Method for measuring fatigue life of service member and fatigue life measuring system

Abstract

This invention discloses a method and system for determining the fatigue life of service components. The method involves transmitting nonlinear ultrasonic guided waves with matched fundamental and second harmonic phase velocities to the service component; acquiring the currently received signal from the service component and calculating a first nonlinear parameter; if the first nonlinear parameter intersects with a first nonlinear ultrasonic calibration curve at a unique point, the remaining fatigue life of the corresponding service component is determined; if two intersection points exist, transmitting nonlinear ultrasonic guided waves with mismatched fundamental and second harmonic phase velocities; acquiring the currently received signal from the service component and calculating a second nonlinear parameter; if the intersection point of the second nonlinear parameter and the second nonlinear ultrasonic calibration curve corresponds to the same remaining fatigue life as the intersection point of the first nonlinear parameter and the first nonlinear ultrasonic calibration curve, then this same remaining fatigue life is determined as the remaining fatigue life of the service component. This invention can determine the remaining fatigue life of service components in the later stages of fatigue damage.

Description

Technical Field

[0001] This invention relates to a method for determining the fatigue life of in-service components and a fatigue life determination system using this method, belonging to the field of fatigue life determination of mechanical components. Background Technology

[0002] Fatigue damage is one of the main failure modes of components in the field of engineering machinery. Studies have found that more than 90% of failures in in-service components are caused by fatigue cracks. Therefore, regular inspection and evaluation of component performance degradation are crucial for preventing catastrophic failures of engineering components.

[0003] Currently, the main methods for predicting the fatigue life of mechanical structural components include the nominal stress method, the local stress-strain method, and the fracture mechanics method. These methods can establish predictive models between the stress, strain, or cracks in a structural component and its fatigue life. However, these methods only address a single operating condition of the structure and cannot consider the dynamic changes in the structural operating conditions during service, thus failing to meet the requirements for online estimation of performance degradation and remaining service life of components during service.

[0004] Non-destructive testing (NDT) methods are widely used because they can inspect components without shutting down equipment or compromising structural integrity. However, traditional NDT methods are only suitable for detecting macroscopic fatigue cracks and cannot effectively detect the accumulation of early fatigue damage or the nucleation and propagation of microcracks. Studies have found that fatigue crack initiation typically occurs before 70%–90% of the fatigue life. Timely and effective evaluation of the fatigue damage level and remaining life of in-service components is crucial to preventing component failures.

[0005] Nonlinear ultrasound is used for early detection of fatigue damage in materials due to its sensitivity to micro-damage / micro-cracks. Studies have found that in the early to mid-stages of fatigue damage, the accumulation of dislocations and precipitates leads to micro-crack nucleation, resulting in enhanced nonlinear effects and an increase in the nonlinear parameter with increasing fatigue life. However, in the later stages of fatigue damage, crack propagation weakens the nonlinearity, and the nonlinear parameter decreases with increasing fatigue life. This results in a "mountain-shaped" calibration curve between the measured nonlinear parameter and fatigue life, where one nonlinear parameter measured in the mid-to-late stages corresponds to two fatigue life fractions. Current techniques cannot determine the remaining fatigue life of a component in later service life based on these two fatigue life fractions, leading to low resolution in nonlinear ultrasound detection methods for fatigue damage. Summary of the Invention

[0006] The main objective of this invention is to provide a method and system for determining the fatigue life of service components, which can determine the remaining fatigue life of fatigue-damaged service components in later stages of service.

[0007] The present invention adopts the following technical solution.

[0008] In a first aspect, the present invention provides a method for determining the fatigue life of service components, comprising:

[0009] For the in-service component, transmit a nonlinear ultrasonic guided wave with phase velocity matching between the fundamental frequency and the second harmonic; acquire the signal currently received by the in-service component and calculate the current first nonlinear parameter;

[0010] If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have a unique intersection point, then the remaining fatigue life of the corresponding service component is determined based on this intersection point.

[0011] If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have two intersection points, then transmit a nonlinear ultrasonic guided wave with a phase velocity mismatch between the fundamental frequency and the second harmonic frequency; collect the signal currently received by the service component and calculate the current second nonlinear parameter; if the intersection point of the second nonlinear parameter and the second nonlinear ultrasonic calibration curve is the same as the remaining fatigue life corresponding to the intersection point of the first nonlinear parameter and the first nonlinear ultrasonic calibration curve, then the same remaining fatigue life is determined as the remaining fatigue life of the service component.

