CN105823826A - Residual stress dynamic distribution ultrasonic array chromatography detecting and monitoring method - Google Patents

Abstract

The invention relates to an ultrasonic array tomographic detection and monitoring method of residual stress distribution. The method uses an ultrasonic array to obtain detection data, is suitable for measuring the average distribution of residual stress in a component to be tested, and can measure the average distribution state and state of residual stress in the component to be tested. The reconstruction of the acoustic image is carried out according to the location of the region. The ultrasonic array tomography detection method proposed by the invention is realized based on the principle of local signal difference. Ultrasonic oblique incidence method is used to obtain the critical refracted longitudinal wave. The transmission method is used to first collect the background data without residual stress, and then use the same method to collect the ultrasonic array data with residual stress. Local detection is based on the presence or absence of residual stress The contrast between the signal and the background signal is combined with the weight coefficient of the occurrence probability of the residual stress distribution in the measured component to reconstruct the image. The pixels in the image represent the acoustic time difference change attribute of the residual stress area that the sound wave passes through, so as to distinguish the distribution state and position of the residual stress. According to the method of residual stress tomography, the influence of array number and arrangement on the distribution of residual stress and the influence of excitation frequency on the detection depth of residual stress are analyzed.

Description

An Ultrasonic Array Tomography Detection and Monitoring Method for Dynamic Distribution of Residual Stress

1. Technical field

The invention relates to an array detection method for non-destructive testing and monitoring of residual stress distribution and dynamic distribution in a local area of a component. Detection method and signal statistical characteristics, so as to realize ultrasonic tomographic detection of local residual stress, and realize detection and monitoring of residual stress distribution state in components.

2. Background technology

Residual stress is the physical source of deformation and cracks in various metal components. Accurate and non-destructive detection of residual stress distribution in components is the premise to ensure component quality and safe operation. Residual stress distribution is an important indicator of the safety of metal components, which directly reflects the The quality and reliability status of the component. The manufacturing and service process will inevitably produce residual stress in the component. The residual compressive stress can improve the corrosion resistance, fatigue resistance and crack resistance of the component, while the residual tensile stress will accelerate corrosion, promote cracks and accelerate component fracture, thereby reducing the strength of the material and the crack resistance. Crack ability also reduces fatigue strength and life.

The existence of residual stress changes the binding force between the lattices of metal materials. The residual compressive stress makes the lattices more compact and firm. It is difficult for external media to invade and the corrosion resistance is enhanced. The residual tensile stress relaxes the tightness between the lattices. Molecules of the external corrosive medium easily enter the lattice gap, chemically react with the metal material, break the inter-lattice constraint relationship, a new residual stress concentration appears, and the corrosion process vicious circle, due to the residual tensile stress leads to corrosion and cracking of the metal material It is called stress corrosion cracking, which is the most likely and serious defect in the service of metal components. Therefore, it is of great significance to effectively detect the distribution of residual stress in metal components.

Ultrasonic array tomography technology forms different array shapes by placing multiple ultrasonic transducers around the residual stress area, transmitting ultrasonic waves from different positions, and receiving ultrasonic waves at other positions. If there is residual stress in the transmitting and receiving path, the received The acoustic time of the signal will change, and the image can be reconstructed through a certain algorithm to obtain the distribution state and position of the residual stress in the structure.

At present, the research on residual stress mainly stays in the measurement of the residual stress of a certain part of the component, and the use of ultrasonic array tomography technology to obtain the distribution state and position of the residual stress in the component is a residual stress detection method with unique advantages.

The literature search found that there are many ultrasonic tomographic detection methods for defect detection, but there is no report at home and abroad on the ultrasonic array tomographic detection method for residual stress distribution. Therefore, the use of ultrasonic array tomography to detect and monitor the residual stress distribution of components has unique advantages and novelty.

3. Contents of the invention

The purpose of the present invention is to provide an ultrasonic array tomographic detection method for residual stress distribution, which can detect and monitor the dynamic distribution state and position of residual stress in metal components.

In order to realize the detection purpose of component residual stress distribution, the ultrasonic array tomographic detection method proposed by the present invention includes two parts: a hardware part and a detection algorithm. The hardware part includes an ultrasonic transducer array (as shown in Figure 1 ), a controller, a multi-channel pulse transceiver device and a data acquisition device (connection as shown in Figure 2 ), and the detection algorithm is implemented based on the principle of signal probability and statistics.

