A dynamic and static coupling accelerated corrosion test method suitable for automobile materials

Abstract

The application discloses a kind of dynamic and static coupling accelerated corrosion test methods suitable for automobile material, it is related to material corrosion test technical field, including establishing corrosion and mechanical coupling damage evolution equation, total damage variable is decomposed into chemical damage variable, mechanical damage variable and coupling damage variable;According to service condition spectrum, test cycle is divided into several cycle units, dynamic loading section and static corrosion section in each unit are alternately executed step etc..The application is by total damage variable is decomposed into chemical damage variable, mechanical damage variable and coupling damage variable, establishes coupling damage evolution equation, solves the existing test control and stays in experience threshold level, lacks physical mechanism support and cannot reflect the problem of real damage evolution law of material, also solves the problem that existing damage evolution model stays in numerical simulation level, does not sink to test control level.

Description

Technical Field

[0001] This invention belongs to the field of material corrosion testing technology, specifically relating to a dynamic and static coupled accelerated corrosion testing method suitable for automotive materials. Background Technology

[0002] Automotive materials are exposed to complex corrosive environments for extended periods during actual service, and their corrosion resistance directly affects the safety and lifespan of the entire vehicle. Accelerated corrosion testing technology has become a core method for evaluating the corrosion resistance of materials during the automotive research and development phase.

[0003] Existing accelerated corrosion tests are mainly divided into two paths: static accelerated testing and dynamic accelerated testing. Static testing, represented by cyclic salt spray testing, involves fixing the sample inside a test chamber and simulating the atmospheric corrosion environment through periodic alternation of environmental factors. Dynamic testing, represented by vehicle chassis mounting plate testing, involves fixing the sample to the vehicle chassis and collecting corrosion data as it travels on actual roads.

[0004] However, static tests keep the specimens stationary, failing to simulate dynamic service factors such as vibration, stress cycling, and temperature shock during vehicle operation. While dynamic tests can reflect real-world conditions, they can take months or even years, involve uncontrollable environmental parameters, and result in highly volatile data. Although recent studies have physically superimposed corrosive environments with mechanical loads, the load programs are all preset fixed values, failing to establish a dynamic feedback relationship between corrosion processes and mechanical responses. The control logic remains at an empirical closed-loop level, lacking physical mechanism support.

[0005] Existing technologies are insufficient to cover the complete service life characteristics of automotive materials in a single test, and there are significant deficiencies in terms of physical mechanism support for test control, quantitative equivalence of acceleration factors, and the application of damage evolution models to the test control level. Summary of the Invention

[0006] The purpose of this invention is to propose a dynamic-static coupled accelerated corrosion test method suitable for automotive materials. This method solves the problems of existing test control being limited to empirical thresholds, lacking physical mechanism support, and failing to reflect the true damage evolution of materials. It also solves the problems of existing dynamic-static corrosion tests being completely disconnected, lacking temporal correlation, and having multiple factors only physically superimposed rather than coupled by mechanisms. Furthermore, it solves the problem that existing acceleration factors are always black-boxed and test results cannot be quantified to be equivalent to actual service.

[0007] This application provides a dynamic-static coupled accelerated corrosion testing method suitable for automotive materials, including the following steps:

[0008] The total damage variable is decomposed into chemical damage variable, mechanical damage variable and coupled damage variable, and a coupled damage evolution equation is established.

[0009] Based on the service condition spectrum of the target vehicle model, the test cycle is divided into several cycle units. Each cycle unit includes a dynamic loading segment and a static corrosion segment, and the dynamic loading segment and the static corrosion segment are executed alternately.

[0010] At the end of each cycle unit, in-situ multi-physics joint testing is performed on the sample to obtain electrochemical, mechanical and microscopic parameters, which are then substituted into the coupled damage evolution equation to identify the stress-free micro-dissolution coefficient and stress dependence coefficient of the current cycle unit online.

[0011] By utilizing the identified stress-free micro-dissolution coefficient and stress dependence coefficient, combined with the coupled damage evolution equation, the total damage increment, chemical damage ratio, mechanical damage ratio, coupled damage ratio, and acceleration equivalent coefficient at the end of the next cycle unit are predicted. Based on this, the duration of the dynamic loading segment, the duration of the static corrosion segment, the load frequency, and the environmental intensity of the next cycle unit are reconstructed, and the reconstruction results are output.

[0012] Based on the reconstruction results, update the configuration of the next cycle unit, accumulate the total damage increment to the cumulative total damage, calculate the acceleration equivalent coefficient and accumulate it to the cumulative equivalent actual service years, and return to alternate execution to form a closed loop iteration;

[0013] The test is terminated when the cumulative total damage reaches the critical damage value or the cumulative equivalent actual service life reaches the target service life, and the results of the dynamic and static coupled accelerated corrosion test of the automotive materials are output.

[0014] In one embodiment, the total damage variable is decomposed into chemical damage variables, mechanical damage variables, and coupled damage variables, including:

[0015] The chemical damage conversion coefficient is determined, and it is multiplied by the corrosion current density to generate the chemical damage evolution rate. The chemical damage evolution rate is then integrated over time to generate the chemical damage variable.

[0016] The fatigue strength coefficient and fatigue damage index are determined. The stress amplitude is calculated as a ratio to the fatigue strength coefficient, and then a power exponentiation is performed to generate the single-cycle mechanical damage increment. The single-cycle mechanical damage increment is accumulated according to the number of cycles to generate the mechanical damage variable.

[0017] Determine the stress-free micro-dissolution coefficient and the stress dependence coefficient, construct the stress state function, and exponentially couple the stress-free micro-dissolution coefficient, the stress dependence coefficient, and the stress state function to generate the stress-dependent micro-dissolution coefficient. Multiply this coefficient with the single-cycle mechanical damage increment to generate the coupled damage evolution rate. Integrate the coupled damage evolution rate over time to generate the coupled damage variable.

[0018] In one embodiment, a coupled damage evolution equation is established, including:

[0019] An evolution expression for chemical damage variables was established, linking the chemical damage evolution rate with the corrosion current density;

[0020] Establish an evolution expression for mechanical damage variables, and correlate the increment of mechanical damage in a single cycle with the stress amplitude and the number of cycles;

[0021] An evolution expression for coupled damage variables is established, with the stress-dependent micro-dissolution coefficient as the core driving term;

[0022] The evolution expressions of chemical damage variables, mechanical damage variables, and coupled damage variables are nonlinearly coupled to establish a coupled damage evolution equation.

[0023] In one embodiment, the test cycle is divided into several cyclic units, each cyclic unit including a dynamic loading segment and a static corrosion segment, and the dynamic loading segment and the static corrosion segment are executed alternately, including:

[0024] Based on the service condition spectrum of the target vehicle model, the initial duration ratio of the dynamic loading segment and the static corrosion segment is calculated by inversion.

[0025] The dynamic loading segment is configured to simulate vibration, stress cycling, and temperature shock during vehicle operation.

[0026] The static corrosion section was configured to simulate the static electrochemical environment during car parking.

[0027] The dynamic loading segment and the static corrosion segment are executed alternately, and the test cycle is divided into several cycle units according to the service condition spectrum.

