment, the second portions <NUM> may be mounted or otherwise disposed on the fiber core <NUM>. <FIG> is a sectional view of the fiber <NUM> taken along the longitudinal axis <NUM> of the fiber <NUM>. Shown is the fiber core <NUM> formed of the first material <NUM> and having a fiber diameter <NUM>. Shown also are a plurality of the second portions <NUM> formed of the second material <NUM> and mounted to the fiber core <NUM>. <FIG> is a sectional view taken along the fiber core <NUM> and illustrating a first cross-sectional area 38a of the fiber core <NUM> and a first cross-sectional shape 40a the fiber core <NUM> formed as a circle.

<FIG> is a sectional view taken along a second portion <NUM> of the fiber <NUM> (<FIG>). In the embodiment shown, the second portion <NUM> has a second cross-sectional shape 40b formed as a square. In an embodiment, each one of the second portions <NUM> may be formed as a fiber bead <NUM> comprised of the second material <NUM> and mounted (e.g., bonded) to the fiber core <NUM>. Although shown as having a square shape, the fiber beads <NUM> may be provided in any one of a variety of cross-sectional shapes. For example, the fiber beads <NUM> may be provided as spheres, square cubes, rectangular cubes, polygonal beads, irregularly-shaped beads, generally rounded beads, or any one of a variety of alternative sizes, shapes, and configurations.

<FIG> illustrate an embodiment of the fiber <NUM> having fiber beads <NUM> which are spherical and which may be formed of a second material <NUM> mounted on a fiber core <NUM> formed of a first material <NUM>. In an embodiment, the fiber beads <NUM> are represented by the cross-hatched area bounded by the outer square and the inner circle and may have a larger cross-sectional area <NUM> than the cross-sectional area <NUM> of the fiber core <NUM> which is represented by the crosshatched area within the circle.

Advantageously, forming the fiber <NUM> of at least two different materials provides an additional means for tailoring the degree of coupling of the fibers <NUM> to the matrix <NUM> (<FIG>). For example, the first material <NUM> may interact with the matrix <NUM> in a manner that differs from the manner in which the second material <NUM> interacts with the matrix <NUM>. In this regard, the first material <NUM> may result in different properties in the bond between the first material <NUM> and the matrix <NUM>. For example, the first material <NUM> may provide different levels of strength, stiffness, ductility, strain-to-failure, and other properties in the adhesive bond between the first material <NUM> in the matrix <NUM> relative to the properties in the adhesive bond between the second material <NUM> and the matrix <NUM>.

Referring to <FIG>, shown is an embodiment of a fiber <NUM> wherein the fiber geometry <NUM> is variable in a semi-periodic <NUM> manner along the fiber length <NUM>. For example, the fiber <NUM> may include groups of second portions <NUM> located at spaced intervals along the fiber length <NUM>. The groups of second portions <NUM> may be separated by a section of the fiber <NUM> having a relatively smaller fiber width <NUM> or fiber diameter <NUM> and which may be of substantially constant cross-sectional area and/or substantially constant cross-sectional shape. The second portions <NUM> may be provided in any one of a variety of different cross-sectional shapes and cross-sectional areas including any one of the configurations disclosed herein. Advantageously, the groups of second portions <NUM> may be separated by relatively constant spacings or the spacing may be variable between two groups of second portions <NUM>. The second portions <NUM> may be sized and positioned along the fiber length <NUM> to provide a desired level of mechanical coupling of the fibers <NUM> to the matrix. In an embodiment, the second portions <NUM> may be formed from a different material than the material of a smaller-diameter core <NUM> upon which the second portions <NUM> may be mounted. The different materials may provide different interactions between the fibers <NUM> and the matrix <NUM> (<FIG>) and which may provide an additional means to control the coupling between the fibers <NUM> and the matrix <NUM>.

In <FIG>, the semi-periodic <NUM> arrangement of the fiber geometry <NUM> may be tailored or configured to provide for discretized control of the movement of the fibers <NUM> relative to the matrix along the fiber length <NUM>. For example, for embodiments wherein it is desired to minimize the area of optical distortion in a composite article <NUM> due to impact by a projectile, the groups of second portions <NUM> may be spaced along the fiber length <NUM> in a manner that minimizes the extent of fiber involvement in the ballistic event (e.g., projectile impact). In this regard, the groups of second portions <NUM> may be provided at relatively small spacings from one another. In contrast, for embodiments wherein it is desired to maximize ballistic performance of the composite article <NUM> during impact by a projectile, the groups of second portions <NUM> may be provided at relatively large spacings from one another in a manner that maximizes the extent of fiber involvement in the ballistic event. In addition, the relative size and geometry of the second portions <NUM> may be tailored or configured to provide discretized or quantized control of the movement of the fibers <NUM> relative to the matrix.

