LOAD FRAME, TEST STAND SYSTEM AND METHOD FOR USING THE LOAD FRAME

Description

[0001] The invention relates to a load frame for a test specimen, in particular for wind turbine subcomponents, for use in a test rig. The invention further relates to a system with such a load frame and a method for its use.

[0002] Wind turbine rotor blades are subjected to high loads and wear during operation. Optimizing performance while maintaining maximum safety presents a major challenge in wind turbine construction, and especially in the development of rotor blades. This requires knowledge of the rotor blade's elastic properties, such as modulus of elasticity, yield strength, tensile strength, elongation at break (i.e., its load-bearing capacity), as well as its plastic and elastic deformability, and other structural parameters.

[0003] Due to the length of rotor blades, which often exceeds 30 meters, they cannot usually be measured in their entirety. Instead, subcomponents of wind turbines, i.e., components of the wind turbine rotor blades, are clamped into a test rig and subjected to tensile or compressive loads. These subcomponents are, for example, sections or partial structures of rotor blades with dimensions of several meters, taken from different points on the rotor blade. From this, conclusions can be drawn about the behavior of the entire rotor blade. To simulate conditions for the subcomponent that correspond to those that exist when the subcomponent is located within the rotor blade and the latter is under load, a targeted and precise application of force is necessary.To achieve such a load on the subcomponent, a test force is applied, for example, at opposite ends of the subcomponent along previously calculated lines of action. The test specimens should therefore be fixed in the test rig in such a way that flexible force application at the ends is possible, where the force is applied, for example, along lines of action that are not perpendicular to an outer surface of the test specimen and / or eccentrically, i.e., with a lever arm relative to the elastic center of the test specimen. In some cases, such force application results in deformation or rotation of the test specimen due to applied bending moments, which should be tolerated by the load frame.

[0004] Document DE 11 2010 002599 T5 shows a protective shield for a jaw of a reciprocating clamping device, comprising: an upper protective shield part for positioning above the jaw; a lower protective shield part for positioning below the jaw; a connecting element part for connecting the upper shield part to the lower shield part; and a fastening part for attaching the protective shield to the jaw.

[0005] DE 38 40 261 A1 discloses a loading device for subjecting a specimen to tension or compression, in which the load is applied by leaf springs which are clamped between a lower yoke and an upper yoke and are subjected to buckling.

[0006] EP 2 741 068 A1 discloses a test rig for a rotor blade with a support structure to which an axial end of the rotor blade can be attached, and at least one excitation unit that can be connected to the rotor blade to excite a vibration of the rotor blade. Spring elements are provided, each of which is attached at a pivot point and can be connected to the rotor blade for testing purposes, such that the rotor blade can be subjected to spring forces by the spring elements to influence the vibration behavior, the direction of which has at least one component that runs parallel to a main loading direction of the rotor blade.

[0007] DE 20 2011 001901 U1 discloses a device for exciting vibrations of rotor blades with a holder that can be attached to the rotor blade, wherein the holder has at least one electrodynamic mass actuator which is controlled by a control device.

[0008] The object of the present invention is to propose a load frame that allows for the secure clamping of test specimens and simultaneously enables the testing of the largest possible section of the test specimen. The test specimen should also be fixed as securely as possible throughout the entire duration of the test procedure, even under bending moments or peel stresses occurring during the test.

[0009] This is achieved by a load frame having the features of independent claim 1, or by a test bench system according to claim 11, or by a method according to claim 13. Advantageous embodiments are described in the dependent claims, the description, and the figures.

[0010] The proposed load frame comprises a sandwich structure with a continuous recess. The recess extends from one top surface to the opposite bottom surface of the sandwich structure, and a sheet metal plate rests against one of the recess's walls. The recess is designed to receive a test specimen. For example, a section of the test specimen, such as an end segment, can be inserted into the recess. The recess can be adapted to the contour of the test specimen in such a way that it can be bonded to the steel sheet located within the recess.

