CN110333292B - Nonlinear imaging method for fatigue closed cracks of metal material - Google Patents
Nonlinear imaging method for fatigue closed cracks of metal material Download PDFInfo
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Abstract
The invention discloses a nonlinear imaging method for fatigue closed cracks of a metal material, which comprises the following steps of A, carrying out phased array distribution control on a test piece to be detected; B. respectively acquiring data of all array element phased arrays and grouped array element phased arrays; C. respectively calculating the corresponding acoustic kinetic energy of all array elements and phased array
Acoustic kinetic energy corresponding to grouped array element phased array
、
、…、
(ii) a D. Calculating a non-linear characterizing parameter
The distribution of (a); E. will be provided with
The calculation results of (1) are imaged. The method has the advantages that the detection can be finished by adopting common phased array equipment, so that the detection cost is reduced; in addition, as data acquisition and data processing are respectively carried out on all array element phased arrays and grouped array element phased arrays, high detection precision and rapid positioning of metal fatigue damage are realized, and the detection precision of early fatigue damage of metal materials is improved; the method realizes the quick positioning and imaging detection of the early fatigue damage of the metal material.
Description
Technical Field
The invention relates to a nonlinear imaging method for detecting early fatigue closed cracks of a metal material.
Background
Metal materials or structures can fatigue under the repeated action of alternating loads. Fatigue refers to the incremental process of localized, permanent damage occurring at some point in a material under cyclic loading. After sufficient stress or strain cycles, as fatigue damage accumulates, the material develops fatigue microcracks (closed cracks) that propagate further into the macrocracks until the component is completely fractured, resulting in complete failure of the component or structure, which is the full life cycle experienced during fatigue failure of the material. The development of fatigue damage and fatigue cracks is an early stage in the life cycle of a material and occupies a large portion of the total life cycle. In practical engineering, when a metal member is in an early stage of fatigue damage, it is often difficult to find it by conventional non-destructive inspection techniques because macroscopic defects that can be detected have not yet formed. However, in the case of a metal member subjected to a reciprocating alternating load for a long period of time, once a macrocrack is formed, the macrocrack rapidly propagates, and there is a high possibility that the macrocrack suddenly breaks, thereby causing a catastrophic accident. The traditional nondestructive imaging method (magnetic powder detection, X-ray, acoustic emission detection, ultrasonic detection and the like) can only find the large-scale defects with formed macroscopic cracks. The application of nonlinear response of materials to ultrasonic waves to carry out nondestructive detection on micro-damage of equipment and components is a hot point of research in recent years, and is an effective supplement to a material micro-defect evaluation method. The currently common non-linear detection method researches include a high-order harmonic detection method based on traditional ultrasound, a mixing modulation detection method based on traditional ultrasound and a non-linear detection method based on an ultrasonic phased array.
1. Higher harmonic detection method based on traditional ultrasound
At present, typical documents are:
(1) the method comprises the steps of von Webber, Wanchuhao, Liu and Steel 7075 aluminum alloy fatigue damage multipoint rapid nonlinear ultrasonic detection [ J ] mechanical engineering report 2018,54(10):23-28.
(2) The non-linear Rayleigh wave imaging method [ J ] of the fatigue damage of the metal surface of Lian ocean, Panqian, Wangzhanba [ nondestructive testing ], 2018,40(08):34-38, the document provides a non-linear Rayleigh surface wave imaging method to realize the detection of the fatigue damage of the metal surface. Test results show that the nonlinear Rayleigh wave imaging method can be used for detecting fatigue damage of the metal surface.
The high-order harmonic detection method based on traditional ultrasound utilizes the nonlinear effect when the ultrasonic wave encounters tiny damage (nonlinear defect) in the propagation process of the test piece: and generating higher harmonic components in integral multiple relation with the fundamental frequency in a frequency domain, and determining damage through harmonic amplitude or nonlinear coefficients, wherein the second harmonic and the third harmonic are widely applied.
The method has the following defects:
(1) the ultrasonic excitation mode with larger amplitude is required to excite higher harmonics, so that the requirement on a detection system is relatively high;
(2) the positioning, the qualification and the imaging of the early fatigue defects cannot be realized.
(3) The instrument itself can bring system nonlinearity, influence actual judgement.
2. Mixing modulation detection method based on traditional ultrasound
At present, there are typical documents:
(1) microcrack positioning method for nonlinear ultrasonic unilateral excitation mixing based on wavelets (publication No. CN 108709934A)
The invention discloses a micro-crack positioning method of nonlinear ultrasonic unilateral excitation frequency mixing based on wavelets, which is used for acquiring the optimal parameters capable of representing the characteristic frequency of a frequency mixing signal by combining simulation and experiment. The result shows the accuracy and feasibility of the nonlinear lamb wave different-side excitation mixing positioning method based on wavelet transformation.