In any of the embodiments disclosed herein, the cross-sectional shape of a fiber <NUM> may be provided in any one of a variety of different configurations. For example, the cross-sectional shape of a fiber <NUM> may comprise a circle, a closed semi-circle, an ellipsoid, a kidney shape, a triangle, a square, a rectangle, a polygon, or any one of a variety of different cross-sectional shapes. Furthermore, a fiber <NUM> may be configured in an embodiment comprising two or more different cross-sectional shapes formed along the fiber length. In addition, a fiber <NUM> may be provided in any irregular or random cross-sectional shape and is not limited to known geometric shapes. One or more of fibers <NUM> may also be provided in a generally hollow configuration such that the fibers <NUM> are not limited to a solid configuration. A fiber <NUM> may optionally include a cross-sectional shape having at least one pair of fiber surfaces <NUM> (<FIG>, <FIG>, <FIG>, <FIG>) that are substantially parallel to one another. In addition, the fiber <NUM> may be provided in a cross-sectional shape (not shown) that combines substantially planar surfaces with curved surfaces.

In any of the embodiments disclosed herein, the matrix <NUM> (<FIG>) and/or the fibers <NUM> (<FIG>) may be formed of any suitable organic or inorganic material, thermoplastic material, thermosetting material, and/or glass material, without limitation. For example, the matrix <NUM> and/or fiber <NUM> including any one of the different materials that may be used in the fibers <NUM> may be formed of a thermoplastic material comprising at least one of the following materials: acrylics, fluorocarbons, polyamides (nylons), polyethylenes, polyesters, polypropylenes, polycarbonates, polyurethanes, polyetheretherketone, polyetherketoneketone, polyetherimides, stretched polymers and any other suitable thermoplastic material. Likewise, the matrix <NUM> and/or the fibers <NUM> including any one of the different materials that may be used in the fibers <NUM> may be formed of a thermoset which may include any one of the following: polyurethanes, phenolics, polyimides, bismaleimides, polyesters, epoxies, silsesquioxanes and any other suitable thermoset material. In addition, the matrix <NUM> and/or the fibers <NUM> may be formed of inorganic material including carbon, silicon carbide, boron, or other inorganic material. Even further, the matrix <NUM> and/or the fibers <NUM> may be formed of glass comprising E-glass (alumino-borosilicate glass), S-glass (alumino silicate glass), pure silica, borosilicate glass, optical glass, ceramics, glass ceramics, and any other glass material, without limitation. Additionally, the matrix <NUM> and/or the fibers <NUM> may at least partially comprise or include metallic material.

In an embodiment, the fibers <NUM> (<FIG>) may be formed of a substantially optically transparent fiber material although the fibers <NUM> may be formed of substantially opaque material. The matrix <NUM> (<FIG>) may also be formed of a substantially optically transparent polymeric matrix material or substantially opaque material. The fibers <NUM> in any of the embodiments disclosed herein may be formed as filament-based fibers, monofilament fibers, poly-component fibers, and other fiber configurations. In an embodiment, the fibers <NUM> may have a fiber thickness <NUM>, a fiber width <NUM>, and/or a fiber diameter <NUM> in the range of from approximately three (<NUM>) microns to <NUM> microns. For example, the fibers <NUM> may have a fiber thickness <NUM>, a fiber width <NUM>, and/or a fiber diameter <NUM> in the range of from approximately three (<NUM>) microns to <NUM> microns. In a further embodiment, the fiber thickness <NUM>, fiber width <NUM>, and/or fiber diameter <NUM> may be in the range of from approximately <NUM> microns to <NUM> microns. However, the fibers <NUM> may be provided in a fiber thickness <NUM>, fiber width <NUM>, or fiber diameter <NUM> that is smaller than <NUM> microns or larger than <NUM> microns.

