WO2015061473A1

WO2015061473A1 - System and methods for instrument design

Info

Publication number: WO2015061473A1
Application number: PCT/US2014/061799
Authority: WO
Inventors: Robert Shepherd; Ilse VAN MEERBEEK
Original assignee: Cornell University
Current assignee: Cornell University
Priority date: 2013-10-22
Filing date: 2014-10-22
Publication date: 2015-04-30
Anticipated expiration: 2016-04-22

Abstract

A device may include liquid metal composites (LMCs) and accompanying support structures. Liquid metal composites may actuate accompanying support structure. A device may be included in a reconfigurable instrument. Reconfigurable instruments may be useful in a variety of applications, including reconfigurable airfoils, soft armor, exoskeletons, and search and rescue robots.

Description

SYSTEM AND METHODS FOR INSTRUMENT DESIGN

[0001] This application claims the benefit of U.S. Provisional Application No. 61/894,412, filed on October 22, 2013, and U.S. Provisional Application No. 61/894,787, filed on October 23, 2013 each of which are incorporated by reference in their respective entirety.

TECHNICAL FIELD

[0002] This disclosure relates to systems and methods for instrument design and more particularly, to reconfigurable devices.

BACKGROUND

[0003] Structures and devices used in aerospace applications typically require lightweight materials, moving parts, and the ability to be used for multiple functions. Metals such as aluminum and titanium are used in many of these applications due to their low density, ultimate strength, and resulting toughness. In many situations, control over the structure's shape is desirable. For example, an aileron is a motorized flap of stiff material that could be replaced by a morphing structure with the appropriate material properties.

[0004] The concept of morphing structures has been demonstrated previously with shape memory alloys (SMAs). SMA materials, however, are limited to thin structures (for efficient actuation) that cannot bear much load, and their function is limited because their shape cannot fundamentally change (i.e., their surface area to volume ratio can be varied over only a very small range).

SUMMARY

[0005] In general, this disclosure describes techniques for developing mo hing structures and reconfigurable instruments. In particular, this disclosure describes liquid metal composites (LMCs) and accompanying support structures that may be useful in a variety of applications. In some examples, LMCs and accompanying support structures described herein may be configured to form reconfigurable instruments, including robots. The techniques described herein may be used to develop a framework to understand the dependence of an LMC's mechanical properties on its material chemistry; develop elastomeric material systems for support structures and skins of LMCs; simulate the appropriate geometries for support structures that transport the LMCs (e.g., analytical and numerical prediction of machine designs for efficient fluid transport and rapid heating and cooling of LMCs); and to fabricate and test lightweight, morphable devices. The techniques described herein may be used to develop lightweight, reconfigurable structures that can bear significant mechanical loading in tension and compression.

[0006] The techniques described herein may be used to catalog materials that will allow for lightweight and morphable airfoils and entirely new small aircraft structures, and other shape changing components that may be used to replace existing aluminum and titanium based designs. Further, the techniques described herein may be used to achieve weight savings by developing tools that can be reformed to perform different functions. For example, tools that can be reformed from a screwdriver into a wrench and back again.

[0007] Further, the techniques described herein may be used to improve the mechanical properties of an LMC. This is, the techniques described herein may be used to understand what effect granules have on metal matrix; optimize the weight reduction for a high stiffness and yield stress composite; optimize self-healing effects; understand what flow properties are like for actuating soft, elastomeric membranes; understand what are loads (e.g., compressive, tensile) that optimized systems can tolerate; understand what applications example systems described herein are suitable for (e.g., reconfigurable airfoils, soft armor, exoskeletons, search and rescue robots). Further, thermal and mass transport of these systems, numerical and analytical modeling techniques may be used, with empirical verification using rheology, x-ray micro computed tomography, and/or device testing.

