A method for detecting fatigue life of a connecting terminal based on nonlinear ultrasonic sideband modulation

Abstract

The application discloses a kind of based on nonlinear ultrasonic sideband modulation's connecting terminal fatigue life prediction detection method, high-frequency ultrasonic probe and low-frequency vibration source are coupled in the wire harness end of plug-in electrical connecting terminal, high-frequency ultrasonic signal of frequency f1 and low-frequency vibration signal of frequency f2 are simultaneously applied to connecting terminal, f2<f1.Broadband ultrasonic receiving probe is coupled to connecting terminal, and response signal under the action of double-frequency excitation is collected.Spectrum analysis is carried out to response signal, sideband component f1±nf2 (n is integer) is identified on the both sides of f1, the peak amplitude of sideband component is extracted and the amplitude at f1 is extracted, and the ratio of the logarithm is calculated as sideband modulation index.The sideband modulation index is input into the correlation model of modulation index and residual plug-in life established by pre-accelerated plug-in fatigue test, and the residual plug-in life prediction value of connecting terminal is output, to realize early evaluation.

Description

Technical Field

[0001] This invention belongs to the field of electrical connector testing technology, specifically relating to a method for predicting and testing the fatigue life of connector terminals based on nonlinear ultrasonic sideband modulation. Background Technology

[0002] During repeated insertion and removal, the contact interface of the connector terminal is subjected to fretting friction, leading to the gradual accumulation of fretting wear and material plastic deformation, eventually causing contact failure. Accelerated life testing methods obtain statistical life distributions by conducting accelerated insertion and removal tests on terminal samples from the same batch, but this method can only provide batch statistics and cannot assess the actual remaining number of insertions and removals for an individual in-service terminal. Contact resistance monitoring methods determine the terminal condition by continuously measuring contact resistance, but they are not sensitive to micro-plastic deformation and fretting wear in the early stages of fatigue. Observable changes in resistance only occur when damage accumulates to the point of significant loss of contact pressure or large-area rupture of the oxide film, making early assessment impossible. Summary of the Invention

[0003] The purpose of this invention is to provide a method for predicting and detecting the fatigue life of connection terminals based on nonlinear ultrasonic sideband modulation, so as to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for predicting and detecting the fatigue life of connection terminals based on nonlinear ultrasonic sideband modulation, comprising the following steps: A high-frequency ultrasonic excitation signal and a low-frequency vibration signal are applied to a pluggable electrical connection terminal, wherein the frequency of the high-frequency ultrasonic excitation signal is f1, the frequency of the low-frequency vibration signal is f2, and f2 < f1; wherein the low-frequency vibration signal is coupled to the wire harness end of the connection terminal. The response signal of the connection terminal under the combined action of the high-frequency ultrasonic excitation signal and the low-frequency vibration signal is collected. Spectral analysis is performed on the response signal to extract the amplitudes of the sideband components f1±nf2 on both sides of frequency f1, where n is an integer, and the logarithm of the ratio of the sideband peak amplitude to the fundamental frequency amplitude is used as the sideband modulation index. The sideband modulation index is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model, and the remaining insertion / removal lifetime prediction value of the connection terminal is output.

[0005] Preferably, the sideband modulation index is calculated using the following formula: MI = 20·log10(A_s / A_0), Where MI is the sideband modulation index, A_s is the peak amplitude of the sideband component, and A_0 is the fundamental frequency amplitude at frequency f1.

[0006] Preferably, the frequency range of the low-frequency vibration signal is 10Hz to 500Hz.

[0007] Preferably, after calculating the sideband modulation index, the method further includes an environmental compensation step: extracting a preset reference nonlinear feature from the response signal, performing differential processing on the sideband modulation index and the reference nonlinear feature to obtain an effective modulation index after environmental compensation, which is then input into the correlation model.

[0008] Preferably, in the environmental compensation step, the effective modulation index is calculated using the following formula: MI_eff = MI - k·MI_ref, Where MI is the sideband modulation index, MI_ref is the modulation index corresponding to the reference nonlinear characteristic, and k is the calibration coefficient.

[0009] Preferably, the reference nonlinear characteristic quantity is selected from the inherent nonlinear response of the connecting terminal housing material, or the nonlinear response of a reference calibration element integrated on the surface of the terminal housing.

[0010] Preferably, the method for establishing the modulation index-remaining insertion and removal life correlation model is as follows: Select a sample terminal of the same model as the connection terminal to be tested, conduct an accelerated insertion and removal fatigue test, collect the modulation index of the sample terminal at predetermined insertion and removal times, until the sample terminal reaches the failure standard, establish a standard curve of the modulation index changing with the number of insertions and removals, and establish a regression model of the modulation index and the remaining number of insertions and removals based on the standard curve.

[0011] Preferably, the frequency f1 of the high-frequency ultrasonic excitation signal is in the range of 1MHz to 20MHz, and the high-frequency ultrasonic excitation signal and the broadband ultrasonic receiving probe are coupled to the housing surface or wire harness end of the connecting terminal through a spring clamp or constant pressure mechanism.

[0012] Preferably, the sideband components are selected from first-order sidebands f1±f2, or from a weighted combination of amplitudes of multiple-order sidebands f1±nf2, and the weighting method is calculated according to the following formula: A_s = ∑w_n·A_n, Where A_n is the peak amplitude of the nth sideband, and w_n is the weighting coefficient of the nth sideband.

[0013] Preferably, the high-frequency ultrasonic excitation probe and the broadband ultrasonic receiving probe are coupled to the wire harness end of the connecting terminal using an annular clamp, and the annular clamp holds the wire harness with a constant clamping force.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention first couples a high-frequency ultrasonic excitation probe and a low-frequency vibration excitation source to the wiring harness end of a pluggable electrical connection terminal. A high-frequency ultrasonic excitation signal with frequency f1 and a low-frequency vibration signal with frequency f2 (where f2 is less than f1) are simultaneously applied to the connection terminal. A broadband ultrasonic receiving probe is coupled to the connection terminal to acquire the response signal of the connection terminal under the combined action of dual-frequency excitation. Spectral analysis is performed on the response signal, identifying sideband components f1±nf2 (where n is an integer) on both sides of frequency f1. The peak amplitude of the sideband components is extracted, and the fundamental frequency amplitude at frequency f1 is extracted. The logarithm of the ratio of the sideband peak amplitude to the fundamental frequency amplitude is calculated as the sideband modulation index. The sideband modulation index is input into a correlation model between the modulation index and remaining pluggable life, pre-established through accelerated pluggable fatigue testing. The model outputs a predicted value of the remaining pluggable life of the connection terminal, enabling early assessment. Attached Figure Description

[0015] Figure 1 This is a timing diagram of the ring clamp coupling excitation / receiving probe of the present invention.

[0016] Figure 2 This is a schematic diagram of the process for establishing the modulation index-remaining insertion / removal lifetime correlation model of the present invention.

[0017] Figure 3 This is a schematic diagram of the process for calculating the effective modulation index of environmental compensation according to the present invention.

[0018] Figure 4 This is a schematic diagram of the process for calculating the sideband modulation index of this invention.

[0019] Figure 5 This is a schematic diagram of the spectrum analysis and sideband identification flow of the present invention.

[0020] Figure 6 This is a timing diagram of the dual-frequency excitation and response acquisition of the present invention.

[0021] Figure 7 This is a flowchart illustrating the present invention.

