Integrated die-cast rear floor monoblock durability test method

Abstract

This application discloses a single-unit durability testing method for an integrated die-cast rear floor, belonging to the field of vehicle engineering technology. The method includes: inverting and fixing the casting onto a dedicated durability testing device, and installing actuators at the shock absorber fixing blocks on both sides. The system frequency response function is identified through white noise frequency sweeping, and the road spectrum load is iteratively corrected based on the frequency response function and damage domain convergence criteria to obtain a corrected loading spectrum; simultaneously, the average load and differential characteristic load in the road spectrum are decoupled. The left and right sides of the casting are loaded independently and sequentially, with the loading command based on the corrected loading spectrum and superimposed with amplified differential characteristic loads to excite local torsional modes. During loading, the stress at local measuring points is monitored, and local durability is determined based on a defined damage sensitivity index. This application achieves high-precision single-unit durability testing of rear floor castings, shortens the development cycle, and effectively identifies local weak areas in asymmetric structures.

Description

Technical Field

[0001] This invention relates to the field of vehicle engineering technology, specifically to a method for durability testing of an integrated die-cast floor unit. Background Technology

[0002] Integrated die casting is a significant trend in current vehicle body structure development. Integrated die casting technology, by casting multiple components into a single unit, significantly reduces the number of parts, simplifies assembly processes, and lowers vehicle weight, leading to its increasingly widespread application in structural components such as front and rear floors and engine compartments. However, due to their complex structure, large size, and uneven wall thickness, integrated die castings may exhibit defects such as internal porosity and shrinkage during the casting process. These potential defects can lead to fatigue cracks under alternating loads, affecting component durability and overall vehicle safety. Therefore, thorough verification of fatigue durability is crucial during the development of integrated castings.

[0003] Currently, the durability evaluation of integrated cast body structural components mainly employs body-in-white or even whole-vehicle level testing methods. However, whole-vehicle or body-in-white testing is not only time-consuming and costly, but also makes it difficult to identify problems in the early stages of component development, hindering rapid product iteration and optimization. Therefore, some existing technologies are beginning to explore durability testing of large integrated castings at the individual component level.

[0004] Currently, a similar solution has been disclosed in the prior art entitled "An Integrated Engine Cabin Unit Durability Test Method and Fixture". This solution is designed for an integrated cast engine compartment unit and includes a fixing fixture comprising left / right front longitudinal beam fixing brackets, first / second shock absorber fixing blocks, left / right brackets (for connecting the front fender inner panels), and a front bulkhead lower fixing bracket. The brackets and fixing blocks simulate the constraint of the engine compartment in a whole vehicle environment, thereby fixing the engine compartment unit on a test bench for durability testing. The test method of this scheme includes: mounting the engine compartment of the base vehicle onto a fixed fixture, installing a force sensor on the engine compartment near the shock absorber mounting block, applying a road spectrum load to the shock absorber mounting block and reading the actual force value of the engine compartment unit, thereby determining the relationship between the applied road spectrum load value and the actual load value of the engine compartment unit; then, based on this relationship, the load value that the engine compartment unit should be subjected to as specified in the durability test specification is deduced back into the road spectrum load value that should be applied to the fixed fixture, and then applying the road spectrum load to the fixed fixture according to the calculated value to conduct a durability test.

[0005] While this approach achieves durability testing at the individual cabin level and reduces testing costs, it has the following drawbacks: Firstly, the technical solution proposed is specifically designed for the integrated engine compartment monolithic structure. The structure of its mounting fixtures—including the front longitudinal beam mounting bracket, the front fender inner panel mounting bracket, and the lower front bulkhead mounting bracket—is designed based on the engine compartment's mounting points and constraint configuration within the vehicle. However, the integrated rear floor differs significantly from the integrated engine compartment in its mounting location, connection relationships, constraint points, and load transfer paths. The rear floor needs to connect to multiple components such as the rear subframe, battery pack, left and right rear wheel arches, rear longitudinal beams, and rear bumper beam. Its constraint configuration and stress conditions are far more complex than those of the engine compartment. The two differ substantially in structural characteristics and testing requirements, making the fixture structure of this proposed solution unsuitable for durability testing of the integrated rear floor casting. Specifically, the integrated rear floor casting is larger and heavier, requiring matching with multiple constraint points such as the rear subframe mounting point, battery pack mounting point, and shock absorber mount mounting point. Furthermore, it has different requirements for the fixture's support strength, load transmission characteristics, and weight control compared to the engine compartment. Therefore, developing specialized durability testing fixtures and methods for integrated floor units remains a pressing technical problem that needs to be solved.

