Test device for carrying out a mechanical load check on a test object

Abstract

The present disclosure describes a test device (100) for carrying out a mechanical load test on a test object. The test device (100) comprises a receiving component (102), which comprises a hollow space (102.1) for receiving the test object, and a load arrangement for loading the receiving component (102) with a tensile force by means of a working cylinder (104A, 104B), wherein the working cylinder (104A, 104B) is mechanically connected to the receiving component (102) via a rod (106A, 106B). The load arrangement further comprises a pretensioning unit (108A, 108B) which is designed to load the rod (106A, 106B) with a tensile force.

Description

[0001] Test device for carrying out a mechanical load test on a test specimen

[0002] The present disclosure describes a test device for carrying out a mechanical stress test on a test specimen and a method for carrying out a mechanical stress test on a test specimen.

[0003] In a mechanical load test, controlled forces are applied to a test specimen using a test rig, e.g., for testing wind turbine shafts, to examine its mechanical stability. Typically, working cylinders, particularly hydraulic cylinders, are used to generate the forces. Large forces also act on the components of the test rig itself. The test rigs must therefore be designed to withstand these forces to ensure a long service life.

[0004] The object of the following disclosure is therefore to describe a particularly advantageous test device. This object is achieved by the test device described in claim 1 for performing a mechanical stress test on a test specimen and the method described in claim 13.

[0005] The test device comprises a receiving component that has a cavity for receiving the test specimen, as well as a loading arrangement for loading the receiving component with a tensile force by means of a working cylinder, wherein the working cylinder is mechanically connected to the receiving component via a rod. The loading arrangement further comprises a preload unit designed to load the rod with a tensile force.

[0006] The test setup described here is based on the knowledge that material fatigue often occurs more quickly the greater the change in operating load between an unloaded and a loaded state of a component. The unloaded state corresponds to a state in which the working cylinder is not subjected to a force, and the loaded state corresponds to a state of the component in which the working cylinder is subjected to a force. The rod, as a connecting element, is particularly affected by material fatigue. The preloading unit can now preload the rod with a tensile force so that the rod has a certain operating load even in the unloaded state. This can reduce the change in operating load.

[0007] It should be understood that the loading arrangement includes the working cylinder and the rod.

[0008] Preferred embodiments of the test device are described below.

[0009] In a preferred embodiment, only a portion of the rod is subjected to tensile stress by the preloading unit. In a variant of this embodiment, the preloading unit applies tensile stress to that portion of the rod which is also subjected to tensile stress when a force is applied to the working cylinder.

[0010] In another preferred embodiment, the prestressing unit comprises, alternatively or additionally, a spacing element that fixes one end of the rod and against which an opposite end of the rod can be tensioned. In particular, the one end is the end of the rod facing the receiving component.

[0011] In the following, various variants of the embodiment with a spacing element are described.

[0012] In a preferred variant of this embodiment, one end of the rod is positively connected to the receiving component. Furthermore, an end of the spacer element facing the receiving component rests against an outer wall of the receiving component. In some of these variants, the receiving component includes an internal thread for positive fixation, and the rod is designed as a bolt that is screwed into the internal thread.

[0013] In at least one of these variants, the spacer element is additionally or alternatively supported on a planar contact surface of the outer wall. Supporting the spacer element on the planar contact surface has the advantage of a self-centering alignment. Furthermore, a planar contact surface, where the spacer element is not forced into a specific position, reduces the occurrence of parasitic forces.

[0014] In another variant of the embodiment with a spacer element, the preloading unit additionally or alternatively comprises a tensioning element that is supported on an end of the spacer element facing away from the receiving component and by means of which one end of the rod can be moved relative to the opposite end of the rod. This serves to load the rod with a tensile force.

[0015] The clamping element can be designed in different ways. In one variant, the clamping element has an internal thread and is screwed onto an external thread of the rod. In one embodiment, the clamping element is a screw nut. In other embodiments, it is a SuperBolt clamping device.

