BACKGROUND ART Ice which may accumulate on the wings of an airplane during foul conditions can cause a grave danger, whereby it its required to remove such ice formations from the airplane prior to take off.

United States Patent No. 4,706,911 issued on November 17, 1987 to Briscoe et al. discloses an airfoil deicer which comprises an outer skin having an elevated modulus of elasticity and a mechanism for introducing a small deflection into this outer skin such as to create a chord- wise tension in the outer skin. The leading edge of each wing of an airplane is fitted with the deicer where ice is expected to accumulate. The outer skin is separated from the wing by a number of chambers formed in a number of elastic tubes which extend spanwise. The elastic tubes are inflated in less than 0.250 seconds and deflated to give very high chordwise distortion of the outer skin. The deflection of the outer skin is induced periodically and is completed within a time span of about 0.250 seconds to remove accumulations of ice as thin as 0.06 centimeters.

The deicer does not alter the profile of the leading edge nor gives risk damage to the leading edge structure.

Also, 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 process" in more than one direction. This means that, depending on the shape and "education process " , a piece made of SMA will exhibit the highest dimensional transformation and force production performances only in the longitudinal, transversal, radial or circumferential direction, but never for any combination of thereof whatsoever. Furthermore the highest performances (i.e.

highest level in dimensional transformation or force 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.

DISCLOSURE OF INVENTION It is therefore an aim of the present invention to provide an active composite membrane which can be actuated to deform in different selected three-dimensional patterns.

It is also an aim of the present invention to provide a composite membrane capable of changing its shape when actuated typically by Shape Memory Alloy (SMA) components, but also by other appropriate mechanical actuators.

It is a further aim of the present invention to provide a three-dimensional active composite membrane, formed of two flexible layers of polymer and of a reinforcement wire net therebetween, actuated into different three dimensional patterns (shapes) by an external Shape Memory Alloy (SMA) wire net, or other types of electrically controlled mechanical actuators to which it is attached.

As presented hereinabove, a piece made of SMA cannot exhibit the same rate of deformation 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 surface (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 properly activated, the linear deformations of the wires of the SMA net are amplified by the elastic buckling of the reinforcement elements embedded in the composite membrane of the present invention. The direct result is a controlled modification of force production or deformation (or both) along the third direction, i.e. along a normal to the membrane's plane.

Therefore, in accordance with the present invention, there is provided a composite membrane comprising at least one flexible sheet-like outer layer, reinforcement means attached to said outer layer, actuating means capable of being at least one of contracted or extended and being attached at outward locations of said reinforcement means, whereby when said actuating means are contracted or extended, said reinforcement means is caused to deform thereby displacing said outer layer therewith.

Also in accordance with the present invention, there is provided a composite membrane comprising two polymer layers and a reinforcement wire means of appropriate geometrical configuration, said reinforcement means having edges thereof attached through one of said polymer layers to opposite edges of an outer Shape Memory Alloy wire actuating means of geometrical configuration compatible with said reinforcement means, said actuator means being adapted to be driven to contraction or extension by direct heat and so cause said reinforcement means and said layers to deform.

Further in accordance with the present invention, there is provided a composite membrane comprising two flexible outer layers and a reinforcement net 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 net and smaller than that of said outer layers, said actuating net being driven to contraction or extension by heat thereby causing a normal deflection of said reinforcement net and thus of said outer layers.

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 thereof, and in which: Fig. la is a schematic representation of a cross sectional elevation of a three-dimensional active, composite membrane attached to a SMA wire net actuator in accordance with the present invention; Fig. lb is a schematic elevation of the membrane and SMA actuator, including an enlarged representation in cross section of one possible attachment system of the membrane to its SMA actuator; Fig. 2a is a simplified isometric view of membrane deformation when X-direction wires of the SMA wire net are driven in contraction by heat; Fig. 2b is a simplified three-dimensional mesh representation of membrane deformation when both X- direction and Y-direction wires of the SMA wire net are driven in contraction by heat; Figs. 3a and 3b are schematic representations of other possible configurations of the reinforcement net and/or of the SMA wire net; Fig. 4a is a simplified isometric view with an additional detail view of one embodiment of the invention used as an ice prevention or de-icing device for 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 of another embodiment of the present invention used as an immersed pumping device; Figs. 6, 6a and 6b are simplified isometric views of a still further embodiment of the present invention used to reduce the afterbody drag of an aircraft's fuselage; and Fig. 7 illustrates a side, bottom and detailed perspective views of the fluid flow control device described in the U.S. Patent No. 4,718,620 issued on January 12, 1988 adapted with an embodiment of the present invention.

MODES FOR CARRYING OUT THE INVENTION 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 actuators.

