Cryogenic test apparatus

Abstract

Cryogenic test apparatus comprising: a load train 27 with a pair of opposed catches 73a, 74a; and a specimen cassette 60 comprising a test portion (80, figure 4, not shown), and a handle (82a,82b) with a pair of opposed projections (83a,84a) at an end of the test portion. The catches and the specimen are immersed in a cryogenic liquid. The handle fits between the catches with each catch contacting an underside of a respective one of the projections; and the load train is configured to apply tensile force to the test portion of the specimen by pulling on the undersides of the projections with the catches. A claim to a load train for cryogenic apparatus having an actuation rod and other features is included in the claims.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to cryogenic test apparatus, a load train for a cryogenic test apparatus, and an associated method. The term “cryogenic” is used herein to refer to temperatures below 120K (or -153 degC). For example, a cryogenic liquid is a liquid (such as liquid nitrogen) at a temperature below 120K. BACKGROUND OF THE INVENTION

[0002] Quantifying the properties of materials and systems at cryogenic temperatures involves specialist test equipment. Test machines may be equipped with cryocoolers or immersion chambers. These are typically bespoke machines that are adapted forms of standard uniaxial servo-hydraulic or electromechanical test frames, with the addition of temperature chambers, immersion cryostats, or continuous flow cryostats. SUMMARY OF THE INVENTION

[0003] A first aspect of the invention provides cryogenic test apparatus comprising: a load train with a pair of opposed catches; and a specimen comprising a test portion, and a handle with a pair of opposed projections at an end of the test portion; wherein the catches and the specimen are immersed in a cryogenic liquid; each catch contacts a respective one of the projections; and the load train is configured to apply tensile force to the test portion of the specimen by pulling on the projections with the catches.

[0004] Optionally the catches are made from a single piece of material.

[0005] Optionally the catches are substantially fixed with respect to each other, in other words the catches cannot move with respect to each other.

[0006] Optionally the apparatus further comprises a catch plate, the catch plate comprising the pair of catches.

[0007] Optionally the load train further comprises an actuation rod, and a pair of retaining parts removably fastened to the actuation rod by fasteners; and the catch plate is clamped between the retaining parts.

[0008] Optionally the retaining parts are removably fastened to each other by fasteners.

[0009] Optionally the projections have concave curved load-bearing surfaces; and the catches have convex curved load-bearing surfaces each contacting a concave curved load-bearing surface of a respective one of the projections.

[0010] Optionally the load train further comprises an actuation rod which carries the catches and is immersed at one end in the cryogenic liquid.

[0011] Optionally the actuation rod comprises a load introduction rod which is immersed at one end in the cryogenic liquid; a grip pad which is not immersed in the cryogenic liquid; and a j oint between the load introduction rod and the grip pad; wherein the joint comprises a thermally insulating gasket which impedes the flow of thermal energy from the grip pad to the load introduction rod.

[0012] Optionally the handle fits into a socket between the catches, the socket comprising a rear wall which contacts the handle.

[0013] Optionally the handle is a first handle at a first end of the test portion, the projections are first projections, and the catches are first catches; the specimen comprises a second handle with a pair of opposed projections at a second end of the test portion; and the apparatus further comprises a load reactor comprising a pair of opposed second catches; wherein the second catches are immersed in the cryogenic liquid; each second catch contacts a respective one of the second projections; and the load reactor is configured to react the tensile force by pulling on the second projections with the second catches.

[0014] Optionally the apparatus further comprises a dewar which contains the catches, the specimen and the cryogenic liquid.

[0015] Optionally the apparatus further comprises a load sleeve in the dewar, wherein the sleeve contains the catches and the specimen; and an outer casing containing the dewar, wherein the handle is at a first end of the test portion; the specimen is joined to the load sleeve by a first joint at a second end of the test portion; the load sleeve is joined to the outer casing by a second joint; and a load path is provided for the tensile force from the load train to the outer casing via the load sleeve and the first and second joints, so that the outer casing can react the tensile force.

[0016] Optionally the cryogenic liquid is liquid nitrogen.

