CA2219057A1 - Three-dimensional active, composite membrane, typically sma actuated - Google Patents

Abstract

A three dimensional active composite membrane, formed of two layers of polymer (100) and a reinforcement wire net (110) therebetween, actuated to assume selected different three dimensional patterns (shapes) by an external Shape Memory Alloy (SMA) wire net (120) or by other types of mechanical actuators to which it is attached.

Description

CA 022190~7 1997-11-26 THREE-DIMENSIONAL ACTIVE, COMPOSITE
MEMBRANE, TYPICALLY SMA ACTUATED

BACKGROUND OF THE II~VENTION
1. Field o~ the Invention The present invention relates to flexible membranes which can be deformed by an actuating mechanism, for instance ~or use on airplane wings ~or the de-icing thereof.

2. Description of the Prior Art As it is well known in the art, Shape Memory Alloys (hereinafter referred to aS SMA's) exhibit the ability to change shape and create force through a reverse martensitic phase transformation when energy is supplied to the SMA material.
Unfortunately, this ability cannot be efficiently induced during the so-called "education pro,~ess" in more than one direction. This means that, cLepending on the shape and "education process", a piece made of SMA will exhibit the highest dimensional transformation and force production performances only in the longituclinal, transversal, racial or circumferential direction, but never ~or any combination of thereof whatsoever. Furthermore the highest performances (i.e. highest level in dimensional transformation or ~orce production) are available in the longitudinal direction of monocristal wires. Many solutions to present problems in different technical fields such as aircraft de-icing, special gaskets, joints, valves, process controls, active turbulence-control of fluid flow, automation, robotics etc., could be simplified or enhanced if elements capable to reversibly change, locally or globally, their own three-dimensional configuration (shape) were available.

CA 022190~7 1997-11-26 SUMMARY OF THE INVENTION
It is there~ore an aim o~ the present invention to provi~e an active composite membrane which can be actuated to de~orm in different selected three-dimensional patterns.
It is also an aim of the present invention to provide an composite membrane capable of changing its shape when actuated typically by Shape Memory Alloy (SMA) components, but also other by appropriate mechanical actuators.
It is a ~urther aim of the present invention to provide a three-dimensional active composite membrane, ~ormed of two layers of polymer and of a rein~orcement wire net therebetween, actuated at different three dimensional ]?atterns (shapes) by an external Shape Memory Alloy (SI~A) wire net, or other types o~ mechanical actuators 1_o which it is attached.
As presented hereinabove, a piece made of SMA cannot exhibit the same rate o~ de~ormation or force production in more than one direction. The composite membrane of the present invention amplifies (by elastic buckling) the actuator's displacement in a direction perpendicular to its sur~ace (i.e. to its at rest plane). Therefore, if the composite membrane of the present invention is attached to a SMA wire net, the above-mentioned limits of the SMA can be overcome. When ~)roperly activated, the linear deformations of t:he wires o~ the SMA net are amplified by the elastic buckling of the rein~orcement elements embedded in the composite membrane of the present invention. The direct result is a controlled modification of force production or de~ormation (or both) along the third direction, i.e.
along a normal to the membrane's plane.

CA 022190~7 1997-11-26 Therefore, in accordance with the present invention, there is provided a composite membrane comprising two elastic outer layers and an reinforcement member therebetween and having edges thereof attached through one of said outer la.yers to edges o~ an outer ',hape Memory Alloy actuating net, said actuating net having an area similar to that o~
said rein~orcement member and smaller than that of said outer layers, ~3aid actuating net being driven to contraction or exl_ension by direct heat thereby causing a normal deflection o~ said reinforcement ember and thus of said outer layers.
Also in accordance with the present invention, there is provided a composite membrane made out of two polymer layers and an embedcled wire net o~ any geometrical configuration hereafte:r called reinforcement ~eature, said rein~orcement feature having its edges attached through one of the polymer layers to the edges of an outer one-way or two-way Shape Memory Alloy wire net of geometrical compatible con~iguration hereafter called actuator feature, said actuator feature having the same area as t:he said reinforcement feature, is smaller than the membrane, it is centered to the middle of the membrane, and is driven to contraction or extension by direct heat.