The composite article <NUM> (<FIG>) may be configured in any one of a variety of different shapes, sizes and configurations. In this regard, the composite article <NUM> may be configured for use in any vehicular or non-vehicular application. For example, the composite article <NUM> may be configured as a transparency of a vehicle such as an aircraft. The composite article <NUM> may also comprise any portion of a windshield or a canopy of an aircraft. The composite article <NUM> may also be configured for use in any portion of a window in any vehicular or non-vehicular application. Furthermore, the composite article <NUM> may be implemented in or incorporated into any portion of a membrane, an armor panel, a structural panel, an architectural panel, a non-structural panel or a non-structural article, a layered system, or in any other implementation of the composite article <NUM>, without limitation.

Referring to <FIG>, shown is a portion of a composite article <NUM> having fibers <NUM> embedded in a matrix <NUM> and wherein the fibers <NUM> are positioned in side-by-side <NUM> arrangement in a plurality of layers <NUM>. The fibers <NUM> in each layer <NUM> are oriented orthogonally relative to the fibers <NUM> in layers <NUM> adjacent thereto. The composite article <NUM> may facilitate engagement <NUM> of the fibers <NUM> by configuring the fibers <NUM> in one layer <NUM> to be complementary to the fibers <NUM> in the layers <NUM> located immediately adjacent thereto. In this regard, the fiber geometry <NUM> in each fiber <NUM> may be varied along the fiber length <NUM> such that the fibers <NUM> include first portions <NUM> and second portions <NUM> that alternate relative to one another. Upon application of a force <NUM> (<FIG>) substantially normal or oblique to the composite article <NUM>, the second portions <NUM> of the fibers <NUM> in one layer <NUM> may at least partially nest within the fibers <NUM> in the layers <NUM> located immediately adjacent thereto.

<FIG> is an end view of the composite article <NUM> of <FIG> and showing the fibers <NUM> in alternating layers <NUM> being generally aligned with the first portions <NUM> of the fibers <NUM> in the layers <NUM> located immediately adjacent thereto. The fibers <NUM> in each layer <NUM> may initially be positioned either above or below a plane defined by a respective uppermost or lowermost surface of the fiber <NUM> in an immediately adjacent layer <NUM>. For example, the bottom surface of the fiber <NUM> of the uppermost layer <NUM> in <FIG> may be located above a plane defined by the uppermost surface of the fibers <NUM> of the immediately-below layer <NUM>.

<FIG> is an end view of the composite article <NUM> of <FIG> illustrating a force <NUM> applied to the fibers <NUM>. The force <NUM> may occur in response to an impact of a projectile with the composite article <NUM>. As can be seen, the force <NUM> may cause the layers <NUM> to move closer together and may result in the engagement <NUM> of the fibers <NUM> with the fibers <NUM> in an immediately adjacent layer. In this regard, the second portions <NUM> of the fibers <NUM> in each layer <NUM> may become at least partially interlocked or at least partially nested <NUM> with the first portions <NUM> of the fibers <NUM> that are immediately adjacent. The engagement <NUM> or nesting of the fibers <NUM> may mechanically couple the fibers <NUM> of the layers <NUM> during a ballistic event such that a relatively large quantity of fibers <NUM> may be involved in a ballistic event.

In any of the embodiments disclosed herein, mechanical coupling of the fibers <NUM> with the matrix <NUM> (e.g., fiber-matrix coupling) due to varying the fiber geometry <NUM> of the fibers <NUM> along the fiber lengths <NUM> may result in an improvement in the ballistic performance and/or the optical performance of the composite article <NUM>. In addition, mechanical coupling of fibers <NUM> with one another in the same layer <NUM> and mechanical coupling of fibers <NUM> in different layers <NUM> (e.g., in-plane fiber-to-fiber coupling and out-of-plane fiber-to-fiber coupling) may result in an improvement in the ballistic performance and/or the optical performance of the composite article <NUM>. For example, during a ballistic event where a composite article <NUM> such as a composite panel <NUM> may be impacted by a projectile, the ability of the fibers <NUM> to move longitudinally along the length of the fiber <NUM> may affect the ballistic performance of the composite panel <NUM>.

As mentioned above, the ability of the fibers <NUM> in the matrix <NUM> to move longitudinally along the fiber length <NUM> relative to the matrix <NUM> may improve the ability of the fibers <NUM> to stretch longitudinally prior to fiber <NUM> failure. The ability of the fibers <NUM> to move or slip relative to one another may also improve the ability of the fibers <NUM> to stretch longitudinally. The ability of the fibers <NUM> to stretch longitudinally may increase the ability of the fibers <NUM> to absorb energy of a projectile during impact with the composite panel <NUM>. An increase in the energy-absorbing capability of the fibers <NUM> may improve the ballistic performance of the composite panel <NUM> by improving resistance of the composite panel <NUM> to penetration by the projectile <NUM>.