[0006] Secondly, while this scheme applies road spectrum loads to the shock absorber mounting blocks and establishes a relationship between the applied load and the actual force on the engine compartment unit, its technical solution only focuses on the transmission relationship of load values ​​and does not address the correction of the road spectrum load itself. In bench tests, the test bench generates vibrations via motors or hydraulic cylinders, and the vibrations are transmitted to the casting through a fixture. This transmission path is fundamentally different from the vibration transmission path of road excitation transmitted to the vehicle body via tires and the suspension system under actual vehicle conditions. Therefore, a deviation inevitably exists between the actual load spectrum borne by the casting and the original road spectrum load. For large, integrated castings, this deviation may affect the accuracy of the test results, requiring adaptive correction of the road spectrum load. However, this scheme does not provide corresponding technical guidance on this. Especially for large, asymmetrical castings such as integrated rear floors, the stiffness distribution and stress characteristics of different regions vary significantly. Overall loading makes it difficult to effectively verify local durability performance. How to further improve the accuracy of durability testing for large, asymmetrical castings based on road spectrum correction is also a problem that existing technologies have not yet solved. Summary of the Invention

[0007] The present invention aims to solve at least one technical problem existing in the above-mentioned background art, and provides a method for durability testing of integrated die-cast floor units.

[0008] The technical solution of this application is: a method for durability testing of an integrated die-cast floor unit, comprising: The integrated die-cast floor casting to be tested is fixed to the durability testing device in an inverted and suspended manner. The durability testing device includes two sets of fixing structures placed on the left and right sides of the casting to constrain the installation position of the casting. Actuators are installed at the rear shock absorber fixing blocks on both the left and right sides of the casting, respectively; The road spectrum load of the base vehicle is obtained, and based on the actual loading requirements of the casting, the corrected loading spectrum is obtained by iterative correction through the transfer function, and the characteristic load representing the difference between the left and right loads is decoupled from the road spectrum load. The left and right sides of the casting are subjected to endurance loading tests independently, one after the other; when loading a single side, an independent loading command is generated for the actuator on that side and the load is applied based on the corrected loading spectrum and the characteristic load. During the loading process on this side, the stress response at local measuring points is monitored, and the local durability performance of this side is determined based on the response.

[0009] According to the integrated die-cast rear floor unit durability test method provided by the present invention, each fixed structure includes multiple columns, and a suspension replacement plate and a front fixing plate installed on the multiple columns; the suspension replacement plate is arranged along the X direction, and bolt holes are provided at its front and rear ends for fixed connection with the front fixing point and the rear fixing point of the casting rear bracket; the front fixing plate is provided with bolt holes for fixed connection with the Y-direction side of the front part of the casting rear longitudinal beam area.

[0010] According to the integrated die-cast floor unit durability test method provided by the present invention, the method for obtaining the corrected loading spectrum through transfer function iterative correction includes: The fixed casting and test device system were subjected to white noise frequency sweep excitation to obtain the actuator input force spectrum. Response stress spectrum of key measuring points in casting The system frequency response function H( )= ( ) / F( ); Based on the system frequency response function H( and the actual vehicle target response stress spectrum The input force spectrum of the actuator is iteratively corrected by applying a preset iterative equation until the preset convergence condition is met.

[0011] According to the integrated die-cast floor unit durability testing method provided by the present invention, the iterative equation is: in, For the first k+1 The input force spectrum of the next iteration This is the convergence step size factor.

[0012] According to the integrated die-cast floor unit durability testing method provided by the present invention, the preset convergence condition is a damage domain convergence condition, including: The cumulative damage to the target under the actual vehicle target load spectrum was calculated using the rainflow counting method and the material SN curve. and in the k After the second iteration, the measured cumulative damage of the test bench under the measured response stress spectrum was determined. ; When the relative error between the measured cumulative damage of the test bench and the target cumulative damage / If the threshold value is less than or equal to the preset threshold, the iteration is considered to have converged.

[0013] According to the integrated die-cast floor unit durability testing method provided by the present invention, the method for decoupling characteristic loads characterizing the difference between left and right loads from road spectrum loads includes: Obtain the time history of vertical force at the left and right wheel centers in the basic vehicle road spectrum. and ; Calculate the average load spectrum and differential characteristic load spectrum The differential characteristic load spectrum This is the characteristic load.

