A method for developing a multi-channel durability bench test scheme for a subframe

Abstract

A kind of subframe multi-channel durability bench test scheme development method relates to the field of automobile parts fatigue durability test, including steps 1: defining target damage;Step 2: screening main damage working condition;Step 3: calculating test loading direction, for each control arm connecting hard point, find the optimal direction to make the maximum projection load reserve original load characteristics;Step 4: load spectrum merging and simplification;Step 5: each channel fatigue damage influence degree analysis;Step 6, calculate initial constant amplitude test load;Step 7: iterative adjustment constant amplitude test load, according to influence matrix iterative adjustment load until damage deviation meets the requirements;Step 8: output final test scheme, output final constant amplitude load parameters and loading direction.The present application reduces the dependence of suspension test piece, simplifies the bench building, while truly reproducing the load coupling effect between each control arm connecting point, improves the test accuracy and efficiency.

Description

Technical Field

[0001] This invention relates to the field of fatigue durability testing technology for automotive parts, specifically a method for developing a multi-channel durability bench test scheme for subframes. Background Technology

[0002] As a key load-bearing component of the automotive chassis, the subframe's durability directly affects the safety and reliability of the entire vehicle. In the automotive development process, bench durability testing is an important means of verifying the subframe structural design.

[0003] Currently, subframe bench durability testing is mainly divided into two categories: wheel-end loading and single-hole loading. Wheel-end loading requires a complete suspension system as a test specimen. While it can simulate real-vehicle conditions well, it involves a large number of test specimens, a long procurement cycle, high testing costs, and complex bench construction. Single-hole loading requires fewer test specimens, but each loading point is independently controlled, making it impossible to reproduce the load coupling effect between different connection points during actual road driving. This results in deviations between the subframe stress distribution and damage mode and the actual vehicle condition, leading to insufficient test accuracy.

[0004] With the continuous shortening of automotive development cycles, the industry urgently needs a subframe durability testing scheme that can reduce reliance on test specimens while accurately simulating the multi-axis coupled stress state of real vehicles. This invention proposes a method for developing a multi-channel durability testing scheme that transforms road load spectra into efficient test bench operations, in order to solve the aforementioned problems. Summary of the Invention

[0005] In view of this, the present invention aims to propose a method for developing a multi-channel durability bench test scheme for subframes, in order to solve the problem in the prior art of lacking a subframe durability bench test method that requires few test specimens, has high test accuracy, and can realistically simulate the load coupling effect between the connection points of each control arm.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A method for developing a multi-channel durability bench test scheme for subframes includes step 1, defining the target damage. A finite element model of the subframe is established, and a complete six-component road load spectrum (Fx, Fy, Fz, Mx, My, Mz) collected from the test field is simultaneously applied at each hard point connecting the subframe to the control arm for fatigue simulation analysis. The fatigue damage distribution of the subframe under the complete road load spectrum is calculated, and the locations of the main stress concentration points and their logarithmic damage values ​​are determined. This damage value is defined as the target damage, serving as the benchmark for subsequent load simplification and equivalence.

[0008] Step 2: Screening of Major Damage Conditions. Based on the slope of the material's SN curve, a pseudo-damage calculation method is used to evaluate the contribution of each pavement condition to the total damage, selecting several conditions with a relatively large damage proportion as major damage conditions. Subsequently, the minimum value of the original cycle count for each condition is used as the baseline cycle count, and the ratio of the original cycle count for the remaining conditions to this baseline is calculated. If the ratio is not an integer, the number of repetitions for each condition sub-spectrum is determined by rounding up, and the conditions are concatenated into a continuous load time series file according to the corresponding multiples. This load spectrum is used for subsequent analysis to improve computational efficiency while ensuring the damage contribution.

[0009] Step 3: Calculate the test loading direction. For each control arm connection hard point on the subframe, find an optimal direction vector in three-dimensional space. The criterion for determining this direction is: projecting the three-dimensional force vectors (Fx, Fy, Fz) from the spliced ​​load spectrum obtained in Step 2 onto this direction, the resulting uniaxial projected load can retain the amplitude and energy characteristics of the original load to the greatest extent. This direction is defined as the test loading direction for this hard point. For special cases such as spring-loaded arms that bear large vertical forces, their vertical loads contribute significantly to structural damage and need to be retained as independent loading channels, with the direction defined as vertical. At the same time, for their horizontal loads (Fx, Fy), find the optimal direction in the XY horizontal plane according to the above method and project and merge them. Such connection points ultimately form a dual-channel loading scheme.