[0008] According to one example of the disclosure, a reconfigurable device comprises a support structure comprising a stretchable material, and a liquid metal composite, wherein the liquid metal composite is configured to flow into the support structure when in a liquid state and increase the mechanical loading capability of the support structure when in a solid state. [0009] According to another example of the disclosure, a method for designing instruments, comprises the steps of identifying a liquid metal composite that is low density and high stiffness, developing a support structure comprising a stretchable material, and developing a mechanism to reversibly transport the liquid metal composite into the support structure.

[0010] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1 is a series of images illustrating an example of a pneumatically actuated machine including a plurality of support structures configured to change shape.

[0012] FIG. 2A is a block diagram illustrating an example of a system that may implement one or more techniques of this disclosure.

[0013] FIG. 2B is a block diagram illustrating an example of a system that may implement one or more techniques of this disclosure.

[0014] FIG. 3 is a conceptual diagram illustrating an example of a system that may implement one or more techniques of this disclosure.

[0015] FIG. 4 is a series of images illustrating properties of an example liquid metal composite that may implement one or more techniques of this disclosure.

[0016] FIG. 5 is a graph illustrating properties of example support structures that may implement one or more techniques of this disclosure.

[0017] FIG. 6 is a series of images illustrating an example support structures that may implement one or more techniques of this disclosure.

[0018] FIG. 7 is a conceptual diagram and a corresponding graph illustrating properties of example support structures that may implement one or more techniques of this disclosure.

[0019] FIG. 8A is an image illustrating an example of a support structure that may implement one or more techniques of this disclosure.

[0020] FIG 8B is an image illustrating an example of a support structure that may implement one or more techniques of this disclosure. [0021] FIGS. 9A-9D is a series of images illustrating properties of an example metal/elastomer composite that may implement one or more techniques of this disclosure.

DETAILED DESCRIPTION

[0022] Certain tasks could be completed more easily with morphable instruments. That is, an instrument that can easily change shape. For purposes of this disclosure, an instrument may include any tool, device, unit of a larger device, or coating, to name a few examples. As an example, an aileron could function more efficiently if it was replaced with a morphable instrument. Instruments configured for use during outer space travel are often made from lightweight, but heavy-duty material (e.g., aluminum and titanium). Aluminum alloys have high elastic moduli (e.g., Al 7075 has a G' ~ 72 GPa) compared to plastics and many metals. The density of Al 7075, pAi ~ 2.8 g ml^"1, is approximately a third that of steel. One drawback to aluminum, however, is its low fatigue strength, i.e., over enough loading and unloading cycles it will fail. Titanium is an intermediate option between steel and Al alloys. Titanium has a high elastic moduli and high fatigue strength, but has a density twice that of aluminum. Steel, aluminum alloys, and titanium, once cast, do not change their shape except through plastic deformation and failure. The basic shapes of instruments fabricated from these metals, therefore, are static. Thus, such instruments typically are configured to take one form, and do not undergo any substantial changes in physical form. Such instruments would have more value if they could be quickly and easily reshaped into different forms for multiple tasks. Attempts to create appropriate morphable instruments have resulted in devices that either could not make sufficient change in shape or could not bear sufficient load to perform the functions necessary.

[0023] Soft robotics may coarsely be referred to as an effort to reduce the complexity of machine control by using the compliance of soft materials. For example, a tree's leaves will collapse in a strong wind to prevent its branches from breaking. This example demonstrates embodied intelligence, i.e., the distribution of control away from a central computer (e.g., brain, or CPU) throughout an organism or machine. Examples of soft robots includes pneumatically actuated machines, including purely elastomeric pneumatically actuated machines. Pneumatically actuated machines may embody intelligence to perform sophisticated functions and/or based on their elastomeric material properties may have the ability to dramatically change then- shapes.

[0024] Pneumatically actuated machines configured to perform sophisticated functions typically include a plurality of support structures that have the ability to change their shapes. FIG. 1 is a series of images illustrating an example of a pneumatically actuated machine including a plurality of support structures configured to change shape. As illustrated in FIG. 1, each of the elastomeric actuators may take a different shape under neutral pressure, a positive pressure, and a negative pressure, which results in a different overall shape of the machine. In the example illustrated in FIG. 1, each actuator that may change its volume by nearly 1000% depending on the pneumatic pressure.

