Systems and methods for applying a force to an object

Abstract

A system for applying force to an object is disclosed. The system, which may find application in mechanical or material testing, comprises a sample holder 105 securable to the object 103, shape memory

Description

Field of the invention The present invention relates to systems and methods for applying a force to an object. Background of the invention Systems for applying force to objects often find utility in the mechanical (or material) testing of said objects. Such mechanical (or material) testing may be performed to determine the mechanical properties of an object under test such as, for example, tensile strength, torsional strength, shear strength, hardness, ductility, brittleness, toughness, elasticity and fatigue limit. With the recent rapid expansion of the Space sector, there is an increasing interest in mechanical testing of objects (or materials) for space applications. In general, rigorous testing of potential Space hardware such as spacecraft panels is required before it is deployed in its intended Space application, for example due to certification requirements. Traditionally, this mechanical testing has been performed on Earth. However, to assess the performance of an object (or material) in Space via an on-Earth mechanical test, there is a need to test the object (or material) in an environment which simulates the conditions of Space. For example, tests may be performed in a vacuum and / or under simulated cosmic radiation. The need to simulate a Space environment can make on-Earth testing for certification of space components time consuming and expensive. Thus, it would be desirable to advantageously exploit the increasing number of Space launches to provide in-orbit qualification of advanced materials via in-Space mechanical (or material) testing. Such in-orbit qualification is not without its own challenges. In particular, existing systems for applying a force to an object (for mechanical testing) rely on gears and / or motors and / or hydraulics to generate or apply said force. However, gears, motors and hydraulics are unsuitable for in-Space testing applications. This is because they suffer from the extreme cold of the Space environment. For example, gears, motors and hydraulics have a tendency to freeze in Space and become stuck in position. In addition, gears, motors and hydraulics can suffer from cold-welding in Space (cold-welding is a solid-state process in which joining of objects / materials occurs without fusion or heating at their interface, as described at the entire contents of which are incorporated herein by reference). Both freezing and cold-welding of mechanical components of a system for applying a force to an object can degrade the performance of that system. The system may fail to generate and apply the intended force to the object under test, which may render any mechanical test performed using the system invalid. Thus, it would be advantageous to provide a system (and method) for applying a force to an object that solves the above problems associated with use for in-orbit mechanical testing. Summary of the invention It is an aim of this invention to provide improved systems and methods for applying a force to an object. In particular, systems and methods for applying a force to an object that are suitable for use in in-orbit mechanical testing (or more broadly, suitable for use in Space). For example, there is provided a system for applying a force to an object (for inorbit mechanical testing of the object), the system comprising: one or more shape memory alloy components; and a control system, wherein the control system is configured to cause deformation of one or more of the shape memory alloy components so as to cause the deformed one or more of the shape memory alloy components to apply a (predetermined) force to the object. In a first aspect of the invention there is provided a system for applying a force to an object, the system comprising: a sample holder securable to (a first end of) the object; a plurality of shape memory alloy components secured relative to the sample holder, wherein each of the shape memory alloy components is securable to (a second end of) the object; biasing means configured to apply a return force to each of the components; and control means configured to: apply a first force to the object by selectively applying a voltage to a first subset of the components; and apply a second force to the object by selectively applying a voltage to a second subset of the components. In some embodiments, the first force is a tensile force and the second force is a tensile force. In some embodiments, each of a third subset of the components has a first cross sectional area; and each of a fourth subset of the components has a second cross sectional area different from the first cross sectional area. In some embodiments, the biasing means comprises a plurality of tensioners, each tensioner comprising: a) a threaded portion configured to engage with a recess in a fastening block; and b) a spring portion. In some embodiments, each tensioner comprises an electrically conductive portion, the conductive portion providing an electrical connection between the fastening block and a respective one of the components. In some embodiments, each of the components comprises a respective first end and a respective second end, and each respective first end is secured to the fastening block by a respective tensioner for that component. In some embodiments, each of the components comprises a central portion equidistant between the first end and the second end; and each of the components is securable to the object at its respective central portion. In some embodiments, the system further comprises a clamp carriage configured to be axially slidable within a structural body; wherein the clamp carriage is: a) attached to each of the components; and b) configured to attach to the object such that each of the components is securable to the object via the clamp carriage. In some embodiments, the system further comprises one or more temperature sensors configured to provide temperature data for the shape memory alloy components; wherein the control means is configured to selectively apply a voltage determined based in part on the temperature data. In some embodiments, one or more of the temperature sensors is configured to provide temperature data for the object. In some embodiments, the system further comprises a mechanical property sensor configured to measure a mechanical property of the object. In some embodiments, the mechanical property sensor is integrated into the clamp carriage such that the mechanical property sensor is configured to secure the object to the clamp carriage. In some embodiments, mechanical property sensor is a strain gauge. In some embodiments, the strain gauge is arranged as an S-beam load cell. In some embodiments, each of the components is made from an alloy comprising nickel and titanium. In a second aspect of the invention, there is provided a method of applying a force to an object, wherein the object is secured by a sample holder, the method comprising: applying a first force to the object by selectively applying a voltage to a first subset of a plurality of shape memory alloy components, wherein each of the plurality of shape memory alloy components is connected to: a) the object; and b) a biasing means configured to apply a respective return force to the respective component; and applying a second force to the object by selectively applying a voltage to a second subset of the components. In a third aspect of the invention, there is provided a computer program comprising instructions which, when executed by one or more processors, cause the one or more processors to carry out a method according to the second aspect of the invention. In a fourth aspect of the invention, there is provided a computer readable medium storing a computer program according to the third aspect of the invention. Brief description of the drawings Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1a schematically illustrates an example of a system for applying a force to an object. Figure 1b schematically illustrates an example of a general system for applying a force to an object. Figures 2a and 2b respectively illustrate an upper and lower view of an example system for sensing and securing an object. The system for sensing and securing the object is a subsystem of the system for applying a force to the object illustrated in Figure 1a. Figures 3a and 3b respectively illustrate a back and front view of an example tensioning system. The tensioning system is a subsystem of the system for applying a force to the object illustrated in Figure 1a. Figures 4a and 4b illustrate an example construction for a tensioner. The tensioner may be a component of the tensioning system of Figures 3a and 3b. Figure 5 schematically illustrates an example tensile test lab. Figure 6 schematically illustrates an example of a method for applying a force to an object. The method may be implemented using the system of Figure 1a. Figure 7 schematically illustrates an example of a computer system suitable for implementing various aspects of the invention. Detailed description of embodiments of the invention In the description that follows and in the figures, certain embodiments of the invention are described. However, it will be appreciated that the invention is not limited to the embodiments that are described and that some embodiments may not include all of the features that are described below. It will be evident, however, that various modifications and changes may be made herein without departing from the broader spirit and scope of the invention as set forth in the appended claims. Figure 1a illustrates an example of a system 100 for applying a force to an object 103. The object 103 is a test sample (or specimen) of a material intended for use in a Space application (e.g. an advanced material, wherein an advanced material is a material intentionally designed to possess desired or enhanced technical properties, as described at M Casini “Sustainability of Advanced Materials in Construction”, Encyclopedia of Renewable and Sustainable Materials Volume 4, 2020, Pages 221-231, which can be accessed from https: / / doj,.o^ and A Kennedy et. al, “A Definition and Categorization System for Advanced Materials: The Foundation for Risk-Informed Environmental Health and Safety Testing”, Risk Analysis Journal, Volume 39, Issue 8, 2019Pages 1783-1795, which can be accessed from https.; / / pn.Hnefe^ both of which are incorporated herein by reference in their entirety). The object 103 is a dogbone shaped tensile test sample and comprises a first end and a second end with a transition section in between. The first end and the second end are wider than the transition section such that when a tensile force is applied to the object 103 a stress concentration occurs in the transition section. The object 103 may be formed, for example, via a cutting or a molding process as described at https:#www.tegr^ the entire contents of which are incorporated herein by reference. One or more components of the system 100 may be housed within (or contained within) a structural body (not shown). The system 100 comprises a sample holder 105 configured to secure a first end of the object 103. The sample holder 105 may be configured to (rigidly or fixedly) attach to the first end of the object 103 such that the first end of the object cannot move (or slide or rotate) relative to the sample holder 105. The sample holder 105 may comprise a first clamp as will be discussed in more detail later. The first clamp may be (rigidly or fixedly) attached to the structural body (not shown) The system 100 also comprises a plurality of shape memory alloy components 107. It will be appreciated that shape memory alloys (also variously known as memory metals, memory alloys, smart metals, smart alloys, and the like) are known to the skilled person. Shape memory alloys exhibit a property whereby following some sort of mechanical deformation they tend to revert to their original (or pre-deformed) shape upon the application of heat. In this way shape memory alloys are typically thought of as “remembering” their