CN109738526B - Method for positioning and size determination of weak stress area of lower layer of metal shell - Google Patents
Method for positioning and size determination of weak stress area of lower layer of metal shell Download PDFInfo
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Abstract
The invention discloses a method for positioning and size determination of a weak stress area at the lower layer of a metal shell, which comprises the steps of firstly carrying out area division on the surface of a tested piece to obtain a boundary positioning reference array of the weak stress area, then carrying out primary positioning on the weak stress area by utilizing an acoustic impedance principle to find out a primary contour line and a contour point of the weak stress area, finally adjusting the contour line and the contour line, connecting to form a closed area to be regarded as the finally measured weak stress area, and calculating the area of the area.
Description
Technical Field
The invention belongs to the technical field of measurement, and particularly relates to a method for positioning and size determination of a weak stressed area of a lower layer of a metal shell.
Background
The aerospace and chemical industries often involve detailed quality control and certification. It is necessary to ensure the quality and safety of the related equipment, and the strength detection of the critical structure is an important part of the equipment, and has been receiving wide attention in recent years. The wing structure taking metal as a shell, the tank body structure for storing chemical products and the like are widely applied to the fields of aviation, chemical industry and the like, and if the conditions such as debonding, uneven stress distribution, incomplete filling and the like occur inside the structure, the reliability and safety of aircraft and chemical production can be influenced, and subversive consequences can be generated. At present, the testing method aiming at the stress distribution of the lower layer of the metal shell is mainly divided into destructive testing and nondestructive testing.
The destructive detection method is a method such as a force loading test, a contour method, a longitudinal cutting method, a grooving method, a drilling method and the like. The force loading test can change the original structure detection of a test object, and the contour method and the longitudinal cutting method need to carry out electric spark cutting on the test object. The grooving method and the drilling method realize stress detection by releasing the internal stress of a test object. The small-diameter blind hole method is a standard test method for field actual measurement due to small damage to workpieces and reliable measurement. However, these methods are limited by the principle of testing and cannot be used for evaluating the wear and tear and health of the equipment already put into use.
Nondestructive testing methods include X-ray diffraction, neutron diffraction, magnetic, ultrasonic, tapping, and acoustic impedance. The X-ray diffraction method is perfect in theory, but the application of the method is greatly limited due to ray damage and the fact that only surface stress can be measured, and the test depth is about 1-30 mu m; the principle of the neutron imaging technology is similar to that of X-ray imaging widely applied at present, the internal condition of a sample is explained by detecting the intensity distribution of rays after the rays pass through the sample, but the neutron imaging has stronger penetrability. Neutron imaging needs to meet more rigorous conditions and is only available to large scientific research units such as the U.S. aerospace agency, the los alamos national laboratory, the japan atomic energy institute, the china engineering and physics research institute, and the like; the magnetic method is used for determining according to the change relation between stress and a magnetization curve in the ferromagnetic body magnetic saturation process, and is applicable within a certain range (generally not more than 10mm of measurement depth); the acoustic detection utilizes an acoustic transducer, and mainly comprises an acoustic elasticity detection method and an acoustic resistance detection method, wherein the acoustic elasticity detection method obtains the stress condition inside a test object by analyzing the relationship between the propagation speed of elastic waves in a solid material and stress, but the acoustic elasticity effect is very weak, the influence of stress change on the ultrasonic propagation speed is very small, and the accurate measurement of the sound speed has higher requirements on the precision and the sensitivity of detection equipment; the tapping method is to tap a tested object to generate vibration, and to use the sound heard by human ears as a judgment result to judge whether the tested object has defects. Its advantages are high convenience, low cost and easy implementation. The disadvantage is that it relies on the subjective judgment of the operator and can only resolve larger or shallower defects. The acoustic impedance detection method is also called a mechanical impedance detection method, and can convert mechanical impedance reflecting the vibration characteristics of the material into load impedance of the ultrasonic transducer. The mechanical impedance of the material has a certain relation with the internal stress distribution, and the change of the mechanical impedance of the material can be judged by measuring the characteristics of the ultrasonic transducer, so that the aim of detection is fulfilled. However, when the detection is performed by the acoustic group method, it is generally known that the amplitude, phase and frequency variation of the detection signal distinguish whether the detected object has defects, but it is difficult to perform quantitative analysis.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a method for positioning and judging the size of a weak stress area on the lower layer of a metal shell.