[0011] The sheet metal attached to the cavity wall, to which the test specimen can be bonded, results in a significantly better adhesive bond between the load frame and the test specimen than with load frames where the test specimen is bonded directly to the sandwich structure. The proposed load frame thus achieves a particularly secure and reliable fixation. Furthermore, the sheet metal protects the cavity wall from cracks or other damage caused by peel stress. It has been shown that the use of a sheet metal provides good reinforcing properties at a low weight, while at the same time preserving at least some of the desired elastic properties of the sandwich structure.

[0012] The sandwich structure can consist of stacked panels or be manufactured layer by layer, for example, using an additive manufacturing process. Different layers exhibit different properties, such as flexural characteristics, which can be tailored to a specific load. In both stacked panels and layered manufacturing, a layer direction is defined that extends from the bottom to the top, in the same direction as the continuous cutout.

[0013] Bending moments introduced during the testing of specimens can cause peel stress at the adhesive joint between sandwich structure panels or at the adhesive joint between the load frame and the specimen. Sandwich structures with fiber orientation perpendicular to the adhesive joint are particularly prone to failure under such stress and act as initiators of cracks in the load frame. This reduces the effective force-transmitting area. The load frame proposed here counteracts this problem. By preventing cracks, the shear-transmitting area available during the testing procedure is protected. This eliminates the need for additional fasteners, such as bolts connecting the load frame and specimen, which could influence the specimen's behavior and are subject to high wear.

[0014] In the proposed load frame, the sheet metal can be flush with the top and / or bottom of the sandwich structure at an upper and / or lower outlet opening of the recess. The load frame can include a first metal plate located on the top of the sandwich structure and / or a second metal plate located on the bottom of the sandwich structure, each projecting beyond the respective outlet opening of the recess where they are positioned, such that the sheet metal abuts the first and second metal plates and is clamped between them. For example, at least one of the metal plates is positioned so that the recess remains accessible. One of the metal plates can also project beyond the outlet opening where it is positioned, partially or completely obstructing it.The test specimen is then inserted and connected to the load frame in such a way that it does not contact the metal plate closing the exit opening, but rather a gap is maintained between the test specimen and the metal plate. This ensures that the force on the test specimen continues to be applied via the adhesive bond, preventing the metal plate from pressing down on the test specimen.

[0015] At least one of the metal plates, and in some designs both metal plates, can encircle the respective exit opening at which they are arranged, thus each having a through-opening. The contour or shape of the through-opening can correspond to the contour of the recess. A section of the test specimen can then be inserted into the recess through the respective through-opening.

[0016] The sheet metal can, for example, be held solely by the two metal plates between which it is clamped and does not need to be additionally bonded to the load frame. With such a fixed sheet metal structure, it is also possible that, after the test specimen has been examined, the sheet metal can be released by removing one or both of the metal plates, allowing it to be removed from the recess along with the test specimen. The sandwich structure can then be reused.

[0017] The sheet metal is made of metal, for example steel.

[0018] In some designs, the sheet metal completely lines the wall of the recess. This allows for the largest possible bonding surface.

[0019] The openings in the first and / or second metal plate are designed, for example, such that the surrounding surface of each opening is flush with the inner surface of the sheet metal. This means that the inner surface continues seamlessly through the opening, achieving maximum overlap between the metal plate and the top or bottom edge of the sheet metal for securing the sheet. This is achieved without the metal plate protruding beyond the sheet metal and hindering or obstructing the insertion of the test specimen or the application of adhesive. Alternatively, the first and / or second metal plate may protrude beyond the inner surface of the sheet metal.

[0020] As mentioned, a sandwich structure is, for example, a structure formed from layers or strata, where the layers can have different properties, such as different elastic properties, like different bending or compression behavior. The layers or strata are stacked or layered from the top to the bottom, so that the opening extends through the layers or strata. For example, the sandwich structure can be formed from stacked plates. These plates can be at least partially oriented with a preferred bending direction. For this purpose, the plates can, for example, contain stiffening structures aligned in a stiffening direction. The stacked plates are then bonded together, for example, by adhesive.