[0016] In another variant, the working cylinder additionally or alternatively has a hollow piston, wherein the rod and the spacing element are arranged in an interior of the hollow piston.

[0017] In other variants, the spacing element, alternatively or additionally, has a projection behind which the working cylinder engages to apply a tensile force to the receiving component. In some of these variants, the projection is designed as a collar. Additionally or alternatively, in some of these variants, the projection is designed as a contact surface for the clamping element on another side, which is opposite the side for the working cylinder to engage behind.

[0018] In another variant, the spacing element comprises, additionally or alternatively, a sleeve that encloses the rod.

[0019] In a combined variant, the spacer element is designed as a sleeve that surrounds the rod, and the working cylinder has a hollow space, with the rod and the spacer element being arranged inside the hollow piston. Additionally or alternatively, in some of these variants, the working cylinder is a hydraulic cylinder, with the sleeve forming an outer wall of a pressure chamber of the hydraulic cylinder.

[0020] In another embodiment, the loading arrangement additionally or alternatively comprises two working cylinders positioned along a tensile axis on opposite sides of the receiving component. This is advantageous for loading the receiving component, and thus the test specimen, symmetrically from two opposite sides. Furthermore, it allows the receiving component to be subjected to defined tensile forces that can be adjusted using the working cylinders.

[0021] In a variant of this design, both working cylinders are supported by contact surfaces on opposite sides of a support element, with the contact surfaces being designed as planar contact surfaces perpendicular to the pull axis. Due to the alignment of the contact surfaces, they have a self-centering effect with respect to the pull direction of the working cylinders. Furthermore, the planar contact surfaces, which do not force the working cylinders into a specific position, reduce parasitic loads. In some embodiments of this variant, the support element at least partially encloses the receiving component.

[0022] In a preferred embodiment, the test device is a test device for conducting a mechanical load test on a component of a wind turbine. In another embodiment, additionally or alternatively, the test device is a test device for conducting a mechanical load test on cylindrically symmetrical components such as rolling bearings or shafts. In embodiments, the receiving component is, alternatively or additionally, designed in the form of a hollow cylinder. In another embodiment, alternatively or additionally, the receiving component is designed and / or the working cylinder with the rod is arranged such that the tensile force acts in a radial direction of the cylindrically symmetrical component.

[0023] The procedure already mentioned above for carrying out a mechanical load test on a test specimen is described below.

[0024] The procedure includes the following steps:

[0025] Inserting the test specimen into a cavity of a receiving component;

[0026] Carrying out the load test by loading the receiving component with a tensile force by means of a working cylinder which is mechanically connected to the receiving component by means of a rod; whereby the rod is pre-tensioned by means of a tensile force before the receiving component is subjected to the load.

[0027] The method has the same advantages as the test facility described above.

[0028] In one embodiment of the method, the load test is carried out using two working cylinders, each of which applies a tensile force to the receiving component from opposite sides using a rod, whereby both working cylinders are always subjected to a force during the load test. This method is particularly advantageous because by applying a force to both cylinders, one of the cylinders can be prevented from locking. In a variant of this embodiment, both working cylinders are each subjected to a minimum pressure of 20 bar during the load test. By preventing locking, it is ensured that the receiving component is loaded essentially in one direction and can reliably transmit the applied force to other components.If the cylinders were to be locked, an undesirable deformation of the receiving component could occur. In another variant, both rods are preloaded, either alternatively or additionally.

[0029] In a further embodiment, alternatively or additionally, a test device according to one of the claims described above is used to carry out the mechanical stress test.

[0030] In the following, exemplary embodiments of the test device and the method are described using the attached figures. An overview of the figures is provided first.

[0031] Fig. 1 shows a cross-section of an embodiment of a test device for carrying out a mechanical stress test on a test specimen;

[0032] Fig. 2 shows an illustration of the operation of a pretensioning unit of the test device shown in Fig. 1;

[0033] Fig. 3 shows a method for performing a mechanical stress test on a test specimen; and Fig. 4 shows a modified procedure of the method shown in Fig. 3 for performing a mechanical stress test on a test specimen.

