Sine load equivalence method of multi-degree-of-freedom load system

Abstract

The invention provides a sine load equivalence method of a multi-degree-of-freedom load system. The method comprises the following steps: calculating a principal stress and a principal stress angle according to a strain signal of a target part of a chassis; the multi-component load signals serve as a first group of load signals, and the multi-component load signals are recombined to obtain an in-phase recombined load component and a reverse-phase recombined load component to serve as a second group of load signals; identifying a frequency response function corresponding to each recombined load component in the second group of load signals according to the principal stress, and calculating a time domain response caused by the frequency response function on the chassis target part and a contribution degree to the principal stress; selecting the phase of the recombination load component with the maximum contribution degree as the phase of the equivalent sine load; and if the principal stress angle of the target part of the chassis and the principal stress angle under the action of the multi-component load signal meet a preset similar condition under the action of the equivalent sine load, setting a durability test target. According to the method, the problem that coupling among six components of an original complex road spectrum is difficult to effectively decompose in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of structural durability testing, and more particularly to a sinusoidal load equivalent method for multi-degree-of-freedom load systems. Background Technology

[0002] In the development of automotive structural durability, road load spectrum is a core input parameter for evaluating vehicle structural strength and optimizing design schemes, directly affecting the accuracy and reliability of durability analysis results. Multi-axis coupled road load spectrum, as key load data reflecting complex driving conditions of real vehicles, contains six components of force with significant coupling characteristics, which current technologies struggle to accurately decompose. Since subsequent structural durability testing and simulation analysis often require converting the actual complex load spectrum into a more readily applicable sinusoidal load spectrum, the aforementioned coupling decomposition problem directly hinders the accurate conversion of multi-axis coupled road load spectrum to sinusoidal load spectrum. This, in turn, affects the efficiency and quality of automotive structural durability development, making it difficult to meet the stringent requirements for structural reliability in the automotive engineering field. Summary of the Invention

[0003] Based on the above problems, this invention proposes a sinusoidal load equivalent method for multi-degree-of-freedom load systems. This invention solves the technical problem that although the nodal load spectra obtained in the prior art cover 6 degrees of freedom, they are difficult to effectively decompose the coupling between the six component forces, resulting in limited accuracy and application adaptability of the load spectrum, and failing to fully meet the needs of subsequent vehicle performance analysis, structural optimization, and other scenarios. The sinusoidal load equivalent method for multi-degree-of-freedom load systems provided by this invention achieves decoupling of multi-component loads, selects the load direction and phase with the largest contribution, and the equivalent sinusoidal load spectrum can accurately reflect the damage to the target parts of the chassis structure. By equating the complex multi-axis random load spectrum to a sinusoidal load with a single direction and phase, high-confidence durability testing can be completed on low-cost single-axis or dual-axis test benches, greatly reducing the cost, cycle, and operational complexity of testing equipment. The structural damage location and morphology caused by the sinusoidal load spectrum obtained by this method are highly consistent with the actual vehicle road spectrum results, and the equivalent mileage deviation is within an acceptable engineering range, strongly verifying the effectiveness and practicality of this method.

[0004] This invention proposes a sinusoidal load equivalent method for a multi-degree-of-freedom load system, comprising: Acquire multi-component force load signals at the left and right wheel ends and strain signals at target locations on the chassis; Calculate the principal stresses and principal stress angles based on the strain signals of the target parts of the chassis; The multi-component force load signal is used as the first set of load signals. The multi-component force load signal is recombined to obtain two recombined load components, namely in-phase and out-of-phase, which are used as the second set of load signals. Based on the principal stress, identify the frequency response function corresponding to each recombined load component in the second set of load signals, calculate the time domain response caused by each recombined load component at the target part of the chassis based on the frequency response function of each recombined load component, and calculate the contribution of each time domain response to the principal stress. The phase of the recombinant load component with the largest contribution is selected as the phase of the equivalent sinusoidal load; The direction of the equivalent sinusoidal load is selected from the direction of the recombined load component that contributes the most, or the direction of the load signal that contributes the most to the principal stress in the time domain response corresponding to the multi-component force load signal in the first group of load signals. If the principal stress angle of the target part of the chassis under the action of equivalent sinusoidal load meets the preset similarity condition with the principal stress angle under the action of multi-component force load signal, then based on the principle of damage equivalence, the durability test target of equivalent sinusoidal load is set.

[0005] Furthermore, the direction of the equivalent sinusoidal load is selected from either the direction of the recombined load component that contributes the most or the direction of the load signal that contributes the most to the principal stress in the time-domain response corresponding to the multi-component force load signal in the first set of load signals, including: If the target area of ​​the chassis is the subframe load area, the direction of the equivalent sinusoidal load should be selected from the direction of the recombined load component that contributes the most. If the target part of the chassis is outside the subframe load area, the direction of the equivalent sinusoidal load is selected from the direction of the load signal that contributes the most to the principal stress in the time domain response of the multi-component force load signal in the first group of load signals. The process of calculating the contribution of the multi-component force load signals in the time-domain response to the principal stress in the first set of load signals includes: Based on the principal stress, identify the frequency response function corresponding to each load component in the first set of load signals, calculate the time domain response caused by each load component at the target part of the chassis based on the frequency response function of each load component, and calculate the contribution of each time domain response to the principal stress.

[0006] Furthermore, the frequency response function corresponding to each load component in the first group of load signals identified by the principal stress, and the frequency response function corresponding to each recombined load component in the second group of load signals identified by the principal stress, are calculated using the following process: The mathematical expression for the relationship between input and output in the frequency domain of a linear system is: , in, For the Fourier transform of the i-th input signal, It is the frequency response function of the i-th input signal. For the Fourier transform of the output signal; By substituting the first set of load signals as input signals and the principal stress as output signals into the above mathematical expression, the frequency response function corresponding to each recombined load component in the first set of load signals is obtained. Using the second set of load signals as input signals and the principal stress as output signals, we can substitute these into the above mathematical expression to obtain the frequency response function corresponding to each recombined load component in the second set of load signals.