[0010] Step 4, Load Spectrum Merging and Simplification. Based on the test loading direction determined in Step 3, the original loads at each control arm connection hardpoint are simplified. Specifically, the three torque components (Mx, My, Mz) are ignored. For general control arm connection hardpoints: the three forces (Fx, Fy, Fz) are vector-projected and merged onto the spatially optimal direction determined in Step 3 to obtain a single-channel target load signal. For special cases such as spring-loaded arms: the vertical Fz channel is retained as an independent loading signal; Fx and Fy are projected and merged onto the horizontally optimal direction determined in Step 3 to obtain a second-channel target load signal. Thus, the complex six-component load spectrum is simplified into single-channel / dual-channel target load spectrum signals at each hardpoint.

[0011] Step 5: Analysis of the impact of fatigue damage on each channel. In the finite element model, the merged path spectrum obtained in Step 4 is simulated under two modes: 1) all channels are loaded simultaneously; 2) a single channel is removed each time, while the remaining channels are loaded. By comparing the damage value changes at the main stress concentration points in Step 1 under the above simulation modes, the influence of each loaded channel on the fatigue damage of different key areas is quantitatively analyzed, and a channel-damage influence matrix is ​​established.

[0012] Step 6: Calculate the initial amplitude-fixed test load. Using the merged road spectrum generated in Step 4 as the target, and based on the fatigue damage equivalence principle, calculate the initial amplitude-fixed test load required for each control arm connection hardpoint. The characteristic parameters of this amplitude-fixed load include amplitude, mean, frequency, and number of cycles, used to replace the complex road spectrum signal. This is the initial value of the amplitude-fixed test load and serves as the benchmark input for subsequent iterative optimization.

[0013] Step 7: Iteratively adjust the constant-amplitude test load. In the subframe finite element model, apply the initial constant-amplitude test load calculated in Step 6 simultaneously at the hard points connecting each control arm along the direction determined in Step 3, perform fatigue simulation, and extract the damage values ​​of the stress concentration points in Step 1. Compare the calculation results with the target damage defined in Step 1. Based on the channel-damage influence matrix established in Step 5, perform targeted iterative adjustments to the mean and amplitude of the constant-amplitude load for each channel. Adjust the load of one channel each time and recalculate until the deviation between the simulated damage and the target damage at all key points meets the preset requirements.

[0014] Step 8: Output the final test plan. Once the damage comparison results meet the requirements, the final average value, amplitude, number of loading cycles, frequency, phase, and loading direction of each channel are used as the final subframe multi-channel durability bench test load output. This plan can be directly used to guide the physical bench setup and test execution.

[0015] In some embodiments, the specific method for screening the main damage conditions in step 2 is as follows: For each load spectrum condition, the load time history of the three force component channels Fx, Fy, and Fz at the connection hard points of each control arm is extracted, and the rainflow counting method is used for cyclical statistics. Combined with the SN curve of the material, the pseudo-damage value of each channel under a single condition is calculated. The pseudo-damage values ​​of all control arms and all three force component channels in the same condition are algebraically summed and superimposed to obtain the total pseudo-damage of the condition. Each condition is arranged in descending order of pseudo-damage value from largest to smallest, and the cumulative damage ratio is calculated by accumulating them sequentially. The condition covered when the cumulative damage ratio first exceeds a preset threshold is defined as the main damage condition.

[0016] In some embodiments, the method for determining the number of repetitions of each major damage condition in step 2 of screening major damage conditions is as follows: the minimum value of the original number of cycles of each major damage condition is used as the baseline number of cycles, the ratio of the original number of cycles of the remaining conditions to the baseline is calculated, and if the ratio is not an integer, the number of repetitions of each condition is determined by rounding up.

[0017] In some embodiments, in step 3, the triaxial force vector (Fx, Fy, Fz) in the load spectrum during the calculation of the experimental loading direction is denoted as... The unit direction vector is defined at the hardpoint where the control arm connects, denoted as . , and The X, Y, and Z directions are defined in the same way as the actual vehicle coordinate system; the unit direction vector The definition method is as follows: taking the hard point connecting the control arm as the origin, traverse all possible direction vectors on the unit sphere with a certain step size; unit direction vector Projected load on for: , residual load for: For each control arm connection hardpoint, calculate the three-dimensional force vectors. unit direction vector Projected load on and residual load When the projected load With triaxial force vector load When the average ratio is at its maximum, or when the residual load When the value is at its minimum, the corresponding unit direction vector is the experimental loading direction.