[0012] Furthermore, the first nonlinear ultrasonic calibration curve represents the relationship between the fatigue damage lifespan of the service component and the nonlinear parameter under excitation conditions where the fundamental frequency and second harmonic phase velocities are matched; the second nonlinear ultrasonic calibration curve represents the relationship between the fatigue damage lifespan of the service component and the nonlinear parameter under excitation conditions where the fundamental frequency and second harmonic phase velocities are mismatched.

[0013] Furthermore, the entire life cycle of fatigue damage is represented by fatigue life fractions at equal intervals.

[0014] Furthermore, the calculation of the first and second nonlinear parameters is expressed as follows:

[0015]

[0016] Where β is a nonlinear parameter, A2 is the amplitude of the second harmonic signal received by the service component, and A1 is the amplitude of the fundamental frequency signal received by the service component.

[0017] Furthermore, the method for determining the phase velocity matching between the fundamental frequency and the second harmonic is as follows:

[0018] The phase velocity matching degree is calculated as follows: in, and The phase velocities are the fundamental frequency ω and the second harmonic 2ω, respectively.

[0019] The condition for phase velocity matching between the fundamental frequency and the second harmonic is: D is less than or equal to a preset value;

[0020] The condition for phase velocity mismatch between the fundamental frequency and the second harmonic is that D is greater than the preset value.

[0021] In a second aspect, the present invention provides a fatigue life determination system for service components, comprising: a signal generator, a power amplifier, an excitation transducer, a first inclined block, a second inclined block, a receiving transducer, an oscilloscope, and a determination control module;

[0022] The signal generator is used to transmit nonlinear ultrasonic guided waves with matching fundamental and second harmonic phase velocities to the service component, or to transmit nonlinear ultrasonic guided waves with mismatched fundamental and second harmonic phase velocities.

[0023] The power amplifier is used to amplify the nonlinear ultrasonic guided wave;

[0024] The excitation transducer is used to excite the service component under test according to the nonlinear ultrasonic guided wave;

[0025] The receiving transducer is used to receive signals received by the service component under set excitation conditions;

[0026] The oscilloscope is used to display and store signals received by the in-service component;

[0027] The first and second inclined blocks are used to adjust the excitation angle of the excitation transducer and the receiving ultrasonic guided wave of the transducer, respectively.

[0028] The measurement and control module is used to calculate the current first nonlinear parameter based on the signal received by the service component under nonlinear ultrasonic guided wave excitation conditions with phase velocity matching of the fundamental frequency and second harmonic frequency stored in the oscilloscope.

[0029] If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have a unique intersection point, then the remaining fatigue life of the corresponding service component is determined based on this intersection point.

[0030] If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have two intersection points, the signal received by the service component under the nonlinear ultrasonic guided wave excitation condition of phase velocity mismatch between the fundamental frequency and the second harmonic frequency, acquired by the oscilloscope, is obtained, and the current second nonlinear parameter is calculated. If the intersection point of the second nonlinear parameter and the second nonlinear ultrasonic calibration curve is the same as the intersection point of the first nonlinear parameter and the first nonlinear ultrasonic calibration curve, the same remaining fatigue life is determined as the remaining fatigue life of the service component.

[0031] Furthermore, the method for calculating the excitation angle of the ultrasonic guided wave is as follows:

[0032] sinθ=c wedge-L / c (f，l)

[0033] Where θ is the excitation angle of the ultrasonic guided wave, and cwedge-L Let c be the volume longitudinal wave velocity of the oblique block material. (f,l) It is the phase velocity of the fundamental frequency Lamb wave of the l-mode to be excited at a frequency of f.

[0034] Furthermore, the first and second inclined blocks are made of plexiglass.

[0035] Furthermore, two signal generators were built, one for transmitting nonlinear ultrasonic guided waves under excitation conditions of matching fundamental and second harmonic phase velocities to the service component, and the other for transmitting nonlinear ultrasonic guided waves under excitation conditions of mismatched fundamental and second harmonic phase velocities.

[0036] Furthermore, the measurement and control module is configured to communicate with an oscilloscope on a computer to obtain the signal received by the service component under set excitation conditions.