[0014] According to the integrated die-cast floor unit durability testing method provided by the present invention, when applying independent loading to one side, the method for generating independent loading commands for the actuators on that side includes: Based on the principle of linear elastic superposition, a stress response model for local measuring points under unilateral loading is established. ,in and These are the transfer coefficients of the average load and the differential characteristic load to the unilateral local stress, respectively; Based on the stress response model, the characteristic load After amplitude amplification, it is positively superimposed onto the average load spectrum. The initial loading command is then used to generate an independent loading command for forcibly stimulating the local torsional mode of the structure on that side.

[0015] According to the integrated die-cast floor unit durability testing method provided by the present invention, the independent loading command introduces a local strengthening factor. To forcibly excite the local torsional mode of the structure on this side, the independent loading command takes the form of: in, .

[0016] According to the integrated die-cast floor unit durability testing method provided by the present invention, the step of monitoring the stress response of local measuring points on that side and determining the local durability performance of that side based on the response specifically includes: Define local damage sensitivity index , like If the value is greater than or equal to the set value, the local area is determined to be a torsion-sensitive area, and the fatigue damage of the area must be calculated and determined using the corrected stress amplitude after superimposing the characteristic load.

[0017] According to the integrated die-cast floor unit durability test method provided by the present invention, the basis for judging the local durability performance of the torsion-sensitive area is as follows: if the number of cycles accumulated in the area under the corrected stress amplitude does not reach the target life, or the local strain mutation exceeds the set percentage of the initial calibration value, then the structure on that side is judged to be insufficiently redundant.

[0018] The advantages of this invention are: 1. It establishes an independent durability test method for the integrated die-cast floor unit.

[0019] Currently, the industry lacks single-item-level durability evaluation methods for integrated rear floor castings, requiring testing to be conducted on the body-in-white or the entire vehicle. This technical solution, through the construction of a specialized bench fixture, combined with an inverted, suspended fixing method and load decoupling and iterative correction strategies, enables the integrated rear floor casting to be detached from the body-in-white or the entire vehicle for independent single-item durability testing. This completely changes the passive situation of being unable to conduct testing without a vehicle.

[0020] 2. Significantly shorten the development and verification cycle and significantly reduce testing costs.

[0021] Testing using a body-in-white or complete vehicle requires waiting for the body prototype to be completed, which is time-consuming and extremely costly. This solution directly tests individual castings, eliminating the need to wait for complete vehicle resources and allowing for early intervention in durability performance verification during the early stages of product development. When failures occur during testing, the problem can be quickly located and design iterations can be initiated, avoiding large-scale design changes caused by discovering problems only at the complete vehicle stage. This significantly shortens the overall development cycle and saves on the high costs of complete vehicle testing and body-in-white manufacturing.

[0022] 3. The test device has a simple structure, is easy to install and debug, and is highly operable.

[0023] The durability test mounting structure designed in this scheme mainly consists of columns, suspension replacement plates, front mounting plates, and front floor simulation plates, and the structure is relatively simple and modular. Compared with bulky and complex body-in-white or whole vehicle mounting methods, this device is lightweight, easy to transport and assemble. Test personnel can quickly complete the hoisting of castings, bolting connections, and actuator alignment, which greatly saves the debugging and installation time in the test preparation stage and significantly improves test efficiency.

[0024] 4. Based on the iterative correction of the transfer function, high-precision damage equivalence between bench loading and actual vehicle road spectrum is ensured.

[0025] This approach does not directly apply road spectrum force, but instead innovatively introduces a system transfer function of "input force and response stress," and employs a damage domain convergence criterion (relative error ≤ 5%) based on Miner's linear cumulative damage theory for closed-loop iterative correction. This fundamentally solves the response distortion problem caused by the difference in mechanical impedance between the test bench and the vehicle, ensuring that the final loading spectrum at key points of the casting is highly equivalent to the actual fatigue damage of the real vehicle road spectrum. This makes the test results reliable and effectively guarantees the first-pass yield of subsequent vehicle tests.

[0026] 5. The unique strategy of split-side loading and characteristic load decoupling accurately reproduces and evaluates the local durability performance of asymmetric weak areas in castings.

[0027] The integrated floor structure is asymmetrical, and traditional synchronous overall loading can mask the torsional effect. This solution decouples the differential characteristic loads in the road spectrum and, during independent loading on each side, introduces a local reinforcement factor to superimpose it into the single-sided actuator command, forcibly stimulating the local torsional mode. Simultaneously, it defines a local damage sensitivity index (…). η ≥15%) Special quantitative judgment on asymmetric areas of castings can accurately identify and assess local structural weak points that cannot be found by conventional loading. It can effectively confirm the failure mode in the early stage of R&D and avoid repeated rectification due to local cracking in the later vehicle road test. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the fixed state of the integrated die-cast floor unit of the present invention; Figure 2 This is a schematic diagram of the fixing structure of the present invention; Figure 3 This is a schematic diagram of the integrated die-cast floor unit structure of the present invention; Figure 4 This is a flowchart of the integrated die-cast floor unit test method of the present invention.