[0021] The wall thickness of the frame can be, for example, between 5 cm and 30 cm, or preferably between 10 cm and 20 cm.

[0022] The panels of the sandwich structure can be made of laminated wood. Laminated wood panels can have a preferred bending direction, determined by their fiber orientation. Laminated wood panels are characterized by their low weight and low cost, and are also relatively easy to machine, making it easy, for example, to create a recess. The presented load frame allows for the secure clamping of a test specimen even when using simple materials such as laminated wood panels for the sandwich structure.

[0023] The panels of the sandwich structure can, in some configurations, also be designed as panels infused with reinforcements. These reinforcements can impart a stiffening direction and thus a preferred bending direction. For example, panels infused with epoxy and / or polyester resin, such as foamed panels, can be used. Examples include PU panels, PVC panels, PET panels, or balsa wood panels. The panels can also contain ribs and / or be made of slotted foam and / or contain fibers arranged in a grid-like structure. Combinations of different panel types are also possible.

[0024] The proposed steel sheet allows the adhesive bond to be three to four times stronger than a bond where the test specimen is glued to, for example, the wooden or polyurethane panels of the sandwich structure of the load frame. Advantageous properties of the wooden or polyurethane panels, such as their flexural behavior and low weight, are largely retained.

[0025] The layers, for example the plates of the sandwich structure, can be oriented such that a preferred bending direction of at least one of the layers or plates differs from a preferred bending direction of at least one other layer or plate. Thus, the preferred bending directions of the different plates or layers can be rotated relative to each other by an angle.

[0026] For example, the layers or plates can have alternating preferred bending directions from layer to layer, rotated by 90° or another angle relative to each other. It is also possible, for instance, that every third or fourth layer or plate has a preferred bending direction rotated relative to the other layers or plates. Other stacking schemes are also possible.

[0027] The thickness of the sandwich structure, extending from the top to the bottom (for example, in the case of a stack of panels in the stacking direction), can be at least 20 cm and / or at most 50 cm, preferably at least 25 cm and / or at most 40 cm. The sheet metal allows for particularly stable and robust load frames, even with a small thickness. For example, a load frame suitable for supporting an end section of a wind turbine subcomponent with a length of 3 m can be 30 cm thick. The achievable small thickness of the load frame allows for the testing of the longest possible section of the specimen.

[0028] The sheet metal can, for example, have a thickness of at least 1 mm and / or at most 3 mm. Such a sheet can be easily shaped and adapted to the contour of the recess, while also being relatively lightweight.

[0029] As mentioned, the recess can be adapted to the contour of the test specimen's end region so that the end region can be inserted into the recess. In some designs, a gap is provided between the sheet metal arranged on the recess's outer wall and the test specimen's contour. This gap can have a width of, for example, between 0.2 mm and 5 mm, allowing adhesive to be applied. Accordingly, the recess in the sandwich structure has a tolerance relative to the test specimen's end region that corresponds to the sum of the sheet metal thickness and the width of the adhesive application gap.

[0030] In some designs, the first and / or second metal plate is screwed to the sandwich structure. This means that screws are driven through the respective metal plate and into the top and / or bottom of the sandwich structure. For example, wood screws can be used, such as when the sandwich structure is a stack of wooden panels. Alternatively or additionally, the first and / or second metal plate can be joined to the sheet metal, for example, by welding.

[0031] The thickness of the first and / or second metal plate can, for example, be at least 0.2 cm and / or at most 3 cm, preferably at least 0.5 cm and / or at most 2 cm.

[0032] A test rig system for testing, for example, wind turbine subcomponents, in which the load frame described above can be used, comprises, for example, two load frames whose respective recesses are adapted to the contours of opposing end regions of the test specimen. The load frames are each connected to load-introducing structures of the test rig system, which are movable relative to each other to introduce forces.

