CN115144336A - Multilayer structure stress relaxation detection method based on mixing of ultrasonic tail waves and pumping waves - Google Patents
Multilayer structure stress relaxation detection method based on mixing of ultrasonic tail waves and pumping waves Download PDFInfo
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Abstract
The invention provides a multilayer structure stress relaxation detection method based on ultrasonic wake waves and pumping waves, which comprises the following steps: preparing a standard sample which is the same as the multilayer structure to be detected, determining the mode and parameters of a frequency mixing excitation signal, and building a multilayer structure stress relaxation frequency mixing detection system; exciting and receiving the mixing excitation signal under different stress states of the standard sample respectively; selecting a tail wave signal subjected to band-pass filtering in a time window, and extracting characteristic parameters of a standard sample in each stress state by adopting a gradual expansion method; establishing a quadratic relation model of the stress state and the characteristic parameters of the standard sample through nonlinear fitting; collecting signals of the multilayer structure to be detected under the unknown stress state, filtering out low-frequency pumping signals, extracting corresponding characteristic parameters, and determining the stress state of the multilayer structure according to a quadratic relation model. Compared with a linear model, the method is relatively easy, strong in practicability, low in cost, high in detection accuracy and good in measurement stability.
Description
Technical Field
The invention belongs to the technical field of multilayer structure stress nondestructive testing, and particularly relates to a multilayer structure stress relaxation testing method based on ultrasonic tail wave and pumping wave mixing.
Background
The prestressed multilayer structure is used as a typical and key structure of long-storage precision parts and widely applied to the fields of aerospace, industry, military and the like. The multilayer structure needs to be in a high compressive stress state for a long time within the life cycle under long-term service conditions. Furthermore, the multilayer structure is always exposed to variable loads, temperatures and radiation, which leads to irreversible chemical ageing, mechanical property degradation, in particular stress relaxation, and even to functional failure of the structure. Therefore, the stress relaxation of the prestressed multilayer structure is monitored in real time, so that the service life of the structure is prolonged, the structure safety is improved, and the important engineering practical value is achieved.
The currently common stress detection methods are mainly divided into two types, namely destructive detection methods and nondestructive detection methods. The destructive detection technology indirectly calculates the corresponding stress by measuring the strain before and after the stress is released in the detected area. Although destructive testing methods can simply and accurately measure stress, structural damage due to stress relaxation is sometimes intolerable, which limits its range of application. Therefore, nondestructive testing techniques have been highly developed, such as methods based on the acoustic elastic effect, electromechanical impedance methods, nonlinear ultrasonic methods, and methods based on the interference of a wake wave. The method based on the acoustic elastic effect relies on the relationship between the wave velocity and the applied stress in the medium to detect the stress variation, but the detection accuracy is easily affected by the sensing path, the test environment, the couplant and the measuring equipment. The monitoring principle of the electromechanical impedance method is to combine a piezoelectric transducer with a structure to be measured, and the electrical impedance of the transducer can reflect the change of the stress state, but the sensitivity and the robustness of the method are still challenging problems. Nonlinear ultrasound methods are based on the appearance of new frequency components with nonlinear effects, where higher harmonics and sidebands are the most interesting features, with higher accuracy and sensitivity, but are susceptible to nonlinear errors in test parameters and boundary conditions, instruments and materials. The tail wave is formed by multiple scattering of the ultrasonic wave in the inhomogeneous medium and appears as a tail behind the direct wave. The method based on the wake wave interference is highly sensitive to the tiny stress changes of the medium due to the repeated sampling and amplification of multiple scattering wake waves. Therefore, it is very urgent and important to find a method for detecting stress relaxation of a multilayer structure based on the mixing of ultrasonic wake waves and pump waves by combining the advantages of the nonlinear ultrasonic modulation technology and the wake wave interference technology to monitor the stress variation of the multilayer structure with high sensitivity.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a multilayer structure stress relaxation detection method based on the mixing of ultrasonic tail waves and pumping waves. Preparing a standard sample which is the same as a multilayer structure to be detected, determining the mode and parameters of a mixing excitation signal, and building a multilayer structure stress relaxation mixing detection system; exciting and receiving the mixing excitation signal under different stress states of the standard sample respectively; selecting a tail wave signal subjected to band-pass filtering in a time window, and extracting characteristic parameters of a standard sample in each stress state by adopting a gradual expansion method; establishing standard specimen stress by non-linear fitting a quadratic relation model of the state and the characteristic parameters; collecting signals of the multilayer structure to be detected in an unknown stress state, filtering out low-frequency pumping signals, extracting corresponding characteristic parameters, and determining the stress state of the multilayer structure according to a quadratic relation model. Compared with a linear model, the method is relatively easy, strong in practicability, low in cost, high in detection accuracy and good in measurement stability.
