Composite material suitable for a morphing skin
A morphing skin for an air vehicle structure, the skin being formed by a composite material which includes: a multiplicity of fibers, a matrix incorporating the fibers, and a thermo-sensitive material, such as a thermo-plastic. The thermo-sensitive material can be reversibly transitionable in response to a change in temperature, between (i) an ambient temperature mode in which the thermo-sensitive material is capable of transferring loads in the composite material, and (ii) a heated mode in which the ability of the thermo-sensitive material to transfer the loads is reduced. This can allow the stiffness of the skin to be temporarily reduced to enable the skin to be morphed into a different shape.
1. A morphing skin for an air vehicle structure, the skin comprised of a composite material comprising:
a multiplicity of fibers coated with a thermo-sensitive material which is reversibly transitionable in response to a change in temperature, between: (i) an ambient temperature mode in which the thermo-sensitive material will transfer loads in the composite material, and (ii) a heated mode in which an ability of the thermo-sensitive material to transfer loads is reduced, and
a matrix material that incorporates said fibers coated with a thermo-sensitive material, the matrix material remaining stiff when the thermo-sensitive material is heated;
wherein:
the thermo-sensitive material reduces skin stiffness in the heated mode, allowing a change in shape of the skin in the heated mode and maintaining a changed shape of the skin in the ambient mode.
2. A morphing skin according to claim 1 , wherein the thermo-sensitive material is a thermoplastic.
3. A morphing skin according to claim 1 , wherein when in the heated mode, the thermo-sensitive material is at a temperature above a transition temperature, such that the thermo-sensitive material has changed state.
4. A morphing skin according to claim 1 , wherein the composite material comprises:
a first layer comprising said multiplicity of fibers coated with the thermo-sensitive material and incorporated into said matrix material; and
a layer of thermo-sensitive material, adjacent to the first layer.
5. A morphing skin according to claim 4 , wherein the composite material comprises:
a plurality of layers, each of which comprises said multiplicity of fibers coated with the thermo-sensitive material and incorporated into said matrix material, the plurality of layers interleaved with layers of thermo-sensitive material.
6. A morphing skin according to claim 1 wherein the fibers in said multiplicity of fibers are uni-directional.
7. A morphing skin according to claim 1 , wherein the skin comprises, or is configured for connection to, a heating apparatus for heating the thermo-sensitive material from the ambient temperature mode to the heated mode.
8. A morphing skin according to claim 7 , wherein the fibers in said multiplicity of fibers are electrically conductive and the heating apparatus is configured to pass a current through the multiplicity of fibers to heat the thermo-sensitive material.
9. A morphing skin according to claim 1 , wherein the fibers in said multiplicity of fibers are carbon fibers.
10. A morphing skin according to claim 1 , comprising: an actuator for changing and reverting a shape of the skin when the thermo-sensitive material is in the heated mode.
11. A method of morphing a skin on an air vehicle, comprising:
(i) heating the skin, the skin being configured to reversibly reduce in stiffness in reaction to an increase in temperature;
(ii) deforming the skin; and
(iii) cooling the skin in the deformed state, the skin being configured to return to higher stiffness in reaction to a decrease in temperature;
wherein the skin comprises a composite material comprised of a multiplicity of fibers coated with a thermo-sensitive material, and a matrix material that incorporates said fibers coated in a thermo-sensitive material;
wherein the thermo-sensitive material is reversibly transitionable in response to a change in temperature, between: (i) an ambient temperature mode in which the thermo-sensitive material will transfer loads in the composite material, and (ii) a heated mode in which an ability of the thermo-sensitive material to transfer loads is reduced, thereby reducing skin stiffness;
the matrix material remaining stiff when the thermo-sensitive material is heated, and
the thermo-sensitive material thereby reducing a stiffness of the composite material in the heated mode, allowing a change in shape of the skin in the heated mode, and maintaining a changed shape of the skin in the ambient mode.
12. A method according to claim 11 wherein heating of the skin comprises passing an electrical current through the multiplicity of fibers.
13. An article comprising a composite material which comprises:
a multiplicity of fibers coated with a thermo-sensitive material, and
a matrix material that incorporates said fibers coated in a thermo-sensitive material;
wherein the thermo-sensitive material is reversibly transitionable in response to a change in temperature, between: (i) an ambient temperature mode in which the thermo-sensitive material will transfer loads in the composite material; and (ii) a heated mode in which an ability of the material to transfer the loads is reduced, thereby reducing a stiffness of the composite material;
the matrix material remaining stiff when the thermo-sensitive material is heated,
the thermo-sensitive material thereby reducing a stiffness of the composite material in the heated mode, allowing a change in shape of the article in the heated mode, and maintaining a changed shape of the article in the ambient mode.
14. The morphing skin according to claim 1 , wherein said thermo-sensitive material is a thermoplastic polymer and said matrix is an epoxy matrix.
15. The morphing skin according to claim 14 , wherein said thermoplastic polymer is selected from poly(methyl methacrylate-co-acrylamide), polystyrene, and liquid crystal polymer.