PLANAR TEST SYSTEM

Abstract

An apparatus for applying a force to a specimen is provided. The apparatus comprises: an output rotatable member comprising a plurality of connection points; a plurality of rigid connection means, each comprising a first end and a second end, wherein the first end of each connection

means is pivotably coupled to one of the plurality of connection points of the output rotatable member; a plurality of guide members; and a plurality of specimen holders, each slidably mounted to one of the guide members and pivotably coupled to the second end of one of the plurality of connection means.

Claims

1. An apparatus for applying a force to a specimen, the apparatus comprising: an output rotatable member comprising a plurality of connection points; a plurality of rigid connection means, each comprising a first end and a second end, wherein the first end of each connection means is pivotably coupled to one of the plurality of connection points of the output rotatable member; a plurality of guide members; and a plurality of specimen holders, each slidably mounted to one of the guide members and pivotably coupled to the second end of one of the plurality of connection means.

2. The apparatus of claim 1 further comprising a drive shaft coupled to the output rotatable member.

3. The apparatus of claim 2 further comprising an input rotatable member coupled to the drive shaft.

4. The apparatus of claim 2, further comprising a rigid drive member arranged to rotate the output rotatable member.

5. The apparatus of claim 1, wherein the output rotatable member is a disc.

6. The apparatus of claim 1, wherein there is a first number of connection points and a second number of rigid connection means, and wherein the first number is greater than the second number.

7. The apparatus of claim 6, wherein the connection means are configured to be coupled to different connection points of the plurality of connection points in order to apply two or more different strain paths to a specimen.

8. The apparatus of claim 1, further comprising a rigid base plate.

9. The apparatus of claim 8, wherein the plurality of guide members are coupled to the base plate.

10. The apparatus of claim 8, wherein the base plate comprises a plurality of fixing points arranged to couple to the specimen holders.

11. The apparatus of claim 1, wherein the connection points are distributed in a plane of the output rotatable member.

12. The apparatus of claim 11, wherein the plane of the output rotatable member is perpendicular to an axis of rotation of the output rotatable member.

13. The apparatus of claim 1, wherein each of the plurality of guide members extends in a direction perpendicular to an axis of rotation of the output rotatable member.

14. The apparatus of claim 1, wherein each guide member extends perpendicular to the guide members adjacent to it.

15. The apparatus of claim 1, wherein the plurality of guide members define a plane parallel to the plane of the output rotatable member.

16. The apparatus of any of claim 1, wherein each guide member comprises two rails orientated parallel to one another.

17. The apparatus of claim 1 wherein the plurality of specimen holders hold the specimen.

18. The apparatus of claim 1 further comprising an environmental chamber housing the apparatus.

19. The apparatus of claim 1, further comprising a temperature control for controlling a temperature of the specimen.

20. The apparatus of claim 19, wherein the temperature control is configured to control a heating rate of the specimen and a subsequent cooling rate of the specimen in order to simulate hot forming and cold quenching of the specimen.

21. The apparatus of claim 1, further comprising a measurement system configured to measure a strain in the specimen and/or a force applied to the specimen.

22. The apparatus of claim 21, further comprising at least one sensor configured to sense the force applied to the specimen.

23. The apparatus of claim 22, further comprising at least one sensor configured to sense the strain in the specimen.

24. A method for applying a force to a specimen, the method comprising: providing an apparatus, the apparatus comprising: an output rotatable member comprising a plurality of connection points, a plurality of rigid connection means, each comprising a first end and a second end, wherein the first end of each connection means is pivotably coupled to one of the plurality of connection points of the output rotatable member, a plurality of guide members, and a plurality of specimen holders, each slidably mounted to one of the guide members and pivotably coupled to the second end of one of the plurality of connection means; providing a specimen, wherein the plurality of specimen holders hold the specimen; rotating the output rotatable member to apply a force to the specimen.