original shape. The original shape is usually one which is achieved by hot-forming, whereas the mechanical deformation is typically a cold-forming process. For shape memory alloys such hot-forming is usually carried out above a phase transition temperature, and the cold forming below a phase transition temperature. In such cases the subsequent heating of the alloy to recover the original shape involves heating the shape memory alloy past said phase transition temperature. Shape memory alloys are described at P.K. Sekhar et. al “Review of sensor and actuator mechanisms for bioMEMS”, MEMS for Biomedical Applications Woodhead Publishing Series in Biomaterials 2012, Pages 46-77, which can be accessed from https: / / d;Q;Lorg / 1and which is incorporated herein by reference in its entirety A shape memory alloy component 107 is a component comprising (or made from) an alloy that is configured to deform from a first configuration (or home configuration or preset configuration or memorized configuration) to a second configuration (or temporary configuration or deformed configuration) and, in response to a change in temperature, tends to return (or revert) from the second configuration to the first configuration (e.g. by heating the shape memory alloy component which has been deformed when cold). The deformation from the first configuration to the second configuration may be in response to a mechanical applied force (e.g. the shape memory alloy component may be manually or mechanically or physically stretched or biased). The change in configuration (or deformation) may comprise an elongation or compression or bending of the shape memory alloy component 107. As set out above the change in configuration (or deformation) is typically a cold-forming process. It will be appreciated that in some cases, the respective first configuration may be an austenite phase configuration and the respective second configuration may be a martensite phase configuration. Each of the shape memory alloy components 107 may be made from an alloy comprising nickel and titanium, though it will be appreciated that other shape memory alloys are also suitable for use in (or for making) the shape memory alloy components 107. The shape memory alloy components 107 may be made from the same shape memory alloy or different shape memory alloys. The plurality of shape memory alloy components 107 may be configured as a bundle of wires made from shape memory alloy material. Each of the shape memory alloy components 107 is configured to connect to a second end of the object 103 (the second end being different from the first end). Each of the shape memory alloy components 107 may be configured to (rigidly or fixedly) connect (or attach) to the second end of the object 103 (indirectly) via a clamp carriage 109. That is the system 100 may further comprise a clamp carriage 109 (or movable clamp, or slidable clamp or movable connector); wherein the clamp carriage 109 is: a) attached to each of the shape memory alloy components 107; and b) configured to attach to the second end of the object 103 such that each of the shape memory components 107 is configured to connect to the second end of the object 103 via the clamp carriage 109. The clamp carriage 109 is not fixed (in position) relative to the sample holder 105. In particular, the clamp carriage 109 may be configured to be axially slidable within the structural body (not shown) as will be discussed in more detail later. Each of the shape memory alloy components 107 has a first end 107a and a second end 107b. The system 100 further comprises a (fastening) block 111 (or connecting block). Each of the shape memory alloy components 107 is connected (or secured or fixed) to the block 111 at its respective first end 107a and its respective second end 107b. Each of the shape memory alloy components 107 comprises a central portion equidistant between the first end 107a and the second end 107b. The central portion may be a point (the point equidistant between the first end 107a and the second end 107b) or a region (a region equidistant between the first end 107a and the second end 107b). Each of the shape memory alloy components 107 is configured to connect to the second end of the object 103 at (or in) its respective central portion. The system 100 further comprises biasing means (not shown) configured to apply a return force to each of the shape memory alloy components 107. In this way, the biasing means may deform (or bias) each of the shape memory alloy components 107 from its respective first configuration to its respective second configuration. In other words the biasing means may be configured to cold-form the shape memory alloy component into the second configuration. The biasing means may be connected between each shape memory alloy component 107 and the fastening block 111 (for example, at one (or both) of the first end 107a and the second end 107b, the biasing means may be used to secure each of the shape memory alloy components 107a to the fastening block 111). The operation of the biasing means will be discussed in more detail below. The system further comprises first and second fixed pegs 113. The first and second fixed pegs 113 are rigid cylindrical components. Each of the first and second fixed pegs 113 are fixed in position relative to the sample holder 105. Each of the first and second and second fixed pegs 113 may be independently attached to the structural body. The first and second fixed pegs 113 act as a pulley arrangement for the shape memory alloy components 107. That is, each of the first and second fixed pegs 113 is arranged such that each of the shape memory alloy components 107 passes around it, and thereby each of the first and second fixed pegs 113 acts to change the direction of the return force applied on each respective shape memory alloy component 107 by the biasing means (not shown). In figure 1a, the sample holder 105 is fixed in place forward of the fastening block, the clamp carriage 109 is located forward of the sample holder 105 and is configured to slide or translate along a path which is forward of the sample holder 105. The first and second fixed pegs 113 are located forward of the clamp carriage 109. The first fixed peg is located to the left (and forward) of the clamp carriage 109 and the second fixed peg is located to the right (and forward) of the clamp carriage 109. Each of the shape memory alloy components projects 107, at its first end 107a, forward from the fastening block 111, wraps around the first fixed peg, passes through an aperture in (or connects to) the clamp carriage 109 at (or in) its central portion, wraps around the second fixed peg, and returns to connect, at its second end 107b to the fastening block 111. In this way, first and second 115 pulley loops are formed in each shape memory alloy component 107. For each shape memory alloy component 107, the respective first pulley loop is located between the respective first end 107a and the respective central portion, and the respective second pulley loop is located between the respective central portion and the respective second end 107b. The use of the above described pulley arrangement results in a given deformation of a shape memory alloy component 107 in use applying a greater force (roughly double the force) to the object 103 than if the pulley arrangement were not present (and that shape memory alloy component were, for example, instead connected to the fastening block at its first end 107a and configured to connect to the object 103 at its second end 107b). The system 100 further comprises a control means (not shown) configured to: apply a first force to the object 103 by selectively applying a voltage to a first subset of the shape memory alloy components 107; and apply a second force to the object by selectively applying a voltage to a second subset of the shape memory alloy components 107. The system 100 further comprises an electronics system (not shown). The control means is configured to apply a voltage to the shape memory alloy components 107 via the electronics system. That is, the control means may be electrically connected to the electronics system. The control means may additionally or alternatively be in (or configured for) telemetric communication with the electronics system. That is, the electronics system and the control means may be in wired and / or wireless communication with one another. The wireless communication may be, for example, satellite communication. The electronics system may comprise one or more of: a processor and a power source (or power distribution unit, the power distribution unit may also be connected to the shape memory alloy components 107). The electronics system may also comprise telemetry components configured to provide for communication between the electronics system and the control means. In this way, the control means may be remote from the object 103 (for example, the structural body may be in-orbit, and the control means may be on Earth, controlling the system via telemetry between the control means and the electronics system, which may be local to the object (and structural body). The first force and the second force may have different magnitudes. The first force and the second force are tensile forces. The voltage applied to the first subset of the shape memory alloy components 107 heats the first subset of shape memory alloy components 107. This heating is a result of the joule (or resistive or ohmic) heating effect by which passing an electric current through a conductor produces heat as described at hUgs^ / en.wkjgediajOrs^^ the entire contents of which are incorporated herein by reference. The heating of the first subset of shape memory alloy components 107 causes deformation (e.g. a contraction) of each component of the first subset of shape memory alloy components 107 from a respective second configuration to a respective first configuration (e.g. a mechanical deformation applied by the biasing means is reversed or reduced or counteracted by the heating, which itself acts to bias the shape memory alloy components 107 of the first subset to their respective first configuration). As the first subset of shape memory alloy components 107 are connected both to the (fastening) block 111 and to the object, the deformation of the first subset of shape memory alloy components 107 produces (or applies) the first (tensile) force on (or to) the object 103. Responsive to reversal of the voltage applied to the first subset of the shape memory alloy components 107, each component of the first subset of the shape memory alloy components 107 returns to its respective second configuration, biased by (or under action of) the return force generated by the biasing means. Each component of the first subset of the shape memory alloy components 107 may provide a different amount of tensile force via its deformation from its respective second configuration to its respective first configuration. The difference in applied (or provided) force may be, for example, due to a difference in thickness (or diameter) between shape memory alloy components 107 of the first subset, a difference in pre-tension (i.e. the tension in a shape memory alloy component in its respective second configuration) between shape memory alloy components 107 of the first subset, and / or a difference in shape memory alloy between shape memory alloy components 107 of the first subset. The voltage applied to the second subset of the shape memory alloy components 107 heats the second subset of shape memory alloy components 107. This heating is a result of the joule (or resistive or ohmic) heating effect. The heating of the second subset of shape memory alloy components 107 causes deformation (e.g. a contraction) of each component of the second subset of shape memory alloy components 107 from a respective second configuration to a respective first configuration. As the second subset of shape memory alloy components 107 are connected both to the (fastening) block 111 and to the object, the deformation of the second subset of shape memory alloy components 107 produces (or applies) the second (tensile) force on (or to) the object 103. Responsive to reversal of the voltage applied to the second subset of the shape memory