For composite panels <NUM> that are substantially transparent, movement of the fibers <NUM> relative to the matrix <NUM> and movement of the fibers <NUM> relative to one another may also affect the optical performance of the composite panel <NUM> following impact by a projectile. For example, an increase in the energy-absorbing capability of the fibers <NUM> may result in a decrease in the size of the area around an impact site <NUM> (<FIG>). In contrast, providing the fibers <NUM> with an increased ability to move relative to the matrix <NUM> and relative to one another may decrease the post-impact optical performance of a composite panel <NUM>. The decrease in the post-impact optical performance of a composite panel <NUM> may be characterized by an increase in the size of the area around an impact site <NUM>.

Referring to <FIG>, shown is a side view of a test article <NUM> during impact of projectile <NUM> against a front side <NUM> of the test article <NUM>. The test article <NUM> may be constructed in a manner similar to the embodiments of the composite article <NUM> (<FIG>) described above wherein a plurality of fibers <NUM> are embedded in a matrix <NUM>. As indicated above, the fibers <NUM> may have a fiber geometry <NUM> (<FIG>) that varies along the fiber lengths <NUM> (<FIG>) of the fibers <NUM>. The impact of the projectile <NUM> against the front side <NUM> occurs at an impact site <NUM> of the article surface <NUM>.

<FIG> shows a back side <NUM> of the test article <NUM> of <FIG> and illustrating a relatively large area of local and global involvement of the fibers <NUM> due to a relatively small amount of fiber-to-matrix coupling and/or fiber-to-fiber coupling in response to the impact of the projectile <NUM> against the front side <NUM> of the test article in <FIG>. In <FIG>, the local involvement <NUM> of the fibers <NUM> includes the portion of the fibers <NUM> in the area immediately surrounding the impact site <NUM> on the opposite (i.e., front side <NUM>) of the test article <NUM>. The global involvement <NUM> of the fibers <NUM> can be seen extending generally away from the impact site <NUM>. The relatively large extent of the global involvement <NUM> may be due to a relatively small amount of fiber-to-matrix coupling and/or fiber-to-fiber coupling in response to the impact of the projectile <NUM> against the front side <NUM> of the test article <NUM>.

<FIG> is a view of the back side of a test article having a relatively small area of local and global involvement of the fibers due to an increased amount of fiber-to-matrix coupling and/or fiber-to-fiber coupling relative to the coupling occurring in <FIG>. the increased amount of fiber-to-matrix coupling and/or fiber-to-fiber coupling may be achieved by increasing the magnitude of the variations in fiber geometry along the fiber length of the fibers. Increased fiber-to-matrix coupling and/or fiber-to-fiber coupling may also be achieved by decreasing the spacings between the adjacent second portions or between groups of the second portions in the semi-periodic <NUM> arrangement shown in <FIG>.

<FIG> are perspective views of a layered system <NUM> wherein the composite article <NUM> may be mounted in stacked formation with a first layer <NUM> and a second layer <NUM>. In an embodiment, the first layer <NUM> may be comprised of ceramic and/or glass material or other material and may comprise a strike face (not shown) of the layered system <NUM>. The second layer <NUM> may be formed as a relatively high-stiffness composite layer (not shown) and may be mounted adjacent to the first layer <NUM>. The composite article <NUM> may be mounted on a side of the second layer <NUM> opposite the first layer <NUM> such that the composite article <NUM> is located on a back face or a back side of the layered system <NUM>.

Although <FIG> illustrate a single one of the composite articles <NUM> located on a back side of the layered system <NUM>, any number of composite articles <NUM> may be provided. Furthermore, although only a single one of the first layers <NUM> and a single one of the second layers <NUM> are shown in <FIG>, any number of first layers <NUM> and second layers <NUM> may be provided in combination with any number of composite articles <NUM>. Even further, a layered system <NUM> may be formed comprising only a first layer <NUM> and a composite article <NUM>. In an embodiment, the layered system <NUM> may comprise an armor panel. However, the layered system <NUM> may be incorporated into any article, without limitation, and is not limited to an armor panel.

The first layer <NUM> may be comprised of a material that preferably has relatively high hardness and relatively high stiffness such as a monolithic layer of ceramic and/or glass. However, the first layer <NUM> may be formed in a variety of alternative materials which are preferably relatively stiff and relatively hard. The first layer <NUM> may be configured to function as a strike face for ballistic applications. For example, the first layer <NUM> may be configured to be impacted by a projectile.