[0034] The embodiments shown in the figures are described in detail below.

[0035] First, an embodiment of a test device will be described with reference to Fig. 1 and Fig. 2.

[0036] Fig. 1 shows a cross-section of an embodiment of a test device 100 for performing a mechanical load test on a test specimen. Fig. 2 shows an illustration of the mode of operation of a preload unit of the test device 100 shown in Fig. 1.

[0037] The test device 100 comprises a receiving component 102 and a loading arrangement.

[0038] The receiving component 102 has a cavity 102.1 for receiving a test specimen. In the exemplary embodiment shown in Fig. 1, the test device 100 is used to perform a mechanical load test on a shaft for wind turbines. For this purpose, the receiving component 102 is designed in the form of a hollow cylinder so that a shaft to be tested can be inserted into the cavity 102.1. However, the concept described in the present disclosure can also be used to perform a mechanical load test on other components, even from other fields of technology.

[0039] The loading arrangement also included in the test device 100 serves to load the receiving component 102 with a tensile force. For this purpose, the loading device comprises two working cylinders 104A and 104B, which are arranged symmetrically on opposite sides of the receiving component 102. In the embodiment shown in Fig. 1, the working cylinders 104A and 104B are hydraulic cylinders. However, other working cylinders, such as electric or pneumatic cylinders, can also be used. The mechanical power transmission of the working cylinders 104A and 104B is each achieved via a rod 106A and 106B designed as a bolt. The rods 106A and 106B are each connected to the receiving component via a screw thread 102.3A and 102.3B.To enable a compact and thus space-saving arrangement of the test device 100, the working cylinders 104A and 104B are designed as hollow piston cylinders, with the rods 106A and 106B being guided through a hollow space 104A.1 and 104B.1 of one of the working cylinders 104A and 104B, respectively. Due to the symmetrical arrangement of the cylinders on opposite sides of the receiving component 102, the receiving component 102 can be loaded with opposing tensile forces along a common tensile axis A. This makes it possible to load the receiving component 102 (and thus also the test specimen) with a tensile load under defined test conditions.

[0040] When the supporting component 102 is subjected to tensile stress by the working cylinders 104A and 104B, the rods 104A and 104B are also subjected to tensile stress. Frequent alternation between loading and unloading of the rods 106A and 106B can lead to accelerated material fatigue. To prevent material fatigue, the loading arrangement comprises two preload units 108A and 108B, each assigned to one of the working cylinders or one of the rods. The preload units 108A and 108B are designed to allow the rods 106A and 106B to be loaded with a tensile force that ensures a basic load on the rods 106A and 106B. Due to the base load on rods 106A and 106B, differences in the load on rods 106A and 106B between loading and unloading phases with working cylinders 104A and 104B are less significant. The preload units 108A and 108B are constructed identically.Therefore, only the preload unit 108A will be discussed below.

[0041] To produce the basic load, the preload unit 108A comprises a spacing element 108A.2 and a tensioning element 108A.1.

[0042] The spacing element 108A.2 has the shape of a sleeve and encloses a central region of the rod 106A. The spacing element 108A.2 has the function of fixing an end of the rod 106A facing the receiving component 102 and of enabling tensile bracing of the end of the rod 106A facing away from the receiving component 102 against the fixed end of the rod 106A. The fixing is achieved by supporting an end of the spacing element 108A facing the receiving component 102 on an outer wall 102.2 of the receiving component 102. The tensile bracing is produced through the interaction of the spacing element 108A.2 and the tensioning element 108A.1. The spacing element 108A.2 is supported on a planar contact surface 102.4A of the outer wall 102.2 of the receiving component 102, which is only indicated in Fig. 1. The planar contact surface 102.4A is formed largely perpendicular to the tension axis A.