alloy components 107, each component of the second subset of the shape memory alloy components 107 returns to its respective second configuration, biased by (or under action of) the return force generated by the biasing means. Each component of the second subset of the shape memory alloy components 107 may provide a different amount of tensile force via its deformation from its respective second configuration to its respective first configuration. The difference in applied (or provided) force may be, for example, due to a difference of thickness (or diameter) of shape memory alloy components 107 of the second subset, a difference in pre-tension between shape memory alloy components 107 of the second subset, and / or a difference in shape memory alloy between shape memory alloy components 107 of the second subset. In general, for a component made from a given shape memory alloy material (of a given length) and a given applied voltage, the larger the cross-sectional area of the component, the greater the force produced by application of that voltage (i.e. the greater the force applied to the object 103). Where the shape memory alloy component 107 is a wire, the thicker the diameter of the wire, the greater the cross-sectional area of the component. The first and second subsets may be overlapping. The first and second subsets may be non-overlapping. It will be appreciated that there may be further subsets of the plurality of shape memory alloy components and the above description and operation would apply correspondingly to the further subsets. Selectively applying a voltage means applying the voltage to a selected subset of the plurality of shape memory alloy components (as opposed to collectively applying a voltage to all shape memory alloy components 107). Selectively applying the voltage may comprise applying a first voltage (the same voltage) to a selected subset of the shape memory alloy components 107, and / or applying a different voltage to different shape memory alloy components 107. The selected voltage (i.e. the voltage to be selectively applied) may be determined by an operator and transmitted to the electronics system (by the control means) to effect the selectively applied voltage (live or in response to changing conditions of the object). Additionally or alternatively, the selected voltage may be predefined as part of a (activation) sequence of selected voltages (i.e. by a program running on or controlling the action of the control means). Additionally or alternatively, the selected voltage may be determined by a machine learning algorithm trained based on previous mechanical tests. Additionally or alternatively, the system 100 (or system 150) may further comprise one or more shape memory alloy component temperature sensors (not shown) configured to measure the temperature of the shape memory alloy components (or each of the shape memory alloy components) (i.e. configured to provide temperature data for the shape memory alloy components). In general, the control means may be configured to selectively apply a voltage determined based in part on the temperature data. More specifically, the measured temperature (data) may be used in a closed feedback loop. This closed feedback loop allows the selectively applied voltage to be determined so as to control the heating of the shape memory alloy components 107 in use and prevent under- or over- heating. That is, if a selectively applied voltage is not producing the expected force on the object 103, the selectively applied voltage can be tailored (via the closed loop feedback) based on the measured temperature(s) of the shape memory alloy components 107 to produce the expected (or desired) force on the object 103 (by tweaking the applied voltage). This is because the deformation of a given shape memory alloy component 107 is dependent on the temperature of that component 107 e.g. the greater the temperature, the greater the deformation may be (up to a limit). In this way, a plurality of shape memory alloy components 107 can be used to provide selective (or configurable) force application to an object 103 (via a selectively applied voltage). The force applied to the object 103 can be tailored (or configured or determined) via a selection of a subset of the plurality of shape memory alloy components 107 that a voltage is applied to. Application of a voltage to different subsets of the plurality of shape memory alloy components 107 will apply different forces to the object 103 in use. That is, the force applied to the object 103 can be controlled electronically via the application of a voltage to different locations (or the application of a different voltage). This electronic control is advantageous as it allows the system 100 to be readily controlled (or operated) remotely. The use of different subsets of a plurality of shape memory alloy components 107 is advantageous because it allows robust force control. If one or more of the shape memory alloy components 107 in a subset used to provide a desired force is damaged, a voltage can be applied to an alternative subset (not including the damaged components), the alternative subset being selected to also provide the desired force. This redundancy is particularly useful for in-Space applications, where system maintenance may be challenging. To allow for greater tailoring of the force applied to the object 103, the plurality of shape memory alloy components 107 may comprise components of different (substantially uniform) cross sectional areas. In other words, each of a third subset of the shape memory alloy components 107 has a first (substantially uniform) cross sectional area; and each of a fourth subset of the shape memory alloy components 107 has a second cross sectional area different from the first cross sectional area. The third subset may overlap the first and / or second subsets. The third and fourth subsets are non-overlapping. The fourth subset may overlap the first and / or second subset. It will be appreciated that there may be further subsets - that is, the plurality of shape memory alloy components 107 may comprise components with more than two different cross-sectional areas. In one example, each of the plurality of shape memory alloy components 107 may have a different crosssectional area (i.e. no two of the shape memory alloy components 107 has the same crosssectional area). The use of different cross-sectional areas (different diameters where the shape memory alloy components are wires), enables more granular force control than using a plurality of shape memory alloy components 107 all having the same diameter. This is because force levels can be tailored based not only on the number of components a voltage is applied to (or that are activated / deformed), but also which specific components the voltage is applied to (or that are activated / deformed). This use of varied diameters of wires means that fewer components are required to produce a desired level of force granularity, and those fewer components take up a smaller volume (important for in-orbit applications where volume is at a premium). In addition, this use of varied diameters of wires means that less power is required to produce a desired level of force granularity, since the voltage need be applied to fewer components (while still allowing for the desired level of force granularity). An example illustrating the effect of (or operation of) plural shape memory alloy wires of different thicknesses is described below. Furthermore, the plurality of shape memory alloy components 107 can be used to provide reversible (or repeatable) force application to an object 103. This is because, when an applied voltage is removed, the shape memory alloy components 107 return to their second (or original) configuration (under bias of the biasing means) and any (tensile) force applied by the applied voltage is thereby reversed. In addition, the first force and the second force are produced via deformation (or activation) of shape memory alloy components (rather than gears, motors and / or hydraulics). The system 100 is therefore robust to (does not suffer from) cold welding and freezing problems. System 100 is accordingly suitable use for in-orbit mechanical testing (and more generally suitable for use in Space). It will be appreciated that the object (or sample or test component) 103 may be many different shapes and sizes and is not limited to the dogbone configuration illustrated. The object 103 need not be a test sample and may additionally or alternatively be, for example, a component intended for future use in or on a spacecraft - such as a spacecraft panel. It will be appreciated that the clamp carriage 109 is an optional feature, and other means could be used to connect the second end of the object 103 to each of the shape memory alloy components 107 (directly or indirectly). For example, one or more of the shape memory alloy components 107 could (instead) be glued to the second end of the object 103 in use. Additionally or alternatively, one or more of the shape memory alloy components 107 could (instead) be connected to the second end of the object using a respective bolt through both a respective shape memory alloy component 107 and the second end of the object 103. Different shape memory alloy components 107 could be configured to connect to the second end of the object 103 via different connection means. One or more of the shape memory alloy components 107 may be configured to connect to the second end of the object 103 via more than one possible connection means simultaneously. It will be appreciated that each shape memory alloy component 107 need not be connected to the (fastening) block 111 at both its first 107a and second 107b ends. Instead, a shape memory alloy component 107 could be connected to the (fastening) block 111 at its first end 107a or its second end 107b (but not both). That is, the connection at both the first 107a and second 107b ends is advantageous (to enable the pulley arrangement described above) but not essential. Moreover, it will be appreciated that the (fastening) block 111 is an optional feature and other arrangements for the first 107a and second 107b ends of the shape memory alloy components 107 would be appreciated by the skilled person. For example, the first 107a and second 107b ends of each shape memory alloy component 107 could be connected directly to a structural body, the sample holder 105 and / or some other anchoring component of the system 100. It will be appreciated that each of the shape memory alloy components 107 may be configured to connect to the second end of the object 103 at regions other than its central portion. For example, each of the shape memory alloy components 107 may (instead) be configured to connect to the second end of the object 103 at its first end 107a or its second end 107b. It will be appreciated that the sample holder 105 may be securable to any part (or region) of the object 103, and that it is not necessary to secure the sample holder 105 at a first end of the object 103 (or just at the first end of the object 103). Additionally, or alternatively, each shape memory alloy component 107 may be securable to any part (or region) of the object 103, and it is not necessary to secure each (or any) shape memory alloy component 107 at a second end of the object 103 (or just at the second end of the object 103). It will be appreciated that the first and second fixed pegs 113 need not be cylindrical and may instead be any shape. Additionally or alternatively, the first and second fixed pegs 113 may be integral components of the structural body. Moreover, the first and second fixed pegs 113 could be removed entirely (the pulley arrangement is optional). It will be appreciated that the control means could work in other ways, for example, the control means could be arranged to apply heat directly to the shape memory alloy components 107, rather than achieving the heating via the joule heating effect (by applying a voltage). Any control means configured to cause deformation (or activation) of shape memory alloy is suitable. It will be appreciated that system 100 is one example of a system for applying a force to an object which overcomes the problems associated with use for in-orbit mechanical