Device and method for testing structures with structure-integrated energy storage devices

Abstract

Device for testing structures with structure-integrated energy storage devices, comprising a device for mechanical excitation (100) with at least one degree of freedom, a test specimen (1) comprising a section (2) of a car body with a structure-integrated energy storage device (3), and connecting elements (20) for connecting the test specimen (1) to the device for mechanical excitation (100), wherein the connecting elements (20) each comprise an adjustable bearing (21) with a stiffness adjustable in at least one spatial direction, characterized in that the connecting elements (20) are coupled to the device for mechanical excitation (100) via a frame (40).

Description

The invention relates to a device and a method for testing structures with integrated energy storage devices. The structures to be tested are, in particular, parts of car bodies into which high-voltage storage devices are integrated. In the field of electromobility, particularly in the development of electric passenger cars, the testing of structurally integrated energy storage systems, especially high-voltage storage systems, is a crucial issue. The term high-voltage storage (HVS) here refers to a battery used to power hybrid and electric vehicles. Generally, batteries with a voltage rating exceeding 60 VDC are classified as high-voltage storage systems. "Structurally integrated" means that the battery is mounted within the vehicle body in such a way that deformation of the body also results in significant deformation of the battery. The connection between the body and the energy storage system is not merely a point connection, such as at its corners, but rather a continuous connection, for example, via multiple attachment points along several edges of the storage system, resulting in static indeterminacy. The investigation of structurally integrated energy storage systems and adjacent substructures is therefore complex, but necessary to ensure the service life and operational reliability of "battery-adjacent" substructures of vehicle bodies with structurally integrated high-voltage storage systems, as well as the energy storage systems themselves. Test benches and procedures are required that are capable of reproducing strains that primarily correlate with global deformation of the body. This can be achieved either by conducting tests with a complete body or a complete vehicle, by separately testing the energy storage system without the body structure, or by connecting the energy storage system to a test bench using a section of the body. However, testing a complete body requires a full vehicle prototype, meaning that such testing can only be applied late in the development process.Tests on a complete vehicle test rig are also more expensive and prone to errors. Testing the energy storage system without the vehicle body does not allow for realistic testing of structurally integrated energy storage systems, as this test only applies the stresses from inertial loads due to the system's own inertia, not the loads exerted on the energy storage system by body deformations. Using body cutouts to simulate stiffness only serves to replicate local stiffness effects in the connection area. This may be useful for compact batteries, but not for large-area, structurally integrated energy storage systems, for which global body deformation is crucial. DE 10 2016 206 146 A1 discloses, for example, a test rig for testing vehicle parts, which has several attachment points for securing a vehicle part to be tested and at least one actuator for moving the attachment points, wherein the stiffness of the attachment points can be varied by controlling the at least one actuator. DE 10 2021 131 262 A1 also describes a method for performing a fatigue strength test on an energy module for a motor vehicle, which enables the determination of structural data of an energy module and of an overall vehicle structure. The purpose of the present patent application is therefore to solve the aforementioned problems of known testing methods and to propose a device and a method for testing structures with integrated energy storage systems, with which, in particular, integrated high-voltage storage systems can be tested under realistic boundary conditions, so that a meaningful characterization of the lifetime properties of substructures of vehicle bodies with integrated high-voltage storage systems can be carried out. This problem is solved by a device according to claim 1 and by a method according to claim 8. An inventive device for testing structures with integrated energy storage devices comprises in particular a device for mechanical excitation with at least one degree of freedom, a test specimen comprising a section of a car body with integrated energy storage devices, and connecting elements for connecting the test specimen to the device for mechanical excitation, wherein the connecting elements each comprise an adjustable bearing with a stiffness adjustable in at least one spatial direction, characterized in that the connecting elements (20) are coupled to the device for mechanical excitation (100) via a frame (40). Structures with integrated energy storage systems are primarily car bodies. An integrated energy storage system is, in particular, a high-voltage storage system or a battery for providing electrical energy to a hybrid or electric car, which is continuously connected to the body, for example via multiple connection points on several edges of the energy storage system, and is therefore particularly susceptible to deformations of the body. The mechanical excitation device can be a multi-axial vibration table (MAST), as commonly used for testing vehicle components. However, the mechanical excitation can also be achieved by at least four actuators, analogous to a four-post system. The mechanical excitation device has at least one degree of freedom (DOF), but preferably six degrees of freedom, to allow