Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-06-04
2001-05-15
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S169000, C156S175000, C181S292000
Reexamination Certificate
active
06231710
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is in the field of sandwich-type structural materials, and in particular relates to sandwich-type structural materials with acoustic attenuation characteristics.
2. Description of the Prior Art
Existing launch vehicle and aircraft structures are still overwhelmingly fabricated using aluminum and steel. These materials are often very heavy for this weight critical application by today's structural standards. These materials are utilized, though, due to their damage tolerance and low cost manufacturing techniques. Aerospace structures that are fabricated using advanced composite materials, while lighter weight, suffer from poor damage tolerance and very high manual labor requirements during fabrication.
An additional problem, specific to launch vehicles, is that a significant number of spacecraft failures can be attributed to the conditions experienced by the spacecraft during launch into orbit. These conditions include very high accelerations, severe vibration due to lift-off and staging and very high broadband acoustic levels, particularly during liftoff. Current launch vehicle systems require that spacecraft be designed to withstand these high acceleration and vibration levels. To protect the spacecraft in this extreme acoustic environment, every existing launch vehicle system incorporates very heavy acoustic blankets and distributed masses in the fairing surrounding the payload area of the vehicle.
The Boeing Company's “MacroCore” concept incorporates Helmholtz resonators to attenuate sound. Although a very good idea, this structural concept requires a wall thickness that is unrealistic for most launch vehicle applications. The Helmholtz resonators, in this concept, are a product of the sandwich core construction, and are, therefore, limited by the sandwich core concept. Specifically, this concept is susceptible to the weaknesses of core/facesheet delamination and moisture retention.
Leppington discusses the use of perforated facesheets to create Helmholtz resonators out of honeycomb core pockets (Leppington, F. G, K. H. Heron, E. G. Broadbent, and S. M. Mead, “The Acoustic Transmission Properties of Anisotropic Sandwich Panels With Perforations,” Proc. R. Soc. Lond. A 428, 27-47, 1990). This structure is limited in that it is, similar to the MacroCore concept, basically a sandwich core construction. Therefore, it is limited in that it is susceptible to facesheet/core delamination and moisture incursion. Additionally, the structural requirements on the core material drives the resonator volume which, for any practical geometry, is targeted at a frequency range higher than that which is useful for launch vehicle applications.
U.S. Pat. No. 3,831,710 entitled “Sound Absorbing Panels” incorporated Helmholtz resonators into a sandwich core structural concept. This concept visualizes the incorporation of Helmholtz resonators into structures but doesn't describe how such structures could be constructed. The concept envisions “grid-stiffened” structures to create this geometry. “Grid-Stiffened” structures have not, to date, been fabricated in this form and are very difficult to fabricate in the geometry envisioned by the patent.
SUMMARY OF THE INVENTION
An innovative new structure has been developed that is inherently damage tolerant, easy to manufacture, and has an inherent design feature that can be exploited to drastically reduce acoustic transmission through the structure. This structure is being called “ChamberCore.”
The structure is composed of previously cured tubes that are sectioned to form chambers and co-cured with facesheets to form a sandwich-type structure. Each chamber has a hole to it through the inner facesheet effectively converting it into a Helmholtz resonator. These resonators can be tuned to attenuate broadband or specific acoustic transmission through the structure.
There are a number of manufacturing advantages to ChamberCore, including reduced stiffener fabrication cost, core placement cost and scrap material. The result is a high-quality co-cured structure fabricated with low cost methods and having very simple tailoring of axial-hoop properties. Structurally, ChamberCore is damage tolerant due to its lack of a honeycomb/facesheet interface. It is lighter weight than traditional sandwich constructions and results in a very high strength core-facesheet bond. ChamberCore also provides broadband acoustic attenuation that can be tailored to specific acoustic environments. Enclosed structures fabricated of ChamberCore produce a reduction in both the internal sound level and in sound through transmission.
REFERENCES:
patent: 2755216 (1956-07-01), Lemons
patent: 3490983 (1970-01-01), Lee
patent: 3795559 (1974-03-01), Horn et al.
patent: 4025675 (1977-05-01), Jonda
patent: 4433021 (1984-02-01), Riel
patent: 4600619 (1986-07-01), Chee et al.
patent: 5025888 (1991-06-01), Arcas et al.
Leppington, F. G, K. H. Heron, E. G. Broadbent, and S. M. Mead, “The Acoustic Transmission Properties of Anisotropic Sandwich Panels With Perforations,” Proc. R. Soc. Lond. A 428, 27-47, 1990.
Griffin Steven
Herup Eric
Huybrechts Steven
Tsai Stephen
Aftergut Jeff H.
Callahan Kenneth E.
The United States of America as represented by the Secretary of
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