US20060024483A1

US20060024483A1 - Transparent composite panel

Info

Publication number: US20060024483A1
Application number: US10/901,808
Authority: US
Inventors: William Koch; Paul Nordman
Original assignee: Boeing Co
Current assignee: Boeing Co
Priority date: 2004-07-29
Filing date: 2004-07-29
Publication date: 2006-02-02
Also published as: GB2434770A; WO2006014961A1; GB0703374D0

Abstract

A transparent nanofiber composite panel that includes a plurality of transparent nanofibers integrated in random orientations within a transparent matrix is provided. The transparent nanofibers have a diameter that is less than the wavelength of visible light. The extremely small diameter of the transparent nanofibers allows the transparent panel to be substantially insensitive to an RI ‘mismatch’ between the transparent nanofibers and the transparent matrix. Additionally, due to random orientation of the transparent nanofibers within the transparent matrix the transparent nanofiber composite panel possesses substantially isotropic material properties such that the transparent nanofiber composite panel can be incorporated as a structural, load bearing, component of a larger structure.

Description

FIELD OF THE INVENTION

The present invention relates to composite transparencies and more particularly to transparent composites utilized to provide transparent structural panels that can be incorporated into the structure of a mobile platform.

BACKGROUND OF THE INVENTION

Composite transparencies have many applications in many devices and structures. For example, composite transparencies can be utilized in eyeglasses, high security display cases, high-rise building windows and fighter jet cockpit canopies. In a particular instance, composite transparencies can be utilized to construct windows of a mobile platform such as an aircraft, train, bus, tank or ship. Generally, mobile platform windows formed of known transparent materials are not suitable for use as structural component of the mobile platform. In many instances, windows in many commercial mobile platforms are relatively small in size, due, at least in part, to the limited capabilities of current transparent window materials to carry a load and also due to the heavy and complex support structure needed to carry mobile platform fuselage loads around the window cutout in the absence of a load bearing transparency.
Typically, these transparent window materials consist of a transparent polymer that exhibits such useful qualities as good transparency and easy formation of complex shapes. However, these polymer windows typically have a limited strength capability, tend to be notch sensitive, and craze, i.e. form nuisance cracks, over time at very low stress levels. Moreover, these windows generally require a heavy support structure in order to support the window within the fuselage structure of the mobile platform. Each component of such a support structure is designed to strengthen panels of the fuselage that surround and support each window. However, each component increases the cost and weight of the completed window assembly, thereby providing an incentive to keep some mobile platform windows relatively small.
In at least some known instances, fiber reinforced transparent composites have been utilized in constructing mobile platform windows that are lighter and stronger than the transparent polymer windows typically used. Such composite windows typically include a transparent fiber integrated within a transparent polymer matrix, e.g. an epoxy resin. To provide high quality transparent properties of such composites, the refraction index (RI) of the transparent fiber must substantially match that of the polymer matrix to a third decimal place. While such RI matching is straightforward, problems arise due to a ‘mismatch’ in the RI's as a function of temperature change. That is, as the environmental temperature to which the transparent composite is exposed changes, the RI of the polymer matrix and/or the RI of the fiber will change such that there is a ‘mismatch’ between the RI's of the matrix and the fiber. Typically, the RI changes significantly for the polymer matrix but is relatively constant for the fiber. Therefore, changes in the environmental temperature, either increases and/or decreases, can cause a ‘mismatch’ of RI's of the matrix and the fiber. A significant ‘mismatch’, e.g. greater than 0.01, between the RI of the matrix and the RI of the fiber causes clouding of the transparent composite.
Accordingly, the present invention seeks to provide the art with a strong composite transparency that can provide excellent structural strength and does not suffer from opacity at extreme temperatures. The present invention is focused on use with an aircraft window, however it is applicable to any transparency where high strength and lightweight construction are of paramount importance.

