CN112255121A - Fatigue limit evaluation method based on Matlab blade - Google Patents
Fatigue limit evaluation method based on Matlab blade Download PDFInfo
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- G—PHYSICS
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- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
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Abstract
The invention discloses a fatigue limit evaluation method for a blade based on Matlab, wherein the fatigue test data of the blade comprises picture data, temperature data, frequency response data and fatigue test data, and the blade fatigue test data post-processing method is a set of test data post-processing method established on a Matlab software platform, can quickly, comprehensively and systematically analyze the fatigue test data of the blade in batches, can quickly obtain the vibration characteristics, the fatigue limit and an S-N curve of the blade, can effectively reduce the processing time of the fatigue test data of the blade, reduces the human factors in the processing process, reduces the number of people involved in the processing of the blade data, and greatly improves the efficiency.
Description
Technical Field
The invention relates to the technical field of blade fatigue test data processing, in particular to a fatigue limit evaluation method based on a Matlab blade.
Background
Blade fatigue tests under laboratory conditions are the key to obtaining the working life of blades and are more and more concerned by aviation design and manufacturing units. More picture data, temperature data, frequency response data and fatigue test data are obtained through a blade fatigue test, when the data volume is larger, different software is used for processing manually, the efficiency is obviously lower, and the reliability of the processed data cannot be effectively guaranteed. After the test, a blade fatigue test report needs to be provided by a tester, a key chart in the test needs to be provided in the report, key data needs to be converted into characters and charts in the report, and the key data charts are dispersed in each instrument and equipment, so that a great deal of time and energy is wasted in manual processing.
Disclosure of Invention
In order to solve the above problems, the present application aims to provide a Matlab-based blade fatigue limit evaluation method.
In order to achieve the purpose of the invention, the invention provides a Matlab-based blade fatigue limit evaluation method, wherein the blade fatigue data comprises picture data, temperature data, frequency response data and fatigue test data,
the method comprises the following steps:
a. processing picture data, cutting and converting the format of the picture data by utilizing Matlab, and putting the picture data into a report document;
b. processing temperature data, namely reading a txt document by utilizing Matlab, calculating a temperature field distribution diagram of each measuring point on the surface of the blade and a temperature gradient diagram of each point on the surface of the blade according to temperature data recorded in the txt document, and screenshot and putting the temperature distribution diagram into a report document;
c. the frequency response data is processed, and the frequency response data is processed,
reading speed frequency response data stored in a computer by utilizing Matlab, obtaining an initial value of modal frequency by adopting a peak value identification method, then calculating the modal frequency and modal damping ratio by adopting a least square method,
reading stress frequency response data by utilizing Matlab, identifying modal stress corresponding to modal frequency according to the speed frequency response data, storing the modal stress in a form of a graph, and outputting the graph recording the modal frequency, the modal damping ratio and the modal stress to a report document;
according to the obtained modal stress data, a stress distribution cloud chart is made according to a strain measuring point coordinate grid, the maximum stress points of the first three are marked and used as the positions of the strain measuring points in a stress-displacement calibration test in the fatigue test; if the stresses of the first three are relatively close, increasing the number of the obtained stress points until the difference between the numerical values of the obtained stress points is more than 15%, storing the stress distribution cloud picture, and intercepting a report document;
after all the blade vibration characteristic tests are finished, carrying out statistical analysis on the modal frequency, the modal damping ratio and the modal stress, and outputting statistical results to a report document;
d. the data from the fatigue test were used,
c, according to the natural frequency identified in the step c, using the natural frequency as a fatigue test excitation frequency; according to the stress points obtained in the step c, the stress points are used as stress measuring points of a fatigue test, the maximum stress point is used as a control point, the rest measuring points are used as fatigue strain monitoring points, strain gauges are pasted on the stress measuring points of the fatigue test, basic excitation with different magnitudes is given to the blade by a vibration table, the displacement of the blade tip is obtained by a Doppler laser vibration meter, the strain gauges obtain stress data, the laser vibration meter and the strain gauges are connected into a data acquisition instrument, the data acquisition instrument stores the displacement and the stress data, the obtained stress data and the obtained displacement data are read by Matlab, the stress-displacement slope is calculated by using a least square method, a stress-displacement curve is fitted, and then the stress-displacement curve is stored and intercepted into a report in a form,