The second layer <NUM> may be located adjacent to the first layer <NUM> as shown in <FIG>. The second layer <NUM> may be formed as a relatively high-stiffness composite layer (not shown). The second layer <NUM> may include glass fibers (not shown) embedded in a matrix (not shown). Alternatively, the second layer <NUM> may be comprised of one or more glass layers or sheets such as one or more monolithic sheets of glass. The second layer <NUM> may also be formed as a high stiffness composite layer (not shown) comprised at least partially of glass fibers (not shown) formed of high strength and/or high stiffness polymeric material such as ultra high density polyethylene and which may be embedded within a matrix (not shown). The combination of the first layer <NUM>, the second layer <NUM>, and the composite article <NUM> collectively forms the stiffened layered system <NUM> which provides relatively high global stiffness to the first layer <NUM> and improves the ballistic performance of the layered system <NUM>.

Referring to <FIG>, shown is a flow chart illustrating one or more operations that may be implemented in a method <NUM> for manufacturing a composite article <NUM> (<FIG>). Step <NUM> of the method <NUM> may include providing a plurality of fibers <NUM> (<FIG>) wherein each fiber <NUM> (<FIG>) has a fiber length <NUM> (<FIG>) and a fiber geometry <NUM> (<FIG>).

Step <NUM> may comprise varying the fiber geometry <NUM> (<FIG>) of the fibers <NUM> (<FIG>) along the fiber length <NUM> (<FIG>). For example, the fiber geometry <NUM> may be varied along the fiber length <NUM> by including a series of second portions <NUM> (<FIG>) separated by first portions <NUM> (<FIG>) along the fiber length <NUM>. In an embodiment, the fiber geometry <NUM> may be varied in a periodic <NUM> (<FIG>) manner along the fiber length <NUM>. However, the fiber geometry <NUM> may be also varied in a semi-periodic or in a non-periodic manner.

The fiber geometry <NUM> (<FIG>) may be varied by varying the cross-sectional shape <NUM> (<FIG>) of the fibers <NUM> along the fiber length <NUM> (<FIG>) and/or, in examples not in accordance with the invention to which this European patent relates, by varying the cross-sectional area <NUM> (<FIG>) of the fibers <NUM> (5A-11B and <NUM>-14B) along the fiber length <NUM>. In a further embodiment, the fiber geometry <NUM> may be varied by offsetting the cross-sectional shape <NUM> of the fibers <NUM> on alternating sides of the longitudinal axis <NUM> (<FIG>) as described above or by altering the orientation of the cross-sectional shape <NUM> along the fiber length <NUM>. In an embodiment, the fibers <NUM> may be provided with a serpentine shape <NUM> (<FIG>) or in a helix shape <NUM> (<FIG>) or in other shapes. The fibers <NUM> may be formed of one or more materials as described above in order to attain different interactions between the fibers <NUM> and the matrix <NUM> (<FIG>) and which may affect the coupling between the fibers <NUM> and the matrix <NUM>.

Step <NUM> of the method <NUM> may comprise positioning the fibers <NUM> (<FIG>) in side-by-side <NUM> (<FIG>) arrangement to form a layer <NUM> such as the layers <NUM> shown in <FIG> and <FIG>. However, the fibers may be positioned in non-parallel relation to one another. Furthermore, although not shown, the fibers may be provided in a woven fabric when the fibers are oriented at one or more of a variety of angles relative to one another. In an embodiment, the fibers <NUM> may include a series of second portions <NUM> (<FIG>) interconnected by first portions <NUM> (<FIG>) as described above.

Step <NUM> may comprise arranging the fibers <NUM> such that the second portions <NUM> of the fibers <NUM> are at least partially nested <NUM> (<FIG>) with the first portions <NUM> of immediately adjacent ones of the fibers <NUM> in the layer <NUM>. For example, <FIG> illustrates the positioning of the fibers <NUM> in a layer <NUM> such that the second portions <NUM> of the fibers <NUM> in the layer <NUM> are at least partially nested with the first portions <NUM> of the fibers <NUM> immediately adjacent thereto in the layer <NUM>. In embodiments not shown, the second portions <NUM> of the fibers <NUM> in one layer <NUM> may be configured to at least partially nest with first portions <NUM> of the fibers <NUM> in an adjacent one of the layers <NUM> of a composite article <NUM>.