[0025] Other examples of pneumatically actuated machines include the untethered quadrupeds that walk in a tortoise gate described in Shepherd RF, Ilievski F, Choi W, Morin SA, Stokes AA, Mazzeo AD, Chen X, Wang M, and Whitesides GM (2011) Multigait soft robot, Proceedings of the National Academy of Science 108(51):20400- 20403, which is incorporated by reference in its entirety. The unthered quadrupeds described in Shepherd et al. may be capable of changing their shape to move in two different gaits: undulation and walking. Other examples of pneumatically actuated machines include silicone based robots that take the form of grippers, tentacles, and jumping robots in the shape of a starfish (which may be actuated by combustion). In these examples, soft elastomers (psiiicone ~1 g ml^"1) that can deform at very low stresses (~100's of kPas) were used to program embodied intelligence into lightweight, pneumatically actuated machines.

[0026] While substantial progress has been made in the field of shape changing machines, the same compliance that aids their moφhing may limit the loads they can cany. That is, soft robots are very limited in the loads they can bear. For example, example actuators may not be able to carry loads greater than -300 g in a gripping mode, and mobile robots may not be able to carry loads greater than ~300 g. This loading capacity is a far departure from the capabilities of aluminum, steel, and titanium. Thus, the flexural stiffness of typical pneumatically pressurized soft bodies is too low to sustain greater loads without significant deformation.

[0027] This disclosure describes reconfigurable systems and devices that may have increased load carrying capabilities. Further, this disclosure describes fabrication and testing techniques for example reconfigurable devices. The systems and devices described herein may be configured to control any combination of one or more of the following qualities: morphability, density, stiffness, strength, magnetism, optics, size, ceramic, dissolvability, and self-healing qualities. For example, while morphability may be a desired quality in some example applications described above, certain example embodiments described herein may not be morphable, but may include an otherwise desirable combination of elements or qualities.

[0028] Example embodiments of the systems and methods described herein may be configured to produce strong (e.g., load bearing) morphable instruments. Examples of such instruments may include shape changing airfoils for ailerons, a universal tool, and self-healing armor (e.g, for vehicles). For example, the techniques described herein may be used to implement shape-changing airfoils for the ailerons in small aircraft and unmanned aerial vehicles (UAVs) and to fabricate unique airfoils and flight architectures. In one example, the techniques described herein may also be used to design lightweight, reconfigurable, and self-healing armor for vehicles. Further, in one example, the techniques described herein may be used to implement a universal tool that can be shaped and reshaped for different tasks (e.g., hammer, wrench, and screwdriver). It should be noted that some of the granular media described herein may have the potential to absorb a significant amount of energy upon ballistic impact (e.g., tetragonally stabilized zirconia expands on impact). Vehicles comprised of this material and similar materials could be used to redistribute armor towards more needed areas, and to heal damage when it occurs.

[0029] In one example, instruments may be developed using low-density, liquid metal composites (LMC) that can be selectively frozen into a solid with a variety of mechanical and material properties. In one example, a system may include using a LMC to actuate a soft machine. The flow and then freezing of a LMC may permit the range of motions and shape changing abilities of soft robots, while being able to tolerate much higher loadings without deformation, i.e., when the LMC is solidified. In additional to enabling large changes in the shape of load-bearing structures, LMCs may enable new functions (e.g., optical, electrical, chemical) by adding the appropriate choice of constituent particles (e.g., magnetic granules or colloids) to a LMC. In one example, a pumping system may be used for the efficient transport of a LMC.