In the hardware part, the controller is responsible for controlling the multi-channel pulse transceiver equipment to emit ultrasonic waves and collect echo data of corresponding channels. The ultrasonic transducer array is composed of a plurality of longitudinal wave ultrasonic transducers and acoustic wedges to excite critical refracted longitudinal waves in the component under test. The ultrasonic transducer array can be arranged in an array of any shape according to the shape of the component to be tested, and transmit and receive ultrasonic waves through each channel to complete data acquisition. The multi-channel pulse transceiver device is an ultrasonic pulse signal transceiver device with the same number of elements as the ultrasonic transducer array, and each channel can independently complete the functions of transmitting pulse signals and receiving pulse signals. The data acquisition device can store the waveform signals received by the multi-channel pulse transceiver device in sub-channels. The detection algorithm can complete the detection of the distribution state and position of the residual stress through the probabilistic algorithm for the acoustic time difference of the acquired transmission waveform signal.

The principle of the detection algorithm is to arrange the ultrasonic transducer array in the form of a circular array on the component under test. The transducer on the opposite side of the transducer receives ultrasonic waves. Figure 1 shows that an ultrasonic array composed of 16 array elements is arranged on the surface of the component. While receiving sound waves, the data acquisition device stores the received signals according to the corresponding channel numbers. This process is performed sequentially for 16*16=416 times until all transducers have emitted ultrasonic waves. Multiple sets of background signals are obtained upon completion.

Then, in the state of residual stress, the ultrasonic array detection device is used to perform the same operation as obtaining the background signal, and the transducers in the array are sequentially traversed to transmit and receive ultrasonic waves. The signal collected at this time is called the stress signal.

The one-to-one correspondence between the background signal and the stress signal between the transmitting and receiving transducer pairs is used as the calculation object, and the residual stress distribution image is obtained through the probabilistic reconstruction algorithm.

The process of probabilistic reconstruction consists of two parts: signal comparison and image reconstruction. The process of signal comparison is to find the signal when there is stress (called stress signal) and the non-stress background signal for comparison, and then intercept the local signal corresponding to the detected path sound, and make a statistical ratio between the two. The image reconstruction process is to backsmear the pixel values in the reconstruction matrix according to the probability of the existence of the measured object.

The first step of the signal comparison process needs to obtain the local signal difference coefficient:

in:

are the stress signal and the background signal after partial interception respectively, and are the average values of the local stress signal and the local background signal respectively, the value of k from N ₁ to N ₂ represents the discrete signal sampling point, w(t) represents the window function, and is a time shift:

In the above formula, c _B is the sound velocity in the residual stress region. The width of the window function on the waveform time axis is equivalent to the specified time shift. (x,y), ( _xi ,y _i ) and (x _j ,y _j ) are the coordinates of a reconstructed pixel point, the coordinates of the transmitting transducer and the coordinates of the receiving transducer, respectively, see Figure 3 for details. The part inside the dotted ellipse line is set as the probability reconstruction range of an ultrasonic transmission and reception, and the relative distance of each pixel within the detection range can be expressed by Q _ij (x, y) as:

in

Indicates the calculated value inside the dotted line of the ellipse, where Indicates the relative distance, so the weight function with Q _ij (x,y) as an independent variable can be expressed as:

In the formula, β is a scale parameter, which controls the size of the ellipse detection area. Different transducer pairs can have different β values to adjust the probability range of residual stress on the corresponding sound propagation path. Here, the β value is an empirical value. It is determined according to the size of the residual stress distribution area in the actual inspection.

After all the parameters used in the above probability algorithm can be obtained, the pixel value of the reconstructed image can be obtained from the signal difference coefficient and weight function:

PROB _ij (x, y) in the formula represents the probability pixel contribution of each transceiving transducer pair in the reconstruction matrix, and the final reconstruction result is the probabilistic reconstruction superposition of all transducer pairs.

The residual stress ultrasonic array tomography detection method proposed by the present invention well satisfies the detection requirement of residual stress distribution in components, and has important practical significance.

4. Description of drawings

Fig.1 Schematic diagram of ultrasonic transducer array and probabilistic detection transmitted wave path

Fig.2 System block diagram of ultrasonic array detection device for residual stress distribution

Figure 3 Schematic diagram of the anti-smearing range of a single transceiver pair for the probabilistic detection algorithm

5. Specific implementation

Concrete implementation steps of the present invention are described as follows:

1) Make one channel of the multi-channel pulse transceiver device emit pulses, excite an array element in the transducer array to emit ultrasonic waves, and then all array elements receive ultrasonic waves.

2) The data acquisition device automatically stores the transmitted ultrasonic signal on the opposite side of the transmitting transducer, thereby completing a transceiving process.

3) To excite the critical refraction longitudinal wave in the component under test, each transducer in the array adopts oblique incidence mode, and the ultrasonic longitudinal wave is incident on the surface of the component, and the waveform conversion occurs on the surface of the component. The ultrasonic signal is excited by the piezoelectric transducer. On the interface between the plexiglass and the component under test, waveform conversion occurs, according to Snell's law,

In the formula, V ₁ , V _l , and V _s are the sound speed of ultrasonic longitudinal wave in the plexiglass wedge, the sound speed of ultrasonic longitudinal wave in the tested member, and the sound speed of ultrasonic transverse wave in the tested member. θ ₁ , θ _l , θ _s are the incident angle of ultrasonic longitudinal wave in the plexiglass wedge, the refraction angle of ultrasonic longitudinal wave and the refraction angle of ultrasonic transverse wave in the component under test.