[0028] In one embodiment, at the end of each cycle unit, in-situ multiphysics joint testing is performed on the sample to obtain electrochemical, mechanical, and microscopic parameters, including:

[0029] Electrochemical impedance spectroscopy and potentiodynamic polarization curves were used to obtain polarization resistance, double layer capacitance, corrosion current density and Tafel slope as electrochemical dimension parameters.

[0030] By collecting the hysteresis loop area and testing the elastic modulus attenuation, the plastic dissipation energy and the degree of microcrack propagation are obtained as mechanical dimension parameters.

[0031] By observing the surface morphology and performing micro-area electrochemical scanning, the pitting depth, pitting density, and local corrosion current distribution were obtained as microscopic parameters.

[0032] At the end of each cycle, in-situ multiphysics field tests are performed on the sample to obtain electrochemical, mechanical and microscopic parameters.

[0033] In one embodiment, online identification of the stress-free micro-dissolution coefficient and stress dependence coefficient of the current cycle unit includes:

[0034] Define an observation vector that incorporates the measured corrosion current density, hysteresis loop area, and elastic modulus attenuation.

[0035] Define a parameter vector, with the stress-free micro-dissolution coefficient and the stress dependence coefficient as the parameters to be identified;

[0036] Establish the residual between the output of the forward model based on the coupled damage evolution equation and the observation vector;

[0037] The parameter vector is updated using the recursive least squares method until the residual converges, and the stress-free micro-dissolution coefficient and stress dependence coefficient of the current cycle element are identified online.

[0038] In one embodiment, predicting the total damage increment, chemical damage percentage, mechanical damage percentage, coupled damage percentage, and acceleration equivalent coefficient at the end of the next cycle unit includes:

[0039] The predicted chemical damage increment, mechanical damage increment, and coupled damage increment within the next cycle unit are superimposed to generate the predicted total damage increment at the end of the next cycle unit.

[0040] The chemical damage increment, mechanical damage increment, and coupled damage increment are respectively compared with the total damage increment at the end of the next cycle unit to generate the chemical damage percentage, mechanical damage percentage, and coupled damage percentage.

[0041] The acceleration equivalent coefficient is generated by comparing the total damage increment at the end of the next cycle with the damage increment of the equivalent cycle in actual service.

[0042] The total damage increment, chemical damage percentage, mechanical damage percentage, coupling damage percentage, and acceleration equivalent coefficient at the end of the next cycle are predicted.

[0043] In one embodiment, reconstructing the dynamic loading segment duration, static corrosion segment duration, load frequency, and environmental intensity of the next cycle unit includes:

[0044] When the proportion of chemical damage exceeds the first preset threshold, the duration of the dynamic loading segment is shortened and the duration of the static corrosion segment is extended, and the corrosion-dominant mode is determined.

[0045] When the proportion of mechanical damage exceeds the second preset threshold, the duration of the dynamic loading segment is extended and the duration of the static corrosion segment is shortened, and the mechanically dominant mode is determined.

[0046] When the proportion of coupled damage exceeds the third preset threshold, the load frequency of the dynamic loading section and the environmental intensity of the static corrosion section are increased simultaneously, and it is determined to be a strong coupling dominant mode.

[0047] When the acceleration equivalent coefficient deviates from the target acceleration ratio, adjust the environmental intensity of the static corrosion section or the load intensity of the dynamic loading section to bring the acceleration equivalent coefficient back to the target range.

[0048] Actively reconstruct the duration of the dynamic loading segment, the duration of the static corrosion segment, the load frequency, and the environmental intensity of the next cycle unit.

[0049] In one embodiment, the configuration of the next cycle unit is updated based on the reconstruction result, the total damage increment is accumulated to the total accumulated damage, the acceleration equivalent coefficient is calculated and accumulated to the accumulated equivalent actual service life, and the process is repeated to form a closed loop iteration, including:

[0050] The configuration of the next cycle unit is updated based on the reconstructed dynamic loading segment duration, static corrosion segment duration, load frequency, and environmental intensity.

[0051] Add the total damage increment at the end of the next cycle to the cumulative total damage;

[0052] The acceleration equivalent factor will be converted into equivalent actual service years and added to the cumulative equivalent actual service years.

[0053] Determine whether the cumulative total damage has reached the critical damage value or whether the cumulative equivalent actual service life has reached the target service life;

[0054] If the target is not reached, the process of alternating between dynamic loading and static erosion segments is returned to form a closed-loop iteration.

[0055] In one embodiment, the test is terminated when the cumulative total damage reaches the critical damage value or the cumulative equivalent actual service life reaches the target service life, and the results of the dynamic-static coupled accelerated corrosion test of the automotive materials are output, including:

[0056] When the cumulative total damage reaches the preset critical damage value, it is determined to be a material failure and the test is terminated.

[0057] When the cumulative equivalent actual service life reaches the target service life, it is determined to be a lifespan compliance situation and the test is terminated;

[0058] Based on the material failure condition or the lifespan target being met, the test is terminated and the results of the dynamic and static coupled accelerated corrosion test of the automotive materials are output.

[0059] The beneficial effects of this invention are:

[0060] (1) This invention decomposes the total damage variable into chemical damage variable, mechanical damage variable and coupled damage variable, and establishes a coupled damage evolution equation. This solves the problems that existing experimental control is stuck at the level of empirical threshold, lacks physical mechanism support and cannot reflect the real damage evolution law of materials. It also solves the problem that existing damage evolution models are stuck at the level of numerical simulation and have not been pushed down to the level of experimental control. This invention realizes the accelerated corrosion test paradigm driven by mechanism instead of experience, so that the test process follows the real damage evolution law of materials and realizes the deep coupling of corrosion and mechanical factors at the level of experimental control.

[0061] (2) This invention obtains electrochemical, mechanical and microscopic parameters by conducting in-situ multi-physics joint testing on the sample at the end of each cycle unit, identifies stress-free micro-dissolution coefficient and stress dependence coefficient online, and predicts the total damage increment, chemical damage ratio, mechanical damage ratio, coupled damage ratio and acceleration equivalent coefficient at the end of the next cycle unit. Based on this, the duration of dynamic loading segment, duration of static corrosion segment, load frequency and environmental intensity of the next cycle unit are reconstructed to form a closed loop iteration. This solves the problems of existing dynamic and static corrosion tests being completely separated, lacking temporal correlation and multiple factors being only physically superimposed rather than mechanistically coupled. It realizes predictive working condition reconstruction and deep closed loop control under the dynamic and static alternating temporal architecture, so that the test can truly reflect the dynamic evolution law of mutual promotion between corrosion and mechanical factors in automotive materials during service.

[0062] (3) This invention predicts the acceleration equivalent coefficient and calculates and accumulates it to the cumulative equivalent actual service life. The test is terminated when the cumulative total damage reaches the critical damage value or the cumulative equivalent actual service life reaches the target service life. This solves the problem that the existing acceleration factor is always black box and the test results cannot be quantified to be equivalent to actual service life. It realizes the quantitative equivalence between test results and actual service life, makes the test results of different materials and different working conditions comparable in the horizontal direction, and realizes the precise matching of the test termination time with the actual damage state of the material, avoiding insufficient or excessive testing. Attached Figure Description

[0063] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0064] Figure 1 This is an overall flowchart of the dynamic-static coupling accelerated corrosion test method proposed in this invention;

[0065] Figure 2 This is a logic block diagram for establishing the corrosion-mechanical coupling damage evolution equation and identifying parameters online, as proposed in this invention.

