Spring fatigue life test system and dynamic balance evaluation method

Abstract

The invention relates to the technical field of spring measurement, and discloses a spring fatigue life test system and a dynamic balance evaluation method, and the system comprises a reference length acquisition module, a dynamic balance state determination module, a working condition spectrum loading module, a stress-strain response data acquisition module, a damage feature extraction module and a life evaluation module. Acquiring a reference length in a free state; step increasing preload is applied, and when it is detected that the deformation rate of the to-be-detected spring is smaller than a set threshold value, it is judged that the to-be-detected spring reaches a dynamic balance state; in a dynamic balance state, loading the to-be-tested spring based on the variable amplitude load time sequence signal, and synchronously acquiring stress-strain response data; identifying the stress characteristics of the to-be-tested spring in the load period; generating a life evaluation report based on the stress characteristics; the accuracy of the fatigue life of the spring can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of artificial intelligence, and in particular to a spring fatigue life test system and a dynamic balance evaluation method. BACKGROUND

[0002] In the field of spring fatigue life testing, the existing technology often fails to accurately simulate the complex load environment in the actual service process of the spring, resulting in a large deviation between the test conditions and the actual working conditions, so that the fatigue life data obtained cannot accurately reflect the durability of the spring in actual use. At the same time, when preloading the spring to be tested, the traditional test method is difficult to accurately determine whether it has reached a stable dynamic balance state, thereby affecting the collection accuracy of the subsequent stress-strain response data, and ultimately reducing the reliability of the fatigue life evaluation result.

[0003] In addition, the existing technology is not detailed enough in analyzing the hysteresis loop when extracting the spring damage features, and it is difficult to accurately identify key parameters such as peak stress, valley stress and loop area, resulting in a large error in fitting the damage accumulation trajectory. Moreover, during the load loading process, there is a lack of effective load compensation mechanism, and the deviation between the actual loading load and the target load is large, further exacerbating the inaccuracy of the fatigue life evaluation, and failing to meet the demand of high-precision testing. SUMMARY

[0004] The present application provides a spring fatigue life test system and a dynamic balance evaluation method to solve the problems raised in the background art.

[0005] To achieve the above-mentioned purpose, the spring fatigue life test system and the dynamic balance evaluation method provided by the present application are characterized in that the system reference length acquisition module, the dynamic balance state determination module, the working condition spectrum loading module, the stress-strain response data acquisition module, the damage feature extraction module and the life evaluation module, wherein: The reference length acquisition module is used to acquire the reference length of the spring to be tested in a free state; The dynamic balance state determination module is used to add a step-increment pre-load to the spring to be tested, and when it is detected that the deformation rate of the spring to be tested is less than a set threshold, it is determined that the spring to be tested has reached a dynamic balance state; The working condition spectrum loading module is used to generate a variable amplitude load time sequence signal of the spring to be tested based on the vibration frequency spectrum characteristics of the spring to be tested in the service environment; The stress-strain response data acquisition module is used to load the spring to be tested based on the variable amplitude load time sequence signal under the dynamic balance state, and synchronously collect the stress-strain response data of the spring to be tested; The damage feature extraction module is configured to identify the peak stress, the valley stress and the loop-enclosed area of the spring under test in a load cycle according to the inflection point of the hysteresis loop in the stress-strain response data. The life evaluation module is configured to generate a life evaluation report of the spring under test based on the peak stress, the valley stress and the loop-enclosed area.

[0006] In a preferred embodiment, the reference length acquisition module, when acquiring the reference length of the spring under test in a free state, is specifically configured to: mount the spring under test without load on a test platform base; generate reference length data of the spring under test according to the projection distance of the spring under test from a reference surface in the test platform base.

[0007] In a preferred embodiment, the dynamic balance state determination module, when applying a step-by-step increasing preload to the spring under test, determines that the spring under test reaches a dynamic balance state when the deformation rate of the spring under test is less than a set threshold, and is specifically configured to: determine an incremental step of the step-by-step load according to the rated load-bearing parameter of the spring under test; apply the preload to the spring under test in steps according to the incremental step; collect axial deformation data of the spring under test in real time during the load maintaining period; generate a real-time deformation rate curve of the spring under test based on the axial deformation data; determine that the spring under test reaches a dynamic balance state when the real-time deformation rate curve continuously stays below a rate threshold.

[0008] In a preferred embodiment, the working condition spectrum loading module, when generating the variable-amplitude load time sequence signal of the spring under test based on the vibration frequency spectrum characteristics of the spring under test in a service environment, is specifically configured to: collect vibration acceleration data of the spring under test under typical working conditions; perform frequency domain conversion on the vibration acceleration data to obtain a main energy distribution frequency band of the spring under test; determine a load amplitude variation range of the spring under test according to the main energy distribution frequency band; generate a random amplitude modulation signal based on the load amplitude variation range, and construct the variable-amplitude load time sequence signal of the spring under test based on the random amplitude modulation signal.

[0009] In a preferred embodiment, when the working condition spectrum loading module is executed to generate a random amplitude modulation signal based on the load amplitude variation range, and to construct the variable amplitude load time sequence signal of the spring to be tested based on the random amplitude modulation signal, it is specifically used for: establishing a mapping relationship between the load amplitude variation range and the time sequence; constructing a basic sinusoidal carrier signal under the constraint of the mapping relationship; performing amplitude randomization processing on the basic sinusoidal carrier signal; performing time domain smoothing filtering on the basic sinusoidal carrier signal after randomization processing to obtain the variable amplitude load time sequence signal of the spring to be tested.

[0010] In a preferred embodiment, when the stress-strain response data acquisition module is executed to load the spring to be tested based on the variable amplitude load time sequence signal under the dynamic balance state, and to synchronously collect the stress-strain response data of the spring to be tested, it is specifically used for: loading the spring to be tested according to the variable amplitude load time sequence signal; calculating a compensation value of the load according to a deviation amount between a target load value corresponding to the variable amplitude load time sequence signal and an actual load value of the load, wherein a calculation formula of the compensation value is as follows:

[0011] wherein, the compensation value is, the proportional gain coefficient is, the deviation amount is, the integral gain coefficient is, the time factor is; superimposing the compensation value into a drive current instruction of the load, and synchronously collecting the stress-strain response data of the spring to be tested.

[0012] In a preferred embodiment, when the damage feature extraction module is executed to identify the peak stress, the valley stress and the loop enclosed area of the spring to be tested in a load cycle according to the hysteresis loop inflection point in the stress-strain response data, it is specifically used for: dividing the stress-strain response data into independent loop blocks according to the load cycle; positioning a curvature mutation point in the independent loop block as a candidate inflection point; screening the candidate inflection points that meet the same sign condition of the cross product of three consecutive points as effective inflection points; dividing the uplink segment and the downlink segment of the loop based on the effective inflection points to obtain the peak stress, the valley stress and the loop enclosed area of the spring to be tested in the load cycle.