[0037] The beneficial technical effects achieved by this invention are as follows:

[0038] This method combines nonlinear ultrasonic measurement under phase velocity matching and phase velocity mismatch conditions to overcome the problem of insufficient detection resolution of nonlinear ultrasonic in fatigue damage. It can determine the remaining fatigue life of components in the later service stage of fatigue damage, and realize the detection and evaluation of fatigue damage throughout the entire service life cycle. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the fatigue life determination system for service components provided in the embodiment;

[0040] Figure 2 This is a flowchart of the fatigue life determination method for service components provided in the embodiment;

[0041] Figure 3 This is the dispersion curve of the nonlinear ultrasonic guided wave emitted in the embodiment;

[0042] Figure 4 This is a schematic diagram of the fundamental frequency amplitude A1 at 100kHz and the second harmonic amplitude A2 at 200kHz in the embodiment.

[0043] Figure 5 This is a schematic diagram showing the comparison results between nonlinear parameters and nonlinear ultrasonic calibration curves in the embodiment;

[0044] The attached figures are labeled as follows:

[0045] 1. Signal generator; 2. Power amplifier; 3. Excitation transducer; 4. First inclined block; 5. Component under test; 6. Second inclined block; 7. Receiving transducer; 8. Oscilloscope; 9. Computer; 11. Nonlinear ultrasonic calibration curve of the entire life cycle of fatigue damage of service components under phase velocity matching conditions and nonlinear parameter β under phase velocity mismatch conditions and nonlinear ultrasonic calibration curve of the entire life cycle of fatigue damage of service components under phase velocity matching conditions. Detailed Implementation

[0046] To make the creative features, technical means, and objectives of this invention easier to understand, the invention is further described below in conjunction with specific embodiments.

[0047] Example 1: Method for determining the fatigue life of in-service components, such as... Figure 2 As shown, it includes:

[0048] Step 1: For the in-service component, transmit a nonlinear ultrasonic guided wave with phase velocity matching between the fundamental frequency and the second harmonic;

[0049] Step 2: Collect the signals received by the in-service components and calculate the current first nonlinear parameter;

[0050] Step 3: Compare the first nonlinear parameter with the first nonlinear ultrasonic calibration curve.

[0051] If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have a unique intersection point, then the remaining fatigue life of the corresponding service component is determined based on this intersection point.

[0052] If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have two intersection points, then transmit a nonlinear ultrasonic guided wave with a phase velocity mismatch between the fundamental frequency and the second harmonic frequency; collect the signal currently received by the service component and calculate the current second nonlinear parameter; if the intersection point of the second nonlinear parameter and the second nonlinear ultrasonic calibration curve is the same as the remaining fatigue life corresponding to the intersection point of the first nonlinear parameter and the first nonlinear ultrasonic calibration curve, then the same remaining fatigue life is determined as the remaining fatigue life of the service component.

[0053] In a specific embodiment, two sets of signal transmitting devices can be selected to transmit nonlinear ultrasonic guided waves according to the material parameters, geometric dimensions, etc. of the service component. The excitation parameters and excitation modes are as follows: one set is the excitation parameters under the condition of matching fundamental frequency and second harmonic phase velocity, and the other set is the excitation parameters under the condition of mismatch between fundamental frequency and second harmonic phase velocity.

[0054] In this embodiment, the excitation parameters under the condition of fundamental frequency and second harmonic phase velocity matching are used to perform nonlinear ultrasonic online / offline measurements on the test structure to obtain the nonlinear parameter β under the current state. m+c .

[0055] In this application, the first nonlinear ultrasonic calibration curve represents the relationship between the fatigue damage life cycle of the service component and the nonlinear parameter under the excitation condition of matching fundamental frequency and second harmonic phase velocity; the second nonlinear ultrasonic calibration curve represents the relationship between the fatigue damage life cycle of the service component and the nonlinear parameter under the excitation condition of mismatched fundamental frequency and second harmonic phase velocity.

[0056] In specific implementation, the methods for obtaining the first nonlinear ultrasonic calibration curve and the second nonlinear ultrasonic calibration curve include:

[0057] Fatigue tests were conducted on specimens prepared based on the materials and operating conditions of the service components.

[0058] A nonlinear ultrasonic online acquisition system for fatigue damage was constructed. Starting from the original state of the sample, two nonlinear ultrasonic online measurements were carried out at N% of the fatigue life. These measurements included nonlinear ultrasonic guided waves with matching phase velocities of the fundamental frequency and the second harmonic, and nonlinear ultrasonic guided waves with mismatched phase velocities of the fundamental frequency and the second harmonic.