after all the blade fatigue tests are finished, the obtained slope data is utilized to statistically analyze the discreteness of the stress-displacement slope, calculate the average value, the maximum value, the minimum value and the discrete area of the slope, and store the average value, the maximum value, the minimum value and the discrete area in a set path in a form of a chart;
based on the stress-slope numerical value (the stress slope is the stress-slope of a single blade in the fatigue test), a certain blade is subjected to a stress-displacement calibration test, then a fatigue test is carried out, the next blade is replaced after the fatigue test is finished, the stress-slope calibration is carried out, and then the fatigue test is carried out), the stress magnitude of a stress control point of the set fatigue test is converted into the displacement magnitude of a displacement measuring point, then a controller is used for controlling the displacement magnitude of the displacement measuring point, so that the displacement magnitude of the point is kept unchanged in the fatigue test process, when the fatigue test reaches the specified cycle number or the blade cracks, the fatigue test is finished, and the test magnitude and the corresponding cycle number are recorded. Firstly, measuring the fatigue limit of the blade according to a small sample lifting method, wherein the small sample lifting method is a blade test magnitude adjustment method, and if the corresponding cycle times of the blade under a certain stress magnitude reach a preset value and no crack appears, the stress magnitude of the next blade is increased by one step length according to the preset step length; if the blade does not reach the preset cycle number and cracks appear under a certain stress magnitude, the stress magnitude of the next blade is reduced by one step length, the lifting process of the stress magnitude is repeated until the condition that a small subsample lifting method obtains the median fatigue limit is met, Matlab is used for reading the stress magnitude of the small subsample lifting method fatigue test and the corresponding cycle number data, the median fatigue limit is calculated according to the small subsample lifting method, and then the median fatigue limit is output to a report in a chart form,
after the median fatigue limit is obtained, an S-N curve of the blades is obtained by using a grouping method, the grouping method is firstly based on the median fatigue limit, a plurality of stress magnitude levels higher than the median fatigue limit are set, a plurality of blades are distributed under each stress magnitude level, and then the blade fatigue test is carried out based on a preset group; reading the stress magnitude of the grouped fatigue test and the corresponding cycle data, calculating the average value, standard deviation, coefficient of variation and confidence coefficient of the fatigue life under logarithmic coordinates, then storing to a set position in the form of a chart,
fitting an S-N curve based on the fatigue limit and fatigue life results obtained in this step,
and after the vibration characteristic statistical result and the fatigue test statistical result are processed, reading the processed result according to the path, outputting the processed result to a report, and then judging the test result and obtaining a conclusion.
Wherein the content of the first and second substances,
the picture data comprise the overall blade state picture shot before the test, the overall blade state picture shot after the test and the local blade crack picture.
Wherein the content of the first and second substances,
in the step a, the image data is cut and converted into a format by using Matlab, and is put into a report document, which specifically comprises the following steps:
reading in a blade overall state picture shot before a test and a blade overall state picture shot after the test, which are stored in a computer, by utilizing Matlab, identifying the position of a target in the picture, and after removing information irrelevant to the target, putting a screenshot into a report document;
and reading in local crack picture data stored in a computer by utilizing Matlab, and carrying out graying, filtering and binarization processing so as to clearly display cracks, putting the screenshot into a report document, and meanwhile, calculating crack length information and putting the crack length information into the report document.
Wherein the content of the first and second substances,
in step b, the method further comprises the following steps:
and (3) measuring the temperature of the temperature field environment where the blade is positioned before the fatigue test, ensuring that the temperature environment where the blade is positioned meets the test requirements, and outputting a txt document for recording temperature data.
Wherein the content of the first and second substances,
in step c, the method further comprises the following steps:
before fatigue test, the vibration characteristic of each blade needs to be tested, the blade is fixed on a vibration table, a force hammer or the vibration table is used for excitation, the laser vibration meter is used for obtaining the surface speed response of the set position of the blade, the strain gauge is used for obtaining the surface stress of the set position of the blade, wherein the laser vibration meter and the strain gauge are connected to a data acquisition instrument, and the data acquisition instrument stores speed frequency response data and stress frequency response data to a computer hard disk.