[0017] Optionally the load sleeve has perforations. Optionally the perforations enable the liquid nitrogen to flow through the load sleeve via the perforations and into contact with the test portion.

[0018] Optionally each catch has a front face and a rear face; each projection has a front face and a rear face; the rear face of each catch contacts the rear face of a respective one of the projections; and the load train is configured to apply the tensile force to the test portion of the specimen by pulling on the rear faces of the projections with the rear faces of the catches.

[0019] A further aspect of the invention provides a method of testing a specimen with the apparatus of the preceding aspect, the method comprising: fitting the handle between the catches; immersing the catches and the specimen in the cryogenic liquid; and applying tensile force to the test portion of the specimen by pulling on the projections with the catches.

[0020] A further aspect of the invention provides a load train for a cryogenic test apparatus, the load train comprising; an actuation rod; a pair of retaining parts removably fastened to the actuation rod by fasteners; and a catch plate clamped between the retaining parts, wherein the catch plate comprises a socket with a rear wall, and an entrance between an opposed pair of catches. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

[0022] Figure 1 is an isometric view of cryogenic test apparatus;

[0023] Figure 2 is a cross-sectional view of the cryogenic test apparatus of Figure 1;

[0024] Figure 3 is an isometric view of a load sleeve;

[0025] Figure 4 is an isometric view of a specimen cassette;

[0026] Figure 5 is an isometric view of the specimen cassette with a retaining part removed;

[0027] Figure 6 is a cross-sectional view of the specimen cassette;

[0028] Figure 7 is a cross-sectional view through parts of the apparatus. DETAILED DESCRIPTION OF EMBODIMENT(S)

[0029] Cryogenic test apparatus 1 shown in Figure 1 comprises an outer casing with a cylindrical body 10 which contains a dewar 40 shown in Figure 2. The dewar 40 is a commercial off-the-shelf item, comprising a double-walled vacuum flask configured to contain a cryogenic liquid (typically liquid nitrogen). In the cross-section of Figure 2, the double-walled construction of the dewar 40 is not shown for the sake of simplicity. The dewar 40 maintains the temperature at -196 degC, or any other suitable cryogenic temperature.

[0030] A load sleeve 54 shown in Figure 3 is fitted inside the dewar 40 via the open top of the dewar 40. The load sleeve has a cylindrical wall 50 with perforations 51, and a flange 52 at its upper end with fastener holes 53.

[0031] The perforations 54 act primarily to reduce the thermal mass of the load sleeve 54.

[0032] The perforations 51 also make it easy for liquid nitrogen to move through the cylindrical wall 50 via the perforations and into contact with the specimen The perforations 51 facilitate free movement of the cryogenic liquid through the cylindrical wall 60 and thus a greater volume capacity for cryogenic liquid in the test chamber. This high volume capacity reduces the frequency at which the dewar 40 must be topped up with cryogenic liquid.

[0033] The test apparatus 1 further comprises a load train 27, best shown in Figure 2, comprising a two-part actuation rod. The two-part actuation rod comprises a SAE / ANSI / AISI316 stainless steel load introduction rod 21 with a flange 27 at its distal end which is received in the load sleeve 54 within the dewar 40 (and hence is immersed in the cryogenic liquid); and a grip pad 20 which is not immersed in the cryogenic liquid.

[0034] An advantage of SAE / ANSI / AISI 316 stainless steel is that its strength significantly increases as temperature decreases.

[0035] In use, a test machine (not shown) grips the grip pad 20 and pulls up to place the specimen in tension. The grip pad 20 may have a threaded hole for a lifting eye.

[0036] The load introduction rod 21 and the grip pad 20 meet at a joint comprising a flange 23 at an end of the load introduction rod 21 connected to a flange 22 at an end of the grip pad 20 by fasteners 24. A thermally insulating gasket 25 prevents contact between the flanges 22, 23. The gasket 25 impedes the flow of thermal energy from the grip pad 20 to the load introduction rod 21. The gasket 25 may be made from any suitable thermally insulating material, for example a polymer such as Nylon 6.

[0037] An air pocket may also be machined into the flanges 22, 23 to augment the insulating effect of the gasket 24.