In order to achieve the above purpose, the present invention provides a method for positioning and determining the size of a weak stressed area on a lower layer of a metal casing, which is characterized by comprising the following steps:
(1) dividing the surface of the tested piece into regions
(1.1) dividing the surface of the tested piece into n multiplied by n small blocks marked as SijEach small block SijIs L × L, where i, j ∈ {1,2, …, n }, i is the number of rows, and j is the number of columnsL is the side length of the small block;
(1.2) setting the weak stress area as a closed area and the size of the minimum weak stress area as Lw×Lw，LwThe length of the minimum weak stress area is the side length, the area of the small block is k times of the area of the minimum weak stress area, and k is more than 0 and less than or equal to 1;
(2) obtaining the boundary positioning reference array of the weak stress area
(2.1) placing two acoustic transducers at two sides of the boundary of the weak stress area, wherein the distance between the two acoustic transducers and the boundary is L/2, one acoustic transducer is used as a sending end and is placed in the weak stress area, and the other acoustic transducer is used as a receiving end and is placed in the non-weak stress area;
(2.2) at the sending end, the exciting end probe of the acoustic transducer emits mechanical waves to the tested piece at a certain frequency; at a receiving end, a receiving end probe of the acoustic transducer collects a vibration signal of the surface vibration of the tested piece caused by mechanical waves, and performs frequency domain transformation on the vibration signal to obtain a boundary positioning reference array corresponding to the reference frequency and the reference amplitude, and the boundary positioning reference array is marked as [ f [ ]ref、Aref]；
(3) Preliminary positioning of the weak stressed area
(3.1) placing two acoustic transducers in the centers of the two small blocks, wherein one acoustic transducer is used as a sending end, and the other acoustic transducer is used as a receiving end;
(3.2) acquiring a group of corresponding frequency and amplitude arrays marked as [ f ] according to the method in the step (2.2)1、A1](ii) a Then exchanging the transmitting end and the receiving end, acquiring another group of corresponding frequency and amplitude arrays according to the method in the step (2.2), and recording the arrays as [ f2、A2]；
(3.3) Small Block scanning
Scanning the small blocks in a longitudinal manner: sequentially selecting two small blocks S adjacent to each other up and down in each rowijAnd Si+1jThen, consistency analysis is carried out, when two adjacent small blocks are inconsistent groups, whether the inconsistent group number is an odd number or an even number is judged, when the inconsistent group number is an even number, the intersection line position corresponding to the two adjacent small blocks is marked, and when the inconsistent group number is an even number, the intersection line position corresponding to the two adjacent small blocks is markedWhen the number of the groups is odd, no mark is made;
scanning the small blocks in a transverse mode: minimum row number i of small block above intersection position marked by longitudinal scanningLminMaximum number of rows i of small block under intersection of marking lineLmaxSequentially selecting small blocks S adjacent to each other left and right in each row as a transverse scanning rangeijAnd Sij+1Carrying out consistency analysis, judging whether the number of the inconsistent groups is an odd number or an even number when the two adjacent small blocks are inconsistent groups, marking the intersection line position corresponding to the two adjacent small blocks when the number of the inconsistent groups is the even number, and not marking when the number of the inconsistent groups is the odd number;
(3.4) selecting the arrays [ f ] respectively1、A1]And [ f2、A2]The maximum amplitude and its corresponding frequency in (d) are denoted as [ f [ ]1am、A1max]And [ f2am、A2max]；
Let h be | f1ma-f2maI, calculating (f)1ma-h,f1ma+ h) and (f)2ma-h,f2maEnergy E in the range of + h)1,E2；
(3.5) setting a consistency determination threshold s1，0＜s1Less than 1; when in use
Or
When it is determined [ f1、A1]And [ f2、A2]If the two arrays are inconsistent, marking a group of corresponding small blocks with larger maximum amplitude values as outer sides, and marking a group of corresponding small blocks with smaller maximum amplitude values as inner sides, and then entering the step (4); otherwise, reducing the k value, repeating the step (3), and judging that no weak stress area exists on the surface of the tested piece when the k value reaches the lower limit and no inconsistent array still exists;
(4) taking the marked intersecting line as a primary contour line of the weak stress area