BRIEF DESCRIPTION OF THE DRAWINGS
Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereo~, and in which:
Fig. la is the simpli~ied schematic representation of a cross sectional elevati.on o~ a three-dimensional active, composite membrane attached to a SMA wire net. actuator in accordance with the present invention;

CA 022190~7 1997-11-26 Fig. lb is a schematic elevation of the membrane and SMA actuator, including an enlarged representation in cross section of one possible attachment system o~ the membrane to its SMA
actuator;
Fig. 2a is a simplified isometric view o~
membrane de~ormation when X-direction wires o~ the SMA wire net are driven in contraction by heat;
Fig. 2b is a simplified three-dimensional mesh representation o~ membrane de~ormation when both X and Y-directions wires of the SMA wire net are driven in contraction by heat;
Figs. 3a and 3b are schematic representations o~ some possible con~igurations o~
the rein~orcement net and/or of the SMA wire net;
Fig. 4a i's a simpli~ied isometric view with an additional detaiLl view of one embodiment o~ the invention used as an ice prevention or de-icing device ~or airplanes;
Fig. 4b is a perspective three-dimensional mesh representation of the membrane's shape when actuated on a leading edge of an airplane wing's;
Figs. 5a and 5b are respectively simplified vertical and detailed horizontal cross sectional representations o~ another embodiment o~ the present invention used as an immersed pumping device;
Figs. 6, 6a and 6b are simplified isometric views o~ a still ~urther embodiment o~ the present invention used to reduce the afterbody drag o~ an aircra~t's ~uselage; and Fig. 7 illustrates a side, bottom and detailed perspective views of the fluid flow control device described Ln the U.S. Patent No. ~L,718,620 issued on January ]2, 1988 adapted with an embodiment o~ the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