[0030] It should be noted, that building morphable structures driven by LMCs requires an understanding of the complex interaction between several material and mechanical systems (e.g., elastomeric polymers, colloids, granular media, fluid transport, and machine design). To properly address the complexity of this problem, this disclosure describes example techniques for developing a catalog of low density materials and support structure geometries. Such a catalog may be used to construct machines that drastically and reversibly change their shape (e.g., area changes of over 1000%), while displaying metallic and even ceramic material properties. In one example, a catalog may include a material database of low-density LMCs that can be selectively frozen into a solid with a variety of mechanical and material properties (e.g., density, stiffness, magnetic, and optical).

[0031] As described above, pneumatically actuated machines may include a plurality of support structures that have the ability to change their shapes. In a similar manner to air, without a support structure, the shape of a molten LMC may be ill defined. In order to impart a specific geometry to a LMC, example systems and devices described herein may include support structures. In some examples, support structures may include soft, tough, self-healing, and transient skins to transport LMCs. Further, in some examples support structures may include membranes as a support scaffold and use capillarity and pressure driven flows to transport LMCs in a fluid state. In some examples, these membranes may be self-healing and, in some cases, dissolvable. In one example, support structures may include geometries that permit the rapid heating and cooling of LMCs.

[0032] FIGS. 2A-2B arc block diagrams illustrating an example of a system that may implement one or more techniques of this disclosure. As described above, while pneumatically actuated machines may have an excellent range of motion, the forces they can tolerate (e.g., their own body weight, lifting by grippers, or hold on their "backs") are typically in the range of 1 N. System 100 is an example of a system that may provide a lightweight reconfigurable structure that can bear significant mechanical loading in tension and compression. FIG. 2A illustrates system 100 in a first configuration and FIG. 2B illustrates system 100 in a second configuration. As illustrated in FIGS. 2A-2B, system 100 includes liquid metal composite 102, reservoir 104, support structure 106, and pump mechanism 108.

[0033] In the example illustrated in FIG. 2A, system 100 is in a compressed state. That is, liquid metal composite 102 is contained in reservoir 104 and may be in a liquid or solid state. As described in detail below, in one example, support structure 106 may include an expandable material, (e.g., organic polymers). In the example illustrated in FIG. 2B, system 100 is in an expanded or actuated state. That is, liquid metal composite 102 is contained in support structure 106 and may be in a solid or a liquid state. As illustrated in FIG. 2B, the volume and surface area of support structure 106 are increased in FIG. 2B, as compared to FIG. 2A. Further, once liquid metal composite 102 flows into support structure 106, liquid metal composite 102 may freeze, thereby enabling support structure 106 to tolerate much higher loadings without deformation. In this manner, support structure 106 and system 100 may be in a load-bearing state. As described in detail below, the properties of liquid metal composite 102 and support structure 106 may determine how system 100 transitions from a compressed state to an expanded state. In addition to containing liquid metal composite 102, reservoir 104 may be configured to provide a suitable environment for liquid metal composite 102, e.g., configured to keep liquid metal composite 102 at a particular temperature. Pump mechanism 108 may be configured to pump liquid metal composite 102 to/from reservoir 104 to support structure 106. In one example, pump mechanism 108 may be based on capillary action.

[0034] FIG. 3 is a conceptual diagram illustrating an example of a system that may implement one or more techniques of this disclosure. FIG. 3 illustrates an example, where system 100 includes a reconfigurable array of box beams. This geometry may be particularly easy to fabricate and also is a high strength to weight ratio architecture. Using the Young's modulus of pure, solid gallium (-10 GPa), FIG. 3(d) shows simulations of an array of box beams in an actuated and bent geometry and an unactuated and straight geometry these structures can withstand >5 kN of loading without deformation. As described in detail below, the mechanical properties of gallium composites may allow for greater loads.

[0035] In one example, liquid metal composite 102 may include a material with the ability to melt and freeze at near room temperature, which may allow its mass transport and allow shape changing and function reconfiguration of machines. In additional to being able to actuate soft bodies, liquid metal composite 102 may be configured to enable the lifting of much larger loads than pneumatic actuators, e.g., liquid metal composite 102 may have high stiffness in solid form. Further, liquid metal composite 102 may be a low density material.