testing. The system 100 is configured to apply a tensile force to the object. A more general illustration of such a system is provided by Figure 1b. This system can be configured to apply different types of force to an object, for example a torsional force and / or a bending force. Figure 1 b illustrates a system 150 for applying a force to an object 151. The system 150 comprises a sample holder 153 securable to (or connectable to, or configured to connect to, or configured to secure, or configured to fix) the object 151; a plurality of shape memory alloy components 155 secured (or fixed or connected) relative to (or secured to, indirectly or directly) the sample holder 153, wherein each of the shape memory alloy components 155 is securable to (or connectable to, or configured to connect to, or configured to secure, or configured to fix) the object 151 (directly or indirectly); biasing means 157 configured to apply a return force to each of the components; and control means (not shown) configured to apply a first force to the object by selectively applying a voltage to a first subset of the components; and apply a second force to the object by selectively applying a voltage to a second subset of the components. It will be appreciated that, in system 100, the object 151 is object 103, the sample holder 153 is sample holder 105, the shape memory alloy components 155 are shape memory alloy components 107 and the biasing means 157 is the biasing means described above. In this way, system 100 is configured to apply a tensile force to object 103. However, it will be appreciated that system 150 is more generally applicable than system 100. For example, system 150 may be configured to apply a torsional force. To apply a torsional force, the plurality of shape memory alloy components 155 may be, for example, a plurality of concentric hollow tubes (having different diameters). The biasing means may deform (or bias) each of the shape memory alloy components 155 from its respective first configuration to its respective second configuration e.g. in a cold-forming process. Each respective second configuration may be a twisted configuration (with the degree of twisting determined by the biasing means). The sample holder 153 may be securable to a first end of the object 151, and each shape memory alloy component 155 may be securable to a second end of the object 151. The control means (not shown) may be configured to apply a first force to the object by selectively applying a voltage to a first subset of the components (and thereby heating the first subset of the components); and apply a second force to the object by selectively applying a voltage to a second subset of the components (and thereby heating the second subset of the components). Selectively applying a voltage to a subset of the components causes each shape memory alloy component of that subset to deform from its respective second configuration to its respective first configuration (e.g. by untwisting). This (un)twisting of the shape memory alloy components 155 applies a torsional force on the object 151. In another example, system 150 may be configured to apply a bending force. To apply a bending force, the plurality of shape memory alloy components 155 may be, for example, a plurality of solid bars. The biasing means may deform (or bias) each of the shape memory alloy components 155 from its respective first configuration to its respective second configuration e.g. in a cold-forming process. Each respective second configuration may be a bent configuration (with the degree of bending determined by the biasing means). The sample holder 153 may be securable to a central portion of the object 151, and each shape memory alloy component 155 may be securable to both a first end of the object 151 and a second end of the object 151. The control means (not shown) may be configured to apply a first force to the object by selectively applying a voltage to a first subset of the components (and thereby heating the first subset of the components); and apply a second force to the object by selectively applying a voltage to a second subset of the components (and thereby heating the second subset of the components). Selectively applying a voltage to a subset of the components causes each shape memory alloy component of that subset to deform from its respective second configuration to its respective first configuration (e.g. by unbending (or straightening)). This (un)bending of the shape memory alloy components 155 applies a bending force on the object. Many other configurations of system 150 will be appreciated by the skilled person. The key feature of the system 150 being that force is applied to the object 151 by deformation of shape memory alloy components 155 (from a biased configuration to a home configuration), the deformation being caused (or activated) by heating (via application of a voltage. In a first worked example, tables 1 and 2 below illustrate how granular control of a force applied to an object 103 can be implemented using shape memory alloy components 107 (in the form of wires A, B, C and D) having a range of different diameters. More specifically, tables 1 and 2 illustrate the performance (applied force to the object 103 for a given applied voltage) for wires A, B, C and D when wires A, B, C and D are respectively arranged as per system 100 of figure 1a (i.e. are respectively configured as shape memory alloy components 107 as per system 100). Table 1: Wires in group Wire ID Wire Diameter Contraction force A 0.1 5N B 0.2 ION C 0.5 25N D 1 50N Table 1 illustrates the contraction force applied on (or to) an object 103 by each of wires A, B, C and D respectively in response to the respective application of a first voltage X to that wire. The contraction force is the force produced on the object 103 (in the arrangement shown in system 100, this is a tensile force), in response to the contraction of a respective shape memory alloy component 107, the contraction of the respective shape memory alloy component 107 caused by the application of a voltage (and therefore the application of heat) to that shape memory alloy component 107. Wire A has a relative diameter of 0.1, and, in response to an application of voltage X to wire A, produces a contraction force of 5N on object 103. Wire B has a relative diameter of 0.2, and, in 5 response to an application of voltage X to wire B, produces a contraction force of 10N on object 103. Wire C has a relative diameter of 0.5, and, in response to an application of voltage X to wire C, produces a contraction force of 25N on object 103. Wire D has a relative diameter of 1, and, in response to an application of voltage X to wire D, produces a contraction force of 50N on object 103. 10 Table 1 therefore illustrates how, for a given applied voltage, the greater (or larger) the diameter of a wire (and this generalises to the greater or larger the cross-sectional area of a component), the greater (or larger) the (contraction) force. Table 2: Activation sequence Step NO. Wires active Total Force 1 A 5N 2 B 10N 3 A, B 15N 4 B, B 20N 5 C 25N 6 A, C 30N 7 B, C 35N 8 A, B, C 40N 9 B, B, C 45N W D 50N 15 Table 2 illustrates how using five shape memory alloy wires (1x wire A, 2x wire B, 1x wire C and 1x wire D as described above) as the plurality of shape memory alloy components 107 (in system 100), at least ten different force magnitudes can be selectively applied to object 103. To selectively apply a desired force magnitude to object 103, a voltage is selectively 20 applied to a subset of the five shape memory alloy wires. A desired force magnitude can also be applied in steps, which advantageously allows measurements to be taken during application of the desired force (for example, strain measurements to be taken). If the desired force magnitude is beyond the yield or failure point of the object 103, by applying the desired force magnitude gradually in steps, object measurement data can be obtained up until the point of failure. Table 2 illustrates how, via selective application of a voltage to the five shape memory alloy wires, a 50N (tensile) force can be applied to the object 103. The 50N (tensile) force is applied gradually in 10 steps of 5N. In other words, there is an activation sequence of wires (a sequence of selective voltage applications (to the five shape memory alloy wires)), which produces (or applies) a respective sequence of forces on the object 103. The sequence of (tensile) forces on the object 103 is 5N, 10N, 15N, 20N, 25N, 30N, 35N, 40N, 45N and 50N (in that order). When a voltage (voltage X) is applied to a wire, that wire deforms from a second configuration to a first configuration. The deformation in this case is a contraction. When a given wire deforms (or contracts), that wire produces (or applies) a (tensile) force on the object 103 as per table 1. When a voltage (voltage X) is selectively applied to more than one wire, those wires each deform from a respective second configuration to a respective first configuration. The deformation in this case is a contraction. When the (more than one) wires deform (or contract), those wires collectively produce (or apply) a (tensile) force on the object 103 equal to the superposition (or sum) of their respective individual forces (in response to voltage X) as per table 1. In the arrangement of system 100, each shape memory alloy component 107 (and therefore each of the five shape memory alloy wires described here) is biased by a biasing means. That is, there is a biasing means which applies a return force to each of the wires. Accordingly, under action of the return force, when the selectively applied voltage is removed from a given wire, that wire returns to its original (second) configuration and any applied voltage (as per table 1) is reversed - in other words, the return force acts to stretch or elongate the wire (and bias it away from its first configuration). The reversibility of the applied forces allows for many different combinations of wires in different consecutive steps of an activation sequence (a wire, once activated, need not always be activated). In table 2, column 1 (“Step NO.”) illustrates a step of the activation sequence (the steps are applied consecutively from 1 to 10). In table 2, column 2 (“Wires active”) illustrates the wires active (i.e. the wires that a voltage X is selectively applied to) at the corresponding step of the activation sequence. In table 2, column 3 (“Total force”) illustrates the total force collectively applied by the active wires (i.e. the wires that a voltage X is selectively applied to) in combination at the corresponding step of the activation sequence. This total force is a superposition of (or sum) of the respective individual forces applied by the active wires (in response to voltage X) as per table 1. For example, in step 1, to produce a 5N force, a voltage X is selectively applied to wire A only. This selective application of voltage (and therefore heat) causes wire A to deform from its respective second configuration to its respective first configuration (a contraction) and thereby produce a force of 5N on the object 103 (as per table 1). In step 2, to produce a 10N force a voltage X is selectively applied to a wire B only (one of the two wire Bs present). As voltage X is selectively applied to a wire B only, the voltage X is removed from wire A (where it was applied in step 1). This selective application of voltage (and therefore heat) causes wire B to deform from its respective second configuration to its respective first configuration (a contraction) and thereby produce a force of 10N on the object 103 (as per table 1). This selective application of voltage (and therefore heat) means that voltage is removed from wire A which causes wire A to deform from its respective first configuration to its respective second configuration (under action of the return force) and thereby the force of 5N on the object 103 applied by wire A in step 1 is reversed. Accordingly, the total force applied on the object 103 by the five shape memory alloy wires is 10N in step 2. This can be repeated for the different wire combinations shown in column 2 in sequence (as per column 1) to produce the 5N force steps up to 50N as illustrated in table 2. It will be appreciated