[0007] In addition, the calculation of principal stresses and principal stress angles based on strain signals from the target area of ​​the chassis includes: The strain signal of the target part of the chassis is obtained from the strain gauge set on the chassis. The tensile principal strain and compressive principal strain of the target part of the chassis are calculated based on the strain signal. The tensile principal stress and compressive principal stress are calculated based on the tensile principal strain and compressive principal strain respectively. The larger absolute value of the tensile principal stress and compressive principal stress is taken as the principal stress.

[0008] In addition, the strain rosette installed on the chassis is a right-angle strain rosette, and the strain signal is the strain in three directions measured by the right-angle strain rosette, namely the strain in the 0° direction. Strain in the 45° direction Strain in the 90° direction ; Tensile principal strain and compressive principal strain The calculation formula is:

[0009]

[0010] Principal stress angle The calculation formula is: ; when hour, for Axis and maximum strain The angle between the principal stresses is such that the principal stresses are tensile principal stresses. when hour, for Axis and Minimum Strain The angle between the principal stresses is such that the principal stresses are compressive principal stresses.

[0011] In addition, the multi-component force load signal is used as the first group of load signals. The multi-component force load signal is recombined to obtain two recombined load components, namely in-phase and out-of-phase, which are used as the second group of load signals, including: In-phase recombination load components and the reverse-phase recombination load component The calculation formula is: , , in, Represents the load on the left wheel center. Represents the load on the right wheel center, subscript These represent the load directions x, y, and z.

[0012] Furthermore, the calculation of the time-domain response at the target location on the chassis based on the frequency response function of each recombined load component includes: The frequency domain representation of each recombined load component is obtained by performing a Fourier transform on it. Multiply the frequency domain representation of each recombined load component by its corresponding frequency response function in the frequency domain to obtain the frequency domain response of each recombined load component. Perform an inverse Fourier transform on the frequency domain response of each recombined load component to obtain the time domain response caused by each recombined load component at the target location.

[0013] Furthermore, the calculation of the contribution of each time-domain response to the principal stress includes: First, calculate the time-domain contribution of the time-domain response of each recombined load component to the principal stress. Time-sharing contribution = Time-domain response of each recombined load component at that time point / Total time-domain response at that time point, where the total time-domain response at that time point is the sum of the time-domain responses of all recombined load components at that time point; Then calculate the overall contribution, which is the average or maximum value of the time-sharing contribution at all times; or the overall contribution is the average or maximum value of the time-sharing contribution at the peak and trough of the previous preset percentage with the larger absolute value. The overall contribution is taken as the contribution of each time-domain response to the principal stress.

[0014] In addition, the preset similarity condition is: under the action of equivalent sinusoidal load and multi-component force load signals respectively, the absolute value of the difference between the angle values ​​corresponding to the main peak of the principal stress angle distribution histogram of the target part of the chassis is less than a preset threshold. Alternatively, the preset similar condition is: under the action of equivalent sinusoidal load and multi-component force load signals respectively, the cumulative distribution function of the principal stress angle distribution of the target part of the chassis has a higher degree of overlap in the main interval than the preset overlap. Alternatively, the preset similar condition is: under the action of equivalent sinusoidal load and multi-component force load signals respectively, the absolute value of the average value of the principal stress angle distribution of the target part of the chassis is less than or equal to the preset degree.

[0015] Furthermore, the durability test target based on the damage equivalence principle includes: determining the target number of cycles for the equivalent sinusoidal load; The process of determining the target number of iterations includes: Calculate the cumulative pseudo-damage value D_road caused by the multi-component force load signal at the target location on the chassis; Determine the pseudo-damage value d_sin caused by a single cycle of equivalent sinusoidal load at the target location on the chassis; The target number of cycles N_target for the equivalent sinusoidal load is calculated using the formula N_target = D_road / d_sin. The calculation of the load amplitude of the equivalent sinusoidal load includes: Calculate the cumulative damage value caused by multi-component force load signals at the target location on the chassis. Based on the target cycle number, calculate the load amplitude of the equivalent sinusoidal load according to the damage equivalence equation.

[0016] This invention addresses the technical problem that while existing technologies obtain nodal load spectra covering all six degrees of freedom, they often fail to effectively decompose the coupling between the six component forces, resulting in limited accuracy and application adaptability of the load spectra, and thus failing to fully meet the needs of subsequent vehicle performance analysis, structural optimization, and other scenarios. The sinusoidal load equivalent method for multi-degree-of-freedom load systems provided by this invention achieves decoupling of multi-component loads, selecting the load direction and phase with the greatest contribution. The equivalent sinusoidal load spectrum accurately reflects the damage to target parts of the chassis structure. By equating the complex multi-axis random load spectrum to a sinusoidal load with a single direction and phase, high-confidence durability testing can be completed on low-cost single-axis or dual-axis test benches, significantly reducing testing equipment costs, cycle time, and operational complexity. The structural damage location and morphology caused by the sinusoidal load spectrum obtained by this method are highly consistent with the actual vehicle road spectrum results, and the equivalent mileage deviation is within an acceptable engineering range, strongly verifying the effectiveness and practicality of this method. Attached Figure Description