translational movement along the x, y, and z axes as well as rotations about them. The test specimen consists of a section of a passenger car body into which an energy storage device is integrated. In addition to the structurally integrated energy storage device and directly adjacent body structures, the test specimen may also include components connected to the partial body. The partial body exhibits interfaces and cutting planes resulting from the fact that the partial body was either cut from a complete body or only partially assembled. Furthermore, the test specimen may include components with masses of a stress-relevant magnitude, whose inertial forces act directly on the energy storage device and its connections. The test specimen is connected to the mechanical excitation device via one or more connecting elements. These are force-fit, preferably detachable, for example by means of screws, and are connected to the mechanical excitation device and the test specimen. The connecting elements thus serve to transmit the mechanical excitation to the test specimen. The connecting elements each comprise an adjustable bearing with a stiffness that can be adjusted in at least one spatial direction. The adjustable bearing thus has defined stiffness properties in one spatial direction, preferably along all three axes. One part of the adjustable bearing is mounted immovably relative to the device for mechanical excitation, and the second part (the "moving part") is rigidly connected to the test specimen. The adjustable bearings can, for example, be those described in EP 2 694 836 B1, whose stiffness can be adjusted by rotating the bearing. By adjusting the stiffness of the connecting elements when introducing mechanical excitation into the test specimen, i.e., a section of a car body, the stiffness of the entire body can be simulated. The device according to the invention thus enables realistic testing of the body structure with integrated energy storage devices, without requiring testing of the entire body. The stiffness of adjustable bearings can be adjusted by means of an actuator. For example, an actuator located outside the force flow of the adjustable bearings can be used to adjust the stiffness by rotating the respective bearings. Furthermore, an active system can simulate dynamic stiffness in the vehicle body during testing. This allows for realistic testing of a wide variety of loads on the body and energy storage system. For this purpose, the device can include actuators positioned within the force flow, which adjust the stiffness of the adjustable bearings during testing. The actuators generate forces, for example, using hydraulic, electric, or pneumatic cylinders, piezoelectric actuators, or electrodynamic / moving-coil actuators, and transmit these forces to the adjustable bearing to adjust its stiffness. The device can also include sensors for detecting forces, displacements, velocities, and / or accelerations between or on the moving part of the adjustable bearings and the test specimen.Based on this sensor data, power electronics can then perform dynamic control and generate a signal to control the actuators, dynamically adjusting the stiffness of the adjustable bearings. This allows for control based on force, acceleration, velocity, or displacement feedback, or for the simulation of a previously defined dynamic target stiffness (e.g., from previous measurements or simulation models). Such an active system can be used to generate virtual stiffnesses, inertias, damping, or simulated vibration responses via force / velocity or displacement feedback; to generate defined dynamic target stiffnesses (e.g., from previous measurements or simulation models) using a suitable controller; or to generate defined load / frequency spectra for exciting the test specimen. The device can comprise a frame made of transverse and longitudinal beams, which serves to connect the connecting elements to the mechanical excitation device. In this case, the connecting elements are positively connected to the frame (preferably detachably, e.g., by means of screws), and the frame is positively connected to the mechanical excitation device, for example, also by screws. Such a frame is particularly useful if the test specimen is larger than the base area of ​​the mechanical excitation device or if the basic shape of the test specimen and the mechanical excitation device differ. The frame consists, for example, of two transverse and two longitudinal beams. These can be system profiles.The necessary dimensions of the frame are determined by the size of the test specimen, and in an advantageous embodiment, the crossbeams can be shifted relative to the longitudinal beams to adapt the frame to different specimen lengths. The crossbeams and longitudinal beams can also be designed so that the connecting elements can be moved along their main direction to position them for different test specimens. Furthermore, the frame can be constructed with an interior space within the crossbeams and longitudinal beams, which can, for example, house the actuators and sensors for measuring the dynamic stiffness of the adjustable bearings. At least some connection elements can include a surface-mounted test specimen connection element. Such a surface-mounted test specimen connection element could, for example, be a milled part that is connected to the local surfaces of the test specimen. This milled part could be made from a material with a lower modulus of elasticity than the material of the body shell and be shaped to minimize changes in stiffness on the body shell. This component is attached to the test specimen, for example, by screws, rivets, adhesives, or a combination of these methods. A surface-mounted test specimen connection element allows forces to be introduced into surfaces of the test specimen where no force application is intended during normal driving on the actual vehicle, but where such force application is necessary to simulate specific loads. Additionally or alternatively, some