that this example illustrates how granular force control can be obtained via the arrangement of figure 1a through the use of a plurality of shape memory ally components 107, wherein each of a third subset of the components has a first (substantially uniform) cross sectional area; and each of a fourth subset of the components has a second (substantially uniform) cross sectional area different from the first cross sectional area. It will be appreciated that many other different force steps and applied forces are possible using different numbers of, different combinations of, and / or different activation sequences of shape memory alloy components. These forces are applied by deformation (or activation) of the shape memory alloy components (i.e. without gears, motors or hydraulics or other moving parts). Thus, such system arrangements (e.g. system 100, system 150) are suitable for use for mechanical testing applications in Space (in-orbit), as well as in remote areas where maintenance of the system is challenging and therefore low maintenance systems (few moving parts) are preferred. Figures 2a and 2b respectively illustrate an upper and lower view of an example system 200 for sensing and securing an object 103. The system 200 for sensing and securing the object 103 is a subsystem of the system 100 for applying a force to an object 103 illustrated in Figure 1a. The system 200 comprises the sample holder 105 and the clamp carriage 109 described above. The system 200 further comprises a sensor 203. For clarity of illustration, sensor 203 is visible in Figure 2b but not Figure 2a. The sample holder 105 comprises a first clamp. The first clamp of the sample holder 105 is configured to (releasably) secure a first end of the object 103 in use. The first clamp comprises two jaws between which the object 103 can be placed. To secure the object, the first clamp is tightened (e.g. via screwing by hand or via electronic operation) to move the jaws closer together until they secure the object 103 as an interference (or pressed or friction) fit. The tightness of the fit (closeness of the jaws) is adjustable, for example by tightening machine screws of the first clamp using a torque wrench (wherein the first clamp is configured such that tightening a machine screw moves the jaws closer together). The first clamp may be designed and the tightness of the fit may be determined (or selected) in accordance with the relevant material standard for the object 103 under test (for example, the ASTM E8M standard for metallic materials, which can be accessed from The sensor 203 comprises a first section configured for securing to the first clamp of sample holder 105. The sensor 203 forms part of a clamping mechanism with the first clamp of the sample holder 105 to secure a first end of the object 103. In particular, the sensor 203 comprises a sensor face which abuts a lower face of the first end of the object 103 and a lower face of the first clamp of the sample holder 105 in use to prevent the first end of the object slipping out from first clamp in a downwards direction. In this way, the sensor 203 is integrated into system 200 (and system 100). The sensor 203 measures strain. The sensor 203 is arranged as an S-Beam strain gauge load cell (an S-Beam load cell). The S-Beam strain gauge load cell comprises an S-shaped component and a plurality of strain gauges attached to the S-shaped component as described at https.7 / en.wikipedia.org / w / index.php?titte^^ ceH&psdsd^ 1215456494, the entire contents of which are incorporated herein by reference. The plurality of strain gauges are arranged in a Wheatstone bridge configuration to monitor distortion (bending or shape change) of the S-shaped component. The force applied to the S-shaped component can be determined (e.g. by a processor) using the monitored distortion and known mechanical properties of the beam. As the S-Beam strain gauge load cell is integrated into the system 200, and is used to secure the object 103, the force applied to the object 103 can be determined as the calculated force applied to the S-Shaped component. In this way, the (tensile) force applied to the object 103 by the action of the shape memory alloy components 107 can be determined using system 200. System 200 may additionally comprise further sensors (not shown) configured to sense (or measure) (other) properties of the object 103. One or more of the further sensors may be a temperature sensor configured (or arranged) to monitor (or sense) the temperature of the object 103 during application of a force to object 103 (e.g. during mechanical testing of object 103). Knowledge of the temperature of the object is advantageous because mechanical properties of materials (and therefore the mechanical properties of the object) are temperature dependent. The one or more temperature sensors may be (or comprise) a thermocouple or a resistance temperature detector. A resistance temperature detector (RTD) is a sensor comprising a wire of material with a resistance / temperature relationship from which temperature can be determined from a measured resistance in the wire, as described at the entire contents of which are incorporated herein by reference). One or more of the further sensors may be an optical instrument such as a camera. The camera (or other optical instrument) can be used to image the object 103 during application of the force (e.g. during mechanical testing). If the object 103 is tested beyond its yield point, the location and mode of failure can be determined from images (or video or other optical signals) taken by (or measured by) the camera (or other optical instrument). The clamp carriage 109 comprises a second clamp configured to attach to the second end of the object 103 such that each of the shape memory components 107 is configured to connect to the second end of the object 103 via the clamp carriage 109. The second clamp may be arranged as described above for the first clamp, and may operate in the same way (except being configured to secure the second end of the object 103 rather than the first end of the object 103). The clamp carriage 109 may comprise a through-aperture or loop in an end of the clamp carriage that is distal from the sample holder 105 in use. The clamp carriage 109 may comprise a protrusion of material through which the aperture or loop is formed. The aperture or loop may be configured such that the plurality of shape memory alloy components 107 can be threaded through the aperture (or loop). The clamp carriage 109 is: a) attached to each of the shape memory alloy components 107; and b) configured to attach to the second end of the object 103 such that each of the shape memory components 107 is configured to connect to the second end of the object 103 via the clamp carriage 109. It will be appreciated that the structure of the first clamp and / or the second clamp can be readily adapted (or selected) for different types of object 103 - for example, the first clamp and / or the second clamp can be many different sizes, and have many different jaw shapes. The first clamp and the second clamp are modular parts of the system 200 and so can readily be removed and replaced (e.g. with a different clamp or the same clamp again). It will be appreciated that sensor 203 may be configured to measure other properties instead of (or in addition to) strain. For example, sensor 203 may be configured to measure hardness, toughness, torsional strength, yield strength, tensile stress, fracture toughness, fatigue, stiffness or ductility. It will be appreciated that where sensor 203 measures strain, other sensor configurations may also be suitable and the invention is not limited to an S-Beam strain gauge load cell. It will be appreciated that the aperture or loop of the clamp carriage 109 is an optional feature. Instead, the shape memory alloy components 107 could be fixed to the clamp carriage 109, for example using screws, glue or a welded joint. Figures 3a and 3b respectively illustrate a back and front view of an example tensioning system 300. The tensioning system is a subsystem of the system 100 for applying a force to an object 103 illustrated in Figure 1a. The system 300 comprises a (fastening) block 111 (or connecting block) and the biasing means. The (fastening) block 111 provides a mechanical fastening point for the shape memory alloy components 107. The system 300 further comprises a printed circuit board (PCB) 303 affixed to the back of the (fastening) block 111. A PCB is a component comprising conductive material and is used to electrically connect other components in a circuit as described at the entire contents of which are incorporated herein by reference. The PCB 303 provides electrical connections between the shape memory alloy components 107 and the electronics system (not shown). Both the (fastening) block 111 and the PCB 303 comprise a plurality of through-apertures. Each of the shape memory alloy components 107 passes through (or is passed through, or is threaded through) one of the through-apertures in the fastening block 111 and the PCB 303. For each of the shape memory alloy components 107, at one of its respective first end 107a and its respective second end 107b, the shape memory alloy component comprises (or is connected to) a ball (or end or stopper) of conductive material 305. This ball (or end or stopper) of conductive material 305 prevents that respective shape memory alloy component 107 from moving forwards axially (i.e. it ensures that the respective shape memory alloy component 107 is maintained in a configuration in which it is threaded through both the (fastening) block 111 and the PCB 303, even under tension). Each ball (or end or stopper) of conductive material 305 additionally provides an electrical connection between the respective shape memory alloy component 107 and the PCB 303 (e.g. at a brass (or other conductive material) pad on the PCB 303). Each ball (or end or stopper) of conductive material 305 may be formed by plasma welding the end of the respective shape memory alloy component 107 to form a ball. That is, each shape memory alloy component 107 may comprise an integral ball (or end or stopper or knot) of conductive material 305. Each ball 305 (or end or stopper) has a greater (or larger) diameter than the respective through-aperture in the fastening block 111 and the PCB 303 (which the respective shape memory alloy component 107 having that balled end is passed through). Thus, the end (formed by the ball 305) is prevented from passing back through the respective through-aperture(s). Nonetheless, since the balled end (or stopper) 305 is not fixedly attached to the fastening block 111 or PCB 303 (e.g. it is not welded to the fastening block 111 or PCB 303), via the balled-end connection (or stopper), the respective component 107 can rotate freely relative to the fastening block 111 and the PCB 303. It will be appreciated that the balled end (or stopper) 305 need not be spherical (i.e a ball), and may be any shape or configuration, provided it has a dimension larger than the respective through-aperture such that the end or stopper 305 cannot pass back through the respective through-aperture. For each of the shape memory alloy components 107, at the other one of its respective first end 107a and its respective second end 107b (i.e. the one that does not comprise a ball (or end or stopper) of conductive material 305), the shape memory alloy component is secured (or connected) to the biasing means. The biasing means comprises a plurality of tensioners, each tensioner 307 comprising: a) a threaded portion configured to engage with a recess in a (fastening) block 111; and b) a spring portion. There is a respective tensioner 307 for each respective shape memory alloy component 107. For each of the shape memory alloy components 107, at the other one of its respective first end 107a and its respective second end 107b (i.e. the one that does not comprise a ball (or end or stopper) of conductive material 305), the shape memory alloy component is secured (or connected or fixed) to a respective tensioner 307. Each respective tensioner 307 is secured (or fixed) within (or to) the (fastening) block 111 by screwing (or securing or engaging) its respective threaded portion to a