Apparatus for testing thermomechanical loads

Abstract

The invention provides an apparatus for testing a thermomechanical load, comprising gripping portions (3) for gripping a test sample (2) and a frame (1) connecting the gripping portions (3) to each other, the gripping portions (3) having a greater coefficient of thermal expansion than the frame (1). The invention allows the provision of a simplified test device relative to conventional test devices, which is inexpensive than those known test devices.

Description

Technical Field

[0001] The present invention relates to an apparatus for testing thermomechanical loads, and in particular to a testing apparatus designed to introduce biaxial loads in a test sample by means of thermal contraction / expansion combined with thermomechanical loads. Background Art

[0002] Many test equipment systems exist for biaxial and even triaxial testing. Typically, a test equipment system consists of two actuators that apply loads in two directions, or even just one pair of actuators with a linkage system to apply loads in another direction. The same equipment can be used for uniaxial loading if desired.

[0003] These test equipment systems can operate at various temperature levels. When cryogenic temperatures are involved, part or all of the unit is immersed in a coolant.

[0004] For uniaxial testing at low temperatures, several solutions exist within the industry. These primarily consist of standard uniaxial testing machines, where the test specimen and clamping area are enclosed in a cryostat, leaving the actuator external.

[0005] This technique is not as common for biaxial testing at cryogenic conditions as it is for uniaxial testing, but both rely on actuators to apply the load.

[0006] These tests are quite expensive due to the required machinery, the assembly work for each test specimen and the amount of cryogenic liquid required to cool everything. Summary of the Invention

[0007] It is therefore an object of the present invention to provide a test device which is simplified with respect to conventional test devices and which is less expensive than these known test devices.

[0008] With the test rig according to the invention, the disadvantages described can be solved, providing further advantages described below.

[0009] A test rig according to the invention is defined in a first aspect and further optional features are defined in other aspects.

[0010] In particular, the apparatus for testing thermomechanical loads includes a gripping portion for gripping a test sample and a frame connecting the gripping portions to each other, the gripping portion having a thermal expansion coefficient greater than a thermal expansion coefficient of the frame.

[0011] Advantageously, the frame is made of a metallic material, in particular of an alloy of iron and another metal, such as an alloy of iron and nickel, for example an alloy containing 64% iron and 36% nickel.

[0012] Furthermore, the gripping portions are preferably associated in pairs, and a spacer may be disposed between the two gripping portions of the paired gripping portions.

[0013] Advantageously, each gripping portion is attached to the frame by only one attachment element.

[0014] Furthermore, the frame may include a strengthening element.

[0015] According to a possible embodiment, each gripping portion includes a plurality of fixing elements.

[0016] According to two alternative embodiments, the frame includes only a first part disposed on one side of the gripping portion, or the frame includes a first part and a second part disposed on two sides of the gripping portion.

[0017] Furthermore, according to two alternative embodiments, the gripping portion defines two axes, or the gripping portion defines only one axis.

[0018] The main advantages of the test device according to the present invention are as follows:

[0019] Mechanical loading can be achieved without using any actuators, because the loading of the test sample is accomplished by utilizing the deformation of the device caused by the temperature difference. Therefore, only a cooling chamber is required for testing.

[0020] The assembly of the test device will be carried out outside the cryostat to minimize the setup work.

[0021] As long as there is no need for a connection between the test device and the outside, it allows for the simplification of the cooling chamber or the cryostat.

[0022] The testing activity is much cheaper than using standard test devices.

[0023] The same device can be used for uniaxial testing under cryogenic conditions.

[0024] The test device design can be used for test samples of different sizes and thicknesses with only minor modifications. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] For a better understanding of the above explanations and for illustrative purposes only, some non - restrictive drawings schematically depicting actual embodiments are included.

[0026] Figure 1 is a plan view of a test device according to a first embodiment of the present invention, the test device having a test sample placed in position and being placed in a cryogenic chamber;

[0027] Figure 2 is a plan view of a test device according to a second embodiment of the present invention, the test device having a test sample placed in position;

[0028] Figure 3 is a side cross-sectional view of a test device according to a first embodiment of the present invention;

[0029] Figure 4 is a side cross-sectional view of a test device provided with a fixed frame according to a first embodiment of the present invention, the fixed frame being provided with a first or upper part and a second or lower part; and

[0030] Figure 5 is a side cross-sectional view of a test device provided with a fixing element for fixing a test sample to a holding part according to a first embodiment of the present invention. Detailed Embodiment

[0031] The present invention relates to a device for testing thermo-mechanical loads in a test sample 2, the device comprising a frame 1 which is fixed and which is preferably made of any material having a very low coefficient of thermal expansion, for example made of invar alloy, i.e. an iron-nickel alloy having, for example, 64% iron and 36% nickel.

