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.
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.
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.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
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
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
Turning to
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 1×106 PSI 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
In a preferred implementation, the transparent nanofibers 18 are integrated with the transparent matrix 20 utilizing an injection molding process as illustrated in
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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.