[0022] Figure 8 This is a schematic diagram of the multi-level sideband weighted combination processing of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0024] A method for predicting and detecting the fatigue life of connection terminals based on nonlinear ultrasonic sideband modulation includes the following steps: A high-frequency ultrasonic excitation signal and a low-frequency vibration signal are applied to the pluggable electrical connection terminal. The frequency of the high-frequency ultrasonic excitation signal is f1, and the frequency of the low-frequency vibration signal is f2, where f2 < f1. The low-frequency vibration signal is coupled to the wire harness end of the connection terminal. The response signal of the connection terminal under the combined action of high-frequency ultrasonic excitation signal and low-frequency vibration signal is acquired; Spectral analysis is performed on the response signal to extract the amplitudes of the sideband components f1±nf2 on both sides of frequency f1, where n is an integer. The logarithm of the ratio of the sideband peak amplitude to the fundamental frequency amplitude is used as the sideband modulation index. The sideband modulation index is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model, and the predicted remaining insertion / removal lifetime of the connection terminal is output. The sideband modulation index is calculated using the following formula: MI = 20·log10(A_s / A_0), Where MI is the sideband modulation index, A_s is the peak amplitude of the sideband component, and A_0 is the fundamental frequency amplitude at frequency f1. The frequency range of the low-frequency vibration signal is 10Hz to 500Hz. After calculating the sideband modulation index, an environmental compensation step is also included: extracting a preset reference nonlinear characteristic quantity from the response signal, performing differential processing between the sideband modulation index and the reference nonlinear characteristic quantity to obtain the environmentally compensated effective modulation index, which is used as input to the correlation model. In the environmental compensation step, the effective modulation index is calculated according to the following formula: MI_eff = MI - k·MI_ref, Where MI is the sideband modulation index, MI_ref is the modulation index corresponding to the reference nonlinear characteristic, and k is the calibration coefficient. The reference nonlinear characteristic is selected from the inherent nonlinear response of the connection terminal housing material, or the nonlinear response of the reference calibration element integrated on the surface of the terminal housing. The method for establishing the modulation index-remaining insertion and removal life correlation model is as follows: Select a sample terminal of the same model as the connection terminal under test, conduct accelerated insertion and removal fatigue test, collect the modulation index of the sample terminal at predetermined insertion and removal times until the sample terminal reaches the failure criterion, establish a standard curve of the modulation index changing with the number of insertion and removal times, and establish a regression model of the modulation index and the remaining insertion and removal times based on the standard curve. The frequency f1 of the high-frequency ultrasonic excitation signal is in the range of 1MHz to 20MHz. The high-frequency ultrasonic excitation signal and the broadband ultrasonic receiving probe are coupled to the housing surface or wire harness end of the connection terminal through a spring clamp or constant pressure mechanism. The sideband component is selected as the first-order sideband f1±f2, or the amplitude weighted combination of multiple-order sidebands f1±nf2 is selected. The weighted combination method is calculated according to the following formula: A_s = ∑w_n·A_n, Where A_n is the peak amplitude of the nth sideband, and w_n is the weighting coefficient of the nth sideband. The high-frequency ultrasonic excitation probe and the broadband ultrasonic receiving probe are coupled to the wire harness end of the connection terminal using a ring clamp, and the ring clamp holds the wire harness with a constant clamping force.

[0025] Based on the above technical solution, Example Six: In this embodiment, when performing environmental compensation on pluggable electrical connection terminals, a preset reference nonlinear characteristic is extracted from the spectrum of the response signal. This reference nonlinear characteristic corresponds to a reference modulation index MI_ref, which is obtained through pre-calibration. During calibration, with the connection terminal in its initial unplugged state, a high-frequency ultrasonic excitation signal and a low-frequency vibration signal are applied. The response signal is collected, and the sideband modulation index is calculated. This initial sideband modulation index is recorded as MI_ref. Simultaneously, a calibration coefficient k is determined. This calibration coefficient k is obtained through an environmental variable variation experiment. In the experiment, temperature or humidity conditions are changed, and the drift of the sideband modulation index MI with changes in environmental variables is measured. The drift is then linearly fitted to the reference modulation index MI_ref, and the fitting slope is used as the calibration coefficient k.

[0026] When predicting the fatigue life of the connection terminal under test, the sideband modulation index MI is first calculated according to the aforementioned steps. Then, the modulation index corresponding to the reference nonlinear characteristic is extracted from the response signal acquired in the same session. This reference nonlinear characteristic is selected as the fundamental frequency amplitude at frequency f1 or the amplitude of a specific order sideband component in the response signal. The sideband modulation index MI, the reference modulation index MI_ref, and the calibration coefficient k are substituted into the effective modulation index calculation formula MI_eff = MI - k·MI_ref, and subtraction and multiplication operations are performed to obtain the environmentally compensated effective modulation index MI_eff. This effective modulation index MI_eff eliminates the nonlinear characteristic drift caused by environmental factors and only reflects the nonlinear modulation effect caused by fretting wear and plastic deformation accumulation at the connection terminal contact interface.

[0027] The effective modulation index MI_eff is input into a pre-established correlation model between modulation index and remaining insertion / removal lifetime. This correlation model is established through accelerated insertion / removal fatigue testing. During the test, the same batch of connector samples undergoes repeated insertion / removal operations. The effective modulation index MI_eff is measured at different insertion / removal counts, and the correspondence between the number of insertions / removals and the effective modulation index MI_eff is recorded, forming a mapping curve or lookup table. The model receives the effective modulation index MI_eff as input, matches the corresponding number of insertions / removals in the mapping curve or lookup table, and outputs the predicted remaining insertion / removal lifetime of the connector. The predicted remaining insertion / removal lifetime represents the number of insertions / removals the connector can withstand under the current damage condition. Example

[0028] In this embodiment, a high-frequency ultrasonic excitation signal and a low-frequency vibration signal are first applied to the pluggable electrical connection terminal. The frequency of the high-frequency ultrasonic excitation signal is f1, and the frequency of the low-frequency vibration signal is f2, where f2 is less than f1. The low-frequency vibration signal is coupled to the wire harness end of the connection terminal. The response signal of the connection terminal under the combined action of the high-frequency ultrasonic excitation signal and the low-frequency vibration signal is collected. Spectral analysis is performed on the response signal to extract the amplitude of the sideband components f1±nf2 on both sides of frequency f1, where n is an integer. The logarithm of the ratio of the peak amplitude of the sideband to the fundamental frequency amplitude is used as the sideband modulation index MI.

[0029] After calculating the sideband modulation index MI, an environmental compensation step is performed. A preset reference nonlinear characteristic is extracted from the response signal. This reference nonlinear characteristic is selected from the inherent nonlinear response of the connection terminal housing material or the nonlinear response of a reference calibration element integrated on the surface of the terminal housing. When the reference nonlinear characteristic is selected from the inherent nonlinear response of the connection terminal housing material, during the calibration stage without applying a low-frequency vibration signal, a high-frequency ultrasonic excitation signal with frequency f1 is applied to the connection terminal alone. The nonlinear response signal of the housing material itself is acquired, and the amplitude of the harmonic components or specific frequency components caused by the inherent nonlinearity of the housing material is extracted from the spectrum of this response signal. The corresponding reference modulation index MI_ref is then calculated. When the reference nonlinear characteristic is selected from the nonlinear response of the reference calibration element integrated on the surface of the terminal housing, the reference calibration element is a piezoelectric ceramic sheet or magnetostrictive sheet with known nonlinear characteristics, which is fixed to the surface of the terminal housing in advance by bonding or mechanical clamping. During the detection process, the reference calibration element is synchronously subjected to high-frequency ultrasonic excitation signal and low-frequency vibration signal along with the terminal housing. The characteristic frequency component generated by the reference calibration element is separated from the spectrum of the acquired response signal, the amplitude of the characteristic frequency component is extracted, and the corresponding reference modulation index MI_ref is calculated.

[0030] The effective modulation index MI_eff, after environmental compensation, is obtained by differential processing between the sideband modulation index MI_eff and the modulation index MI_ref corresponding to the reference nonlinear characteristic. The calculation formula is MI_eff = MI - k·MI_ref, where k is a calibration coefficient. The calibration coefficient k is determined through prior experiments. Under known environmental conditions, MI and MI_ref are measured at different temperatures or humidity levels, and the value of k is solved using linear regression to ensure that MI_eff is insensitive to environmental fluctuations. The effective modulation index MI_eff is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model, which outputs the predicted value of the remaining insertion / removal lifetime of the connection terminal. The modulation index-remaining insertion / removal lifetime correlation model is established through accelerated insertion / removal fatigue testing. Repeated insertion / removal operations are performed on connection terminal samples from the same batch. Response signals are collected at different insertion / removal counts, and the effective modulation index MI_eff is calculated. The correspondence between the number of insertion / removal counts and MI_eff is recorded, and a correlation model is formed by fitting these results. Example

[0031] In this embodiment, the frequency f1 of the high-frequency ultrasonic excitation signal is selected as 5MHz, and the frequency f2 of the low-frequency vibration signal is selected as 100Hz, where f2 is less than f1. The high-frequency ultrasonic excitation probe is coupled to the outer shell surface of the connecting terminal via a spring clamp, which provides a constant clamping force to maintain stable contact between the probe and the outer shell surface. The broadband ultrasonic receiving probe is coupled to the outer shell surface of the connecting terminal via another spring clamp, located at a different position on the outer shell surface than the high-frequency ultrasonic excitation probe. The low-frequency vibration excitation source is fixed to the wire harness end of the connecting terminal via a mechanical clamp, and a low-frequency vibration signal with a frequency of 100Hz is applied to the wire harness end.

[0032] A high-frequency ultrasonic excitation probe emits a continuous sinusoidal ultrasonic signal at a frequency of 5 MHz onto the surface of the connector terminal housing, while a low-frequency vibration excitation source simultaneously applies mechanical vibration at a frequency of 100 Hz to the wire harness end. Under the combined action of dual-frequency excitation, the nonlinear characteristics of the contact interface caused by fretting wear and plastic deformation are excited, generating modulation sideband components in the response signal. A broadband ultrasonic receiving probe acquires the response signal propagating from the housing surface, which includes a fundamental frequency of 5 MHz and sideband components generated by nonlinear modulation.