25. The method of claim 24, wherein the step of rotating comprises applying a linear force to a rigid drive member arranged to rotate the output rotatable member.

26. The method of claim 24, the method further comprising: controlling a temperature of the specimen.

27. The method of claim 26, wherein the apparatus is housed in an environmental chamber, and the step of controlling the temperature of the specimen comprises controlling a temperature within the environmental chamber containing the specimen.

28. The method of claim 26, wherein the step of controlling the temperature of the specimen comprises controlling a heating rate of the specimen and a subsequent cooling rate of the specimen in order to simulate hot forming and cold quenching of the specimen.

29. The method of claim 24, further comprising measuring a strain in the specimen and/or a force applied to the specimen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0046] FIG. 1A is a top view of an apparatus according to a preferred embodiment of the present invention;

[0047] FIG. 1B is a side view of the apparatus of the preferred embodiment shown in FIG. 1 taken along line A-A;

[0048] FIG. 2 is a bottom view of the apparatus according to the preferred embodiment of the present invention;

[0049] FIG. 3 is a top view of a specimen for use with the apparatus;

[0050] FIG. 4 is a perspective view of the apparatus of the preferred embodiment of the present invention together with the specimen shown in FIG. 3;

[0051] FIG. 5 is a schematic illustration of a system including the apparatus according to an embodiment of the present invention;

[0052] FIG. 6A is a perspective view of the apparatus illustrating the position of the components of the apparatus at a first point during operation of the apparatus;

[0053] FIG. 6B is a perspective view of the apparatus illustrating the position of the components of the apparatus at a second point during operation of the apparatus; and

[0054] FIGS. 7A to 7E illustrate different modes of operation of the apparatus of the preferred embodiment.

DETAILED DESCRIPTION

[0055] With reference to FIG. 1A, a top view of a biaxial force apparatus 100 according to a preferred embodiment is shown. The apparatus 100 comprises an output rotatable member 102, a plurality of connection points 104, a plurality of rigid connection means 106, a plurality of guide members 108 and a plurality of specimen holders 110. The apparatus 100 is designed to apply a biaxial force to a specimen (not shown), which is held in place by the plurality of specimen holders 110. The apparatus 100 can be formed to be small in dimension; for example, the apparatus can be 250 mm250 mm100 mm with a load capacity of 80 kN. Alternatively, the apparatus could be larger than this in order to accommodate more substantial material specimens, or the apparatus could be formed smaller than the above dimensions. The load capacity of the apparatus is dependent on the strength of the components in the apparatus.

[0056] In the preferred embodiment of the apparatus 100 there are four specimen holders 110, each mounted on one of four guide members 108. The specimen holders 110 are arranged in two pairs. Each pair of specimen holders 110 is arranged along an axis, and the axes along which each of the two pairs of specimen holders 110 lies are orthogonal to one another. Each of the four guide members 108 extends perpendicular to the two guide members adjacent to it. The four guide members 108 are arranged to lie in a plane parallel to a plane defined by the axes of alignment of the specimen holders 110. This arrangement facilitates the application of a planar, biaxial, force to a specimen; each pair of specimen holders 110 can apply a force to a specimen along a single axis when the apparatus is in use.

[0057] In this preferred embodiment, each of the plurality of guide members 108 comprises two rails, which are aligned parallel with one another. The specimen holders 110 are slidably mounted on the respective guide members 108 such that they can slide back and forth along the rails of the guide member with very low friction. In other embodiments, each of the guide members may comprise only one rail, or may comprise more than two rails. Alternatively, the guide members 108 may be any other geometry which facilitates the sliding of the specimen holders 110.

[0058] In the preferred embodiment, the output rotatable member 102 is formed to have a disc shape, with the plurality of connection points 104 distributed in a plane on a surface of the disc. In this embodiment, there are at least four connection points. Each of the plurality of rigid connection means 106 are pivotably coupled at a first end to one of the connection points 104 and at a second end to one of the specimen holders 110. Clearly, in this preferred embodiment there are four rigid connection means 106. The connection points 104 can be threaded holes, for example for receiving bolts or screws, or unthreaded holes for push fastenings. Alternatively, any other form of connection points suitable for pivotably coupling a rigid connection means to the output rotatable member can be used.