When the critical refracted longitudinal wave is excited, θ _l =90°, then To excite the critical refracted longitudinal wave in the tested component, the incident angle of the ultrasonic longitudinal wave in the plexiglass wedge is:

4) Repeat the above-mentioned sending and receiving process for each array element in the absence of residual stress to obtain multiple sets of background signal data, and then repeat the sending and receiving process when there is residual stress.

5) Compare the stress signals obtained through the traversal with the background signals measured by the corresponding transceiver transducers, judge the probability of residual stress in the corresponding detection path through the acoustic time difference, and complete the reconstruction of the image of the residual stress area.

6) The number of arrays and arrangement will have an impact on the distribution of residual stress. Using different numbers of arrays, ultrasonic tomography is used to detect the distribution of residual stress. Due to the difference in the number and arrangement of probes, the amount of data obtained by the receiving transducer Different, the impact on the residual stress distribution state is different during tomography, and the best residual stress distribution state can be found by changing different numbers and arrangements.

7) The influence of the excitation frequency on the detection depth, because the lower the frequency, the smaller the ultrasonic attenuation, and the deeper the propagation depth in the component. Different excitation frequencies are used to obtain different penetration depths of the ultrasound, and the tomographic detection method is used Obtain the distribution state of residual stress and master the influence of excitation frequency on detection depth.

Claims (10)

1. a residual stress distribution supersonic array chromatography detection and monitoring method, it is characterized in that: utilization sound time difference of arrival technique, ultrasonic oblique incidence mode is used to build ultrasonic stress mornitoring array apparatus, supersonic array is arranged in tested component surface, transmitting is set and receives transducer acquisition ultrasound data, detection and the monitoring of residual stress distribution state in component is completed by probability CT calculating method, according to component residual stress distribution state, analyze the impact on the detection degree of depth on the change of residual stress distribution state and driving frequency of array number and arrangement.

2. in claim 1 each transducer between residual-stress value can according to the sound time difference change obtain, ultrasonic incident employing oblique incidence mode, waveform can be occurred during oblique incidence to change, for going out critical refraction longitudinal wave at measured medium surface actuator, Snell law can be used to derive the design angle of lucite voussoir.

3. the effect characteristics that in claim 1, residual stress state is changed by matrix arrangement and number is: considers that change matrix arrangement receives transducer and obtains the impact of signal sound time difference change excitation, and then obtains the variation characteristic of the residual stress distribution state after tomography.

4. in claim 1, the effect characteristics of the detection degree of depth is by driving frequency: under selected incident angle, consider to change probe driving frequency, obtain the propagation change in depth characteristic of ultrasonic critical refraction longitudinal wave, and then obtain the impact on the residual stress detection degree of depth of the different driving frequency.

5. the residual stress supersonic array described in claim 1 can select probe number as required, for adapting to the tested component of variously-shaped type, can be arranged to (arbitrarily) shapes such as square, circular or hexagon in component surface.

6. the transmitting that arranges described in claim 1 receives transducer, and its transducer transmitting-receiving set-up mode is: using the mode that single transducer excites, multiple transducer receives successively, the transmitting-receiving between transducer is independent of each other.

7. the probability CT calculating method described in claim 1 is characterised by: first obtain component without the ultrasonic signal in the presence of residual stress as background signal, then record component inside and have the transmission ultrasonic signal in the presence of residual stress as stress signal, the reconstruction of component residual stress distribution figure is realized, simultaneously the DYNAMIC DISTRIBUTION of dynamic monitoring component residual stress and development trend in conjunction with local signal difference coefficient and probability right function.

8. the local signal difference coefficient characteristics described in claim 4 is: the time point waveshape signal intercepting background signal ultrasonic direct wave compares with the waveshape signal of intercepting in stress signal, obtains local signal difference coefficient according to the sound time difference characteristic of Vocal cord injection.

9. the probability right Function feature described in claim 4 is: probability right function mesoscale parameter is adjusted correspondingly according to residual stress distribution area size in array range, this scale parameter is empirical value, each transducer between transmitting-receiving combination different scale parameter values can be set.

10. in claim 7, DYNAMIC DISTRIBUTION and the development trend of dynamic monitoring component residual stress are characterised by: supersonic array is arranged and tested component surface, it is possible not only to obtain the distribution of residual stress, and can periodically carry out dynamic monitoring according to component surface and being continually changing of internal residual stress value, thus grasp the safe operation state of tested component.