[0043] The clamping element 108A.2 is supported on an end of the spacing element 108A.2 facing away from the receiving component 102 and is designed to move one end of the rod 106A relative to the opposite end of the rod 106A. In the embodiment shown in Fig. 1, this is made possible by using a so-called SuperBolt for the clamping element 108A.1. The clamping element 108A.1 has a central internal thread by means of which the clamping element 108A.1 is screwed onto an end of the rod 106A facing away from the receiving component. In addition, the clamping element 108A.1 has a number of pressure screws 108A.1.1, by tightening which the end of the rod 106A facing away from the receiving component can be displaced in a direction away from the receiving component 102. As a result of this and the fixation of the end of the rod 106A facing the receiving component, the rod is subjected to tensile stress.

[0044] The mode of operation of the pretensioning unit 108A is also shown schematically in Fig. 2.

[0045] Therein, the preload of the rod 106A is indicated by an arrow 120. Furthermore, the arrows 122A and 122B indicate a force flow caused by tightening the clamping element 108A.1 of the preload unit 108A. As can be seen in Fig. 2, this force is predominantly conducted through the components of the preload unit 108A. The preload force of the rod 106A is thus not conducted via the cylinders 104A and 104B. To load the receiving component 102 with a tensile force by the working cylinder 104A, the spacing element 108A.2 comprises a projection 108A.2.1 in the form of a collar, behind which the working cylinder engages. As already described above, the working cylinders 104A and 104B are hollow piston cylinders, each with a cavity 104A.1 and 104B.1. In the embodiment shown in Fig. 1, the spacing element 108A.2 fulfills a dual function in that the spacing element 108A.2 additionally serves as an outer wall of a pressure chamber 104A.2 of the working cylinder 104A.

[0046] The working cylinders 104A and 104B are each supported by a contact surface 110.1A and 110.1B on opposite sides of a support element 110. The contact surfaces 110.1A and 110.1B are formed perpendicular to the tension axis. As a result, the contact surfaces 110.1A and 110.1B have a self-centering effect on the working cylinders 104A and 104B.

[0047] In the following, a procedure for carrying out a mechanical load test on a test specimen is described with reference to Fig. 3 and Fig. 4.

[0048] Fig. 3 shows a method 200 for performing a mechanical stress test on a test specimen.

[0049] The method 200 comprises three steps. In a first step 202, the test specimen is inserted into a cavity of a receiving component. In a second step 204, a rod, by means of which a working cylinder is mechanically connected to the receiving component, is preloaded with a tensile force. In a third step 206, the load test is then performed by applying a tensile force to the receiving component using the working cylinder.

[0050] However, particularly with a symmetrical arrangement of at least two working cylinders on opposite sides of the receiving component, there is a risk that loading one working cylinder will cause the other working cylinder to lock up, which will subsequently limit the use of the test device. For this reason, a modified procedure is advantageous when arranging working cylinders on opposite sides of the receiving component. This is explained below using Fig. 3.

[0051] Fig. 4 shows a modified procedure 300 for performing a mechanical stress test on a test specimen.

[0052] The first two steps of method 300 are identical to method 200 in Fig. 2. These two steps are also designated by the same reference symbols. A different procedure for method 300 occurs primarily in the third step 306.

[0053] In step 306, the load test is carried out by applying a tensile force to the receiving component by means of the working cylinder, whereby two opposing working cylinders are subjected to a force during the load test and both working cylinders are constantly kept under a minimum hydraulic stress of 20 bar during the load test.

[0054] By applying force to two opposing working cylinders, a defined test condition is also created, as the total force acting on the supporting component can be derived from the forces of the individual working cylinders. Furthermore, this prevents the working cylinders from locking up in the initial position and / or in the two possible extreme positions. Preventing locking ensures that the central component is loaded primarily in one direction and can reliably transmit the applied force to other components. If the cylinders were locked up, an undesirable deformation of the central component could occur.