[0018] In some embodiments, in step 4, load spectrum merging and simplification, for the spring bearing arm, its vertical load is retained as an independent loading channel, and its direction is defined as vertical. At the same time, its horizontal load is projected and merged in the XY horizontal plane according to the method of finding the optimal direction, forming a dual-channel loading scheme.

[0019] In some embodiments, in step 5, the method for establishing the channel-damage influence matrix in the fatigue damage influence analysis of each channel is as follows: perform full-channel working condition simulation and channel-missing working condition simulation, extract the fatigue damage values ​​of the main stress concentration points under the two working conditions, calculate the damage difference based on the target damage value, with the loading channel as the row and the main stress concentration point as the column, and the matrix elements represent the damage change amount or relative change ratio caused by the missing channel.

[0020] In some embodiments, in step 6, the method for calculating the amplitude of the initial fixed-amplitude test load is as follows: perform rainflow statistics on the merged road spectrum, superimpose the rainflow matrices of all working conditions, and obtain the total amplitude range, mean, and total number of cycles; based on Miner's linear cumulative damage rule, adjust the intercept of the SN curve iteratively to make the total pseudo-damage value 0.5 to determine the intercept; solve for the load amplitude corresponding to the target number of cycles based on the determined SN curve, and use it as the amplitude of the initial fixed-amplitude test load.

[0021] In some embodiments, in step 6, when calculating the initial fixed-amplitude test load, the main concentration interval of the number of cycles is identified based on the total amplitude range, mean, and total number of cycles under all road spectrum conditions, and a mean value within that interval is selected as the mean value of the initial fixed-amplitude test load.

[0022] In some embodiments, during step 7, when iteratively adjusting the fixed amplitude test load, the test loads of the control arms at the symmetrical positions on the left and right sides are always set symmetrically; the amplitude adjustment range does not exceed the total amplitude of the control arm connection hard point under all road spectrum conditions as statistically analyzed in step 6; when adjusting the amplitude alone cannot make the damage reach the target range, the number of test loading cycles for all control arm connection hard point channels is increased synchronously, and the number of cycles for all channels is adjusted in a consistent manner.

[0023] In some embodiments, in step 7, iteratively adjusting the fixed-amplitude test load, the convergence criterion for iterative adjustment is that the error between the simulated damage and the target damage at the main stress concentration points is controlled within -10% to +50%.

[0024] In some embodiments, in the final test scheme output in step 8, the loading scheme is to implement in-phase loading at the connection hard points between each control arm and the subframe, and the test loading frequency is controlled within the range of 1 to 3 Hz. The constraint scheme uses the original vehicle bolts to fix each body connection point of the subframe according to the actual vehicle state, and the suspension bushings at the connection points are fitted with original bushings.

[0025] This invention establishes a subframe finite element model and performs fatigue simulation using a complete six-component road load spectrum to define target damage. It then selects the main damage conditions and stitches them together into a continuous load spectrum. For each control arm connection hard point, it calculates the optimal test loading direction based on the principle of maximum damage retention, merging the triaxial load projections into single-channel or dual-channel target loads. An influence matrix is ​​established through channel-damage influence analysis. Based on the damage equivalence principle, the initial fixed-amplitude test load is calculated and iteratively adjusted according to the influence matrix until the deviation between the key point damage and the target damage meets the requirements, at which point the final test plan is output. This invention reduces reliance on suspension test components, simplifies test bench setup, and realistically reproduces the load coupling effect between the control arm connection points, improving test accuracy and efficiency. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0027] Figure 1 This is a schematic diagram of the technical route for the development method of the multi-channel durability bench test scheme for the subframe of the present invention.

[0028] Figure 2This is a schematic diagram of the subframe simulation model of the present invention.

[0029] Figure 3 This is a schematic diagram of the load time series file spliced ​​from the main damage conditions of this invention.

[0030] Figure 4 This is a schematic diagram of the load vector projection of the present invention.

[0031] Figure 5 is a schematic diagram of the relationship between the projected load and the residual load of the present invention. Detailed Implementation

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0033] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The following is for reference. Figures 1 to 5 The development method of the subframe multi-channel durability bench test scheme of the present invention is described in conjunction with the embodiments.

[0035] Please see Figure 1 As shown, the present invention provides a method for developing a multi-channel durability bench test scheme for subframes, specifically including the following steps:

[0036] Step 1, define the target damage.

