Testing apparatus and a method for testing

Abstract

The invention relates to a testing apparatus comprising a chamber frame (3) with with a load opening (5), the load opening (5) is covered by a cap (6). A first (8) and a second (9) sample contact element is provided in the chamber. A shaft (11) has a second end protruding out of the chamber frame through an opening in the cap (6). An interface is provided for pressurizing the chamber with fluid. A bellows tube (13) which seals the shaft (11) to the cap (6). A loading frame (2) with load shafts (16) has first ends attached to the cap (6) and second ends attached to the second sample contact element (9, 9'), whereby the second sample contact element (9, 9') is connected to the chamber frame (3) via the cap and the loading frame (2) and suspended in the chamber at a distance from a second end (18) of the chamber frame, which is opposite to said first end (17).

Description

BACKGROUND OF THE INVENTIONFIELD OF THE INVENTION

[0001] This invention relates to a testing apparatus and to a method for testing.DESCRIPTION OF PRIOR ART

[0002] In order to determine how well different materials are suited for being used in environments where they are subjected to a fluid, a need exists to be able to test materials which are in contact with a fluid during the test.

[0003] A challenge with such tests is that the used fluid may have properties requiring, for safety reasons, that the fluid is all the time kept in an isolated space. An additional challenge is that the number of tests and test cycles which need to be carried out for a specific material in order to obtain reliable results is very large.

[0004] Consequently, a need exists for a simple and reliable testing apparatus, which has a structure remaining fluid-tight over time despite frequent use, and which facilitates easy and quick replacement of the sample after each test has been completed. The fluid may be in the form of gas or liquid, depending on the implementation.SUMMARY OF THE INVENTION

[0005] An object of the present invention is to solve the above-mentioned problem and to provide an easy and reliable solution for testing. These objects are achieved with the testing apparatus according to claim 1 and with the method according to claim 11 .

[0006] By using a bellows tube to seal a cap to a shaft which is connected to first sample contact element in a chamber, it becomes possible to seal the shaft to the cap in a way avoiding abrasive wear of the shaft and seal during testing. Simultaneously, the second sample contact element can be suspended in the chamber by a loading frame having load shafts attached to the cap. Consequently, to load and unload the sample from the chamber, only one load opening in the first end of the frame needs to be accessed by attaching and removing the cap. Once the cap is removed, the loading frame, the shaft andthe sample are simultaneously also removed with the cap. Due to this a solution is obtained which remains fluid tight over time while facilitating easy and quick replacement of the sample.

[0007] Preferred embodiments of the invention are disclosed in the dependent claims.BRIEF DESCRIPTION OF DRAWINGS

[0008] In the following the present invention will be described in closer detail by way of example and with reference to the attached drawings, in which

[0009] Figures 1 to 3 illustrate a testing apparatus,

[0010] Figure 4 illustrates testing with the testing apparatus of Figures 1 to 3, and

[0011] Figures 5 and 6 illustrate a second embodiment of a testing apparatus.DESCRIPTION OF AT LEAST ONE EMBODIMENT

[0012] Figures 1 to 3 illustrate a testing apparatus. Figure 1 is an outside view of the testing apparatus 1 , in Figure 2 the test apparatus 1 is shown in cross-section along line II - II of Figure 1 , and Figure 3 illustrates the loading frame 2 and the chamber frame 3 separated from each other.

[0013] The testing apparatus 1 comprises a chamber frame 3 with walls 4 and a load opening 5 in a first end 17 (upper end in the illustrated example). During testing, the load opening 5 is covered by a cap 6 so that the walls 4 and the cap 6 together delimit a fluid-tight chamber 7 within the chamber frame 3. The used fluid may be in the form of gas or liquid, depending on the implementation.

[0014] In Figure 2 a sample 10 to be tested is arranged into the chamber 7, where it during testing is subjected to a force by a first 8 and a second 9 sample contact element. A shaft 11 is via a first end connected to the first sample contact element 8. A second end of the shaft 11 protrudes out of the chamber 7 through an opening 12 in the cap 6. The second sample contact element 9 is connected to the chamber frame 3 in a non-movable way. During testing, when the shaft 11 and chamber frame 3 are moved in relation to each other, the shaft 11 and the first sample contact element 8 will move inwards into the chamber (downwards in the illustrated example) or outwards from the chamber (upwards in the illustrated example) which subjects the sample 10 to a force during testing.