[0017] Figure 1 A flowchart of a sinusoidal load equivalent method for a multi-degree-of-freedom load system provided in one embodiment of the present invention; Figure 2 A schematic diagram of a suspension component sinusoidal load test bench provided in one embodiment of the present invention; Figure 3 A frequency domain diagram showing the input and output relationship of a linear system provided in one embodiment of the present invention; Figure 4 A right-angle strain rosette arrangement diagram provided in one embodiment of the present invention; Figure 5 A diagram illustrating the position of a right-angle strain gauge attachment according to an embodiment of the present invention; Figure 6 This is a comparison diagram of the calculated time-domain response and the original multi-component force time-domain response provided in one embodiment of the present invention; Figure 7This is a comparison diagram of the calculated frequency domain response and the original multi-force frequency domain response provided in one embodiment of the present invention; Figure 8 This is a schematic diagram of the response of each load component according to an embodiment of the present invention; Figure 9 A schematic diagram of contribution calculation provided for one embodiment of the present invention; Figure 10 A comparison chart of the contribution analysis of the six-component force load signal and the contribution analysis of the recombined load component provided in one embodiment of the present invention; Figure 11 This is a histogram of the principal stress angle frequencies of the six-component force response provided in one embodiment of the present invention; Figure 12 This is a histogram of principal stress angle frequencies of a sinusoidal response provided in one embodiment of the present invention; Figure 13 This is a schematic diagram comparing MRS and sinusoidal load test results according to an embodiment of the present invention; Figure 14 This is a schematic diagram comparing the crack morphology under MRS and sinusoidal load, provided as an embodiment of the present invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. This description is intended only to illustrate specific embodiments of the invention and does not constitute any limitation on the invention. The scope of protection of the invention is defined by the claims.

[0019] Reference Figure 1 This invention proposes a sinusoidal load equivalent method for a multi-degree-of-freedom load system, comprising: Step S001: Obtain the multi-component force load signals at the left and right wheel ends and the strain signals at the target parts of the chassis; Step S002: Calculate the principal stress and principal stress angle based on the strain signal of the target part of the chassis; Step S003: The multi-component force load signal is used as the first set of load signals. The multi-component force load signal is recombined to obtain two recombined load components, in-phase and out-of-phase, as the second set of load signals. Step S004: Identify the frequency response function corresponding to each recombined load component in the second set of load signals based on the principal stress, calculate the time domain response caused by each recombined load component at the target part of the chassis based on the frequency response function of each recombined load component, and calculate the contribution of each time domain response to the principal stress. Step S005: Select the phase of the recombinant load component with the largest contribution as the phase of the equivalent sinusoidal load; Step S006: Select the direction of the equivalent sinusoidal load that contributes the most to the recombined load component or the direction of the load signal that contributes the most to the principal stress in the time domain response of the multi-component load signal in the first set of load signals. Step S007: If the principal stress angle of the target part of the chassis under the action of the equivalent sinusoidal load meets the preset similarity condition with the principal stress angle under the action of the multi-component force load signal, then based on the damage equivalence principle, the durability test target of the equivalent sinusoidal load is set.

[0020] In the field of load spectrum extraction in vehicle engineering, existing technologies for obtaining nodal load spectra of the vehicle body and suspension system mainly include two core solutions: constraint loading method and virtual iteration method. Among them, the constraint loading method constructs a vehicle body and suspension model in ADAMS software, fixes the vehicle body to the ground, and applies vibration excitation collected from the actual vehicle to the wheel ends to extract the 6-DOF load spectrum of the target node. However, this method will suppress the response of the vehicle body inertia and damping to the suspension system, affecting the authenticity of load transfer. The virtual iteration method obtains the time domain signal of the vehicle body Z-direction displacement through virtual iteration technology, uses this signal to replace the Z-direction load, and finally completes the extraction of the 6-DOF nodal load spectrum. However, both of the above methods have obvious limitations. Although the nodal load spectra they obtain cover all six degrees of freedom, they are both unable to effectively decompose the coupling between the six component forces, which limits the accuracy and application adaptability of the load spectra and cannot fully meet the needs of subsequent vehicle performance analysis, structural optimization and other scenarios.

[0021] Existing research also includes analyses of the damage coupling of the six-component load on the mid-section of the chassis torsion beam, decomposing it into a sinusoidal load composed of upper and lower and left and right forces at the wheel ends. However, this approach is suitable for torsion beam chassis and has limitations for multi-link chassis. The analysis of shaft components and linkage components affected only by single-sided wheel end loads introduces interference load components. Furthermore, the equivalent analysis of the subframe under simultaneous loads at both wheel ends neglects the influence of the principal stress direction.

[0022] This embodiment proposes to combine the multi-component loads on both wheel ends into two sets of loads, and select the appropriate set for analysis of different parts; and introduces the principal stress angle parameter to analyze the degree of restoration of the principal stress direction.

[0023] In step S001, the multi-component force load signals of the left and right wheel ends and the strain signals of the target parts of the chassis are acquired; Optionally, the multi-component force load signal is a six-component force load signal, transmitted through... and express, Represents the load on the left wheel center. Represents the load on the right wheel center, subscript These represent the load directions x, y, and z.

[0024] The six-component force refers to the load on the vehicle's wheel end from the road surface in six degrees of freedom, with each degree of freedom corresponding to a component force. Right-angle strain gauges are attached to the target area to collect strain signals, such as... Figure 2 As shown.

[0025] In step S002, the principal stresses and principal stress angles are calculated based on the strain signals of the target location on the chassis. The strain signal of the target part of the chassis is obtained from the strain gauge set on the chassis. The tensile principal strain and compressive principal strain of the target part of the chassis are calculated based on the strain signal. The tensile principal stress and compressive principal stress are calculated based on the tensile principal strain and compressive principal strain respectively. The larger absolute value of the tensile principal stress and compressive principal stress is taken as the principal stress.

[0026] like Figure 4 and 5 As shown, optionally, the strain signal of the target part of the chassis is the strain in three directions measured from a right-angle strain rosemary, namely the strain in the 0° direction. Strain in the 45° direction Strain in the 90° direction Since the coordinate system of the right-angle strain rosette is consistent with the right-angle coordinate system of the whole vehicle, coordinate system correspondence can be performed, so the right-angle strain rosette is preferred.

[0027] Tensile principal strain and compressive principal strain The calculation formula is:

[0028]

[0029] According to the principal strain of tension and compressive principal strain Calculate the tensile principal stress and compressive principal stress separately, and take the larger absolute value of the two principal stresses as the principal stress.