(4.1) placing two acoustic transducers on the inner small block and the outer small block marked in the step (3.5), wherein the acoustic transducers placed on the inner small block are used as sending ends, and the acoustic transducers placed on the outer small block are used as receiving ends;
(4.2) acquiring a group of corresponding frequency and amplitude arrays marked as [ f ] according to the method in the step (2.2)3、A3]Then calculate A3And ArefInter-euclidean distance d1；
(4.3) keeping the distance between the sending end and the receiving end unchanged, moving the acoustic transducer upwards or downwards or leftwards or rightwards for a short distance, and then respectively acquiring corresponding frequency and amplitude arrays in the two moving modes according to the method in the step (2.2), and recording the frequency and amplitude arrays as [ f4、A4]、[f5、A5]Respectively calculating A4、A5And ArefInter-euclidean distance d2、d3；
(4.4) comparison of d2、d3And d1If d is large or small2、d3Are all greater than d1Marking the intersecting line of the distance centers of the sending end and the receiving end as an adjusted contour line; if d is2、d3One of which is less than d1Keeping the distance between the transmitting end and the receiving end unchanged and being less than d1Continuously moving the small distance in the direction corresponding to the moving mode, recalculating the Euclidean distance according to the method in the step (4.3), if the recalculated Euclidean distance is still smaller than the Euclidean distance calculated in the step (4.3), continuously moving according to the direction, and when the moving upper limit is reached, taking the distance center point of the small distance moved at the upper limit position as a final contour point; otherwise, taking the distance center point of the last moving small distance as a final contour point; and the other conditions are regarded as test failure;
(5) obtaining the final weak stress area and size
And regarding the closed area formed by connecting the adjusted contour points and the contour lines as a finally measured weak stress area, and calculating the area of the area.
The invention aims to realize the following steps:
the invention relates to a method for positioning and judging the size of a weak stress area at the lower layer of a metal shell, which comprises the steps of firstly carrying out area division on the surface of a tested piece to obtain a boundary positioning reference array of the weak stress area, then carrying out initial positioning on the weak stress area by utilizing an acoustic impedance principle to find out an initial contour line and contour points of the weak stress area, finally adjusting the contour points and the contour lines, connecting to form a closed area to be regarded as the finally measured weak stress area, and calculating the area of the area.
Meanwhile, the method for positioning and judging the size of the lower layer weak stress area of the metal shell has the following beneficial effects:
(1) the test depth is deeper compared with the X-ray diffraction method and the magnetic method; compared with a neutron imaging technology, the test condition is easy to meet;
(2) the method for scanning the defect edge is provided, the outline of the weak stress area is preliminarily marked, the reference signal acquisition method is provided, the preliminarily marked area is further adjusted, and therefore quantitative analysis of the position and the size of the stress area is achieved.
Drawings
FIG. 1 is a flow chart of a method for positioning and determining the size of a weak stressed area at the lower layer of a metal shell according to the present invention;
FIG. 2 is a schematic view of a test piece;
FIG. 3 is a schematic diagram of a boundary positioning reference array for obtaining a weak stress area;
FIG. 4 is a schematic diagram of one embodiment of a preliminary outline marker;
FIG. 5 is a schematic view of one embodiment of a final outline marker;
Detailed Description
The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.
Examples
FIG. 1 is a flow chart of a method for positioning and determining the size of a weak stressed area of a lower layer of a metal shell according to the present invention.
In this embodiment, as shown in fig. 1, a method for positioning and determining a size of a weak stressed area of a lower layer of a metal casing according to the present invention includes the following steps:
as shown in fig. 2(a), the test piece without the weak force-receiving area is composed of a metal case 1 and an internal filler 2; as shown in fig. 2(b), the test piece having a weak force receiving area is composed of a metal case 1, an internal filler 2, and a weak force receiving area 3.
Next, we will explain the test piece shown in FIG. 2(b) in detail.