[0059] The received signal is subjected to a Fast Fourier Transform to obtain the fundamental frequency amplitude A1 and the second harmonic amplitude A2 of the nonlinear signal under two excitation conditions; the nonlinear parameters are calculated based on the amplitudes, using the following formula:

[0060]

[0061] Based on fatigue life and nonlinear parameters, a nonlinear ultrasonic calibration curve for the entire fatigue damage life cycle of the in-service component is constructed.

[0062] This invention compares the nonlinear parameters of a component under phase velocity matching with a calibration curve. If a unique intersection point exists, the abscissa of the intersection point is the lifespan fraction N of the currently serving component. f The remaining fatigue life of the component can be calculated, and the measurement ends. If the nonlinear parameter of the component under phase velocity matching has two intersection points with the calibration curve, the excitation parameters under the fundamental frequency and second harmonic phase velocity mismatch conditions are used to perform nonlinear ultrasonic online / offline measurements on the component under test to obtain the nonlinear parameter β under the current state. c The nonlinear parameter is compared with the calibration curve under mismatch conditions to obtain the lifetime fraction corresponding to the nonlinear parameter in the curve. This is then compared with the lifetime fraction obtained under phase velocity matching conditions. The component with the same value is the lifetime fraction N of the currently serving component. f The remaining fatigue life of a component can be calculated by %. This invention combines nonlinear ultrasonic measurement under phase velocity matching and phase velocity mismatch conditions, overcoming the problem of insufficient resolution in nonlinear ultrasonic testing for fatigue damage. It enables the determination of the remaining fatigue life of components in later service stages of fatigue damage, achieving full-life-cycle detection and evaluation of fatigue damage.

[0063] Example 2: Fatigue life determination system for service components, such as Figure 1 As shown, including

[0064] Signal generator 1, power amplifier 2, excitation transducer 3, first ramp 4, second ramp 6, receiving transducer 7, oscilloscope 8, and measurement and control module;

[0065] The signal generator 1 is used to control the service components (i.e., Figure 1 The structure under test shown in the figure 5) emits a nonlinear ultrasonic guided wave with a matching fundamental frequency and second harmonic phase velocity, or emits a nonlinear ultrasonic guided wave with a mismatched fundamental frequency and second harmonic phase velocity.

[0066] The power amplifier 2 is used to amplify the nonlinear ultrasonic guided wave;

[0067] The excitation transducer 3 is used to excite the service component under test according to the nonlinear ultrasonic guided wave;

[0068] The receiving transducer 7 is used to receive signals received by the service component under set excitation conditions;

[0069] The oscilloscope 8 is used to display and store signals received by the in-service component;

[0070] The first inclined block 4 and the second inclined block 6 are used to adjust the excitation angle of the excitation transducer and the receiving ultrasonic guided wave of the transducer, respectively.

[0071] The measurement and control module is used to calculate the current first nonlinear parameter based on the signal received by the service component under nonlinear ultrasonic guided wave excitation conditions with phase velocity matching of the fundamental frequency and second harmonic frequency stored in the oscilloscope.

[0072] If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have a unique intersection point, then the remaining fatigue life of the corresponding service component is determined based on this intersection point.

[0073] If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have two intersection points, the signal received by the service component under the nonlinear ultrasonic guided wave excitation condition of phase velocity mismatch between the fundamental frequency and the second harmonic frequency, acquired by the oscilloscope, is obtained, and the current second nonlinear parameter is calculated. If the intersection point of the second nonlinear parameter and the second nonlinear ultrasonic calibration curve is the same as the intersection point of the first nonlinear parameter and the first nonlinear ultrasonic calibration curve, the same remaining fatigue life is determined as the remaining fatigue life of the service component.

[0074] The measurement and control module is located on the computer 9 and communicates with the oscilloscope 8 to obtain the signal received by the service component under the set excitation conditions.

[0075] The test and evaluation object is an engineering machinery component with a thickness of 5mm. The component material is Q460 high-strength steel with a density of 7827.81kg / m3, a longitudinal wave velocity of 5938.76m / s, a transverse wave velocity of 3248.43m / s, and a yield strength of 560MPa.