[0038] The load sleeve 54 contains a specimen cassette 60 shown in detail in Figures 4-6. The upper half of the specimen cassette 60 is a mirror image of the lower half.

[0039] The specimen cassette 60 comprises first and second pairs of retaining parts 61a, 62a; 61b, 62b. Each retaining part 61a, 62a at the top of the specimen cassette 60 is removably fastened to the flange 27 at the distal end of the load introduction rod 61 by five threaded fasteners, one of which is indicated at 63a in Figure 7. Each retaining part 61b, 62b at the bottom of the specimen cassette 60 is removably fastened to the base of the load sleeve by threaded fasteners 63b, one of which is indicated at 63b in Figure 7.

[0040] First and second catch plates 70a,b, shown most clearly in Figure 6, are clamped between the retaining parts 61a, 62a; 61b, 62b. The retaining parts 61a, 62a; 61b, 62b are removably fastened to each other by fasteners 71a,b which pass through holes 72a in the catch plates 70a,b. The fasteners 63a, 71a; 63b, 71b can be removed to separate the retaining parts, enabling each catch plate 70a,b to be removed and replaced by another catch plate, with a different geometry, if required for a different geometry of specimen. The fasteners 71a,b can be tightened to securely clamp the catch plate between the retaining parts.

[0041] Each catch plate 70a,b is cut out to form a socket with a rear wall 75a,b, and an entrance between an opposed pair of first hooks or catches 73a, 74a; 73b, 74b. The catches are inwardly directed towards each other. Each catch has a flat front face, and a curved rear face.

[0042] The test apparatus 1 is used to test a specimen comprising a test portion 80, and first and second handles 82a,b at each end of the test portion 80. The test portion has a hole 81 which is designed to fail when the test portion 80 is in tension. By way of example, the specimen may be an adapted open-hole fatigue ‘T Type’ to CSN standard EN 6072, with added handles 82a,b.

[0043] Each handle 82a,b comprises a pair of opposed projections, or lugs, 83a, 84a; 83b, 84b. Each projection 83a, 84a; 83b, 84b has a flat front face, and a curved rear face.

[0044] Each handle 82a,b fits snugly into the socket between the catches, with the curved rear face of each catch contacting the curved rear face of a respective one of the projections 83a, 84a; 83b, 84b, and the flat rear face 75a, 75b of the socket contacting the front faces of the projections 83a, 84a; 83b, 84b.

[0045] The load train 27 is configured to apply tensile force to the test portion 80 of the specimen by pulling on the rear faces of the first projections 83 a, 84a of the first handle 82a with the rear faces of the first catches 73a, 74a of the first catch plate 70a.

[0046] The second catch plate 70b acts as a load reactor, configured to react this tensile force by pulling on the rear faces of the second projections 83b, 84b with the rear faces of the second catches 73b, 74b.

[0047] The rear faces of the projections 83a, 84a; 83b, 84b have concave curved loadbearing surfaces; and the rear faces of the catches 73a, 74a; 73b, 74b have matching convex curved load-bearing surfaces each contacting a concave curved load-bearing surface of a respective one of the projections. An exemplary one of the convex curved load-bearing surfaces is labelled 85a in Figure 6 and an exemplary one of the concave curved load-bearing surfaces is labelled 86b in Figure 6.

[0048] As shown in Figure 7, the specimen cassette 60 is joined to the base of the load sleeve by a first joint with fasteners 63b at the (lower) second end of the test portion 80. At the top of the assembly, the load sleeve is joined to the outer casing 10 by a second joint described below.

[0049] A pair of rings 31,32 are fitted inside the top of the load sleeve.

[0050] The ring 32 may be made from insulating foam.

[0051] The ring 31 is a guide ring to ensure accurate alignment of the load train 27 so that the specimen is not loaded eccentrically.

[0052] Optionally the guide ring 31 is a split ring (two semi-circular parts), to enable it to be removed after the specimen cassette 60 has been loaded and the test machine has gripped the grip pad 20.