[0059] In some embodiments, there may only be two specimen holders and two connection means and the apparatus may be arranged to apply a uniaxial force rather than a biaxial one. Alternatively, the apparatus may have any other number of specimen holders and connection means necessary to apply the desired strain path to a specimen.

[0060] Preferably, there are more connection points than connection means, such that the connection means can be configured in different arrangements by connecting the connection means to different of the plurality of connection points in order to achieve the desired strain path. For example, uniaxial, uniaxial to plane strain, plane strain, plane stain to biaxial, and biaxial strain can all be achieved with the apparatus by adjusting which of the plurality of the connection points the connection means are coupled to. For example, as shown in FIG. 1A, the plurality of connection points 104 are distributed across the output rotatable member 102; more connection points 104 are provided than there are connection means 106, enabling the configuration of the connection means 106 to be altered.

[0061] With reference to FIG. 1B, a side view of the apparatus 100 of the preferred embodiment is shown. It can be seen from FIG. 1B that the apparatus 100 further comprises a drive shaft 112 and an input rotatable member 114. The output rotatable member 102 is coupled to the drive shaft 112, which is in turn coupled to the input rotatable member 114. The drive shaft 112 has an axis of rotation 118 which is orientated perpendicular to the plane of the output rotatable member 102 in this preferred embodiment. The plane of the output rotatable member 102 is also parallel to the plane in which the guide members 108 extend.

[0062] FIG. 2 shows a perspective view of the apparatus 100, illustrating the input force mechanism of this embodiment. With reference to FIG. 2, it can be seen that the apparatus 100 is further provided with a rigid drive member 116. A first end of the rigid drive member 116 is pivotably coupled to the input rotatable member 114 and a second end of the rigid drive member 116 is coupled directly to a movable jaw 120 of a uniaxial test machine. The jaw 120 is not part of the apparatus 100.

[0063] In use, the movable jaw 120 moves in a linear fashion and displaces the drive member 116. The displacement of the drive member 116 rotates the input rotatable member 114, which in turn rotates the drive shaft 112. The drive shaft 112 rotates around the axis of rotation 118, thereby rotating the output rotatable member 102 to which it is coupled around the axis of rotation 118. This causes the rigid connection means 106 to push the plurality of specimen holders 110 away from the axis of rotation 118, or pull the specimen holders 110 towards the axis of rotation 118, depending on the direction of rotation of the output rotatable member 102. In this preferred embodiment, the drive shaft 112, output rotatable member 102 and input rotatable member 114 all rotate around the axis of rotation 118.

[0064] In other embodiments, the output rotatable member can be driven by a different mechanism. For example, the drive member may be coupled directly to the output rotatable member and driven by the moving jaw 120. Alternatively, the drive member can be driven by a different mechanism. In still other embodiments, the apparatus may not comprise a drive member arranged to drive the output rotatable member; instead the output rotatable member can be driven by another means, for example a motor may be arranged to turn the drive shaft directly.

[0065] With reference to FIG. 3, an exemplary specimen 300 for use in combination with the apparatus 100 has a cruciform shape. This facilitates attachment of the specimen to the perpendicularly orientated pairs of specimen holders 110 of the preferred embodiment of the apparatus. The specimen 300 has fillets 334 to reduce stress concentrations in the corners of the cruciform and slots 332 which act to distribute the applied load more uniformly to the test area 330. The thickness (gauge) of the test area 330 is reduced to ensure that the major plastic deformation, such as necking or fracture, induced during use of the apparatus with the specimen occurs in the test area 330 of the specimen 300. A different geometry and material of specimen can be used for determining the forming limit diagram of different metals.