[0033] The load frames can each be bolted to the load-bearing structures. The bolting can be done, for example, by having screws extend through the sandwich structure in the layer direction. The bolting can also pass through the first and / or second metal plate and serve additionally or alternatively to the aforementioned screws or wood screws for fixing the metal plates. Alternatively, the bolting can run outside the metal plates and only extend through the sandwich structure. In the latter case, additional metal washers can be provided for the bolting.

[0034] Spacer rings can be placed between the load frames and the load-bearing structures. These spacer rings can be made of metal, for example, steel.

[0035] The test rig system can be designed so that the distance between the load frames is, for example, between 1 m and 12 m or between 1 m and 6 m, in order to accommodate and test specimens with lengths of approximately between 1 m and 12 m or between 1 m and 6 m. The distance between the load frames can then be reduced or increased for testing purposes to apply compressive or tensile stress to the specimen. Depending on the arrangement of the load-introducing structures relative to the load frames and the relative direction of movement of the load frames to each other, forces and bending moments can be introduced into the specimen.

[0036] The application continues to relate to a procedure for using the presented load frame.

[0037] In such a process, a section of the test specimen is inserted into the recess of the load frame and bonded to the steel sheet. For example, an end section of the test specimen is inserted into the recess, such that the test specimen is flush or substantially flush with the load frame on one side, in order to obtain a maximum bonding surface and to keep the length of the test area between the load frames as long as possible.

[0038] In the methods presented here, a gap circumferential to the test specimen, with a width of between 0.2 mm and 5 mm, can be provided between the sheet metal arranged in the recess and the inserted test specimen for the application of adhesive. For example, the load frame is adapted to the test specimen by cutting the recess into the sandwich structure to match the dimensions of the test specimen, or by manufacturing the sandwich structure or the sandwich structure panels with a corresponding recess.

[0039] To test the specimen, a first end section can be inserted into the load frame and bonded in place, and a second end section opposite the first can be inserted into a second load frame and bonded to it. The second load frame can have the same features as the one described above. The two load frames can then be moved relative to each other to introduce tensile and / or compressive stress into the specimen. For this purpose, the load frames are each connected to load-inducing structures, for example.

[0040] It should be emphasized that features presented only in connection with the load frame can also be claimed for the test bench system or the procedure, and vice versa. Furthermore, features shown for the procedure can also be claimed for the test bench system, and vice versa.

[0041] The invention will be explained in more detail below using figures.

[0042] They show: Figure 1 shows a section through a load frame with a load-introducing structure and a clamped test specimen; Figure 2 shows an enlarged section of the view from Figure 1 , wherein a sandwich structure of the load frame is formed from laminated wood panels; Figure 3 shows one of the panels of the sandwich structure made of Figure 2 Figure 4 shows an oblique view of a test rig system with two load frames and a clamped test specimen; Figure 5 shows a similar view. Figure 2 , for an alternative design of the load frame, wherein the sandwich structure is formed from infused PU panels; Figure 6 shows one of the panels of the sandwich structure made of Figure 6 ; and Figure 7 shows a top view of one embodiment of the load frame.

[0043] Figure 1 shows a section AA through a load frame with a section of a test specimen 2 clamped therein and Figure 2 an enlarged section of the Figure 1 , as indicated by a box. The load frame comprises a sandwich structure 1 which has a continuous recess 15 extending from a top surface 12 to a bottom surface 13 opposite the top surface 12 of the sandwich structure 1. A section of the test specimen 2, in this case an end region of the test specimen 2, is inserted into the recess 15. A sheet 10 rests against a wall 14 of the recess 15.

[0044] The recess 15 is shaped to conform to a previously known contour of the end region of the test specimen 2, so that the test specimen 2 can be attached using an adhesive 3, as described in the Figures 1 and 2 shown, into which recess 15 can be glued.

[0045] This type of load frame achieves a significantly better adhesive bond between the load frame and the test specimen 2 than with load frames where the test specimen 2 is bonded directly to the sandwich structure 1. The proposed load frame thus provides a particularly secure and reliable fixation. Furthermore, the sheet 10 protects the wall 14 of the recess 15 from cracks or other damage caused by peel stress. It has been shown that the use of the sheet 10 offers good reinforcing properties at a low weight, while at the same time preserving at least some of the desired elastic properties of the sandwich structure 1. This avoids disadvantages of load frames known in the prior art.