[0033] The acquired response signal is converted into a digital signal by a preamplifier and an analog-to-digital converter, and then sent to the spectrum analysis module. The spectrum analysis module performs a Fast Fourier Transform on the digital signal to obtain spectral data. The fundamental frequency peak amplitude at 5MHz is identified in the spectrum, and sideband components are searched around 5MHz. The sideband frequency is 5MHz ± n × 100Hz, where n is an integer from 1 to 5. The peak amplitude of each sideband component is extracted, and the ratio of the peak amplitude to the fundamental frequency amplitude is calculated. The natural logarithm of this ratio is taken as the modulation index of that sideband. The arithmetic mean of the modulation indices of each sideband is taken as the current sideband modulation index of the connection terminal.

[0034] The sideband modulation index is input into the modulation index-remaining insertion / removal lifetime correlation model. This model is pre-established through accelerated insertion / removal fatigue tests of the same type of connector and stored in the data processing unit. Based on the input modulation index value, the model outputs the corresponding predicted value of the remaining insertion / removal lifetime, which is expressed in terms of the number of insertions / removals. Example

[0035] In this embodiment, a high-frequency ultrasonic excitation signal and a low-frequency vibration signal are first applied to the pluggable electrical connection terminal. The frequency of the high-frequency ultrasonic excitation signal is f1, and the frequency of the low-frequency vibration signal is f2, where f2 is less than f1. The low-frequency vibration signal is coupled to the wire harness end of the connection terminal. The response signal of the connection terminal under the combined action of the high-frequency ultrasonic excitation signal and the low-frequency vibration signal is collected. Spectral analysis is performed on the response signal to extract the amplitude of the sideband components f1±nf2 on both sides of frequency f1, where n is an integer.

[0036] When the first-order sideband f1±f2 is selected, the peak amplitudes at frequencies f1+f2 and f1-f2 are directly extracted as characterization values ​​of the sideband components. The extracted first-order sideband peak amplitudes are compared with the fundamental frequency amplitude at frequency f1, and the logarithm of the ratio is calculated to obtain the sideband modulation index. The sideband modulation index is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model, and the model outputs the predicted value of the remaining insertion / removal lifetime of the connection terminal.

[0037] When using a weighted combination of amplitudes from multiple sidebands f1±nf2, the peak amplitudes of the sideband components of multiple orders are extracted, with n taking different integer values, such as n=1, 2, 3. For each order of sideband component, its peak amplitude A_n is recorded. The comprehensive sideband amplitude is calculated according to the weighted combination method A_s=∑w_n·A_n, where w_n is the weighting coefficient of the nth order sideband. The weighting coefficient w_n is predetermined based on the sensitivity of each order of sideband to fretting wear and plastic deformation of the contact interface; for example, the weight of the first-order sideband is set to 0.6, the weight of the second-order sideband to 0.3, and the weight of the third-order sideband to 0.1. The calculated comprehensive sideband amplitude A_s is compared with the fundamental frequency amplitude at frequency f1, and the logarithm of the ratio is calculated as the sideband modulation index. The sideband modulation index is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model, and the model outputs the predicted value of the remaining insertion / removal lifetime of the connection terminal. The modulation index-remaining insertion / removal lifetime correlation model was pre-established through accelerated insertion / removal fatigue tests. During the tests, different numbers of insertion / removal operations were applied to samples of the same type of terminals, and the sideband modulation index after each insertion / removal was recorded. The curve of the modulation index changing with the remaining insertion / removal lifetime was fitted to form the correlation model. Example

[0038] In this embodiment, a high-frequency ultrasonic excitation probe and a low-frequency vibration excitation source are first coupled to the wiring harness end of the pluggable electrical connection terminal. The high-frequency ultrasonic excitation probe applies a high-frequency ultrasonic excitation signal with a frequency of f1 to the connection terminal. The low-frequency vibration excitation source applies a low-frequency vibration signal with a frequency of f2 to the connection terminal, where the frequency range of f2 is set from 10Hz to 500Hz, and f2 is less than f1. The low-frequency vibration signal is coupled to the contact interface area of ​​the connection terminal through the wiring harness end.

[0039] A broadband ultrasonic receiver probe is coupled to the housing or wiring harness end of the connector terminal. The broadband ultrasonic receiver probe acquires the response signal of the connector terminal under the combined action of a high-frequency ultrasonic excitation signal and a low-frequency vibration signal. The response signal contains nonlinear modulation information of the connector terminal contact interface to the dual-frequency excitation.

[0040] Spectral analysis is performed on the acquired response signal. The spectral analysis process identifies sideband components f1±nf2 on both sides of frequency f1, where n is an integer. The peak amplitude of each sideband component is extracted. The fundamental frequency amplitude at frequency f1 is extracted. The ratio of the sideband peak amplitude to the fundamental frequency amplitude is calculated. The logarithm of this ratio is taken to obtain the sideband modulation index.

[0041] The calculated sideband modulation index is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model. This model is calibrated using accelerated insertion / removal fatigue tests on samples of the same type of connection terminal to establish a mapping relationship between the sideband modulation index and the remaining insertion / removal lifetime. The model outputs a predicted value for the remaining insertion / removal lifetime of the connection terminal. The predicted value for the remaining insertion / removal lifetime represents the number of insertions and removals that the connection terminal can continue to withstand under the current damage state.

[0042] Example 11: In this embodiment, a high-frequency ultrasonic excitation probe and a broadband ultrasonic receiving probe are first coupled to the wire harness end of the connecting terminal using ring clamps. The ring clamps hold the wire harness with a constant clamping force of 50 Newtons to ensure a stable acoustic coupling interface between the probe and the wire harness surface. The center frequency of the high-frequency ultrasonic excitation probe is 2.5 MHz, and the frequency response range of the broadband ultrasonic receiving probe is 0.5 MHz to 5 MHz. A low-frequency vibration excitation source is connected to the same wire harness end through an independent mechanical coupling device, and the low-frequency vibration excitation source generates a sinusoidal vibration signal with a frequency of 20 Hz.

[0043] A continuous sinusoidal excitation signal with a frequency of 2.5 MHz (f1) is applied to the high-frequency ultrasonic excitation probe, while a sinusoidal vibration signal with a frequency of 20 Hz (f2) is applied to the low-frequency vibration excitation source. The high-frequency ultrasonic excitation signal propagates along the metal conductor of the connecting terminal, while the low-frequency vibration signal is conducted to the contact interface area of ​​the connecting terminal through the wiring harness. Under the action of the low-frequency vibration, the contact interface of the connecting terminal undergoes periodic, minute opening and closing displacements, which modulate the propagation path length of the high-frequency ultrasonic signal and the contact stress state.

[0044] The broadband ultrasonic receiver probe acquires the response signal of the connection terminal under the combined action of dual-frequency excitation. The response signal contains a high-frequency carrier component and a modulation sideband component generated by the nonlinear effect of the contact interface. The acquired response signal is amplified by 40 dB by a preamplifier and then transmitted to the data acquisition system. The sampling rate of the data acquisition system is set to 10 MHz, and the sampling duration is 1 second.

[0045] The acquired response signal is subjected to a Fast Fourier Transform (FFT) to obtain spectral data. The fundamental frequency component with frequency f1 of 2.5 MHz is located in the spectrum, and its amplitude A0 is extracted. Sideband components with frequencies f1 ± nf2 are searched on both sides of the fundamental frequency component, where n is an integer (1, 2, or 3), identifying sideband components with frequencies of 2.5 MHz ± 20 Hz, 2.5 MHz ± 40 Hz, and 2.5 MHz ± 60 Hz. The peak amplitude An of each sideband component is extracted, and the ratio of the sideband peak amplitude An to the fundamental frequency amplitude A0 is calculated. The logarithm of this ratio, base 10, is taken to obtain the sideband modulation index M, calculated as M = log10(An / A0).