[0015] During testing, the shaft 11 or a bracket 23 in the second end 18 of the chamber frame 3 is connected to an actuator generating a testing force which moves the shaft or the bracket 23, while the other one of the shaft 11 or the bracket 23 in the second end 18 of the chamber frame 3 is kept steady in place by a support.

[0016] In order to provide a fluid tight chamber 7, the shaft 11 is sealed to the cap 6 with a bellows tube 13. The bellows tube 13 surrounds a part of the shaft 11 and has a first end 14 fluid-tightly attached to the cap 6 and a second end 15 fluid-tightly attached to the outer surface of the shaft 11 . Such a structure makes it possible to move the shaft 11 in relation to the cap 6 as the bellows yield. Movement of the shaft 11 also moves the first sample contact element 8 in relation to the chamber 7 and to the second sample contact element 9. An advantage with using the bellows tube 13 instead of a traditional seal is that abrasive wear of the shaft and seal can be avoided.

[0017] One alternative to implement the bellows tube 13 is to utilize a corrugated steel tube which is fluid-tightly attached to the cap 6 and to the shaft 11 by welding. In some implementations such a tube may be manufactured as a multilayer tube having at least two tubes arranged coaxially inside each other. In this configuration the tubes are shaped to have bellows by pressing. The result is a bellows tube 13 as illustrated in the encircled enlargement in Figure 2.

[0018] The loading frame 2 is during testing located within the chamber 7, as illustrated in Figure 2. The loading frame comprises load shafts 16 having first ends (upper ends in the illustrated example) attached to the cap 6, and second ends (lower ends in the illustrated example) attached to the second sample contact element 9. Consequently, the second sample contact element 9 is connected to the chamber frame 3 via the cap 6 and the loading frame 2, so that it is suspended in the chamber 7 at a distance X from the second end 18 (lower end in the illustrated example) of the chamber frame 3. The forces progressing from the shaft 11 to the sample 10 and the second sample contact element 9 are therefore transmitted from the second sample contact element 9 via the shafts 16 and the cap to the chamber frame 3, and further via the bracket 23. This is an advantageous solution as it makes it simplifies replacement of the sample between tests, as a load opening is needed only in the first end 17 of the chamber frame 3. Dismantling of the testing apparatus 1 to change the sample 10 between tests becomes very easy. As illustrated in Figure 3, it issufficient to open the bolts 22 connecting the cap 6 to the chamber frame 3 in order to unload the cap 6 together with the shaft 11 and the loading frame 2 from the chamber via the load opening 5. At that stage the sample 10 located between the first 8 and second 9 contact element can be replaced by a new sample before the loading frame 2 is loaded back into the chamber via the load opening 5, and the bolts 22 are tightened so that new tests can be performed. Consequently, changing the sample can be done without releasing the bracket 23 in the second end 18 of the chamber frame 3 from a support to which it is attached during testing.

[0019] An additional advantage obtained by having a load opening 5 only in the first end 17 of the chamber frame, is that attention needs to be paid only to efficient sealing in the first end 17 of the chamber frame 3, at the cap 6.

[0020] In order to introduce a fluid into the chamber 7 during testing, the testing apparatus is provided with an interface 19 to pressurize the chamber with fluid. In some implementations this fluid may be hydrogen. In the illustrated example, the testing apparatus 1 is provided also with a second interface 20 for receiving a thermoelement which can be used for measuring the temperature of the chamber frame 3 or of the fluid 7 in the chamber during testing. In case a specific temperature or temperature range needs to be maintained during testing, the testing apparatus may be additionally provided with a piping for fluid circulation on an outside of the chamber frame 3, for instance, for passing a cooling fluid during the test.

[0021] The fluid pressure may vary depending on the implemented test. For lover pressures a polyurethane seal 21 may be provided between the chamber frame 3 and the cap 6 to provide a fluid-tight connection. However, in other implementations where higher pressures are in use and the chamber frame 3 and the cap 6 are made of metal, typically steel, metal surfaces of the cap 6 and of the chamber frame 3 may be in direct contact of each other and provide the fluid-tight sealing without a separate seal. The illustrated testing apparatus may be dimensioned for testing with fluid pressures of more than 400 bar.