connecting elements may also include a discrete test specimen connection element. Such a discrete test specimen connection element can be designed to be attached to discrete mounting points on the test specimen, such as threads, existing screw connections, mounting points for elastomer bearings, or chassis components. This allows force to be applied during testing to points on the test specimen that are intended to establish a force flow between the components typically mounted there and the vehicle body. Furthermore, the connecting elements can each include a height and angle adjustment element. By providing height and angle adjustment options for the individual connecting elements, they can be adapted to the shape of the test specimen, resulting in more possibilities for positioning and direction of force application. A method according to the invention for testing structures with integrated energy storage devices comprises in particular the following steps: manufacturing the test specimen, wherein the test specimen comprises a section of a car body with an integrated energy storage device; determining the positions and direction of connection elements for connecting the test specimen to a device for mechanical excitation, wherein the connection elements each comprise an adjustable bearing with a stiffness adjustable in at least one spatial direction; determining stiffness values ​​of the adjustable bearings to be set for the test; connecting the test specimen to the device for mechanical excitation by means of the connection elements and setting the adjustable bearings to the determined stiffness values; and carrying out a mechanical excitation of the test specimen by means of the device for mechanical excitation in order to achieve defined stresses on the test specimen. There are two options for manufacturing the test specimen: Firstly, the test specimen can be produced using prototype construction. This is particularly useful in early development phases, as this option does not require that a complete car body has already been produced. Alternatively, the test specimen can be cut from a complete car body. The cutting pattern can be determined either by evaluating different variations of the cutting surfaces and planes based on numerical calculations and / or by engineering estimation of the cutting surfaces and planes, taking into account, for example, car body structures with a special reinforcing and stiffening effect. The next step is to determine the positions and directions in which the connecting elements will be attached to the test specimen. These connecting elements serve to link the specimen to the mechanical excitation device and each includes an adjustable bearing. Depending on the type of tests to be performed, the adjustable bearings may be located in one spatial direction or may extend to multiple directions. The number and orientation of the adjustable bearings must be selected to strike a balance between achievable accuracy and the technical complexity of the test environment. The stiffness values ​​to be set for the test must be determined before the actual test is carried out. Numerical models and reference loads can be used for this purpose. By adjusting the stiffness of the connecting elements when the mechanical excitation is introduced into the test specimen, the stiffnesses of the entire car body can be simulated. Only then does the actual construction of the test setup take place, along with the connection of the test specimen to the device for mechanical excitation via the connecting elements and the adjustment of the adjustable bearings to the specified stiffness values. Finally, the mechanical excitation of the test specimen is carried out by the mechanical excitation device to achieve defined stresses on the specimen. Known iteration methods can be used to achieve minimal deviations from the reference stresses at the relevant output positions. Possible iteration targets could be, for example, force, acceleration, or strain values ​​at the test specimen or its connections. During the test, the stiffness of the adjustable bearings can be adjusted by an actuator. For example, an actuator located outside the force path of the adjustable bearings can be used to adjust the stiffness by rotating the respective bearings, allowing for adjustments even during the test. Active control also allows dynamic stiffnesses in the vehicle body to be simulated during testing. This enables realistic testing of a wide range of loads on the body and energy storage system. In particular, the stiffness of the adjustable bearings can be controlled based on sensor data acquired at the mounting elements. This allows for control based on force, acceleration, velocity, or displacement feedback, or for the simulation of a previously defined dynamic target stiffness (e.g., from previous measurements or simulation models). Such active control can be used to generate virtual stiffnesses, inertias, damping, or simulated vibration responses using force / velocity or displacement feedback, and to generate defined dynamic target stiffnesses, for example.from previous measurements or from simulation models, using a suitable controller or to generate defined load / frequency spectra to excite the test specimen. The test specimen can be connected to the device for mechanical excitation via a frame made of transverse and longitudinal beams, which serves to connect the connecting elements to the device for mechanical excitation. The positions and directions of the connection elements can be determined based on a numerical model of the test specimen. Advantageous criteria for selecting the positions of the connection elements include, for example, the realization of the vibration modes of the test specimen necessary to achieve the test results, local stresses, or damage. Similarly, the stiffness of the adjustable bearings can be determined based on a numerical model of the test specimen and reference stresses.In particular, determining stiffness