[0046] The sandwich structure 1 has a layering direction or stacking direction that extends from the bottom 13 to the top 12.

[0047] The thickness of the sandwich structure 1 is between 25 cm and 40 cm. The figure shows only a lower part of the test specimen 2, which includes the end section that is glued into the load frame and protrudes only a few centimeters from the frame.

[0048] In Figure 2 is the one through which in the Figure 1 The section marked in the box is shown enlarged. Figure 2 It can be seen that a sheet metal 10, 1 to 3 mm thick, rests against a wall 14 of the recess 15, so that the end region of the test specimen 2, which is positioned in the recess 15, is bonded to an inner surface of the sheet metal and not directly to the sandwich structure. The sheet metal 10 is made of steel, but in other versions it can also be made of, for example, another metal.

[0049] Furthermore, it shows Figure 2The sandwich structure consists of laminated wood panels 11 stacked in the stacking direction, as will be explained in more detail later. The sandwich structure 1 can also be designed in other configurations as a layered structure, for example as an additively manufactured structure, or as a stack of differently designed panels 11. The individual laminated wood panels have a thickness of between 0.5 cm and 5 cm.

[0050] The sheet 10 is flush with the top surface 12 of the sandwich structure 1. A first metal plate 4, arranged on the top surface 12 of the sandwich structure and lying flat on the sandwich structure, projects over an opening in the recess 15 of the sandwich structure 1, so that the sheet 10 abuts the first metal plate 4 and is secured by it. The metal plate is flush with the inner surface of the sheet 10. However, one or both of the metal plates 4, 8 can also project beyond the inner surface and, for example, extend a few millimeters beyond the sheet 10.

[0051] A second metal plate 8, designed identically to the first metal plate 4, is arranged on an underside 13 of the sandwich structure. The sheet 10 is fixed to this plate from below, so that it is clamped between the first metal plate 4 and the second metal plate 8. The first and second metal plates each have a thickness of between 0.5 cm and 2 cm and are screwed to the laminated wood panels 11 of the sandwich structure 1 by means of wood screws 9.

[0052] The first metal plate 4 and the second metal plate 8 secure the sheet 10 by clamping as described. By removing the first 4 and / or the second metal plate 8, the sheet 10, which is bonded to the test specimen 2 for testing, is released and the test specimen 2 is removed. It is then possible to insert a new sheet 10 and reuse the remaining components of the load frame, for example, if the sandwich structure 1 has remained intact. In some designs, the first 4 and / or the second metal plate 8 may also be additionally connected to the sheet, for example, by welding.

[0053] The recess 15 of the sandwich structure 1 is adapted to the contour of the end region of the test specimen 2 such that a gap circumferential to the test specimen 2 with a width of between 0.2 mm and 5 mm is provided between the sheet 10 arranged on the wall 14 of the recess 15 and the contour of the test specimen 2, so that adhesive 3 can be introduced into the gap.

[0054] The sheet metal completely lines the wall 14 of the recess 15, so that the test specimen 2 is bonded to the sheet metal 10 all around. The test specimen 2 is only connected to the sheet metal 10, which in turn is fixed by the first 4 and the second metal plate 8.

[0055] The load frame is connected to a load-introducing structure 6 by a screw connection 5, with spacer rings 7 arranged between the load frame and the load-introducing structure. The spacer rings are made of steel. The load-introducing structure is located on the underside 13 of the load frame. The screw connection 5 extends through the entire sandwich structure 1 and the metal plates 4, 8. In this example, the test specimen 2 terminates at one end, on the underside of the load frame, with the lower metal plate 8. In other embodiments, however, the test specimen 2 can also project beyond the load frame due to the spacer rings 7 on the underside. Alternatively, it can terminate within the load frame. In this case, the lower metal plate 8 can also be designed as a continuous metal plate and close the recess 15 at the bottom.