[0037] In this embodiment, an aluminum alloy frame-type rear subframe with a 5-link suspension is selected. First, a refined finite element model of the subframe is constructed using pre-processing software such as HyperMesh, with an average mesh size of 4mm. 1-6 degrees of freedom are constrained at the connection points between the subframe and the vehicle body. The hard points connecting the subframe and the five control arms are linked at their centers using RBE2 rigid elements. Figure 2 As shown, unit force loads (including three unit force components Fx, Fy, and Fz and three unit torques Mx, My, and Mz) in six directions are applied at the connection hard points of each control arm. Static analysis software such as ABAQUS is used to calculate and output the stress results corresponding to the loads in each direction.

[0038] Then, in fatigue analysis software such as nCode DesignLife or Femfat, the stress calculation results corresponding to each unit force are imported sequentially, along with the complete six-component road load spectrum collected from the test track after filtering and resampling. The test track road load spectrum conditions and cycle number used in this embodiment are shown in Table 1. The stress results of each unit force are matched one-to-one with each channel of the load spectrum; then, the measured SN curve of the subframe material ZAlSi7MgA is input to calculate the fatigue damage distribution under the entire durability test specification cycle. At least five hot spots with the highest damage values ​​are identified (e.g., the sand leakage hole in the middle of the rear crossbeam, the rear motor mounting hole, etc.), and their damage values ​​are recorded. This damage value is the target damage for this load development.

[0039] Table 1. Load spectrum conditions and cycle number of the test track road

[0040]

[0041] Step 2: Screen the main damage conditions.

[0042] Import the test track road load spectrum used in step 1 using data processing software such as LMS Tecware or nCode GlyphWorks. Define the slope k of the material's SN curve; in this embodiment, k=4. For each load spectrum condition, extract the load time history of the three force component channels (Fx, Fy, Fz) at the connection hard points of each control arm under that condition. Use the rainflow counting method to perform cyclical statistics on the load of each channel. Combined with the defined SN curve, and based on Miner's linear cumulative damage rule, calculate the pseudo-damage value of each channel under a single condition. Algebraically sum and superimpose the pseudo-damage values ​​of all control arms and all three force component channels within the same condition to obtain the total pseudo-damage for that condition. Following the above method, calculate all load spectrum conditions included in the test track load spectrum to obtain the total pseudo-damage value corresponding to each condition. Subsequently, statistical analysis was performed on the spurious damage for all working conditions, calculating the damage percentage for each condition. The working conditions were then sorted in descending order of spurious damage values, and the cumulative damage percentage was calculated by summing these values. The working conditions whose cumulative damage percentage first exceeded 85% were defined as the primary damage working conditions. In this embodiment, after the above screening process, four primary damage working conditions were identified: Working Condition 2, Working Condition 4, Working Condition 14, and Working Condition 15. The cumulative spurious damage of these four working conditions accounted for 90% of the total spurious damage, and they were defined as the primary damage working conditions.

[0043] Subsequently, the minimum number of original cycles for each major damage condition is used as the baseline number of cycles, and the ratio of the original number of cycles for the remaining conditions to this baseline is calculated. If the ratio is not an integer, the number of repetitions for each condition is determined by rounding up. Using data processing software such as LMS Tecware or nCode GlyphWorks, each major damage condition is spliced ​​into a continuous load time series file according to the corresponding multiples. This load spectrum is used for subsequent analysis to improve computational efficiency while ensuring damage contribution. In this embodiment, the original number of cycles for the four major damage conditions are 1600, 2400, 4800, and 4800, respectively, the baseline number of cycles is 1600, and the number of repetitions required when splicing the four major damage conditions are 1, 2, 3, and 3, respectively. The left upper control arm Fy force component channel in the load time series spliced ​​from the major damage conditions is shown below. Figure 3 As shown.

[0044] Step 3: Calculate the test loading direction.

[0045] A unit direction vector is defined at each control arm connection hard point. The projected load of the test track load spectrum onto the unit direction vector is calculated. The unit direction vector that best preserves the original load amplitude and energy characteristics is determined as the test loading direction for that control arm connection hard point. Given that the control arms on the left and right sides of the subframe are symmetrically arranged, the loading direction of the right control arm is symmetrically set based on the definition results of the left control arm.

[0046] Using data processing software such as NI-DIAdem or LMS Tecware, import the load time series file spliced ​​from the main damage conditions obtained in step 2, and export the three force components Fx, Fy, and Fz at the connection hard points of each control arm on the left to an Excel spreadsheet.