The invention provides a multilayer structure stress relaxation detection method based on ultrasonic wake waves and pumping waves, which comprises the following steps:
s1, preparing a standard sample which is the same as a multilayer structure to be detected, determining a mode and parameters of a mixing excitation signal, and building a multilayer structure stress relaxation mixing detection system;
s2, exciting and receiving the mixing excitation signals under different stress states of the standard sample respectively;
s3, selecting a time window of t 1 ,t 2 ]Extracting characteristic parameters of the standard sample in each stress state by adopting a gradual expansion method for the band-pass filtered tail wave signal;
s31, in the selected time window [ t ] 1 ,t 2 ]Inner, i-th stress state tail wave signal u i (t) signal u after stretching at the stretch coefficient τ i [t(1+τ)]And the i-1 th stress state reference wake wave signal u i-1 Correlation coefficient C between (t) i (τ) is:
the correlation coefficient C i (τ) is u i [t(1+τ)]And u i-1 (t) a quality factor of the degree of match between;
s32, gradual relative wave speed change delta epsilon under the ith stress state i To make the correlation coefficient C i (τ) maximize the corresponding coefficient of expansion:
wherein v is i Representing the velocity of the wake wave in the ith stress state; v. of i-1 Representing the wave speed of the reference wake wave in the i-1 th stress state;
s33, cumulative relative speed change epsilon of ith stress state relative to initial stress state i By multiplying the stepwise relative wave velocity changes in the correct way:
wherein v is 0 Representing the velocity of the wake wave in the initial stress state; delta epsilon i-1 Representing the gradual relative wave speed change in the i-1 th stress state; delta epsilon 1 Representing the gradual relative wave speed change in the 1 st stress state;
s4, establishing a quadratic relation model of the stress state of the standard sample and the characteristic parameter epsilon through nonlinear fitting;
ε＝a(T-T 0 ) 2 +b(T-T 0 ) (4)
wherein T represents a torque corresponding to a stress state; t is 0 Representing the torque at an initial reference stress state; a. b represents a first fitting parameter of the model and a second fitting parameter of the model respectively; the characteristic parameter epsilon is the extracted cumulative relative velocity change;
s5, collecting signals of the multilayer structure to be detected in the unknown stress state, filtering out low-frequency pumping signals, extracting corresponding characteristic parameters, and determining the stress state of the multilayer structure according to a quadratic relation model of the stress state and the characteristic parameters of the standard sample.