(2) Nonlinear ultrasonic mixing method for detecting structural fatigue crack orientation (publication No. CN 108872393A)
The invention discloses a nonlinear ultrasonic frequency mixing method for detecting the structural fatigue crack direction, which is used for carrying out continuous wavelet transformation on each received signal, extracting the amplitude of a frequency mixing wave and carrying out frequency mixing sound field directivity analysis. The result shows that the fatigue crack direction is calculated according to the change rule of the reflection mixed wave propagation direction along with the fatigue crack direction.
The method has the following defects:
(1) the characterization and imaging of early fatigue defects cannot be achieved.
(2) The nonlinear damage component is very small and difficult to extract, the amplitude of the acquired signal is very small, the detection and judgment requirements cannot be met, a special signal processing method is often needed to correct the ultrasonic signal, and the signal processing requirement is high.
(3) The instrument itself can bring system nonlinearity, influence actual judgement.
3. Nonlinear detection method based on ultrasonic phased array
At present, there are typical documents:
(1) nonlinear ultrasonic phased array imaging method for microcrack detection (publication No. CN 105004792A)
According to the technical scheme, the fundamental wave energy loss difference at each focusing point is used as nonlinear response representation by utilizing two focusing modes of parallel and sequential, and whether damage exists at the focusing point can be judged. Because the influence caused by the system nonlinearity can be eliminated in the difference operation under the two focusing modes, the method perfectly solves the problem of the influence caused by the system nonlinearity.
The method has the following defects:
(1) the prerequisite requirement of the method is that the phased array system has sequential focusing capability, namely the phased array instrument has Full Matrix Capture (FMC) function, namely in one acquisition (detection) period, the array element adopts a single-transmission multi-reception working mode: a certain single array element in the array is excited, and all N array elements receive at the same time, so that the requirement on equipment is high;
(2) the data processing is very complex and time-consuming, and is difficult to apply to the actual rapid inspection site.
Disclosure of Invention
The invention aims to solve the technical problem of providing a fatigue damage nonlinear imaging method which has simple equipment, no interference, high detection precision and can quickly position and image.
The invention adopts the technical scheme that a nonlinear imaging method for the fatigue closed crack of the metal material comprises the following steps,
A. carrying out phased array distribution control on the test piece;
B. respectively acquiring data of all array element phased arrays and grouped array element phased arrays;
C. respectively calculating the corresponding acoustic kinetic energy of all array elements and phased array
Acoustic kinetic energy corresponding to grouped array element phased array
、
、…、
；
D. Calculating a non-linear characterizing parameter
The distribution of (a);
E. will be provided with
The calculation results of (1) are imaged.
The step a arranges transducer elements of a phased array system,Nthe arrangement mode of the array elements is a one-dimensional array mode;
the step C utilizes all array elements (the number of the array elements is set asN) Parallel focusing mode, calculating different focus points
Acoustic kinetic energy in the fundamental frequency band of
。
Wherein
Is the starting frequency of the fundamental wave,
is the termination frequency of the fundamental wave,
is as follows
The time domain of each array element receives signals as
The spectrum of (a) is:
then, the acoustic kinetic energy in the fundamental wave frequency band obtained by phased array focusing under each group is calculated by the formula (1)
、
、…、
。
The invention has the advantages that the detection can be finished by adopting common phased array equipment, so that the detection cost is reduced; in addition, as data acquisition and data processing are respectively carried out on all array element phased arrays and grouped array element phased arrays, high detection precision and rapid positioning of metal fatigue damage are realized, and the detection precision of early fatigue damage of metal materials is improved; the method realizes the quick positioning and imaging detection of the early fatigue damage of the metal material.
Drawings
FIG. 1 is a schematic diagram of an ultrasonic phased array experiment of the present invention;
FIG. 2 is a phased array grouping method of the present invention;
FIG. 3 is a schematic diagram of the block phased array algorithm of the present invention;
fig. 4 is a flow chart of the imaging algorithm of the present invention.
Detailed Description
The invention is described in further detail below with reference to the following figures and detailed description:
as shown in fig. 1-4, the invention relates to a nonlinear imaging method for fatigue closed cracks of metal materials, which comprises the following steps:
A. carrying out phased array arrangement on a detection test piece; the transducer elements of a phased array system are arranged,Nthe arrangement mode of the array elements is a one-dimensional array form; will be provided withNGrouping the array elements, supposing to be divided intoMGroup, the 1 st array element and the 1 stM+1 array element, 2 ndM+1 piecesArray elements are in a group, the 2 nd array element and the 2 nd array elementM+2 array elements, 2 ndM+2 array elements are grouped, and so on, to obtainMAnd a grouped phased array.