[0047] The three-dimensional force vectors (Fx, Fy, Fz) in the load spectrum are denoted as The unit direction vector is defined at the hardpoint where the control arm connects, denoted as . , and The X, Y, and Z directions are defined consistent with the actual vehicle coordinate system. Unit direction vector. The definition method is as follows: taking the control arm connection hard point as the origin, traverse all possible direction vectors on a unit sphere with a certain step size (e.g., 15°). Prioritize defining the direction vectors in the region surrounding the control arm link direction.

[0048] and The cosine of the angle between the two vectors is:

[0049]

[0050] unit direction vector Projected load on for:

[0051]

[0052] The residual load is :

[0053]

[0054] , , , Relationship such as Figure 4 As shown.

[0055] For each control arm connection hardpoint, calculate each triaxial force vector in an Excel spreadsheet. unit direction vector Projected load on and residual load Simultaneously calculate each projected load. With triaxial force vector load The ratio of the projected load, and the average of all ratios. In principle, when the projected load... With triaxial force vector load When the average ratio is at its maximum, the corresponding unit direction vector is the experimental loading direction. Furthermore, the projected load is plotted. and residual load The curve is shown in Figure 5 to more intuitively illustrate the relationship between the two and facilitate the adjustment of the unit direction vector. In principle, when the residual load... When the value is at its minimum, the unit direction vector is the direction of the experimental loading.

[0056] For components such as spring-loaded arms that bear significant vertical forces, the vertical load contributes substantially to structural damage and must be retained as an independent loading channel, with its direction defined as vertical. Simultaneously, for the horizontal loads (Fx, Fy), the experimental loading direction is determined in the XY horizontal plane using the method described above.

[0057] Step 4: Road spectrum merging and simplification.

[0058] Import the test track road load spectrum used in step 1 into data processing software such as LMS Tecware or nCode GlyphWorks. Then, using the software formula calculation module, calculate the projected load channel on the test loading direction vector determined in step 3 for each control arm connection hard point based on the three force component channels Fx, Fy, and Fz.

[0059] In this embodiment, for the connection hard points of the four control arms—the front upper control arm, the front lower control arm, the rear upper control arm, and the front toe arm—the three force component channels (Fx, Fy, and Fz) are calculated and merged to obtain a single-channel load time series. For the connection hard points of the spring-loaded arm, since its vertical force Fz is extremely critical, a dual-channel strategy is adopted. The vertical Fz channel is retained as an independent loading channel, and the two force component channels (Fx and Fy) are calculated and merged to obtain a single-channel load time series. The original road load spectrum is merged for each working condition, and 12 load time series channels can be obtained for each working condition (6 channels each for the left and right sides of the subframe).

[0060] The load time series channel obtained from this step will be used for the calculation of subsequent fixed-amplitude test loads.

[0061] Step 5: Analysis of the impact of fatigue damage on each channel.

[0062] In static analysis software such as ABAQUS, based on the refined finite element model of the subframe established in step 1, a unit force load is applied at each control arm connection hard point along the test loading direction determined in step 3, and the stress results under the unit load are calculated. In fatigue analysis software such as nCode DesignLife or Femfat, the stress results under the unit load are imported, and fatigue simulations are performed under the following two loading modes to quantitatively evaluate the sensitivity and influence of each loading channel on the damage contribution of key stress concentration points:

[0063] 1) Full-channel operation: Use all control arm connection hard points as loading channels and apply the combined road spectrum load obtained in step 4 simultaneously;

[0064] 2) Missing Channel Condition: While maintaining the synchronous application of the combined road spectrum load obtained in step 4 to the remaining control arm connection hard points, the road spectrum load of one control arm connection hard point is removed sequentially. Simulations are performed one by one to obtain the fatigue damage distribution under each channel removal condition.

[0065] In the simulation results above, the damage values ​​of the main stress concentration points determined in step 1 are extracted. All results are compared and analyzed with the stress concentration points and damage values ​​from step 1, and the damage difference is calculated. Based on the difference, the main stress concentration points affected by each loading channel are determined. A channel-damage influence matrix is ​​then constructed to guide subsequent load adjustments.

[0066] After completing the two simulation modes, the fatigue damage values ​​of the main stress concentration points identified in step 1 are extracted under each working condition. Using the target damage value calculated in step 1 as the baseline value, the damage values ​​under the full-channel working condition and the individually missing-channel working condition are compared and analyzed with the baseline value to calculate the damage difference. The damage difference under the full-channel working condition reveals which stress concentration points are the main points of deviation between the current loading scheme and the target damage. The damage difference under the individually missing-channel working condition identifies the primary and secondary contributions of each loading channel to the damage at each stress concentration point, determining the stress concentration point with the most significant impact from that channel.