[0030] Optionally, based on the tensile principal strain and compressive principal strain Calculate the tensile principal stress and compressive principal stress separately, and calculate the tensile principal stress according to the generalized Hooke's law. and compressive principal stress : E / (1- )*( +v* ); E / (1- )*( +v* ); Where E is the elastic modulus of the material, and v is the Poisson's ratio of the material.

[0031] Take the tensile principal stress and compressive principal stress The largest absolute value is taken as the principal stress.

[0032] Principal stress angle The calculation formula is: ; when hour, for Axis and maximum strain The angle between the principal stresses is such that the principal stresses are tensile principal stresses. when hour, for Axis and Minimum Strain The angle between the principal stresses is such that the principal stresses are compressive principal stresses.

[0033] The reason for making a judgment here is... and The magnitude is due to: the principal stress angle is calculated. After that, it is necessary to... and Size relationship judgment This refers to the principal strain, which can be either tensile or compressive. Correct identification ensures that the sinusoidal load and the original road spectrum induce the same stress state at the target location on the chassis. Incorrect identification can lead to completely different stress modes even with similar load directions, resulting in loss calculations that deviate entirely from reality. This step ensures physical equivalence when converting from complex multi-load to sinusoidal load equivalent processes.

[0034] In step S003, the multi-component force load signal is used as the first set of load signals, and the multi-component force load signal is recombined to obtain two recombined load components, namely in-phase and out-of-phase, which are used as the second set of load signals. In-phase recombination load components and the reverse-phase recombination load component The calculation formula is: , , in, Represents the load on the left wheel center. Represents the load on the right wheel center, subscript These represent the load directions x, y, and z.

[0035] The six component loads at the wheel ends are reorganized to identify the phase relationship between the loads on the left and right wheels.

[0036] In step S004, the frequency response function corresponding to each recombined load component in the second group of load signals is identified according to the principal stress, and the time domain response caused by each recombined load component at the target part of the chassis is calculated according to the frequency response function of each recombined load component, and the contribution of each time domain response to the principal stress is calculated. The frequency response function corresponding to each load component in the first group of load signals identified by the principal stress, and the frequency response function corresponding to each recombined load component in the second group of load signals identified by the principal stress, are calculated using the following process: The mathematical expression for the relationship between input and output in the frequency domain of a linear system is: , in, For the Fourier transform of the i-th input signal, It is the frequency response function of the i-th input signal. For the Fourier transform of the output signal; By substituting the first set of load signals as input signals and the principal stress as output signals into the above mathematical expression, the frequency response function corresponding to each recombined load component in the first set of load signals is obtained. Using the second set of load signals as input signals and the principal stress as output signals, we can substitute these into the above mathematical expression to obtain the frequency response function corresponding to each recombined load component in the second set of load signals.

[0037] The time-domain response of each recombined load component at the target location on the chassis is calculated based on its frequency response function, including: The frequency domain representation of each recombined load component is obtained by performing a Fourier transform on it. Multiply the frequency domain representation of each recombined load component by its corresponding frequency response function in the frequency domain to obtain the frequency domain response of each recombined load component. Perform an inverse Fourier transform on the frequency domain response of each recombined load component to obtain the time domain response caused by each recombined load component at the target location.

[0038] The calculation of the contribution of each time-domain response to the principal stress includes: First, calculate the time-domain contribution of the time-domain response of each recombined load component to the principal stress. Time-sharing contribution = Time-domain response of each recombined load component at that time point / Total time-domain response at that time point, where the total time-domain response at that time point is the sum of the time-domain responses of all recombined load components at that time point; Then calculate the overall contribution, which is the average or maximum value of the time-sharing contribution at all times; or the overall contribution is the average or maximum value of the time-sharing contribution at the peak and trough of the previous preset percentage with the larger absolute value. The overall contribution is taken as the contribution of each time-domain response to the principal stress.

[0039] In step S005, the phase of the recombined load component with the largest contribution is selected as the phase of the equivalent sinusoidal load; the recombined load component with the largest contribution is the load component to be found in this invention.

[0040] In step S006, the direction of the equivalent sinusoidal load is selected from the direction of the recombined load component with the largest contribution or the direction of the load signal with the largest contribution to the principal stress in the time domain response corresponding to the multi-component force load signal in the first group of load signals. The recombinant load component that contributes the most determines the stress mode and loss mechanism of the target part of the chassis. Therefore, its corresponding phase is selected as the phase of the equivalent sinusoidal load, and there are two choices for the direction of the equivalent sinusoidal load. The force application mode of the load can be determined by the direction and phase.

[0041] like Figure 2 As shown, if the target part of the chassis is the subframe load area, such as point A, then the direction of the equivalent sinusoidal load is chosen to be the direction of the recombinant load component that contributes the most; the load in the subframe load area is more affected by the forces of the two wheels. If the target part of the chassis is outside the subframe load area, such as at points B and C, where point B is the connecting rod component on the chassis and point C is the axle component on the chassis, then the direction of the equivalent sinusoidal load is selected from the direction of the load signal that contributes the most to the principal stress in the time domain response corresponding to the multi-component force load signal in the first set of load signals; the load in the area outside the subframe load area is more affected by the single wheel force. The process of calculating the contribution of the multi-component force load signals in the time-domain response to the principal stress in the first set of load signals includes: Based on the principal stress, identify the frequency response function corresponding to each load component in the first set of load signals, calculate the time domain response caused by each load component at the target part of the chassis based on the frequency response function of each load component, and calculate the contribution of each time domain response to the principal stress.

[0042] In step S007, if the principal stress angle of the target part of the chassis under the action of the equivalent sinusoidal load meets the preset similarity condition with the principal stress angle under the action of the multi-component force load signal, then based on the damage equivalence principle, the durability test target of the equivalent sinusoidal load is set.