Step <NUM> may comprise embedding the fibers <NUM> in a matrix <NUM> (<FIG>) and curing or solidifying the matrix <NUM> to form the composite article <NUM> (<FIG>). Advantageously, the variation in fiber geometry <NUM> along the fiber length <NUM> of the fibers <NUM> may facilitate fiber-to-matrix mechanical coupling and/or fiber-to-fiber mechanical coupling as a means to tailor the degree of relative fiber movement such as during a ballistic event. By tailoring the degree of fiber movement relative to the matrix and relative to other fibers, ballistic performance and post-impact optical performance of a composite article may be controlled or improved.

In an embodiment, the composite article <NUM> (<FIG>) may be configured to provide enhanced structural performance due to the use of fibers <NUM> having fiber geometry <NUM> that varies periodically or semi-periodically along the fiber length <NUM>. For example, by forming the composite article <NUM> from fibers <NUM> with along-the-length variations in cross-sectional area (in examples not in accordance with the invention to which this European patent relates), cross-sectional shape, and/or orientation, the damage tolerance of the composite article <NUM> and resistance to crack growth may be improved relative to the damage tolerance and resistance to crack growth of a conventional composite article formed of fibers that have generally non-varying geometry along the fiber length.

Advantageously in the presently disclosed composite article <NUM> (<FIG>), variations in fiber geometry <NUM> along the fiber length <NUM> may result in some amount of crack deflection in the matrix <NUM> material. In this regard, the varying of the fiber geometry <NUM> may cause a crack in the matrix <NUM> of the composite article <NUM> to propagate along a torturous path instead of propagating along a generally straight path. Propagation along a tortuous path may result in the suppression of crack growth in the matrix <NUM> relative to crack growth in the matrix of a conventional composite article having conventional fibers with fiber geometry that is generally non-varying along the fiber length. Such non-varying fiber geometry of conventional fibers may include a substantially continuous or constant cross-sectional shape, a substantially continuous or constant cross-sectional area, and/or a substantially continuous or constant orientation of the cross-sectional shape. The conventional fibers may also be formed of a substantially constant material type along the fiber length.

In an embodiment, the composite article <NUM> (<FIG>) disclosed herein may include fibers <NUM> having fiber geometry <NUM> that varies in a manner causing a matrix crack to propagate along a tortuous path through one layer <NUM> or through multiple layers <NUM>. In this regard, the variations in fiber geometery along the fiber length <NUM> may improve the intralaminar (e.g. within one layer) toughness and/or the interlaminar (e.g., between adjacent layers) toughness of the composite article <NUM> relative to a conventional composite article having conventional fibers with generally non-varying fiber geometry. Improvements in intralaminar toughness may represent a general increase in resistance to matrix crack propagation within a layer <NUM> and/or improved resistance to crack propagation at a de-bond of the fiber-matrix interface. Improvements in interlaminar toughness may represent a general increase in resistance to delamination of adjacent layers <NUM>. In an embodiment, the fiber geometry <NUM> of the fibers <NUM> may be varied in a manner causing an increase in the mode I interlaminar fracture toughness and/or an increase in the mode <NUM> interlaminar fracture toughness. Mode <NUM> interlaminar fracture toughness may be characterized as the resistance to an opening force or a peeling force oriented along a direction generally normal to adjacent layers <NUM> of the composite article <NUM>. Mode II interlaminar fracture toughness may be characterized as the resistance to a shearing force oriented generally parallel to adjacent layers <NUM> of the composite article <NUM>.

In the composite article <NUM> disclosed herein, the fibers <NUM> may be configured such that the varying geometry may suppress crack growth or crack propagation in a manner which improves the damage tolerance of the composite article. Damage tolerance may be measured as an increase in compression-after-impact strength and/or an increase in open-hole compression strength. An increase in compression-after-impact strength may represent an improvement in residual strength of the composite article <NUM> following a relatively low-velocity impact of an object against the composite article. Non-limiting examples of low-velocity impacts may include an impact due to a dropped tool or impact of flying debris against the composite article <NUM> when in service. An increase in open-hole compression strength may represent an increase in the buckling strength of the composite article <NUM> when loaded in compression.