[0029] Wherein: 1-Column; 2-Suspension replacement plate; 3-Front fixing plate; 4-Actuator; 11-Casting. Detailed Implementation

[0030] The embodiments of this application are described in detail below, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0031] In the description of this application, it should be understood that the terms "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0032] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the description herein is for illustrative purposes only and is not intended to limit the scope of protection of this invention.

[0034] Example 1: This example provides a method for durability testing of a single die-cast floor unit. Specifically, as follows... Figure 4 As shown, follow these steps: First, the integrated die-cast floor casting to be tested is fixed to the durability testing device in an inverted, suspended manner. The durability testing device includes two sets of fixing structures placed on the left and right sides of the casting. The two sets of fixing structures are fixedly connected to the mounting parts on the left and right sides of the casting, thereby firmly constraining the casting on the test bench, simulating its installation posture in the whole vehicle, but in an inverted state to facilitate the application of loads from below.

[0035] Next, actuators are installed at the rear shock absorber mounting blocks on both sides of the casting. The actuators, as the execution units for applying loads, are used to transmit the forces and displacements of the simulated road spectrum to the casting.

[0036] Next, the load spectrum is prepared. The road spectrum loads collected by the base vehicle during actual road testing are obtained, and the corrected load spectrum is obtained by iterative correction using the transfer function based on the actual loading requirements of the casting. At the same time, characteristic loads representing the difference between the left and right loads are decoupled from the original road spectrum loads of the base vehicle.

[0037] After preparing the load spectrum, endurance loading tests were conducted independently on the left and right sides of the casting. When loading a single side (taking the left side as an example), only the left actuator was activated, while the right actuator remained inactive or in a follow-up state. Based on the corrected load spectrum and characteristic loads, independent loading commands were generated for the left actuator, and a load was applied to the left rear shock absorber fixing block to simulate the actual stress state of that side under the torsional condition of the entire vehicle.

[0038] During the loading process, the stress response of local measuring points on that side (such as the wheel arch root, longitudinal beam corners, and other key assessment areas) is monitored in real time, and the local durability performance of that side is judged based on the response. After the test on the left side is completed, the right side is independently loaded and judged in the same way, thereby completing the single-unit durability evaluation of the entire integrated die-cast floor.

[0039] This embodiment constructs a test strategy of independent loading on each side sequentially. Due to the asymmetrical mass distribution and structural stiffness of the integrated die-cast floor, the loads borne by the left and right sides differ significantly during vehicle operation. This difference can lead to complex torsional and bending coupled stresses. If simultaneous loading is applied to both sides, the averaging effect will mask the local stress concentration caused by this asymmetrical load, resulting in test distortion.

[0040] This invention employs independent side loading, applying load to only one side at a time, and combining it with differential characteristic loads decoupled from the road spectrum to forcibly excite local torsional modes on that side. This method enables independent durability testing of the integrated floor unit detached from the body-in-white and the entire vehicle. Since it eliminates the need to wait for vehicle prototype resources, it allows for early intervention in product development, significantly shortening the development and verification cycle and reducing testing costs.

[0041] Example 2: This example is a further specification of the fixed structure in Example 1.

[0042] like Figures 1-3 As shown, each fixed structure specifically includes multiple vertical columns 1 erected on the test bench base, and a suspension replacement plate 2 and a front fixing plate 3 mounted on the columns 1. The suspension replacement plate 2 is a rigid metal plate, arranged horizontally along the X-axis (front-rear direction) of the vehicle coordinate system. Precisely positioned bolt holes are provided at both the front and rear ends of the suspension replacement plate 2, with the front bolt hole used for fixing to the front fixing point of the rear bracket of the casting 1 (e.g., ...). Figure 3Point A (as shown) is fastened with bolts, and the bolt holes at the rear end are used to connect with the rear fixing point of the casting rear bracket (such as...). Figure 3 Point B (as shown) is fastened with bolts. In this way, the suspension replacement plate 2 simulates the constraint stiffness of the vehicle suspension system on the rear bracket.