Further, the step S1 specifically includes the following steps:
s11, a high-frequency ultrasonic signal in the mixing excitation signal is a sine pulse train modulated by a single-frequency Hanning window, and the selection of the frequency of the high-frequency ultrasonic signal maintains good balance between sensitivity caused by scattering and attenuation caused by absorption; the low-frequency pumping signal in the mixing excitation signal is a single-frequency continuous sinusoidal signal, the frequency of the low-frequency pumping signal is selected according to the structural resonance information, and the frequency corresponding to the peak value of the response frequency spectrum is selected;
s12, outputting high-frequency ultrasonic waves by a CH1 channel of an arbitrary function generator, outputting low-frequency pumping waves by a CH2 channel of the arbitrary function generator, and mixing signals of the CH1 channel and the CH2 channel through a BNC three-way joint;
s13, transmitting a mixing excitation signal to an excitation transducer probe through a high-voltage power amplifier by means of a first output end of a BNC three-way joint, and directly transmitting a second output end to a CH1 channel of a mixing domain oscilloscope to serve as trigger;
s14, the excitation transducer probe and the receiving transducer probe are always kept in a consistent coupling state with the center position of the surface of the standard sample through a coupling agent and a specific fixing clamp;
and S15, collecting the frequency mixing response signal transmitted in the standard sample by the receiving transducer probe, transmitting the frequency mixing response signal to a CH2 channel of the mixed domain oscilloscope to receive the signal, and performing further data processing through a computer.
It may be preferable to use a solution of, the step S2 specifically includes the steps of:
s21, applying a set torque value to the standard sample by using a torque wrench and keeping the torque value;
s22, detecting the standard sample by adopting a one-transmitting-one-receiving mode, wherein the exciting transducer emits a mixing exciting signal, and the receiving transducer receives a signal transmitted in the standard sample;
and S23, changing the torque based on the set torque interval, and repeatedly executing the steps S21 and S22 until the detection of all the torque levels is completed.
Preferably, in the step S2, the bolt torque is changed by a torque wrench, so as to simulate a stress relaxation process of a multilayer structure; in consideration of the attention in the early stage of the stress relaxation, the set torque interval gradually increases as the applied torque decreases; the signal received by the receiving transducer is the average value of 64 continuous signal acquisitions of the mixed domain oscilloscope.
Preferably, the starting time t of the time window selected in the step S3 1 Should be larger than the arrival time of the direct wave, the time interval is set to be 2-4 times the length of the mixing excitation signal, and the wake wave signal in the selected time window must have a high signal-to-noise ratio.
Preferably, in step S3, a band-pass filter is used to perform filtering processing on the wake wave signal, remove frequency components corresponding to the low-frequency pump wave, and perform characteristic parameter extraction on the filtered high-frequency ultrasonic signal.
Preferably, the characteristic parameters extracted in step S3 in each stress state are based on an initial maximum stress state.
Preferably, the multilayer structure stress relaxation frequency mixing detection system in step S1 includes an arbitrary function generator, a BNC tee, a high voltage power amplifier, an excitation transducer probe, a reception transducer probe, a standard sample, a mixed domain oscilloscope, and a computer.
Compared with the prior art, the invention has the technical effects that:
1. the multilayer structure stress relaxation detection method based on the mixing of the ultrasonic wake waves and the pumping waves, provided by the invention, utilizes the modulation effect of high-frequency ultrasonic wake waves and low-frequency pumping waves, and extracts wake wave characteristic parameters corresponding to the stress state of the multilayer structure through a gradual expansion and contraction method, so that the stress relaxation of the multilayer structure can be monitored with high sensitivity; the detection method combines the advantages of the nonlinear ultrasonic modulation technology and the wake wave interference technology, provides a mode of mixing the high-frequency ultrasonic wake wave and the low-frequency pumping wave to detect the change of the stress state of the multilayer structure, and has high detection sensitivity and good measurement robustness.
2. Compared with the traditional waveform stretching method adopting a fixed reference, the adopted gradual stretching method firstly obtains gradual change by taking the previous stress state as the reference, and then accumulates to obtain the total relative wave speed change relative to the initial stress state; the improved gradual stretching method is not only suitable for the condition of small stress change, but also can be expanded to the condition of large relative stress change, and has larger application range and higher detection accuracy.
3. Compared with a linear model, the multilayer structure stress relaxation detection method based on the mixing of the ultrasonic tail waves and the pumping waves has the advantages that a quadratic relation model of the stress state and the characteristic parameters of the standard sample is constructed, the fitting effect is better, and the stress relaxation of the multilayer structure can be detected with high precision and high sensitivity; the detection method has the advantages of strong practicability, high detection accuracy and good measurement stability.