[0043] Optionally, under the action of an equivalent sinusoidal load, the principal stress angle of the target part of the chassis and the principal stress angle under the action of multi-component force load signals can satisfy a preset similarity condition as follows: Under the action of equivalent sinusoidal load and multi-component force load signals respectively, the absolute value of the difference between the angle values ​​corresponding to the main peak of the principal stress angle distribution histogram of the target part of the chassis is less than a preset threshold; the preset threshold is, for example, 10 degrees.

[0044] Alternatively, a similar condition can be preset: under the action of equivalent sinusoidal load and multi-component force load signals respectively, the cumulative distribution function of the principal stress angle distribution of the target part of the chassis has a higher degree of overlap in the main interval than the preset overlap; the preset overlap is, for example, 80%.

[0045] Alternatively, a similar condition can be preset: under the action of an equivalent sinusoidal load and multiple component load signals, the absolute value of the average value of the principal stress angle distribution at the target location of the chassis is less than or equal to a preset degree. The preset degree is, for example, 10 degrees.

[0046] Reference Figure 11 and Figure 12 Two anti-phase sinusoidal loads were applied to the wheel center front and rear abutting forces on a test bench, and the response at the target location was simultaneously acquired. The principal stress direction distribution at the target location under the action of the six-component force load at the wheel end and the equivalent sinusoidal load was analyzed using frequency histograms. It can be seen that the principal stress angles are similar, at -57.6° and -64.8° respectively, indicating that the scheme of using anti-phase sinusoidal loads to reconstruct the six-component force load at the target location is reasonable.

[0047] Based on plane stress theory, the maximum principal stress is extracted. Using the SN curve and Miner's linear damage accumulation theory, pseudo-damage values ​​are calculated for the responses to six-component force loads and sinusoidal loads, respectively. The target durability test number for the sinusoidal load can be set according to the damage equivalence principle.

[0048] This invention addresses the technical problem that while existing technologies obtain nodal load spectra covering all six degrees of freedom, they often fail to effectively decompose the coupling between the six component forces, resulting in limited accuracy and application adaptability of the load spectra, and thus failing to fully meet the needs of subsequent vehicle performance analysis, structural optimization, and other scenarios. The sinusoidal load equivalent method for multi-degree-of-freedom load systems provided by this invention achieves decoupling of multi-component loads, selecting the load direction and phase with the greatest contribution. The equivalent sinusoidal load spectrum accurately reflects the damage to target parts of the chassis structure. By equating the complex multi-axis random load spectrum to a sinusoidal load with a single direction and phase, high-confidence durability testing can be completed on low-cost single-axis or dual-axis test benches, significantly reducing testing equipment costs, cycle time, and operational complexity. The structural damage location and morphology caused by the sinusoidal load spectrum obtained by this method are highly consistent with the actual vehicle road spectrum results, and the equivalent mileage deviation is within an acceptable engineering range, strongly verifying the effectiveness and practicality of this method.

[0049] In one embodiment, calculating the principal stresses and principal stress angles based on the strain signals of the target location on the chassis includes: The strain signal of the target part of the chassis is obtained from the strain gauge set on the chassis. The tensile principal strain and compressive principal strain of the target part of the chassis are calculated based on the strain signal. The tensile principal stress and compressive principal stress are calculated based on the tensile principal strain and compressive principal strain respectively. The larger absolute value of the tensile principal stress and compressive principal stress is taken as the principal stress.

[0050] In one embodiment, the strain gauge on the chassis is a right-angle strain gauge, and the strain signal is the strain measured by the right-angle strain gauge in three directions, namely the strain in the 0° direction. Strain in the 45° direction Strain in the 90° direction ; Tensile principal strain and compressive principal strain The calculation formula is:

[0051]

[0052] Optionally, based on the tensile principal strain and compressive principal strain Calculate the tensile principal stress and compressive principal stress separately, and calculate the tensile principal stress according to the generalized Hooke's law. and compressive principal stress : E / (1- )*( +v* ); E / (1- )*( +v* ); Where E is the elastic modulus of the material, and v is the Poisson's ratio of the material.

[0053] Take the tensile principal stress and compressive principal stress The largest absolute value is taken as the principal stress.

[0054] Calculating the principal stresses prepares the basis for subsequent calculations of equivalent damage.

[0055] Principal stress angle The calculation formula is: ; when hour, for Axis and maximum strain The angle between the principal stresses is such that the principal stresses are tensile principal stresses. when hour, for Axis and Minimum Strain The angle between the principal stresses is such that the principal stresses are compressive principal stresses.

[0056] The reason for making a judgment here is... and The magnitude is due to: the principal stress angle is calculated. After that, it is necessary to... and Size relationship judgment This refers to the principal strain, which can be either tensile or compressive. Correct identification ensures that the sinusoidal load and the original road spectrum induce the same stress state at the target location on the chassis. Incorrect identification can lead to completely different stress modes even with similar load directions, resulting in loss calculations that deviate entirely from reality. This step ensures physical equivalence when converting from complex multi-load to sinusoidal load equivalent processes.

[0057] The value can be positive or negative, so when comparing sizes, the sign of the value must be considered. For example: when , at this time Tensile force is the principal stress.

[0058] when , If we only look at the numerical values ​​at this point, we will get... The larger the value, the more erroneous the conclusion. In reality, at this point... The compressive force is the principal stress.

[0059] In one embodiment, the multi-component force load signal is used as the first set of load signals. The multi-component force load signal is then recombined to obtain two recombined load components, in-phase and out-of-phase, which are used as the second set of load signals. In-phase recombination load components and the reverse-phase recombination load component The calculation formula is: , , in, Represents the load on the left wheel center. Represents the load on the right wheel center, subscript These represent the load directions x, y, and z.

[0060] The principal stress signal at the target location is calculated based on the signal from the right-angle strain gauge. After filtering the principal stress signal, for example, using a 0.8~40Hz bandpass filter, the frequency response function is identified using two methods: Option 1: Using the six-component force signal as input and the maximum principal stress signal as output, the frequency response function is identified using MTS RPC software. MTS RPC software is a core professional software developed by MTS Systems, Inc. for its road simulation testing system.