Wherein the content of the first and second substances,
in the step c, the process is carried out,
obtaining an initial value of modal frequency by adopting a peak value identification method, then calculating the modal frequency and modal damping ratio by adopting a least square method, and adopting the following method:
firstly, the imaginary part of the frequency response function is taken as an identification object, and the following formula is shown:
wherein I is frequency response data, N is the order of the mode to be identified,ω i in order to be the frequency of the mode shape,ωin order to be the frequency of the radio,ξ i in order to achieve modal damping,A i in order to be the modal amplitude,
the parameter vectors to be identified are:
is provided withI k As a function of frequencyω=ω k The imaginary part data of the frequency response function obtained by time measurement are sharedLThe imaginary component value vector of the actually measured frequency response function formed by the frequency points is as follows:
the imaginary part vector of the theoretical frequency response function formed by corresponding to the L frequency points can be expressed as:
the error vector of the theoretical frequency response function imaginary part and the actually measured frequency response function imaginary part at each frequency point is as follows:
and solving the modal parameters according to the operation steps of the complex modal least square iteration method.
Wherein the content of the first and second substances,
in step d, calculating the median fatigue limit by a small subsample lifting method, and adopting the following method:
median fatigue limit σ-1Expression (c):
wherein n represents the number of tests;
m-stress level progression;
σi-level i stress;
vi-represents the stress σ in the i-th orderiNumber of tests performed.
Wherein the content of the first and second substances,
in the step d, the process is carried out,
the stress-displacement slope was calculated using the least squares method as follows:
stress data arey={y iThe displacement data isx={x i }, then Y =in the linear fitting equationa 0+a 1The coefficient calculation formula in X is as follows:
in the formula:nis the number of data points.
The correlation coefficient r is:
wherein the content of the first and second substances,
the empirical formula for S-N curve fitting is as follows:
in the formula, N-cycle number, C, m, S0As the parameters of the material, it is,
let X = logN, y = log (σ)max-S0)，a 0=C，a 1= -m, fitting according to formulae (3) and (4), obtaining an S-N curve.
Wherein the content of the first and second substances,
in the step d, the process is carried out,
the average value, standard deviation and variation coefficient of the fatigue life under logarithmic coordinates are calculated by adopting the following method:
average of subsamples
Expression (c):
subsample standard deviation S expression:
coefficient of variation of subsampleC v Expression:
in the formula (I), the compound is shown in the specification,n-number of test pieces in the test group;
x i stress levels in the test group.
Compared with the prior art, the invention has the advantages that,
the blade fatigue test data post-processing method is a set of test data post-processing method established on a Matlab software platform, can quickly, comprehensively and systematically analyze blade fatigue test data in batches, can quickly obtain the vibration characteristics, the median fatigue limit and the S-N curve of the blade, can effectively reduce the processing time of the blade fatigue test data, reduces the human factors in the processing process, reduces the number of people participating in the blade data processing, and greatly improves the efficiency.
Detailed Description
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 embodiment of the invention provides a Matlab-based blade fatigue test data post-processing method, wherein the blade fatigue data comprises picture data, temperature data, frequency response data and fatigue test data,
the method comprises the following steps:
a. the data of the picture is processed, and the picture data is processed,
the picture data comprises a blade overall state picture shot before the test, a blade overall state picture shot after the test and a blade local crack picture; and (4) shooting the overall state picture of the blade before and after the test, and shooting a local picture of the crack if the blade cracks. And acquiring picture data by using a high-definition camera, and storing the picture data in a computer.
Reading in a blade overall state picture shot before a test and a blade overall state picture shot after the test, which are stored in a computer, by utilizing Matlab, identifying the position of a target in the picture, and after removing information irrelevant to the target, putting a screenshot into a report document;
reading in local crack picture data stored in a computer by utilizing Matlab, and carrying out graying, filtering and binarization processing so as to clearly display cracks, putting a screenshot into a report document, and meanwhile, calculating crack length information and putting the crack length information into the report document;
b. the temperature data is processed, and the temperature data is processed,
measuring the temperature of the temperature field environment of the blade before the fatigue test, ensuring that the temperature environment of the blade meets the test requirements, and outputting a txt document for recording temperature data;
reading a txt document by utilizing Matlab, calculating a temperature field distribution diagram of each measuring point on the surface of the blade and a temperature gradient diagram of each point on the surface of the blade according to temperature data recorded in the txt document, and screenshot and putting the temperature field distribution diagram into a report document;
the temperature measurement adopts a system consisting of a thermocouple and a temperature polling instrument, the thermocouple is arranged on the surface of the blade according to a preset position, and the temperature polling instrument acquires a thermocouple temperature signal and outputs a txt format measurement result.