[0013] In a preferred embodiment, the loop encloses an area including: Decomposing the independent loop block into polygonal sub-regions with the effective inflection point as a boundary; The polygonal sub-region is triangulated, and the polygonal sub-regions after triangulation are accumulated to obtain the loop enclosing area of ​​the independent loop block, wherein the calculation formula of the loop enclosing area is as follows:

[0014] Where, is the area enclosed by the loop, is the total number of boundary points of the independent loop block, is the ordinal number of the boundary point of the independent loop block, For the The coordinates of the boundary points, is the coordinate of the geometric center point of the loop, For the The coordinates of the boundary points, is the vector cross product operator, It is a modulo operation.

[0015] In a preferred embodiment, when the life assessment module generates a life assessment report of the spring to be tested based on the peak stress, the valley stress, and the loop enclosed area, it is specifically configured to: Constructing a stress characteristic matrix using the peak stress and the valley stress as row vectors; Converting the loop enclosed area into an energy dissipation density value, and correlating it to the additional dimension of the stress characteristic matrix; Performing nonlinear fitting on the associated stress characteristic matrix to obtain a damage accumulation trajectory curve of the spring to be tested; A life assessment report of the spring to be tested is generated according to the number of load cycles corresponding to the inflection point of the damage accumulation trajectory curve.

[0016] In order to solve the above problems, the present invention also provides a method for dynamic balance evaluation of spring fatigue life, the method comprising: S1. Obtain the reference length of the spring to be tested in the free state; S2. Adding a stepwise incremental preload to the spring to be tested, and when the deformation rate of the spring to be tested is detected to be less than a set threshold, determining that the spring to be tested has reached a dynamic equilibrium state; S3. Based on the vibration spectrum characteristics of the spring to be tested in the service environment, a variable amplitude load timing signal of the spring to be tested is generated; S4. In the dynamic balance state, load the to-be-tested spring based on the variable-amplitude load time sequence signal, and synchronously collect stress-strain response data of the to-be-tested spring; S5. Identify peak stress, valley stress and hysteresis loop enclosed area of the to-be-tested spring in a load cycle according to an inflection point of a hysteresis loop in the stress-strain response data; S6. Generate a life evaluation report of the to-be-tested spring based on the peak stress, the valley stress and the hysteresis loop enclosed area.

[0017] Compared with the prior art, the present application has the following beneficial effects: 1. The present application can accurately determine the dynamic balance state of the to-be-tested spring by setting a dynamic balance state determination module, adopting a stepwise incremental preload method and combining deformation rate judgment, providing a stable benchmark for subsequent load loading and data collection, ensuring that the stress-strain response data collection is more in line with the actual stress condition, thereby improving the accuracy of fatigue life evaluation. At the same time, the working condition spectrum loading module generates a variable-amplitude load time sequence signal based on the vibration spectrum characteristics of the service environment, making the loading process closer to the real working state of the spring, laying a foundation for accurate evaluation.

[0018] 2. The present application can fully capture the spring damage law by identifying key stress parameters and hysteresis loop enclosed area through the inflection point of the hysteresis loop, combining the stress feature matrix and damage accumulation trajectory curve constructed by the life evaluation module, effectively reducing the deviation between the actual load and the target load through the compensation mechanism during load loading, further improving the data reliability, and finally generating a life evaluation report that can more truly reflect the fatigue life of the spring, providing strong support for spring performance evaluation. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The system architecture diagram of the spring fatigue life test system provided by an embodiment of the present application is shown; Figure 2 The flowchart of a spring fatigue life dynamic balance evaluation method provided by an embodiment of the present application is shown.

[0020] The implementation, functional features and advantages of the present application will be further described with reference to the drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments belong to some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0022] The terms used in the embodiments of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The singular forms "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates otherwise, and "a plurality" generally includes at least two.

[0023] As used herein, the words “if” or “when” may be interpreted as “at the time of” or “when” or “in response to determining” or “in response to detecting,” depending on the context. Similarly, the phrases “if it is determined” or “if (stated condition or event) is detected” may be interpreted as “when it is determined” or “in response to the determination” or “when detecting (stated condition or event)” or “in response to detecting (stated condition or event),” depending on the context.

[0024] In addition, the step sequence in the following method embodiments is only an example and not a strict limitation.

[0025] In fact, the server-side device deployed by the spring fatigue life test system may be composed of one or more devices. The above-mentioned spring fatigue life test system can be implemented as: a business instance, a virtual machine, and a hardware device. For example, the spring fatigue life test system can be implemented as a business instance deployed on one or more devices in a cloud node. Simply put, the spring fatigue life test system can be understood as a software deployed on a cloud node, which is used to provide a spring fatigue life test system for each user terminal. Alternatively, the spring fatigue life test system can also be implemented as a virtual machine deployed on one or more devices in a cloud node. The virtual machine is installed with application software for managing each user terminal. Alternatively, the spring fatigue life test system can also be implemented as a server-side composed of many hardware devices of the same or different types, and one or more hardware devices are set to provide a spring fatigue life test system for each user terminal.

[0026] In terms of implementation, the spring fatigue life test system and the user end are mutually compatible. That is, if the spring fatigue life test system is an application installed on a cloud service platform, the user end is the client that establishes a communication connection with the application; or if the spring fatigue life test system is implemented as a website, the user end is implemented as a web page; or if the spring fatigue life test system is implemented as a cloud service platform, the user end is implemented as a mini-program in an instant messaging application.

[0027] like Figure 1 FIG. 1 is a system architecture diagram of a spring fatigue life testing system provided by an embodiment of the present invention.

[0028] The spring fatigue life test system 100 can be set in a cloud server, and in an implementation form, can be used as one or more service devices, can be installed as an application on a cloud (for example, a server of a mobile service operator, a server cluster, or the like), or can be developed as a website. According to an implementation function, the spring fatigue life test system 100 can include a reference length acquisition module 101, a dynamic balance state determination module 102, a working condition spectrum loading module 103, a stress-strain response data acquisition module 104, a damage feature extraction module 105, and a life evaluation module 106. The modules in the application can also be referred to as units, which refer to a series of computer program segments that can be executed by an electronic device processor and can complete a fixed function, and are stored in the memory of the electronic device.

[0029] In the embodiment of the application, each of the modules in the spring fatigue life test system can be independently implemented and called by other modules. The calling here can be understood as that a module can be connected to multiple modules of another type and provide corresponding services for the connected multiple modules. In the spring fatigue life test system provided by the embodiment of the application, the application range of the spring fatigue life test system architecture can be adjusted by increasing modules and directly calling without modifying program codes, horizontal expansion in a cluster mode is realized, and the purpose of quickly and flexibly expanding the spring fatigue life test system is achieved. In actual application, the modules can be set in the same device or different devices, or can be set in a virtual device, for example, a service instance in a cloud server.

[0030] The following will be described in combination with specific embodiments, respectively for each component of the spring fatigue life test system and the specific working process: The reference length acquisition module 101 is configured to acquire the reference length of the spring to be tested in a free state. In the embodiment of the application, when the reference length acquisition module acquires the reference length of the spring to be tested in a free state, it is specifically configured to: Install the spring to be tested without load on the test platform base; According to the projection distance of the spring to be tested and the reference surface in the test platform base, the reference length data of the spring to be tested is generated.