Reference is now made to Figs. la and lb wherein one embodiment of the present invention is presented to show the general principle thereof. It consists of a composite material membrane M attached to a rectangular one-way type Shape Memory Alloy net (which represents the external actuator feature). More particularly, the composite membrane M consists of two layers 100 of elastic material (e.g. elastomer) reinforced by a rectangular wire net 110 sandwiched therebetween, which provides to the membrane M the desired stiffness. The reinforcement net 110, having a smaller surface then the flexible layers 100 of the membrane M, is located between the elastic layers 100. The edges of the reinforcement net 110 are attached to an external SMA net 120 by attachment elements 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 the reinforcement net 110, the deformations induced by the SMA net 120, when actuated, will be uniformly distributed over the entire reinforced area of the membrane M. The SMA net 120 is made up of knitted SMA wires, individually connected to an appropriate electrical power supply. Therefore, any combination of actuated and non-actuated wires of the SMA net 120 is available. For instance, if the X-direction wires of the SMA net 120 are actuated, the SMA wire net 120 will contract itself along the X-direction and will pull on the corresponding edges of the reinforcement net 110. The reinforcement net 110 cannot contract itself so the only possibility for it to accommodate the new X-dimension of the SMA net 120 is to bend upward (i.e. in a normal or perpendicular way along the Z-direction), as represented in Fig. 2a. The outer layers 100 are thus deflected by the reinforcement net 110. The non-reinforced zones of the elastic membrane 100 generate the bias force for 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 wires) at the same time, a more complex three-dimensional shape will result, as presented in Fig. 2b. Furthermore, if selected wires of the SMA net 120 are actuated sequentially, a corresponding dynamic modification of the three-dimensional shape of the membrane M will result. The shape, grid size and grid orientation of the SMA nets 120 with respect to the shape, grid size and grid orientation of the reinforcement net 110 are essential design parameters that govern the membrane's performances. Parameters such as elasticity modulus and thickness of the elastomer layers 100, material and stiffness of the reinforcements 110, etc., are also to be considered in the design process of the composite membrane M. Different 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 from the elastic layers 100 in the previous embodiment 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 of 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 reinforcement net inside the membrane M is replaced by several sets of a plurality of strings or straps 110 parallel to each other, each set being positioned parallel to the leading edge E of the wing W. The reinforcement elements 110 (strings or straps) within one set are each individually attached (clamped) through the lower elastic layer 100 to their own respective SMA wire 120, hereinafter called actuator, located between the membrane M and the wing surface S. One end of each SMA actuator 120 is electrically connected to a general bus bar 130, 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 corresponding 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 current and driven into contraction with each corresponding reinforcement element within the activated set undergoing 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 invention, the membrane has a more complex three-dimensional configuration. In this case, the membrane is 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, hereinafter called stiffeners, are placed between the elastic layers 100 of the membrane at the star edges. The ends of the stiffeners 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 other by several SMA wires, strings or straps 120, hereinafter called actuators.

The collar rings 160 are connected to an electrical power supply. The lower collar ring 160 lodging an intake one-way valve 170 is fixed and sealed to an outer cylinder 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 force being due to the elasticity of the stiffeners) when the actuators 120 are deactivated. A one-way exhaust valve 200 installed at the top of the outer cylinder 180 prevents the fluid back- flow when the actuators 120 are deactivated.

Therefore, when the actuators 120 are activated, the volume of the suction chamber S increases while the volume of the pressure chamber P decreases. Thus the two actions (suction and pumping) are fulfilled within the same stroke. When the actuators 120 are deactivated, the fluid from the suction chamber S passes through the one-way transfer valve 190 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 stiffeners 210 are added to the reinforcement net 110. The position and orientation of the stiffeners 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 of SMA wires 120, hereinafter called actuators, which are attached to each stiffener 210 in a row. A thin strip 220 of appropriate stiffness is fixed along one of its edges to the upper elastic layer 100 at one edge of each row of stiffeners 210. The width of the strip 220 may or may not exceed the width of the corresponding row (to which it is attached).

The ends of 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 stiffener 210 bends upward (due to the contraction of the corresponding actuator 120) thereby tilting the strip 220 upwards, as illustrated in Fig. 6a.

Thus each row can independently generate a ridge when activated. The advantage of using the present invention in conjunction with the above-mentioned U.S. Patent resides in the fact that the ridges can be dynamically produced or removed (in function of flight conditions), by simply activating or deactivating the appropriate zones of 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 Fig. 6b.

In this configuration, the present embodiment of the invention can be used as an active turbulence-control system of the airflow on the wing upper surface or of the upswept afterbody, as shown in the Fig. 7.

In the previous embodiments, various configurations of shape memory alloys have been proposed as actuators for the membrane. It must however be noted that the force required to cause the reinforcement element 110 (net, string, strap, or otherwise) of the composite membrane to buckle can be generated, not only by Shape Memory Alloy elements, but also by any appropriate mechanic, electro-magnetic, hydraulic or pneumatic system or by any combination of thereof.