Drawings
Other features, objects and advantages of the present application will become more apparent upon reading of the following detailed description of non-limiting embodiments thereof, made with reference to the accompanying drawings.
FIG. 1 is a flow chart of a multilayer structure stress relaxation detection method based on ultrasonic wake waves and pump waves mixing;
FIG. 2 is a schematic diagram of a system and process for stress relaxation detection of a multi-layer structure according to an embodiment of the present invention;
FIG. 3 is a schematic composition diagram of a multilayer structure sample according to an embodiment of the present invention;
FIG. 4 is a comparison of the filtered wake waveforms within a time window [150 μ s,250 μ s ] for different stress conditions measured in an embodiment of the present invention;
FIG. 5 is a comparison graph of fitting results of a quadratic relation model and a linear model to a characteristic parameter of a wake wave and a stress state in an embodiment of the invention.
Detailed Description
The present application will be described in further detail with reference to the following drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the relevant invention and not restrictive of the invention. It should be noted that, for convenience of description, only the portions related to the related invention are shown in the drawings.
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.
Fig. 1 shows a multilayer structure stress relaxation detection method based on ultrasonic wake wave and pump wave mixing, which comprises the following steps:
s1, preparing a standard sample which is the same as the multilayer structure to be detected, determining the mode and parameters of a mixing excitation signal, and building a multilayer structure stress relaxation mixing detection system.
The multilayer structure stress relaxation frequency mixing detection system comprises an arbitrary function generator, a BNC three-way joint, a high-voltage power amplifier, an excitation transducer probe, a receiving transducer probe, a standard sample, a mixed domain oscilloscope and a computer for processing data.
The standard sample of the multilayer structure is to paste a silicone foam pad between the different parts to maintain the high compressive stress state, consisting mainly of an inner layer of polymer composite, two layers of silicone foam in the middle, and an outer layer of stainless steel plates connected by bolts and nuts.
S11, a high-frequency ultrasonic signal in the mixing excitation signal is a sine pulse train modulated by a single-frequency Hanning window, and the selection of the frequency of the high-frequency ultrasonic signal maintains good balance between sensitivity caused by scattering and attenuation caused by absorption; and the low-frequency pumping signal in the mixing excitation signal is a single-frequency continuous sinusoidal signal, the frequency of the low-frequency pumping signal is selected according to the structural resonance information, and the frequency corresponding to the peak value of the response spectrum is selected.
And S12, outputting high-frequency ultrasonic waves by a CH1 channel of the arbitrary function generator, outputting low-frequency pump waves by a CH2 channel of the arbitrary function generator, and mixing signals of the CH1 channel and the CH2 channel through a BNC three-way joint.
And S13, transmitting the mixing excitation signal to an excitation transducer probe through a high-voltage power amplifier by means of a first output end of the BNC three-way joint, and directly transmitting a second output end to a CH1 channel of the mixed domain oscilloscope to serve as trigger.
And S14, the excitation transducer probe and the receiving transducer probe are always kept in a consistent coupling state with the center position of the surface of the standard sample through the coupling agent and a specific fixing clamp.
And S15, collecting the frequency mixing response signal transmitted in the standard sample by the receiving transducer probe, transmitting the frequency mixing response signal to a CH2 channel of the mixed domain oscilloscope to receive the signal, and performing further data processing through a computer.
S2, exciting and receiving the mixing excitation signals under different stress states of the standard sample respectively; the torque of the bolt is changed through the torque wrench, and the stress relaxation process of the multilayer structure is simulated.
And S21, applying a set torque value to the standard sample by using a torque wrench and keeping the set torque value.
S22, detecting the standard sample by adopting a mode of transmitting and receiving, wherein the exciting transducer transmits a mixing exciting signal, and the receiving transducer receives a signal transmitted in the standard sample and is an average value of 64 continuous signal acquisition of the mixed domain oscilloscope, so that the signal-to-noise ratio and the detection precision can be improved.