[0031] Specifically, the test platform base is placed steadily on a horizontally calibrated workbench, a level is attached to the upper surface of the base, and the bubble in the level is observed to determine whether it is in the center position. If the bubble is off-center, the support feet of the workbench are adjusted until the bubble is centered, ensuring that the base is in a horizontal state. The circular mounting hole on the base for mounting the spring to be tested is checked, a cylindrical cleaning rod with a diameter slightly smaller than the mounting hole is inserted into the hole, and the hole is wiped back and forth to remove metal debris, dust and other impurities remaining in the hole. The spring to be tested without load is removed, the two ends of the spring are flat circular end faces, the two end faces are gently wiped with a dust-free cloth dipped in alcohol to remove fingerprints and oil stains on the surface, and the spring is placed on clean filter paper for 2 minutes to allow the alcohol to evaporate completely. The spring is picked up, the circular end face at one end of the spring is aligned with the mounting hole on the base, the axis of the spring is kept coincident with the axis of the mounting hole, the end of the spring is slowly inserted into the mounting hole, and the insertion depth is 1 / 3 of the diameter of the end of the spring. At this time, the inner wall of the mounting hole is in close contact with the end of the spring, the spring is gently shaken by hand, no obvious looseness is felt, and the spring remains vertical under its own gravity without tilting, and the installation is completed.

[0032] Further, a reference surface is determined at the edge region of the test platform base. The reference surface is a rectangular metal plate inlaid on the base, and the surface is precisely ground with a flatness error of not more than 0.01 mm. The laser range finder is fixed on an adjustable height support, so that the laser emission port of the range finder is at the same height as the reference surface. The position of the support is adjusted so that the laser beam is perpendicular to the reference surface. The range finder is turned on, and at this time the laser beam forms a clear spot on the reference surface. The initial distance value displayed by the range finder is recorded, which is the distance from the range finder to the reference surface. The position of the range finder and the support is kept unchanged, and the position of the spring to be tested is adjusted so that the axis of the spring is in the same vertical plane as the laser beam. At this time, the laser beam is emitted from the reference surface, passes through the space and is projected onto the end face of the spring far from the base, forming a spot at the center of the end face. After the value displayed by the range finder stabilizes, the value is recorded. The result obtained by subtracting the initial distance value recorded previously from the value is the projection distance of the spring to be tested from the reference surface of the test platform base.

[0033] Further, the projection distance of the obtained to-be-tested spring from the reference surface in the base of the test platform is taken as original data, the installation state of the to-be-tested spring is checked again, it is confirmed that the spring is in a natural stretched state without load, is not subjected to stretching or compression force during installation, the axis of the spring always remains vertical and does not bend. Since the projection distance precisely corresponds to the straight-line distance between the two ends of the spring in the case of no load and correct installation, the value of the projection distance is directly determined as the reference length data of the to-be-tested spring, and the data is recorded in a special test data table, and the measurement time, the test platform number and the number of the to-be-tested spring are indicated in the data table.

[0034] In general, the reference length of the to-be-tested spring in a free state is obtained by installing the to-be-tested spring in a load-free state on the base of the test platform and generating the reference length data according to the projection distance from the reference surface in the base, which can provide an initial reference for subsequent dynamic balance state determination, load loading and stress-strain response analysis.

[0035] In general, the accurate acquisition of the reference length ensures that subsequent test links are carried out under a unified initial size reference, reduces the interference of the initial length measurement deviation on the dynamic balance state determination, load application accuracy and stress-strain data interpretation, thereby laying a foundation for the accuracy of the entire spring fatigue life test process and helping to improve the reliability of the final life evaluation result.

[0036] The dynamic balance state determination module 102 is configured to apply a stepwise increasing preload to the to-be-tested spring, and determine that the to-be-tested spring reaches a dynamic balance state when it is detected that the deformation rate of the to-be-tested spring is less than a set threshold value. In the embodiment of the application, when the dynamic balance state determination module applies a stepwise increasing preload to the to-be-tested spring and determines that the to-be-tested spring reaches a dynamic balance state when it is detected that the deformation rate of the to-be-tested spring is less than a set threshold value, the dynamic balance state determination module is specifically configured to: determine an incremental step length of the stepwise load according to the rated load parameter of the to-be-tested spring; apply a preload to the to-be-tested spring at the incremental step length; collect axial deformation data of the to-be-tested spring in real time during load retention; generate a real-time deformation rate curve of the to-be-tested spring based on the axial deformation data; determine that the to-be-tested spring reaches a dynamic balance state when the real-time deformation rate curve continuously stays below a rate threshold value.

[0037] Specifically, the rated load parameter of the spring to be tested is obtained, which is the maximum load value that the spring can bear and is recorded on the product manual or identification card of the spring. The rated load parameter is evenly divided into 10 equal parts, and the value of each part is the incremental step of the step load. For example, if the rated load parameter is 1000 Newton, the incremental step is 100 Newton.

[0038] Further, the loading device is installed on the test platform, which includes a tray on which weights can be placed, and the tray is connected to the upper end of the spring to be tested through a rope. According to the determined incremental step, standard weights corresponding to the determined incremental step are prepared, and the weight of each weight is equal to the value of the incremental step. The first weight is placed on the tray, at which time the weight force is transmitted to the spring to be tested through the rope, so that the spring bears a load equal to the value of the incremental step, and the load is maintained for 5 minutes to complete the first pre-load application. After 5 minutes, the first weight is removed, and the second weight is placed to increase the load on the spring by an incremental step, and the load is also maintained for 5 minutes. In this way, the number of weights is gradually increased to gradually apply pre-load to the spring to be tested according to the incremental step.

[0039] Further, a displacement sensor is fixed at the upper end and the lower end of the spring to be tested, respectively. The upper end sensor is fixed at the bottom of the loading device tray, and the lower end sensor is fixed on the test platform base. The connection lines of the two sensors are consistent with the axial direction of the spring. The sensors are connected to the data acquisition instrument, which is set to collect data once per second. When the spring is pre-loaded and the load is maintained, the sensors monitor the distance change between the upper end and the lower end of the spring in real time, and the distance change value is the axial deformation data of the spring to be tested, which is automatically recorded by the data acquisition instrument.

[0040] Further, the data acquisition instrument is connected to the computer to retrieve the collected axial deformation data. Taking time as the horizontal axis and the axial deformation data change in unit time as the vertical axis, the deformation change at different time points is marked in the coordinate system in turn, and a smooth curve is used to connect these marked points to generate a real-time deformation rate curve of the spring to be tested.

[0041] Further, a rate threshold value is set, which is a fixed value representing the maximum allowed value of the spring deformation rate. The generated real-time deformation rate curve is compared with the rate threshold value in real time. When the rate values of all points on the curve are less than the rate threshold value, and this state continues for 10 minutes without change, a prompt signal is automatically sent, and it is determined that the spring to be tested reaches a dynamic equilibrium state.