[0036] Examples of metals that melt at low temperatures, where a low melting temperature may be defined as less than 100° C (i.e., T_m< 100° C) include gallium, Ga, (T_m ^Ga = 30° C), and alloys of tin, bismuth, and indium, including Field's metal, which is ~33% bismuth. In one example, liquid metal composite 102 may include one or more of these metals. Metals that melt at low temperatures can be liquefied, flowed, and reformed in the presence of plastics and elastomers without thermal degradation of the constituent organic polymers of plastics and elastomers. It should be noted that these low T_m metals have been used in their liquid state in soft, elastomeric devices to impart electrical conductivity, as sensors, and to add reversible stiffness. These metals, however, may have relatively high densities (e.g., Ga= 6.1 g ml^"1 and pKeids ~ 8.0 g ml^"1) and low Young's moduli (e.g., YGa= 9.8 GPa and YKeids ~ 1 GPa) when compared to aluminum (pAi = 2.5 g ml^"1, YAI = 70 GPa).

[0037] In one example, a granular and a colloidal material may be used to lower the density of liquid metal composite 102, while simultaneously improving material properties of interest. Granular media has been used to add stiffness to soft machines via a jamming phenomenon. The jamming granules, while having low densities, are very weak in tension and have a large hysteresis in loading and loading. The limitations in mechanical properties of these systems are therefore unsuitable for many applications in aerospace, where materials and structures must be reliable, lightweight, and tough. Combinations of jamming granular systems with low T_m metal matrices, as may be used for liquid metal composite 102, drastically improve the stiffness of the metal structures and the tensile strength of the granular systems. [0038] Γη one example, liquid metal composite 102 may include a combination of granular matter and metal matrices. Composites of low T_m metals with granular and colloidal materials (e.g., tetragonally stabilized zirconia) will allow for examples of liquid metal composite 102 with some trade-off between aluminum like densities, elastic moduli, and ultimate strength. For example, as described below, an example liquid metal composite 102 of gallium and granules of hollow glass spheres (e.g., μ- balloons) may have a resultant density, PLMC = 2.7 g ml^"1, approximately that of aluminum and flexural elastic modulus similar to aluminum at strains approaching 0.2%.

[0039] There are numerous combinations of granular matter and metal matrices that could yield a variety of properties (e.g., high elastic moduli, yield stress, and ultimate strain, as well as magnetic and optical properties). For example, using hollow granules will impart porosity to liquid metal composite 102 and radically reduce its density, while also increasing its stiffness. By using low T_m metals as the matrix, it will be easy to melt, transport, form and reform the structure, or heal a damaged one. Further, it should be noted that fatigue strength issues (as in Aluminum) can potentially be eliminated, because the metal matrices could simply be melted and recrystallized to relieve built up stresses.

[0040] Gallium is a good choice for metal matrix material because it melts at ~30°C. Thus, in some applications, gallium may be kept in an always liquid state and frozen when desirable. However, it should be noted, that several reasons exist for gallium's general lack of use structurally: (i) it is a relatively soft solid (flexural yield stress, o_y ~1 MPa), (ii) it is heavy (p_s = 5.9 g cm^"3), (iii) expensive (~$600/kg), and (iv) it melts at slightly above room temperature (29.8°C; 85.6°F) requiring active cooling to ensure it remains solid. It should be noted that gallium has been used in medicine (for cancer drug therapies), lower melting temperature alloys of including gallium (eutectic compositions of gallium-indium) have been used as pressure sensors in soft robotics, and when cocrystallized with nitrogen gallium is routinely used as a III/V semiconductor. It has not, however, been used as a structural material. Field's metal is another example of a low melt temperature matrix: T_m ^FieIds = 64°C, Ypieids = 9.3 GPa, and ppieids = 8.0 g ml^"1. Using this Field's metal as the matrix is beneficial because it melts at 64°C. A Field's metal matrix could then serve the purpose of being in an always solid state and melted only when transport is needed. Tin is also compatible with melting and reforming in some silicone elastomer and has a higher Young' modulus, as such in some application may be a good metal matrix. As As described below, additional capabilities may be imparted onto these materials by investigating colloidal and granular media with functional properties (e.g., optical, magnetic, chemical).