[0046] The calculated sideband modulation index M is input into a pre-established correlation model between the modulation index and remaining insertion / removal lifetime. This correlation model is established through accelerated insertion / removal fatigue testing. In the test, samples of the same type of connector are repeatedly inserted and removed. After every 50 insertions / removals, the sideband modulation index is measured, and the curve of the modulation index changing with the number of insertions / removals is recorded until contact failure occurs. The correlation model uses the modulation index as the input variable and the remaining insertion / removal lifetime as the output variable, and fits the test data using an exponential decay function. The model outputs a predicted value of the remaining insertion / removal lifetime of the connector, expressed as the remaining insertion / removal lifetime. Example

[0047] In this embodiment, a high-frequency ultrasonic excitation probe and a low-frequency vibration excitation source are first coupled to the wiring harness end of the pluggable electrical connection terminal. The high-frequency ultrasonic excitation probe generates a high-frequency ultrasonic excitation signal with frequency f1, and the low-frequency vibration excitation source generates a low-frequency vibration signal with frequency f2, where f2 is less than f1. The high-frequency ultrasonic excitation signal and the low-frequency vibration signal are simultaneously applied to the connection terminal, and the low-frequency vibration signal is coupled to the contact interface of the connection terminal through the wiring harness end. A broadband ultrasonic receiving probe is coupled to the connection terminal to acquire the response signal of the connection terminal under the combined action of dual-frequency excitation. Spectral analysis is performed on the acquired response signal, and sideband components f1±nf2 are identified on both sides of frequency f1 in the spectrum, where n is an integer. The peak amplitude A_s of the sideband components is extracted, and the fundamental frequency amplitude A_0 at frequency f1 is extracted. The sideband modulation index MI is calculated as MI = 20·log10(A_s / A_0). The calculated sideband modulation index (MI) is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model. This model is calibrated using accelerated insertion / removal fatigue tests on terminal samples from the same batch to establish a mapping relationship between the sideband modulation index and the remaining insertion / removal lifetime. The model outputs a predicted value for the remaining insertion / removal lifetime of the terminal, which represents the number of insertions and removals the terminal can withstand under the current damage condition. Example

[0048] In this embodiment, sample terminals of the same model as the connection terminal to be tested are selected, with a minimum of thirty sample terminals. These sample terminals are then installed in an accelerated insertion / removal fatigue testing device, which includes an insertion / removal drive mechanism and a contact resistance monitoring module. A high-frequency ultrasonic excitation signal and a low-frequency vibration signal are applied to the sample terminals. The frequency of the high-frequency ultrasonic excitation signal is f1, and the frequency of the low-frequency vibration signal is f2, where f2 is less than f1. The low-frequency vibration signal is coupled to the wire harness end of the sample terminal. The response signal of the sample terminal under the combined action of dual-frequency excitation is acquired. Spectral analysis is performed on the response signal, and the amplitudes of the sideband components f1±nf2 on both sides of frequency f1 are extracted, where n is an integer. The logarithm of the ratio of the sideband peak amplitude to the fundamental frequency amplitude is calculated and recorded as the initial modulation index.

[0049] The accelerated insertion and extraction fatigue test is initiated. The insertion and extraction drive mechanism performs insertion and extraction actions on the sample terminals at a constant rate, stopping after a predetermined number of insertions and extractions (set to 50). After each stop, a high-frequency ultrasonic excitation signal and a low-frequency vibration signal are repeatedly applied, the response signal is collected, and the modulation index is calculated. Simultaneously, the contact resistance of the sample terminals is measured. The accelerated insertion and extraction fatigue test is continued until the contact resistance of the sample terminals exceeds 200% of the initial contact resistance or the insertion and extraction force drops to 50% of the initial insertion and extraction force. At this point, the sample terminal is deemed to have met the failure criteria, and the total number of insertions and extractions at the time of failure is recorded.

[0050] Data on the modulation index (MCI) variation with the number of insertions and removals for all sample terminals were compiled. A standard curve was plotted with the number of insertions and removals on the x-axis and the MCI on the y-axis. The standard curve shows a monotonically increasing trend in the MCI with the number of insertions and removals. The growth rate of the MCI is low in the early stages of fatigue and increases significantly in the near-failure stage. Based on the standard curve, a regression model between the MCI and the remaining number of insertions and removals was established using the least squares method. The regression model expression is N_remain = a * exp(-b * MI) + c, where N_remain is the remaining number of insertions and removals, MI is the MCI, and a, b, and c are regression coefficients. The regression coefficient values ​​were determined by fitting the sample data. The regression model was stored as a MCI-remaining insertion and removal lifetime correlation model for subsequent prediction of the remaining insertion and removal lifetime of the connection terminal under test. Example

[0051] In this embodiment, after applying a high-frequency ultrasonic excitation signal and a low-frequency vibration signal to the pluggable electrical connection terminal and acquiring the response signal, spectral analysis is performed on the response signal to extract the amplitude of the sideband components f1±nf2 on both sides of frequency f1, where n is an integer. The logarithm of the ratio of the sideband peak amplitude to the fundamental frequency amplitude is used as the sideband modulation index. After calculating the sideband modulation index, an environmental compensation step is performed. In the environmental compensation step, a preset reference nonlinear characteristic is extracted from the spectrum of the response signal. This reference nonlinear characteristic corresponds to a fixed nonlinear source in the connection terminal structure that is independent of the fatigue state of the contact interface. The sideband modulation index and the reference nonlinear characteristic are differentially processed, and the reference nonlinear characteristic is subtracted from the sideband modulation index to obtain the environmentally compensated effective modulation index. This effective modulation index eliminates common-mode nonlinear interference introduced by temperature fluctuations, changes in wire harness clamping force, or differences in probe coupling pressure. The effective modulation index is input into a pre-established modulation index-remaining insertion / removal life correlation model, which is constructed based on the mapping relationship between the effective modulation index and the remaining insertion / removal times in accelerated insertion / removal fatigue tests. The correlation model outputs a predicted value for the remaining insertion and removal life of the connection terminals, which reflects the cumulative degree of fretting wear and plastic deformation at the contact interface. Example

[0052] In this embodiment, a high-frequency ultrasonic excitation probe is first coupled to the wiring harness end of a pluggable electrical connection terminal, and a high-frequency ultrasonic excitation signal with a frequency of f1 is applied to the connection terminal. A low-frequency vibration excitation source is coupled to the same wiring harness end, and a low-frequency vibration signal with a frequency of f2 (f2 is less than f1) is applied to the connection terminal. The high-frequency ultrasonic excitation signal and the low-frequency vibration signal act simultaneously on the connection terminal, and the low-frequency vibration signal is transmitted to the contact interface area of ​​the connection terminal through the wiring harness end.

[0053] A broadband ultrasonic receiver probe is coupled to the wire harness end or housing surface of the connector terminal to acquire the response signal of the connector terminal under the combined action of a high-frequency ultrasonic excitation signal and a low-frequency vibration signal. The response signal contains the nonlinear modulation information of the connector terminal contact interface to the dual-frequency excitation.

[0054] Spectral analysis is performed on the acquired response signal to locate the fundamental frequency component at frequency f1. Sideband components f1±nf2 (where n is an integer) are identified on both sides of frequency f1. The peak amplitude of each sideband component is extracted, and the fundamental frequency amplitude at frequency f1 is also extracted. The ratio of the sideband peak amplitude to the fundamental frequency amplitude is calculated, and the logarithm of this ratio is taken to obtain the sideband modulation index.

[0055] The sideband modulation index is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model. This model is established through accelerated insertion / removal fatigue testing. In the test, different numbers of insertion / removal operations are applied to samples of the same type of connector, and the sideband modulation index of each sample is measured at the corresponding number of insertion / removal operations. The total number of insertion / removal operations when contact failure occurs is recorded, establishing a mapping relationship between the modulation index and the remaining insertion / removal lifetime. The model receives the sideband modulation index as input and outputs a predicted value of the remaining insertion / removal lifetime of the connector. The predicted value of the remaining insertion / removal lifetime characterizes the number of insertion / removal operations that the connector can continue to withstand under the current damage state.

[0056] Example 12: In this embodiment, a high-frequency ultrasonic excitation signal and a low-frequency vibration signal are first applied to the pluggable electrical connection terminal. The frequency f1 of the high-frequency ultrasonic excitation signal is selected as 3 MHz, and the frequency f2 of the low-frequency vibration signal is selected as 80 Hz, where f2 is less than f1. The high-frequency ultrasonic excitation probe is coupled to the surface of the connection terminal housing via a spring clamp, which applies a constant contact pressure of 15 Newtons. Ultrasonic coupling agent is applied to the probe tip to eliminate air gaps. The low-frequency vibration excitation source is fixed to the wire harness end of the connection terminal via a mechanical clamp, with the clamping force set to 30 Newtons. The vibration excitation source generates sinusoidal displacement vibration with a peak amplitude of 50 micrometers. A broadband ultrasonic receiving probe is coupled to the surface of the housing via another spring clamp, with a distance of 20 mm between it and the excitation probe. The frequency response range of the receiving probe is 0.5 MHz to 10 MHz.