CA 022190~7 1997-11-26 Generally, the present invention relates to composite membranes and, more particularly, to composite membranes that can change their shape when actuated by Shape Memory Alloys (SMA) components or any other appropriate mechanical actuator.
Re~erence is now made to Figs. la and lb wherein one embodiment o~ the present invention is presented. It cclnsists of a composite rnaterial membrane M attached to a rectangular one-way type Shape Memory Alloy rLet ~which represents the external actuator ~eature). More particularly, the membrane consists o~ two layers (100) o~ elastic material (e.g. elastomer) rein~orced by a rectangular wire net (110) sandwiched therebetween, which provides to the membrane the desire(1 sti~ness. The rein~orcement net (110), having a s~Laller sur~ace then the membrane, is located between the elastic layers ~100). The edges o~ the reinforcement net (110) are attached to an external SMA net (120) by attachment elemen1s (115) and (116). The flexible ribbon (115) that passes through the lower layer (100) is bonded or riveted to the reinforcement net (110) and to the transitional member (116) to which the external actuator (120) is also attached by any appropriate means (bond, screws, rivets, etc.), as presented in detail in Fig. lb.
Due to t:he reintorcement net (1]0), the de~ormations induced by the SMA net (12CI), when actuated, will be uni~ormly distributed over the entire rein~orced area of the membrane M. The SMA net (120) is made up o~ knitted SMA wires, individually connected to an appropriate electrical power supply.
Theretore, any combination of actuated and non-actuated wires o~ the SMA net (120) is available. For instance, i~ the X-direction wires o~ the SMA net (120) are actuated, the SMA wire net (120) will contract itsel~ along the X-direction and will pull on the corresponding edges of the rein~orcement net CA 022190~7 1997-11-26 (110) The reinforcement net (110) cannot contract itsel~ so the only possibility ~or it to accommodate the new X-dimension o~ the SMA net (120) is to bend upward (i.e in the Z-direction), as represented in Fig. 2a. The non-rein~orced zones o~ the elastic membrane (100) generate the bias ~orce ~or membrane shape recovery once the one-way type SMA net (120) is deactivated.
If the SMA wire net (120) is activated in both directions (i.e. the X and Y direction w-res) at the same time, a more complex three-dimensional shape will result, as pres,ented in Fig. 2b. Furtherrnore, if selected wires of the SMA net (120) are actuated sequentially, a corresponding dynamic modi~icaLtion o~
the three-dimensional shape o~ the membrane M will result. The shape, grid size and grid orient~tion of the SMA nets (120) with respect to the shape, grid size and grid orientation o~ the rein~orcement net (110) are essential design parameters that go~ern the membrane's per~ormances. Parameters such as elasticity modulus and thickness o~ the elastomer layers (100), maLterial and stiffness of the reinforcements (110), etc., are also to be considered in the design process of the composite membrane M.
Dif~erent net (reinforcement and actuator) shapes are represented in Fig. 3.
Another embodiment of the present invention makes use of a two-way type SMA wire net. In this case, the bias force is no longer needed as the SMA
net is capable to perform by itself the entire cycle (contraction and extension) while being driven by temperature changes. Therefore, the layers (100) o~
the composite membrane M can be made of plastic polymer and the reinforcement wire net (110) can extend to the membrane's edges.
Now referring to Fig. 4 wherein the present invention is used as an ice-prevention and/or de-icing device for airplanes, the rein~orcement net inside the membrane M is replaced by several sets of a plurality o~ str:;ngs or straps (110) parallel to each other, each set; being positioned parallel to the leading edge of the wing W The reinforcement elements (strings or straps) within one set are each individually attach,ed (clamped) through the lower elastic layer (100) to their own respective SMA wire (lZ0), hereina~ter called actuator, located between the membrane M and the wing surface S. One end o~
each SMA actuator (120) is electrically connected to a general bus bar l130), while the other end of the SMA actuators (120) within an actuator set is electrically connected to a set bus bar (135), as schematically represented in Fig. 4a. Thus each set (reinforcement elements and their corresponcLing SMA
actuators) can be independently connected and activated from the same electrical power supply When one set is activated, all the corresponding SMA
actuators are heated by the electrical cur~ent and driven into contraction. So each corresponding reinforcement element within the activat:ed set undergoes a buckling deformation in a direction perpendicular to the wing surface S.
If all the actuator sets (120) are activated at the same time, the general change in shape of the membrane M, presented in Fig. 4b will shed the ice accumulated thereon. If the actuator sets (120) are actuated sequentially, the membrane M
will undergo a dynamic wave-like deformation that will prevent the ice accretion on the membrane surface.
Reference is now made to Fig. 5 wherein the present invention is used as an immersed pumping device. In this embodiment of the invent:Lon, the membrane has a more complex three-dimensional configuration. In this case, the membrane is CA 022190~7 1997-11-26 cylindrical, having a star-like cross sectional shape (in its at rest or deactivated state), as shown in Fig. 5b. In addition to the reinforcement net (110), several longitudinal strings or straps (140), hereina~ter called sti~eners, are placed between the elastic layers (100) of the membrane at the star edges. The ends o~ the sti~eners (140) are attached to the top and bottom rings (150) which are also embedded in the membrane. The upper and lower collar rings (160) attached and sealed to the top and bottom ends of the membrane are attached to each c,ther by several SMA wires, strings or straps (120), hereina~ter called actuators. The collar rinc~s (160) are connected to an electrical power supply. The lower collar ring (160) lodging an intake one-way valve (170) is ~ixed and sealed to an outer l-ylinder (180). The upper collar ring (160) lodging a one-way transition valve (190) is free to move downward when the actuators (120) are activated and upward (the return bias ~orce bleing due to the elasticit~r o~ the stif~eners) when the actuators (120) are deactivated.
A one-way exhaust valve (200) installed at the top of the outer cylinder (180) prevents the ~luid back-~low when the actuators (120) are deactivated. ~hen the actuators (120) are activated, the volume o~ the suction chamber (S) increase while the volume o~ the pressure chamber (E') decreases. Thus the two actions (suction and pumping) are ~ul~illed within the same stroke. When the actuators (120) are deactivated, the ~luid ~rom the suction chamber (S) passes through the one-way trans~er valve (180) into the pressure chamber (P).
Now turning to Fig. 6 which presents another possible embodiment of the present invention used to generate the ridges described U.S. Patent No.
4,718,620 entitled "TERRACED CHANNELS FOR REDUCING
AFTERBODY DRAG", rows of sti~eners (210) are added CA 022190~7 1997-11-26 to the rein~orcement net (110). The posit:Lon and orientation o~ the sti~eners (210) with respect to the grid size and orientation of the reinforcement net (110) depend on the ridge's characteristics The SMA wire net is replaced by a plurality o~ SMA wires (120), hereinafter called actuators, which are attached to each st:if~ener (210) in a row. A thin strip (220) o~ appropriate sti~ness is ~ixed along one of its edges to the upper elastic layer (100) at one edge o~ each row of sti~eners (210). The width o~ the strip (220) may or may not exceed the width o~
the corresponding row (to which it is attached). The ends o~ each actuator (120) within a row are electrically connected through the row's bus bars to an electrical power supply. When one row is activated, each corresponding sti~ener (210) bends upward (due to the contraction o~ the corresponding actuator) thereby tilting the strip (220) upwards, as illustrated in Fig. 6a. Thus each row can independently generate a ridge wen activated. The advantage o~ using the present invention in conjunction with the above-mentioned U.S. Patent resides in the ~act that the ridges can be dynamically produced or removed (in function of flight conditions), by simply activating or deactivating the appropria-te zones o~ the membrane.
Higher flexibility and performance can be achieved if the strip (220) is replaced by a row of threads (230) in a brush-like arrangement, as presented in ~ig. 6b.
In this configuration, the present embodimenl: of the invention can be used as an active turbulence-control system of the air~low on the wing upper sur~ace or of the upswept afterbody, as shown in the Fig. 7.