[0022] In the example of Figures 1 - 3 it has been assumed that the testing apparatus is a tensile testing apparatus or a fatigue testing apparatus provided with grippers as the first 8 and second 9 sample contact elements. With such grippers the opposite ends of a steel sample can be pulled away from each other to implement tensile testing or pulled away and pushed against each other inseveral cycles to implement fatigue strength testing under hydrogen pressure, for instance.

[0023] Figure 4 illustrates testing with the testing apparatus 1 of Figures 1 to 3. In the example of Figure 4 the testing force is generated with a pulsator 40. In this context a pulsator refers generally to any force creating device having an actuator capable of generating force cycles with a suitable amplitude and magnitude. With such a device several different types of tests are possible, such as small punch testing, where a small spherical first sample contact element is punched against a planar sample, tensile testing, where a sample is pulled in one direction until breaking occurs, and fatigue testing where a sample is subjected in cycles to a pulling and a pushing force where the magnitude of the force may vary.

[0024] Initially the chamber frame 3 may via the bracket 23 be connected to a load sensor 42 via a lower fixing element of the pulsator 40. At this stage the loading frame 2 with the cap 6 may still be detached from the chamber frame 3, as illustrated in Figure 3. This makes it possible to provide the sample 10 between the first sample contact element 8 and the second sample contact element 9 which are still easily accessible, as the loading frame 2 with the second sample contact element 9 and the shaft 11 connected to the first sample contact element 8 are both connected to the cap 6.

[0025] With the sample 10 in position, the loading frame 2 with the sample 10 is lowered downwards into the chamber 7 via the load opening 5 in the chamber frame 3 from the position illustrated in Figure 3. Once the cap 6 contacts the chamber frame 3, the cap may be attached to the chamber frame by bolts 22, for instance, to fluid-tightly seal-off the chamber from the surroundings. Depending on the implementation, a seal 21 may be provided between the cap 6 and the chamber frame 3. Alternatively, metal surfaces of the cap 6 and the chamber frame may directly contact each other to provide a metalmetal sealing capable of handling a significant pressure.

[0026] Once the cap 6 is attached to the chamber frame 3, the second end of the shaft 11 may be connected to an actuator 41 of the pulsator, as shown in Figure 4.

[0027] At this stage the testing apparatus 1 is ready to be pressurized with a fluid. In Figure 4 nitrogen 50 and hydrogen 49 bottles are placed behind a wall 43 in another room than the testing apparatus 1 and the pulsator 40. A vacuumpump 44 can be placed in the same room with the testing apparatus 1 and the pulsator 40.

[0028] Initially the chamber of the testing apparatus 1 can be depressurized using the vacuum pump 44. The pressure connection to the vacuum pump 44 is opened with a valve 45. Valves 46, 47 and 48 are closed. Next, a vacuum is created in the chamber of the test apparatus 1 . The load sensor 42 force reading is checked, and it should be negative. The valve 45 is closed and valve 47 is opened, filling the chamber of the testing apparatus 1 with nitrogen gas. The nitrogen pressure is slowly raised to a maximum pressure, which in this example may be 120 bar by means of a pressure regulator in the nitrogen bottle 50. When the chamber is pressurized, a pulling force is applied to the test rod, which must be compensated by moving the upper beam of the pulsator, in which case the pulling force caused by the pressure can be compensated and the test can be started from zero force.

[0029] The nitrogen line is then closed by valve 47 and by closing the pressure regulator in the nitrogen bottle 50. Any leaks in the pipelines can be checked with a leak detector substance. After this, the nitrogen is removed from the testing device by opening the drain valve 48.

[0030] Next, the chamber of the testing apparatus 1 is again depressurized by the vacuum pump 44 by closing valve 48 and opening valve 45, valves 46 and 47 are closed. The vacuuming level can be checked from the load sensor 42. The chamber of the testing apparatus 1 can then be pressurized with hydrogen by closing valve 45 and opening valve 46. Hydrogenation is performed by means of a pressure reducer valve in the hydrogen bottle 49. In this example, the maximum pressure of the hydrogen is assumed to be 100 bar, though in other implementations, the testing apparatus may be dimensioned to be dimensioned to be pressurized with a fluid pressure of more than 100 bar. With the disclosed structure of the apparatus, testing in very high fluid pressures, such as with a pressure of more than 400 bar becomes possible. When the desired pressure level is achieved, the pressure reducer valve from the hydrogen bottle 49 and then the valve 46 can be closed. At this stage the testing apparatus 1 is ready to test a sample which in the chamber is subjected to hydrogen. The pressure in the chamber will cause a force reading from the load sensor 42. This force reading needs to be taken into account in the test results. The actual forces used during testing, the duration of the tests and other details may vary case specifically depending on the test in question.