[0057] A high-frequency ultrasonic excitation probe emits a continuous sinusoidal ultrasonic signal at a frequency of 3 MHz to the connection terminal, while a low-frequency vibration excitation source synchronously applies 80 Hz mechanical vibration to the wire harness end. Under the action of low-frequency vibration, the contact interface of the connection terminal undergoes periodic micro-displacement. The contact area and contact stress of the contact interface change with the vibration period, and this change produces a nonlinear modulation effect on the propagation of the high-frequency ultrasonic signal. A broadband ultrasonic receiving probe acquires the response signal propagating from the outer shell surface. The response signal contains a 3 MHz fundamental frequency component and sideband components generated by the nonlinear modulation of the contact interface. The acquired response signal is amplified by 30 dB by a preamplifier and then converted into a digital signal by an analog-to-digital converter at a sampling rate of 20 MHz for a sampling time of 0.5 seconds.

[0058] Perform a Fast Fourier Transform (FFT) on the digital signal to obtain the spectral data. Locate the fundamental frequency component at 3 MHz in the spectrum and extract its amplitude A_0. Search for sideband components with frequencies of 3 MHz ± n × 80 Hz on both sides of the fundamental frequency component, where n is an integer of 1, 2, or 3. Identify sideband components with frequencies of 3 MHz ± 80 Hz, 3 MHz ± 160 Hz, and 3 MHz ± 240 Hz. Extract the peak amplitude A_n of each sideband component, calculate the ratio of each sideband peak amplitude to the fundamental frequency amplitude, take the logarithm to base 10 of this ratio, and multiply by 20 to obtain the modulation index of each sideband. Use the first-order sideband modulation index as the current sideband modulation index MI of the connection terminal, MI = 20·log10(A_1 / A_0).

[0059] The sideband modulation index (MI) is input into a pre-established correlation model of modulation index and remaining insertion / removal life. The model is established as follows: Thirty sample terminals of the same model as the terminals under test are selected and installed in an accelerated insertion / removal fatigue testing device. The device includes a servo motor-driven insertion / removal mechanism and a four-wire contact resistance measurement module. A 3 MHz high-frequency ultrasonic excitation signal and an 80 Hz low-frequency vibration signal are applied to the sample terminals. Initial response signals are acquired and the initial modulation index is calculated. Insertion / removal operations are initiated at a rate of 15 times per minute. After every 50 insertions / removals, the process is paused, and the dual-frequency excitation is repeated while acquiring response signals, calculating the modulation index, and simultaneously measuring the contact resistance. Failure is determined when the contact resistance of the sample terminal exceeds 200% of the initial value, and the total number of insertions / removals at the time of failure is recorded. The modulation index data of the thirty sample terminals as a function of the number of insertions / removals is summarized, and a modulation index variation curve is plotted with the number of insertions / removals on the x-axis and the modulation index on the y-axis. The data is fitted using the exponential function N_remain=a·exp(-b·MI)+c at least squares to determine the coefficients a, b, and c, thus obtaining the mapping relationship between the modulation index and the remaining insertion / removal counts. This mapping relationship is stored as an association model. The association model receives the sideband modulation index MI as input, matches the corresponding remaining insertion / removal counts in the mapping relationship, and outputs the predicted value of the remaining insertion / removal lifetime of the connection terminal, expressed in terms of the remaining insertion / removal counts. Example

[0060] In this embodiment, when performing environmental compensation on pluggable electrical connection terminals, a preset reference nonlinear characteristic is extracted from the spectrum of the response signal. This reference nonlinear characteristic corresponds to a reference modulation index MI_ref, which is obtained through pre-calibration. During calibration, with the connection terminal in its initial unplugged state, a high-frequency ultrasonic excitation signal and a low-frequency vibration signal are applied. The response signal is collected, and the sideband modulation index is calculated. This initial sideband modulation index is recorded as MI_ref. Simultaneously, a calibration coefficient k is determined. This calibration coefficient k is obtained through an environmental variable variation experiment. In the experiment, temperature or humidity conditions are changed, and the drift of the sideband modulation index MI with changes in environmental variables is measured. The drift is then linearly fitted to the reference modulation index MI_ref, and the fitting slope is used as the calibration coefficient k.

[0061] When predicting the fatigue life of the connection terminal under test, the sideband modulation index MI is first calculated according to the aforementioned steps. Then, the modulation index corresponding to the reference nonlinear characteristic is extracted from the response signal acquired in the same session. This reference nonlinear characteristic is selected as the fundamental frequency amplitude at frequency f1 or the amplitude of a specific order sideband component in the response signal. The sideband modulation index MI, the reference modulation index MI_ref, and the calibration coefficient k are substituted into the effective modulation index calculation formula MI_eff = MI - k·MI_ref, and subtraction and multiplication operations are performed to obtain the environmentally compensated effective modulation index MI_eff. This effective modulation index MI_eff eliminates the nonlinear characteristic drift caused by environmental factors and only reflects the nonlinear modulation effect caused by fretting wear and plastic deformation accumulation at the connection terminal contact interface.

[0062] The effective modulation index MI_eff is input into a pre-established correlation model between modulation index and remaining insertion / removal lifetime. This correlation model is established through accelerated insertion / removal fatigue testing. During the test, the same batch of connector samples undergoes repeated insertion / removal operations. The effective modulation index MI_eff is measured at different insertion / removal counts, and the correspondence between the number of insertions / removals and the effective modulation index MI_eff is recorded, forming a mapping curve or lookup table. The model receives the effective modulation index MI_eff as input, matches the corresponding number of insertions / removals in the mapping curve or lookup table, and outputs the predicted remaining insertion / removal lifetime of the connector. The predicted remaining insertion / removal lifetime represents the number of insertions / removals the connector can withstand under the current damage condition. Example

[0063] In this embodiment, a high-frequency ultrasonic excitation signal and a low-frequency vibration signal are first applied to the pluggable electrical connection terminal. The frequency of the high-frequency ultrasonic excitation signal is f1, and the frequency of the low-frequency vibration signal is f2, where f2 is less than f1. The low-frequency vibration signal is coupled to the wire harness end of the connection terminal. The response signal of the connection terminal under the combined action of the high-frequency ultrasonic excitation signal and the low-frequency vibration signal is collected. Spectral analysis is performed on the response signal to extract the amplitude of the sideband components f1±nf2 on both sides of frequency f1, where n is an integer. The logarithm of the ratio of the peak amplitude of the sideband to the fundamental frequency amplitude is used as the sideband modulation index MI.

[0064] After calculating the sideband modulation index MI, an environmental compensation step is performed. A preset reference nonlinear characteristic is extracted from the response signal. This reference nonlinear characteristic is selected from the inherent nonlinear response of the connection terminal housing material or the nonlinear response of a reference calibration element integrated on the surface of the terminal housing. When the reference nonlinear characteristic is selected from the inherent nonlinear response of the connection terminal housing material, during the calibration stage without applying a low-frequency vibration signal, a high-frequency ultrasonic excitation signal with frequency f1 is applied to the connection terminal alone. The nonlinear response signal of the housing material itself is acquired, and the amplitude of the harmonic components or specific frequency components caused by the inherent nonlinearity of the housing material is extracted from the spectrum of this response signal. The corresponding reference modulation index MI_ref is then calculated. When the reference nonlinear characteristic is selected from the nonlinear response of the reference calibration element integrated on the surface of the terminal housing, the reference calibration element is a piezoelectric ceramic sheet or magnetostrictive sheet with known nonlinear characteristics, which is fixed to the surface of the terminal housing in advance by bonding or mechanical clamping. During the detection process, the reference calibration element is synchronously subjected to high-frequency ultrasonic excitation signal and low-frequency vibration signal along with the terminal housing. The characteristic frequency component generated by the reference calibration element is separated from the spectrum of the acquired response signal, the amplitude of the characteristic frequency component is extracted, and the corresponding reference modulation index MI_ref is calculated.

[0065] The effective modulation index MI_eff, after environmental compensation, is obtained by differential processing between the sideband modulation index MI_eff and the modulation index MI_ref corresponding to the reference nonlinear characteristic. The calculation formula is MI_eff = MI - k·MI_ref, where k is a calibration coefficient. The calibration coefficient k is determined through prior experiments. Under known environmental conditions, MI and MI_ref are measured at different temperatures or humidity levels, and the value of k is solved using linear regression to ensure that MI_eff is insensitive to environmental fluctuations. The effective modulation index MI_eff is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model, which outputs the predicted value of the remaining insertion / removal lifetime of the connection terminal. The modulation index-remaining insertion / removal lifetime correlation model is established through accelerated insertion / removal fatigue testing. Repeated insertion / removal operations are performed on connection terminal samples from the same batch. Response signals are collected at different insertion / removal counts, and the effective modulation index MI_eff is calculated. The correspondence between the number of insertion / removal counts and MI_eff is recorded, and a correlation model is formed by fitting these results. Example

[0066] In this embodiment, the frequency f1 of the high-frequency ultrasonic excitation signal is selected as 5MHz, and the frequency f2 of the low-frequency vibration signal is selected as 100Hz, where f2 is less than f1. The high-frequency ultrasonic excitation probe is coupled to the outer shell surface of the connecting terminal via a spring clamp, which provides a constant clamping force to maintain stable contact between the probe and the outer shell surface. The broadband ultrasonic receiving probe is coupled to the outer shell surface of the connecting terminal via another spring clamp, located at a different position on the outer shell surface than the high-frequency ultrasonic excitation probe. The low-frequency vibration excitation source is fixed to the wire harness end of the connecting terminal via a mechanical clamp, and a low-frequency vibration signal with a frequency of 100Hz is applied to the wire harness end.