[0056] Figure 3 shows in an oblique view one of the plywood panels of the in Figure 2recognizable sandwich structure 1. The fiber orientation of the laminated wood panel runs essentially parallel to a z-axis and thus defines a preferred bending direction of the laminated wood panel about an axis parallel to an x-axis, for example, when ends of the panel 11 are loaded parallel to a y-axis. If several such panels 11 are used as in the Figure 2When stacked on top of each other, the fiber orientations of the sandwich structure 1 can be parallel to each other or form an angle by rotating one or more of the plates around the y-axis. For example, at least one of the plates 11 of the sandwich structure 1 can have a different fiber orientation than the other plates 11. The plates 11 can also be alternately rotated by 90° relative to each other or arranged according to another scheme, whereby angles other than 90° are also possible. In this way, it can be achieved that the sandwich structure 1 as a whole exhibits different bending behavior along different axes. For example, every third or every fourth plate can also be rotated by 90°.

[0057] Figure 4Figure 1 shows a test rig system comprising two load frames between which the test specimen 2 is clamped. Both load frames are load frames according to this application and have the same features. In the figure, features belonging to the second of the two load frames are marked with dashes for differentiation, while undashed reference numerals are used for the first of the two load frames. The dashes serve for differentiation where necessary. Since both load frames have the same properties, it should be noted that such features referred to only by undashed reference numerals may also be present in the second load frame and vice versa. In particular, both load frames have plates 10 (not shown, see Figure 1). Figures 1 and 2 ), which are arranged on the walls of the recesses 15, 15'.

[0058] The two load frames are arranged in a mirrored configuration.

[0059] The test specimen 2 extends between the two load frames, is inserted into the load frames with its end regions and emerges from the load frames at the tops 12, 12', where the term top is defined here as the side at which the section of the test specimen 2 to be tested emerges from the load frame.

[0060] Each load frame is between 25 cm and 50 cm thick. Test specimen 2, as a wind turbine subcomponent, has a length of between 1 m and 12 m.

[0061] On the upper surface 12 of the sandwich structure 1 of the first load frame, the first metal plate 4 is arranged with a through-opening, which is screwed to the plates 11 of the sandwich structure 1 by means of wood screws 9. The through-opening of the first metal plate 4 is designed such that the first metal plate 4 conforms to the recess 15 of the first load frame and secures the sheet metal abutting the wall 14. From the recess 15, the test specimen 2, which was inserted into the first load frame with its first end region, protrudes from the upper surface 12 of the first load frame and extends through the through-opening of the first metal plate 4.

[0062] The second end section of the test specimen 2 is inserted into the recess 15' of the second load frame from the top 12'. The bottom 13' of the second load frame is in the Figure 4Visible. An outlet opening of the recess 15' is visible, through which the recess on the underside 13' of the sandwich structure 1' protrudes and which is surrounded by the second metal plate 8'. The second metal plate 8' secures the sheet 10' also present in the second load frame. In other embodiments, the second metal plate 8 can also cover or partially cover the outlet opening on the underside 13'. The test specimen 2 is essentially flush with the underside 13' of the sandwich structure 1' and does not project into the area of ​​the second metal plate 8'. The test specimen can also terminate within the test specimen, for example, in embodiments where the second metal plate 8' completely or partially covers the outlet opening of the recess 15'.

[0063] The two load frames can be connected to load-introducing structures 6, which can be arranged on the undersides 13, 13' of the load frames (see Figure 1 and 7The two load frames are movable relative to each other by means of the load-introducing structures 6, which allows, for example, tensile or compressive stress to be introduced into the test specimen 2 when the load frames are used to test it. This makes it possible to determine elastic properties of the test specimen, such as modulus of elasticity, yield strength, strength, elongation at break, i.e., its load-bearing capacity as well as its plastic and elastic deformability.