[0042] In general, the step load increment step is determined according to the rated load parameter of the to-be-tested spring, the pre-load is applied step by step, and the axial deformation data is collected in real time, so that the deformation change rule of the spring under the action of the load can be accurately tracked. When the deformation rate continuously remains below the set threshold, it is determined that the dynamic balance state is reached, so that the spring can be ensured to be in a stable mechanical state in the subsequent load loading process, and the stress-strain response data fluctuation caused by the unstable initial state is avoided, thereby providing a reliable reference condition for subsequent tests.

[0043] In general, the determination method of the dynamic balance state can fully release the residual stress and unstable deformation of the spring in the initial loading stage, so that the mechanical performance of the spring is closer to the stable state in the long-term service. Based on this state, subsequent variable amplitude load loading and data collection can be performed, so that the authenticity and consistency of the stress-strain response data can be significantly improved, and more accurate original data can be provided for damage feature extraction and life assessment, thereby helping to improve the credibility of the final life assessment report.

[0044] The working condition spectrum loading module 103 is configured to generate a variable amplitude load time sequence signal of the to-be-tested spring based on vibration spectrum characteristics of the to-be-tested spring in a service environment. In the embodiment of the present application, when the working condition spectrum loading module generates a variable amplitude load time sequence signal of the to-be-tested spring based on vibration spectrum characteristics of the to-be-tested spring in a service environment, it is specifically configured to: Collect vibration acceleration data of the to-be-tested spring under a typical working condition; Perform frequency domain conversion on the vibration acceleration data to obtain a main energy distribution frequency band of the to-be-tested spring; Determine a load amplitude change range of the to-be-tested spring according to the main energy distribution frequency band; Generate a random amplitude modulation signal based on the load amplitude change range, and construct the variable amplitude load time sequence signal of the to-be-tested spring based on the random amplitude modulation signal.

[0045] When the working condition spectrum loading module generates a random amplitude modulation signal based on the load amplitude change range, and constructs the variable amplitude load time sequence signal of the to-be-tested spring based on the random amplitude modulation signal, it is specifically configured to: Establish a mapping relationship between the load amplitude change range and a time sequence; Construct a basic sinusoidal carrier signal under the constraint of the mapping relationship; Perform amplitude randomization processing on the basic sinusoidal carrier signal; Perform time domain smoothing filtering on the basic sinusoidal carrier signal after the randomization processing to obtain the variable amplitude load time sequence signal of the to-be-tested spring.

[0046] Specifically, the spring to be tested is installed on a vibration test bench simulating typical working conditions, i.e. the vibration environment commonly encountered by the spring in actual work, such as the vibration state of an automobile suspension system. A three-axis acceleration sensor is fixed at the middle position of the spring, and the sensor is connected to a data acquisition device through a wire. The data acquisition device is turned on and set to a sampling frequency of 1000 times per second. The vibration test bench is started to operate according to the vibration parameters of the typical working conditions, and at the same time the data acquisition device starts to record the acceleration values of the spring detected by the sensor during the vibration process. These values are the vibration acceleration data of the spring to be tested under the typical working conditions, and the collection duration is 30 minutes, during which the operation parameters of the test bench are kept stable.

[0047] Further, the time-domain waveform corresponding to the vibration acceleration data is selected, and the "frequency domain conversion" function button is clicked to process the acceleration data in the time domain, converting the acceleration values at each time into energy values at different frequencies. After processing, a frequency spectrum graph is generated with frequency as the horizontal axis and energy value as the vertical axis. From the frequency spectrum graph, several continuous frequency intervals with higher energy values can be clearly observed, which are the main energy distribution frequency bands of the spring to be tested.

[0048] Further, according to the obtained main energy distribution frequency bands, the load amplitude conversion standard of the type of spring under the corresponding frequency interval is consulted, which clearly specifies the load amplitude range corresponding to different frequency intervals. The lowest frequency and the highest frequency in the main energy distribution frequency band are substituted into the conversion relationship in the standard to obtain two corresponding load amplitudes, where the lower load amplitude is the lower limit of the range and the higher load amplitude is the upper limit of the range. The interval formed by these two values is the load amplitude variation range of the spring to be tested.

[0049] Further, the determined load amplitude variation range is input, the modulation mode of the signal is set to random amplitude modulation, and the modulation frequency range is consistent with the main energy distribution frequency band. The "generate signal" button is clicked to randomly select different amplitudes within the load amplitude variation range and modulate these amplitudes according to random time intervals to form a series of amplitude signals that vary with time. These signals are the random amplitude modulation signals. Subsequently, the random amplitude modulation signals are arranged in chronological order to form a continuous signal sequence with varying amplitudes over time, which is the variable amplitude load time sequence signal of the spring to be tested.

[0050] Specifically, a two-dimensional table is created, the first column of the table is set as a time sequence, the starting time of the time sequence is 0, and then a time point is recorded every 0.1 seconds, and 1000 time points are recorded to form a complete time sequence. The second column of the table is set as the load amplitude, and the determined load amplitude variation range is divided into 1000 specific load amplitude values in a uniform distribution manner, each of which is within the range. The 1000 load amplitude values obtained by the division are sequentially filled into the row where each time point is located in the time sequence, so that each time point has a unique corresponding load amplitude, thereby establishing a mapping relationship between the load amplitude variation range and the time sequence. The mapping relationship is automatically saved and displayed in a chart form, with the horizontal axis being the time sequence and the vertical axis being the corresponding load amplitude.

[0051] Further, the established mapping relationship is called, and the period of the basic sinusoidal carrier signal is determined according to the interval of the time sequence in the mapping relationship, and the period is consistent with the time interval. The frequency of the basic sinusoidal carrier signal is set, and the frequency value is referenced to the main vibration frequency of the spring under typical working conditions, so as to ensure that the signal can reflect the actual stress characteristics of the spring. According to the time sequence and the corresponding load amplitude variation range, a continuous waveform signal is generated according to the variation law of the sinusoidal curve, and the variation trend of the signal is constrained by the mapping relationship, that is, the signal amplitude corresponding to each time point does not exceed the load amplitude variation range. This signal is the basic sinusoidal carrier signal constructed, and the waveform diagram of the signal is displayed in real time.

[0052] Further, a list containing 1000 random numbers is prepared, the value range of the random numbers is between 0.8 and 1.2, and the random numbers are generated by a random number generator and ensured to be non-repetitive. The random number list is imported into the signal processing software, and the basic sinusoidal carrier signal is divided into 1000 small segments according to the interval of the time sequence, each small segment corresponding to the signal amplitude of a time point. Then, each random number in the random number list is sequentially multiplied by the corresponding signal segment amplitude to obtain a new signal amplitude, so that the signal amplitude of each time point is randomly changed on the basis of the original amplitude, and the changed amplitude is still within the load amplitude variation range. The amplitude randomization processing of the basic sinusoidal carrier signal is completed, and the waveform of the processed signal will present an irregular fluctuation state.