[0066] Figure 3This is a schematic diagram of the dynamic-static alternating timing architecture and predictive operating condition reconfiguration strategy proposed in this invention;

[0067] Figure 4 This is a schematic block diagram of the dynamic-static coupling accelerated corrosion test system proposed in this invention. Detailed Implementation

[0068] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0069] In related technologies, accelerated corrosion testing of automotive materials typically suffers from the following problems: static and dynamic tests are completely separated and lack temporal correlation; multiple factors are only physically superimposed rather than mechanistically coupled; the acceleration factor is always a black box, and the test results cannot be quantified to be equivalent to actual service; closed-loop control remains at the level of empirical thresholds and lacks physical mechanism support; damage evolution models remain at the level of numerical simulation and have not been implemented at the level of test control.

[0070] To this end, this application provides a dynamic-static coupled accelerated corrosion testing method suitable for automotive materials. By establishing a corrosion-mechanical coupled damage evolution equation, the total damage variable is decomposed into chemical damage variables, mechanical damage variables, and coupled damage variables. The test cycle is divided into several cyclic units based on the service condition spectrum, with dynamic loading and static corrosion segments alternating within each unit. At the end of each unit, in-situ multi-physics joint testing is performed to obtain electrochemical, mechanical, and microscopic parameters. These parameters are substituted into the damage evolution equation to identify the stress-free micro-dissolution coefficient and stress dependence coefficient online. The identified coefficients are used to predict the total damage increment, the proportion of each damage type, and the acceleration equivalent coefficient at the end of the next cyclic unit. The test parameters for the next cyclic unit are reconstructed based on the proportions and acceleration equivalent coefficients. The configuration is updated based on the reconstruction results, and the alternating execution is resumed, forming a closed-loop iteration. The test is terminated when the cumulative total damage reaches the critical damage value or the cumulative equivalent actual service life reaches the target service life, and the test results are output.

[0071] Please see Figure 1 , Figure 1 This is a schematic diagram of the overall process of the dynamic-static coupling accelerated corrosion test method provided in this application embodiment. The dynamic-static coupling accelerated corrosion test method provided in this application embodiment is applied to an automotive material corrosion testing system and is executed through control software installed in the testing system.

[0072] It should be noted that the application scenarios described in the following embodiments of this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0073] The following is a detailed description of the dynamic-static coupling accelerated corrosion test method for automotive materials provided in this application.

[0074] like Figure 1 As shown, the method includes the following steps S110 to S160.

[0075] S110. Establish a corrosion-mechanical coupled damage evolution equation and decompose the total damage variable into chemical damage variable, mechanical damage variable and coupled damage variable.

[0076] Specifically, for commonly used automotive materials, including cold-rolled steel, aluminum alloys, magnesium alloys, and galvanized steel, a corrosion-mechanical coupled damage evolution equation is established. The total damage variable adopts a nonlinear coupling form:

[0077] ;

[0078] In the formula, The total damage variable is dimensionless and ranges from 0 to 1. Material failure is determined when the critical value is reached. It is a chemical damage variable, which is dimensionless and driven by the electrochemical dissolution process; It is a mechanical damage variable, which is dimensionless and driven by the fatigue process under cyclic loading; As a coupled damage variable, it is dimensionless and characterizes the mutually reinforcing effect of corrosion damage and mechanical damage. It is a time variable, and its unit is seconds (s).

[0079] In some embodiments, such as Figure 2 As shown, step S110 includes steps S111 to S114.

[0080] S111. Establish an evolution expression for chemical damage variables and correlate the chemical damage evolution rate with the corrosion current density.

[0081] Specifically, the evolution rate of chemical damage variables is positively correlated with corrosion current density, as expressed by:

[0082] ;

[0083] In the formula, The chemical damage conversion coefficient is expressed in m. 2 / (A∙s), this coefficient is related to the type of material and the composition of the corrosive medium, and is calibrated through preliminary tests; This is the corrosion current density, with units of μA / cm. 2 .

[0084] The time integral form of the chemical damage variable is:

[0085] ;

[0086] In the formula, The time variable is the integral time variable, and its unit is seconds (s). This is a function of corrosion current density as a function of time, with units of μA / cm. 2 .

[0087] S112. Establish an evolution expression for mechanical damage variables, and correlate the increment of mechanical damage in a single cycle with the stress amplitude and the number of cycles.

[0088] Specifically, the evolution of the mechanical damage variable follows the modified Miner linear cumulative damage theory, and the expression for the single-cycle mechanical damage increment is:

[0089] ;

[0090] In the formula, The increment of mechanical damage in a single cycle is dimensionless. This represents the stress amplitude, and its unit is MPa. This is the fatigue strength coefficient, and its unit is MPa; It is the fatigue damage index, which is dimensionless.

[0091] The cumulative expression for the mechanical damage variable is:

[0092] ;

[0093] In the formula, The number of load cycles is dimensionless. For the first The stress amplitude of each cycle, in MPa.

[0094] For cold-rolled steel used in automobile bodies Typical values ​​range from 200 MPa to 400 MPa. Typical values ​​range from 3 to 5. These values ​​are determined based on the statistical range of rotational bending fatigue limit test data for high-quality carbon structural steel and low-alloy high-strength steel in the GB / T 3077 standard, covering the fatigue strength dispersion band of commonly used cold-rolled steel grades for automobile bodies. The value is based on the modified empirical index of Miner's criterion in automotive metallic materials, obtained by fitting constant amplitude fatigue test data, and reflects the sensitivity of the material to cyclic loads.

[0095] For aluminum alloys Typical values ​​range from 100 MPa to 250 MPa. Typical values ​​are 4 to 6, which are determined based on the fatigue limit statistics of Al-Si and Al-Mg cast aluminum alloys in GB / T228.1 and the Fatigue Handbook for Aerospace Aluminum Alloys.

[0096] S113. Establish the evolution expression of coupled damage variables, with the stress-dependent micro-dissolution coefficient as the core driving term.

[0097] Specifically, the core of the coupled damage variable is the stress-dependent micro-dissolution coefficient, expressed as:

[0098] ;

[0099] In the formula, This is the stress-dependent micro-solubility coefficient, with units of m / s; The stress-free micro-solubility coefficient is expressed in m / s. This is the stress dependence coefficient; It is a stress state function, which is dimensionless.

[0100] When the stress state function is taken as equivalent stress:

[0101] ;

[0102] In the formula, This is the equivalent stress, and its unit is MPa; This represents the stress deviatoric tensor component, with units of MPa.

[0103] When the stress state function is taken as hydrostatic stress:

[0104] ;

[0105] In the formula, This is hydrostatic stress, and its unit is MPa; , , These are the three principal stresses, and their units are MPa.