S23, setting the torque interval to gradually increase with a decrease in the applied torque in consideration of the attention in the early stage of the stress relaxation, and changing the torque based on the set torque interval, and repeatedly performing steps S21 and S22 until the detection at all the torque levels is completed.
S3, selecting a time window of t 1 ,t 2 ]The characteristic parameters of the standard sample in each stress state are extracted from the wake wave signal after band-pass filtering by adopting a step-by-step extension method.
And a proper wake wave time window is selected to extract characteristic parameters, so that the sensitivity and the accuracy of monitoring can be improved. The start time t of the selected time window 1 Should be larger than the arrival time of the direct wave, the time interval is set to be 2-4 times the length of the mixing excitation signal, and the wake wave signal in the selected time window must have a high signal-to-noise ratio.
And filtering the wake wave signal by adopting a band-pass filter, removing frequency components corresponding to the low-frequency pumping wave, and extracting characteristic parameters of the filtered high-frequency ultrasonic signal, wherein the extracted characteristic parameters under each stress state take the initial maximum stress state as a reference.
S31, in the selected time window [ t ] 1 ,t 2 ]Inner, i-th stress state tail wave signal u i (t) signal u after stretching at the stretch coefficient τ i [t(1+τ)]And the i-1 th stress state reference wake wave signal u i-1 Correlation coefficient C between (t) i (τ) is:
coefficient of correlation C i (τ) is u i [t(1+τ)]And u i-1 (t) quality factor of the degree of match between.
S32, gradual change Delta epsilon of relative wave speed under the ith stress state i To make the correlation coefficient C i (τ) maximize the corresponding coefficient of expansion:
wherein v is i Representing the velocity of the wake wave in the ith stress state; v. of i-1 Representing the reference wake velocity in the i-1 th stress state.
S33, accumulating the ith stress state relative to the initial stress stateProduct relative velocity change epsilon i By multiplying the stepwise relative wave velocity changes in the correct way:
wherein v is 0 Representing the velocity of the wake wave in the initial stress state; delta epsilon i-1 Representing the gradual relative wave speed change in the i-1 th stress state; delta epsilon 1 Showing the gradual change in relative wave velocity in the 1 st stress state.
S4, establishing a quadratic relation model of the stress state of the standard sample and the characteristic parameter epsilon through nonlinear fitting;
ε＝a(T-T 0 ) 2 +b(T-T 0 ) (4)
wherein T represents a torque corresponding to a stress state; t is 0 Representing the torque at an initial reference stress state; a. b represents a first fitting parameter of the model and a second fitting parameter of the model respectively; the characteristic parameter epsilon is the extracted cumulative relative velocity change.
And S5, collecting signals of the multilayer structure to be detected in the unknown stress state, filtering out low-frequency pumping signals, extracting corresponding characteristic parameters, and determining the stress state of the multilayer structure according to a quadratic relation model of the stress state and the characteristic parameters of the standard sample.
The present invention will be further described in detail with reference to a specific stress relaxation test case of a multi-layer structure, as shown in fig. 2.
S1, preparing a standard sample with the same multilayer structure to be detected, wherein the standard sample is formed by pasting a silica gel foam pad between different parts to keep a high-pressure stress state and mainly comprises an inner polymer composite material as shown in figure 3
Intermediate two-layer silicon foam
And outer part connected by M6 bolt and nutLaminated stainless steel plate
And (4) forming.
S11, high-frequency ultrasonic signals in the mixing excitation signals are sine pulse trains modulated by a single-frequency Hanning window with the 3-cycle central frequency of 100KHz, and low-frequency pumping signals in the mixing excitation signals are single-frequency continuous sine signals with the frequency of 5 KHz.
S12, a CH1 channel of an arbitrary function generator (Tektronix, AFG 31022) outputs high-frequency ultrasonic waves, a CH2 channel outputs low-frequency pump waves, and then signals of the two channels are mixed through a BNC three-way joint.