[0053] Further, a time domain smoothing filter function is selected, which processes the signal by means of sliding average, and the size of the sliding window is set to 5 time intervals, that is, each window contains the signal amplitudes of 5 consecutive time points. Starting from the first time point of the randomized basic sinusoidal carrier signal, the average value of the 5 signal amplitudes in each sliding window is calculated, and the average value is taken as the new signal amplitude of the middle time point of the window. In this way, the entire signal is processed in turn by sliding, so that the sharp waveform with sudden changes in the signal becomes smooth. The processed signal has continuous and smooth amplitude changes, which meets the actual dynamic characteristics of the stress of the spring to be tested. The signal is saved and the corresponding time domain waveform diagram is generated.

[0054] In summary, the amplitude load time sequence signal is generated based on the vibration frequency spectrum characteristics of the spring to be tested in the service environment, and the beneficial effects are remarkable. By collecting vibration acceleration data under typical working conditions and performing frequency domain conversion, the main energy distribution frequency band can be accurately captured, and the load amplitude change range determined accordingly is more consistent with the actual stress characteristics of the spring, so that the generated amplitude load time sequence signal can truly simulate the dynamic load action in the service environment.

[0055] In summary, by establishing the mapping relationship between the load amplitude and the time sequence, the amplitude randomization processing and time domain smoothing filtering of the basic sinusoidal carrier signal further improve the accuracy and continuity of the amplitude load time sequence signal. Based on this, the load loading can ensure that the load on the spring is highly consistent with the actual service working conditions, providing reliable input for the accurate collection of subsequent stress-strain response data, thereby laying a solid foundation for the scientificity of damage feature extraction and life assessment, and effectively improving the authenticity and effectiveness of fatigue life test.

[0056] The stress-strain response data acquisition module 104 is configured to perform load loading on the spring to be tested based on the amplitude load time sequence signal in the dynamic balance state, and synchronously collect stress-strain response data of the spring to be tested. In the embodiment of the present application, when the stress-strain response data acquisition module performs load loading on the spring to be tested based on the amplitude load time sequence signal in the dynamic balance state, and synchronously collects stress-strain response data of the spring to be tested, it is specifically configured to: perform load loading on the spring to be tested according to the amplitude load time sequence signal; calculate a compensation value of the load according to the deviation between the target load value corresponding to the amplitude load time sequence signal and the actual load value of the load, wherein the calculation formula of the compensation value is as follows:

[0057] In the formula, the compensation value, the proportional gain coefficient, the deviation amount, the integral gain coefficient, the time factor; superimpose the compensation value to the driving current command of the load, and synchronously collect the stress-strain response data of the spring to be tested.

[0058] Specifically, the spring to be tested is fixed on a loading test bench, ensuring that the connection of both ends of the spring is stable and the axis is consistent with the loading direction. The loading test bench is equipped with a loading device that can adjust the output load according to the electrical signal, and the device is connected to a signal generator. The generated variable amplitude load time sequence signal is input into the signal generator, and the signal generator sends an electrical signal to the loading device according to the load value corresponding to each time point in the time sequence signal. After receiving the electrical signal, the loading device applies a corresponding load to the spring through the internal power mechanism, and the size of the load changes with time, which is consistent with the variable amplitude load time sequence signal, thereby realizing the loading of the spring to be tested according to the variable amplitude load time sequence signal.

[0059] Further, a load sensor is installed on the loading device, which is connected to a data collector and can detect the actual load value in real time during loading and transmit it to the data collector. At the same time, the load value corresponding to each time point in the variable amplitude load time sequence signal as the target load value will also be transmitted to the data collector synchronously. The data collector will compare the target load value with the actual load value detected by the sensor at each time point, subtract the actual load value from the target load value, and obtain the deviation amount of the load at that time point. Then, according to the size and direction of the deviation amount, the load compensation value to be adjusted is determined, and the size of the compensation value is equal to the deviation amount and the direction is opposite to the deviation amount, so as to complete the calculation of the load compensation value.

[0060] Further, the calculated compensation value is transmitted to a control module of the loading device, and the control module has a pre-stored corresponding relationship between the load driving current instruction and the load output. After receiving the compensation value, the control module converts the compensation value into a corresponding current adjustment value according to the corresponding relationship, then superimposes the current adjustment value on the original load driving current instruction to form a new driving current instruction and sends it to the actuator of the loading device, so that the actual load value output by the loading device is closer to the target load value. At the same time of adjusting the driving current instruction, the stress sensor and the strain sensor installed on the spring surface are started, the stress sensor is used to detect the stress of the spring, and the strain sensor is used to detect the deformation degree of the spring. Both sensors are connected with a data recording instrument, and the data recording instrument synchronously collects and stores the stress data and the strain data output by the sensors at the same time interval as the variable amplitude load timing signal. These data together constitute the stress-strain response data of the spring to be tested.

[0061] Specifically, in the formula for calculating the compensation value, the compensation value is the final calculated value for adjusting the load, the deviation is the difference between the target load value corresponding to the variable amplitude load timing signal and the actual load value, the proportional gain coefficient and the integral gain coefficient are fixed values pre-set according to the performance of the loading device, the characteristics of the spring to be tested and the past test experience, and the time factor is the time elapsed from the start of loading to the current time.

[0062] Further, the formula has the significance that by comprehensively considering the current deviation and the accumulation of the deviation over a period of time, a suitable compensation value is calculated. The part of the proportional gain coefficient multiplied by the current deviation is used to quickly respond to the current deviation, and the part of the integral gain coefficient multiplied by the accumulation of the deviation over time is used to eliminate the long-term deviation. The two parts work together to make the calculated compensation value more accurately adjust the load, so that the actual load value is closer to the target load value.

[0063] Further, from the trend, when the deviation is positive and remains unchanged, as the time increases, the accumulation of the deviation over time will continuously increase, so that the value of the integral part of the compensation value gradually increases, while the value of the proportional part remains unchanged, so the compensation value gradually increases. When the deviation is negative and remains unchanged, as the time increases, the accumulation of the deviation over time will continuously decrease, so that the value of the integral part of the compensation value gradually decreases, while the value of the proportional part remains unchanged, so the compensation value gradually decreases. When the deviation is zero, the value of the proportional part is zero. If there is accumulation of the deviation before, the value of the integral part will remain the corresponding value according to the accumulation, and if there is no accumulation of the deviation before, the value of the integral part is also zero. At this time, the compensation value is zero.

[0064] In general, the dynamic balance state provides stable initial mechanical conditions for load loading, avoids additional deformation interference of the spring due to not reaching a stable state, and ensures consistency between the load loading process and the actual stress state of the spring. At the same time, based on the variable amplitude load timing signal loading, the dynamic stress process of the spring in the service environment can be accurately reproduced, and the stress-strain response data is more consistent with the mechanical performance under the actual working condition.

[0065] In general, the synchronous acquisition mechanism can ensure the time correlation of the stress-strain response data and the load loading process, and ensure the timeliness and correspondence of the data. In addition, the deviation between the actual load and the target load is corrected by the compensation formula during load loading, which further improves the accuracy of load loading, makes the acquired stress-strain response data more accurate and reliable, provides high-quality original data support for subsequent damage feature extraction and life evaluation, and helps to improve the accuracy of fatigue life evaluation.