SUMMARY OF THE INVENTION

A transparent nanofiber composite panel is provided in accordance with a preferred embodiment of the present invention. The transparent nanofiber composite panel includes a plurality of transparent nanofibers integrated in random orientations within a transparent matrix. The transparent nanofibers have a diameter that is less than the wavelength of visible light. In a preferred exemplary embodiment, the transparent nanofibers are constructed of glass. Alternatively, the transparent nanofibers can be constructed of any other suitable transparent material having high strength properties, for example, silicon dioxide, graphite or a transparent polymer such as nylon or polycarbonate.
In a preferred form, the transparent matrix is formed from a transparent epoxy resin. The high transmittance of the transparent nanofibers resulting from having a diameter less than the wavelength of visible light permits variations in the refraction index (RI) of the matrix that may occur due to extreme temperatures, without affecting the translucency of the transparent nanofiber composite panel. More specifically, the extremely small diameter of the transparent nanofibers allows the transparent panel to be substantially insensitive to an RI ‘mismatch’ between the transparent nanofibers and the transparent matrix.
Due to the random orientation of the transparent nanofibers within the transparent matrix, the transparent nanofiber composite panel comprises substantially isotropic material properties. For example, the transparent nanofiber composite panel possesses approximately equal strength in all directions. Therefore, the transparent nanofiber composite panel can be incorporated as a structural, load bearing, component of a larger structure, e.g. a mobile platform fuselage.
The features, functions, and advantages can be achieved independently in various embodiments of the present inventions or may be combined in yet other embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
FIG. 1 is an illustration of an exemplary mobile platform including a transparent nanofiber composite panel according to the principles of the present invention;
FIG. 2 is a sectional view of the transparent nanofiber composite panel shown in FIG. 1;
FIG. 3 is an exemplary schematic view of a method of forming transparent nanofibers for use with the transparent nanofiber composite panel shown in FIG. 1;
FIG. 4A is a schematic view of an injection mold used to construct the transparent nanofiber composite panel, shown in FIG. 1, in accordance with a preferred embodiment of the present invention; and
FIG. 4B is a schematic view of a nanofiber pre-impregnated tape used to construct the transparent nanofiber composite panel, shown in FIG. 1, in accordance with another preferred embodiment of the present invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
With reference to FIG. 1, a transparent nanofiber composite panel 10 constructed according to the principles of the present invention is shown in operative association with a mobile platform 12. More particularly, the transparent nanofiber composite panel 10 is an optical quality fiber reinforced transparency having high structural strength properties. Although the mobile platform 12 is shown as an aircraft, the mobile platform 12 could also be represented in the form of other mobile platforms, such as a ship, a train, a bus or an automobile. Additionally, although the present invention will be described below as particularly applicable for use in association with mobile platforms, the invention should not be so limited in application. It is envisioned that the invention is equally applicable to aircraft, trains, buses, tanks, ships, buildings, or any application where a composite transparency having high strength and lightweight construction is of paramount importance.
In the particular example provided, the transparent nanofiber composite panel 10 is shown as a window of the mobile platform 12. It should be appreciated, however, that the transparent nanofiber composite panel 10 may be used in any portion of the mobile platform 12 and may include the cockpit window or a door window. Moreover, the transparent nanofiber composite panel 10 may be used in any number of environments not strictly limited to conventional “windows”. For example, skylights, running light covers, satellite dome covers, view ports on undersea watercraft, and various other environments may employ the transparent nanofiber composite panel 10 of the present invention.
The mobile platform 12 generally includes a fuselage 14 that surrounds the transparent nanofiber composite panel 10. A traditional prior art side window is shown in FIG. 1 in phantom lines and is generally indicated by reference numeral 16. As is apparent, the transparent nanofiber composite panel 10 has a larger field of view than the traditional prior art side window 16. This is due, in part, to the greater strength and load carrying capability of the transparent nanofiber composite panel 10, as further described below.
Turning to FIG. 2, a portion of the transparent nanofiber composite panel 10 is illustrated. The transparent nanofiber composite panel 10 generally includes a plurality of transparent nanofibers 18 integrated within a transparent matrix 20. The transparent nanofibers 18 have a diameter, “d”. In a preferred embodiment the diameter d of the transparent nanofibers 18 is less than the wavelength of visible light, i.e., less than approximately 400 to 600 nm. Preferably, the transparent nanofibers 18 have a diameter d of between approximately 10 to 400 nm. In the particular example provided, the transparent nanofibers 18 are constructed of glass. However, the transparent nanofibers 18 can be constructed of any other suitable transparent material having high strength properties as described herein; for example, silicon dioxide, graphite or a transparent polymer such as nylon or polycarbonate.
In a preferred form, the matrix 20 is formed from a transparent epoxy resin. The epoxy resin is selected based on transparency, strength, and refractive index (RI). Preferably, the RI of the matrix 20 is substantially similar to the RI of the transparent nanofibers 18. However, the high transmittance of the transparent nanofibers 18 of the present invention, as described below, permits variations in the RI of the matrix 20 that may occur due to extreme temperatures, without affecting the translucency of the transparent nanofiber composite panel 10.