[0067] A high-frequency ultrasonic excitation probe emits a continuous sinusoidal ultrasonic signal at a frequency of 5 MHz onto the surface of the connector terminal housing, while a low-frequency vibration excitation source simultaneously applies mechanical vibration at a frequency of 100 Hz to the wire harness end. Under the combined action of dual-frequency excitation, the nonlinear characteristics of the contact interface caused by fretting wear and plastic deformation are excited, generating modulation sideband components in the response signal. A broadband ultrasonic receiving probe acquires the response signal propagating from the housing surface, which includes a fundamental frequency of 5 MHz and sideband components generated by nonlinear modulation.

[0068] The acquired response signal is converted into a digital signal by a preamplifier and an analog-to-digital converter, and then sent to the spectrum analysis module. The spectrum analysis module performs a Fast Fourier Transform on the digital signal to obtain spectral data. The fundamental frequency peak amplitude at 5MHz is identified in the spectrum, and sideband components are searched around 5MHz. The sideband frequency is 5MHz ± n × 100Hz, where n is an integer from 1 to 5. The peak amplitude of each sideband component is extracted, and the ratio of the peak amplitude to the fundamental frequency amplitude is calculated. The natural logarithm of this ratio is taken as the modulation index of that sideband. The arithmetic mean of the modulation indices of each sideband is taken as the current sideband modulation index of the connection terminal.

[0069] The sideband modulation index is input into the modulation index-remaining insertion / removal lifetime correlation model. This model is pre-established through accelerated insertion / removal fatigue tests of the same type of connector and stored in the data processing unit. Based on the input modulation index value, the model outputs the corresponding predicted value of the remaining insertion / removal lifetime, which is expressed in terms of the number of insertions / removals. Example

[0070] In this embodiment, a high-frequency ultrasonic excitation signal and a low-frequency vibration signal are first applied to the pluggable electrical connection terminal. The frequency of the high-frequency ultrasonic excitation signal is f1, and the frequency of the low-frequency vibration signal is f2, where f2 is less than f1. The low-frequency vibration signal is coupled to the wire harness end of the connection terminal. The response signal of the connection terminal under the combined action of the high-frequency ultrasonic excitation signal and the low-frequency vibration signal is collected. Spectral analysis is performed on the response signal to extract the amplitude of the sideband components f1±nf2 on both sides of frequency f1, where n is an integer.

[0071] When the first-order sideband f1±f2 is selected, the peak amplitudes at frequencies f1+f2 and f1-f2 are directly extracted as characterization values ​​of the sideband components. The extracted first-order sideband peak amplitudes are compared with the fundamental frequency amplitude at frequency f1, and the logarithm of the ratio is calculated to obtain the sideband modulation index. The sideband modulation index is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model, and the model outputs the predicted value of the remaining insertion / removal lifetime of the connection terminal.

[0072] When using a weighted combination of amplitudes from multiple sidebands f1±nf2, the peak amplitudes of the sideband components of multiple orders are extracted, with n taking different integer values, such as n=1, 2, 3. For each order of sideband component, its peak amplitude A_n is recorded. The comprehensive sideband amplitude is calculated according to the weighted combination method A_s=∑w_n·A_n, where w_n is the weighting coefficient of the nth order sideband. The weighting coefficient w_n is predetermined based on the sensitivity of each order of sideband to fretting wear and plastic deformation of the contact interface; for example, the weight of the first-order sideband is set to 0.6, the weight of the second-order sideband to 0.3, and the weight of the third-order sideband to 0.1. The calculated comprehensive sideband amplitude A_s is compared with the fundamental frequency amplitude at frequency f1, and the logarithm of the ratio is calculated as the sideband modulation index. The sideband modulation index is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model, and the model outputs the predicted value of the remaining insertion / removal lifetime of the connection terminal. The modulation index-remaining insertion / removal lifetime correlation model was pre-established through accelerated insertion / removal fatigue tests. During the tests, different numbers of insertion / removal operations were applied to samples of the same type of terminals, and the sideband modulation index after each insertion / removal was recorded. The curve of the modulation index changing with the remaining insertion / removal lifetime was fitted to form the correlation model. Example

[0073] In this embodiment, a high-frequency ultrasonic excitation probe and a low-frequency vibration excitation source are first coupled to the wiring harness end of the pluggable electrical connection terminal. The high-frequency ultrasonic excitation probe applies a high-frequency ultrasonic excitation signal with a frequency of f1 to the connection terminal. The low-frequency vibration excitation source applies a low-frequency vibration signal with a frequency of f2 to the connection terminal, where the frequency range of f2 is set from 10Hz to 500Hz, and f2 is less than f1. The low-frequency vibration signal is coupled to the contact interface area of ​​the connection terminal through the wiring harness end.

[0074] A broadband ultrasonic receiver probe is coupled to the housing or wiring harness end of the connector terminal. The broadband ultrasonic receiver probe acquires the response signal of the connector terminal under the combined action of a high-frequency ultrasonic excitation signal and a low-frequency vibration signal. The response signal contains nonlinear modulation information of the connector terminal contact interface to the dual-frequency excitation.

[0075] Spectral analysis is performed on the acquired response signal. The spectral analysis process identifies sideband components f1±nf2 on both sides of frequency f1, where n is an integer. The peak amplitude of each sideband component is extracted. The fundamental frequency amplitude at frequency f1 is extracted. The ratio of the sideband peak amplitude to the fundamental frequency amplitude is calculated. The logarithm of this ratio is taken to obtain the sideband modulation index.

[0076] The calculated sideband modulation index is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model. This model is calibrated using accelerated insertion / removal fatigue tests on samples of the same type of connection terminal to establish a mapping relationship between the sideband modulation index and the remaining insertion / removal lifetime. The model outputs a predicted value for the remaining insertion / removal lifetime of the connection terminal. The predicted value for the remaining insertion / removal lifetime represents the number of insertions and removals that the connection terminal can continue to withstand under the current damage state.

[0077] Example 11: In this embodiment, a high-frequency ultrasonic excitation probe and a broadband ultrasonic receiving probe are first coupled to the wire harness end of the connecting terminal using ring clamps. The ring clamps hold the wire harness with a constant clamping force of 50 Newtons to ensure a stable acoustic coupling interface between the probe and the wire harness surface. The center frequency of the high-frequency ultrasonic excitation probe is 2.5 MHz, and the frequency response range of the broadband ultrasonic receiving probe is 0.5 MHz to 5 MHz. A low-frequency vibration excitation source is connected to the same wire harness end through an independent mechanical coupling device, and the low-frequency vibration excitation source generates a sinusoidal vibration signal with a frequency of 20 Hz.

[0078] A continuous sinusoidal excitation signal with a frequency of 2.5 MHz (f1) is applied to the high-frequency ultrasonic excitation probe, while a sinusoidal vibration signal with a frequency of 20 Hz (f2) is applied to the low-frequency vibration excitation source. The high-frequency ultrasonic excitation signal propagates along the metal conductor of the connecting terminal, while the low-frequency vibration signal is conducted to the contact interface area of ​​the connecting terminal through the wiring harness. Under the action of the low-frequency vibration, the contact interface of the connecting terminal undergoes periodic, minute opening and closing displacements, which modulate the propagation path length of the high-frequency ultrasonic signal and the contact stress state.

[0079] The broadband ultrasonic receiver probe acquires the response signal of the connection terminal under the combined action of dual-frequency excitation. The response signal contains a high-frequency carrier component and a modulation sideband component generated by the nonlinear effect of the contact interface. The acquired response signal is amplified by 40 dB by a preamplifier and then transmitted to the data acquisition system. The sampling rate of the data acquisition system is set to 10 MHz, and the sampling duration is 1 second.