can include the following steps: Building a numerical model of the test specimen. This can be a linear numerical or finite element model. Reducing the model's output positions to those relevant for evaluating the test specimen. Determining the reference stresses of the relevant output positions, for example, from a finite element analysis of the entire car body under reference loading.Derivation of linear relationships from the model between 1) the displacements and rotations of the test specimen at the positions of the attachment elements on the test specimen and the forces acting there, in order to obtain a stiffness matrix of the test specimen reduced to the positions of the attachment elements, 2) the accelerations of the device for mechanical excitation and forces and moments at the attachment degrees of freedom of the adjustable bearings with ideally rigid constraint of all degrees of freedom at these attachment points, 3) the displacements and rotations in all six spatial degrees of freedom at the attachment points of the adjustable bearings and the local stress quantities at the relevant output positions, and 4) the accelerations of the device for mechanical excitation and local stress quantities, for example stress components, at the relevant output positions with ideally rigid constraint of all degrees of freedom.Description of the adjustable bearings as a linear stiffness matrix, which describes the forces acting on the test specimen by the adjustable bearings as a function of relative movements between the connections of the adjustable bearings to the mechanical excitation device and the connection of the adjustable bearings to the test specimen. Evaluation of local stress at the relevant output positions using linear relationships and linear superposition for various acceleration excitations and stiffness configurations of the adjustable bearings. This evaluation can be computer-aided and at least approximate. Optimization of the stiffness values ​​of the adjustable bearings and / or the acceleration excitations of the mechanical excitation device using the evaluation of the local stress with respect to the reference stress. In this way, a suitable stiffness setting can be found with relatively little computational effort. Optimizing the stiffness values ​​by varying the model parameters stiffness and excitation to ensure a satisfactory simulation of the reference stress would, however, be significantly less efficient. The described embodiments of the device and method for testing structures with integrated energy storage devices can be used individually or in combination to achieve great flexibility in the realistic testing of a wide variety of structures with integrated energy storage devices, especially high-voltage storage devices. The aforementioned and further aspects of the invention will become apparent from the detailed description of the exemplary embodiments, which is given with the aid of the following figures, of which: Fig. 1 schematically represents an embodiment of the device according to the invention, Fig. 2 represents an embodiment of the device according to the invention with a frame, Figs. 3a-c show different views of a test specimen, Fig. 4 shows the structure of the device with connecting elements and a frame, Fig. 5 shows an enlarged detail from Fig. 4, Fig. 6 shows different embodiments of the connecting elements for planar connections, Fig. 7 shows different embodiments of the connecting elements for discrete connections, Fig. 8 schematically shows an adjustable bearing used, Fig.Figure 9 schematically illustrates 9 different embodiments of an active system for adjusting dynamic stiffness by means of adjustable bearings and Figure 10 shows a flowchart of the method according to the invention. The device and the method will be explained in more detail below, based on the accompanying drawings. Reference numerals refer to the same elements. Fig. 1 shows the main components of the device. This includes a test specimen 1, a mechanical excitation device 100, and connecting elements 20, each depicted as springs with adjustable stiffness. The mechanical excitation device 100 can be a multi-axial vibrating table or an arrangement with at least four actuators, analogous to a four-post system. For simplicity, however, a vibrating table is shown here. Therefore, the mechanical excitation device 100 will henceforth be referred to as the vibrating table 100. In Fig. 2, the connecting elements 20 are coupled to the vibrating table 100 via a frame 40. The test specimen 1 is shown in Fig. 3a from below, in Fig. 3b from a top oblique angle, and in Fig. 3c in section along the xz-plane. The test specimen 1 consists of a section 2 of the car body or partial body 2, a structurally integrated energy storage device 3 therein, for example a high-voltage storage device, components 7 connected to the partial body 2, as well as interfaces 5, 6 and section planes 4. The section planes and points 4, 5, 6 result from the fact that the partial body 2 was cut out of a complete car body or only partially assembled. Fig. 4 shows the testing of structures with integrated energy storage devices without a mounted test specimen 1 and, in one embodiment, with the frame 40. This embodiment is used when the test specimen 1 is geometrically larger than the base area of ​​the vibration table 100, or when the basic shape of the test specimen 1 and the vibration table 100 differs. The frame consists of two crossbeams 41 (y-direction) and two longitudinal beams 42 (x-direction). These can, for example, be made of system profiles and together form the basic frame, which connects the attachment elements 20 to the vibration table 100. The necessary dimensions result from the size of the test specimen 1 to be tested. In an advantageous embodiment, the construction is designed such that the crossbeams 41 are displaceable relative to the longitudinal beams 42 along the x-direction. This allows the setup to be adapted to different test specimen lengths.Optional