B. Respectively acquiring data of all array element phased arrays and grouped array element phased arrays; each group of array elements carries out an independent parallel focusing process, and the focusing points are still selected according to the positions of all the array elements when focusing (namely according to the delay rule that the same array elements are unchanged when all the array elements are focused).
C. Respectively calculating the corresponding acoustic kinetic energy of all array elements and phased array
Acoustic kinetic energy corresponding to grouped array element phased array
、
、…、
(ii) a Using all array elements (given the number of array elements asN) Parallel focusing mode, calculating different focus points
Acoustic kinetic energy in the fundamental frequency band of
。
Wherein
Is the starting frequency of the fundamental wave,
is the termination frequency of the fundamental wave,
is as follows
The time domain of each array element receives signals as
The spectrum of (a) is:
then, the acoustic kinetic energy in the fundamental wave frequency band obtained by phased array focusing under each group is calculated by the formula (1)
、
、…、
。
D. Calculating a non-linear characterizing parameter
The distribution of (a); focusing by using all array elementsMThe linear response and imaging result of the sum of the respective focusing at the focusing point are completely the same, but the nonlinear response, i.e. the energy loss in the excitation bandwidth (fundamental wave), of the two modes excited at the focusing point is greatly different.
For example, consider the case where only second harmonics are breeding: it is still assumed that the phased array system includesNThe amplitude of the linear response part caused at the focusing point for one array element can be set
If the focus point is defectivePosition, amplitude of the second harmonic
In direct proportion, the energy of the second harmonic is
Proportional, i.e. energy loss of fundamental wave and
is in direct proportion. For the case of focusing with all array elements, the total linear response component amplitude induced at the focus point is
The energy loss is
。
For the case of group focusing, the linear response at the focal point within each group has a partial amplitude of
And the energy loss of the focusing point is
M groups of energy losses and are
。
Thus, the energy loss in the fundamental band where all array elements are focused at the focal point will be the sum of the values at the time of focusing the packets
The energy difference will gradually increase as the number of packets increases, and the imaging result will become more obvious. For practical ultrasound systems, it is of course possible to expect the energy difference to be more pronounced than for the generation of the second harmonic.
E. Will be provided with
The calculation results of (1) are imaged.
Wherein
Is as followsmAcoustic kinetic energy in the fundamental frequency band at the focal point of the group.
By calculating different focal points
The value distribution obtains the imaging result of the nonlinear defect, and because the experimental conditions are completely the same when all array elements are adopted for focusing and when the array elements are grouped for focusing, the influence of the nonlinear arrival of the system can be completely eliminated in the difference.
The invention can finish the detection by adopting the common phased array equipment, thereby reducing the detection cost; in addition, as data acquisition and data processing are respectively carried out on all array element phased arrays and grouped array element phased arrays, high detection precision and rapid positioning of metal fatigue damage are realized, and the detection precision of early fatigue damage of metal materials is improved; the method realizes the quick positioning and imaging detection of the early fatigue damage of the metal material.
It should be noted that the protection scope of the present invention is not limited to the above specific examples, and the object of the present invention can be achieved by substantially the same structure according to the basic technical concept of the present invention, and embodiments that can be imagined by those skilled in the art without creative efforts belong to the protection scope of the present invention.
Claims (1)
1. A nonlinear imaging method for fatigue closed cracks of metal materials is characterized by comprising the following steps,
A. carrying out phased array arrangement on a detection test piece; arranging transducer array elements of a phased array system, wherein the arrangement mode of N array elements is a one-dimensional array form; grouping N array elements, supposing that the N array elements are divided into M groups, then grouping the 1 st array element, the M +1 st array element and the 2M +1 st array element, grouping the 2 nd array element, the M +2 nd array element and the 2M +2 nd array element, and so on to obtain M grouped phased array arrays;
B. respectively acquiring data of all array element phased arrays and grouped array element phased arrays; each group of array elements is subjected to an independent parallel focusing process, and the focusing points are still selected according to the positions of all array elements during focusing;
C. respectively calculating the corresponding acoustic kinetic energy of all array elements and phased array
Acoustic kinetic energy corresponding to grouped array element phased array
Calculating different focus points by using all array elements, setting the number of the array elements as N, and adopting parallel focusing modes
Acoustic kinetic energy in the fundamental frequency band of
Wherein omega1Is the starting frequency of the fundamental wave, ω2Is the termination frequency of the fundamental wave, Hm(omega) is the time domain received signal of the m array element is
I.e. there are:
then, the acoustic kinetic energy in the fundamental wave frequency band obtained by phased array focusing under each group is calculated by the formula (1)
D. Calculating the distribution of a nonlinear characterization parameter gamma;
E. imaging the calculated result of gamma;
wherein
Is the acoustic kinetic energy in the fundamental frequency band at the m-th group of foci.
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