[0055] In summary, the present disclosure describes a test device (100) for conducting a mechanical load test on a test specimen. The test device (100) comprises a receiving component (102) having a cavity (102.1) for receiving the test specimen, and a loading arrangement for loading the receiving component (102) with a tensile force by means of a working cylinder (104A, 104B), wherein the working cylinder (104A, 104B) is mechanically connected to the receiving component (102) via a rod (106A, 106B). The loading arrangement further comprises a preload unit (108A, 108B) configured to load the rod (106A, 106B) with a tensile force.

Claims

1. Test device (100) for carrying out a mechanical load test on a test specimen, comprising: a receiving component (102) which has a cavity (102.1) for receiving the test specimen, and a loading arrangement for loading the receiving component (102) with a tensile force by means of a working cylinder (104A, 104B), wherein the working cylinder (104A, 104B) is mechanically connected to the receiving component (102) via a rod (106A, 106B), and wherein the loading arrangement further comprises a pretensioning unit (108A, 108B) which is designed to load the rod (106A, 106B) with a tensile force.

2. Test device (100) according to claim 1, wherein the pretensioning unit (104A) comprises a spacing element (104A.2) which fixes one end of the rod (106A) and against which an opposite end of the rod (106A) can be tensioned.

3. Test device (100) according to claim 2, wherein one end of the rod (106A) is positively connected to the receiving component (102) and an end of the spacing element (108A.2) facing the receiving component (102) is supported on an outer wall (102.2) of the receiving component (102).

4. Test device (100) according to claim 3, wherein the spacing element (108A.2) is supported on a planar contact surface (102.4A) of the outer wall (102.2).

5. Test device (100) according to one of claims 2 to 4, wherein the pretensioning unit (108A) comprises a tensioning element (108A.1) which is supported on an end of the spacing element (108A.2) facing away from the receiving component (102) and by means of which one end of the rod (106A) can be moved relative to the opposite end of the rod (106A).

6. Test device (100) according to claim 5, wherein the clamping element (108A.1) has an internal thread and is screwed with the internal thread onto an external thread of the rod (106A).

7. Test device (100) according to one of claims 2 to 6, wherein the working cylinder (104A, 104B) has a hollow piston and the rod (106A, 106B) and the spacing element (108A.2, 108B.2) are arranged in an interior of the hollow piston.

8. Test device (100) according to one of claims 2 to 7, wherein the spacing element (108A.2, 108B.2) has a projection (108A.2.1) behind which the working cylinder (104A, 104B) engages in order to load the receiving component (102) with a tensile force.

9. Test device (100) according to one of claims 2 to 8, wherein the spacing element (108A.2) comprises a sleeve enclosing the rod (106A).

10. Test device (100) according to claim 7 and 9, wherein the working cylinder (104A) is a hydraulic cylinder and the sleeve forms an outer wall of a pressure chamber (104A.2) of the hydraulic cylinder (104A).

11. Test device (100) according to one of the preceding claims, wherein the loading arrangement comprises two working cylinders (104A, 104B) positioned along a tension axis (A) on opposite sides of the receiving component (102).

12. Test device (100) according to claim 11, wherein both working cylinders (104A, 104B) are supported on contact surfaces (110.1A) on opposite sides of a support element (110), and wherein the contact surfaces (110.1B) are designed as planar contact surfaces perpendicular to the pulling axis (A).

13. A method (200) for carrying out a mechanical stress test on a test specimen, comprising the following steps: Inserting the test specimen into a cavity of a receiving component (202); Carrying out the load test by loading the receiving component with a tensile force by means of a working cylinder which is mechanically connected to the receiving component by means of a rod (206); wherein, before loading the receiving component, the rod is prestressed by means of a tensile force (204).

14. The method (300) according to claim 13, wherein the load test is carried out by means of two working cylinders which apply a tensile force to the receiving component from opposite sides by means of a rod, wherein both working cylinders are always subjected to a force during the load test (306).

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