c. The frequency response data is processed, and the frequency response data is processed,
the excitation frequency for the blade fatigue test is generally selected to be near the resonant frequency of the blade, and a smaller fundamental excitation forces the blade to produce a larger vibratory response.
Before fatigue test, carrying out a blade vibration characteristic acquisition test on each blade, fixing the blade on a vibration table, exciting by using a force hammer or the vibration table, acquiring surface speed response of a set position of the blade by using a laser vibration meter, and acquiring surface stress of the set position of the blade by using a strain gauge, wherein the laser vibration meter and the strain gauge are connected to a data acquisition instrument, and the data acquisition instrument stores speed frequency response data and stress frequency response data to a computer hard disk;
reading speed frequency response data stored in a computer by utilizing Matlab, obtaining an initial value of modal frequency by adopting a peak value identification method, then calculating the modal frequency and modal damping ratio by adopting a least square method,
reading stress frequency response data by utilizing Matlab, identifying modal stress corresponding to modal frequency according to the speed frequency response data, storing the modal stress in a form of a graph, and outputting the graph recording the modal frequency, the modal damping ratio and the modal stress to a report document;
obtaining an initial value of modal frequency by adopting a peak value identification method, then calculating the modal frequency and modal damping ratio by adopting a least square method, and adopting the following method:
firstly, the imaginary part of the frequency response function is taken as an identification object, and the following formula is shown:
wherein I is frequency response data, N is the order of the mode to be identified,ω i in order to be the frequency of the mode shape,ωin order to be the frequency of the radio,ξ i in order to achieve modal damping,A i is the modal amplitude.
The parameter vectors to be identified are:
is provided withI k As a function of frequencyω=ω k The imaginary part data of the frequency response function obtained by time measurement are sharedLThe imaginary component value vector of the actually measured frequency response function formed by the frequency points is as follows:
the imaginary part vector of the theoretical frequency response function formed by corresponding to the L frequency points can be expressed as:
the error vector of the theoretical frequency response function imaginary part and the actually measured frequency response function imaginary part at each frequency point is as follows:
solving modal parameters according to the operation steps of the complex modal least square iteration method;
according to the obtained modal stress data, a stress distribution cloud chart is made according to a strain measuring point coordinate grid, the maximum stress points of the first three are marked and used as the positions of the strain measuring points in a stress-displacement calibration test in the fatigue test; if the stresses of the first three are relatively close, increasing the number of the obtained stress points until the difference between the numerical values of the obtained stress points is more than 15%, storing the stress distribution cloud picture, and intercepting a report document;
after all the blade vibration characteristic tests are finished, carrying out statistical analysis on the modal frequency, the modal damping ratio and the modal stress, and outputting statistical results to a report document;
d. the data from the fatigue test were used,
c, according to the natural frequency identified in the step c, using the natural frequency as a fatigue test excitation frequency; according to the stress points obtained in the step c, the stress points are used as stress measuring points of a fatigue test, wherein the maximum stress point is used as a control point, the rest measuring points are used as fatigue strain measuring points, strain gauges are pasted on the stress measuring points of the fatigue test, basic excitation with different magnitudes is given to the blade by a vibration table, the displacement of the blade tip is obtained by a Doppler laser vibration meter, the strain gauges obtain stress data, the laser vibration meter and the strain gauges are connected into a data acquisition instrument, the data acquisition instrument stores the displacement and the stress data, the obtained stress data and the obtained displacement data are read by Matlab, the stress-displacement slope is calculated by using a least square method, a stress-displacement curve is fitted, and then the stress-displacement curve is stored and intercepted into a report in,
wherein the stress-displacement slope is calculated using a least squares method as follows:
stress data arey={y iThe displacement data isx={x i }, then Y =in the linear fitting equationa 0+a 1The coefficient calculation formula in X is as follows:
in the formula:nis the number of data points.