[0061] Option 2: Reorganize the six component loads to identify the phase relationship between the loads on the left and right wheels. The reorganization formula is: , , The recombined load components are used as input signals to identify the frequency response function of the system.

[0062] Substitute the six component forces input from the wheel end and their corresponding frequency response functions into the formula. The frequency domain response and total frequency domain response of the target part under each recombined load component can be calculated. The inverse Fourier transform yields the time domain response and total time domain response of the target part under each recombined load component. The calculated total response is then compared with the response under the original path spectrum loading. Figure 6 and 7 As shown, the time domain and spectral shapes of the two are similar, indicating that the results are very accurate.

[0063] In one embodiment, the frequency response function corresponding to each load component in the first group of load signals identified by the principal stress and the frequency response function corresponding to each recombined load component in the second group of load signals identified by the principal stress are calculated using the following process: The mathematical expression for the relationship between input and output in the frequency domain of a linear system is: , in, For the Fourier transform of the i-th input signal, It is the frequency response function of the i-th input signal. For the Fourier transform of the output signal; By substituting the first set of load signals as input signals and the principal stress as output signals into the above mathematical expression, the frequency response function corresponding to each recombined load component in the first set of load signals is obtained. Using the second set of load signals as input signals and the principal stress as output signals, we can substitute these into the above mathematical expression to obtain the frequency response function corresponding to each recombined load component in the second set of load signals.

[0064] When analyzing the contribution of the six component force load signals to the principal stresses, it is necessary to identify the system's transfer function. When there are multiple target locations under study, the chassis system can be considered a multiple-input multiple-output (MIMO) system. To simplify the analysis, this embodiment selects only one target location for study, thereby simplifying the system to a multiple-input single-output (MISO) system.

[0065] For a linear MISO system, when multiple input signals act on the system simultaneously, the system output is a linear combination of the outputs of each input signal acting alone. Assume the system has m input signals. , The system output is According to the principle of linear superposition, the output of the system can be expressed as: , in, It is the system's impulse response to the i-th input signal. This represents the convolution operation.

[0066] In the frequency domain, the relationship between input and output can be described by the frequency response function, such as... Figure 3 As shown, The mathematical expression for the relationship between input and output in the frequency domain of a linear system is: , in, For the Fourier transform of the i-th input signal, It is the frequency response function of the i-th input signal. For the Fourier transform of the output signal; Assuming the chassis structure under study exhibits linear characteristics within the experimental loading range, it is a linear system. Based on the superposition principle of linear systems, although there are complex coupling relationships between the components of the input six-component force load signal and the strain response of the target part, the principal stress responses (contributions) of each component can be linearly superimposed, providing a theoretical basis for contribution analysis and the setting of the sinusoidal load spectrum.

[0067] In one embodiment, calculating the time-domain response at the target location on the chassis based on the frequency response function of each recombined load component includes: The frequency domain representation of each recombined load component is obtained by performing a Fourier transform on it. Multiply the frequency domain representation of each recombined load component by its corresponding frequency response function in the frequency domain to obtain the frequency domain response of each recombined load component. Perform an inverse Fourier transform on the frequency domain response of each recombined load component to obtain the time domain response caused by each recombined load component at the target location.

[0068] The frequency-to-time domain conversion prepares us for finding the component that contributes the most to the principal stress.

[0069] In one embodiment, calculating the contribution of each time-domain response to the principal stress includes: First, calculate the time-domain contribution of the time-domain response of each recombined load component to the principal stress. Time-sharing contribution = Time-domain response of each recombined load component at that time point / Total time-domain response at that time point, where the total time-domain response at that time point is the sum of the time-domain responses of all recombined load components at that time point; Then calculate the overall contribution, which is the average or maximum value of the time-sharing contribution at all times; or the overall contribution is the average or maximum value of the time-sharing contribution at the peak and trough of the previous preset percentage with the larger absolute value. The overall contribution is taken as the contribution of each time-domain response to the principal stress.

[0070] Optionally, the preset percentage is 20%. By taking the comprehensive contribution, a comprehensive value of the time-domain response of each recombined load component at all times is obtained, which better reflects the contribution made by each recombined load component.

[0071] The time-domain response of the target part under each recombined load component is calculated based on the frequency response function, such as... Figure 8 As shown, the response values ​​of each recombinant load component at the main peaks and valleys of the total response are extracted. The contribution of each recombinant load component is determined based on the ratio of its response value to the total response value. Figure 9 As shown.

[0072] Reference Figure 10 As shown, comparing the analysis results of the contribution of the six-component load signal with the analysis results of the contribution of the recombined load component, the x-direction load in the six-component load signal has the largest contribution to the target part; the front and rear phase-opposite loads in the recombined load component have the largest contribution to the target part.

[0073] Through systematic contribution analysis, the scientific decoupling of complex multi-axis coupled loads is achieved. It can accurately identify the load direction and phase that contributes the most to the damage of the target part, overcoming the limitations of traditional methods that rely on experience.

[0074] In one embodiment, the preset similarity condition is: under the action of equivalent sinusoidal load and multi-component force load signals respectively, the absolute value of the difference between the angle values ​​corresponding to the main peak of the principal stress angle distribution histogram of the target part of the chassis is less than a preset threshold; the preset threshold is, for example, 15 degrees.

[0075] Alternatively, a similar condition can be preset: under the action of equivalent sinusoidal load and multi-component force load signals respectively, the cumulative distribution function of the principal stress angle distribution of the target part of the chassis has a higher degree of overlap in the main interval than the preset overlap; the preset overlap is, for example, 80%.

[0076] Alternatively, a similar condition can be preset: under the action of equivalent sinusoidal load and multi-component force load signals respectively, the absolute value of the average value of the principal stress angle distribution of the target part of the chassis is less than or equal to a preset degree. The preset degree is, for example, 5 degrees.