[0066] The specimen 300 attaches to the specimen holders 110 via attachment means 336. The attachment between the specimen 300 and the specimen holders 110 is described with reference to FIG. 4. In the embodiment shown in FIG. 4, each of the specimen holders 110 comprises a top plate 422. The specimen 300 is placed under the top plate 422 and the top plate 422 is fixed to the body of the specimen holders 110 such that the fixing means pass through the attachment means 336 of the specimen 300. The fixing means can be bolts or screws or any other suitable fixing means. In other embodiments the specimen holders 110 may not comprise a top plate 422 and may instead hold the specimen 300 by means of a clamp or grip arrangement. Alternatively, any other suitable means of securing the specimen to the specimen holders can be used so long as they allow a deforming force to be applied to the specimen 300.

[0067] The apparatus 100 can further comprise stops 424 which limit the displacement of the specimen holders 110 along the guide members 108. Therefore, the length of the rigid connection means 106 and their connection points 104 should be adjusted such that the required strain and strain paths are produced within the specimen 300 within the limited range of motion of the specimen holders 110; after the specimen holders 110 reach the stops 424, no more force can be applied to the specimen 300 by the apparatus in order to deform it.

[0068] The apparatus can further comprise a base plate 126. The base plate 126 can be a rigid plate to which components of the apparatus such as the stops 424 and/or guide members 108 can be securely attached. The base plate 126 preferably has further fixing points to fix, for example, the specimen holders 110 in order to prevent them sliding along the guide members 108. For example, the base plate may comprise a plurality of fixing points arranged such that each of the specimen holders can be coupled to one (or more) fixing point. This arrangement can be useful for the creation of different strain paths in the specimen. One or more specimen holders may be coupled to the fixing points. Alternatively, when a biaxial strain path is applied, none of the specimen holders are coupled to the base plate. It is to be understood that when all of the specimen holders are coupled to the base plate, the specimen holders will not slide along the guide members and thus no force would be applied to the specimen held by the specimen holders. The specimen holders 110 may have threaded holes in them to facilitate bolting or screwing of the specimen holders 110 to the base plate 126. Alternatively the specimen holders 110 may be attached to the base plate 126 by any other suitable fixing means.

[0069] In some embodiments, a system is provided in which the apparatus 100 described above is housed in an environmental chamber 500, as shown in FIG. 5. Optionally, the system may further comprise one or both of a temperature feedback control system 550 and a measurement system 558. The environmental chamber 500 provides an isothermal environment in which deformation of the specimen 300 can occur. Commercial environmental chambers can be used. The temperature within the environmental chamber can be controlled, or the temperature of the actual specimen within the environmental chamber can be controlled independently of the ambient temperature within the environmental chamber.

[0070] In other embodiments, the apparatus is not housed in an environmental chamber as shown in FIG. 5. Instead, a system is provided comprising the apparatus 100 and the specimen 300, where the specimen is held in place by the specimen holders 110. The temperature of the specimen 300 can be controlled such that the temperature of the specimen is isothermal after temperatures mimicking the heating and cooling processes experienced during material formation by HFQ, for example, have been applied to the specimen.

[0071] A closed loop temperature feedback control system 550 can be used to control the temperature of the specimen itself (both when the specimen is in the environmental chamber and when it is not) or to control the temperature within the environmental chamber. For example, a thermocouple or other temperature sensor 552, such as an infrared pyrometer, can be integrated into the specimen 300 or placed in the vicinity of the specimen 300. The sensing result of the temperature sensor 552 can feed back into the temperature control system 550, and the temperature can be adjusted based on the sensing result. Alternatively, or additionally, a temperature sensor 554 can be used to sense the ambient temperature inside the environmental chamber 500. The sensing result of temperature sensor 554 can feed into the temperature control system 550 and the temperature within the chamber 500 can be adjusted accordingly.