[0041] FIG. 4 is a series of images illustrated properties of an example liquid metal composite that may implement one or more techniques of this disclosure. FIG. 4 illustrates properties of a gallium metal embedded with hollow glass spheres, where (a) is a micro CT reconstruction (b) is a graphical representation of the hollow spheres, and (c) includes result of a three point bend test. Though most choices of non-metallic granules or colloids would lower the composite density when added to a metal, hollow granules (p~0.15 g ml^"1) are particularly effective and may essentially create a foam in whatever matrix they are embedded, as illustrated in FIG. 4(b). In one example, liquid metal composites 102 may include composites of hollow glass spheres (e.g., glass microspheres available from Fibreglast, Inc.) in matrices of gallium and Field's metal. In one example, the resulting density of the gallium microsphere composites at a volume fraction, φ~0.50, is p~2.7 g ml^"1 which is less than that of Al 7075. Despite the large difference in density between the two systems, they blend well together due to the surface wetting of gallium and Field's metal onto silica. The resulting flexural modulus of elasticity and ultimate strength of these composites increases with the addition of these microspheres, as illustrated in FIG. 4(c). The trade-off is that the strain to failure decreases.

[0042] FIG. 4(c) also includes the three point bend testing results of aluminum. That is, aluminum does not plastically deform within the range of a testing machine that provided an 18 N load). Pure gallium begins to yield at ~l-5 MPa, and gallium loaded with hollow glass spheres begins to deform at approximately two times that loading, ~10 MPa. As illustrated in FIG. 4(c), Field's metal follows a similar curve to that of the gallium with glass bubbles and has a yield strength of ~20-25 MPa. If the Field's metal experiences a similar doubling of the yield strength with the addition of hollow glass sphere, then 40-50 MPa loading pressures can be expected before plastic deformation. [0043] As illustrated in FIG. 4, by formulating composite mixtures of gallium and hollow glass microspheres (i) a_y may be increased -15 times, and (ii) the composite density may be reduced to p_c= 2.7 g cm^"3 (Aluminum has a similar density) for a 55% by volume (v/o), φ~55 v/o, mixture of gallium and microspheres. Further, the material cost may be reduced by -50% compared to pure gallium. It should be noted that tin is a very low cost metal. It should be noted that the maximum random packing for spheres is ψ~64 v/o. In order to determine what is happening in a mixture of gallium and hallow glass microspheres, rheology of the melt, x-ray μ-tomography, and mechanical testing of the solid may be performed.

[0044] Another property of low T_m metal matrix composites is their ability to melt, reform, and even heal at temperatures well below those that degrade silicone (~300°C). Fracturing the composite of glass microspheres (φ~0.50) in a matrix of gallium described above, and then pressing the two pieces together again created enough heat to melt the gallium and heal the fracture.

[0045] It should be noted that although a mixture of gallium and glass microspheres is described in the example above, using other granular and colloidal oxides (e.g., tetragonally stabilized zirconia), as well as mixtures of granules and colloids with different low T_m metal matrices for liquid metal composite 102 will allow for a broad spectrum of densities, elastic moduli, and toughness while still providing the functionality of liquid transport. For example, granules of titanium may offer even higher elastic moduli composites, and tetragonally stabilized zirconia is used in bullet resistant armor. Finally, colloidal particles could fill interstices between granules to increase stiffness while maintaining flowable liquid properties.