[0106] The evolutionary expression for the coupled damage variable is:

[0107] ;

[0108] In the formula, The coupling damage conversion coefficient is calibrated through preliminary experiments.

[0109] The time integral form of the coupled damage variables is:

[0110] ;

[0111] S114. Nonlinearly couple the chemical damage variable evolution expression, the mechanical damage variable evolution expression, and the coupled damage variable evolution expression to establish the corrosion-mechanical coupled damage evolution equation.

[0112] Specifically, the three evolution expressions mentioned above are nonlinearly coupled to generate a corrosion-mechanical coupled damage evolution equation. This equation decomposes the total damage variable into three independent damage components and their interaction terms. The core of the coupling term is the stress-dependent micro-dissolution coefficient, which characterizes the exponential enhancement effect of stress state on corrosion dissolution rate.

[0113] S120. The test cycle is divided into several cyclic units according to the service condition spectrum. Each unit includes a dynamic loading section and a static corrosion section, which are executed alternately.

[0114] Specifically, the test cycle is divided into several cyclic units, each containing a dynamic loading segment and a static corrosion segment, which are executed alternately. The dynamic loading segment simulates the dynamic service state of a car during driving, while the static corrosion segment simulates the static electrochemical environment of a car during parking.

[0115] In some embodiments, such as Figure 3 As shown, step S120 includes steps S121 to S124.

[0116] S121. Based on the service condition spectrum of the target vehicle model, calculate the initial duration ratio of the dynamic loading segment and the static corrosion segment.

[0117] Specifically, the service condition spectrum includes average daily mileage, average annual parking time, and typical route environmental parameters. The initial duration ratio of the dynamic loading section and the static corrosion section is calculated based on the service condition spectrum inversion, and the inversion formula is as follows:

[0118] ;

[0119] In the formula, The duration ratio of the static corrosion segment to the dynamic loading segment is dimensionless. This is the initial duration of the static corrosion phase, expressed in minutes. The initial duration of the dynamically loaded segment is in minutes; This represents the average daily parking time per year, expressed in hours. This represents the average daily driving time per year, expressed in hours.

[0120] For example, for commuter vehicles with an average daily mileage of 50 kilometers and an average annual parking time of 70%, the average daily parking time is 16.8 hours and the average daily driving time is 1.2 hours, with an initial dynamic-to-static time ratio set at 1:3. For long-distance operating vehicles with an average daily mileage of 200 kilometers and an average annual parking time of 40%, the average daily parking time is 9.6 hours and the average daily driving time is 3.6 hours, with an initial dynamic-to-static time ratio set at 1:1.5. This initial ratio is only a starting point and will be dynamically optimized through predictive operating condition reconstruction.

[0121] S122. Configure the dynamic loading segment to simulate vibration, stress cycle and temperature shock during vehicle driving.

[0122] Specifically, random vibration loads were applied to the specimens using an electromagnetic vibration table, with a vibration frequency range of 5 Hz to 200 Hz. The power spectral density was set according to the random vibration spectrum of passenger car chassis in ISO 16750-3 standard. Cyclic stress was applied to the specimens using an electro-hydraulic servo fatigue testing machine, with the stress amplitude set to 10% to 30% of the material's yield strength, the stress ratio R set to 0.1, and the loading waveform being a sine wave or a reconstructed waveform from the measured road spectrum. Temperature cycling was applied to the specimens using a high-low temperature alternating test chamber, with a temperature range of -40℃ to 85℃ and a temperature change rate of 5℃ / min to 15℃ / min, to simulate the environmental temperature shock during vehicle operation. The initial duration of the dynamic loading section was set to 30 to 120 minutes.

[0123] S123. Configure the static corrosion section to simulate the static electrochemical environment during the parking process of a car.

[0124] Specifically, the samples are placed in a salt spray test chamber or an electrolyte immersion tank. The corrosive medium is a 5% sodium chloride solution or a composite salt solution prepared according to the target service environment. The temperature is set to 35°C to 50°C; the relative humidity is set to 90% to 98%; and the salt spray deposition rate is 1 mL / h to 2 mL / h. The initial duration of the static corrosion section is set to 60 minutes to 240 minutes.

[0125] S124. The dynamic loading segment and the static corrosion segment are executed alternately, and the test cycle is divided into several cycle units according to the service condition spectrum.

[0126] S130. At the end of each cycle unit, the sample is subjected to in-situ multi-physics joint testing to obtain electrochemical, mechanical and microscopic parameters, which are then substituted into the corrosion and mechanical coupled damage evolution equation to identify the stress-free micro-dissolution coefficient and stress dependence coefficient of the current cycle unit online.

[0127] Specifically, at the end of each cycle unit, that is, after a dynamic loading segment and a static corrosion segment are completed, the sample is subjected to in-situ multiphysics joint testing to obtain the following three types of parameters.

[0128] Electrochemical parameters: Electrochemical impedance spectroscopy was performed using an electrochemical workstation, with a test frequency range of 100,000 Hz to 0.01 Hz and an AC perturbation amplitude of 10 mV to obtain polarization resistance. and double-layer capacitor Corrosion current density was obtained by potentiodynamic polarization curve testing, with a scan range of -250mV to +250mV relative to the open circuit potential and a scan rate of 1mV / min. Anode Tafel slope and cathode Tafel slope .

[0129] polarization resistor The Nyquist plot of the electrochemical impedance spectroscopy was obtained by fitting the Nyquist plot, and the fitting formula is as follows:

[0130] ;

[0131] In the formula, For complex impedance, the unit is Ω∙cm²; The resistance of the solution is expressed in Ω∙cm². ω is the angular frequency, and its unit is rad / s. , For testing frequency; The imaginary unit; The diffusion index is dimensionless and ranges from 0.8 to 1.0. It reflects the non-ideal capacitive behavior of the electrode surface. This value is determined based on the goodness of fit of the electrochemical impedance spectroscopy and is set when the sum of squared residuals is less than 5%.

[0132] Corrosion current density Calculated according to the Stern-Geary formula:

[0133] ;

[0134] In the formula, This is the corrosion current density, with units of μA / cm. 2 ; This represents the Tafel slope at the anode, with units of mV / dec. This is the cathode Tafel slope, with units of mV / dec; This is the polarization resistance, and its unit is Ω. cm 2 .

[0135] The aforementioned electrochemical parameters directly reflect the electrochemical activity state of the material surface and are key inputs for identifying the rate of chemical damage evolution.

[0136] Mechanical dimension parameters: The hysteresis loop area of ​​the specimen under the current cycle unit is obtained by dynamic mechanical analyzer or strain acquisition system. This area represents the plastic dissipation energy in a single cycle unit and is directly related to fatigue damage accumulation. The elastic modulus attenuation of the specimen is obtained by resonance frequency method or ultrasonic pulse method. The decrease in elastic modulus reflects the initiation and development of microcracks inside the material and is an important basis for assessing the degree of mechanical damage accumulation.

[0137] Hysteresis loop area Calculated by numerical integration of stress-strain hysteresis loop:

[0138] ;

[0139] In the formula, The area of ​​the hysteresis loop is expressed in N. m; Stress is expressed in MPa. The strain is dimensionless; the integration path is a single-cycle stress-strain closed curve.