respective recess in the (fastening) block 111. Each respective recess is a tapped whole and comprises complementary grooves into which the respective threaded portion can be screwed (or threaded or secured in place). Each shape memory alloy component 107 can be pre-tensioned (in a hardware set up phase) by screwing (or threading) the respective tensioner for that shape memory alloy component 107 into the (fastening) block 111. The amount of pre-tension can be controlled (or determined or set) by the extent to which (or how far or how much) the respective tensioner 307 for that shape memory alloy component 107 is screwed (or threaded) into the (fastening) block 111. The pre-tension biases each respective shape memory alloy component to its respective second configuration. The respective second configuration (and the extent of deformation between the respective first configuration and the respective second configuration for a given shape memory alloy component 107) is determined by the amount of pre-tension. Each respective tensioner 307 comprises (or is made from) a conductive material such as brass. In this way, each respective tensioner 307 provides an electrical connection between the respective shape memory alloy component 107 it is secured to and the electronics system. Each respective tensioner 307 may therefore serve as (or provide) one or more electrical contacts of the system 100. For example, power connectors from the electronics system may be soldered (or otherwise fixed) to an electrical contact of a tensioner 307 (or a conductive region of a tensioner 307). It will be appreciated that the (fastening) block 111 may be any shape, and is not limited to a cuboidal block. It will be appreciated that the ball of conductive material 305 may be any shape and need not be a spherical component. Additionally or alternatively, the ball of conductive material need not be integral to its respective shape memory alloy component 107 and formed by welding, but could instead be a distinct component (and may be of a different material) and secured to a respective shape memory alloy component e.g. via a metallic clip. It will be appreciated that the threaded portion (and optional corresponding grooves) are optional, and could be replaced by any mechanical securing arrangement, for example, male-female mechanical fasteners such as alignment holes and corresponding pegs. Figures 4a and 4b illustrate an example construction for a tensioner 307. The tensioner 307 may be one of the plurality of tensioners described in connection with figures 3a and 3b. The tensioner 307 comprises a threaded section 403 configured to engage with (corresponding grooves of) a recess in a (fastening) block 111 and a spring portion 405. The spring portion 405 may be a machined spring portion (formed by machining the tensioner) as described at https: / / en.wikipedia■org / w / sndex.phpVtit^ the entire contents of which are incorporated herein by reference. The spring portion 405 provides a return force on the respective shape memory alloy component 107 that the tensioner is secured to. The return force is provided by the resilient bias in the spring portion 405. Thus, when a voltage is applied to the shape memory alloy component 107 that the tensioner 307 is secured to, and the shape memory alloy component 107 thereby deforms, the spring portion 405 provides a return force on the respective shape memory alloy component 107 (i.e. a force acting against the deformation) such that when the voltage is removed, the respective shape memory alloy component 107 returns to its original (undeformed by heat) state (or configuration or length) under action of the return force provided by the resilient bias in the spring portion 405. This original (undeformed by heat) state may be the respective second configuration for that respective shape memory alloy component 107. This original (undeformed by heat) state may be deformed by the (mechanical) return force applied by the tensioner 307. Each shape memory alloy component 107 is secured to a respective tensioner 307 at one of its first end 107a or its second end 107b. The secured end is so secured by passing that end through (a through-hole in the centre of) a washer (cap) 407 and welding the secured end of the shape memory alloy component 107 to form a ball (or end or stopper) 409. The welding may be plasma welding. The ball 409 (or end or stopper) has a greater (or larger) diameter than the through-hole of the washer 407 (which the respective shape memory alloy component 107 having that balled end is passed through). Thus, the end (formed by the ball 409) is prevented from passing back through the through-hole. Nonetheless, since the balled end (or stopper) 409 is not fixedly attached to the washer 407, via the balled-end connection (or stopper), the respective component 107 can rotate freely relative to the washer 407. It will be appreciated that the balled end (or stopper) 409 need not be spherical (i.e a ball), and may be any shape or configuration, provided it has a dimension larger than the through-hole of the washer 407 such that the end or stopper 409 cannot pass back through the washer 407. The washer (cap) is then welded onto an end of the wire tensioner. The welding may be plasma welding. Figure 5 schematically illustrates an example tensile test lab 500 (tensile test system or arrangement). The tensile test lab 500 is 90mm long and 30mm wide, though it will be appreciated that the tensile test lab 500 could be made any size (the size selected being determined based on the volume constraints of the intended application and the desired applied force magnitudes). The tensile test lab 500 comprises the system 200 for sensing and securing an object 103, the first and second fixed pegs 113, the plurality of shape memory alloy components 107, the (fastening) block 111, the tensioners 307, and the electronics unit. The tensile test lab 500 further comprises a structural body 503. The first clamp of the sample holder 105 may be (rigidly or fixedly) attached to the structural body 503. For example, the first clamp may be screwed into or bolted to the structural body 503 (and (first clamp of) the sample holder 105 may comprise through-holes to receive such screws or bolts). The clamp carriage 109 is not fixed in position in the structural body 503. However, the clamp carriage is configured to be axially slidable (or translatable) within the structural body 503. That is, movement of the clamp carriage 109 within the structural body 503 is not prevented but its direction is constrained to be axial. To enable this, protrusions of (or the edges of) the clamp carriage 109 are engaged with guide rails of a bearing 505 of the structural body 503. The bearing 505 may be a teflon bearing to minimise frictional losses on (or to) the force applied to the object 103 in use. The clamp carriage 109 fits into (and is retained within) the guide rails of the bearing 505 via a ball joint (as described at the entire contents of which are incorporated herein by reference). The (fastening) block 111 may be (rigidly or fixedly) attached to the structural body 503. For example, the (fastening) block 111 may be screwed into, glued onto, or bolted to the structural body 503. Each of the first and second and second fixed pegs 113 may be independently attached to the structural body 503. For example, each of the first and second and second fixed pegs 113 may be screwed into, glued onto or bolted to the structural body 503. The structural body 503 further comprises component channels 507 and a component guide 509. The component channels 507 are cut-outs within the structural body 503 and are configured to receive the plurality of shape memory alloy components 107. The component guide 509 is a smooth region of the structural body configured to receive and direct the plurality of shape memory alloy components 107. The component guide 509 comprises the first and second fixed pegs 113. The first and second fixed pegs may be integral to the component guide 509 and / or the structural body 503. The structural body 503 further comprises an electronics bay (or electronics region) 511. The electronics bay is a recessed region of the structural body 503 configured to receive the electronics system. It will also be appreciated that the electronics bay is an optional feature and the electronics system could instead be, for example, mounted to the outside of the structural body 503. As described above, the electronics system comprises a processor (for example, in the form of a microcontroller unit that runs operating software). This operating software may provide various functionalities including one or more of: telemetry data handling, command reception and processing, actuator handling, timeline execution (of activation sequences) for tests, firmware image updating through a bootloader, and underlying filesystem implementation for secure data read and write access. Telemetry data handling may comprise capturing and processing real-time data from sensors (e.g. the S-Beam strain gauge load cell, the temperature sensors, the camera (or optical sensor)), power monitoring modules, current monitoring modules and voltage monitoring modules). Via the telemetry data handling functionality, data from each sensor is sequentially read and recorded, which enables a complete record of environmental conditions, forces applied, elongation, and energy consumption at every stage of a mechanical testing process. Command handling is the functional counterpart of the telemetry data handling. Via the command handling functionality, the operating software may be configured to receive, process, and execute commands that control the system 100 (or system 150) (in this way, the command handling may implement the control means). Via the command handling functionality, incoming commands are processed in (near) real-time, which allows the system to make (near) instant (or rapid) adjustments based on operator input. Actuator handling is used to control the shape memory alloy components 107 (which act as actuators in system 100 (or system 150)). Via the actuator handling functionality, as the shape memory alloy components 107 are heated (e.g. by passing current through the shape memory alloy components), a controller (e.g. a pulse width modulation controller) is used to control (or set) the amount of voltage (or current) that is selectively applied to (or passed through) the shape memory alloy components 107. There is a temperature control loop which acts in cooperation with the controller (under action of the actuator handling functionality) to use the gathered (or measured) temperature data from the shape memory alloy component temperature sensor to set the correct (or a desired) selectively applied voltage (e.g. via a pulse width modulation value or command) such that the activated shape memory alloy components are kept within a desired temperature range. Timeline (or test) execution is used to enable system 100 (or system 150) to perform automated and semi-automated mechanical testing procedures. Via the timeline execution functionality an operator can create mechanical testing timelines that include sequences of operations (e.g. activation sequences), varying test conditions, and checkpoints. Once set, via the timeline execution functionality, the timeline can be executed by the operating software such that the system 100 (or system 150) automatically performs each step in the designated (activation) sequence. Via the timeline execution functionality, an operator may, for example, initiate tensile, creep, or fatigue tests or adjust actuator settings at specific points during a mechanical test. Figure 6 is a flow diagram schematically illustrating a method 600 of (or for) applying a force to an object 103. Method 600 may be implemented using system 100 described above (or system 150 described above). For method 600, the object 103 is secured by a sample holder (such as sample holder 105). For example, a first end of the object 103 may be secured by the sample holder. In method 600, a step 601 comprises applying a first force to the object 103 by selectively applying a (first) voltage to a first subset of a plurality of shape memory alloy components 107, wherein each of the plurality of