Claims (14)

1. A composite membrane made out of two polymer layers and an embedded wire net of any geometrical configuration hereafter called reinforcement feature, said reinforcement feature having its edges attached through one of the polymer layers to the edges of an outer one-way or two-way Shape Memory Alloy wire net of geometrical compatible configuration hereafter called actuator feature, said actuator feature having the same area as the said reinforcement feature, is smaller than the membrane, it is centered to the middle of the membrane, and is driven to contraction or extension by direct heat.

2. The composite membrane of claim 1 wherein said reinforcement feature and said actuator feature extends to edges of the elastic layers.

3. The composite membrane of claims 1 and 2 wherein all or only specific knots of the said reinforcement feature are attached to the knots of the said actuator feature.

4. The composite membrane of claims 1 to 3 wherein the said actuator feature consists of a plurality of identical or non-identical Shape Memory Alloy elements (straps or strings) arranged in an appropriate regular or irregular pattern.

5. The composite membrane of claim 4 wherein the said reinforcement feature consists of a plurality of identical or non-identical reinforcement elements (straps or strings) of any cross sectional shape arranged in an appropriate regular or irregular pattern and having the extremities attached to the ends of the corresponding said Shape Memory Alloy elements of the said actuator feature.

6. The composite membrane of claim 5 wherein the said reinforcement element is attached to several appropriate knots of the said actuator feature.

7. The composite membrane of claims 1 to 6 wherein the said actuator feature is made up of SMA
monocrystaline elements or an appropriate combination of SMA mono and polycrystaline elements.

8. The composite membrane of claims 1 to 7 provided with any appropriate combination of clamped and/or sliding connection between the said actuator feature and the said reinforcement feature.

9. The composite membrane of claims 1 to 8 wherein each or sets of said actuator elements within the said actuator feature are heated by an electrical power supply to which they are globally connected.

10. The composite membrane of claim 9 wherein each or sets of the said actuator elements within the said actuator feature can be sequentially actuated (by heat) by an appropriate electronic controller.

11. The composite membrane of claims 1 to 10 having two or more independent actuator features each of them independently attached to the same reinforcement feature.

12. The composite membrane of claims 1 to 12 shaped to any open or closed three-dimensional body.

13. The composite membrane of claims 1 to 12 wherein the force causing the said reinforcement feature of the said composite membrane to buckle, is not generated by Shape Memory Alloys elements, but by any appropriate mechanic, electromagnetic, hydraulic or pneumatic system or by any combination of them.

14. A composite membrane comprising two elastic outer layers and an reinforcement member therebetween and having edges thereof attached through one of said outer layers to edges of an outer Shape Memory Alloy actuating net, said actuating net having an area similar to that of said reinforcement member and smaller than that of said outer layers, said actuating net being driven to contraction or extension by direct heat thereby causing a normal deflection of said reinforcement ember and thus of said outer layers.