[0140] elastic modulus attenuation The calculation formula is:

[0141] ;

[0142] In the formula, This is the decrease in elastic modulus, which is dimensionless; This is the initial elastic modulus of the material, and its unit is gigapascal. For the first The measured elastic modulus at the end of each cycle unit, in GPa, is obtained by using the resonant frequency method according to the formula. Calculation, where For material density, The length of the sample. For the first The resonant frequency after one cycle.

[0143] Microscopic parameters: The depth and density of pitting corrosion on the sample surface are obtained using in-situ optical microscopy or scanning electron microscopy; local corrosion current distribution is obtained using micro-area electrochemical scanning technology; and strain field distribution on the sample surface is obtained using digital image correlation technology. These microscopic parameters are primarily used to verify the predictive accuracy of the damage evolution equation and to provide auxiliary constraints for parameter inversion.

[0144] The units and definitions of each dimension parameter are as follows: This is the polarization resistance, and its unit is Ω. cm 2 ; This refers to double-layer capacitance, with units of F / cm. 2 ; This is the corrosion current density, with units of μA / cm. 2 ; and Tafel slopes for the anode and cathode are given, and their units are mV / dec. The area of ​​the hysteresis loop is expressed in N. m; This is the decrease in elastic modulus, which is dimensionless.

[0145] In some embodiments, such as Figure 2 As shown, step S130 includes steps S131 to S134.

[0146] S131. Define the observation vector, incorporating the measured corrosion current density, hysteresis loop area, and elastic modulus attenuation into the observation vector.

[0147] S132. Define a parameter vector, using the stress-free micro-dissolution coefficient and the stress dependence coefficient as parameters to be identified.

[0148] S133. Establish the residual between the output of the forward model and the observation vector based on the corrosion and mechanical coupling damage evolution equation.

[0149] S134. The parameter vector is updated using the recursive least squares method until the residual converges, and the stress-free micro-dissolution coefficient and stress dependence coefficient of the current cycle unit are identified online.

[0150] Specifically, recursive least squares method is used for parameter identification. The observation vector is defined. The measured corrosion current density Hysteresis loop area and elastic modulus attenuation A set. Define the parameter vector. For identification and Establish the observation equation:

[0151] ;

[0152] In the formula, This is the output of the forward model based on the damage evolution equation; To observe noise.

[0153] Forward model output The construction method is as follows: the current parameter vector Substituting the corrosion-mechanical coupled damage evolution equation, the theoretical values ​​of chemical damage variables, mechanical damage variables and coupled damage variables are calculated respectively, and then the theoretical corrosion current density, hysteresis loop area and elastic modulus attenuation are derived.

[0154] The update formula for recursive least squares is:

[0155] ;

[0156] ;

[0157] ;

[0158] In the formula, For the first The parameter estimates at the end of each loop unit; The Kalman gain matrix; Estimate the error covariance matrix for the parameters; This is the Jacobian matrix of the forward model with respect to the parameters; To observe the noise covariance matrix; It is the identity matrix; This is the cyclic unit number.

[0159] Jacobian matrix The elements are calculated using numerical differences:

[0160] ;

[0161] In the formula, For the Jacobian matrix, the first... Line number Column elements; For the forward model One output component; For the first The perturbation step size for each parameter is one-thousandth of the current parameter estimate. This value is determined based on the numerical stability test of parameter identification to ensure that the difference approximation error is less than 0.1%.

[0162] initial parameters Select empirical values ​​from literature based on material type; initial covariance matrix Set it as a diagonal matrix, and take the square of the empirical value for each diagonal element.

[0163] Identified and This directly determines the strength of the positive feedback loop where corrosion and mechanical factors mutually promote each other in the subsequent cycle unit. The larger the value, the higher the material's susceptibility to corrosion under stress, and the more significant the accelerating effect of the dynamic loading section in the subsequent cyclic unit on corrosion. The higher the value, the higher the intrinsic corrosion activity of the material under stress-free conditions, and the faster the damage accumulation rate in the static corrosion section.

[0164] S140. Using the identified stress-free micro-dissolution coefficient and stress dependence coefficient, combined with the corrosion and mechanical coupled damage evolution equation, predict the total damage increment, chemical damage ratio, mechanical damage ratio, coupled damage ratio and acceleration equivalent coefficient at the end of the next cycle unit.

[0165] Specifically, the parameters identified in step S130 and By combining the damage evolution equation, the damage development in the next cycle unit is predicted in advance if the current working condition is maintained.

[0166] The predicted damage increments for each cycle unit are obtained by substituting the current operating parameters into the damage evolution equation and integrating. The formula for predicting chemical damage increments is as follows:

[0167] ;

[0168] In the formula, The predicted increment of chemical damage within the next cycle unit is dimensionless. The predicted corrosion current density for the static corrosion section of the next cycle unit is expressed in μA / cm². 2 ; This is the duration of the static corrosion period, measured in seconds (s).

[0169] The formula for predicting incremental mechanical damage is:

[0170] ;

[0171] In the formula, The number of dynamic loading segment load cycles predicted for the next cycle unit is dimensionless and is determined by... Calculation, where For loading frequency, The duration of the dynamically loaded segment is measured in seconds (s).

[0172] The formula for predicting coupling damage increment is:

[0173] ;

[0174] In the formula, The predicted stress-dependent micro-solubility coefficient for the next cycle element, in m / s, is given by... calculate.

[0175] The predicted total damage increment at the end of the next cycle is:

[0176] ;

[0177] In the formula, This is the predicted total damage increment at the end of the next cycle, and it is dimensionless.

[0178] The predicted proportions of chemical damage, mechanical damage, and coupled damage are as follows:

[0179] ;

[0180] ;

[0181] ;

[0182] In the formula, The percentage of chemical damage is dimensionless. This represents the proportion of mechanical damage, which is dimensionless. The percentage of coupling damage is dimensionless. The sum of the three is 1.

[0183] The predicted acceleration equivalent coefficient is:

[0184] ;

[0185] In the formula, To accelerate the equivalence coefficient, it is dimensionless; It represents the damage increment over an equivalent cycle in actual service, and is dimensionless. It is obtained by calibration using service condition spectrum and material field exposure test data. The calibration formula is:

[0186] ;

[0187] In the formula, This is the critical damage value, which is dimensionless. The design life of a car is measured in years. The physical meaning is: the damage increment generated by the current test cycle unit is equivalent to the damage increment of how many service cycles in actual service.

[0188] S150. Based on the proportion of chemical damage, mechanical damage, coupled damage, and acceleration equivalent coefficient, reconstruct the duration of the dynamic loading segment, the duration of the static corrosion segment, the load frequency, and the environmental intensity of the next cycle unit, and output the reconstruction results.

[0189] Specifically, based on the prediction results of step S140, the experimental parameters of the next cycle unit are actively reconstructed. The specific strategy is as follows.