S1, dividing the surface of the tested piece into regions
S1.1, dividing the surface of the tested piece into n multiplied by n small blocks which are marked as SijEach small block SijThe area of (a) is L multiplied by L, wherein i, j belongs to {1,2, …, n }, i is the row number, j is the column number, and L is the side length of the small block;
s1.2, setting the weak stress area as a closed area and setting the size of the minimum weak stress area as Lw×Lw，LwThe length of the minimum weak stress area is the side length, the area of the small block is k times of the area of the minimum weak stress area, and k is more than 0 and less than or equal to 1;
s2, obtaining the boundary positioning reference array of the weak stress area
S2.1, as shown in figure 3, placing two acoustic transducers at two sides of the boundary of the weak stress area, wherein the distance between the two acoustic transducers and the boundary is L/2, one acoustic transducer 4 is used as a sending end and is placed in the weak stress area, and the other acoustic transducer 5 is used as a receiving end and is placed in the non-weak stress area;
s2.2, at a sending end, a probe at an excitation end of an acoustic transducer emits mechanical waves to a tested piece at the frequency of tens of kilohertz; at a receiving end, a receiving end probe of an acoustic transducer collects vibration signals of the surface vibration of a tested piece caused by mechanical waves, frequency domain transformation is carried out on the vibration signals, n groups of mechanical wave signals are collected, n groups of boundary positioning reference arrays of corresponding reference frequencies and reference amplitudes are obtained, and the boundary positioning reference arrays are marked as [ f [ ]ref、Aref]；
S3, carrying out primary positioning on the weak stress area
S3.1, placing two acoustic transducers in the centers of the two small blocks, wherein one acoustic transducer is used as a sending end, and the other acoustic transducer is used as a receiving end;
s3.2, acquiring an array of n groups of corresponding frequencies and amplitudes according to the method in the step S2.2, and recording the array as [ f1、A1](ii) a Then exchanging the sending end and the receiving end, acquiring the other n groups of corresponding frequency and amplitude arrays according to the method in the step S2.2, and recording the arrays as [ f2、A2]；
S3.3, scanning small blocks
Scanning the small blocks in a longitudinal manner: sequentially selecting two small blocks S adjacent to each other up and down in each rowijAnd Si+1jThen, consistency analysis is carried out, when two adjacent small blocks are inconsistent groups, whether the inconsistent group number is an odd number or an even number is judged, when the inconsistent group number is the even number, the intersection line position corresponding to the two adjacent small blocks is marked, and when the inconsistent group number is the odd number, no marking is carried out;
scanning the small blocks in a transverse mode: minimum row number i of small block above intersection position marked by longitudinal scanningLminMaximum number of rows i of small block under intersection of marking lineLmaxSequentially selecting small blocks S adjacent to each other left and right in each row as a transverse scanning rangeijAnd Sij+1Carrying out consistency analysis, judging whether the number of the inconsistent groups is an odd number or an even number when the two adjacent small blocks are inconsistent groups, marking the intersection line position corresponding to the two adjacent small blocks when the number of the inconsistent groups is the even number, and not marking when the number of the inconsistent groups is the odd number;
s3.4, respectively selecting an array [ f1、A1]And [ f2、A2]The maximum amplitude and its corresponding frequency in (d) are denoted as [ f [ ]1am、A1max]And [ f2am、A2max]；
Let h be | f1ma-f2maI, calculating (f)1ma-h,f1ma+ h) and (f)2ma-h,f2maEnergy E in the range of + h)1,E2；
S3.5, setting a consistency judgment threshold value S1，0＜s1Less than 1; when in use
Or
When it is determined [ f1、A1]And [ f2、A2]If the two arrays are inconsistent, marking a group of corresponding small blocks with larger maximum amplitude values as outer sides, and marking a group of corresponding small blocks with smaller maximum amplitude values as inner sides, and then entering step S4; otherwise, reducing the k value, repeating the step S3, and judging that the surface of the tested piece has no weak stress area when the k value reaches the lower limit and no inconsistent array still exists;
s4, taking the marked intersecting line as the preliminary contour line of the weak stress area
S4.1, placing two acoustic transducers on the inner small block and the outer small block marked in the step S3.5, wherein the acoustic transducers placed on the inner small block are used as sending ends, and the acoustic transducers placed on the outer small block are used as receiving ends;
s4.2, acquiring an array of n groups of corresponding frequencies and amplitudes according to the method in the step S2.2, and recording the array as [ f3、A3]Then calculate A3And ArefInter-euclidean distance d1；
Wherein the Euclidean distance d1The calculation method comprises the following steps:
