Adhesive bonding and miscellaneous chemical manufacture – Surface bonding means and/or assembly means therefor – Automatic and/or material-triggered control
Reexamination Certificate
1999-11-18
2002-09-24
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Surface bonding means and/or assembly means therefor
Automatic and/or material-triggered control
C156S361000, C156S440000, C156S434000, C156S177000
Reexamination Certificate
active
06453962
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the methods and apparatus for manufacturing wavy patterned fiber pre-preg that can be used in conjunction with viscoelastic materials to construct composite structures with unique damping properties. Such pre-pregs not only have an aesthetic appeal but also have the distinction of increasing their stiffness as a function of the angle of the fiber, due to the increase in fiber volume fractions as the fiber angle varies in the wavy or sinuous pattern.
2. Description of Related Art
The control of noise and vibration in composite structures is an important area of current research in aerospace, automotive and other industries. For example, spacecraft vibrations initiated by attitude adjusting thrusters, and motors inhibit accurate aiming of antennas and other equipment carried by the craft. Sound induced or structurally borne vibrations can cause severe damage to the craft and its associated equipment during launch.
Additionally, acoustic and vibration energy can be amplified at or near natural structural resonance due to low inherent damping in the materials used to make fairings and other structural components. A practical way of increasing damping and improving acoustic properties in mechanical structures is required.
Composite materials have been used to construct a wide variety of structural elements, including tubes, enclosures, beams, plates and irregular shapes. Objects as diverse as rocket motor housings and sporting goods, notably skis, archery arrows, vaulting poles and tennis rackets have been constructed from composite materials. While composite constructions have offered many significant advantages, such as excellent strength and stiffness properties, and light weight, the poor vibration damping properties have been of concern.
One of the simplest and often very effective passive damping treatments involves the use of thermo-viscoelastic (TVE) materials. These materials, represented by Avery-Dennison's FT series (FT-1191 is one example), exhibit both elastic and dissipative qualities which make them useful in a number of passive damping treatments.
Some of the first uses of thermo-viscoelastic materials to increase structural damping involved the use of surface patches of aluminum foil and viscoelastic adhesives. Called constrained or embedded-layer damping, these methods produce modest gains in damping.
One of the more common passive damping methods, Constrained Layer Damping or CLD is achieved by bonding a thin layer of metal sheet, usually aluminum, to an existing structure with a viscoelastic adhesive (Kerwin, 1959). Shear strains develop in the viscoelastic material when the original structure bends or extends. Damping occurs when the deformation of the viscoelastic adhesive creates internal friction in the viscoelastic material, generating heat and thus dissipating energy. Compared to an undamped structure, this approach is modestly successful but its effectiveness decreases markedly as the ratio of the thickness of the base structure to the thickness of the viscoelastic material increases (Hwang, et al, 1992).
Co-cured composite-viscoelastic structures are formed when layers of uncured fiber composites (pre-preg) and viscoelastic materials are alternately stacked and cured together in an oven. Damping occurs in these structures when a load causes differential movement of the opposing laminates, causing shearing in the sandwiched viscoelastic material. The various methods that use this concept of differential shearing of the viscoelastic material can be classified by the fiber orientation methods used to induce damping in the TVE material.
Conventional angled ply composite designs use ±&thgr; lay-ups of straight fiber pre-preg materials to encase the viscoelastic layers, and were first proposed by Barrett (1989) in a design for damped composite tubular components. Barrett combined the concepts of constrained layer damping with anisotropic shear coupling in the constraining composite layers to create a tube that achieved both high damping and high axial stiffness. Barrett's research showed that maximum shearing was experienced at the ends of the tubes and that clamping the constraining layers of the tube at the ends eliminated much of the damping effect, rendering the design impractical for most applications.
Chevron patterned designs also use conventional angled ply (±&thgr;) composite lay-ups of straight fibers but vary the fiber orientation several times throughout the structure in a given laminate. It was first proposed by Benjamin Dolgin (1990) of NASA and implemented by Olcott (1992).
In Olcott's implementation of Dolgin's design, each composite layer is comprised of multiple plies of pre-preg composite material arranged in a series of chevron-like patterns. Each composite layer is also comprised of several “segments” of material where the fiber angle in a given segment is oriented in a single direction throughout its thickness. Segments on opposite sides of the embedded viscoelastic material have the opposite angular orientation. At least two adjacent segments in a given composite layer are required to form a chevron and are joined together by staggering and overlapping the pre-preg plies in the segment.
By tailoring the fiber angle, thickness, and segment lengths, significant shearing in the viscoelastic layer was observed over the entire structure, not just at the ends as in Barrett's design (Olcott, 1992). Olcott's research showed that the fiber orientation, segment length, segment overlap length, material choice, and material thickness, had to be carefully controlled to maximize damping in a structure (Olcott, 1992). Pratt, et. al. (co-pending U. S. application Ser. No. 08970141) proposed several processes for making the wavy pre-pregs contemplated by Dolgin, their use in combination with viscoelastic materials for increased damping in composite structures, and the manufacture and use of several specialized wave forms.
The following terms used herein will be. understood to have their ordinary dictionary meaning as follows:
Composite: made up of distinct parts. In the general sense, refers to any fiber reinforced material but especially any cured fiber reinforced matrix structure.
Carrier: a conveyor, transporter. As used in this patent refers to the use of a cloth, plastic, paper, or other sheet products, to convey resin or matrix through a process for combination with a fiber.
Fiber: a thread or a structure or object resembling a thread. A slender and greatly elongated natural or synthetic filament. (Includes metal fibers)
Lamina(te): a thin plate . . . :layer(s)
Matrix: material in which something is enclosed or embedded.
Pre-preg: Fiber reinforced, resin matrix impregnated materials where the matrix is partially cured and ready for use. A special “uncured” case of the more general term “Composite”.
Resin: an uncured binder, especially an uncured polymer binder or matrix used to bind fibers or fibrous materials; the matrix component of a an uncured pre-preg.
Viscoelastic: having appreciable and conjoint viscous and elastic properties. Note: a special case of the term “viscoelastic” is “anisotropic viscoelastic”, which is a viscoelastic material reinforced with fibers which give the material anisotropic properties. When the term viscoelastic is used in the text it should be construed to encompass this special case.
The following publications, incorporated herein by reference, are cited for further details on this subject.
1. Dolgin, Benjamin P., “Composite Passive Damping Struts for Large Precision Structures,” 1990, U.S. Pat. No. 5,203,435.
2. Dolgin, Benjamin P., “Composite Struts Would Damp Vibrations,” NASA Technical Briefs, 1991, Vol. 15, Issue 4, p. 79.
3. Olcott, D. D., “Improved Damping in Composite Structures Through Stress Coupling, Co-Cured Damping Layers, and Segmented Stiffness Layers,” Brigham Young University, Ph.D. Thesis, August 1992.
4. Kerwin, “Damping of Flexural Waves by a Constrained Viscoelastic Layer,” J
Fehr Thompson E.
Yao Sam Chuan
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