[0032] The frame 1 must be stiffer than the test sample 2 in order to be able to actually apply a load to the test sample 2. To this end, the frame 1 may comprise strengthening elements, as Figure 3 shown.

[0033] The device further comprises holding parts 3 for attaching the test sample 2 to the frame 1, and these holding parts 3 are made of any material having a high coefficient of thermal expansion. The design and dimensions of these holding parts 3 can be modified according to the desired load level.

[0034] According to the embodiment shown, the holding parts 3 are associated in pairs such that the test sample 2 is placed between two of said paired holding parts 3, and a spacer 7 is arranged between said paired holding parts 3.

[0035] By changing the characteristics of the holding parts 3, such as the thickness, width or length of the holding parts 3, the strain introduced into the test sample 2 can be changed. By using different holding parts 3 in each direction, the ratio between the loads in each direction can be established.

[0036] The frame 1 can be designed in any way to provide the required stiffness while allowing the assembly of the test sample 2. For example, the frame 1 has additional connections as Figure 1 shown in.

[0037] The device can be immersed in a cryogenic liquid, such as a cryogenic chamber (not shown), such that the different coefficients of thermal expansion of the frame 1 and the holding parts 3 create a tension in the test sample 2 without the need for any actuators.

[0038] In addition, the gripping part 3 is attached to the frame 1 by means of a single attachment element 5, such as a bolt, which contributes to the self-alignment of the test sample 2.

[0039] The frame 1 can be made of one part, such as Figure 3 the first or lower part 11 shown in Figure 4 or made of two parts, also including the

[0040] second or upper part 12 shown in Figure 5 to increase stiffness and stability. In the case where the frame 1 comprises a first part 11 and a second part 12, there is no risk of unwanted out-of-plane bending.

[0041] In addition, the mass of the device is also important, because the greater the mass, the more cryogenic fluid will be required to cool the entire assembly.

[0042] If the liquid to be used is liquid helium, the cost impact can be significant. Therefore, it is important to minimize the frame mass while maintaining its functionality.

[0043] In Figure 2 a second embodiment of the device according to the invention is shown, which is suitable for uniaxial testing and has a reduced mass compared to Figure 1 the first embodiment shown in

Claims

1. An apparatus for testing thermomechanical loads, the apparatus comprising a gripping portion (3) for gripping a test sample (2), characterized in that, The device further includes a frame (1) connecting the gripping portions (3) to each other, and the coefficient of thermal expansion of the gripping portions (3) is greater than that of the frame (1).

2. The device for testing thermomechanical loads according to claim 1, wherein, The frame (1) is made of a metallic material.

3. The device for testing thermomechanical loads according to claim 1 or 2, wherein, The frame (1) is made of an alloy of iron and other metals.

4. The device for testing thermomechanical loads according to any one of the preceding claims, wherein, The frame (1) is made of an alloy of iron and nickel.

5. The device for testing thermomechanical loads according to claim 4, wherein, The frame (1) is made of an alloy containing 64% iron and 36% nickel.

6. The device for testing thermomechanical loads according to any one of the preceding claims, wherein, The gripping portions (3) are associated in pairs.

7. The device for testing thermomechanical loads according to claim 6, wherein, A spacer (7) is disposed between the two gripping portions (3) of the pair.

8. The device for testing thermomechanical loads according to any one of the preceding claims, wherein, Each gripping portion (3) is attached to the frame (1) only by one attachment element (5).

9. The device for testing thermomechanical loads according to any one of the preceding claims, wherein, The frame (1) includes a strengthening element.

10. The device for testing thermomechanical loads according to any one of the preceding claims, wherein, Each gripping portion (3) includes a plurality of fixing elements (6).

11. The device for testing thermomechanical loads according to any one of the preceding claims, wherein, The frame (1) only includes a first portion (11) disposed on one side of the gripping portion (3).

12. The device for testing thermomechanical loads according to any one of claims 1 to 10, wherein, The frame (1) includes a first portion (11) and a second portion (12) disposed on two sides of the gripping portion (3).

13. The device for testing thermomechanical loads according to any one of the preceding claims, wherein, The gripping portion (3) defines two axes.

14. The device for testing thermomechanical loads according to any one of claims 1 to 12, wherein, The gripping portion (3) only defines one axis.

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