[0080] The acquired response signal is subjected to a Fast Fourier Transform (FFT) to obtain spectral data. The fundamental frequency component with frequency f1 of 2.5 MHz is located in the spectrum, and its amplitude A0 is extracted. Sideband components with frequencies f1 ± nf2 are searched on both sides of the fundamental frequency component, where n is an integer (1, 2, or 3), identifying sideband components with frequencies of 2.5 MHz ± 20 Hz, 2.5 MHz ± 40 Hz, and 2.5 MHz ± 60 Hz. The peak amplitude An of each sideband component is extracted, and the ratio of the sideband peak amplitude An to the fundamental frequency amplitude A0 is calculated. The logarithm of this ratio, base 10, is taken to obtain the sideband modulation index M, calculated as M = log10(An / A0).

[0081] The calculated sideband modulation index M is input into a pre-established correlation model between the modulation index and remaining insertion / removal lifetime. This correlation model is established through accelerated insertion / removal fatigue testing. In the test, samples of the same type of connector are repeatedly inserted and removed. After every 50 insertions / removals, the sideband modulation index is measured, and the curve of the modulation index changing with the number of insertions / removals is recorded until contact failure occurs. The correlation model uses the modulation index as the input variable and the remaining insertion / removal lifetime as the output variable, and fits the test data using an exponential decay function. The model outputs a predicted value of the remaining insertion / removal lifetime of the connector, expressed as the remaining insertion / removal lifetime. Example

[0082] In this embodiment, a high-frequency ultrasonic excitation probe and a low-frequency vibration excitation source are first coupled to the wiring harness end of the pluggable electrical connection terminal. The high-frequency ultrasonic excitation probe generates a high-frequency ultrasonic excitation signal with frequency f1, and the low-frequency vibration excitation source generates a low-frequency vibration signal with frequency f2, where f2 is less than f1. The high-frequency ultrasonic excitation signal and the low-frequency vibration signal are simultaneously applied to the connection terminal, and the low-frequency vibration signal is coupled to the contact interface of the connection terminal through the wiring harness end. A broadband ultrasonic receiving probe is coupled to the connection terminal to acquire the response signal of the connection terminal under the combined action of dual-frequency excitation. Spectral analysis is performed on the acquired response signal, and sideband components f1±nf2 are identified on both sides of frequency f1 in the spectrum, where n is an integer. The peak amplitude A_s of the sideband components is extracted, and the fundamental frequency amplitude A_0 at frequency f1 is extracted. The sideband modulation index MI is calculated as MI = 20·log10(A_s / A_0). The calculated sideband modulation index (MI) is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model. This model is calibrated using accelerated insertion / removal fatigue tests on terminal samples from the same batch to establish a mapping relationship between the sideband modulation index and the remaining insertion / removal lifetime. The model outputs a predicted value for the remaining insertion / removal lifetime of the terminal, which represents the number of insertions and removals the terminal can withstand under the current damage condition. Example

[0083] In this embodiment, sample terminals of the same model as the connection terminal to be tested are selected, with a minimum of thirty sample terminals. These sample terminals are then installed in an accelerated insertion / removal fatigue testing device, which includes an insertion / removal drive mechanism and a contact resistance monitoring module. A high-frequency ultrasonic excitation signal and a low-frequency vibration signal are applied to the sample terminals. The frequency of the high-frequency ultrasonic excitation signal is f1, and the frequency of the low-frequency vibration signal is f2, where f2 is less than f1. The low-frequency vibration signal is coupled to the wire harness end of the sample terminal. The response signal of the sample terminal under the combined action of dual-frequency excitation is acquired. Spectral analysis is performed on the response signal, and the amplitudes of the sideband components f1±nf2 on both sides of frequency f1 are extracted, where n is an integer. The logarithm of the ratio of the sideband peak amplitude to the fundamental frequency amplitude is calculated and recorded as the initial modulation index.

[0084] The accelerated insertion and extraction fatigue test is initiated. The insertion and extraction drive mechanism performs insertion and extraction actions on the sample terminals at a constant rate, stopping after a predetermined number of insertions and extractions (set to 50). After each stop, a high-frequency ultrasonic excitation signal and a low-frequency vibration signal are repeatedly applied, the response signal is collected, and the modulation index is calculated. Simultaneously, the contact resistance of the sample terminals is measured. The accelerated insertion and extraction fatigue test is continued until the contact resistance of the sample terminals exceeds 200% of the initial contact resistance or the insertion and extraction force drops to 50% of the initial insertion and extraction force. At this point, the sample terminal is deemed to have met the failure criteria, and the total number of insertions and extractions at the time of failure is recorded.

[0085] Data on the modulation index (MCI) variation with the number of insertions and removals for all sample terminals were compiled. A standard curve was plotted with the number of insertions and removals on the x-axis and the MCI on the y-axis. The standard curve shows a monotonically increasing trend in the MCI with the number of insertions and removals. The growth rate of the MCI is low in the early stages of fatigue and increases significantly in the near-failure stage. Based on the standard curve, a regression model between the MCI and the remaining number of insertions and removals was established using the least squares method. The regression model expression is N_remain = a * exp(-b * MI) + c, where N_remain is the remaining number of insertions and removals, MI is the MCI, and a, b, and c are regression coefficients. The regression coefficient values ​​were determined by fitting the sample data. The regression model was stored as a MCI-remaining insertion and removal lifetime correlation model for subsequent prediction of the remaining insertion and removal lifetime of the connection terminal under test. Example

[0086] In this embodiment, after applying a high-frequency ultrasonic excitation signal and a low-frequency vibration signal to the pluggable electrical connection terminal and acquiring the response signal, spectral analysis is performed on the response signal to extract the amplitude of the sideband components f1±nf2 on both sides of frequency f1, where n is an integer. The logarithm of the ratio of the sideband peak amplitude to the fundamental frequency amplitude is used as the sideband modulation index. After calculating the sideband modulation index, an environmental compensation step is performed. In the environmental compensation step, a preset reference nonlinear characteristic is extracted from the spectrum of the response signal. This reference nonlinear characteristic corresponds to a fixed nonlinear source in the connection terminal structure that is independent of the fatigue state of the contact interface. The sideband modulation index and the reference nonlinear characteristic are differentially processed, and the reference nonlinear characteristic is subtracted from the sideband modulation index to obtain the environmentally compensated effective modulation index. This effective modulation index eliminates common-mode nonlinear interference introduced by temperature fluctuations, changes in wire harness clamping force, or differences in probe coupling pressure. The effective modulation index is input into a pre-established modulation index-remaining insertion / removal life correlation model, which is constructed based on the mapping relationship between the effective modulation index and the remaining insertion / removal times in accelerated insertion / removal fatigue tests. The correlation model outputs a predicted value for the remaining insertion and removal life of the connection terminals, which reflects the cumulative degree of fretting wear and plastic deformation at the contact interface. Example

[0087] In this embodiment, a high-frequency ultrasonic excitation probe is first coupled to the wiring harness end of a pluggable electrical connection terminal, and a high-frequency ultrasonic excitation signal with a frequency of f1 is applied to the connection terminal. A low-frequency vibration excitation source is coupled to the same wiring harness end, and a low-frequency vibration signal with a frequency of f2 (f2 is less than f1) is applied to the connection terminal. The high-frequency ultrasonic excitation signal and the low-frequency vibration signal act simultaneously on the connection terminal, and the low-frequency vibration signal is transmitted to the contact interface area of ​​the connection terminal through the wiring harness end.

[0088] A broadband ultrasonic receiver probe is coupled to the wire harness end or housing surface of the connector terminal to acquire the response signal of the connector terminal under the combined action of a high-frequency ultrasonic excitation signal and a low-frequency vibration signal. The response signal contains the nonlinear modulation information of the connector terminal contact interface to the dual-frequency excitation.

[0089] Spectral analysis is performed on the acquired response signal to locate the fundamental frequency component at frequency f1. Sideband components f1±nf2 (where n is an integer) are identified on both sides of frequency f1. The peak amplitude of each sideband component is extracted, and the fundamental frequency amplitude at frequency f1 is also extracted. The ratio of the sideband peak amplitude to the fundamental frequency amplitude is calculated, and the logarithm of this ratio is taken to obtain the sideband modulation index.

[0090] The sideband modulation index is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model. This model is established through accelerated insertion / removal fatigue testing. In the test, different numbers of insertion / removal operations are applied to samples of the same type of connector, and the sideband modulation index of each sample is measured at the corresponding number of insertion / removal operations. The total number of insertion / removal operations when contact failure occurs is recorded, establishing a mapping relationship between the modulation index and the remaining insertion / removal lifetime. The model receives the sideband modulation index as input and outputs a predicted value of the remaining insertion / removal lifetime of the connector. The predicted value of the remaining insertion / removal lifetime characterizes the number of insertion / removal operations that the connector can continue to withstand under the current damage state.