[0053] An SAE / ANSI / AISI 316 stainless steel clamping ring 30 clamps the flange 52 of the load sleeve 50 against a flange 12 of the outer casing. Threaded fasteners pass through the clamping ring 30, through the flange 52 of the load sleeve, and into the flange 12 of the outer casing, which is also threaded. Figure 1 shows one of these threaded fasteners 33, the others being omitted from this Figure. Hence the clamping ring 30, the fasteners 33 and the flanges 52, 12, provide a second joint which joins the load sleeve to the outer casing. Thermally insulating gaskets may be provided at this second joint.

[0054] This arrangement provides a labyrinthine load path for the tensile force from the load train 27 to the outer casing 10 via the load sleeve 50 and the first and second joints, so that the outer casing 10 can react the tensile force. A grip pad 11 at the bottom of the outer casing can either be gripped by a test machine, or fixed to the ground, thus providing a load path which passes down through the test portion 80 of the specimen, up through the load sleeve 50, 52 (which is in compression if the specimen is loaded in tension) then down via the outer casing 10 to the grip pad 11. This avoids having to provide a load path through the base of the dewar 40.

[0055] The outer casing 10-12 may be made of a common inexpensive structural material such as S355 steel (painted). The load sleeve 50, 52 may be made from SAE / ANSI / AISI 316 stainless steel, or any other suitable material.

[0056] The specimen cassette 60 (including the catches 73a, 74a; 73b, 74b and the specimen 80, 82a,b) are immersed in a cryogenic liquid such as liquid nitrogen. Each handle 82a,b fits between a respective pair of catches 73 a, 74a; 73b, 74b with each catch contacting a respective one of the projections 83 a, 84a. The load train 27 is configured to apply tensile force to the test portion 80 of the specimen by pulling on the rear sides of the first projections 83a, 84a with the first catches 73a, 74a. Equivalent reaction forces occur at the second (lower) end of the specimen cassette 60 which is a mirror image of the first (upper) end of the specimen cassette 60.

[0057] The design of the specimen cassette 60 is particularly advantageous in a cryogenic assembly. In conventional test assemblies, a specimen may be provided as a strip (without a handle) such as the test portion 80, which is gripped by friction between a pair of test machine jaws. Such a friction-based coupling requires moving test machine jaws (for instance hydraulic test machine jaws) which are not suited to a cryogenic environment.

[0058] In the embodiment described above, each pair of catches 73a, 74a; 74b, 74b is made from a single piece of material (in this case a catch plate 70a,b) and are substantially fixed with respect to each other. This is a robust arrangement, with no moving parts (once clamped), able to operate at and withstand cryogenic temperatures.

[0059] Another advantage is that the catches can grip the handles of the specimen without direct clamping or bolting of the specimen.

[0060] The test assembly 1 of Figure 2 can be constructed by first assembling the specimen cassette 60 of Figure 4 by fitting the handles between the catches; then attaching the specimen cassette 60 to the load train 27; then joining the specimen cassette 60 to the base of the load sleeve; then lowering the load sleeve and specimen assembly into the dewar 40 (which is filled with liquid nitrogen after insertion via its open top so that the specimen cassette 60 becomes immersed in liquid nitrogen); then securing the second joint which also seals the upper end of the dewar 40; then applying tensile test forces as described above.

[0061] An indicative position of the upper surface 90 of the liquid nitrogen is indicated in Figure 7, showing that the flange 27 of the actuation rod, and all parts of the specimen cassette 60, are immersed in liquid nitrogen. Sufficient volume is provided in the dewar 40 above the specimen cassette 60 to enable a certain amount of liquid nitrogen to boil off with the specimen cassette 60 remaining fully immersed.

[0062] The test apparatus 1 constitutes an economical and cost-effective test rig that can be used in a wide variety of universal test machines. It enables static and fatigue testing in liquid nitrogen. The rig incorporates a commercial off-the-shelf open-top dewar 40 and inexpensive materials to minimise heat ingress to the specimen and to minimise liquid nitrogen loss to the atmosphere. The apparatus is designed to be modular so it can be installed into different test machines with varying load capacities. A similar approach is also taken on the specimen cassette 60, whereby the modular design allows one or both catch plates to be replaced to accommodate different specimen types and dimensions (from small coupons to cryogenic pipe components).