[0072] In some embodiments, an automatic, electronic control system can be used to program or otherwise define a temperature profile. This can be integrated into the temperature feedback control system 550 described above. Comparison between a programmed temperature and the temperature sensing results can be used to automatically adjust the input to the temperature control so that the temperature of the specimen is adjusted in accordance with the programmed temperature. For example, the temperature control system 550 can replicate the temperatures, and temperature variations, experienced during a hot forming and cold quenching manufacturing process. In this way, the temperature history of the specimen can be controlled.

[0073] A method of using the apparatus 100 to apply a biaxial force to a specimen is described with reference to FIGS. 6A and 6B. FIG. 6A shows the position of the components of the apparatus 100 at a first point in time, T1. In use, a specimen, for example the specimen described above with reference to FIG. 3, would be provided in the specimen holders 110, as shown in FIG. 4 for example.

[0074] In the preferred embodiment, the output rotatable member is rotated by means of a uniaxial force applied to the drive member 116. The uniaxial force is provided by the linear displacement of the movable jaw 120 of a conventional uniaxial test machine. This uniaxial force rotates the input rotatable member 114, which in turn rotates the drive shaft 112 to which it is coupled. As the drive shaft rotates, it rotates the output rotatable member to which it is also coupled. All three of these components rotate around the rotational axis 118. At a time T2, shown in FIG. 6B, the output rotatable member 102 has rotated approximately 30 degrees around the axis of rotation 118 from its position as shown in FIG. 6A at a time T1. The rotation of the output rotatable member 102 causes the rigid connection means 106, which are pivotably coupled to the connection points 104 of the output rotatable member 102, to slide the specimen holders 110 along the guide members 108. This movement causes a force to be applied to the specimen fixed to the specimen holders 110.

[0075] Point T2 can be earlier or later in time than point T1. If the output rotatable member 102 rotates clockwise around the axis of rotation 118 (when the apparatus is viewed from above as in FIG. 6A), T2 is later in time than point T1 and the force applied to the specimen is tensile. Alternatively, if the output rotatable member 102 rotates anti-clockwise around the axis of rotation 118, T2 is earlier in time than point T1 and the force applied to the specimen is compressive.

[0076] When the apparatus 100 is integrated into the system described with reference to FIG. 5, information regarding material failure can be obtained by applying a biaxial, planar, force to the specimen 300 by the method described above (with reference to FIGS. 6A and 6B) after the specimen has been heated and cooled to mimic the hot forming and cold quenching manufacturing process. Tests to determine the forming limit diagram can then be conducted at a constant, elevated, specimen temperature; the temperature of the specimen is controlled by the temperature control system 550 as described above with reference to FIG. 5.

[0077] The specimen 300 can be directly heated by a variety of methods. For example, one or more of the following methods of heating the specimen 300 can be used: resistance heating, in which an electric current is applied to the specimen through two electrodes; induction heating in which an electromagnetic field is used to heat the specimen through eddy currents generated in the specimen; and thermal conduction heating in which the specimen is heated by direct contact with a thermally conductive material. The thermally conductive material can be heated by a furnace or by any other method. Alternatively, any other possible method of heating the specimen can be used.

[0078] Methods of cooling the specimen 300 could comprise one or more of convection cooling or conduction cooling, though the cooling of the specimen 300 is not limited to these methods. The cooling rate must be rapid, as this is a critical condition for the hot stamping and cold die quenching process. In convection cooling, the specimen is exposed to a controlled stream of air, gaseous coolant, water or mist spray; this is a simple but unreliable method of cooling. In conduction cooling, the specimen is in direct contact with a thermal conductive material so that thermal conduction occurs away from the specimen and into the thermally conductive material.

[0079] The force applied to the specimen 300 during operation of the apparatus 100 is measured by a force sensor. The force sensor 128 can be embedded into one of the plurality of specimen holders 110, as shown in FIGS. 1 and 5 for example. Alternatively, the force sensor 128 can be located anywhere else in the system suitable for determining the force applied to the specimen.