[0064] Figure 5 shows a similar section as Figure 2 for an alternative embodiment of the load frame shown. The sandwich structure 1 is formed from plates 11 infused with reinforcements. In Figure 6Figure 11 shows such a plate in detail. It is a PU plate, PVC plate or balsa wood plate infused with resin, epoxy or polyester, which, like the plywood plate described above, has a preferred bending direction about an axis parallel to the x-axis.

[0065] In the sandwich structure in Figure 5 Such reinforced plates 11 are arranged alternately rotated by 90° to each other.

[0066] The metal plates 4, 8, arranged on the top 12 and bottom 13 of the sandwich structure 1, are clamped to the sandwich structure by means of the screws 5. For this purpose, the screws are positioned close to the recess 15, for example, at a distance of 1 cm to 5 cm from the recess 15, to prevent deflection of the metal plates 4, 8 under load. Additional screws for fixing the metal plates 4, 8 are omitted in this example. This is also possible in versions with plywood panels or differently designed panels.

[0067] Figure 7 shows a top view of a top surface 12 of a similar load frame as in the Figure 1 and 4 shown. The section line AA of the Figure 1 is in Figure 7 The figure shows the uppermost of the plates 11 of the sandwich structure 1, in whose recess the test specimen 2 is positioned and fixed by means of adhesive 3.

[0068] The first metal plate 4, which serves to fix the sheet metal 10, surrounds the outlet opening of the recess and has a through-opening following the recess. The first metal plate 4 thus forms a metallic band following the recess with a width of 3 to 10 cm, which is screwed to the sandwich structure 1 by means of wood screws 9.

[0069] The through-opening is so large that its wall 14 is flush with the inner surface of the sheet 10, and thus the recess 15 with the sheet 10 arranged therein continues steplessly through the through-opening, so that a maximum overlap with the sheet 10 is achieved for its fixation and the end area of ​​the test specimen 2 can be inserted into the recess 15 through the through-opening when using the load frame.

[0070] A remaining gap between the sheet metal 10 and the test specimen 2, into which adhesive 3 is applied and which extends through the through-opening between the metal plate 4 and the test specimen 2, then has a width of between 0.2 mm and 5 mm in both the area of ​​the sheet metal 10 and the area of ​​the metal plate 4.

[0071] A wall thickness 16 of the frame, measured from the perimeter 14 of the recess 15 to an outer edge of the sandwich structure 1, is at least 10 cm everywhere.

[0072] The screw connection 5, which serves to connect the load frame to the load-introducing structure 6, is inserted directly into the sandwich structure 1 outside the metal plate; however, in other designs it can also extend through the metal plate.

[0073] The load frame shown allows for the targeted simulation of conditions corresponding to those that would exist if the test specimen were operated or used, for example, as part of a wind turbine rotor blade, particularly by adjusting the position of the load-introducing structure 6 relative to the load frame. For this purpose, bending moments can be introduced into the test specimen 2, for instance, by applying eccentric forces. The screw connection 5 can be arranged accordingly, or the load-introducing structure can be connected to the screw connection 5 using appropriately selected screws. As mentioned, the presented load frame is particularly suitable for tolerating transverse stresses or peel stresses associated with bending moments and for protecting the bond 3 or the sandwich structure 1 from failure.

[0074] A second metal plate 8 is arranged on the underside 13 of the load frame, opposite the upper side 12 shown in the figure. This second metal plate 8 can have the same properties as the first metal plate 4 described here. The second metal plate 8 can then be adapted to the outlet opening on the underside 13 of the load frame, which may differ in shape and / or size from the opening shown in the figure. Figure 7 The upper outlet opening shown can be distinguished. The second metal plate 8 can also be designed differently from the first metal plate 4 in possible versions and, for example, at least partially close the lower outlet opening. Reference symbol list

[0075] 1 Sandwich structure 2 Test specimen 3 Adhesive 4 First metal plate 5 Screw connection 6 Load-bearing structure 7 Spacer ring 8 Second metal plate 9 Wood screw 10 Sheet metal 11 Plate 12 Top side 13 Bottom side 14 Enclosure 15 Recess 16 Wall thickness

Claims

1. A load frame for testing wind turbine subcomponents, to use in a test bench comprising a sandwich structure (1) with a continuous recess (15) for receiving a test specimen (2), characterised in that the recess (15) extends from an upper side (12) to a lower side (13) of the sandwich structure (1) opposite the upper side (12), and the load frame comprising a sheet (10) which rests against a wall (14) of the recess (15), the sandwich structure comprising stacked plates or being manufactured in layers.