[0067] Based on the above analysis results, a "channel-damage influence matrix" was constructed. This matrix uses loading channels as rows and major stress concentration points as columns. Matrix elements represent the damage change (or relative change ratio) caused by the absence of a channel, thus quantitatively reflecting the contribution of each channel to fatigue damage in different parts of the structure. This matrix provides a basis for subsequent load adjustments, channel reduction, or optimization of test bench loading schemes.

[0068] Step 6: Calculate the initial constant amplitude test load.

[0069] Given the geometric symmetry of the left and right control arms of the subframe, the test load of the right control arm can be symmetrically set based on the calculation results of the left side. For the connection hardpoints of each control arm on the left side, the initial constant amplitude test load is solved separately according to the following method, and its parameters include amplitude, mean, loading frequency and number of cycles.

[0070] 1) Road spectrum load rainflow statistics and superposition

[0071] Import the combined road spectrum loads of all operating conditions for each control arm connection hardpoint obtained in step 4 into data processing software such as LMS Tecware or nCode GlyphWorks. Select the load channel to be calculated, and first perform high-resolution rainflow statistics for each operating condition (using the range-mean counting method, it is recommended to set the number of bins to the maximum value of 512) to obtain the amplitude range, mean, and number of cycles for each operating condition, generating the rainflow matrix for each operating condition; then, based on the number of cycles for each operating condition, superimpose the rainflow matrices of all operating conditions, and finally output the total amplitude range, mean, and total number of cycles for the hardpoint under all road spectrum operating conditions.

[0072] 2) Determination of SN curve parameters

[0073] In the Excel spreadsheet, the slope k of the SN curve is defined; in this embodiment, k=4. The initial value of the curve intercept can be arbitrarily given. Based on Miner's linear cumulative damage rule, the pseudo-damage values ​​under each load amplitude are calculated separately, and then summed to obtain the total pseudo-damage value. The curve intercept is iteratively adjusted until the total pseudo-damage value is 0.5, thus determining the final value of the intercept.

[0074] 3) Determination of amplitude and loading parameters

[0075] The bench test frequency for loading at the hardpoints connecting the subframe control arms is typically 1-3 Hz. The number of test cycles is determined based on a suitable test loading time; in this embodiment, the number of test loading cycles at each control arm connection hardpoint is set to 100,000. Based on the newly determined SN curve, the load amplitude corresponding to 100,000 cycles is calculated. This amplitude is the amplitude of the initial constant amplitude test load.

[0076] 4) Determining the mean

[0077] Based on the total amplitude range, mean, and total number of cycles under all road spectrum conditions, the main concentration interval of the number of cycles is identified, and a mean value within this interval is selected as the mean value of the initial fixed amplitude test load.

[0078] Step 7: Iteratively adjust the constant amplitude test load.

[0079] Follow the iterative adjustment process below:

[0080] 1) Static Analysis

[0081] Based on the amplitude and mean values ​​of the connection hard points of each control arm determined in step 6, calculate the maximum and minimum load values. In static analysis software such as ABAQUS, based on the refined finite element model of the subframe established in step 1, apply loads at the connection hard points of each control arm along the test loading direction determined in step 3, and calculate the stress results of the maximum and minimum load values ​​respectively.

[0082] 2) Initial fatigue simulation

[0083] Import the stress calculation results into fatigue analysis software such as nCode DesignLife or Femfat, input the number of cycles, and input the measured SN curve of the subframe material ZAlSi7MgA. Calculate the fatigue damage distribution of the subframe under the applied initial constant-amplitude load. Extract and record the damage values ​​at the same locations as the main stress concentration points identified in step 1.

[0084] 3) Deviation identification

[0085] Calculate the difference between the initial damage value and the target damage value determined in step 1, and identify the stress concentration points where the deviation is mainly concentrated.

[0086] 4) Influence Channel Analysis

[0087] Based on the “channel-damage influence matrix” constructed in step 5, the key loading channels that affect the stress concentration points of the above deviations are identified.

[0088] 5) Load adjustment

[0089] Prioritize adjusting the test load of the corresponding channel. If multiple channels affect the same stress concentration point, adjust them in descending order of influence, adjusting only one channel at a time.