And S13, transmitting the mixing excitation signal to an excitation transducer probe (OLYMPUS, V1011, the center frequency is 100 KHz) through a high-voltage power amplifier (Aigtek, ATA-4012) by means of a first output end of the BNC three-way joint, and directly transmitting a second output end to a CH1 channel of a mixed domain oscilloscope (Tektronix, MDO 3104) to serve as a trigger.
And S14, always keeping consistent coupling state of the excitation transducer probe and the receiving transducer probe with the center position of the surface of the standard sample through a coupling agent (Xin Meida CG-88).
And S15, collecting a mixing response signal propagated in the standard sample by a receiving transducer probe (OLYMPUS, V101-RB, the center frequency of which is 500 KHz), transmitting the mixing response signal to a CH2 channel of a mixed domain oscilloscope to realize signal receiving, and then carrying out further data processing by a computer.
And S2, controlling the stress state of the multilayer structure by a torque wrench (the torque level is set to be 10, 9.8, 9.6, 9.4, 9.2, 9, 8.5, 8, 7.5, 7, 6.5, 6, 5, 4 and 3 Nm), and respectively carrying out excitation and reception of the mixing excitation signals under different stress states of the standard sample.
S3, FIG. 4 shows the acquired tail wave signals after filtering with time windows of [150 μ S,250 μ S ] under different stress states, the tail wave signals pass through a band-pass filter with a passband of [10KHz,200KHz ] to filter frequency components of low-frequency pumping waves, and it can be seen that the time delay of the tail wave signals is in an increasing trend along with the reduction of applied torque. The relative wave velocity change of the standard sample relative to the initial stress state (10 Nm) under each stress state is extracted by adopting a step-by-step stretching method.
And S4, establishing a quadratic relation model of the stress state and the characteristic parameters of the standard sample by nonlinear fitting according to the experimental result, wherein the quadratic relation model is shown in figure 5. A quadratic relation model between the torque (T) corresponding to the stress state and the proposed characteristic parameter relative wave speed change (epsilon) is shown in formula (4). Wherein, T 0 Is the torque (T) at the initial reference stress state 0 =10 Nm), a first fitting parameter of the model a =0.0002947, a second fitting parameter of the model b = -0.002884; coefficient of determination R of quadratic relation fitting model 2 =0.9926 and residual standard deviation RMSE =0.0009339, the fitting results indicate that there is a significant quadratic relationship between the proposed characteristic parameters and the stress state. When the multilayer structure is subjected to stress relaxation, the relative wave velocity change of the tail wave is in a secondary growth trend. Furthermore, in the early stage of stress relaxation, the relative wave velocity change is still significant, and a stress change corresponding to a torque change of 0.2Nm can be detected. Compared to a linear model (determining the coefficient R) 2 =0.9655, residual standard deviation RMSE = 0.001942), the established quadratic relation model has better goodness of fit and smaller fitting error, and can better describe the stress change of the multilayer structure.
And S5, collecting signals of the multilayer structure to be detected in the unknown stress state, filtering out low-frequency pumping signals, extracting corresponding characteristic parameters, and determining the stress state of the multilayer structure according to a quadratic relation model of the stress state and the characteristic parameters of the standard sample.
The invention combines the nonlinear ultrasonic modulation technology and the wake wave interference technology, provides a mode of mixing high-frequency ultrasonic wake waves and low-frequency pumping waves, utilizes the modulation interaction between the two, and extracts the relative wave velocity change of the wake waves relative to the initial stress state by a gradual stretching method to detect the stress relaxation of the multilayer structure, and has high measurement sensitivity and good detection robustness. The results show that the relative wave velocity change of the tail wave shows a trend of secondary increase along with the reduction of the torque. Furthermore, the relative wave velocity variation of the wake wave is still significant in the early stages of stress relaxation, with detectable torque resolution up to 0.2Nm, i.e. with high sensitivity for early stress relaxation detection of the multilayer structure. Compared with a linear model, the established quadratic relation model of the torque corresponding to the stress state and the relative wave speed change has a better fitting effect on an experiment, and the stress relaxation of the multilayer structure can be detected more effectively.