[0076] 1) Based on the density of the component material, the longitudinal wave velocity, and the transverse wave velocity, plot the dispersion curve of the 5mm thick component, such as... Figure 3 As shown. In this example, the selected excitation frequency under phase velocity matching is 100kHz, and the excitation mode is S0 mode. From the phase velocity dispersion curve, it can be seen that the phase velocity of the 100kHz fundamental frequency S0 mode is 5424m / s, and the phase velocity of the 200kHz second harmonic S0 mode is 5384m / s. The phase velocity matching degree between the two is 0.74%, which satisfies the phase velocity matching condition.

[0077] The excitation frequency under phase velocity mismatch is 300 kHz, and the excitation mode is S0 mode. From the phase velocity dispersion curve, it can be seen that the phase velocity of the S0 mode with a fundamental frequency of 300 kHz is 5282 m / s, and the phase velocity of the S0 mode with a second harmonic frequency of 600 kHz is 3456 m / s. The phase velocity matching degree between the two is 34.57%, which satisfies the phase velocity mismatch condition.

[0078] 2) According to Figure 1 A fatigue life measurement system was built using a measuring device. A transducer with a center frequency that meets the fundamental frequency excitation requirement was selected as the excitation transducer 3, and a transducer with a center frequency that meets the second harmonic reception requirement was selected as the receiving transducer 7. The excitation angle of the guided wave was calculated according to Snell's law.

[0079] sinθ=c wedge-L / c (f，l)

[0080] In the formula c wedge-L Let c be the volume longitudinal wave velocity of the oblique block material. (f,l) It is the phase velocity of the fundamental frequency Lamb wave of the L-mode with frequency f to be excited. The first inclined block 4 and the second inclined block 6 are made of plexiglass, the longitudinal wave velocity is 2700 m / s, the angle under the phase velocity matching condition is 30°, and the angle under the phase velocity mismatch condition is 31°.

[0081] 3) Nonlinear ultrasonic measurement of the component under phase velocity matching conditions is performed as follows: An ultrasonic signal with a frequency of 100kHz generated by function generator 1 is amplified by power amplifier 2, and then transmitted to excitation transducer 3. With the assistance of inclined block 4, an ultrasonic guided wave is excited in the structure under test 5. Receiving transducer 7, installed on the other side, detects the weak voltage ultrasonic signal propagating through the component under test and sends it to oscilloscope 8 for display and storage. Computer 9 performs a Fourier transform on the signal stored in oscilloscope 8 to obtain the fundamental frequency amplitude A1 at 100kHz and the second harmonic amplitude A2 at 200kHz. Figure 4 As shown, the ultrasonic nonlinear parameters are calculated.

[0082] 4) The nonlinear parameter β obtained under phase velocity matching conditions is compared with the nonlinear ultrasonic calibration curve of the fatigue damage over the entire service life of the component under phase velocity matching conditions. Figure 5 If β = β2, then the life fraction of the measured component is N1%, and the measurement ends.

[0083] 5) If β = β4, the calibration curve under phase velocity matching has two intersection points, resulting in two lifetime fractions, N2% and N3%. Nonlinear ultrasonic measurement under phase velocity mismatch conditions is required, with the measurement steps being the same as under phase velocity matching. If the nonlinear parameter β = β1 under phase velocity mismatch conditions, the lifetime fraction of the tested component is N2%; if the nonlinear parameter β = β3 under phase velocity mismatch conditions, the lifetime fraction of the tested component is N3%, and the measurement ends.

[0084] The fatigue life measurement system used in this embodiment can detect and evaluate fatigue damage of components throughout their entire life cycle without damaging the components being tested, meeting the requirements for online estimation of performance degradation and remaining service life during component service.

[0085] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for determining the fatigue life of service components, characterized in that, include: For in-service components, nonlinear ultrasonic guided waves with phase velocities matched at the fundamental frequency and second harmonic are emitted; Collect the signals received by the in-service components and calculate the current first nonlinear parameter; If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have a unique intersection point, then the remaining fatigue life of the corresponding service component is determined based on this intersection point. If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have two intersection points, then transmit a nonlinear ultrasonic guided wave with a phase velocity mismatch between the fundamental frequency and the second harmonic frequency; collect the signal currently received by the service component and calculate the current second nonlinear parameter; if the intersection point of the second nonlinear parameter and the second nonlinear ultrasonic calibration curve is the same as the remaining fatigue life corresponding to the intersection point of the first nonlinear parameter and the first nonlinear ultrasonic calibration curve, then the same remaining fatigue life is determined as the remaining fatigue life of the service component. The first nonlinear ultrasonic calibration curve represents the relationship between the fatigue damage lifespan of a service component and the nonlinear parameter under excitation conditions where the fundamental frequency and second harmonic phase velocities are matched; the second nonlinear ultrasonic calibration curve represents the relationship between the fatigue damage lifespan of a service component and the nonlinear parameter under excitation conditions where the fundamental frequency and second harmonic phase velocities are mismatched.