[0077] This embodiment innovatively introduces a method for verifying the consistency of principal stress angles, ensuring that the simplified equivalent sinusoidal load and the original complex road spectrum induce the same stress mode and damage mechanism at the target location, thereby fundamentally improving the scientific validity and accuracy of the equivalence.

[0078] In one embodiment, setting the durability test target for the equivalent sinusoidal load based on the damage equivalence principle includes: determining the target number of cycles for the equivalent sinusoidal load; The process of determining the target number of iterations includes: Calculate the cumulative pseudo-damage value D_road caused by the multi-component force load signal at the target location on the chassis; Determine the pseudo-damage value d_sin caused by a single cycle of equivalent sinusoidal load at the target location on the chassis; The target number of cycles N_target for the equivalent sinusoidal load is calculated using the formula N_target = D_road / d_sin.

[0079] This embodiment proposes a damage equivalence principle, which establishes load equivalence on the mathematical basis of fatigue damage theory (such as Miner's linear cumulative rule), so that the final set equivalent sinusoidal load is physically real and reliable, and can accurately reflect the fatigue life of the structure.

[0080] In one embodiment, the calculation of the load amplitude of the equivalent sinusoidal load includes: Calculate the cumulative damage value caused by multi-component force load signals at the target location on the chassis. Based on the target cycle number, calculate the load amplitude of the equivalent sinusoidal load according to the damage equivalence equation.

[0081] Optionally, the frequency of the equivalent sinusoidal load is determined based on the frequency point where the multi-component force load signal contributes most to the damage to the target part.

[0082] When the maximum frequency is above 5Hz, the effect of frequency can be ignored in fatigue damage theory.

[0083] The parameters of the equivalent sinusoidal load are made complete by calculating the load amplitude and frequency of the equivalent sinusoidal load.

[0084] In one embodiment, a bench test of suspension component durability was conducted to further verify the effectiveness of the contribution analysis method described above.

[0085] When determining the suspension constraint conditions for the bench test of this component, the suspension deformation mode at the target location must be considered. Since the main input is the opposing front and rear forces at the wheel centers of the two wheels, it is deduced that the bending deformation mode of the subframe at the junction of the X-direction main beam and the Y-direction main beam in the XY plane should be reproduced. Accordingly, the test conditions are set as follows (e.g.) Figure 2 (as shown) The connection point between the suspension and the vehicle body is fixed by clamps, and the wheel center is lifted to the standard design position, supported below by a tray that can move freely in the XY plane.

[0086] The two opposing sinusoidal loads, as set above, are applied to the centers of the two wheels respectively. The number of actuations when the crack occurs is recorded.

[0087] The equivalent crack initiation mileage of two samples in the sinusoidal load durability test and the equivalent crack initiation mileage of one sample in the MRS test were compared. The results are as follows: Figure 13 As shown, the relationship between the two is at the -2σ position. The reason is analyzed as follows: The slope parameter m of the SN curve is set to the minimum value specified by IIW to eliminate the possibility that the parameter m is set too high.

[0088] Because the sinusoidal test only set up a single-level load and Miner's linear damage accumulation theory, and did not consider the load sequence and the mutual influence of loads before and after, but the load used in the sinusoidal test was greater than the maximum peak-to-valley value of the MRS road spectrum, this factor is not a key factor.

[0089] All test specimens were hand-made. The MRS specimens had welding defects, with cracks originating in the concave center of the weld, resulting in a lower fatigue life in the MRS test. In contrast, the sinusoidal test specimens had relatively full welds, with cracks originating at the weld edge and propagating along it, which is a normal weld failure mode. This factor should be the cause of the test deviation.

[0090] Overall, the crack initiation locations in the two tests were similar, and the final failure modes were consistent. Figure 14 This result verifies the effectiveness of the equivalent sinusoidal load decomposition method based on contribution analysis.

[0091] MRS is an abbreviation for Multi-Axial Road Simulator.

[0092] The above description is merely the principle and preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several other modifications can be made based on the principle of the present invention, and these modifications should also be considered within the scope of protection of the present invention.

Claims

1. A sinusoidal load equivalent method for a multi-degree-of-freedom load system, characterized in that, include: Acquire multi-component force load signals at the left and right wheel ends and strain signals at target locations on the chassis; Calculate the principal stresses and principal stress angles based on the strain signals of the target parts of the chassis; The multi-component force load signal is used as the first set of load signals. The multi-component force load signal is recombined to obtain two recombined load components, namely in-phase and out-of-phase, which are used as the second set of load signals. Based on the principal stress, identify the frequency response function corresponding to each recombined load component in the second set of load signals, calculate the time domain response caused by each recombined load component at the target part of the chassis based on the frequency response function of each recombined load component, and calculate the contribution of each time domain response to the principal stress. The phase of the recombinant load component with the largest contribution is selected as the phase of the equivalent sinusoidal load; The direction of the equivalent sinusoidal load is selected from the direction of the recombined load component that contributes the most, or the direction of the load signal that contributes the most to the principal stress in the time domain response corresponding to the multi-component force load signal in the first group of load signals. If the principal stress angle of the target part of the chassis under the action of equivalent sinusoidal load meets the preset similarity condition with the principal stress angle under the action of multi-component force load signal, then based on the principle of damage equivalence, the durability test target of equivalent sinusoidal load is set.

2. The sinusoidal load equivalent method for a multi-degree-of-freedom load system according to claim 1, characterized in that, The direction of the equivalent sinusoidal load is selected from the direction of the recombined load component that contributes the most, or the direction of the load signal that contributes the most to the principal stress in the time-domain response of the multi-component load signal in the first group of load signals. This includes: If the target area of ​​the chassis is the subframe load area, the direction of the equivalent sinusoidal load should be selected from the direction of the recombined load component that contributes the most. If the target part of the chassis is outside the subframe load area, the direction of the equivalent sinusoidal load is selected from the direction of the load signal that contributes the most to the principal stress in the time domain response of the multi-component force load signal in the first group of load signals. The process of calculating the contribution of the multi-component force load signals in the time-domain response to the principal stress in the first set of load signals includes: Based on the principal stress, identify the frequency response function corresponding to each load component in the first set of load signals, calculate the time domain response caused by each load component at the target part of the chassis based on the frequency response function of each load component, and calculate the contribution of each time domain response to the principal stress.