[0043] The front fixing plate 3 is also a rigid metal plate with multiple bolt holes on its surface. The positions of these bolt holes are the mounting holes on the front Y-direction (left-right direction) side of the rear longitudinal beam area of ​​the casting (e.g., Figure 3 As shown at point C, the front fixing plate is fixedly connected to the side of the front part of the casting's rear longitudinal beam area using bolts. The function of the front fixing plate is to simulate the constraint between the vehicle's sill beam and front floor and the front part of the casting's rear longitudinal beam area.

[0044] The fixing structure provided in this embodiment accurately replicates the multi-point constraint state of the integrated rear floor casting of the whole vehicle through modular columns, suspension replacement plates, and front fixing plates, using a simple mechanical connection method. Compared with testing using a body-in-white or a complete vehicle, this device has an extremely simple structure, is lightweight, and is easy to transport and install. Test personnel can quickly complete the hoisting of the casting, bolt alignment, and tightening, greatly saving the debugging and installation time of the test, thereby significantly improving the test efficiency.

[0045] Example 3: This example elaborates on and supplements the algorithm for the key step of obtaining the corrected loading spectrum through iterative correction of the transfer function in Example 1.

[0046] Because the overall mechanical impedance of the durability test bench (actuator, stationary structure, and casting) differs from that of the vehicle system, directly using the road spectrum load as the input command for the actuator will cause a significant deviation between the actual stress and strain responses at key measurement points of the casting and the target values ​​on the actual vehicle, especially near the system's resonant frequency. To address this issue, this embodiment employs the following closed-loop iterative correction method.

[0047] S1: System transfer function identification (frequency response function FRF measurement).

[0048] Before formal durability loading, a low-level system identification test was conducted. A white noise sweep excitation was applied to the fixed casting system using an actuator, with the sweep range set from 0.5 Hz to 50 Hz to cover the main loading frequency (1–3 Hz) and possible higher-order resonance peaks. The input force spectrum of the actuator was recorded simultaneously. The response stress spectrum measured by strain gauges placed at key test points of the casting (such as the root of the wheel cover and the corner of the longitudinal beam). Then the system's frequency response function H( ) is defined as: H( )= ( ) / F( ) in, H is the angular frequency. This characterizes the dynamic transmission characteristics of the input force and output stress of the test system in the frequency domain.

[0049] S2: Calculate the initial deviation.

[0050] The target wheel center force spectrum obtained from real vehicle testing The target force spectrum in the frequency domain is obtained by Fast Fourier Transform (FFT). If it is directly used as the actuator input, then theoretically the system will generate a response stress spectrum. for: This response is consistent with the expected target response stress spectrum of the actual vehicle. There is an error spectrum : S3: Iterative correction equation.

[0051] To eliminate bias, this invention constructs the following iterative format. Let the... k In the next iteration, the input force spectrum is Then the first k Input force spectrum of +1 iteration It is given by the following equation: in, This is the convergence step size factor. To ensure the stability and convergence speed of the iteration process and prevent correction overshoot, The preferred value range is (0.5≤ ≤0.8). The physical meaning of the above iteration is: the stress error in the frequency domain between the measured response and the target response after the previous iteration is divided by the system transfer function and converted back into a force spectrum correction amount, then multiplied by a step size factor less than 1 and superimposed on the current input force spectrum.

[0052] S4: Convergence determination based on the damage domain.

[0053] Judging convergence solely by the correlation coefficient of the time-domain waveform is too stringent and lacks engineering and physical significance. This invention creatively employs a damage domain convergence criterion based on Miner's linear cumulative damage theory. Specifically: The measured stress time history was statistically analyzed using the rainflow counting method to obtain the stress amplitude at each level. and the corresponding actual number of loops By combining the SN curve of the material, the fatigue failure limit cycle number corresponding to each stress amplitude can be found. ( The cumulative fatigue damage D at a single measuring point is: Calculate the cumulative damage of the target under the actual vehicle target response stress spectrum. and the k Cumulative damage under the measured response stress spectrum of the back frame in the second iteration Define the relative error between the two. for: Repeat the iterative correction of S3 until ( ≤5%). At this point, the "real fatigue damage" caused by the bench test at the critical points of the casting is highly equivalent to the actual vehicle road spectrum, and the final input force spectrum is obtained. This is the corrected standard durability loading spectrum.

[0054] The core principle of this embodiment is to transform the control objective from traditional force signal reproduction to damage equivalent reproduction. By establishing the system transfer function and performing closed-loop iteration, the response distortion problem caused by the mechanical impedance mismatch between the test bench and the vehicle is fundamentally solved physically. In particular, the damage domain convergence criterion is adopted ( (≤5%), ensuring that the fatigue damage generated at key points of the casting by the final loading spectrum is highly equivalent to that of the actual vehicle road spectrum, making the test conclusions true and reliable, effectively guiding structural design improvements, and strongly guaranteeing the one-time pass rate of subsequent vehicle durability tests.