[0046] Referring again to FIG. 2A-2B support structure 106 is configured to be actuated by liquid metal composite 102. Without a support structure, the shape of the molten liquid metal composite 102 will be defined by a balance between surface tension and gravity. Thus, a support structure may be used to define a coarse shape (e.g., a kite or an under-camber airfoil). In order to impart a specific geometry to the liquid metal composite 102, support structure 106 may include soft membranes, including elastomeric foams, as a support scaffold and pumping mechanism 108 may use capillarity and pressure driven flows to transport liquid metal composite 102 in a fluid state. FIG. 8A illustrates an example of an elastomeric foam. FIG. 8B illustrates an example of an Elastomeric foam imbibed with Field's Metal. In one example, the membranes included in support structure 106 may have high enough elastic moduli, G', to support the weight of liquid metal composite 102, but low enough G' and a high enough ultimate strain to be easily deformed at low pressures (< ~100 psi; ~700 kPa) into radically different geometries (e.g., a plane to a sphere).

[0047] In some examples, system 100 may include a deformation mechanisms that could be stretching a metal/elastomer composite e.g., by hand. FIGS. 9A-9D illustrate example deformation mechanisms that may be applied to a metal/elastomer composite. As respectively illustrated in FIGS. 9A-9D, in one example, an elastomeric foam bar may be bent, twisted, relaxed and stretched.

[0048] It should be noted that the support structures included in the elastomer based machines described above may be an excellent choice for support structure 106. However, the very property that makes them compliant also limits the forces they can apply. The elastic modulus of the silicones used in the systems described above is ~100 kPa, as illustrated in FIG. 5. Further, pressures that can be applied to these systems (~10 psi) allow objects of approximately ~300g to be picked up. The ultimate strength of the silicone is ~1 MPa. Making a simple comparison between the ultimate strength of silicones and the flexural yield stress of an example liquid metal composite 102 including a microsphere laden Field's metal (~50 MPa), it is expected that objects of nearly 15 kg could be lifted with system 100 without further optimization of the material's granular structure, the addition of colloidal particles, or changes in the architecture, (e.g., the example box beam geometry described below could be used).

[0049] As described above, in some example liquid metal composite 102 can repair itself if fractured. For example, pressing two pieces of liquid metal composite 102 together may cause them to weld into a monolithic structure and melting and reforming the structure may also heal a fracture (or hole). In one example, support structure 106 may include soft actuator system (e.g., composed of Kevlar™ and silicone) that is resistant to puncture and will self-seal around puncturing objects, as well as, seal a hole when the object is removed. An example of a support structure 106 that is resistant to puncture and repair itself is illustrated in FIG. 6. By actuating self-sealing membranes with a liquid metal composite that can repair itself when fractured, system 100 may be able to self-seal.

[0050] To further match example liquid metal composite's 106 self-healing properties, the chemistry of an elastomer may also be modified to chemically heal after damage. In some examples, self-healing support structures using polyaramid fibers (Kevlar™) embedded into silicone may prevent crack propagation and allow the conformal silicone surfaces to adhere after puncture, but although the cracks self- seal, there may not be chemical bonding between the crack surfaces. In one example, support structure 106 may be configured to be damage resistant by including tough composites of fibers (e.g., carbon) and organic elastomers, and self-healing polymers. Further, in one example, support structure 106 may include organic elastomers that readily decompose. In combination with liquid metal composites 102 that melt at 30°C, systems including these structures could disappear in warm climates after use. Further, it is possible that these machines could be used and then degrade and vanish to not leave the possibility of reverse engineering.

[0051] Additionally, at high solids loading (i.e., lowest densities if using μ-bubbles), liquid metal composite 102 could jam when flowing through narrow constrictions of support structure 106. Thus, support structure 106 may be configured to correspond to a particular liquid metal composite to avoid jamming.

[0052] It should be noted that using composites of fiber in elastomeric support structures, in some cases, may require that liquid metal composite 102 freeze in a reasonable amount of time in order to produce a useful machine. Additionally, the thickness of support structure and proximity to other support structures will dictate the rates of heating and cooling in liquid metal machines. As illustrated in FIG. 7, simple ID simulations of a thermal transport in a Field's metal and silicone system demonstrate cooling below its freezing point in 10 seconds in stagnant air with no active cooling. In the example illustrated in FIG. 7, the initial temperature was set to 67°C and cooled to 65°C in air held at 37°C. This cooling time is compatible with many applications. In some examples, freezing may be greatly speed up by incorporating active cooling elements (e.g., Peltier coolers).