[0091] Example 12: In this embodiment, a high-frequency ultrasonic excitation signal and a low-frequency vibration signal are first applied to the pluggable electrical connection terminal. The frequency f1 of the high-frequency ultrasonic excitation signal is selected as 3 MHz, and the frequency f2 of the low-frequency vibration signal is selected as 80 Hz, where f2 is less than f1. The high-frequency ultrasonic excitation probe is coupled to the surface of the connection terminal housing via a spring clamp, which applies a constant contact pressure of 15 Newtons. Ultrasonic coupling agent is applied to the probe tip to eliminate air gaps. The low-frequency vibration excitation source is fixed to the wire harness end of the connection terminal via a mechanical clamp, with the clamping force set to 30 Newtons. The vibration excitation source generates sinusoidal displacement vibration with a peak amplitude of 50 micrometers. A broadband ultrasonic receiving probe is coupled to the surface of the housing via another spring clamp, with a distance of 20 mm between it and the excitation probe. The frequency response range of the receiving probe is 0.5 MHz to 10 MHz.

[0092] A high-frequency ultrasonic excitation probe emits a continuous sinusoidal ultrasonic signal at a frequency of 3 MHz to the connection terminal, while a low-frequency vibration excitation source synchronously applies 80 Hz mechanical vibration to the wire harness end. Under the action of low-frequency vibration, the contact interface of the connection terminal undergoes periodic micro-displacement. The contact area and contact stress of the contact interface change with the vibration period, and this change produces a nonlinear modulation effect on the propagation of the high-frequency ultrasonic signal. A broadband ultrasonic receiving probe acquires the response signal propagating from the outer shell surface. The response signal contains a 3 MHz fundamental frequency component and sideband components generated by the nonlinear modulation of the contact interface. The acquired response signal is amplified by 30 dB by a preamplifier and then converted into a digital signal by an analog-to-digital converter at a sampling rate of 20 MHz for a sampling time of 0.5 seconds.

[0093] Perform a Fast Fourier Transform (FFT) on the digital signal to obtain the spectral data. Locate the fundamental frequency component at 3 MHz in the spectrum and extract its amplitude A_0. Search for sideband components with frequencies of 3 MHz ± n × 80 Hz on both sides of the fundamental frequency component, where n is an integer of 1, 2, or 3. Identify sideband components with frequencies of 3 MHz ± 80 Hz, 3 MHz ± 160 Hz, and 3 MHz ± 240 Hz. Extract the peak amplitude A_n of each sideband component, calculate the ratio of each sideband peak amplitude to the fundamental frequency amplitude, take the logarithm to base 10 of this ratio, and multiply by 20 to obtain the modulation index of each sideband. Use the first-order sideband modulation index as the current sideband modulation index MI of the connection terminal, MI = 20·log10(A_1 / A_0).

[0094] The sideband modulation index (MI) is input into a pre-established correlation model of modulation index and remaining insertion / removal life. The model is established as follows: Thirty sample terminals of the same model as the terminals under test are selected and installed in an accelerated insertion / removal fatigue testing device. The device includes a servo motor-driven insertion / removal mechanism and a four-wire contact resistance measurement module. A 3 MHz high-frequency ultrasonic excitation signal and an 80 Hz low-frequency vibration signal are applied to the sample terminals. Initial response signals are acquired and the initial modulation index is calculated. Insertion / removal operations are initiated at a rate of 15 times per minute. After every 50 insertions / removals, the process is paused, and the dual-frequency excitation is repeated while acquiring response signals, calculating the modulation index, and simultaneously measuring the contact resistance. Failure is determined when the contact resistance of the sample terminal exceeds 200% of the initial value, and the total number of insertions / removals at the time of failure is recorded. The modulation index data of the thirty sample terminals as a function of the number of insertions / removals is summarized, and a modulation index variation curve is plotted with the number of insertions / removals on the x-axis and the modulation index on the y-axis. The data is fitted using the exponential function N_remain=a·exp(-b·MI)+c at least squares to determine the coefficients a, b, and c, thus obtaining the mapping relationship between the modulation index and the remaining insertion / removal counts. This mapping relationship is stored as an association model. The association model receives the sideband modulation index MI as input, matches the corresponding remaining insertion / removal counts in the mapping relationship, and outputs the predicted value of the remaining insertion / removal lifetime of the connection terminal, expressed in terms of the remaining insertion / removal counts.

[0095] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0096] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention, as long as they do not depart from the spirit and scope of the technical solution of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for predicting and detecting the fatigue life of connection terminals based on nonlinear ultrasonic sideband modulation, characterized in that, Includes the following steps: A high-frequency ultrasonic excitation signal and a low-frequency vibration signal are applied to a pluggable electrical connection terminal, wherein the frequency of the high-frequency ultrasonic excitation signal is f1, the frequency of the low-frequency vibration signal is f2, and f2 < f1; wherein the low-frequency vibration signal is coupled to the wire harness end of the connection terminal. The response signal of the connection terminal under the combined action of the high-frequency ultrasonic excitation signal and the low-frequency vibration signal is collected. Spectral analysis is performed on the response signal to extract the amplitudes of the sideband components f1±nf2 on both sides of frequency f1, where n is an integer, and the logarithm of the ratio of the sideband peak amplitude to the fundamental frequency amplitude is used as the sideband modulation index. The sideband modulation index is input into a pre-established modulation index-remaining insertion / removal lifetime correlation model, and the remaining insertion / removal lifetime prediction value of the connection terminal is output.

2. The method for predicting and detecting the fatigue life of a connection terminal based on nonlinear ultrasonic sideband modulation according to claim 1, characterized in that, The sideband modulation index is calculated using the following formula: MI = 20·log10(A_s / A_0), Where MI is the sideband modulation index, A_s is the peak amplitude of the sideband component, and A_0 is the fundamental frequency amplitude at frequency f1.

3. The method for predicting and detecting the fatigue life of a connection terminal based on nonlinear ultrasonic sideband modulation according to claim 1, characterized in that, The frequency range of the low-frequency vibration signal is 10Hz to 500Hz.

4. The method for predicting and detecting the fatigue life of a connection terminal based on nonlinear ultrasonic sideband modulation according to claim 1, characterized in that, After calculating the sideband modulation index, an environmental compensation step is also included: extracting a preset reference nonlinear feature from the response signal, performing differential processing on the sideband modulation index and the reference nonlinear feature to obtain an effective modulation index after environmental compensation, which is then input into the correlation model.

5. The method for predicting and detecting the fatigue life of a connection terminal based on nonlinear ultrasonic sideband modulation according to claim 4, characterized in that, In the environmental compensation step, the effective modulation index is calculated using the following formula: MI_eff = MI - k·MI_ref, Where MI is the sideband modulation index, MI_ref is the modulation index corresponding to the reference nonlinear characteristic, and k is the calibration coefficient.

6. The method for predicting and detecting the fatigue life of a connection terminal based on nonlinear ultrasonic sideband modulation according to claim 5, characterized in that, The reference nonlinear characteristic is selected from the inherent nonlinear response of the connecting terminal housing material, or the nonlinear response of a reference calibration element integrated on the surface of the terminal housing.

7. The method for predicting and detecting the fatigue life of a connection terminal based on nonlinear ultrasonic sideband modulation according to claim 1, characterized in that, The method for establishing the modulation index-remaining insertion and removal life correlation model is as follows: Select sample terminals of the same model as the connection terminals to be tested, conduct accelerated insertion and removal fatigue tests, collect the modulation index of the sample terminals at predetermined insertion and removal times, until the sample terminals reach the failure standard, establish a standard curve of the modulation index changing with the number of insertions and removals, and establish a regression model of the modulation index and the remaining number of insertions and removals based on the standard curve.

8. The method for predicting and detecting the fatigue life of a connection terminal based on nonlinear ultrasonic sideband modulation according to claim 1, characterized in that, The frequency f1 of the high-frequency ultrasonic excitation signal ranges from 1MHz to 20MHz. The high-frequency ultrasonic excitation signal and the broadband ultrasonic receiving probe are coupled to the housing surface or wire harness end of the connecting terminal through a spring clamp or constant pressure mechanism.

9. The method for predicting and detecting the fatigue life of a connection terminal based on nonlinear ultrasonic sideband modulation according to claim 1, characterized in that, The sideband components are selected from first-order sidebands f1±f2, or from a weighted combination of the amplitudes of multiple-order sidebands f1±nf2. The weighting method is calculated according to the following formula: A_s = ∑w_n·A_n, Where A_n is the peak amplitude of the nth sideband, and w_n is the weighting coefficient of the nth sideband.

10. The method for predicting and detecting the fatigue life of a connection terminal based on nonlinear ultrasonic sideband modulation according to claim 1, characterized in that, The high-frequency ultrasonic excitation probe and the broadband ultrasonic receiving probe are coupled to the wire harness end of the connecting terminal using a ring clamp, and the ring clamp holds the wire harness with a constant clamping force.

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