[0090] The test loads of the control arms, which are symmetrically positioned on the left and right sides, should always be set symmetrically.

[0091] If the damage at a certain point is lower than the target value, the load amplitude of the corresponding channel is increased; otherwise, it is decreased. The amplitude adjustment range must not exceed the total amplitude of the control arm connection hard point under all road spectrum conditions as statistically analyzed in step 6.

[0092] If adjusting the amplitude alone is insufficient to achieve the target damage range, the number of test loading cycles for all control arm connection hardpoint channels can be increased simultaneously. The number of cycles for all channels should be adjusted consistently.

[0093] 6) Iterative convergence

[0094] The damage is recalculated after each adjustment. This process is repeated multiple times until the error between the damage at the main stress concentration points and the target damage is controlled within -10% to +50%.

[0095] Step 8: Output the final test plan.

[0096] Based on the aforementioned analysis and iterative optimization, a multi-channel bench test scheme for the subframe is compiled and output to guide bench setup and test execution:

[0097] 1) Constraint scheme

[0098] The subframe's various body connection points are fixed using the original vehicle bolts, following the actual vehicle's specifications. If suspension bushings are designed at the connection points, the original bushings must be installed to accurately simulate the boundary conditions of the actual vehicle.

[0099] 2) Loading scheme

[0100] Apply loads at the hard points where each control arm connects to the subframe, with the loading direction determined in step 3.

[0101] 3) Test load

[0102] In-phase loading was applied at the connection points of each control arm. The test load was the final load obtained after multiple adjustments and iterations in step 7, and its error with the target damage met the predetermined requirements. Specific load parameters included: amplitude, mean, and number of loading cycles. The test loading frequency was controlled within the range of 1~3 Hz.

[0103] Compared with existing technologies, the subframe multi-channel durability bench test development method of the present invention has the following advantages:

[0104] This invention discloses a method for developing a multi-channel durability bench test scheme for subframes. By combining loads and projecting the maximum damage direction onto the road spectrum, it effectively reproduces the coupling effect of loads between control arm connection points while retaining the road spectrum's main contribution to subframe damage, making the test results closer to real vehicle operating conditions. This method only requires loading at each control arm connection point, eliminating the need for numerous test components such as suspension assemblies, significantly simplifying bench setup. Furthermore, by simplifying the complex time-domain road spectrum into an equivalent constant-amplitude load, the bench test cycle is greatly shortened.

[0105] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to facilitate the description of this invention and to simplify 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 limiting the scope of protection of this invention.

[0106] 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 invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0107] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0108] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for developing a multi-channel durability bench test scheme for subframes, characterized in that, include: Step 1: Define the target damage. Apply a six-component force road spectrum to the subframe finite element model to perform fatigue simulation and determine the target damage at the main stress concentration points. Step 2: Screen the main damage conditions. Based on the pseudo-damage assessment, screen the main conditions and stitch them together into a continuous load spectrum. Step 3: Calculate the test loading direction. For each control arm connection hard point, find the optimal direction that maximizes the projection load while preserving the original load characteristics. Step 4: Load spectrum merging and simplification. Project the three-dimensional forces onto the optimal direction and merge them into a single-channel or dual-channel target load. Step 5: Analyze the fatigue damage influence of each channel. Establish the channel-damage influence matrix through full-channel and missing-channel simulations. Step 6: Calculate the initial fixed-amplitude test load. Calculate the initial fixed-amplitude test load based on the damage equivalence principle. Step 7: Iteratively adjust the fixed-amplitude test load, adjusting the load iteratively according to the influence matrix until the damage deviation meets the requirements; Step 8: Output the final test plan, output the final fixed-amplitude load parameters and loading direction.

2. The method for developing a multi-channel durability bench test scheme for subframes according to claim 1, characterized in that, In step 2, the specific method for screening the main damage conditions is as follows: For each load spectrum condition, the load time history of the three force component channels Fx, Fy, and Fz at the connection hard points of each control arm is extracted. Rainflow counting is used for cyclical statistics. Combined with the SN curve of the material, the pseudo-damage value of each channel under a single condition is calculated. The pseudo-damage values ​​of all control arms and all three force component channels in the same condition are algebraically summed and superimposed to obtain the total pseudo-damage of the condition. The conditions are arranged in descending order of pseudo-damage value from largest to smallest, and the cumulative damage ratio is calculated by accumulating them sequentially. The condition covered when the cumulative damage ratio first exceeds the preset threshold is defined as the main damage condition.