In accordance with a preferred implementation of the present invention, due to the diameter d being less than the wavelength of visible light, the transparent nanofibers 18 permit transmittance of light on the order of 90%. Moreover, because the transmittance of the transparent nanofibers 18 is very high, it is possible to allow dissimilar RIs between the transparent nanofibers 18 and the transparent matrix 20 without the transparent nanofiber composite panel 10 becoming opaque. Additionally, as the diameter of the transparent nanofibers 18 decreases, fiber strength increases due to a reduction in surface defects. This is especially true of glass nanofibers, which have been shown to exhibit linearly increasing tensile strength up to 1×10⁶PSI for fiber diameters of approximately 1000 nm.
Preferably the transparent nanofibers 18 are distributed within the matrix 20 at approximately 10% to 60% by volume. Due to the high tensile strength of the transparent nanofibers 18, as the diameter of the transparent nanofibers 18 decreases, the concentration of transparent nanofibers 18 integrated with the transparent matrix 20 can decrease without sacrificing the structural strength properties of the transparent nanofiber composite panel 10.
Moreover, due to the high tensile strength of the transparent nanofibers 18, the transparent nanofibers 18 can be distributed within the matrix 20 at random orientations without sacrificing the structural strength properties of the transparent nanofiber composite panel 10. That is, due to the high tensile strength of the small diameter transparent nanofibers 18 sufficient strength will remain in the transparent nanofiber composite panel 10 without integrating the transparent nanofibers 18 within the transparent matrix 20 in a particular orientation. Furthermore, the random orientation of the transparent nanofibers 18 within the transparent matrix 20 provides the transparent nanofiber composite panel 10 with quasi-isotropic material properties, e.g. approximately equal strength in all directions. Therefore, the transparent nanofiber composite panel 10 can be incorporated as a structural, load bearing, component of the mobile platform fuselage 14.
With reference to FIG. 3, the transparent nanofibers 18 are preferably produced by spinning the material through a powerful electric field, known in the art as “electrospinning”, though various other methods may be employed. A polymer melt 22, glass in the particular example provided, is pumped from a source 24 through a feed line 26 to a spinneret 28. The spinneret 28 extends between a top plate 30 and a bottom plate 32. The top plate 30 is charged via a power source 34. An electric field is thereby formed that in turn electrostatically charges the melt 22 as it leaves the spinneret 28. As the polymer melt 22 is spun out from the spinneret 28, the electric field draws out the melt 22 into nanofibers that may then be collected on the bottom plate 32.
In a preferred implementation, the transparent nanofibers 18 are integrated with the transparent matrix 20 utilizing an injection molding process as illustrated in FIG. 4A. A mold 38 generally includes mold halves 40 that combine to form a designated shape, such as, for example, a window shape. Epoxy resin 42 and transparent nanofibers 18 are then injected into the mold 38. Once the epoxy resin 42 has set or cured, the transparent nanofiber composite panel 10 may then be removed from the mold 38. Since the transparent nanofibers 18 may be randomly oriented within the mold 38, it is possible for the mold 38 to take on any shape desired, thereby allowing windows that have complex surfaces.
Turning to FIG. 4B, in an alternative preferred embodiment, the transparent nanofibers 18 are used to form a reinforced pre-impregnated tape 36. For example, the transparent nanofibers 18 may be arranged in a resin that, after solidification, forms the transparent matrix 20 in the form of strips of pre-impregnated tape 36. Successive layers of the pre-impregnated tape 36 may then be laminated to form the transparent nanofiber composite panel 10. Due to the random orientation of the transparent nanofibers 18 on the pre-impregnated tape 36, the pre-impregnated tape 36 need not be aligned in any particular manner when laminated with layers of other pre-impregnated tape 36 to form the transparent nanofiber composite panel 10.
In yet another preferred embodiment, the transparent nanofibers 18 are woven into a ‘cloth’. The transparent nanofiber ‘cloth’ is then exposed to the transparent matrix 20, such that the transparent matrix 20 penetrates the transparent nanofiber ‘cloth’.
By employing transparent nanofibers integrated within a transparent matrix, the transparent nanofiber composite panel 10 is substantially insensitive to RI ‘mismatch’, e.g. ‘mismatch’ caused by changes in the environmental temperature. That is, the transparent nanofiber composite panel 10 will maintain a high level of transparency, e.g. 90%, over a wide range of temperature. In an exemplary embodiment the transparent nanofiber composite panel 10 will maintain a high level of transparency at temperatures ranging between approximately (−60)° F. and approximately 400° F. Moreover, the transparent nanofiber composite panel 10 is substantially stronger and is capable of use as a load bearing structural component of the mobile platform 12. For example, in the case where the transparent nanofiber composite panel 10 is a window in a mobile platform fuselage, a load can be transferred across the window so that additional fuselage structure does not need to be incorporated around the window. Preferably, the transparent nanofibers 18 are constructed of glass to thereby provide significant tensile strength and allow lower concentration of the transparent nanofibers 18 within the transparent matrix 20. The lower concentration provides further increases in transmittance and decreases in optical distortion of light through the transparent nanofiber composite panel 10. If polymer material is used to construct the transparent nanofibers 18, it is preferable to select a polymer material with a RI and an index variation substantially similar to the RI and index variation of the transparent matrix 20.
Furthermore, the transparent nanofiber composite panel 10 constructed with the transparent nanofibers 18 randomly oriented within the transparent matrix 20, as described above, is not limited to unidirectional strength. Thus, the transparent nanofiber composite panel 10 will have quasi-isotropic material properties.
While various preferred embodiments have been described, those skilled in the art will recognize modifications or variations, which might be made without departing from the inventive concept. The examples illustrate the invention and are not intended to limit it. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.