wherein n represents the total number of the collected amplitudes,
representing the i-th amplitude of the acquisition,
reference value representing the ith amplitude；
S4.3, keeping the distance between the sending end and the receiving end unchanged, moving the acoustic transducer upwards or downwards or leftwards or rightwards for a small distance, and then respectively acquiring corresponding frequency and amplitude arrays in the two moving modes according to the method in the step S2.2, and recording the frequency and amplitude arrays as [ f4、A4]、[f5、A5]Respectively calculating A4、A5And ArefInter-euclidean distance d2、d3Specific calculation method and d1The same, which is not described herein;
s4.4, comparison d2、d3And d1If d is large or small2、d3Are all greater than d1As shown in fig. 4, the intersection line of the distance centers between the transmitting end and the receiving end is marked as the adjusted contour line;
if d is2、d3One of which is less than d1Keeping the distance between the transmitting end and the receiving end unchanged and being less than d1Continuously moving the small distance in the direction corresponding to the moving mode, recalculating the Euclidean distance according to the method in the step S4.3, if the recalculated Euclidean distance is still smaller than the Euclidean distance calculated in the step S4.3, continuously moving the small distance according to the direction, and taking the distance center point of the small distance moved at the upper limit position as a final contour point when the moving upper limit is reached; otherwise, taking the distance center point of the last moving small distance as a final contour point;
in the embodiment, the moving range does not exceed L/4, and L/4L is taken as a moving step, wherein L is a positive integer, and the scanning is more precise when the value is larger;
as shown in fig. 5(a), calculating the euclidean distance after moving up once, if the recalculated euclidean distance is still smaller than the euclidean distance calculated in step S4.3, continuing to move up by L/4L, and when the upper limit of movement is reached, taking the distance center point of the L/4L distance moved at the upper limit position as the final contour point; if the recalculated Euclidean distance is larger than the Euclidean distance calculated in the step S4.3, taking the distance center point of the last moved L/4L distance as a final contour point;
as shown in fig. 5(b), calculating the euclidean distance after moving down once, if the recalculated euclidean distance is still smaller than the euclidean distance calculated in step S4.3, continuing to move downward by L/4L, and when the lower limit of movement is reached, taking the distance center point of the L/4L distance moved at the lower limit position as the final contour point; if the recalculated Euclidean distance is larger than the Euclidean distance calculated in the step S4.3, taking the distance center point of the last moved L/4L distance as a final contour point;
otherwise, the other conditions are regarded as test failure;
s5, acquiring final weak stress area and size
And regarding the closed area formed by connecting the adjusted contour points and the contour lines as a finally measured weak stress area, and calculating the area of the area.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.
Claims (2)
1. A method for positioning and size determination of a weak stress area at the lower layer of a metal shell is characterized by comprising the following steps:
(1) dividing the surface of the tested piece into regions
(1.1) dividing the surface of the tested piece into n multiplied by n small blocks marked as SijEach small block SijThe area of (a) is L multiplied by L, wherein i, j belongs to {1,2, …, n }, i is the row number, j is the column number, and L is the side length of the small block;
(1.2) setting the weak stress area as a closed area and the size of the minimum weak stress area as Lw×Lw，LwThe length of the minimum weak stress area is the side length, the area of the small block is k times of the area of the minimum weak stress area, and k is more than 0 and less than or equal to 1;
(2) obtaining the boundary positioning reference array of the weak stress area
(2.1) placing two acoustic transducers at two sides of the boundary of the weak stress area, wherein the distance between the two acoustic transducers and the boundary is L/2, one acoustic transducer is used as a sending end and is placed in the weak stress area, and the other acoustic transducer is used as a receiving end and is placed in the non-weak stress area;
(2.2) at the sending end, the exciting end probe of the acoustic transducer emits mechanical waves to the tested piece at a certain frequency; at a receiving end, a receiving end probe of the acoustic transducer collects a vibration signal of the surface vibration of the tested piece caused by mechanical waves, and performs frequency domain transformation on the vibration signal to obtain a boundary positioning reference array corresponding to the reference frequency and the reference amplitude, and the boundary positioning reference array is marked as [ f [ ]ref、Aref]；
(3) Preliminary positioning of the weak stressed area
(3.1) placing two acoustic transducers in the centers of the two small blocks, wherein one acoustic transducer is used as a sending end, and the other acoustic transducer is used as a receiving end;