Referring to <FIG>, shown is a method <NUM> of implementing the composite article <NUM> (<FIG>) in use such as in a vehicle (not shown). The method <NUM> of using the composite article <NUM> may include step <NUM> of providing the composite article <NUM> as a plurality of fibers <NUM> (<FIG>) embedded in a matrix <NUM> (<FIG>) as described above wherein each one of the fibers <NUM> has a fiber length <NUM> (<FIG>) and a fiber geometry <NUM> (<FIG>) and wherein the fiber geometry <NUM> varies along the fiber length <NUM>.

The method <NUM> of <FIG> may further include step <NUM> of placing the composite article <NUM> (<FIG>) such as a composite panel <NUM> (<FIG>) in a first state in a vehicle that is substantially non-moving. The composite panel <NUM> may be subjected to a static loading condition (not shown). In an embodiment, the vehicle may comprise an aircraft on the ground such as when parked at a gate of an airport terminal. Referring to <FIG>, shown is a perspective illustration of an aircraft <NUM> which may incorporate one or more embodiments of the composite article <NUM> (<FIG>) as disclosed herein. The aircraft <NUM> may include a fuselage <NUM> having a pair of wings <NUM> and a tail section <NUM> which may include a vertical stabilizer <NUM> and horizontal stabilizers <NUM>. The aircraft <NUM> may further include control surfaces <NUM> and propulsion units <NUM>. The aircraft <NUM> may be generally representative of one of a variety of vehicles that may incorporate one or more of the composite articles <NUM> as described herein.

In an embodiment, the composite article <NUM> (<FIG>) may comprise a composite panel <NUM> (<FIG>) that may be at least partially transparent and/or at least partially opaque. In the static loading condition, loads on the composite panel <NUM> may be limited to loads due to gravitational force acting on a mass of the composite panel <NUM>. Loads may also include compression loads due to mounting of the composite panel <NUM> to the vehicle. Static loads may also include tension loads, shear loads, and/or torsional loads acting on the composite panel <NUM> due to mounting of the composite panel <NUM> in the vehicle or due to other phenomena such as differential heating of the adjacent structure or due to other causes.

The method <NUM> of <FIG> may further include step <NUM> of subjecting the composite panel <NUM> (<FIG>) to a second state wherein the vehicle may be in motion and/or the composite panel <NUM> may be subjected to a dynamic loading condition (not shown). For example, the vehicle may comprise the aircraft <NUM> (<FIG>) in motion on a runway during takeoff. In the dynamic loading condition, loads on the composite panel <NUM> may include any one of compression loads, tension loads, shear loads, torsion loads, or any combination thereof. The loads may also include localized loads acting on the composite panel <NUM> due to impact by a projectile or by flying debris. As indicated above, the lengthwise variations in fiber geometry <NUM> of the composite panel <NUM> may facilitate mechanical coupling between the fibers <NUM> (<FIG>) and the matrix <NUM> (e.g., fiber-matrix coupling) and/or between adjacent fibers <NUM> (e.g., fiber-to-fiber coupling) in one or more of the layers <NUM> (<FIG>) that make up the composite panel <NUM>. The mechanical coupling may provide a means to control the fiber-to-matrix movement and/or fiber-to-fiber movement which may increase the ability to decelerate a projectile impacting the composite panel <NUM>.

The method <NUM> of <FIG> may further include step <NUM> of causing any cracks (not shown) in the matrix <NUM> to propagate along a tortuous path (not shown) due to the lengthwise variations in fiber geometry <NUM> of the fibers <NUM> in the composite panel <NUM>. In this regard, the directions of the tortuous path may be defined by the variations in the fiber geometry <NUM> of the fibers <NUM>. The tortuous path of crack propagation may improve the intralaminar (e.g. within one layer) fracture toughness and/or the interlaminar (e.g., between adjacent layers) fracture toughness of the composite panel <NUM>. In this regard, the tortuous crack propagation may improve the compression-after-impact strength of the composite panel <NUM> when the composite panel <NUM> is impacted by a relatively low velocity impact such as due to impact by a tool, or runway debris or gravel in the case of the aircraft <NUM> (<FIG>) in motion during takeoff or landing. Furthermore, the tortuous crack propagation may improve the open-hole compression strength of the composite panel <NUM> resulting in an increase in the buckling strength of the composite panel <NUM> under a compression load.