[0053] A great range of techniques may be employed to measure the dependence of mechanical properties on a liquid and solid metal composite microstructure. In the solid state, mechanical testing (e.g., tensile flexural, and compressive) may be used to achieve the stiffest, highest strength, and toughest materials possible while mamtaining aluminum like densities. In the fluid state, rheology and simulation to may be used optimize the mass transport and rheological of these non-Newtonian fluids. The thermal transport during the liquid to solid transition may be modeled to enable example liquid metal composites to rapidly melt and freeze.

[0054] Examples of modeling that may be useful to configure system 100 include (i) the mass transport of liquid metal composites in soft scaffolding to increase the efficiency and speed of moφhing, and (ii) the thermal transport to and from the metal to reduce the time to melt and freeze the metal matrix. Additionally, the thickness of an elastomeric support structure and proximity to other support structures may dictate the rates of heating and cooling in these liquid metal machines. Structures may be optimized for rapid thermal transport. The non-chaotic flow of liquids at low Reynold's number has been well described and it may be used to predict what the optimal support structure must be for efficient transport of molten metals. However, the incorporation of a high solids loading of granules and colloids will make these fluids non-Newtonian, and thus increase the complexity of our analytical and numerical models. Thus, in some cases, the non-Newtonian flow properties of granule and colloid laden liquid metals in the confined volumes of the elastomeric support structure must be examined analytically and empirically.

[0055] In this manner system 100 represents an example of a reconfigurable device comprising a support structure comprising an expandable material, and a liquid metal composite, wherein the liquid metal composite is configured to flow into the support structure when in a liquid state and increase the mechanical loading capability of the support structure when in a solid state.

[0056] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A reconfigurable device comprising:

a support structure comprising a stretchable material; and

a liquid metal composite, wherein the liquid metal composite is configured to flow into the support structure when in a liquid state and increase the mechanical loading capability of the support structure when in a solid state.

2. The reconfigurable device of claim 1, wherein the liquid metal composite includes a granular material and a metal matrix.

3. The reconfigurable device of claim 2, wherein the metal matrix includes gallium.

4. The reconfigurable device of claim 3, wherein the granular material includes hollow glass microspheres.

5. The reconfigurable device of claim 2, wherein the metal matrix includes Field's metal.

6. The reconfigurable device of claim 5, wherein the granular material includes hollow glass microspheres.

7. The reconfigurable device of claim 2, wherein the metal matrix includes tin.

8. The reconfigurable device of claim 1, wherein the stretchable material includes silicone.

9. The reconfigurable device of claim 8, wherein the support structure includes empty channels or a foam.

10. The reconfigurable device of claim 1 , wherein the stretchable material includes polyaramid fibers embedded into silicone.

11. The reconfigurable device of claim 1 , wherein the support structure includes an array of box beams.

12. A method for designing instruments, comprising the steps of:

identifying a liquid metal composite that is low density and high stiffness, developing a support structure comprising a stretchable material; and developing a mechanism to reversibly transport the liquid metal composite into the support structure.

13. The method of claim 12, wherem the liquid metal composite includes a granular material and a metal matrix.

14. The method of claim 13, wherein the metal matrix includes gallium.

15. The method of claim 13, wherein the granular material includes hollow glass microspheres.

16. The method of claim 13, wherein the metal matrix includes Field's metal.

17. The method of claim 16, wherein the granular material includes hollow glass microspheres.

18. The method of claim 12, wherein the stretchable material includes silicone.

19. The method of claim 12, wherein the stretchable material includes polyaramid fibers embedded into silicone.

20. The method of claim 11, wherein the support structure includes an array of box beams.