stiffening plates 43, 44 can be used to reinforce the base frame. These can be the same size at each frame corner or differ depending on the stiffening requirements. They can be used on only one side of the frame or on the top and bottom of the frame. Fig. 5 shows a more detailed representation of the connection elements 20 on the frame and various embodiments of the test specimen connection. The connection elements 20 consist of a base plate 22, an adjustable bearing 21, a connecting part 23, and an element for connecting the test specimen 24, 26. The longitudinal 42 and transverse beams 41 of the frame 40 are designed such that they have grooves 30 along their main direction, along which the connection elements 20 can be moved. This is achieved by the base plate 22 having bores that correspond to the spacing of the grooves 30. By using screws and T-nuts that fit the grooves 30, movement along the frame parts 41, 42 can be achieved. If stiffening plates 43 are used, corresponding recesses 31 can be provided in them to allow sufficient movement.In an advantageous embodiment, the longitudinal beams 42 and transverse beams 41 can be constructed from several profiles connected to each other in a force-fit manner, resulting in a gap 31. This gap can be used, for example, to accommodate sensors 70 or actuators 80 (see Fig. 9). The connection elements 20 consist of an adjustable bearing 21, the stiffness of which can be adjusted, preferably with defined stiffness properties along the spatial directions x, y, and z. One part of the adjustable bearing 21 is fixed relative to the frame 40 or the device for mechanical excitation 100, and the second part (“moving part”) is rigidly connected to the test specimen 1 by means of the connecting elements 23 and elements for test specimen connection 24, 25, 26. The connecting element 23 can allow angular and / or vertical compensation between the adjustable bearing 21 and the test specimen connection 24 and optionally enable measurement of the forces and / or relative movements transmitted between the test specimen 1 and the adjustable bearing 21. The elements for connecting the test specimen 24, 25, 26 are shown in more detail in Figures 6 and 7. The shapes of the elements for connecting the test specimen 24, 25, 26 are determined by the geometry of the test specimen 1 at the points where it is to be mounted. Elements for planar connection 24, 25 and those for discrete connection 26 can be used. Discrete connection points are, for example, a thread in the test specimen 1 or mounting points for elastomer bearings or chassis components. These differ from planar connections in that these points on the test specimen 1 are intended to establish a force flow between the components typically mounted there and the vehicle body. In contrast, planar connections are used at locations where no force application is intended during driving on the actual vehicle, but where this is necessary for the purposes of the test concept described here.Fig. 6 shows connection elements 20 with elements for surface connection of the test specimen 24, 25. The element for surface connection 25 is a milled part that can be bonded and / or riveted / screwed to the local surfaces of the test specimen. The milled part can, for example, be made of a material with a lower modulus of elasticity than the material of the body shell and be shaped in such a way that changes in stiffness on the body shell are kept to a minimum. This can be achieved, for example, by a tapered cross-section as shown. The connection element 20 on the left in Fig. 6 also has a combined height and angle compensation element 23, while the element for connecting the test specimen 25 in the middle is connected to the adjustable bearing 21 by means of a force sensor 23a and a combined height and angle compensation element 23b.However, it is also possible to connect the element for test specimen connection 25 directly to the adjustable bearing 21. Furthermore, various other sensors can be integrated into the connecting elements 23 or the adjustable bearing 21 to measure not only the forces but also the displacements or accelerations. Displacement measurement can be implemented directly or indirectly, based on acceleration measurements. Fig. 7 shows various versions of the connecting elements 20 with elements for discrete test specimen connections 26. On the left is an embodiment with height adjustment, achieved via a central thread in the adjustable bearing 21 and the adapter screwed into it. The adapter is connected to the bearing 21 by means of a central thread and is designed to accommodate an angle compensation element 23b and a test specimen-side adapter 29. The test specimen-side adapter 29 is designed to function similarly to a washer under the screw 28, which is screwed to the test specimen 1. This creates a force-fit connection between the bearing 21 and the test specimen 1. The right side of the figure shows an embodiment with integrated force measurement by the force sensor 23a and an angle compensation element 23b, but without height adjustment. The actual adjustable bearing is shown in detail in Fig. 8. This is a bearing with adjustable stiffness, based on the disclosure of EP 2 694 836 B1. The adjustable bearing consists of a housing or stationary part 63, which is connected to the base plate 22 by screws 32, and the moving part 61. These are connected by means of a device for achieving adjustable stiffness 60 and thus form a bearing 21 with adjustable stiffness. The function of the device for achieving adjustable stiffness 60 is described in more detail in EP 2 694 836 B1. The moving part 61 has one or more fastening points, e.g., threads 62, which are used to fasten the connecting element 23. These can be, as shown, for example, a central threaded bore or several threaded bores distributed around a bolt circle.Advantageously, centering mechanisms are provided to center the attachable connecting elements 23 relative to the main axis of the bearing 21. In an