According to an aspect of the present disclosure there is provided a composite article, comprising a matrix, a plurality of fibers embedded in the matrix, each one of the fibers having a fiber length and a fiber geometry, and the fiber geometry varying along the fiber length. Advantageously, the fiber is comprised of a first material and a second material. Advantageously at least one of the matrix and the fiber is formed from at least one of the following, a thermoplastic material comprising at least one of the following: acrylics, nylon, fluorocarbons, polyamides, polyethylenes, polyesters, polypropylenes, polycarbonates, polyurethanes, polyctheretherketone, polyetherketoneketone, polyethcrimides, stretched polymers, a thermoset comprising at least one of the following: polyurethanes, phenolics, polyimides, bismaleimides, polyesters, epoxies, silsesquioxanes, inorganic material comprising at least one of the following: carbon, silicon carbide, boron and glass comprising E-glass (alumino-borosilicate glass), S-glass (alumino silicate glass), pure silica, borosilicate glass, optical glass, ceramics, glass ceramics. Advantageously the fibers are at least one of opaque and substantially optically transparent and the matrix being at least one of opaque and substantially optically transparent. Advantageously, the composite article is included in at least one of the following a windshield, a canopy, a window, a membrane, an armor panel, a structural panel, an architectural panel, a non-structural article, a layered system. Advantageously the the fibers are arranged in the matrix such that a variation in the fiber geometry along the fiber length causes a crack in the matrix to propagate along a tortuous path; and the tortuous path causing a suppression of crack growth in the matrix relative to crack growth in a matrix of a composite article having fibers with generally non-varying fiber geometry along the fiber length. Advantageously the tortuous path extends at least partially within at least one of the following matrix material in a layer of the fibers; and matrix material between adjacent layers. Advantageously the fiber geometry of the fibers varies in a manner causing an increase in at least one of the following damage tolerance; mode I interlaminar fracture toughness; and mode <NUM> interlaminar fracture toughness.

According to a yet further aspect of the present disclosure there is provided a method of manufacturing a composite article, comprising the steps of providing a plurality of fibers each having a fiber length and a fiber geometry, at least one of the fibers having a fiber geometry that varies along the fiber length; and embedding the fibers in a matrix. Advantageously the forming the fibers includes a first material and a second material. Advantageously further steps include arranging the fibers in side-by-side arrangement for forming a layer, each one of the fibers having a series of second portions separated by first portions; and positioning the fibers such that the second portions of one of the fibers in the layer are at least partially nested with the first portions of an immediately adjacent one of the fibers in the layer.

According to a further aspect of the present disclosure there is provided a fiber for a composite article, comprising a fiber length and a fiber geometry; and the fiber geometry varying along at least a portion of the fiber length. Advantageously the fiber geometry has a cross-sectional area; and the cross-sectional area being variable along the fiber length (in examples not in accordance with the invention to which this European patent relates). Advantageously the fiber geometry has a cross-sectional shape; and the cross-sectional shape being variable along the fiber length. Advantageously the fiber geometry has a cross-sectional area; and the cross-sectional area being substantially constant along the fiber length. Advantageously the fiber has a longitudinal axis extending along the fiber length; the fiber geometry has a cross-sectional area; and the cross-sectional area being offset relative to the longitudinal axis at different locations along the fiber length. Advantageously a variation in the fiber geometry comprises a series of first portions and second portions along the fiber length. Advantageously the fibers have a fiber thickness in a range of from approximately <NUM> microns to <NUM> microns.

According to yet another aspect of the disclosure there is provided a method of loading a composite article of a vehicle. The method comprises the step of providing the composite article as a plurality of fibers embedded in a matrix, each one of the fibers having a fiber length and a fiber geometry, the fiber geometry varying along the fiber length. The method further comprises placing the composite article in a first state comprising a static loading condition. In addition, the method comprises placing the composite article (<NUM>) in a second state comprising a dynamic loading condition. The method may further comprise the step of causing, in response to the fiber geometry varying along the fiber length, a crack in the matrix to propagate along a tortuous path. The static loading condition may be associated with a vehicle being substantially non-moving. The dynamic loading condition may be associated with the vehicle in motion.

Claim 1:
A composite article, comprising:
a matrix (<NUM>); and
fibers (<NUM>), embedded in the matrix (<NUM>),
wherein:
each one of the fibers (<NUM>) has a fiber length (<NUM>) and a fiber geometry (<NUM>),
the fiber geometry (<NUM>) varies along the fiber length (<NUM>),
the fiber geometry (<NUM>) has a cross-sectional shape having a transverse axis,
the transverse axis has an orientation,
the orientation of the transverse axis twists back-and-forth along the fiber length (<NUM>), and
the fiber geometry (<NUM>) has a constant cross-sectional area along the fiber length (<NUM>).