Patent Application
20070243393
The field of the invention relates to composite materials and the fabrication thereof, for use as insulators in environments that may include high temperatures, high noise levels, and/or corrosive environments. Aspects of the invention are directed to manufacture of sandwich composite materials using processes such as vacuum assisted resin transfer molding (VARTM).
Insulation technologies continue to advance in the commercial marketplace. However, commercially available materials exhibit one or several limitations preventing their use in various applications, such as with hot and/or noisy pieces of equipment including the engine, transmission, power transfer module, and cooling fans in automobile applications.
Aerogels are materials often considered for insulation applications due to their low thermal conductivity. Generally, aerogels are a special class of open-cell foams with unique thermal, chemical, acoustic, optical and electrical properties. They typically have high porosity (>90%), low density (<0.4 g/cm3), ultrafine pore sizes (<50 nm), high internal surface area (400-1000 m2/g), and a solid matrix composed of inter-connected fibrous chains with characteristic diameters of 10 nm. A characteristic of aerogels is low mechanical stability, leading to efforts towards fabricating aerogel composites to combine the low thermal conductivity of aerogels with the structural integrity of other materials, such as fibers. Aerogel blankets, including aerogel/fiber composite blankets, are available commercially.
Vacuum assisted resin transfer molding (VARTM) is a known process for fabricating a composite part by infusing resin into a part, for example, a fibrous preform. VARTM employs a fluid-impervious outer sheet or bag to isolate the part and allow a vacuum to draw resin into the preform. Many improvements have been made on the VARTM method, such as the use of distribution media to more evenly deliver the resin onto the part. High permeability layers (HPL), or breathers, may also be utilized to assist with thorough evacuation of the air within the system and provide a non-directional flow front for improved resin delivery. Another development in the field is co-injection resin transfer molding (CIRTM), in which multiple different resins are simultaneously injected into the part or multiple resins are injected sequentially into one area of the part.
The present invention relates to a sandwich composite construction, and method of fabrication, for use as an insulator. The sandwich composite construction is particularly advantageous in applications requiring a lightweight, mechanically stable material to provide thermal and acoustical insulation. For employment in areas with complex geometry, water soluble tooling may be used as a substrate on which the sandwich composite construction is fabricated. The sandwich composite construction may be manufactured using a vacuum assisted resin transfer molding method (VARTM) subsequent to providing a preform comprising elements of fibrous material, aerogel, separation material and resin. Additionally, an insulative material element, such as a foam, may be provided in the composite construction. A plurality of each element may be included throughout the composite. Numerous embodiments of the present invention are described herein to show tailorable properties of the sandwich composite construction.
There remains a need for an appropriate insulation material with superior thermal and acoustic properties. There also remains a need for multi-functional thermal and acoustic barrier materials that also are capable of resistance to fluids (seawater, oil, and fuel), and to various forms of corrosion. In addition, these newly designed materials must be lightweight, affordable and easily packaged for use in numerous applications.
a is a schematic cross-sectional view of a first sandwich composite construction in accordance with the embodiments of the invention;
b is a schematic cross-sectional view of a second sandwich composite construction in accordance with the embodiments of the invention;
a is a graphical representation of the acoustical insulative effect of sandwich composite constructions in accordance with the embodiments of the invention;
b is a second graphical representation of the acoustical insulative effect of the sandwich composite constructions of
c is a graphical representation of the acoustical insulative effect of sandwich composite construction in accordance with embodiments of the invention.
d is a graphical representation of the acoustical insulative effect of sandwich composite constructions in accordance with embodiments of the invention;
a is a graphical representation of the acoustical insulative effect of sandwich composite constructions in accordance with the embodiments of the invention, showing the effect of pressure on the insulative effect;
b is a second graphical representation of the acoustical insulative effect of the sandwich composite constructions of
The present disclosure provides sandwich composite constructions and methods of manufacture. In certain embodiments, the composite materials employ silica-based aerogel materials as part of a layered composite material. The sandwich composite materials may act as thermal insulators to provide protection against elevated temperatures, as well as resistance to fire. The sandwich composite materials may act as acoustic insulators by reducing the transmission of noise at various frequencies.
In certain applications, it is desirable to utilize multifunctional composite materials having properties such as thermal and acoustic insulation while also providing mechanical integrity. In general, the composite constructions disclosed herein are structurally rigid and withstand various impact forces. By way of example, the composite materials may withstand an impact force of five pounds per square inch or more. In certain embodiments, the composite materials provide enhanced structural rigidity and impact resistance as compared to other materials such as polymer materials. In addition to being structurally rigid, the composite materials also typically are lightweight. In certain embodiments, the weight of the materials is no more than about three pounds per square foot of composite material.