The multilayer structure stress relaxation detection method based on the mixing of the ultrasonic wake waves and the pumping waves, provided by the invention, can be used for extracting wake wave characteristic parameters corresponding to the stress state of the multilayer structure by a gradual expansion and contraction method by utilizing the modulation effect of high-frequency ultrasonic wake waves and low-frequency pumping waves, so that the stress relaxation of the multilayer structure can be monitored with high sensitivity; the detection method combines the advantages of a nonlinear ultrasonic modulation technology and a wake wave interference technology, provides a mode of mixing high-frequency ultrasonic wake waves and low-frequency pumping waves to detect the change of the stress state of the multilayer structure, and has high detection sensitivity and good measurement robustness; compared with the traditional waveform stretching method adopting a fixed reference, the adopted gradual stretching method firstly obtains gradual change by taking the previous stress state as a reference, and then the gradual change is accumulated to obtain the total relative wave speed change relative to the initial stress state; the improved gradual expansion method is not only suitable for the condition of small stress change, but also can be expanded to the condition of large relative stress change, and has larger application range and higher detection accuracy; compared with a linear model, the method has the advantages that the quadratic relation model of the stress state and the characteristic parameters of the standard sample is constructed, the fitting effect is better, and the stress relaxation of the multilayer structure can be detected with high precision and high sensitivity.
Finally, it should be noted that: although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and it is intended to cover in the claims the invention as defined in the appended claims.
Claims (8)
1. A multilayer structure stress relaxation detection method based on ultrasonic wake waves and pump waves is characterized by comprising the following steps:
s1, preparing a standard sample which is the same as a multilayer structure to be detected, determining a mode and parameters of a mixing excitation signal, and building a multilayer structure stress relaxation mixing detection system;
s2, exciting and receiving the mixing excitation signals under different stress states of the standard sample respectively;
s3, selecting a time window as [ t ] 1 ，t 2 ]Extracting characteristic parameters of the standard sample in each stress state by adopting a gradual expansion method for the band-pass filtered tail wave signal;
s31, in the selected time window [ t ] 1 ，t 2 ]Internal, i-th stress state wake signal u i (t) signal u after stretching at the stretch coefficient τ i [t(1+τ)]And the i-1 th stress state reference wake wave signal u i-1 Correlation coefficient C between (t) i (τ) is:
the correlation coefficient C i (τ) is u i [t(1+τ)]And u i-1 (t) degree of matching therebetween the quality factor of (2);
s32, gradual relative wave speed change delta epsilon under the ith stress state i To make the correlation coefficient C i (τ) maximize the corresponding coefficient of expansion:
wherein v is i Representing the velocity of the wake wave in the ith stress state; v. of i-1 Representing the wave speed of the reference wake wave in the i-1 th stress state;
s33, cumulative relative speed change epsilon of ith stress state relative to initial stress state i By multiplying the stepwise relative wave velocity changes in the correct way:
wherein v is 0 Representing the velocity of the wake wave in the initial stress state; delta epsilon i-1 Representing the gradual relative wave speed change in the i-1 th stress state; delta epsilon 1 Representing the gradual relative wave speed change in the 1 st stress state;
s4, establishing a quadratic relation model of the stress state of the standard sample and the characteristic parameter epsilon through nonlinear fitting;
ε＝a(T-T 0 ) 2 +b(T-T 0 ) (4)
wherein T represents a torque corresponding to a stress state; t is 0 Representing the torque at an initial reference stress state; a. b respectively represents a first fitting parameter of the model and a second fitting parameter of the model; the characteristic parameter epsilon is the extracted cumulative relative velocity change;
s5, collecting signals of the multilayer structure to be detected in the unknown stress state, filtering out low-frequency pumping signals, extracting corresponding characteristic parameters, and determining the stress state of the multilayer structure according to a quadratic relation model of the stress state and the characteristic parameters of the standard sample.