[0055] Example 4: This example elaborates on and supplements the algorithm of decoupling the characteristic load representing the difference between the left and right loads from the road spectrum load in Example 1 and generating independent loading commands for the actuator on that side.

[0056] The asymmetrical mass distribution and structural stiffness of the integrated die-cast floor on both sides result in differences in the load on the left and right wheel centers during vehicle operation. This differential load is the root cause of vehicle body torsion and stress concentration in localized asymmetrical areas. This embodiment first decouples this differential component from the original road spectrum.

[0057] S1: Decoupling of road spectrum load characteristics.

[0058] Let the time histories of the original wheel-center vertical forces corresponding to the left and right actuators extracted from the base vehicle road spectrum be respectively... and This invention decomposes it into an average load spectrum. and differential characteristic load spectrum : in, It represents the fundamental component that causes the overall bending deformation of the casting; This refers to the characteristic load that causes the vehicle body to twist and results in asymmetrical local deformation on the left and right sides.

[0059] S2: Linear superposition model of unilateral stress response.

[0060] For asymmetrical weak areas on the integrated floor (such as the right battery pack mounting point or the left shock absorber lateral support rib), when testing is performed on one side (e.g., the left side) using split-side loading, the local stress response of that area is... According to the principle of linear elastic superposition, it can be expressed as the sum of the linear contributions of the average load and the differential characteristic load: in, It is the transfer coefficient of the average load to the local stress, which mainly reflects the global bending stiffness of the structure; This is the transfer coefficient of the differential characteristic load to the local stress, mainly reflecting the local torsional and warping stiffness of the structure. Due to the asymmetry of the casting structure, The value is usually much greater than .

[0061] S3: Generation of independent load instructions.

[0062] To address the problem that traditional overall loading cannot effectively induce and assess local torsional effects, this invention introduces a local enhancement factor into the generation strategy of unilateral loading commands. ( ), and the differential characteristic load After amplitude amplification, it is positively superimposed onto the initial loading command formed by the average load spectrum. When an independent load is applied to one side of the casting (e.g., the left side), the final loading command of its actuator is... for: Among them, the strengthening factor Based on the principle of damage equivalence, it is used to amplify the load difference characteristics between the left and right sides during the loading process without changing the total average energy input, thereby forcibly exciting the local torsional mode of the structure on that side.

[0063] This embodiment decouples the average and differential components of the road spectrum load and, based on the principle of linear elastic superposition, amplifies the weight of the differential component in unilateral loading to achieve decoupled reproduction of the overall bending and local torsional effects. This orthogonal loading strategy, combining overall and local loading, eliminates the need for additional local hydraulic cylinders; stress concentration in asymmetric regions can be precisely induced simply by adjusting the commands of the unilateral actuator through software algorithms. This method enables efficient assessment of local structural weaknesses that conventional overall loading methods cannot detect during single-item testing, thus effectively identifying potential failure modes in the early stages of development.

[0064] Example 5: This example elaborates on the step of monitoring the stress response of a local measuring point on the side in Example 1 and determining the local durability performance of the side based on the response.

[0065] In the process of applying durability loading to one side of the casting using the method of Example 4, a scientific quantitative judgment method is needed to evaluate the durability performance of the local area in order to identify the dangerous areas that are particularly sensitive to torsional loads.

[0066] S1: Definition of local damage sensitivity index.

[0067] First, define the local damage sensitivity index. This index is used to quantify the sensitivity of a local area to differential characteristic loads (torsional effects). The calculation formula is: in, To superimpose characteristic loads The stress amplitude measured at local measuring points under the loading command; To use only the average load spectrum Loading (not stacked) The stress amplitude at the same point under the calibration conditions.

[0068] S2: Determination and handling of sensitive areas of torsion.

[0069] A judgment threshold was set. Through extensive testing and simulation verification, for the integrated die-cast floor, typical asymmetric areas such as the wheel arch root were identified. The value is usually above 15%.

[0070] like( If the percentage is less than 15%, it indicates that this region is not sensitive to torsional loads, and its fatigue damage is mainly dominated by overall bending loads. For such regions, conventional overall load durability assessment methods can be used for evaluation.

[0071] like( If the load is ≥15%, the local area is determined to be a torsion-sensitive area. For such areas, fatigue life assessment must be performed using a method that superimposes characteristic loads. Corrected stress amplitude A recalculation and assessment must be performed, otherwise the extent of the damage will be severely underestimated.