In certain embodiments, the composite constructions have a K value of approximately 0.0305 BTU/hr-ft-° F. for one inch of thickness. In certain embodiments, the surface temperature on the cool side of the composite materials can be maintained at between about 130° F. to about 150° F. or less, or at about 100° F., when the temperature on the hot side is about 250° F. or more. In certain embodiments, the surface temperature on the cool side of the composite materials can be maintained at about 120° F. or less, or at about 100° F. or less, when the temperature on the hot side is about 400° F. or more. Additionally, a protective layer can be utilized on the surface of the composite material facing the hot side to limit the flammability of the material and provide resistance to fire. In certain embodiments, a layer of material having a thickness sufficient to be flame-retardant or flame-resistant is included at or near the outer surface of the composite materials. The layer may be made of a phenolic resin or other suitable material and may have a thickness of between about 0.08 to about 0.1 inches. For complex-shaped structures, the hot side of the structure may be coated with flame-resistant or flame-retardant material.
The composite materials have noise reducing properties. In certain embodiments, the composite materials have a Transmission Loss Factor (STC) of between about 32 to about 36. The composite materials provide the characteristic of acoustic attenuation. In certain embodiments, the materials provide a Transmission Loss (TL) in decibels (dB) when tested at an amplitude of about 1.5 volts as follows:
Generally, the sandwich construction includes a fibrous material/resin composite system and an aerogel sandwich material isolated from the resin matrix through a separation material. A fibrous material, such as fiberglass fabric, can be secured to or about a flexible silica aerogel material and then infiltrated with a resin system which may be an epoxy based resin. Such a composite material system is suitable for thermal and acoustic barrier applications and overcomes the difficulties associated with use of commercially-available flexible aerogel materials.
The composite materials are resistant to fluids and corrosion. Corrosive conditions may be encountered due at least in part to fluids present in the operating environment or contact with other surrounding materials. Fluids that may be present in the operating environment include sea water, ethylene glycol, diesel fuel, hydraulic fluid, battery acid and the like.
The insulating materials of the various embodiments include sandwich construction configurations that impart tailorable properties to the constructions, e.g., thermal protection and/or acoustic protection, depending on the service environment. As shown in
Other numbers and combinations of layers to form the composite constructions also are contemplated as being within the scope of the invention. For example, one, four, six, or more layers of silica aerogel material may be provided between two fiberglass face sheets. As another example, one, two or more sheets of fiberglass fabric may be provided on the surface of the aerogel material. Various combinations of layers of fiberglass fabric, aerogel material and other structural and/or insulative materials also are contemplated. As an example, one or more foam materials may be included in the composite constructions to provide enhanced strength and/or insulation. One suitable foam material is Divinycell® PVC foam (Grades H45 and H60), which can provide structural integrity and acoustical shielding.
In one aspect of the invention, a one-step co-curing fabrication process (co-injection resin transfer method or “CIRTM”) can be used to manufacture the sandwich composites. That is, highly viscous resin slurries can be co-injected into fibrous preforms. In another aspect of the invention, a vacuum assisted resin transfer method (VARTM) can be used to manufacture the sandwich composites.
Referring to
Referring to
In other aspects, a water soluble tooling material can be used to fabricate sandwich panels having complex geometries. One such water soluble tooling material is described in U.S. Pat. No. 6,828,373, incorporated herein by reference. The sandwich constructions are made as described above except that the water soluble tooling material is used as the substrate instead of a flat surface. The ability to directly fabricate complex geometries provides the ability to make sandwich panels to fit any given profile in a design. The composite panels can also be fabricated for modular construction to provide high repair/replaceability at low cost.
The composite constructions can be used in various applications. In particular, it may be desirable to use the composite constructions in applications where elevated temperatures and/or noise may be encountered. Examples of possible applications include uses in automotive, aircraft and housing constructions, such as for engines, transmission components, power transfer modules, cooling fans, and hull frames. Primers and/or topcoat paints also can be applied to the surface of the composite constructions to provide additional sealing properties or aesthetic characteristics, as desired.
The following examples are intended to illustrate embodiments of the present invention and should not be construed as in any way limiting or restricting the scope of the present invention. The following examples illustrate the fabrication process for sandwich composite materials and testing of properties, such as thermal and acoustic properties, of the composite materials.
A first panel of the sandwich composite material was made to evaluate the fabrication process. The panel was made with plies in the following arrangement:
This fabrication attempted to isolate the aerogel from the resin while using a one-step infusion process. The edges of the panel were closed out to both incorporate the aerogel and to provide mounting points for the panel. The separation membrane was sealed to itself around the aerogel using “tacky-tape”. This panel was infused from both sides to completely encapsulate the aerogel. Post inspection of the panel indicated that the aerogel remained dry during the infusion process. After processing, the aerogel compressed from about 5.6 mm down to about 4.7 mm.