[0190] Corrosion Dominant Mode Determination and Reconstruction: When the predicted proportion of chemical damage When the threshold exceeds the first preset threshold, the system is determined to be in a corrosion-dominant mode. The first preset threshold is set to 0.5. When the proportion of chemical damage exceeds 0.5, the contribution of chemical damage to the total damage exceeds that of mechanical damage, and the corrosion mechanism becomes dominant. This threshold is determined based on the equilibrium boundary between the contributions of chemical damage and mechanical damage to the total damage, ensuring that corrosion behavior is fully exposed during the corrosion-dominant stage. At this point, the duration of the next dynamic loading stage is shortened and the duration of the next static corrosion stage is extended. The reconstruction formula is as follows:

[0191] ;

[0192] ;

[0193] In the formula, The duration of the reconstructed dynamically loaded segment is in minutes; This represents the current duration of the dynamically loaded segment, in minutes. The dynamic loading period reduction coefficient is dimensionless and ranges from 0.5 to 0.7. This value is determined based on the experimental statistics of the masking effect of mechanical loading on corrosion behavior during the corrosion-dominant stage. When the reduction is below 50%, the corrosion behavior is fully exposed but the mechanical damage accumulation is insufficient. When the reduction is above 70%, the mechanical loading still significantly masks the corrosion behavior. Therefore, the range of 50% to 70% is taken. The duration of the reconstructed static corrosion segment is in minutes. This represents the duration of the current static corrosion phase, in minutes. The static corrosion period duration extension coefficient is dimensionless and ranges from 1.2 to 1.5. This value is determined based on experimental data showing a positive correlation between the static corrosion period duration and the pitting density. When the duration is extended to 120%, the pitting density reaches an observable level. When the duration is extended to 150%, the accumulation of corrosion products leads to a shift in the subsequent mechanical response. Therefore, the range of 120% to 150% is taken.

[0194] Mechanical Dominant Mode Determination and Reconstruction: When the predicted proportion of mechanical damage When the damage exceeds the second preset threshold, it is determined to be a mechanically dominant mode. The second preset threshold is set to 0.5. When the proportion of mechanical damage exceeds 0.5, the contribution of mechanical factors to the total damage exceeds that of chemical damage, and the fatigue mechanism becomes dominant. This threshold is determined based on the equilibrium boundary between the contributions of mechanical damage and chemical damage. At this time, the duration of the next dynamic loading stage is extended and the duration of the next static corrosion stage is shortened. The reconstruction formula is as follows:

[0195] ;

[0196] ;

[0197] In the formula, The dynamic loading segment duration extension coefficient is dimensionless and ranges from 1.2 to 1.5. This value is determined based on the power law relationship between the dynamic loading segment duration and the fatigue crack propagation rate. When the extension reaches 120%, the crack propagation enters a stable stage. When the extension reaches 150%, the crack propagation rate rises sharply, leading to premature fracture. Therefore, the range of 120% to 150% is taken. The static corrosion period duration reduction factor is dimensionless and ranges from 0.5 to 0.7. This value is determined based on the experimental results on the effect of static corrosion period duration reduction on corrosion pits as fatigue crack initiation sources.

[0198] Simultaneously, by increasing the stress amplitude or introducing an impact load waveform, the stress amplitude reconstruction formula is:

[0199] ;

[0200] In the formula, The reconstructed stress amplitude is expressed in MPa. This represents the current stress amplitude, and its unit is MPa. The stress amplitude enhancement factor is dimensionless and ranges from 1.1 to 1.3. This value is determined by inverse calculation based on the SN curve of stress amplitude and fatigue life. When the value is increased by 10%, the fatigue life decreases to 50% to 70% of the original life. When the value is increased by 30%, the fatigue life decreases to 20% to 35% of the original life. Therefore, the range of 110% to 130% is selected to fully expose the local stress concentration effect caused by corrosion pits.

[0201] Strong Coupling Dominant Mode Determination and Reconstruction: When the predicted proportion of coupling impairment When the damage exceeds the third preset threshold, it is determined to be a strongly coupled dominant mode. The third preset threshold is set to 0.3. Coupled damage characterizes the nonlinear synergistic amplification effect of corrosion and mechanics. When the proportion of coupled damage reaches 0.3, it indicates that corrosion and mechanics have entered a significant positive feedback stage, and the synergistic effect cannot be ignored. This value is determined based on the nonlinear contribution threshold of the coupled damage variable to the total damage. When it is below 0.3, the synergistic effect is weak; when it is above 0.3, the synergistic amplification effect is sharply enhanced. At this time, the duration of the dynamic loading segment and the static corrosion segment is kept relatively balanced, but the load frequency of the dynamic loading segment and the environmental intensity of the static corrosion segment are increased. The reconstruction formula is as follows:

[0202] ;

[0203] ;

[0204] In the formula, The reconstructed load frequency is expressed in Hz. This is the current load frequency, and its unit is Hz; The load frequency enhancement factor is dimensionless and ranges from 1.2 to 1.5. This value is determined based on the matching relationship between the load frequency and the corrosion product film rupture frequency. When the frequency is increased by 20%, the corrosion product film rupture period and the load period enter a resonant state. When the frequency is increased by 50%, the rupture frequency is too high, which prevents the fresh metal surface from being sufficiently passivated. Therefore, the range of 120% to 150% is used. The reconstructed chloride ion concentration is expressed in mol / L. This represents the current chloride ion concentration, expressed in mol / L. The chloride ion concentration enhancement factor is dimensionless and ranges from 1.2 to 1.5. This value is determined based on the exponential relationship between chloride ion concentration and pitting corrosion initiation probability. When the concentration increases by 20%, the pitting corrosion initiation probability increases by 1.5 times, and when the concentration increases by 50%, the pitting corrosion initiation probability increases by 3 times. Therefore, the range of 120% to 150% is selected to enhance electrochemical activity.

[0205] Acceleration Equivalent Calibration: If the predicted acceleration equivalent coefficient If the deviation from the target acceleration ratio exceeds 10%, the environmental intensity of the static corrosion section or the load intensity of the dynamic loading section should be adjusted accordingly. The acceleration equivalent calibration formula is:

[0206] ;

[0207] ;

[0208] In the formula, The target acceleration ratio is dimensionless, with a typical value of 50 to 200. This value is determined based on the compression ratio of the vehicle's design life and the test cycle. When the design life is 15 years and the test cycle is required to be 1 month, the target acceleration ratio is about 180. When the design life is 10 years and the test cycle is required to be 2 months, the target acceleration ratio is about 60. Therefore, the range of 50 to 200 is taken. The predicted acceleration equivalent coefficient is dimensionless. Temperature is used to characterize the reconstructed environmental intensity; its unit is °C. The temperature is used to characterize the current environmental intensity, and its unit is ℃; The environmental intensity enhancement factor is dimensionless and has a value of 1.05. This value is determined based on the Arrhenius empirical relationship that the corrosion rate increases by about 5% for every 1°C increase in salt spray temperature. The environmental intensity reduction factor is dimensionless and has a value of 0.95.

[0209] S160. Update the configuration of the next cycle unit based on the reconstruction results, accumulate the total damage increment to the cumulative total damage, calculate the acceleration equivalent coefficient and accumulate it to the cumulative equivalent actual service life, return to alternate execution to form a closed loop iteration; when the cumulative total damage reaches the critical damage value or the cumulative equivalent actual service life reaches the target service life, terminate the test and output the dynamic and static coupling accelerated corrosion test results of automotive materials.