[0072] S3: Final assessment of local durability performance.

[0073] For areas identified as torsion-sensitive, the final criteria for determining structural redundancy and durability are as follows: During 1 million equivalent durability cycles (or other target number of cycles), if the corrected high stress amplitude in this region after superimposed characteristic load... Below, the cumulative actual number of loops Failed to reach the design target life If the sudden increase in local strain exceeds 15% of the initial calibration value as detected by strain gauges, it is determined that the local structure on that side has insufficient redundancy and there is a risk of failure.

[0074] This embodiment defines a dimensionless local damage sensitivity index. A quantitative criterion was established to distinguish between normal regions and torsional sensitive regions. Its physical significance lies in quantitatively assessing the increase in local stress caused by the introduction of differential characteristic loads. For For highly sensitive areas of ≥15%, it is mandatory to use the modified stress for damage calculation. This can effectively avoid misjudgment of durability performance due to load simplification, ensure accurate identification of structural weak points that cannot be exposed by conventional testing methods, and thus effectively confirm the failure mode in the early stage of product development, avoiding repeated rectification due to local cracking during later vehicle road tests.

[0075] In actual operation, such as Figure 4 As shown, the durability test of the integrated die-cast floor unit of the present invention is carried out according to the following steps: I. Experimental Preparation Phase 1. Casting Fixing: The integrated die-cast rear floor casting to be tested is hoisted onto the durability testing rig in an inverted position. It is secured using two sets of fixing structures located on the left and right sides of the casting. Each fixing structure is supported by multiple columns, on which a suspension replacement plate is bolted to the front and rear fixing points of the casting's rear bracket to simulate suspension constraints. The front fixing plate is bolted to the Y-direction side of the front of the casting's rear longitudinal beam area to simulate sill beam and front floor constraints. The front floor simulation plate provides fixing points to simulate the front floor.

[0076] 2. Actuator installation: Install and adjust two independent actuators at the rear shock absorber fixing blocks on the left and right sides of the casting.

[0077] II. Load Spectrum Generation and Correction Stage 3. System Transfer Function Identification: A white noise sweep excitation of 0.5Hz to 50Hz is applied to the fixed casting system using an actuator on one side. The actuator input force spectrum F( The response stress spectrum of key measuring points such as the root of the casting wheel cover and the corner of the longitudinal beam. ( ), calculate the system frequency response function H( )= ( ) / F( ).

[0078] 4. Load spectrum iterative correction: Set the convergence step size factor α =0.5~0.8. Applying iterative equations: The input force spectrum is iterated multiple times. After each iteration, the measured damage on the test bench is calculated using the rainflow counting method and the material SN curve. Damage to actual vehicle target relative error .when The iteration terminates when the percentage is ≤5%, and the input spectrum at this point is the corrected standard endurance loading spectrum.

[0079] 5. Characteristic load decoupling: Obtain the vertical forces at the left and right wheel centers of the base vehicle road spectrum. and According to the formula Calculate the average load spectrum according to the formula Calculate the differential characteristic load spectrum.

[0080] III. Side-by-side durability loading and monitoring phase 6. Left-side independent loading test: Instruction generation: Based on the principle of linear elastic superposition Introducing reinforcement factors Generate the independent loading command for the left actuator in this experiment. .

[0081] Loading execution: Activate only the left actuator and apply a durability cyclic load to the left rear shock absorber mounting block as instructed above.

[0082] Real-time monitoring: Collect stress response data at measuring points in the asymmetric region on the left.

[0083] 7. Left-side local durability assessment: Calculate sensitivity index like If it is ≥15%, then it must be accumulated. The fatigue damage in the region is reassessed using the corrected stress amplitude. If the corrected cycle count does not meet the standard or the strain mutation exceeds 15%, the left-side structure is deemed to have insufficient redundancy.

[0084] 8. Independent loading test on the right side: After the test and judgment on the left side are completed, the same procedure is used to independently load and judge the durability performance on the right side.

[0085] IV. Experimental Conclusion Output Stage 9. Summarize the monitoring data and judgment conclusions from both the left and right sides, and output a complete durability performance evaluation report for the integrated die-cast floor unit, clearly indicating whether there are areas with insufficient local structural redundancy and their corresponding failure modes.

[0086] The foregoing has shown and described the basic principles, main features, and advantages of this application. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the appended claims and their equivalents.