advantageous embodiment, the housing 63 and the base plate 22 have a central opening 64. This makes it possible to connect additional sensors 70 or actuators 80 to the moving part 61 from below / through the frame, thus actively simulating dynamic stiffnesses, as described below. An actuator 69 can also be used to statically adjust the stiffness of the adjustable bearing 21. The housing 63 is clamped to the base plate 22 by means of screws 67 and a counter-holding plate 65. The through holes 66 in the base plate 22 required for the screws 67 and the pocket to recess the counter-holding plate 65 in the base plate 22 are designed in such a way that - with the screws loosened - the housing 63 can be moved relative to the base plate 22.This allows for fine positioning of the adjustable bearing relative to the frame 40 or the vibration table 100 in the xy-direction. Furthermore, the adjustable bearing can be equipped with a scale 68, which allows the current stiffness setting to be read. Fig. 9 shows an embodiment for the active simulation of defined, dynamic stiffnesses. This comprises an actuator 80 suitable for generating forces, for example in the form of hydraulic, electric, or pneumatic cylinders, piezoelectric actuators, or electrodynamic actuators / moving-coil actuators. This actuator is positively connected to the moving part 61 of the adjustable bearings 21. Two examples of this connection are shown: On the right in Fig. 9, a coaxial installation of the actuator 80 in the frame 40, here in the space 31 between the symmetrically arranged profiles of the longitudinal / transverse beams 42, 41, and a direct connection by means of an adapter 81 are shown. By applying a force to the actuator 80, the adapter 81, and thus also the moving part of the adjustable bearing 21, is moved, so that the stiffness of the adjustable bearing 21 can be adjusted. Alternatively, a direct connection of the actuator 80 would also be possible, e.g.One possibility is to coaxially install a moving-coil actuator directly into the adjustable bearings 21. On the left in Fig. 9, the actuator 80 is installed in the space 31 of the frame 40, and the force transmission is achieved using a device 82 (for example, a lever mechanism / rocker / mechanical gearbox) and a coaxial adapter 81 connected to it. Alternatively, it would also be possible to install the actuator 80 on the vibrating table 100 in an orientation that does not correspond to the orientation of the supports 41, 42 of the frame, and to connect it to the adjustable bearings 21 by means of a device 82 for connecting the actuator 80 to the adjustable bearings 21, modifying the frame 40 (e.g., by adding openings) to enable these connections. The active system for adjusting the adjustable bearings 21 shown in Fig. 9 also includes sensors 70 for acquiring sensor data 71 at the moving part 61, or between the moving part 61, the adjustable bearings 21 and the connecting elements 23 or the test specimen 1. This sensor data can be measured forces, displacements, velocities and / or accelerations. A control unit 72 generates a signal 73 to control the actuators 80 in order to perform either control based on force, acceleration, velocity, or displacement feedback, or control to replicate a previously defined dynamic target stiffness (e.g., from previous measurements or simulation models).Such an active system can be used to generate virtual stiffnesses, inertias, dampings or simulated vibration responses by means of force / velocity or displacement feedback, to generate defined dynamic target stiffnesses, e.g. from previous measurements or from simulation models, by means of a suitable controller, or to generate defined load / frequency spectra to excite the test specimen 1. Fig. 10 shows a flowchart of a method according to the invention for testing structures with integrated energy storage devices. This method comprises the following steps: manufacturing S1 of the test specimen 1, determining S2 the positions and directions of the connection elements 20, determining S3 the stiffness values ​​of the adjustable bearings 21 to be set for the test, connecting S4 of the test specimen 1 to the device for mechanical excitation 100 by means of the connection elements 20 and setting the adjustable bearings 21 to the determined stiffness values, and carrying out S5 the mechanical excitation of the test specimen 1 by the device for mechanical excitation 100 in order to achieve defined stresses on the test specimen 1. In this way, the method includes both the configuration of the previously described device for a specific test specimen 1 and the actual execution of the test. The individual steps are explained in more detail below. S1: Manufacturing the test specimen / Cutting the bodywork The test specimen 1 must contain the following elements: the energy storage device 3, directly connected body structures 2, surrounding structural components important for local stiffness (local stiffness here is a stiffness whose stiffening effect acts primarily on an environment that is smaller than or similar in size to the selected spacing of the adjustable bearings 21 and is therefore not replaced by them), and components with masses of a stress-relevant magnitude whose inertial forces act directly on the energy storage device and its connections. There are two ways to manufacture the physical test specimen 1: It can be manufactured by means of prototype construction, or it can be separated from an existing, complete body, for example, from test vehicles.The determination of the cutting pattern can be based either on an evaluation of different variants of the cutting surfaces / planes 4, 5, 6 through numerical calculations or on an engineering estimation of the cutting surfaces / planes 4, 5, 6 based on expert knowledge, whereby the expert can, for example, refer to body structures with a particular reinforcing / stiffening effect. Parallel to the construction of a physical test specimen 1, a numerical finite element model of the test specimen 