[0066] The damage feature extraction module 105 is configured to identify peak stress, valley stress and hysteresis loop area of the spring to be tested in a load cycle according to a hysteresis loop inflection point in the stress-strain response data. In the embodiment of the present application, when the damage feature extraction module identifies the peak stress, valley stress and hysteresis loop area of the spring to be tested in the load cycle according to the hysteresis loop inflection point in the stress-strain response data, it is specifically used for: Dividing the stress-strain response data into independent loop blocks according to the load cycle; Positioning the curvature mutation point in the independent loop block as a candidate inflection point; Screening the candidate inflection point meeting the same sign condition of the cross product of three consecutive points as an effective inflection point; Dividing the uplink segment and the downlink segment of the loop based on the effective inflection point to obtain the peak stress, the valley stress and the hysteresis loop area of the spring to be tested in the load cycle.

[0067] The hysteresis loop area includes: The independent loop block is divided into a polygon sub-region with the effective inflection point as a boundary; Triangular subdivision is performed on the polygon sub-region, and the polygon sub-region after triangular subdivision is accumulated to obtain the hysteresis loop area of the independent loop block, wherein the calculation formula of the hysteresis loop area is as follows:

[0068] In the formula, The hysteresis loop area is A, The total number of boundary points of the independent loop block is N, The boundary point sequence number of the independent loop block is n, is the coordinate of the first boundary point, is the coordinate of the geometric center point of the hysteresis loop, is the coordinate of the first boundary point, is the coordinate of the geometric center point of the hysteresis loop, is the coordinate of the first boundary point, is the vector cross product operator, is the modulo operation.

[0069] Specifically, the stress-strain response data of the spring to be tested is imported, which is a set of stress values and corresponding strain values recorded in chronological order, and the variable amplitude load time sequence signal is also imported, from which the load cycle, i.e. the time experienced by the load from the starting state through changes to the same starting state, is extracted. The division parameters are set to divide the stress-strain response data into multiple continuous segments with the load cycle as the interval, each segment containing all stress-strain data within a load cycle. These segments are independent hysteresis blocks, each of which is presented in the form of a separate curve, with the horizontal axis representing strain and the vertical axis representing stress.

[0070] Further, a curvature analysis tool is called to analyze the stress-strain curve of each independent hysteresis block. The tool calculates the bending degree of the curve at each point, i.e. the curvature. When the curve starts from a point and its bending degree suddenly changes significantly, i.e. the curvature value increases or decreases significantly, this point is the curvature inflection point. All such points are marked on the curve, and these points are determined as candidate inflection points, each of which corresponds to a specific set of stress and strain values.

[0071] Further, each candidate inflection point is processed. Each candidate inflection point and its adjacent two points before and after it, i.e. three consecutive points, are taken. The three points are respectively recorded as the first point, the second point and the third point in order on the curve. The vector formed by the first point and the second point, and the vector formed by the second point and the third point are calculated, and the cross product of the two vectors is calculated. The result of the cross product will show a positive or negative sign. If the cross product of the three consecutive points is of the same sign, i.e. both positive or both negative, the candidate inflection point is screened as an effective inflection point. The marks of these effective inflection points are retained, and the marks of the candidate inflection points that do not meet the conditions are removed.

[0072] Further, according to the position of the effective inflection point on the stress-strain curve of the independent hysteresis block, the curve is divided into an uplink segment and a downlink segment. The uplink segment refers to the part extending in the direction of increasing stress from the starting point of the curve to the effective inflection point. The downlink segment refers to the part extending in the direction of decreasing stress from the effective inflection point to the end point of the curve. In the uplink segment after division, find the point with the maximum stress value. The stress value corresponding to this point is the peak stress of the spring to be tested in the load cycle. In the downlink segment, find the point with the minimum stress value. The stress value corresponding to this point is the valley stress. Calculate the closed area enclosed by the uplink segment and the downlink segment along the stress-strain curve. The area of the region obtained is the hysteresis loop area.

[0073] Specifically, the independent hysteresis block stress-strain curve with the marked effective inflection points is called out, and is arranged in the order of the appearance of the effective inflection points on the curve. Starting from the first effective inflection point, a straight line is connected between the inflection point and the next adjacent effective inflection point. The next adjacent effective inflection point is connected, and so on, until the last effective inflection point is connected to the first effective inflection point with a straight line, forming a closed dividing line. These dividing lines and the curve segments of the independent hysteresis block together enclose a plurality of continuous and non-overlapping regions. Each region is composed of three or more edges, i.e. a polygonal sub-region. Each polygonal sub-region is marked with a different color for distinction.

[0074] Further, in selecting a polygonal sub-region, a vertex of the region is determined as a reference point. From the reference point, straight lines are drawn to all non-adjacent vertices in the polygon. These straight lines divide the polygon into a plurality of triangles. Each triangle has three vertices that are vertices of the original polygon and there is no overlap between the triangles. In the same way, all polygonal sub-regions are divided to obtain all triangles. For each triangle, one of the edges is selected as the base, the length of the base is measured, and the perpendicular distance from the opposite vertex to the base is measured as the height. The base length is multiplied by the height, and the result is divided into two equal parts to obtain the area of the triangle. The areas of all triangles in the same polygonal sub-region are added to obtain the area of the polygonal sub-region. Finally, the areas of all polygonal sub-regions are added to obtain the total hysteresis loop area of the independent hysteresis block. The area value is recorded and displayed in the result panel.

[0075] Specifically, the loop-enclosed area is the total area of the region enclosed by the calculated independent loop block boundary, the total number of boundary points of the independent loop block refers to the number of all points constituting the boundary of the independent loop block, which come from the stress-strain curve of the independent loop block, including the effective inflection point and other characteristic points on the curve; the boundary point sequence number is the numbering of these boundary points in order, starting from 1 and increasing sequentially; the i th boundary point coordinate and the i+1 th boundary point coordinate are the specific position values of each boundary point in the coordinate system with strain as the horizontal axis and stress as the vertical axis, which are obtained by recording the stress-strain response data; the loop geometric center point coordinate is the position value of the point obtained by taking the average value of the horizontal coordinates of all boundary points as the x coordinate and the average value of the vertical coordinates of all boundary points as the y coordinate.

[0076] Further, the meaning of the formula is that by calculating the modulus of the cross product of the vectors formed by the loop geometric center point and the adjacent two boundary points, and then taking half of the sum of all these moduli, the loop-enclosed area of the independent loop block is obtained, wherein the modulus of the cross product of the vector formed by each adjacent boundary point and the geometric center point corresponds to the area of a triangle, and after adding up the areas of these triangles and taking half of the sum, the area of the closed region enclosed by all the boundary points, i.e. the loop-enclosed area, can be accurately calculated.