The correlation coefficient r is:
after all the blade fatigue tests are finished, the obtained slope data is utilized to statistically analyze the discreteness of the stress-displacement slope, calculate the average value, the maximum value, the minimum value and the discrete area of the slope, and store the average value, the maximum value, the minimum value and the discrete area in a set path in a form of a chart;
converting the stress magnitude of a stress control point of a set fatigue test into the displacement magnitude of a displacement measuring point based on the stress-slope numerical value in the step, controlling the displacement magnitude of the displacement measuring point by a controller to keep the displacement magnitude of the point unchanged in the fatigue test process, recording the test magnitude and the corresponding cycle number when the fatigue test reaches the specified cycle number or the blade cracks, measuring the fatigue limit of the blade according to a small subsample lifting method, wherein the small subsample lifting method is a blade test magnitude adjusting method, and if the corresponding cycle number of the blade reaches a preset value and no crack occurs under a certain stress magnitude, the stress magnitude of the next blade is lifted by one step length according to the preset step length; if the blade has cracks under a certain stress magnitude and does not reach the preset cycle number, the stress magnitude of the next blade is reduced by one step length, the lifting process of the stress magnitude is repeated until the condition that the small subsample lifting method obtains the median fatigue limit is met, Matlab is used for reading the stress magnitude of the small subsample lifting method fatigue test and the corresponding cycle number data, the median fatigue limit is calculated according to the small subsample lifting method, and then the median fatigue limit is output to a report in a chart form,
specifically, the median fatigue limit is calculated by a small subsample lifting method in the following way:
median fatigue limit σ-1Expression (c):
wherein n represents the number of tests;
m-stress level progression;
σi-level i stress;
vi-represents the stress σ in the i-th orderiThe number of tests performed;
after the median fatigue limit is obtained, an S-N curve of the blades is obtained by using a grouping method, the grouping method is firstly based on the median fatigue limit, a plurality of stress magnitude levels higher than the median fatigue limit are set, a plurality of blades are distributed under each stress magnitude level, and then the blade fatigue test is carried out based on a preset group; reading the stress magnitude of the grouped fatigue test and the corresponding cycle data, calculating the average value, standard deviation, coefficient of variation and confidence coefficient of the fatigue life under logarithmic coordinates, then storing to a set position in the form of a chart,
the following calculation is adopted:
average of subsamples
Expression (c):
subsample standard deviation S expression:
coefficient of variation of subsampleC v Expression:
in the formula (I), the compound is shown in the specification,n-number of test pieces in the test group;
x i -stress level in the test group;
fitting an S-N curve based on the fatigue limit and fatigue life results obtained in this step,
the empirical formula for S-N curve fitting is as follows:
in the formula, N-cycle number, C, m, S0As the parameters of the material, it is,
let X = logN, y = log (σ)max-S0)，a 0=C，a 1= -m, fitting according to formulae (3) and (4) obtaining an S-N curve,
and after the vibration characteristic statistical result and the fatigue test statistical result are processed, reading the processed result according to the path, outputting the processed result to a report, and then judging the test result and obtaining a conclusion.