Claims

1. A method for durability testing of a single integrated die-cast floor unit, characterized in that, include: The integrated die-cast floor casting to be tested is fixed to the durability testing device in an inverted and suspended manner. The durability testing device includes two sets of fixing structures placed on the left and right sides of the casting to constrain the installation position of the casting. Actuators are installed at the rear shock absorber fixing blocks on both the left and right sides of the casting, respectively; The road spectrum load of the base vehicle is obtained, and based on the actual loading requirements of the casting, the corrected loading spectrum is obtained by iterative correction through the transfer function, and the characteristic load representing the difference between the left and right loads is decoupled from the road spectrum load. The left and right sides of the casting are subjected to endurance loading tests independently, one after the other; when loading a single side, an independent loading command is generated for the actuator on that side and the load is applied based on the corrected loading spectrum and the characteristic load. During the loading process on this side, the stress response at local measuring points is monitored, and the local durability performance of this side is determined based on the response.

2. The method for durability testing of a single integrated die-cast floor unit according to claim 1, characterized in that, Each set of fixed structures includes multiple columns (1), and a suspension replacement plate (2) and a front fixing plate (3) installed on the multiple columns (1); the suspension replacement plate (2) is arranged along the X direction, and bolt holes are provided at its front and rear ends for fixed connection with the front fixing point and the rear fixing point of the casting (11); the front fixing plate (3) is provided with bolt holes for fixed connection with the Y-direction side of the front part of the rear longitudinal beam area of ​​the casting (1).

3. The method for durability testing of a single integrated die-cast floor unit according to claim 1, characterized in that, The method for obtaining the corrected loading spectrum through iterative correction of the transfer function includes: The fixed casting and test device system were subjected to white noise frequency sweep excitation to obtain the actuator input force spectrum. Response stress spectrum of key measuring points in casting The system frequency response function H( )= ( ) / F( ); Based on the system frequency response function H( and the actual vehicle target response stress spectrum The input force spectrum of the actuator is iteratively corrected by applying a preset iterative equation until the preset convergence condition is met.

4. The method for durability testing of a single integrated die-cast floor unit according to claim 3, characterized in that, The iterative equation is: in, For the first k+1 The input force spectrum of the next iteration This is the convergence step size factor.

5. The method for durability testing of a single integrated die-cast floor unit according to claim 4, characterized in that, The preset convergence condition is the damage domain convergence condition, including: The cumulative damage to the target under the actual vehicle target load spectrum was calculated using the rainflow counting method and the material SN curve. and in the k After the second iteration, the measured cumulative damage of the test bench under the measured response stress spectrum was determined. ; When the relative error between the measured cumulative damage of the test bench and the target cumulative damage / If the threshold value is less than or equal to the preset threshold, the iteration is considered to have converged.

6. The method for durability testing of a single integrated die-cast floor unit according to claim 1, characterized in that, The method for decoupling characteristic loads representing the difference between left and right loads from road spectrum loads includes: Obtain the time history of vertical force at the left and right wheel centers in the basic vehicle road spectrum. and ; Calculate the average load spectrum and differential characteristic load spectrum The differential characteristic load spectrum This is the characteristic load.

7. The method for durability testing of a single integrated die-cast floor unit according to claim 6, characterized in that, When applying independent loading to one side, the method for generating independent loading commands for that side's actuator includes: Based on the principle of linear elastic superposition, a stress response model for local measuring points under unilateral loading is established. ,in and These are the transfer coefficients of the average load and the differential characteristic load to the unilateral local stress, respectively; Based on the stress response model, the characteristic load After amplitude amplification, it is positively superimposed onto the average load spectrum. The initial loading command is then used to generate an independent loading command for forcibly stimulating the local torsional mode of the structure on that side.

8. The method for durability testing of a single integrated die-cast floor unit according to claim 7, characterized in that, The independent loading command introduces a local enhancement factor. To forcibly excite the local torsional mode of the structure on this side, the independent loading command takes the form of: in, .

9. The method for durability testing of a single integrated die-cast floor unit according to claim 8, characterized in that, The step of monitoring the stress response of a local measuring point on that side and determining the local durability performance of that side based on the response specifically includes: Define local damage sensitivity index , like If the value is greater than or equal to the set value, the local area is determined to be a torsion-sensitive area, and the fatigue damage of the area must be calculated and determined using the corrected stress amplitude after superimposing the characteristic load.

10. The method for durability testing of a single integrated die-cast floor unit according to claim 9, characterized in that, The basis for determining the local durability of the torsion-sensitive region is as follows: if the number of cycles accumulated in the region under the corrected stress amplitude does not reach the target life, or the sudden change in local strain exceeds the set percentage of the initial calibration value, then the structure on that side is deemed to have insufficient redundancy.

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