[0077] Further, in terms of trends, when the total number of boundary points of the independent loop block increases and the distribution range of the boundary points expands, i.e. the distance between adjacent boundary points increases, the modulus of each vector cross product will increase accordingly, the sum of all moduli will also increase, and the loop-enclosed area will show an increasing trend; when the total number of boundary points decreases or the distribution range of the boundary points narrows, i.e. the distance between adjacent boundary points decreases, the modulus of each vector cross product will decrease accordingly, the sum of all moduli will also decrease, and the loop-enclosed area will show a decreasing trend; when the distribution of the boundary points remains unchanged and only the total number of boundary points increases proportionally, and the new points are uniformly distributed between the original adjacent boundary points, the sum of the moduli of the vector cross products changes little, and the loop-enclosed area remains basically stable.

[0078] In summary, by dividing the stress-strain response data into independent loop blocks according to the load cycle, locating the curvature discontinuity points as candidate inflection points, and screening the effective inflection points that satisfy the condition of the same sign of the cross product of the vectors of three consecutive points, the uplink segment and the downlink segment of the loop can be accurately divided, and the peak stress and the valley stress can be accurately identified, thereby providing a reliable basis for capturing the extreme stress state of the spring in the load cycle.

[0079] In summary, the independent hysteresis loop blocks are decomposed into polygonal sub-regions by the effective inflection point, and the hysteresis loop area is calculated by triangulation and accumulation, so as to accurately quantify the energy dissipation of the spring in the load cycle. This process not only ensures the accuracy and integrity of the damage feature parameter extraction, but also provides high-quality data support for subsequent damage accumulation trajectory fitting and life assessment based on these features, which helps to improve the scientificity and accuracy of spring fatigue life assessment.

[0080] The life assessment module 106 is configured to generate a life assessment report of the spring under test based on the peak stress, the valley stress and the hysteresis loop area.

[0081] In the embodiment of the present application, when the life assessment module generates the life assessment report of the spring under test based on the peak stress, the valley stress and the hysteresis loop area, it is specifically configured to: construct a stress feature matrix with the peak stress and the valley stress as row vectors; convert the hysteresis loop area into an energy dissipation density value and associate it with an additional dimension of the stress feature matrix; nonlinearly fit the associated stress feature matrix to obtain a damage accumulation trajectory curve of the spring under test; generate a life assessment report of the spring under test according to the load cycle number corresponding to the curve inflection point in the damage accumulation trajectory curve.

[0082] Specifically, the peak stress and the valley stress obtained by the spring under test in each load cycle are imported, and these values are arranged in the order of load cycles. A matrix table is created, each row of the table represents a load cycle, the peak stress corresponding to each cycle is taken as the first element of the row, and the valley stress is taken as the second element of the row. The peak stress and the valley stress of each row vector are filled in the table in the order of load cycles, and the constructed table is the stress feature matrix, which is automatically saved and displayed in the form of a two-dimensional array.

[0083] Further, the hysteresis loop area of each independent hysteresis loop block is taken out, the cross-sectional area of the spring under test and the effective length in the loading direction are measured, and the hysteresis loop area is divided by the product of the cross-sectional area and the effective length to obtain the energy dissipation density value. The result is the energy dissipation density value corresponding to each hysteresis loop area. The stress feature matrix constructed is called out, a new column is added as an additional dimension in the matrix, and the calculated energy dissipation density value is filled in the column in the order of load cycles, so that the stress feature row vector of each load cycle is associated with the energy dissipation density value one by one, forming a stress feature matrix containing an additional dimension.

[0084] Further, the data in the associated stress characteristic matrix is corresponded with the load cycle number, the load cycle number is the horizontal axis, and the damage accumulation amount calculated by the peak stress, the valley stress and the energy dissipation density value in each cycle in the matrix is the vertical axis. According to the distribution trend of the data, a smooth curve is automatically generated, the bending degree of the curve is adjusted, the curve is as close to all data points as possible, and it is ensured that the curve can reflect the overall trend of the change of the damage accumulation amount with the load cycle number. The curve is the damage accumulation trajectory curve of the spring to be tested, and the curve is displayed in the chart and the key data points are labeled.

[0085] Further, the damage accumulation trajectory curve is enlarged and displayed, and the change trend of the curve is observed. When the curve suddenly becomes steep from gentle rising, or suddenly becomes gentle from steep rising, the change point is the inflection point of the curve, and the load cycle number corresponding to the inflection point on the horizontal axis is recorded. The number is the service life value of the spring to be tested. The report generation tool is opened, the number of the spring to be tested, the test environment parameters, the load cycle characteristics are input, the change process of the damage accumulation trajectory curve and the inflection point characteristics are described in detail, the load cycle number corresponding to the inflection point is clearly labeled as the service life evaluation result, and the damage accumulation trajectory curve is attached to form a complete service life evaluation report of the spring to be tested. The report is saved as an electronic document after format verification.

[0086] In summary, by constructing the stress characteristic matrix with the peak stress and the valley stress, and converting the hysteresis loop area to the energy dissipation density value and relating it to the additional dimension of the matrix, the key mechanical characteristics and energy dissipation information of the spring in the load cycle can be comprehensively integrated to form a multi-dimensional damage evaluation basis. On this basis, the nonlinear fitting is performed on the associated stress characteristic matrix, and the damage accumulation trajectory curve obtained can accurately reflect the evolution law of the spring damage with the load cycle.

[0087] In summary, the service life evaluation report is generated according to the load cycle number corresponding to the inflection point in the trajectory curve, which can directly relate the critical state of the spring damage to the actual service cycle number, so that the evaluation result is more suitable for the real fatigue failure process of the spring. This evaluation method based on the fusion of multiple characteristic parameters greatly improves the comprehensiveness and accuracy of the service life evaluation, and provides a reliable basis for the scientific judgment of the spring fatigue life.

[0088] Referring to Figure 2 Fig. 1 shows a flowchart of a spring fatigue life dynamic balance evaluation method provided by an embodiment of the present application. In the embodiment, the spring fatigue life dynamic balance evaluation method comprises: S1. obtaining the reference length of the spring to be tested in a free state; S2. applying a stepwise increasing preload to the spring to be tested, and determining that the spring to be tested reaches a dynamic balance state when the deformation rate of the spring to be tested is detected to be less than a set threshold. S3. generating a variable amplitude load time sequence signal of the to-be-tested spring based on the vibration spectrum characteristics of the to-be-tested spring in the service environment; S4. loading the to-be-tested spring with a load based on the variable amplitude load time sequence signal in the dynamic balance state, and synchronously collecting stress-strain response data of the to-be-tested spring; S5. identifying peak stress, valley stress and hysteresis loop enclosed area of the to-be-tested spring in a load cycle according to an inflection point of a hysteresis loop in the stress-strain response data; S6. generating a life evaluation report of the to-be-tested spring based on the peak stress, the valley stress and the hysteresis loop enclosed area.

[0089] It is apparent for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application.

