Stock material or miscellaneous articles – Nonparticulate element embedded or inlaid in substrate and...
Reexamination Certificate
1999-09-27
2002-09-10
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Nonparticulate element embedded or inlaid in substrate and...
C428S332000, C428S364000, C428S369000, C428S374000
Reexamination Certificate
active
06447871
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to composite materials, and more particularly to composite materials including machines embedded in a polymeric matrix material.
BACKGROUND
Many composite materials have been suggested as an alternative to traditional materials, such as metal or wood. Generally, such materials include fabric or strands of fiber, such as kevlar, carbon or glass, that are impregnated within a binding matrix, such as an epoxy resin. The strands are arranged within the matrix in a predetermined orientation to provide desired physical properties for the material. For example, composite materials are often designed to provide increased rigidity and strength at substantially less weight as compared to traditional materials.
Composite honeycomb materials have also been suggested which include a honeycomb core sandwiched between two skins. The honeycomb material may be formed from plastic, metal or fiber reinforced plastic, which may also provide enhanced structural properties at substantially less weight as compared to traditional materials. Foam-core structures formed from a variety of plastics or fiber reinforced plastics have also been suggested, which have similar properties to honeycomb materials.
One disadvantage of composite materials is that their physical properties are generally considered to be “passive,” i.e., their physical properties remain substantially constant during their use. Stated differently, the physical properties of the materials do not change substantially as they are subjected to loads, until the materials begin to plastically strain and/or fail. Thus, although composite materials may provide enhanced rigidity as compared to traditional materials, their physical properties may not be programmed to respond to changing conditions during their use in an article.
To further modify the properties of composite materials, particles may be introduced into the matrix, such as sand, weighting agents or powders, and microballoons. Such particles, however, do not generally allow the properties of the material to change during use, as may be desirable for certain applications, but merely change the initial properties of the material, such as density or rigidity.
For this reason, “active” materials have been suggested which respond to external stimuli to change one or more physical properties of the material. For example, shape memory alloys, such as those of Nickel and Titanium (“Nitinol” alloys), may be designed to respond to heat to change the shape of an article formed from the shape memory material. The article may have an initial shape programmed at a higher temperature (for example, in an austenitic phase), and then cooled (for example, to a martensitic phase), whereupon the article may be malleably deformed from the initial shape. During or after its use, the article may be heated until it exceeds a transition temperature (for example, returning to the austenitic phase), whereupon the article may revert automatically back to its initial shape.
Piezo-electric materials have also been suggested, which respond to the application of electricity. The material may have an initial set of physical properties when not subjected to an electric potential. When an electrical potential is applied across the material, it may change shape and/or exhibit a second set of physical properties. Each set of physical properties may be selected for different operating conditions which the material may encounter during its use.
Active materials, however, require the application of external energy, such as heat or electricity, in order to invoke a change in the materials. Such energy may interfere with other performance aspects of an article made from the material, or may affect other systems with which the article is interacting. Further, such materials fail to respond to changing operating conditions, but are generally limited to two discrete property sets.
Accordingly, it is believed that a composite material exhibiting physical properties that change in response to changing operating conditions and/or which provides improved physical properties would be considered useful.
SUMMARY OF THE INVENTION
The present invention is directed to composite materials having machines embedded in a matrix material. In accordance with one aspect of the present invention, a composite material is provided that includes a matrix material, and a plurality of machines disposed in the matrix material, the plurality of machines acting to modify one or more physical properties of the composite material in response to forces acting upon the composite material. Preferably, the machines have a maximum cross-sectional dimension which is less than about 1 cm, and more preferably more than about 100 microns, with machines having a maximum cross-sectional dimension of about 1 mm being most preferred.
In a preferred form, the plurality of machines have an elongate shape defining a longitudinal axis, which are disposed within the matrix material in a predetermined array. The elongate members preferably have an asymmetrical cross-section which is deflectable between first and second shapes, wherein the composite material exhibits different physical properties as the elongate members deflect between the first and second shapes.
The machines may include a variety of asymmetrical cross-sections, such as a generally “Z” shape, an hourglass shape, a cantilever shape or a leaf spring shape. These structures enable the machines to modify one or more physical properties of the composite material in a direction substantially transverse to the longitudinal axis.
In accordance with another aspect of the present invention, a composite material is provided with an array of deflectable members arranged in a predetermined configuration, and a matrix material substantially surrounding the array of deflectable members, the matrix material comprising a relatively soft material compared to the deflectable members. When the composite material is subjected to stress, one or more of the deflectable members deflect within the matrix material between first and second shapes.
In a preferred form, the array of deflectable members are disposed in a plane, such that the deflectable members are deflectable substantially transverse to the plane. For example, the deflectable members may include a cantilever beam structure and a stop portion for limiting movement of a free end of the cantilever beam structure.
In a further alternative, the deflectable members may include one or more transverse portions extending between opposing planar portions. The opposing planar portions may be movable relative to one another about the transverse portion. In one preferred form, the opposing planar portions and transverse portion define a generally “Z” shape for transferring a force acting upon the composite material between a tensile/compressive condition and a shear condition. In another preferred form, the transverse portions may be curved to define a generally hourglass shape, which may result in a material having a negative Poisson's Ratio.
In still another alternative, the deflectable members may include a base portion and a convex portion extending from the base portion, the convex portion being deflectable to a concave shape at a predetermined force. Upon removal of the force, the concave portion may return to its convex shape, thereby being able to store and release energy from the forces acting on the composite material.
A composite material in accordance with the present invention exhibits physical properties which cannot be attained with traditional “natural” materials. The machines embedded therein may have a predetermined cross-sectional shape which may be deflected when the material is subjected to certain forces. As the machines are deflected, the overall shape of the material may change, e.g., its thickness or width, and/or the structural properties of the material may change. Thus, the term “machine” as used herein refers to a structure which modifies the forces acting upon the overall material, for e
Jones Deborah
Lyon & Lyon LLP
McNeil Jennifer
The Aerospace Corporation
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