1 can be built. S2: Defining the positions and direction of the adjustable bearings 21 The number and directions of the adjustable bearings 21 represent a compromise between achievable accuracy and the technical or instrumental effort required for the test environment. Depending on the type of tests to be performed, the adjustable directions may only encompass one spatial direction, e.g., the z-direction (as shown in Fig. 1 and Fig. 2); however, additional spatial directions are advantageous depending on the objective of the investigation. Similarly, numerical evaluation and selection of different bearing positions and directions can be carried out. Advantageous criteria for selecting the connection points include, for example, the realization of the vibration modes of the test specimen 1 necessary for achieving the test results, local stresses, or damage. S3: Determining the stiffness values ​​to be set The stiffness values ​​to be set are determined based on numerical models and reference stresses. The procedure can include determining stiffness values ​​for the test based on the following steps: 1. Construction of a linear numerical / finite element model of the test specimen 1 2. Reduction to a significantly smaller number of output items relevant for the test specimen evaluation compared to the number of output items of model 1, which are relevant for a realistic evaluation of the test specimen 3. Determination of reference stresses at the output items from 2, for example, by an FE analysis of the reference or overall structure under reference load 4. Derivation of linear relationships (e.g.Transfer matrices (static / dynamic) from the model in 1 between: ◯ the displacements and rotations in all six spatial degrees of freedom at the connection points with the forces and moments at these degrees of freedom (stiffness matrix of the test specimen 1 reduced to the bearing connection points, H); ◯ the accelerations on the vibration table 100 and the forces and moments at the connection degrees of freedom of the adjustable bearings 21 (with ideally rigid constraint of all degrees of freedom at these connection points) (P); ◯ the displacements and rotations in all six spatial degrees of freedom at the connection points of the adjustable bearings 21 and the local stress quantities at the output positions from 2 (G); ◯ the accelerations on the vibration table 100 and the local stress quantities (e.g., stress components) at the output positions from 2 with ideally rigid constraint of all degrees of freedom at the connection points of the adjustable bearing 21. (Q)5.Description of the adjustable bearings 21 as a linear stiffness matrix, which describes the forces and moments acting by the bearing 21 on the test specimen 1 as a function of the relative movement between the test stand and test assembly-side connection of the adjustable bearing (K). 6. Computer-aided, at least approximate, evaluation of the local stress / damage at the output positions from 2 with the linear relationships from 4 using linear superposition for different acceleration excitations and stiffness configurations of the adjustable bearings 21 from 5. 7. Optimization of the stiffness configuration and / or the acceleration excitation using the evaluation from 6 with regard to the reference stress from 3. The matrices from 4 and 5 form the following system of equations, which can be used for the evaluation in 6: uHVS: Displacement / rotational degrees of freedom at the connection points of the adjustable bearings 21.s(t): Stress components at the output positions from 2. As an alternative to the described procedure, simulations using a model of the test specimen 1 with the adjustable bearings 21 under acceleration excitation would be performed by varying the model parameters stiffness and excitation to find the configuration that satisfactorily replicates the reference stress. However, due to the typically long computation times of the models, this would be significantly less efficient than the described procedure. It would take longer, and far fewer possible solutions could be investigated and evaluated, which would very likely result in finding only a less suitable solution in the end. S4: Setting up the test environment and adjusting the stiffnesses from S3 The device for testing structures with integrated energy storage systems is assembled, or the test specimen 1 is placed onto the already assembled device. The stiffnesses determined in S3.7 are set at the adjustable bearings 21. S5: Examination procedure Finally, the mechanical excitation of the test specimen 1 is carried out by the mechanical excitation device 100 to achieve defined stresses on the test specimen 1. Known iteration methods can be used to achieve minimal deviations from the reference stresses at the relevant output positions. Possible iteration targets could be, for example, force, acceleration, or strain values ​​on the test specimen 2 or the connecting elements 20. The simulation of dynamic stiffnesses is also possible through active control of the adjustable bearings 21. As can be seen from the above, the device and method according to the invention enable realistic tests for verifying or characterizing the operational reliability and service life, in particular of structure-integrated high-voltage storage systems and the surrounding vehicle bodies, for testing structures with integrated energy storage devices. The described testing method is simpler and more cost-effective, as it does not require test benches for a complete vehicle, and can be implemented earlier in the development process than conventional testing methods. The embodiments shown here are not limiting. In particular, the features of these embodiments can be combined to achieve additional effects. It is obvious to the person skilled in the art that modifications can be made to these embodiments without departing from the fundamental principles of the subject matter of this patent application, the scope of which is defined in the claims.