2. The method for determining the fatigue life of service components according to claim 1, characterized in that, The entire life cycle of fatigue damage is represented by fatigue life fractions at equal intervals.

3. The method for determining the fatigue life of service components according to claim 1, characterized in that, The calculation of the first and second nonlinear parameters is expressed as follows: ， in It is a nonlinear parameter. A1 is the amplitude of the second harmonic signal received by the in-service component, and A2 is the amplitude of the fundamental frequency signal received by the in-service component.

4. The method for determining the fatigue life of service components according to claim 1, characterized in that, The method for determining phase velocity matching between the fundamental frequency and the second harmonic is as follows: The phase velocity matching degree is calculated as follows: ,in, and They are the basebands and double frequency phase velocity; The condition for phase velocity matching between the fundamental frequency and the second harmonic is: D is less than or equal to a preset value; The condition for phase velocity mismatch between the fundamental frequency and the second harmonic is that D is greater than the preset value.

5. A fatigue life determination system for service components, characterized in that, include: Signal generator, power amplifier, excitation transducer, first ramp, second ramp, receiving transducer, oscilloscope, and measurement control module; The signal generator is used to transmit nonlinear ultrasonic guided waves with matching fundamental and second harmonic phase velocities to the service component, or to transmit nonlinear ultrasonic guided waves with mismatched fundamental and second harmonic phase velocities. The power amplifier is used to amplify the nonlinear ultrasonic guided wave; The excitation transducer is used to excite the service component under test according to the nonlinear ultrasonic guided wave; The receiving transducer is used to receive signals received by the service component under set excitation conditions; The oscilloscope is used to display and store signals received by the in-service component; The first and second inclined blocks are used to adjust the excitation angle of the excitation transducer and the receiving ultrasonic guided wave of the transducer, respectively. The measurement and control module is used to calculate the current first nonlinear parameter based on the signal received by the service component under nonlinear ultrasonic guided wave excitation conditions with phase velocity matching of the fundamental frequency and second harmonic frequency stored in the oscilloscope. If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have a unique intersection point, then the remaining fatigue life of the corresponding service component is determined based on this intersection point. If the first nonlinear parameter and the first nonlinear ultrasonic calibration curve have two intersection points, the signal received by the service component under nonlinear ultrasonic guided wave excitation conditions with mismatched fundamental and second harmonic phase velocities, acquired by the oscilloscope, is obtained, and the current second nonlinear parameter is calculated. If the intersection point of the second nonlinear parameter and the second nonlinear ultrasonic calibration curve corresponds to the same remaining fatigue life as the intersection point of the first nonlinear parameter and the first nonlinear ultrasonic calibration curve, the same remaining fatigue life is determined as the remaining fatigue life of the service component. Here, the first nonlinear ultrasonic calibration curve represents the relationship between the total fatigue damage life cycle of the service component and the nonlinear parameter under excitation conditions with matched fundamental and second harmonic phase velocities; the second nonlinear ultrasonic calibration curve represents the relationship between the total fatigue damage life cycle of the service component and the nonlinear parameter under excitation conditions with mismatched fundamental and second harmonic phase velocities.

6. The fatigue life determination system for service components according to claim 5, characterized in that, The method for calculating the excitation angle of ultrasonic guided waves is as follows: ， in The excitation angle of the ultrasonic guided wave. The volume longitudinal wave velocity of the inclined block material. It is the phase velocity of the fundamental frequency Lamb wave of the l-mode to be excited at a frequency of f.

7. The fatigue life determination system for service components according to claim 5, characterized in that, The first and second inclined blocks are made of plexiglass.

8. The fatigue life determination system for service components according to claim 5, characterized in that, Two signal generators were built to transmit nonlinear ultrasonic guided waves under excitation conditions of matching fundamental and second harmonic phase velocities to service components, and to transmit nonlinear ultrasonic guided waves under excitation conditions of mismatched fundamental and second harmonic phase velocities.

9. The fatigue life determination system for service components according to claim 5, characterized in that, The measurement and control module is located on a computer and communicates with an oscilloscope to obtain the signals received by the service component under set excitation conditions.

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