2. The load frame according to claim 1, the sheet metal (10) being flush with the upper side (12) and the lower side (13) of the sandwich structure, and the load frame further comprising a first metal panel (4) arranged on the upper side (12) of the sandwich structure (1) and a second metal panel (8) arranged on the lower side (13) of the sandwich structure (1), the first (4) and second metal panels (8) each protruding beyond the outlet openings of the recess (15) such that the sheet metal (10) abuts against the first (4) and second metal panels (8) and is clamped between the first (4) and second metal panels (8), the first metal panel (4) and / or the second metal panel (8) having preferably a through-opening, so that the recess (15) continues through the respective through-opening.

3. The load frame according to claim 2, a wall (14) of the through-opening of the first (4) and / or second metal panel (8) terminating flush with the inner surface of the sheet (10).

4. The load frame according to any one of the preceding claims, the sheet (10) completely lining the wall (14) of the recess (15).

5. The load frame according to any one of the preceding claims, the sheet (10) being formed as steel sheet.

6. The load frame according to any one of the preceding claims, the sandwich structure (1) being formed from stacked panels (11), preferably at least partially from panels (11) with a preferred bending direction.

7. The load frame according to claim 6, the panels (11) of the sandwich structure (1) being designed as laminated wood panels or the panels (11) of the sandwich structure (1) being formed as panels infused with reinforcements, preferably as foamed PU panels, PVC panels, PET panels, or balsa wood panels infused with epoxy resin or polyester resin.

8. The load frame according to any of the claims 6 or 7, the panels (11) of the sandwich structure (1) are oriented such that a preferred bending direction of at least one of the panels (11) is different from a preferred bending direction of at least one further panel (11), the panels being preferably arranged alternately with preferred bending directions rotated by 90° relative to each other.

9. The load frame according to any one of the preceding claims, a thickness of the sandwich structure (1) measured from the upper side (12) to the lower side (13) is at least 20 cm and / or at most 50 cm, preferably at least 25 cm and / or at most 40 cm, and / or a thickness of the sheet (10) being at least 1 mm and / or at most 3 mm.

10. The load frame according to claim 2 or according to any one of claims 3 to 9, insofar as it refers back to claim 2, the first (4) and / or the second metal plate (8) being screwed to the sandwich structure (1) and / or a thickness of the first (4) and / or second metal plate (8) being at least 0.2 cm and / or at most 3 cm, preferably at least 0.5 cm and / or at most 2 cm.

11. A test bench system comprising two load frames according to any one of the preceding claims, the load frames each being connected to load-introducing structures (6) of the test bench system, which are movable relative to each other.

12. The test bench system according to claim 11, each of the load frames being screwed to a load-introducing structure (6) and spacer rings (7) being arranged between the load frame and the respective load-introducing structure (6) to which it is screwed and / or a distance between the two load frames being between 1 m and 12 m, for testing test specimens (2) with lengths of essentially between 1 m and 12 m.

13. A method for using the load frame according to any one of claims 1 to 10 for testing a test specimen (2), characterised in that a section of the test specimen (2) is inserted into the recess (15) of the load frame and glued to the sheet (10).

14. The method according to claim 13, a gap with a width of between 0.2 mm and 5 mm being provided between the sheet (10) arranged in the recess (15) and the inserted test specimen (2) for the purpose of introducing adhesive (3).

15. The method according to claim 13 or 14, a first end region of the test specimen (2) is inserted into the load frame and glued in place, and a second end region opposite the first end region is inserted into a second load frame and glued to the second load frame, and the two load frames are moved relative to each other to induce a tensile and / or compressive stress in the test specimen (2).