A second panel was constructed to further evaluate the manufacturing process of the first panel. The second panel included the same construction layers but with slight modifications to the membrane configuration and edge sealing details to improve manufacturability. It was infused with Vantico/Huntsman Resinfusion 8605 resin and postcured. This second panel subsequently was used for thermal and mechanical testing.
A set of panels was made for acoustic testing. These panels followed the form of panels of Example 1. The construction was as follows.
The sandwich construction panels were made with plies in the following consecutive arrangement:
An additional set of panels (panels 4 and 5) was constructed for acoustic testing using the VARTM method. The sandwich construction panels were made with plies in the following consecutive arrangement:
The panels were constructed according to the method described in Example 1. To ensure timely and even resin infusion into the panels, 5 inch width distribution media and high permeability layers (breathers) were placed opposite one another along the long sides of the panel. Three layers of each were provided, such that the three fiberglass fabric materials would all simultaneously receive infusion of the resin system.
Omega channels of lengths of 53.5 inch and 61 inch were placed on the top breather and two vent channels were connected. This external vent line was connected to a bypass tubing assembly to control the bleed-out of the resin. A 55 inch Omega channel was placed on the distribution media.
The entire part was bagged with gas-impermeable sheeting, then vacuum pressure was applied and the sealing was ensured for 15 minutes. Care was taken that all sides of the lay-up were under vacuum pressure.
Both panels 4 and 5 were infused for two hours with a vinyl ester resin (Derakane 8084) system. Additives to the resin included DMA, 2,4-pentadione, cobalt (Conap) and peroxide (Trigonox).
The panels were allowed to cure for 24 hours, followed by postcuring at 80° C. for six hours. The final dimensions and surface masses of the postcured panels are given in Table 2.
Thermal testing was conducted on panels of different aerogel thicknesses. In the bench-scale experimental setup, the panels of Example 1 were placed on a hot plate with a small standoff distance. The edges of the panels were insulted in order to better contain hot air in the cavity below the panel. Thermocouples were placed on the hot plate surface on the bottom, or “hot” side, and the top, or “cold” side, of the panel. The hot side was initially heated to about 200° F., and the temperature on the “cold” side was recorded. The temperature on the “hot” side was increased to 300° F. and 390° F. and additional measurement were taken. The results are shown in Table 3.
The results are further illustrated in
Acoustic testing was conducted using a bench-scale experimental setup that included a sound generator, amplifier, speaker (sound driver), sound meter and oscilloscope. Acoustic measurements were performed on 6″×6″ panels of the one layer and four layer sandwich constructions of Example 2. The panels had a thickness of 0.4 inch and 1 inch for the one-layer and four-layer aerogel panels, respectively.
Table 4 shows TL values for one-layer and four-layer aerogel panels. Table 5 shows the normalized values of TL by sound pressure levels (SPL) (air).
The results indicate that the four-layer construction provides enhanced acoustic performance/noise reduction at high frequencies as compared to the one-layer construction. In the lower frequency range, 125-500 Hz, noise appears to affect the results of the experimental setup.
A second test of the acoustic properties of the panels was conducted with one-layer and four-layer panels using the setup of Example 5. Additionally, panels including six layers of aerogel also were tested. The transmission loss factors for each of the panels at the various test frequencies are set forth in
The tests were conducted on one-layer and four-layer panels at pressures of 14.7 psi and 0 psi to evaluate the effects of vacuum pressure. The results are shown in
Comparative acoustical testing was conducted for a sandwich construction including face sheets, foam and aerogel materials and also separately for the different materials of the sandwich constructions. The results are shown in
The mechanical strength of the composite materials was tested in accordance with D790 ASTM Standard. Four point bend tests were conducted on the panels of Example 1 to evaluate the structural integrity of the panels. The results of the flexure tests are set forth in Table 6 and further illustrated in
Based on this testing, the composite constructions should withstand loads of five pound per square inch or greater.
Numerous modifications and variations may be made in the techniques and structures described and illustrated herein without departing from the spirit and scope of the present invention. Thus, modifications and variations in the practice of the invention will be apparent to those skilled in the art upon consideration of the foregoing detailed description of the invention. Although preferred embodiments have been described above and illustrated in the accompanying drawings, there is no intent to limit the scope of the invention to these or other particular embodiments. Consequently, any such modifications and variations are intended to be included within the scope of the following claims.
This application is based on, and claims the benefit of, U.S. Provisional Application No. 60/729,732, filed Oct. 25, 2005, and entitled “Sandwich Composite Materials,” which is incorporated herein by reference.
Certain embodiments of the inventions disclosed herein were made with U.S. Government support under SBIR Contract Number M67854-05-C-0029, Topic N03-157 awarded by the U.S. Navy. Accordingly, the Government may have certain rights in embodiments disclosed herein.
| Number | Date | Country | |
|---|---|---|---|
| 60729732 | Oct 2005 | US |