Claims

1. A transparent panel comprising:

a transparent matrix; and

a plurality of transparent nanofibers integrated within the transparent matrix, the transparent nanofibers having a diameter less than the wavelength of visible light.

2. The transparent panel of claim 1, wherein the transparent nanofibers have a diameter between approximately 10 nm and 400 nm.

3. The transparent panel of claim 1, wherein the transparent nanofibers comprise glass transparent nanofibers.

4. The transparent panel of claim 1, wherein the transparent nanofibers comprise approximately 10% to 60% of the transparent panel by volume.

5. The transparent panel of claim 1, wherein an index of refraction of the transparent nanofibers approximately equals an index of refraction (RI) of the transparent matrix.

6. The transparent panel of claim 1, wherein the transparent nanofibers are integrated within the transparent matrix to form a non-woven transparent nanofiber mat tape used to construct the transparent panel.

7. The transparent panel of claim 1, wherein the transparent nanofibers form a mat cloth that is integrated within the transparent matrix to form the transparent panel.

8. The transparent panel of claim 1, wherein the transparent nanofibers and the transparent matrix are injected into a mold to form the transparent panel.

9. The transparent panel of claim 1, wherein the transparent matrix comprises an epoxy resin.

10. The transparent panel of claim 1, wherein the transparent nanofibers comprise a polymer.

11. The transparent panel of claim 1, wherein the transparent nanofibers are integrated within the transparent matrix in a random orientation to provide a structural load bearing transparent panel comprising substantially isotropic strength such that a load can be transferred across the transparent panel in any direction.

12. The transparent panel of claim 11, wherein the structural load bearing transparent panel is adapted to be incorporated as a transparent structural, load bearing member within a fuselage of a mobile platform.

13. The transparent panel of claim 1, wherein the transparent panel comprises an optical quality transparent panel adapted to permit approximately 90% transmittance of light.

14. The transparent panel of claim 1, wherein the transparent panel is adapted to maintain an approximately constant level of transparency at temperatures ranging between approximately (−60)° F. and approximately 400° F.

15. The transparent panel of claim 1, wherein the transparent panel is adapted to be substantially insensitive to an RI ‘mismatch’ between the transparent nanofibers and the transparent matrix

16. A method for providing a structural load bearing transparent panel having substantially isotropic material properties over a wide range of temperatures, the method comprising:

providing a transparent matrix;

providing a plurality of transparent nanofibers having a diameter less than the wavelength of visible light;

integrating the transparent nanofibers within a transparent matrix to form the transparent panel comprising substantially isotropic strength such that a load can be transferred across the transparent panel in any direction and adapted to be substantially insensitive to a difference between a refractive index (RI) of the transparent matrix and a RI of the transparent nanofibers.