(3.2) acquiring a group of corresponding frequency and amplitude arrays marked as [ f ] according to the method in the step (2.2)1、A1](ii) a Then exchanging the transmitting end and the receiving end, acquiring another group of corresponding frequency and amplitude arrays according to the method in the step (2.2), and recording the arrays as [ f2、A2]；
(3.3) Small Block scanning
Scanning the small blocks in a longitudinal manner: sequentially selecting two small blocks S adjacent to each other up and down in each rowijAnd Si+1jThen, consistency analysis is carried out, when two adjacent small blocks are inconsistent groups, whether the inconsistent group number is an odd number or an even number is judged, when the inconsistent group number is the even number, the intersection line position corresponding to the two adjacent small blocks is marked, and when the inconsistent group number is the odd number, no marking is carried out;
scanning the small blocks in a transverse mode: minimum row number i of small block above intersection position marked by longitudinal scanningLminMaximum number of rows i of small block under intersection of marking lineLmaxSequentially selecting small left and right adjacent lines in each row as a transverse scanning rangeBlock SijAnd Sij+1Carrying out consistency analysis, judging whether the number of the inconsistent groups is an odd number or an even number when the two adjacent small blocks are inconsistent groups, marking the intersection line position corresponding to the two adjacent small blocks when the number of the inconsistent groups is the even number, and not marking when the number of the inconsistent groups is the odd number;
(3.4) selecting the arrays [ f ] respectively1、A1]And [ f2、A2]The maximum amplitude and its corresponding frequency in (d) are denoted as [ f [ ]1am、A1max]And [ f2am、A2max]；
Let h be | f1ma-f2maI, calculating (f)1ma-h,f1ma+ h) and (f)2ma-h,f2maEnergy E in the range of + h)1,E2；
(3.5) setting a consistency determination threshold s1，0＜s1Less than 1; when in use
Or
When it is determined [ f1、A1]And [ f2、A2]If the two arrays are inconsistent, marking a group of corresponding small blocks with larger maximum amplitude values as outer sides, and marking a group of corresponding small blocks with smaller maximum amplitude values as inner sides, and then entering the step (4); otherwise, reducing the k value, repeating the step (3), and judging that no weak stress area exists on the surface of the tested piece when the k value reaches the lower limit and no inconsistent array still exists;
(4) taking the marked intersecting line as a primary contour line of the weak stress area
(4.1) placing two acoustic transducers on the inner small block and the outer small block marked in the step (3.5), wherein the acoustic transducers placed on the inner small block are used as sending ends, and the acoustic transducers placed on the outer small block are used as receiving ends;
(4.2) acquiring a group of corresponding frequency and amplitude arrays marked as [ f ] according to the method in the step (2.2)3、A3]Then calculate A3And ArefInter-euclidean distance d1；
(4.3) keeping the distance between the sending end and the receiving end unchanged, moving the acoustic transducer upwards or downwards or leftwards or rightwards for a short distance, and then respectively acquiring corresponding frequency and amplitude arrays in the two moving modes according to the method in the step (2.2), and recording the frequency and amplitude arrays as [ f4、A4]、[f5、A5]Respectively calculating A4、A5And ArefInter-euclidean distance d2、d3；
(4.4) comparison of d2、d3And d1If d is large or small2、d3Are all greater than d1Marking the intersecting line of the distance centers of the sending end and the receiving end as an adjusted contour line; if d is2、d3One of which is less than d1Keeping the distance between the transmitting end and the receiving end unchanged and being less than d1Continuously moving the small distance in the direction corresponding to the moving mode, recalculating the Euclidean distance according to the method in the step (4.3), if the recalculated Euclidean distance is still smaller than the Euclidean distance calculated in the step (4.3), continuously moving according to the direction, and when the moving upper limit is reached, taking the distance center point of the small distance moved at the upper limit position as a final contour point; otherwise, taking the distance center point of the last moving small distance as a final contour point; and the other conditions are regarded as test failure;
(5) obtaining the final weak stress area and size
And regarding the closed area formed by connecting the adjusted contour points and the contour lines as a finally measured weak stress area, and calculating the area of the area.
2. The method as claimed in claim 1, wherein the Euclidean distance d is determined by the location and size of the weak stress area of the lower layer of the metal shell1The calculation method comprises the following steps:
wherein n represents the total number of the collected amplitudes,
representing the i-th amplitude of the acquisition,
a reference value representing the ith amplitude.
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