[0210] Specifically, the configuration of the next cycle unit is updated based on the reconstructed duration of the dynamic loading segment, the duration of the static corrosion segment, the load frequency, and the environmental intensity; the total damage increment at the end of the next cycle unit is added to the cumulative total damage; the acceleration equivalent coefficient is converted into equivalent actual service years and added to the cumulative equivalent actual service years; it is determined whether the cumulative total damage has reached the critical damage value or whether the cumulative equivalent actual service years have reached the target service years; if not, the process of alternating between the dynamic loading segment and the static corrosion segment is returned to form a closed loop iteration.

[0211] The update formula for cumulative total damage is:

[0212] ;

[0213] In the formula, For the first The cumulative total damage at the end of each cycle unit is dimensionless. For the first The cumulative total damage at the end of each cycle unit is dimensionless. For the first The total damage increment predicted by each cyclic unit is dimensionless.

[0214] The test termination criterion adopts the equivalent lifetime depletion criterion based on the damage evolution equation, which specifically includes the following two scenarios.

[0215] Scenario 1: The cumulative total damage reaches the critical damage value. When the cumulative total damage reaches the preset critical damage value... The experiment terminates at this point. Critical damage value. The criteria are set based on material type and failure standards. For steel used in vehicle body structures, Typical values ​​are 0.7 to 0.8, determined based on failure test data of steel used in vehicle body structures when its stiffness decreases to 70% to 80% of its initial stiffness under combined corrosion fatigue; for aluminum alloys, Typical values ​​range from 0.6 to 0.75, determined statistically based on the failure criterion of crack penetration through wall thickness in aluminum alloys under the coupled effects of pitting corrosion and fatigue; for magnesium alloys, Typical values ​​range from 0.5 to 0.65, determined based on the lower limit of the lifetime dispersion band of magnesium alloys under stress corrosion cracking.

[0216] Scenario 2: The cumulative equivalent actual service life reaches the target service life. (Cumulative equivalent actual service life) The calculation formula is:

[0217] ;

[0218] In the formula, The unit for accumulating equivalent actual service years is years; The number of completed cycle units is dimensionless. For the first The acceleration equivalent coefficient of each cycle unit, which is dimensionless; For the first The actual service cycle duration corresponding to each cycle unit is expressed in years. The test ends when the target service life is reached. The target service life is set based on the vehicle's design life, with a typical value of 10 to 15 years.

[0219] This application also provides a dynamic-static coupling accelerated corrosion testing system suitable for automotive materials, which is used to perform any of the aforementioned dynamic-static coupling accelerated corrosion testing methods suitable for automotive materials.

[0220] For details, please refer to Figure 4 , Figure 4 This is a schematic block diagram of the dynamic-static coupling accelerated corrosion test system provided in the embodiments of this application.

[0221] like Figure 4 As shown, the dynamic-static coupled accelerated corrosion test system includes: an equation establishment module, a time sequence division module, an in-situ testing module, a parameter identification module, a damage prediction module, a working condition reconstruction module, and an iterative control module.

[0222] The equation building module is used to decompose the total damage variable into chemical damage variables, mechanical damage variables and coupled damage variables, and to build corrosion and mechanical coupled damage evolution equations.

[0223] The timing division module is used to divide the test cycle into several cyclic units based on the service condition spectrum. Each unit contains a dynamic loading segment and a static corrosion segment, which are executed alternately.

[0224] The in-situ testing module is used to perform in-situ multi-physics joint testing on the sample at the end of each cycle unit to obtain electrochemical, mechanical and microscopic parameters.

[0225] The parameter identification module is used to substitute the above parameters into the corrosion and mechanical coupling damage evolution equation to identify the stress-free micro-dissolution coefficient and stress dependence coefficient of the current cycle unit online.

[0226] The damage prediction module is used to predict the total damage increment, chemical damage percentage, mechanical damage percentage, coupled damage percentage, and acceleration equivalent coefficient at the end of the next cycle unit by using the identified stress-free micro-dissolution coefficient and stress dependence coefficient, combined with the corrosion and mechanical coupled damage evolution equation.

[0227] The working condition reconstruction module is used to reconstruct the dynamic loading segment duration, static corrosion segment duration, load frequency, and environmental intensity of the next cycle unit based on the proportion of chemical damage, mechanical damage, coupled damage, and acceleration equivalent coefficient, and output the reconstruction results.

[0228] The iterative control module is used to update the configuration of the next cycle unit based on the reconstruction results, accumulate the total damage increment to the cumulative total damage, calculate the acceleration equivalent coefficient and accumulate it to the cumulative equivalent actual service life, and return to alternate execution to form a closed loop iteration; when the cumulative total damage reaches the critical damage value or the cumulative equivalent actual service life reaches the target service life, the test is terminated and the results of the dynamic and static coupled accelerated corrosion test of automotive materials are output.

[0229] It should be noted that those skilled in the art can clearly understand that the specific implementation process of the above-mentioned dynamic and static coupling accelerated corrosion test system and its modules can be referred to the corresponding descriptions in the foregoing method embodiments. For the sake of convenience and brevity, these will not be repeated here.

[0230] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A dynamic-static coupled accelerated corrosion test method suitable for automotive materials, characterized in that, Includes the following steps: The total damage variable is decomposed into chemical damage variable, mechanical damage variable, and coupled damage variable, and a coupled damage evolution equation is established, as shown in the following expression: ； In the formula, For total damage variable; Chemical damage variable; For mechanical damage variables; For coupling damage variables; Based on the service condition spectrum of the target vehicle model, the test cycle is divided into several cycle units. Each cycle unit includes a dynamic loading segment and a static corrosion segment, and the dynamic loading segment and the static corrosion segment are executed alternately. At the end of each cycle unit, in-situ multi-physics joint testing is performed on the sample to obtain electrochemical, mechanical and microscopic parameters, which are then substituted into the coupled damage evolution equation to identify the stress-free micro-dissolution coefficient and stress dependence coefficient of the current cycle unit online. By utilizing the identified stress-free micro-dissolution coefficient and stress dependence coefficient, combined with the coupled damage evolution equation, the total damage increment, chemical damage ratio, mechanical damage ratio, coupled damage ratio, and acceleration equivalent coefficient at the end of the next cycle unit are predicted. Based on this, the duration of the dynamic loading segment, the duration of the static corrosion segment, the load frequency, and the environmental intensity of the next cycle unit are reconstructed, and the reconstruction results are output. Based on the reconstruction results, update the configuration of the next cycle unit, accumulate the total damage increment to the cumulative total damage, calculate the acceleration equivalent coefficient and accumulate it to the cumulative equivalent actual service years, and return to alternate execution to form a closed loop iteration; The test is terminated when the cumulative total damage reaches the critical damage value or the cumulative equivalent actual service life reaches the target service life, and the results of the dynamic and static coupled accelerated corrosion test of the automotive materials are output. Among them, the online identification of the stress-free micro-dissolution coefficient and stress dependence coefficient of the current cycle unit includes: Define an observation vector that incorporates the measured corrosion current density, hysteresis loop area, and elastic modulus attenuation. Define a parameter vector, with the stress-free micro-dissolution coefficient and the stress dependence coefficient as the parameters to be identified; Establish the residual between the output of the forward model based on the coupled damage evolution equation and the observation vector; The parameter vector is updated using the recursive least squares method until the residual converges, and the stress-free micro-dissolution coefficient and stress dependence coefficient of the current cycle unit are identified online. The prediction of the total damage increment, chemical damage percentage, mechanical damage percentage, coupled damage percentage, and acceleration equivalent coefficient at the end of the next cycle unit includes: The predicted chemical damage increment, mechanical damage increment, and coupled damage increment within the next cycle unit are superimposed to generate the predicted total damage increment at the end of the next cycle unit. The chemical damage increment, mechanical damage increment, and coupled damage increment are respectively compared with the total damage increment at the end of the next cycle unit to generate the chemical damage percentage, mechanical damage percentage, and coupled damage percentage. The acceleration equivalent coefficient is generated by calculating the ratio of the total damage increment at the end of the next cycle unit to the damage increment of the equivalent cycle in actual service.