shape memory alloy components 107 is connected to: a) the object 103 (for example, a second end of the object 103); and b) a biasing means 405 configured to apply a respective return force to the component 107. This biasing means may be configured to bias each respective shape memory alloy component 107 to a respective second (or original) configuration (e.g. by tensioning or stretching each respective shape memory alloy component 107). In method 600, a step 602 comprises applying a second force to the object 103 by selectively applying a (second) voltage to a second subset of the components 107. The first and second subsets may be overlapping. The voltage applied to the first subset may be equal in magnitude to the voltage applied to the second subset. Selectively applying a voltage means applying the voltage to selected components of the plurality of components. The components may be selected such that, collectively, they apply a desired (tensile) force on the object 103. The components may be selected based on their diameter (or cross-sectional area) as described in the first worked example above. The selectively applied voltage may be determined based on (or in response to) user (or operator) input. The selectively applied voltage may be predefined based on an activation sequence. The selectively applied voltage may be determined based (in part) on temperature data from one or more shape memory alloy component temperature sensors (temperature sensors which measure the temperature or provide temperature data on or for one or more of the shape memory alloy components 107). The temperature data may be used in a closed feedback loop to tailor (or adjust) a selectively applied voltage. For example, the selectively applied voltage may be based on a predefined activation sequence, but then (or and) tailored (or adjusted) based on the temperature data (temperature data on the shape memory alloy components of the relevant subset, i.e. the subset that the predefined activation sequence suggests the voltage is selectively applied to) to achieve a desired force on the object 103. For example, at temperature S, to achieve a force of T on the object 103, it may be predefined in an activation sequence that the selectively applied voltage is a voltage of R applied to a subset Q of the shape memory alloy components 107. However, at temperature S’ (S’ >S), to achieve a force of T on the object 103, it may be predefined in an activation sequence that the selectively applied voltage is a voltage of R applied to a subset Q’ of the shape memory alloy components 107 (where Q # Q’). It will be appreciated that this method 600 may be performed using (or on) a computer system, which may be a cloud-based computer system such as described above. For example, the method may be implemented by a control means which may be (or comprise) a processor (such as the processor of the electronics unit described above). Figure 7 schematically illustrates an example of a computer system 1000. This computer system may be used to implement (one or more components of) the system 100 of figure 1a or the system 150 of figure 1b. In particular, the control means and / or the electronic system and / or the operating software may be implemented on (or by or using) system 1000. This computer system 1000 may also be used to implement the method 600 of figure 6. The system 1000 comprises a computer 1002. The computer 1002 comprises: a storage medium 1004, a memory 1006, a processor 1008, an interface 1010, a user output interface 1012, a user input interface 1014 and a network interface 1016, which may be linked together over one or more communication buses 1018. The storage medium 1004 may be any form of non-volatile data storage device such as one or more of a hard disk drive, a magnetic disc, a solid-state-storage device, an optical disc, a ROM, etc. The storage medium 1004 may store an operating system for the processor 1008 to execute in order for the computer 1002 to function. The storage medium 1004 may also store one or more computer programs (or software or instructions or code). These computer programs may comprise instructions which when executed by one or more processors, cause the one or more processors to carry out the method 600. The memory 1000 may be any random access memory (storage unit or volatile storage medium) suitable for storing data and / or computer programs (or software or instructions or code). The processor 1008 may be any data processing unit suitable for executing one or more computer programs (such as those stored on the storage medium 1004 and / or in the memory 1006), some of which may be computer programs according to embodiments of the invention or computer programs that, when executed by the processor 1008, cause the processor 1008 to carry out a method according to an embodiment of the invention such as, for example, method 600 and configure the system 1000 to be a system according to an embodiment of the invention such as, for example, the control means of system 100 (or another component of system 100) or the control means of system 150 (or another component of system 150) and / or to implement the operating software described above. The processor 1008 may comprise a single data processing unit or multiple data processing units operating in parallel, separately or in cooperation with each other. The processor 1008, in carrying out data processing operations for embodiments of the invention, may store data to and / or read data from the storage medium 1004 and / or the memory 1006. The interface 1010 may be any unit for providing an interface to a device 1022 external to, or removable from, the computer 1002. The device 1022 may be a data storage device, for example, one or more of an optical disc, a magnetic disc, a solid-statestorage device, etc. The device 1022 may have processing capabilities - for example, the device may be a smart card. The interface 1010 may therefore access data from, or provide data to, or interface with, the device 1022 in accordance with one or more commands that it receives from the processor 1008. The user input interface 1014 is arranged to receive input from a user, or operator, of the system 1000. The user may provide this input via one or more input devices of the system 1000, such as a mouse (or other pointing device) 1026 and / or a keyboard 1024, that are connected to, or in communication with, the user input interface 1014. However, it will be appreciated that the user may provide input to the computer 1002 via one or more additional or alternative input devices (such as a touch screen). The computer 1002 may store the input received from the input devices via the user input interface 1014 in the memory 1006 for the processor 1008 to subsequently access and process, or may pass it straight to the processor 1008, so that the processor 1008 can respond to the user input accordingly. The user output interface 1012 is arranged to provide a graphical / visual and / or audio output to a user, or operator, of the system 1000. As such, the processor 1008 may be arranged to instruct the user output interface 1012 to form an image / video signal representing a desired graphical output, and to provide this signal to a monitor (or screen or display unit) 1020 of the system 1000 that is connected to the user output interface 1012. Additionally or alternatively, the processor 1008 may be arranged to instruct the user output interface 1012 to form an audio signal representing a desired audio output, and to provide this signal to one or more speakers 1021 of the system 1000 that is connected to the user output interface 1012. Finally, the network interface 1016 provides functionality for the computer 1002 to download data from and / or upload data to one or more data communication networks. It will be appreciated that the architecture of the system 1000 illustrated in figure 7 and described above is merely exemplary and that other computer systems 1000 with different architectures (for example with fewer components than shown in figure 7 or with additional and / or alternative components than shown in figure 7) may be used in embodiments of the invention. As examples, the computer system 1000 could comprise one or more of: a personal computer; a server computer; a mobile telephone; a tablet; a laptop; a television set; a set top box; a games console; other mobile devices or consumer electronics devices; etc.. Additionally, it is possible that some components of the computer system 1000 are not located in the computer 1002 and are, instead, part of a computer network connected to the computer 1002 via the network interface 1016. Additionally or alternatively, the computer system 1000 may comprise multiple computers 1002, e.g. in a network of computers such as a cloud system of computing resources. Modifications It will be appreciated that the methods described have been shown as individual steps carried out in a specific order. However, the skilled person will appreciate that these steps may be combined or carried out in a different order whilst still achieving the desired result. It will be appreciated that embodiments of the invention may be implemented using a variety of different information processing systems. In particular, although the figures and the discussion thereof provide exemplary systems and methods, these are presented merely to provide a useful reference in discussing various aspects of the invention. Embodiments of the invention may be carried out on any suitable data processing device, such as a personal computer, laptop, personal digital assistant, mobile telephone, set top box, television, server computer, etc. Of course, the description of the systems and methods has been simplified for purposes of discussion, and they are just one of many different types of system and method that may be used for embodiments of the invention. It will be appreciated that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks or elements, or may impose an alternate decomposition of functionality upon various logic blocks or elements. It will be appreciated that the above-mentioned functionality may be implemented as one or more corresponding modules as hardware and / or software. For example, the above-mentioned functionality may be implemented as one or more software components for execution by a processor of the system. Alternatively, the above-mentioned functionality may be implemented as hardware, such as on one or more field-programmable-gate-arrays (FPGAs), and / or one or more application-specific-integrated-circuits (ASICs), and / or one or more digital-signal-processors (DSPs), and / or one or more graphical processing units (GPUs), and / or other hardware arrangements. Method steps implemented in flowcharts contained herein, or as described above, may each be implemented by corresponding respective modules; multiple method steps implemented in flowcharts contained herein, or as described above, may be implemented together by a single module. It will be appreciated that, insofar as embodiments of the invention are implemented by a computer program, then one or more storage media and / or one or more transmission media storing or carrying the computer program form aspects of the invention. The computer program may have one or more program instructions, or program code, which, when executed by one or more processors (or one or more computers), carries out an embodiment of the invention. The term “program” as used herein, may be a sequence of instructions designed for execution on a computer system, and may include a subroutine, a function, a procedure, a module, an object method, an object implementation, an executable application, an applet, a servlet, source code, object code, byte code, a shared library, a dynamic linked library, and / or other sequences of instructions designed for execution on a computer system. The storage medium may be a magnetic disc (such as a hard drive or a floppy disc), an optical disc (such as a CD-ROM, a DVD-ROM or a BluRay disc), or a memory (such as a ROM, a RAM, EEPROM, EPROM, Flash memory or a portable / removable memory device), etc. The transmission medium may be a communications signal, a data broadcast, a communications link between two or more computers, etc.