[0031] During the test, the actuator 41 of the pulsator 40 moves the shaft with a predetermined force cycle depending on the selected test, while the load sensor 42 is used to determine the actual force subjected to the sample 10. The force generated by the actuator may be generated in various ways, such as by one or more hydraulic or pneumatic cylinders, or by an electric motor via a screw mechanism, for instance.

[0032] During testing, the spring force of the bellows tube 13 causes a loss in the testing force, which can be considered in the magnitude of the final force with the help of calibration. Determination of own stiffness can be done with the pulsator 40 by changing its stroke and measuring the spring constant of the bellows tube 13. During the spring constant test, no sample is provided to the testing apparatus 1. In practical tests it has been determined that the spring constant of the bellows tube 13 is linear and that a specific fixed force loss occurs with a typical stroke of a predetermined length. This makes it easy to correlate the actual test load as function of the stroke. Therefore, elimination of the effect of the spring force of the bellows tube 13 in the test results becomes possible.

[0033] Depending on the type of pulsator used, the location of the force cell and the actuator may be opposite to the previous explanation, so that the shaft 11 is connected to the force cell located above the testing apparatus 1 and the bracket 23 to the actuator located below the testing apparatus. In any case, the pulsator 40 generates a sufficient amount of force cycles with a desired intensity to test a sample located in the testing apparatus 1 , while the load sensor measures the actual load subjected to the sample 10.

[0034] In some implementations the pulsator 40 does not have a load sensor, but instead the load sensor may be arranged into the chamber 7 of the testing apparatus 1 . However, in many cases it is preferable to utilize a pulsator with a load sensor 42, because this simplifies the structure of the testing apparatus 1 .

[0035] Figures 5 and 6 illustrate a second embodiment of a testing apparatus. The embodiment of Figures 5 and 6 is very similar to the one explained in connection with Figures 1 to 4. Due to this, in the following the embodiment of Figures 5 and 6 will mainly be explained by pointing out the differences.

[0036] In the embodiment of Figures 5 and 6 the chamber frame, the cap and the bellows tube are similar as in the previous embodiment. However, thefirst 8' and second 9' sample contact elements and the sample 10' are of a different type. In Figures 5 and 6 the first sample contact element 8' is puncher designed with a spherical lower end while the second sample contact element 9' is a die shaped to receive a sample 10' which during testing is punched by the first sample contact element 9'. When implementing Small Punch testing, the sample 10' may be a disc having a diameter of about 8 mm and a thickness of about 0,5 mm.

[0037] Consequently, the same test apparatus 1 , which has been explained in connection with Figures 1 to 4, can be used with the pulsator 40, for instance, to perform a series of punching tests against the sample 10' under hydrogen pressure. The conversion of the testing apparatus 1 for punch testing is very simple, as it is sufficient to replace the first 8 and second 9 sample contact elements in the loading frame 2 from grippers used in tensile testing or fatigue strength testing to a puncher and a die suitable for punch testing. Additionally, the same pulsator 40 may be used for testing after some re-programming.

[0038] It is to be understood that the above description and the accompanying figures are only intended to illustrate the present invention. It will be obvious to a person skilled in the art that the invention can be varied and modified without departing from the scope of the invention.