The technical means not described in detail in the present application are known techniques.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A Matlab-based blade fatigue limit evaluation method is provided, wherein blade fatigue data comprise picture data, temperature data, frequency response data and fatigue test data,
characterized in that the method comprises the following steps:
a. processing picture data, cutting and converting the format of the picture data by utilizing Matlab, and putting the picture data into a report document;
b. processing temperature data, namely reading a txt document by utilizing Matlab, calculating a temperature field distribution diagram of each measuring point on the surface of the blade and a temperature gradient diagram of each point on the surface of the blade according to temperature data recorded in the txt document, and screenshot and putting the temperature distribution diagram into a report document;
c. the frequency response data is processed, and the frequency response data is processed,
reading speed frequency response data stored in a computer by utilizing Matlab, obtaining an initial value of modal frequency by adopting a peak value identification method, then calculating the modal frequency and modal damping ratio by adopting a least square method,
reading stress frequency response data by utilizing Matlab, identifying modal stress corresponding to modal frequency according to the speed frequency response data, storing the modal stress in a form of a graph, and outputting the graph recording the modal frequency, the modal damping ratio and the modal stress to a report document;
according to the obtained modal stress data, a stress distribution cloud chart is made according to a strain measuring point coordinate grid, the maximum stress points of the first three are marked and used as the positions of the strain measuring points in a stress-displacement calibration test in the fatigue test; if the stresses of the first three are relatively close, increasing the number of the obtained stress points until the difference between the numerical values of the obtained stress points is more than 15%, storing the stress distribution cloud picture, and intercepting a report document;
after all the blade vibration characteristic tests are finished, carrying out statistical analysis on the modal frequency, the modal damping ratio and the modal stress, and outputting statistical results to a report document;
d. the data from the fatigue test were used,
c, according to the natural frequency identified in the step c, using the natural frequency as a fatigue test excitation frequency; according to the stress points obtained in the step c, the stress points are used as stress measuring points of a fatigue test, the maximum stress point is used as a control point, the rest measuring points are used as fatigue strain monitoring points, strain gauges are pasted on the stress measuring points of the fatigue test, basic excitation with different magnitudes is given to the blade by a vibration table, the displacement of the blade tip is obtained by a Doppler laser vibration meter, the strain gauges obtain stress data, the laser vibration meter and the strain gauges are connected into a data acquisition instrument, the data acquisition instrument stores the displacement and the stress data, the obtained stress data and the obtained displacement data are read by Matlab, the stress-displacement slope is calculated by using a least square method, a stress-displacement curve is fitted, and then the stress-displacement curve is stored and intercepted into a report in a form,
after all the blade fatigue tests are finished, the obtained slope data is utilized to statistically analyze the discreteness of the stress-displacement slope, calculate the average value, the maximum value, the minimum value and the discrete area of the slope, and store the average value, the maximum value, the minimum value and the discrete area in a set path in a form of a chart;
converting the stress magnitude of a stress control point of a set fatigue test into the displacement magnitude of a displacement measuring point based on the stress-slope numerical value in the step, then controlling the displacement magnitude of the displacement measuring point through a controller to keep the displacement magnitude of the point unchanged in the fatigue test process, and when the fatigue test reaches the specified cycle number or the blade cracks, finishing the fatigue test, and recording the test magnitude and the corresponding cycle number;
firstly, measuring the fatigue limit of the blade according to a small sample lifting method, wherein the small sample lifting method is a blade test magnitude adjustment method, and if the corresponding cycle times of the blade under a certain stress magnitude reach a preset value and no crack appears, the stress magnitude of the next blade is increased by one step length according to the preset step length; if the blade does not reach the preset cycle number and cracks appear under a certain stress magnitude, the stress magnitude of the next blade is reduced by one step length, the lifting process of the stress magnitude is repeated until the condition that a small subsample lifting method obtains the median fatigue limit is met, Matlab is used for reading the stress magnitude of the small subsample lifting method fatigue test and the corresponding cycle number data, the median fatigue limit is calculated according to the small subsample lifting method, and then the median fatigue limit is output to a report in a chart form,
after the median fatigue limit is obtained, an S-N curve of the blades is obtained by using a grouping method, the grouping method is firstly based on the median fatigue limit, a plurality of stress magnitude levels higher than the median fatigue limit are set, a plurality of blades are distributed under each stress magnitude level, and then the blade fatigue test is carried out based on a preset group; reading the stress magnitude of the grouped fatigue test and the corresponding cycle data, calculating the average value, standard deviation, coefficient of variation and confidence coefficient of the fatigue life under logarithmic coordinates, then storing to a set position in the form of a chart,
fitting an S-N curve based on the fatigue limit and fatigue life results obtained in this step,
and after the vibration characteristic statistical result and the fatigue test statistical result are processed, reading the processed result according to the path, outputting the processed result to a report, and then judging the test result and obtaining a conclusion.
2. The Matlab-based blade fatigue limit evaluation method of claim 1,
the picture data comprise the overall blade state picture shot before the test, the overall blade state picture shot after the test and the local blade crack picture.