2. The method for accelerating corrosion testing of automotive materials using dynamic and static coupling as described in claim 1, characterized in that, The total damage variable is decomposed into chemical damage variables, mechanical damage variables, and coupled damage variables, including: The chemical damage conversion coefficient is determined, and it is multiplied by the corrosion current density to generate the chemical damage evolution rate. The chemical damage evolution rate is then integrated over time to generate the chemical damage variable. The fatigue strength coefficient and fatigue damage index are determined. The stress amplitude is calculated as a ratio to the fatigue strength coefficient, and then a power exponentiation is performed to generate the single-cycle mechanical damage increment. The single-cycle mechanical damage increment is accumulated according to the number of cycles to generate the mechanical damage variable. Determine the stress-free micro-dissolution coefficient and the stress dependence coefficient, construct the stress state function, and exponentially couple the stress-free micro-dissolution coefficient, the stress dependence coefficient, and the stress state function to generate the stress-dependent micro-dissolution coefficient. Multiply this coefficient with the single-cycle mechanical damage increment to generate the coupled damage evolution rate. Integrate the coupled damage evolution rate over time to generate the coupled damage variable.

3. The method for accelerating corrosion testing of automotive materials using dynamic and static coupling as described in claim 2, characterized in that, Establish the coupled damage evolution equation, including: An evolution expression for chemical damage variables was established, linking the chemical damage evolution rate with the corrosion current density; Establish an evolution expression for mechanical damage variables, and correlate the increment of mechanical damage in a single cycle with the stress amplitude and the number of cycles; An evolution expression for coupled damage variables is established, with the stress-dependent micro-dissolution coefficient as the core driving term; The evolution expressions of chemical damage variables, mechanical damage variables, and coupled damage variables are nonlinearly coupled to establish a coupled damage evolution equation.

4. The method for accelerating corrosion testing of automotive materials using dynamic and static coupling as described in claim 1, characterized in that, The test cycle is divided into several cyclic units, each containing a dynamic loading segment and a static corrosion segment, which are executed alternately. These include: Based on the service condition spectrum of the target vehicle model, the initial duration ratio of the dynamic loading segment and the static corrosion segment is calculated by inversion. The dynamic loading segment is configured to simulate vibration, stress cycling, and temperature shock during vehicle operation. The static corrosion section was configured to simulate the static electrochemical environment during car parking. The dynamic loading segment and the static corrosion segment are executed alternately, and the test cycle is divided into several cycle units according to the service condition spectrum.

5. The method for accelerating corrosion testing of automotive materials using dynamic and static coupling as described in claim 1, characterized in that, At the end of each cycle, in-situ multiphysics joint testing was performed on the sample to obtain electrochemical, mechanical, and microscopic parameters, including: Electrochemical impedance spectroscopy and potentiodynamic polarization curves were used to obtain polarization resistance, double layer capacitance, corrosion current density and Tafel slope as electrochemical dimension parameters. By collecting the hysteresis loop area and testing the elastic modulus attenuation, the plastic dissipation energy and the degree of microcrack propagation are obtained as mechanical dimension parameters. By observing the surface morphology and performing micro-area electrochemical scanning, the pitting depth, pitting density, and local corrosion current distribution were obtained as microscopic parameters. At the end of each cycle, in-situ multiphysics field tests are performed on the sample to obtain electrochemical, mechanical and microscopic parameters.

6. The method for accelerating corrosion testing of automotive materials using dynamic and static coupling as described in claim 1, characterized in that, The duration of the dynamic loading segment, the duration of the static corrosion segment, the load frequency, and the environmental intensity of the next cycle unit are reconstructed, including: When the proportion of chemical damage exceeds the first preset threshold, the duration of the dynamic loading segment is shortened and the duration of the static corrosion segment is extended, and the corrosion-dominant mode is determined. When the proportion of mechanical damage exceeds the second preset threshold, the duration of the dynamic loading segment is extended and the duration of the static corrosion segment is shortened, and the mechanically dominant mode is determined. When the proportion of coupled damage exceeds the third preset threshold, the load frequency of the dynamic loading section and the environmental intensity of the static corrosion section are increased simultaneously, and it is determined to be a strong coupling dominant mode. When the acceleration equivalent coefficient deviates from the target acceleration ratio, adjust the environmental intensity of the static corrosion section or the load intensity of the dynamic loading section to bring the acceleration equivalent coefficient back to the target range. Actively reconstruct the duration of the dynamic loading segment, the duration of the static corrosion segment, the load frequency, and the environmental intensity of the next cycle unit.

7. The method for accelerating corrosion testing of automotive materials using dynamic and static coupling as described in claim 1, characterized in that, Based on the reconstruction results, update the unit configuration for the next cycle, accumulate the total damage increment to the cumulative total damage, calculate the acceleration equivalent coefficient and accumulate it to the cumulative equivalent actual service life, and return to alternate execution to form a closed-loop iteration, including: The configuration of the next cycle unit is updated based on the reconstructed dynamic loading segment duration, static corrosion segment duration, load frequency, and environmental intensity. Add the total damage increment at the end of the next cycle to the cumulative total damage; The acceleration equivalent factor will be converted into equivalent actual service years and added to the cumulative equivalent actual service years. Determine whether the cumulative total damage has reached the critical damage value or whether the cumulative equivalent actual service life has reached the target service life; If the target is not reached, the process of alternating between dynamic loading and static erosion segments is returned to form a closed-loop iteration.

8. The method for accelerating corrosion testing of automotive materials using dynamic and static coupling as described in claim 1, characterized in that, The test is terminated when the cumulative total damage reaches the critical damage value or the cumulative equivalent actual service life reaches the target service life, and the results of the dynamic and static coupled accelerated corrosion test of the automotive materials are output, including: When the cumulative total damage reaches the preset critical damage value, it is determined to be a material failure and the test is terminated. When the cumulative equivalent actual service life reaches the target service life, it is determined to be a lifespan compliance situation and the test is terminated; Based on the material failure condition or the lifespan target being met, the test is terminated and the results of the dynamic and static coupled accelerated corrosion test of the automotive materials are output.

Images