3. The sinusoidal load equivalent method for a multi-degree-of-freedom load system according to claim 2, characterized in that, The frequency response function corresponding to each load component in the first group of load signals identified by the principal stress, and the frequency response function corresponding to each recombined load component in the second group of load signals identified by the principal stress, are calculated using the following process: The mathematical expression for the relationship between input and output in the frequency domain of a linear system is: ， in, For the Fourier transform of the i-th input signal, It is the frequency response function of the i-th input signal. For the Fourier transform of the output signal; By substituting the first set of load signals as input signals and the principal stress as output signals into the above mathematical expression, the frequency response function corresponding to each recombined load component in the first set of load signals is obtained. Using the second set of load signals as input signals and the principal stress as output signals, we can substitute these into the above mathematical expression to obtain the frequency response function corresponding to each recombined load component in the second set of load signals.

4. The sinusoidal load equivalent method for a multi-degree-of-freedom load system according to claim 1, characterized in that, The calculation of principal stresses and principal stress angles based on strain signals from target areas of the chassis includes: The strain signal of the target part of the chassis is obtained from the strain gauge set on the chassis. The tensile principal strain and compressive principal strain of the target part of the chassis are calculated based on the strain signal. The tensile principal stress and compressive principal stress are calculated based on the tensile principal strain and compressive principal strain respectively. The larger absolute value of the tensile principal stress and compressive principal stress is taken as the principal stress.

5. The sinusoidal load equivalent method for a multi-degree-of-freedom load system according to claim 4, characterized in that, The strain gauge on the chassis is a right-angle strain gauge, and the strain signal is the strain measured by the right-angle strain gauge in three directions, with the strain in the 0° direction being the strain. Strain in the 45° direction Strain in the 90° direction ; Tensile principal strain and compressive principal strain The calculation formula is: Principal stress angle The calculation formula is: ； when hour, for Axis and maximum strain The angle between the principal stresses is such that the principal stresses are tensile principal stresses. when hour, for Axis and Minimum Strain The angle between the principal stresses is such that the principal stresses are compressive principal stresses.

6. The sinusoidal load equivalent method for a multi-degree-of-freedom load system according to claim 1, characterized in that, The multi-component force load signal is used as the first group of load signals. The multi-component force load signal is then recombined to obtain two recombined load components, in-phase and out-of-phase, which are used as the second group of load signals. In-phase recombination load components and the reverse-phase recombination load component The calculation formula is: ， ， in, Represents the load on the left wheel center. Represents the load on the right wheel center, subscript These represent the load directions x, y, and z.

7. The sinusoidal load equivalent method for a multi-degree-of-freedom load system according to claim 1, characterized in that, The calculation of the time-domain response at the target location on the chassis based on the frequency response function of each recombined load component includes: The frequency domain representation of each recombined load component is obtained by performing a Fourier transform on it. Multiply the frequency domain representation of each recombined load component by its corresponding frequency response function in the frequency domain to obtain the frequency domain response of each recombined load component. Perform an inverse Fourier transform on the frequency domain response of each recombined load component to obtain the time domain response caused by each recombined load component at the target location.

8. The sinusoidal load equivalent method for a multi-degree-of-freedom load system according to claim 1, characterized in that, The calculation of the contribution of each time-domain response to the principal stress includes: First, calculate the time-domain contribution of the time-domain response of each recombined load component to the principal stress. Time-sharing contribution = Time-domain response of each recombined load component at that time point / Total time-domain response at that time point, where the total time-domain response at that time point is the sum of the time-domain responses of all recombined load components at that time point; Then calculate the overall contribution, which is the average or maximum value of the time-sharing contribution at all times; or the overall contribution is the average or maximum value of the time-sharing contribution at the peak and trough of the previous preset percentage with the larger absolute value. The overall contribution is taken as the contribution of each time-domain response to the principal stress.

9. The sinusoidal load equivalent method for a multi-degree-of-freedom load system according to claim 1, characterized in that, The preset similarity condition is: under the action of equivalent sinusoidal load and multi-component force load signals respectively, the absolute value of the difference between the angle values ​​corresponding to the main peak of the principal stress angle distribution histogram of the target part of the chassis is less than the preset threshold. Alternatively, the preset similar condition is: under the action of equivalent sinusoidal load and multi-component force load signals respectively, the cumulative distribution function of the principal stress angle distribution of the target part of the chassis has a higher degree of overlap in the main interval than the preset overlap. Alternatively, the preset similar condition is: under the action of equivalent sinusoidal load and multi-component force load signals respectively, the absolute value of the average value of the principal stress angle distribution of the target part of the chassis is less than or equal to the preset degree.

10. The sinusoidal load equivalent method for a multi-degree-of-freedom load system according to any one of claims 1-8, characterized in that, The durability test target based on the damage equivalence principle includes: determining the target number of cycles for the equivalent sinusoidal load; The process of determining the target number of iterations includes: Calculate the cumulative pseudo-damage value D_road caused by the multi-component force load signal at the target location on the chassis; Determine the pseudo-damage value d_sin caused by a single cycle of equivalent sinusoidal load at the target location on the chassis; The target number of cycles N_target for the equivalent sinusoidal load is calculated using the formula N_target = D_road / d_sin. The calculation of the load amplitude of the equivalent sinusoidal load includes: Calculate the cumulative damage value caused by multi-component force load signals at the target location on the chassis. Based on the target cycle number, calculate the load amplitude of the equivalent sinusoidal load according to the damage equivalence equation.

Images