3. The method for developing a multi-channel durability bench test scheme for subframes according to claim 2, characterized in that, In step 2, the method for determining the number of repetitions of each major damage condition in the screening of major damage conditions is as follows: take the minimum value of the original number of cycles of each major damage condition as the benchmark number of cycles, calculate the ratio of the original number of cycles of the remaining conditions to the benchmark, and if the ratio is not an integer, round up to determine the number of repetitions of each condition.

4. The method for developing a multi-channel durability bench test scheme for subframes according to claim 1, characterized in that, In step 3, when calculating the experimental loading direction, the triaxial force vector (Fx, Fy, Fz) in the load spectrum is denoted as... The unit direction vector is defined at the hardpoint where the control arm connects, denoted as . , and The X, Y, and Z directions are defined in the same way as the actual vehicle coordinate system; the unit direction vector The definition method is as follows: taking the hard point connecting the control arm as the origin, traverse all possible direction vectors on the unit sphere with a certain step size; unit direction vector Projected load on for: , residual load for: ; For each control arm connection hardpoint, calculate each triaxial force vector. unit direction vector Projected load on and residual load When the projected load With triaxial force vector load When the average ratio is at its maximum, or when the residual load When the value is at its minimum, the corresponding unit direction vector is the experimental loading direction.

5. The method for developing a multi-channel durability bench test scheme for subframes according to claim 1, characterized in that, In step 4, load spectrum merging and simplification, for the spring bearing arm, its vertical load is retained as an independent loading channel, and its direction is defined as vertical. At the same time, its horizontal load is projected and merged in the XY horizontal plane according to the method of finding the optimal direction, forming a dual-channel loading scheme.

6. The method for developing a multi-channel durability bench test scheme for subframes according to claim 1, characterized in that, In step 5, the method for establishing the channel-damage influence matrix in the fatigue damage influence analysis of each channel is as follows: perform full-channel working condition simulation and channel-missing working condition simulation, extract the fatigue damage value of the main stress concentration point under the two working conditions, calculate the damage difference based on the target damage value, with the loading channel as the row and the main stress concentration point as the column, and the matrix element represents the damage change amount or relative change ratio caused by the missing channel.

7. The method for developing a multi-channel durability bench test scheme for subframes according to claim 1, characterized in that, In step 6, the method for calculating the amplitude of the initial fixed-amplitude test load is as follows: Rainflow statistics are performed on the merged road spectrum, and the rainflow matrices of all working conditions are superimposed to obtain the total amplitude range, mean, and total number of cycles; based on Miner's linear cumulative damage rule, the intercept of the SN curve is iteratively adjusted to make the total pseudo-damage value 0.5 to determine the intercept; the load amplitude corresponding to the target number of cycles is solved according to the determined SN curve, which is used as the amplitude of the initial fixed-amplitude test load.

8. The method for developing a multi-channel durability bench test scheme for subframes according to claim 1, characterized in that, In step 6, when calculating the initial fixed-amplitude test load, the main concentration interval of the number of cycles is identified based on the total amplitude range, mean, and total number of cycles under all road spectrum conditions. A mean value within this interval is selected as the mean value of the initial fixed-amplitude test load.

9. The method for developing a multi-channel durability bench test scheme for subframes according to claim 1, characterized in that, In step 7, during the iterative adjustment of the fixed amplitude test load, the test loads of the control arms at the symmetrical positions on the left and right sides are always set symmetrically. The amplitude adjustment range does not exceed the total amplitude of the control arm connection hard point under all road spectrum conditions as statistically analyzed in step 6. When adjusting the amplitude alone cannot make the damage reach the target range, the number of test loading cycles for all control arm connection hard point channels is increased simultaneously, and the number of cycles for all channels is adjusted in a consistent manner.

10. The method for developing a multi-channel durability bench test scheme for subframes according to claim 1, characterized in that, In step 7, the convergence criterion for iteratively adjusting the fixed-amplitude test load is that the error between the simulated damage and the target damage at the main stress concentration points is controlled within -10% to +50%.

11. The method for developing a multi-channel durability bench test scheme for subframes according to claim 1, characterized in that, In the final test plan output in step 8, the loading scheme is to implement in-phase loading at the connection hard points between each control arm and the subframe, and the test loading frequency is controlled within the range of 1 to 3 Hz. The constraint scheme uses the original vehicle bolts to fix each body connection point of the subframe according to the actual vehicle state, and the suspension bushings at the connection points are fitted with original bushings.

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