[0063] In the embodiment described herein, the test apparatus is designed to apply tensile forces to the specimen. In other embodiments, the test apparatus may be modified to enable it to apply both tensile and compressive forces.

[0064] Where the word ‘or’ appears this is to be construed to mean ‘and / or’ such that items referred to are not necessarily mutually exclusive and may be used in any appropriate combination.

[0065] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. Cryogenic test apparatus comprising: a load train with a pair of opposed catches; and a specimen comprising a test portion, and a handle with a pair of opposed projections at an end of the test portion; wherein the catches and the specimen are immersed in a cryogenic liquid; each catch contacts a respective one of the projections; and the load train is configured to apply tensile force to the test portion of the specimen by pulling on the projections with the catches.

2. Apparatus according to claim 1 wherein the catches are made from a single piece of material.

3. Apparatus according to claim 1 or 2 wherein the catches are substantially fixed with respect to each other.

4. Apparatus according to any preceding claim further comprising a catch plate, the catch plate comprising the pair of catches.

5. Apparatus according to claim 4 wherein the load train further comprises an actuation rod, and a pair of retaining parts removably fastened to the actuation rod by fasteners; and the catch plate is clamped between the retaining parts.

6. Apparatus according to claim 5, wherein the retaining parts are removably fastened to each other by fasteners.

7. Apparatus according to any preceding claim wherein the projections have concave curved load-bearing surfaces; and the catches have convex curved load-bearing surfaces each contacting a concave curved load-bearing surface of a respective one of the projections.

8. Apparatus according to any preceding claim wherein the load train further comprises an actuation rod which carries the catches and is immersed at one end in the cryogenic liquid.

9. Apparatus according to claim 8, wherein the actuation rod comprises a load introduction rod which is immersed at one end in the cryogenic liquid; a grip pad which is not immersed in the cryogenic liquid; and a joint between the load introduction rod and the grip pad; wherein the joint comprises a thermally insulatinggasket which impedes the flow of thermal energy from the grip pad to the load introduction rod.

10. Apparatus according to any preceding claim wherein the handle fits into a socket between the catches, the socket comprising a rear wall which contacts the handle.

11. Apparatus according to any preceding claim wherein the handle is a first handle at a first end of the test portion, the projections are first projections, and the catches are first catches; the specimen comprises a second handle with a pair of opposed projections at a second end of the test portion; and the apparatus further comprises a load reactor comprising a pair of opposed second catches; wherein the second catches are immersed in the cryogenic liquid; each second catch contacts a respective one of the second projections; and the load reactor is configured to react the tensile force by pulling on the second projections with the second catches.

12. Apparatus according to any preceding claim, further comprising a dewar which contains the catches, the specimen and the cryogenic liquid.13 Apparatus according to claim 12, further comprising a load sleeve in the dewar, wherein the sleeve contains the catches and the specimen; and an outer casing containing the dewar, wherein the handle is at a first end of the test portion, the specimen is joined to the load sleeve by a first joint at a second end of the test portion, the load sleeve is joined to the outer casing by a second joint, and a load path is provided for the tensile force from the load train to the outer casing via the load sleeve and the first and second joints, so that the outer casing can react the tensile force.

14. Apparatus according to any preceding claim, wherein the cryogenic liquid is liquid nitrogen.

15. Apparatus according to any preceding claim, wherein each catch has a front face and a rear face; each projection has a front face and a rear face; the rear face of each catch contacts the rear face of a respective one of the projections; and the load train is configured to apply the tensile force to the test portion of the specimen by pulling on the rear faces of the projections with the rear faces of the catches.

16. A method of testing a specimen with the apparatus of any preceding claim, the method comprising: fitting the handle between the catches; immersing the catches and the specimen in the cryogenic liquid; and applying tensile force to the test portion of the specimen by pulling on the projections with the catches.

17. A load train for a cryogenic test apparatus, the load train comprising; an actuation rod; a pair of retaining parts removably fastened to the actuation rod by fasteners; and a catch plate clamped between the retaining parts, wherein the catch plate comprises a socket with a rear wall, and an entrance between an opposed pair of catches.

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