Claims

1. A system for applying a force to an object, the system comprising:a sample holder securable to the object;a plurality of shape memory alloy components secured relative to the sample holder, wherein each of the shape memory alloy components is securable to the object;biasing means configured to apply a return force to each of the components; andcontrol means configured to:apply a first force to the object by selectively applying a voltage to a first subset of the components; andapply a second force to the object by selectively applying a voltage to a second subset of the components.

2. The system of claim 1, wherein the first force is a tensile force and the second force is a tensile force.

3. The system of claim 1 or 2, wherein:each of a third subset of the components has a first cross sectional area; andeach of a fourth subset of the components has a second cross sectional area different from the first cross sectional area.

4. The system of any one of the preceding claims, wherein the biasing means comprises a plurality of tensioners, each tensioner comprising:a) a threaded portion configured to engage with a recess in a fastening block; andb) a spring portion.

5. The system of claim 4, wherein each tensioner comprises an electrically conductive portion, the conductive portion providing an electrical connection between the fastening block and a respective one of the components.

6. The system of claim 5, wherein each of the components comprises a respective first end and a respective second end, andwherein each respective first end is secured to the fastening block by a respective tensioner for that component.

7. The system of claim 6, wherein each of the components comprises a central portion equidistant between the first end and the second end; andwherein each of the components is securable to the object at its respective central portion.

8. The system of any one of the preceding claims, further comprising a clamp carriage configured to be axially slidable within a structural body;wherein the clamp carriage is:a) attached to each of the components; andb) configured to attach to the object such that each of the components is securable to the object via the clamp carriage.

9. The system of any one of the preceding claims, further comprising one or more temperature sensors configured to provide temperature data for the shape memory alloy components;wherein the control means is configured to selectively apply a voltage determined based in part on the temperature data.

10. The system of claim 9, wherein one or more of the temperature sensors is configured to provide temperature data for the object.

11. The system of any one of the preceding claims, further comprising a mechanical property sensor configured to measure a mechanical property of the object.

12. The system of claim 11 when dependent on claim 8, wherein the mechanical property sensor is integrated into the clamp carriage such that the mechanical property sensor is configured to secure the object to the clamp carriage.

13. The system of claim 11 or claim 12, wherein the mechanical property sensor is a strain gauge.

14. The system of claim 13, wherein the strain gauge is arranged as an S-beam load cell.

15. The system of any one of the preceding claims, wherein each of the components is made from an alloy comprising nickel and titanium.

16. A method of applying a force to an object, wherein the object is secured by a sample holder, the method comprising:applying a first force to the object by selectively applying a voltage to a first subset of a plurality of shape memory alloy components, wherein each of the plurality of shape memory alloy components is connected to:a) the object; andb) a biasing means configured to apply a respective return force to the respective component; andapplying a second force to the object by selectively applying a voltage to a second subset of the components.

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