17. The method of claim 16, wherein integrating the transparent nanofibers within a transparent matrix comprises integrating the transparent nanofibers within a transparent matrix in a random orientation such that the transparent panel comprises substantially isotropic material properties.

18. The method of claim 16, wherein providing the plurality of transparent nanofibers comprises providing the transparent nanofibers having a diameter between approximately 10 nm and 400 nm.

19. The method of claim 16, wherein providing the plurality of transparent nanofibers comprises providing glass nanofibers.

20. The method of claim 16, wherein integrating the transparent nanofibers within a transparent matrix comprises integrating the transparent nanofibers such that the transparent nanofibers comprise approximately 10% to 60% of the transparent panel by volume.

21. The method of claim 16, wherein providing the plurality of transparent nanofibers comprises providing the nanofibers having a RI approximately equal to RI of the transparent matrix.

22. The method of claim 16, wherein integrating the transparent nanofibers within a transparent matrix comprises:

integrating the transparent nanofibers within the transparent matrix to form a non-woven transparent nanofiber mat tape; and

bonding together a plurality of pieces of the transparent nanofiber mat tape to construct the transparent panel.

23. The method of claim 16, wherein integrating the transparent nanofibers within a transparent matrix comprises:

forming a mat cloth from the transparent nanofibers; and

integrating within the transparent matrix with the mat cloth to form the transparent panel.

24. The method of claim 16, wherein integrating the transparent nanofibers within a transparent matrix comprises injecting the transparent nanofibers and the transparent matrix into a mold to form the transparent panel.

25. The method of claim 16, wherein providing the transparent matrix comprises providing an epoxy resin to be integrated with the transparent nanofibers.

26. The transparent panel of claim 16, wherein providing the transparent nanofibers comprises providing a polymer to be integrated with the transparent matrix.

27. The method of claim 16, wherein the method further comprises incorporating the transparent panel within a fuselage of a mobile platform as a transparent structural, load bearing member.

28. The method of claim 16, wherein integrating the transparent nanofibers within a transparent matrix comprises integrating the transparent nanofibers within the transparent matrix such that the transparent panel permits approximately 90% transmittance of light.

29. The method of claim 16, wherein integrating the transparent nanofibers within a transparent matrix comprises integrating the transparent nanofibers within the transparent matrix such that such that the transparent panel is maintains an approximately constant level of transparency at temperatures ranging between approximately (−60)° F. and approximately 400° F.

30. A nanofiber composite panel for use in the structure of a mobile platform, said panel comprising:

a transparent epoxy resin; and

a plurality of transparent nanofibers integrated within the transparent epoxy resin in a random orientation to provide a transparent panel having substantially isotropic strength such that a load can be transferred across the transparent panel in any direction; wherein the transparent nanofibers comprise:

a diameter having a length less than the wavelength of visible light such that the transparent panel is substantially insensitive to a difference between a refractive index (RI) of the transparent epoxy resin and a RI of the transparent nanofibers.

31. The panel of claim 30, wherein the length of the diameter of the transparent nanofibers is between approximately 10 nm and 400 nm.

32. The panel of claim 30, wherein the transparent nanofibers comprise glass nanofibers.

33. The panel of claim 30, wherein the transparent nanofibers comprise polymer nanofibers.

34. The panel of claim 30, wherein the transparent nanofibers comprise approximately 10% to 60% of the transparent panel by volume.

35. The panel of claim 30, wherein an index of refraction of the transparent nanofibers approximately equals an index of refraction (RI) of the transparent epoxy resin.

36. The panel of claim 30, wherein the transparent nanofibers are integrated within the transparent epoxy resin to form a non-woven transparent nanofiber mat tape used to construct the transparent panel.

37. The panel of claim 30, wherein the transparent nanofibers form a mat cloth that is integrated within the transparent epoxy resin to form the transparent panel.

38. The panel of claim 30, wherein the transparent nanofibers and the transparent epoxy resin are injected into a mold to form the transparent panel.

39. The panel of claim 11, wherein the transparent panel is adapted to be incorporated as a transparent structural, load bearing member within a fuselage of a mobile platform.

40. The panel of claim 30, wherein the transparent panel comprises an optical quality transparent panel adapted to permit approximately 90% transmittance of light.