[0090] The embodiments of the present application can acquire and process related data based on artificial intelligence technology. The artificial intelligence is a theory, method, technology and application system for simulating, extending and expanding human intelligence by using a digital computer or a machine controlled by a digital computer, perceiving an environment, acquiring knowledge and using the knowledge to obtain optimal results.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A spring fatigue life testing system, characterized in that: The system includes a reference length acquisition module, a dynamic equilibrium state determination module, a working condition spectrum loading module, a stress-strain response data acquisition module, a damage feature extraction module and a life assessment module, wherein: The reference length acquisition module is used to obtain the reference length of the spring to be tested in a free state; The dynamic equilibrium state determination module is configured to apply a step-by-step incremental preload to the spring to be tested, and determine that the spring to be tested has reached a dynamic equilibrium state when it is detected that the deformation rate of the spring to be tested is less than a set threshold; The working condition spectrum loading module is used to generate a variable amplitude load time series signal of the spring to be tested based on the vibration spectrum characteristics of the spring to be tested in the service environment; The stress-strain response data acquisition module is used to load the spring to be tested based on the variable amplitude load time sequence signal in the dynamic equilibrium state, and synchronously collect the stress-strain response data of the spring to be tested; The damage feature extraction module is used to identify the peak stress, valley stress and loop enclosed area of ​​the spring to be tested during the load cycle based on the hysteresis loop inflection point in the stress-strain response data; The life assessment module is used to generate a life assessment report of the spring to be tested based on the peak stress, the valley stress and the loop enclosed area.

2. The spring fatigue life testing system according to claim 1, characterized in that: When executing the acquisition of the reference length of the spring to be tested in the free state, the reference length acquisition module is specifically used to: Install the unloaded spring to be tested on the test platform base; The reference length data of the spring to be tested is generated according to the projection distance between the spring to be tested and the reference plane in the test platform base.

3. The spring fatigue life testing system according to claim 1, characterized in that: The dynamic equilibrium state determination module is specifically configured to: Determining the incremental step length of the step load according to the rated load parameters of the spring to be tested; Applying preload to the spring to be tested step by step according to the incremental step size; During the load holding period, collecting axial deformation data of the spring to be tested in real time; generating a real-time deformation rate curve of the spring to be tested based on the axial deformation data; When the real-time deformation rate curve is continuously below the rate threshold, it is determined that the spring to be tested has reached a dynamic equilibrium state.

4. The spring fatigue life testing system according to claim 1, wherein: When the working condition spectrum loading module generates a variable amplitude load time sequence signal of the spring to be tested based on the vibration spectrum characteristics of the spring to be tested in the service environment, it is specifically used to: Collecting vibration acceleration data of the spring to be tested under typical working conditions; Performing frequency domain conversion on the vibration acceleration data to obtain the main energy distribution frequency band of the spring to be tested; Determining a load amplitude variation range of the spring to be tested according to the main energy distribution frequency band; A random amplitude modulation signal is generated based on the load amplitude variation range, and a variable amplitude load timing signal of the spring to be tested is constructed based on the random amplitude modulation signal.

5. The spring fatigue life testing system according to claim 4, characterized in that: When the working condition spectrum loading module generates a random amplitude modulation signal based on the load amplitude variation range and forms a variable amplitude load time sequence signal of the spring to be tested based on the random amplitude modulation signal, it is specifically used to: Establishing a mapping relationship between the load amplitude variation range and the time series; Constructing a basic sinusoidal carrier signal under the constraints of the mapping relationship; Performing amplitude randomization processing on the basic sinusoidal carrier signal; The randomized basic sinusoidal carrier signal is subjected to time domain smoothing filtering to obtain a variable amplitude load time series signal of the spring to be tested.

6. The spring fatigue life testing system according to claim 1, characterized in that: When the stress-strain response data acquisition module is executed in the dynamic equilibrium state, it applies a load to the spring to be tested based on the variable amplitude load time sequence signal, and synchronously collects the stress-strain response data of the spring to be tested, specifically for: Loading the spring to be tested according to the variable amplitude load timing signal; The compensation value of the load is calculated according to the deviation between the target load value corresponding to the variable amplitude load time sequence signal and the actual load value during the load operation. The calculation formula of the compensation value is as follows: Where, is the compensation value, is the proportional gain coefficient, is the deviation amount, is the integral gain coefficient, is the time factor; The compensation value is added to the driving current instruction of the load, and the stress-strain response data of the spring to be tested is collected synchronously.

7. The spring fatigue life testing system according to claim 1, wherein: When the damage feature extraction module is executed to identify the peak stress, valley stress and loop enclosed area of ​​the spring to be tested in the load cycle according to the inflection point of the hysteresis loop in the stress-strain response data, it is specifically used to: Splitting the stress-strain response data into independent loop blocks according to the load cycle; Locating a curvature mutation point in the independent loop block as a candidate inflection point; Selecting the candidate inflection points that satisfy the condition that the cross products of three consecutive point vectors have the same sign as the valid inflection points; The loop is divided into an upward segment and a downward segment based on the effective inflection point, and the peak stress, valley stress and loop enclosed area of ​​the spring to be tested in the load cycle are obtained.

8. The spring fatigue life testing system according to claim 7, wherein: The area enclosed by the loop includes: Decomposing the independent loop block into polygonal sub-regions with the effective inflection point as a boundary; The polygonal sub-region is triangulated, and the polygonal sub-regions after triangulation are accumulated to obtain the loop enclosing area of ​​the independent loop block, wherein the calculation formula of the loop enclosing area is as follows: Where, is the area enclosed by the loop, is the total number of boundary points of the independent loop block, is the ordinal number of the boundary point of the independent loop block, For the The coordinates of the boundary points, is the coordinate of the geometric center point of the loop, For the The coordinates of the boundary points, is the vector cross product operator, It is a modulo operation.

9. The spring fatigue life testing system according to claim 1, wherein: When the life assessment module generates a life assessment report for the spring to be tested based on the peak stress, the valley stress, and the loop enclosed area, the life assessment module is specifically configured to: Constructing a stress characteristic matrix using the peak stress and the valley stress as row vectors; Converting the loop enclosed area into an energy dissipation density value, and correlating it to the additional dimension of the stress characteristic matrix; Performing nonlinear fitting on the associated stress characteristic matrix to obtain a damage accumulation trajectory curve of the spring to be tested; A life assessment report of the spring to be tested is generated according to the number of load cycles corresponding to the inflection point of the damage accumulation trajectory curve.

10. A method for dynamic balance assessment of spring fatigue life, characterized in that: For implementing the spring fatigue life testing system according to claim 1, the method comprises: S1. Obtain the reference length of the spring to be tested in the free state; S2. Adding a stepwise incremental preload to the spring to be tested, and when the deformation rate of the spring to be tested is detected to be less than a set threshold, determining that the spring to be tested has reached a dynamic equilibrium state; S3. Based on the vibration spectrum characteristics of the spring to be tested in the service environment, a variable amplitude load timing signal of the spring to be tested is generated; S4. In the dynamic equilibrium state, loading the spring to be tested based on the variable amplitude load timing signal, and synchronously collecting stress-strain response data of the spring to be tested; S5. Identify the peak stress, valley stress, and loop enclosed area of ​​the spring to be tested during the load cycle according to the inflection point of the hysteresis loop in the stress-strain response data; S6. Generate a life assessment report for the spring to be tested based on the peak stress, the valley stress, and the loop enclosed area.

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