[0080] The arrangement of the specimen holders 110 into two pairs of opposing specimen holders, where each pair is orientated perpendicular to the other pair and all four specimen holders are arranged in a plane, facilitates the application of a force to each end of the specimen 300 when the apparatus 100 of the preferred embodiment is in use. As each specimen holder 110 can be configured to displace an equal distance along the guide members 108 when the output rotatable member 102 is rotated, each end of the specimen 300 is pushed or pulled (depending on whether the apparatus is operating in compression or tension) an equal distance in each direction by the sliding specimen holders 110 by which it is held. Therefore, strain rate is uniform and the central test area 330 remains located at the centre of the specimen 300, even during the deformation of the specimen 300.

[0081] Furthermore, this arrangement can facilitate the application of a constant strain rate to the specimen 300, if the output rotatable member 102 is rotated at a constant speed. The strain undergone by the specimen 300 during the operation of the apparatus 100 is calculated using a strain sensor 556. In preferred embodiments, the strain sensor 556 uses digital image correlation (DIC). A (stochastic) speckle pattern can be sprayed onto the test area 330 of the specimen 300 before deformation, and a camera used to track the subsequent movement of the speckles in the pattern during deformation of the specimen. Images from the camera can then be analysed to determine the deformation history of the material specimen. Alternatively, the strain sensor 556 can be another kind of sensor, for example one or more linear potentiometers arranged to measure displacement of an edge or edges of the specimen.

[0082] The planar testing arrangement provided by the apparatus of the preferred embodiment facilitates the recording of the entire deformation history of the specimen; in contrast, time-dependent measurement of the strain in the specimen is very difficult to measure using conventional out-of-plane and in-plane methods.

[0083] Any other suitable methods of determining force and/or strain rate can also be used. The sensing results of the force sensor 128 and/or the strain sensor 556 are measured by the measurement system 558 during the specimen deformation process in which a planar, biaxial force is applied by the apparatus 100 of the preferred embodiment. This facilitates the determination of forming limit diagrams of the specimen material under conditions which mimic the manufacturing processes of the sheet metal.

[0084] As mentioned above, the apparatus 100 of the preferred embodiment can be used to apply different strain paths to the specimen 300 by varying the length and connection points of the connection means 106. These different strain pathsuniaxial, uniaxial to plane strain, plane strain, plane strain to biaxial, and biaxialare described below with reference to FIGS. 7A-7E. Each of FIGS. 7A-E shows a schematic of the apparatus 100 for each of the strain paths (on the left) and the direction of the forces experienced by the specimen 300 (on the right). In these examples, an end of the specimen 300 (not shown) is held by each of the specimen holders 110 shown in FIGS. 7A to 7E.

[0085] To achieve uniaxial strain, two opposing specimen holders are disconnected from the output rotatable member 102 and the specimen is held only by the other two opposing and connected specimen holders 110 which are each connected to the output rotatable member by a connection means. Therefore, when the apparatus is in use and the output rotatable member 102 is rotated, a force is only applied to two opposing ends of the specimen (as shown in FIG. 7A).

[0086] Plane strain can be achieved by fixing the two disconnected specimen holders to the base plate 126. The specimen holders 110 can be fixed by bolts or screws or other fastening means. The disconnected specimen holders 110 could also be fixed any other way that prevents them from sliding along the guide members 108; for example, they could be fixed to the guide members 108 themselves. The two connected specimen holders 110 are still free to slide along the guide members, as in the application of uniaxial strain. However, to form a plane strain path, the specimen is held in place by all four specimen holders 110. Therefore, the specimen is prevented from deforming in the same way as in the uniaxial strain scenario (FIG. 7C), for example, thinning of the specimen in the direction perpendicular to the direction of applied force is prevented by the opposing pair of fixed specimen holders 110. In plane strain, the tensile force applied to the specimen by the fixed specimen holders 110 counteracts thinning of the specimen in the direction perpendicular to the two connected and sliding specimen holders.