2. The method for detecting stress relaxation of multilayer structure based on ultrasonic wake wave and pump wave mixing according to claim 1, wherein the step S1 specifically comprises the following steps:
s11, a high-frequency ultrasonic signal in the mixing excitation signal is a sine pulse train modulated by a single-frequency Hanning window, and the selection of the frequency of the high-frequency ultrasonic signal maintains good balance between sensitivity caused by scattering and attenuation caused by absorption; a low-frequency pumping signal in the mixing excitation signal is a single-frequency continuous sinusoidal signal, the frequency of the low-frequency pumping signal is selected according to the structural resonance information, and the frequency corresponding to the peak value of the response frequency spectrum is selected;
s12, outputting high-frequency ultrasonic waves by a CH1 channel of an arbitrary function generator, outputting low-frequency pumping waves by a CH2 channel of the arbitrary function generator, and mixing signals of the CH1 channel and the CH2 channel through a BNC three-way joint;
s13, transmitting the mixing excitation signal to an excitation transducer probe through a high-voltage power amplifier by means of a first output end of a BNC three-way joint, and directly transmitting a second output end to a CH1 channel of the mixed domain oscilloscope to serve as trigger;
s14, the excitation transducer probe and the receiving transducer probe are always kept in a consistent coupling state with the center position of the surface of the standard sample through a coupling agent and a specific fixing clamp;
and S15, collecting the frequency mixing response signal transmitted in the standard sample by the receiving transducer probe, transmitting the frequency mixing response signal to a CH2 channel of the mixed domain oscilloscope to receive the signal, and performing further data processing through a computer.
3. The method for detecting stress relaxation of multilayer structure based on ultrasonic wake wave and pump wave mixing according to claim 1, wherein the step S2 specifically comprises the following steps:
s21, applying a set torque value to the standard sample by using a torque wrench and keeping the torque value;
s22, detecting the standard sample by adopting a one-transmitting-one-receiving mode, wherein the exciting transducer emits a mixing exciting signal, and the receiving transducer receives a signal transmitted in the standard sample;
and S23, changing the torque based on the set torque interval, and repeatedly executing the steps S21 and S22 until the detection at all the torque levels is completed.
4. The method for detecting the stress relaxation of the multilayer structure based on the mixing of the ultrasonic tail wave and the pump wave as claimed in claim 1, wherein the bolt torque is changed through a torque wrench in the step S2 to simulate the stress relaxation process of the multilayer structure; in consideration of the attention in the early stage of the stress relaxation, the set torque interval gradually increases as the applied torque decreases; the signal received by the receiving transducer is the average value of 64 continuous signal acquisitions of the mixed domain oscilloscope.
5. The method for detecting stress relaxation of multilayer structure based on ultrasonic tail wave and pump wave mixing as claimed in claim 1,the starting time t of the time window selected in the step S3 1 Should be larger than the arrival time of the direct wave, the time interval is set to be 2-4 times the length of the mixing excitation signal, and the wake wave signal in the selected time window must have a high signal-to-noise ratio.
6. The multilayer structure stress relaxation detection method based on ultrasonic wake waves and pump waves mixing as claimed in claim 1, characterized in that in step S3, a band-pass filter is adopted to filter wake wave signals, frequency components corresponding to low-frequency pump waves are removed, and feature parameters of the obtained filtered high-frequency ultrasonic signals are extracted.
7. The method for detecting stress relaxation of multilayer structure based on ultrasonic tail wave and pump wave mixing as claimed in claim 1, wherein the characteristic parameters extracted in step S3 under each stress state are all based on the initial maximum stress state.
8. The method for detecting the stress relaxation of the multilayer structure based on the mixing of the ultrasonic tail wave and the pump wave according to claim 1, wherein the multilayer structure stress relaxation mixing detection system in the step S1 comprises an arbitrary function generator, a BNC tee joint, a high-voltage power amplifier, an excitation transducer probe, a receiving transducer probe, a standard sample, a mixed domain oscilloscope and a computer.
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