Claims

CLAIMS:1 . A testing apparatus characterized in that the testing apparatus(I ) comprises: a chamber frame (3) with walls (4) and with a load opening (5) in a first end (17), the load opening (5) is covered by a cap (6), the walls and the cap together delimiting a fluid-tight chamber (7) within the chamber frame (3), a first (8, 8') and a second (9, 9') sample contact element in the chamber, the first and second sample contact elements being movable in relation to each other for subjecting a sample (10, 10') in the chamber to a force during testing with the apparatus, a shaft (11 ) having a first end connected to the first sample contact element (8) and a second end protruding out of the chamber frame through an opening in the cap (6), an interface (19) for pressurizing the chamber with fluid, a bellows tube (13) which seals the shaft (11 ) to the cap (6) by surrounding the shaft and having a first end (14) fluid-tightly attached to the cap (6) and a second end (15) fluid-tightly attached to an outer surface of the shaft(I I ), and a loading frame (2) within the chamber (7), said loading frame (2) having load shafts (16) with first ends attached to the cap (6) and second ends attached to the second sample contact element (9, 9'), whereby the second sample contact element (9, 9') is connected to the chamber frame (3) via the cap and the loading frame (2) and suspended in the chamber at a distance from a second end (18) of the chamber frame, which is opposite to said first end (17).

2. The testing apparatus according to one of claims 1 , wherein the chamber frame (3) and the cap (6) are made of metal and connected to each other by fluid-tight contact between metals surfaces of the cap (6) and the chamber frame (3).

3. The testing apparatus according to one of claims 1 , wherein a polyurethane seal (21 ) is provided between the the chamber frame (3) and the cap (6) to provide a fluid-tight connection.

4. The testing apparatus according to one of claims 1 to 3, wherein the bellows tube (13) is a corrugated tube fluid-tightly attached to the the cap (6) and to the shaft (11 ) by welding.

5. The testing apparatus according to one of claims 1 to 4, wherein said interface is an interface (19) for pressurizing the chamber (7) with hydrogen.

6. The testing apparatus according to one of claims 1 to 5, wherein the testing apparatus (1 ) is dimensioned to be pressurized with a fluid pressure of more than 100 bar.

7. The testing apparatus according to one of claims 1 to 6, wherein the testing apparatus (1 ) comprises a second interface (20) for receiving a thermoelement.

8. The testing apparatus according to one of claims 1 to 7, wherein the apparatus (1 ) is a tensile testing or fatigue strength testing apparatus comprising first (8) and second (9) sample contact elements in the form of grippers gripping opposite ends of a sample (10).

9. The testing apparatus according to one of claims 1 to 7, wherein the testing apparatus is a small punch testing apparatus comprising a puncher as the first sample contact element (8'), and a die as the second sample contact element (9').

10. The testing apparatus according to one of claims 1 to 9, wherein one of the second end of the shaft (11 ) and the second end (18) of the chamber frame (3) is attached to a load sensor (42), and the other one of the second end of the shaft (2) and the second end (18) of the chamber frame (3) is attached to an actuator (41 ) generating a testing force.11 . A method for testing a sample, characterized in that the method comprises: providing a sample (10, 10') between a first sample contact element (8, 8'), which is connected to a first end of a shaft (11 ), and a second sample contact element (9, 9'), which is connected to a cap (6) by load shafts (16) of a loading frame (2), said shaft (11 ) protruding through an opening (12) in the cap while a bellows tube (13) having a first end fluid-tightly attached to the cap (6) and a second end attached to the shaft, seals the shaft (11 ) to the cap (6), moving the loading frame (2) with the sample (10, 10') and the first (8, 8') and second (9, 9') sample contact elements into a chamber (7) delimited by walls (4) of a chamber frame (3) until the cap (6) contacts the chamber frame (3), attaching the cap (6) to the chamber frame (3) to fluid-tightly seal off the chamber from surroundings,introducing a pressurized fluid into the chamber (7) via an interface(19), and moving a second end of the shaft (11 ) in relation to the chamber frame (3) to subject the sample (10, 10') to a force during testing.

12. The method according to claim 11 , comprising: connecting one of the shaft (11 ) and the chamber frame (3) to an actuator (41 ) generating a test force, and connecting the other one of the shaft (11 ) and the chamber frame (3) to a load sensor (42).

13. The method according to one of claims 11 to 12, wherein the method comprises: selecting for use a first sample contact element (8) and a second sample contact element (9) in the form of grippers for preforming tensile testing or fatigue strength testing, or alternatively, selecting for use a first sample contact element (8') in the form of a punch and a second sample contact element (9') in the form of a die for performing punch testing, and providing a sample (10, 10') between the selected first sample contact element (8, 8') which is connected to the first end of the shaft (11 ), and the second sample contact element (9, 9'), which is connected to the cap (6) by load shafts (16) of the loading frame (2).

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