[0087] For biaxial force, all four specimen holders 110 are connected to the output rotatable member 102, preferably with connection means 106 of equal length, and each specimen holder 110 holds an end of the specimen (FIG. 7E).

[0088] A capability of the invention is shown in FIG. 7B. All four specimen holders 110 are connected to the output rotatable member 102 and each specimen holder 110 holds an end of the specimen. However, the lengths and orientations of the connection means 106 are adjusted so that the specimen is prevented from stretching as much as in the uniaxial case of FIG. 7A, but without two of the four ends of the specimen being held fixed, as in the plane strain case. For example, a first pair of opposing connection means 106 are shorter than a second pair of opposing connection means 106 and are orientated in the opposite direction to the first pair in order to control compression of the specimen when the second pair applies a tensile force to the specimen (FIG. 7B).

[0089] The intermediate strain paths between plane strain and biaxial strain and between uniaxial and plane strain are shown in FIG. 7D. All four specimen holders 110 are connected to the output rotatable member 102 and each specimen holder 110 holds an end of the specimen. However, the lengths and orientations of the connection means 106 are adjusted to apply an unequal tensile biaxial force in orthogonal directions. For example, a first pair of opposing connection means 106 are shorter than a second pair of opposing connection means 106 (FIG. 7D). In the uniaxial to plane strain case, the tensile force applied to the specimen by two opposing specimen holders 110 is less than the force required to prevent thinning of the specimen due to the displacement of the other two opposing specimen holders 110. The overall force on the specimen is therefore compressive along one axis and tensile along another axis. In the plane to biaxial strain case, the force applied by one pair of opposing specimen holders 110 to the specimen is less than that applied by the other pair of opposing specimen holders 110 but more than the force required to prevent thinning of the specimen. The force on the specimen is then tensile in all directions. Different connection points and different lengths of connection means are used to achieve these two different intermediate strain paths.

[0090] As illustrated by FIGS. 7A to 7E, to achieve two or more of the above strain paths (uniaxial, uniaxial to plane strain, plane strain, plane strain to biaxial, and biaxial) with the same apparatus, it is preferable that more connection points 104 are provided than the number of connection means 106. For example, the connection means 106 are coupled to different connection points 104 in FIGS. 7E and 7D to enable the application of biaxial strain and an intermediate strain path between plane strain and biaxial strain to a specimen, respectively. As such, a change in the configuration of the apparatus to enable the realisation of two or more different strain paths can be facilitated, without the requirement to replace or remove any components of the apparatus.

[0091] As described above, the apparatus 100 facilitates a linear strain path in a specimen 300, an isothermal temperature distribution in the test area 330 of the specimen 300 and a constant strain rate during deformation of a specimen. The system described above, either with or without the environmental chamber 500, also facilitates precise control of these conditions. A linear strain path can be controlled by using different lengths and combinations of connection means 106 and connecting them to different connection points 104. The temperature of the specimen 300, both the heating and cooling temperature profile and the subsequent isothermal temperature, can be controlled by the feedback control system 550. Control of the rotation of the output rotatable member 102 enables the application of a constant strain rate to the specimen during deformation.

[0092] Other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known and which may be used instead of, or in addition to, features described herein. Features that are described in the context of separate embodiments may be provided in combination in a single embodiment. Conversely, features which are described in the context of a single embodiment may be also provided separately or in any suitable sub-combination.

[0093] It should be noted that the term comprising does not exclude other elements or steps, the term a or an does not exclude a plurality, a single feature may fulfil the functions of several features recited in the claims and reference signs in the claims shall not be construed as limiting the scope of the claims. It should be noted that the Figures are not necessarily to scale; emphasis instead generally being placed upon illustrating the principles of the present disclosure.

[0094] The work leading to this invention has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement number 604240.