Claims

Device for testing structures with structure-integrated energy storage devices, comprising a device for mechanical excitation (100) with at least one degree of freedom, a test specimen (1) comprising a section (2) of a car body with a structure-integrated energy storage device (3), and connecting elements (20) for connecting the test specimen (1) to the device for mechanical excitation (100), wherein the connecting elements (20) each comprise an adjustable bearing (21) with a stiffness adjustable in at least one spatial direction, characterized in that the connecting elements (20) are coupled to the device for mechanical excitation (100) via a frame (40). Device according to claim 1, characterized in that the stiffness of the adjustable bearings (21) is adjustable by an actuator (80). Device according to claim 2, further comprising the actuator (80) for adjusting the stiffness of the adjustable bearings (21), a sensor system (23a, 70) for acquiring sensor data (71) at the connecting elements (20), and a power electronics system (72) for control based on the sensor data (71) and for controlling (73) the actuator (80) to replicate a dynamic stiffness through the adjustable bearings (21). Device according to one of the preceding claims, characterized in that the frame (40) comprises cross members (41) and longitudinal members (42) for connecting the connecting elements (20) to the device for mechanical excitation (100). Device according to one of the preceding claims, characterized in that at least some connecting elements (20) comprise an element for planar test specimen connection (24, 25). Device according to one of the preceding claims, characterized in that at least some connecting elements (20) comprise an element for discrete test specimen connection (26). Device according to one of the preceding claims, characterized in that the connecting elements (20) each comprise a height and angle compensation element (23, 23b). Method for testing structures with integrated energy storage devices, comprising the steps of: manufacturing (S1) a test specimen (1), wherein the test specimen (1) comprises a section (2) of a car body with an integrated energy storage device (3); determining (S2) the positions and direction of connection elements (20) for connecting the test specimen (1) to a mechanical excitation device (100), wherein the connection elements (20) each comprise an adjustable bearing (21) with a stiffness adjustable in at least one spatial direction; determining (S3) stiffness values ​​of the adjustable bearings (21) to be set for the test; connecting (S4) the test specimen (1) to the mechanical excitation device (100) by means of the connection elements (20) and setting the adjustable bearings (21) to the determined stiffness values, wherein the connection elements (20) are coupled to the mechanical excitation device (100) via a frame (40).and carrying out (S5) the mechanical excitation of the test specimen (1) by the device for mechanical excitation (100) in order to achieve defined stresses on the test specimen (1). Method according to claim 8, characterized in that the stiffness of the adjustable bearings (21) is adjusted during the execution (S5) of the mechanical excitation of the test specimen (1). Method according to claim 8 or 9, characterized in that the stiffness of the adjustable bearings (21) is controlled on the basis of sensor data acquired at the connecting elements (20) in order to replicate a dynamic stiffness through the adjustable bearings (21). Method according to one of claims 8 to 10, characterized in that the connection (S4) of the test specimen (1) to the device for mechanical excitation (100) is made via the frame (40), wherein the frame (40) comprises cross members (41) and longitudinal members (42) for connecting the connection elements (20) to the device for mechanical excitation (100). Method according to one of claims 8 to 11, characterized in that the determination (S2) of the positions and direction of the connecting elements (20) is based on a numerical model of the test specimen (1). Method according to one of claims 8 to 12, characterized in that the determination (S3) of the stiffness values ​​to be set for the test is based on a numerical model of the test specimen (1) and on reference stresses. The method according to claim 13, characterized in that determining (S3) the stiffness values ​​to be set for the test comprises the following steps: constructing a numerical model of the test specimen (1), which is a linear numerical model or a finite element model; reducing output positions of the model to output positions relevant for evaluating the test specimen (1); determining the reference stresses of the relevant output positions; deriving linear relationships from the model between displacements and rotations of the test specimen (1) at positions of the attachment elements (20) on the test specimen (1) and forces acting there, accelerations and forces of the device for mechanical excitation at positions of the attachment elements (20), displacements and rotations of the adjustable bearings (21) at positions of the attachment elements (20) on the test specimen (1) and the relevant output positions.and accelerations of the device for mechanical excitation and local stress quantities at the relevant output positions, description of the adjustable bearings (21) as a linear stiffness matrix, which describes the forces acting on the test specimen (1) by the adjustable bearings (21) as a function of relative movements between the connections of the adjustable bearings (21) to the device for mechanical excitation (100) and the connection of the adjustable bearings (21) to the test specimen (1), evaluation of a local stress at the relevant output positions with the linear relationships using linear superposition for different acceleration excitations and stiffness configurations of the adjustable bearings (21),and optimization of the stiffness values ​​of the adjustable bearings (21) and / or the acceleration excitations of the device for mechanical excitation (100) using the evaluation of the local stress with regard to the reference stress.

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