3. The Matlab-based blade fatigue limit evaluation method of claim 2,
in the step a, the image data is cut and converted into a format by using Matlab, and is put into a report document, which specifically comprises the following steps:
reading in a blade overall state picture shot before a test and a blade overall state picture shot after the test, which are stored in a computer, by utilizing Matlab, identifying the position of a target in the picture, and after removing information irrelevant to the target, putting a screenshot into a report document;
and reading in local crack picture data stored in a computer by utilizing Matlab, and carrying out graying, filtering and binarization processing so as to clearly display cracks, putting the screenshot into a report document, and meanwhile, calculating crack length information and putting the crack length information into the report document.
4. The Matlab-based blade fatigue limit evaluation method of claim 1,
in step b, the method further comprises the following steps:
and (3) measuring the temperature of the temperature field environment where the blade is positioned before the fatigue test, ensuring that the temperature environment where the blade is positioned meets the test requirements, and outputting a txt document for recording temperature data.
5. The Matlab-based blade fatigue limit evaluation method of claim 1,
in step c, the method further comprises the following steps:
before fatigue test, the vibration characteristic of each blade needs to be tested, the blade is fixed on a vibration table, a force hammer or the vibration table is used for excitation, the laser vibration meter is used for obtaining the surface speed response of the set position of the blade, the strain gauge is used for obtaining the surface stress of the set position of the blade, wherein the laser vibration meter and the strain gauge are connected to a data acquisition instrument, and the data acquisition instrument stores speed frequency response data and stress frequency response data to a computer hard disk.
6. The Matlab-based blade fatigue limit evaluation method of claim 1,
in the step c, the process is carried out,
obtaining an initial value of modal frequency by adopting a peak value identification method, then calculating the modal frequency and modal damping ratio by adopting a least square method, and adopting the following method:
firstly, the imaginary part of the frequency response function is taken as an identification object, and the following formula is shown:
(1)
wherein I is frequency response imaginary data, N is the order of the mode to be identified,ω i in order to be the frequency of the mode shape,ωin order to be the frequency of the radio,ξ i in order to achieve modal damping,A i in order to be the modal amplitude,
the parameter vectors to be identified are:
is provided withI k As a function of frequencyω=ω k The imaginary part data of the frequency response function obtained by time measurement are sharedLThe imaginary component value vector of the actually measured frequency response function formed by the frequency points is as follows:
the imaginary part vector of the theoretical frequency response function formed by corresponding to the L frequency points can be expressed as:
the error vector of the theoretical frequency response function imaginary part and the actually measured frequency response function imaginary part at each frequency point is as follows:
and solving the modal parameters according to the operation steps.
7. The Matlab-based blade fatigue limit evaluation method of claim 1,
in step d, calculating the median fatigue limit by a small subsample lifting method, and adopting the following method:
median fatigue limit σ-1Expression (c):
wherein n represents the number of tests;
m-stress level progression;
σi-level i stress;
vi-represents the stress σ in the i-th orderiNumber of tests performed.
8. The Matlab-based blade fatigue limit evaluation method of claim 1,
in the step d, the process is carried out,
the stress-displacement slope was calculated using the least squares method as follows:
stress data arey={y iNumber of displacementsAccording to the followingx={x i }, then Y =in the linear fitting equationa 0+a 1The coefficient calculation formula in X is as follows:
in the formula:nin order to count the number of data points,
the correlation coefficient r is:
9. the Matlab-based blade fatigue limit evaluation method of claim 8,
the empirical formula for S-N curve fitting is as follows:
in the formula, N-cycle number, C, m, S0As the parameters of the material, it is,
let X = logN, y = log (σ)max-S0)，a 0=C，a 1= -m, fitting according to formulae (3) and (4), obtaining an S-N curve.
10. The Matlab-based blade fatigue limit evaluation method of claim 1,
in the step d, the process is carried out,
the average value, standard deviation and variation coefficient of the fatigue life under logarithmic coordinates are calculated by adopting the following method:
average of subsamplesValue of
Expression (c):
subsample standard deviation S expression:
coefficient of variation of subsampleC v Expression:
in the formula (I), the compound is shown in the specification,n-number of test pieces in the test group;
x i stress levels in the test group.
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