Negative coefficient thermal expansion engineered particles for composite fabrication
Methods for the fabrication of negative coefficient thermal expansion engineered elements, and particularly, wherein such elements provide for fillers possessing a low or even potentially zero coefficient thermal expansion and which are employable as fillers for polymers possessing high coefficients of thermal expansion. Further, disclosed are novel structures, which are obtained by the inventive methods.
1. A negative coefficient of expansion-engineered element or particle, comprising:
two layers of a sheet material in surface contact with each other, each said layer comprising two superimposed sheets having differing coefficients of thermal expansion forming a bilayer;
said bilayers being laser welded about an enclosing path so as to produce a closed structure;
said bilayer sheets further being laser cut in a path extending externally of said laser welded path to separate said closed structure from the remaining bilayer sheets; and
said closed structure being responsive to a cooling action whereby said different coefficients of thermal expansion of said bilayers causes said closed structure to assume a volume, wherein each said bilayer is initially formed from superimposed sheets constituted of identical metallic material, each said sheet having the contiguous surfaces thereof oxidized to a half-thickness of the respective sheet subsequent to being laser welded so as to form said closed bilayer structure.
2. An element or particle as claimed in claim 1 , wherein each said bilayer is initially formed from superimposed sheets each constituted of a different material from the other sheet.
3. An element or particle as claimed in claim 1 , wherein said metallic material comprising aluminum, and said oxidizing forms a layer of aluminum oxide.
4. An element or particle as claimed in claim 1 , wherein said closed structure is essentially of a disk-shaped cushion configuration.
5. An element or particle as claimed in claim 1 , wherein a plurality of said closed structures are formed from said layers of sheet material.
6. An element or particle as claimed in claim 1 , wherein said closed structure consisting of said elements or particles is utilized for filling of polymers so as to increase the volumes of polymer products.
7. An element or particle as claimed in claim 1 , possessing a net negative CTE which has enhanced volumetric expansion capability by virtue of reducing the fraction of the edge perimeter that is welded or otherwise attached to a bottom layer.
8. An element or particle as claimed in claim 1 , wherein said laser welding is implemented at three spots about the perimeter of said structure at 120-degreees from each other to facilitate freedom of movement of the remaining areas thereof.
9. A structure comprising:
top and bottom disk shaped components, each component comprising two superimposed sheets having differing coefficients of thermal expansion forming a bilayer, wherein an outer sheet of each top and bottom component is of a lower CTE and an inner sheet of each top and bottom component possesses a higher CTE, said top and bottom disk shaped components defining an edge; and
the sequence of the high and low CTE layers near the edge are reversed.
10. An element as claimed in claim 9 , wherein said top and bottom disk shaped components comprising respective bilayers enhance a negative CTE overall behavior by imposing a curvature bias.
11. An element or particle as claimed in claim 9 , wherein said top and bottom disk shaped components comprises two identical sheets of said lower CTE being adhered together by an adhesive material possessing said higher CTE.