CN106442708A - Stress evaluation method based on magnetic domain motor threshold magnetic field - Google Patents
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Abstract
The invention discloses a stress evaluation method based on a magnetic domain motor threshold magnetic field. The method comprises the following steps: for each stress parameter, obtaining a normalized magnetic domain quantization value in different magnetic field intensities: firstly obtaining the magnetic domain image of a ferromagnetic metal component in the stress parameter and magnetic field intensity, preprocessing and then binarizing the magnetic domain image, counting the number of pixel points representing the magnetic domains of 180 degrees and -180 degrees, calculating the area of the magnetic domain of 180 degrees and the area of the magnetic domain of -180 degrees, and obtaining the normalized magnetic domain quantization value; and fitting to obtain an SNom-H curve of which the normalized magnetic domain quantization value changes with the magnetic field intensity value to obtain four threshold magnetic fields, and fitting to obtain the expressions of the four threshold magnetic fields relative to the stress parameters, wherein the stress evaluation of the ferromagnetic metal component is implemented by the following steps: firstly obtaining the SNom-H curve, obtaining four threshold magnetic fields, calculating to obtain four stress values, and averaging to obtain a final stress value. In the invention, the high-linearity, high-sensitivity and high-spatial resolution detection of the ferromagnetic metal component stress and tiny stress change is realized through the threshold magnetic fields.
Description
Technical field
The invention belongs to technical field of nondestructive testing, more specifically, it is related to one kind and is based on domain motion threshold field
Stress evaluation method.
Background technology
Now in the industry, feeromagnetic metal component, in railway traffic, Aero-Space, the department such as metallurgical industry boiler, pipeline,
A large amount of uses of bridge, rail, pressure vessel etc., extend with active time, and feeromagnetic metal component unavoidably has stress
Concentration phenomenon so that component fracture etc. and accidents caused.Stress mornitoring is to ensure that in engineering, feeromagnetic metal component is on active service safely
Important means.Traditional magnetic stress detection includes the skills such as hysteresis curve method, Barkhausen's method (MBN), detection method of eddy, magnetic memory method
Art.These conventional arts, from material macroscopic view magnetic characteristic, set up macroscopical parameter of magnetic characteristic such as coercivity, remanent magnetism, magnetic domain loss
With the corresponding relation of stress, have the shortcomings that to stress evaluation sensitivity is low, spatial resolution is not high it is impossible to accurate assessment is ferromagnetic
The stress state of property material microcosmos area.
In recent years, with observation of magnetic domain technological progress, magnetic microstructure dynamic behaviour progressively obtains in field of non destructive testing
It is widely applied.Magnetic domain dynamic behaviour assessment can achieve feeromagnetic metal component inside stress high-resolution, high accuracy quick detection.
However, current magnetic domain characterizes is also limited to qualitative description, the quantifying and its domestic to the evaluation studies of stress of domain motion characteristic
It is in outward space state.
Content of the invention
It is an object of the invention to overcoming the deficiencies in the prior art, provide a kind of stress based on domain motion threshold field
Appraisal procedure, realize to feeromagnetic metal component stress and minimal stress change high linearity, high sensitivity, high spatial resolution
Detection.
For achieving the above object, the concrete steps based on the stress evaluation method of domain motion threshold field for the present invention
For：
S1：Determine the stress parameters collection φ={ σ of the required simulation of feeromagnetic metal component according to actual needs1,σ2…,σKWith
And change of magnetic field strength scope [- Hmax,Hmax], wherein K represents stress parameters quantity, HmaxRepresent maximum field strength；
S2：Setting stress parameters sequence number k=1；
S3：By magnetic field intensity H from-HmaxIt is gradually increased to Hmax, more progressively it is decreased to-Hmax, obtain stress parameters σkLower every
Individual magnetic field intensity H corresponding normalization magnetic domain quantized value SNom, each magnetic field intensity H corresponding normalization magnetic domain quantized value SNom's
Acquisition methods comprise the following steps：
S3.1：Obtain feeromagnetic metal component in stress parameters σkWith the domain pattern under magnetic field intensity H；
S3.2：Denoising is carried out to domain pattern；
S3.3：Binaryzation is carried out to domain pattern, with 0 representative -180 degree magnetic domain, 1 represents 180 degree magnetic domain；
S3.4：To binaryzation domain pattern, count in binaryzation domain pattern 0 and 1 pixel quantity, be designated as respectively
n-180°And n180°, calculate 180 degree magnetic domain areaWith -180 degree magnetic domain areaS represents
The area of single pixel point in domain pattern；Then magnetic domain quantized value Δ S is calculated according to below equation：
S3.5：Using below equation, magnetic domain quantized value is normalized, obtains normalizing magnetic domain quantized value SNom：
S4：According to the corresponding normalization magnetic domain quantized value S of each magnetic field intensity H in step S3Nom, matching obtain currently should
Force parameter σkLower normalization magnetic domain quantized value is with the S of magnetic field intensity value changesNom- H curve；According to SNom- H curve obtains 4 orders
SNomThreshold limit value magnetic field H for 1 or -1th1(k)、Hth2(k)、Hth3(k)、Hth4(k)；
S5：If k is ＜ K, makes k=k+1, return to step S3, otherwise enter step S6；
S6：According to K stress parameters σkCorresponding 4 threshold fields carry out linear fit and obtain threshold field expression formula：
Hth1=a1σ+b1
Hth2=a2σ+b2
Hth3=a3σ+b3
Hth4=a4σ+b4
Wherein, am、bmIt is the linear dimensions in threshold field expression formula respectively, m=1,2,3,4；
S7：When stress evaluation is carried out to feeromagnetic metal component, obtain initially with the same way in step S3
SNom- H curve, obtains 4 threshold fields, then substitutes in the threshold field expression formula of step S6, is calculated 4 stress value σ
(1), σ (2), σ (3) and σ (4), 4 stress value σ (1), σ (2), σ (3) and σ (4) are averagely obtained final stress value σ.
The stress evaluation method based on domain motion threshold field for the present invention, for each stress parameters, obtains different magnetic
Normalization magnetic domain quantized value under field intensity, acquisition methods are：First obtain feeromagnetic metal component in stress parameters and magnetic field intensity
Under domain pattern, binaryzation again after domain pattern is pre-processed, binaryzation domain pattern statistics is represented 180 degree and-
The pixel quantity of 180 degree magnetic domain, calculates 180 degree magnetic domain area and -180 degree magnetic domain area, is then calculated magnetic domain and quantifies
Value, then be normalized；Matching obtains normalizing the S with magnetic field intensity value changes for the magnetic domain quantized valueNom- H curve, obtains 4 thresholds
Value magnetic field, matching obtains the expression formula with regard to stress parameters for 4 threshold fields, is carrying out stress evaluation to feeromagnetic metal component
When, obtain S firstNom- H curve, obtains 4 threshold fields, is then calculated 4 stress values according to threshold field expression formula,
Final stress value is obtained after average.Corresponding relation between research domain motion threshold field and stress for the present invention, proposes
Magnetic domain quantitative formula, realizes high linearity, the height that feeromagnetic metal component stress and minimal stress are changed by threshold field
Sensitivity, high spatial resolution detection.
Brief description
Fig. 1 is magneto-optical kerr microscope schematic diagram；
Fig. 2 is magneto-optic thin film structural representation；
Fig. 3 is magneto-optic thin film domain pattern illustraton of model under different situations；
Fig. 4 is magnetizing assembly block schematic illustration；
Fig. 5 is the domain pattern of highly oriented electrical sheet under 0MPa stress different magnetic field intensity；
Fig. 6 is the domain pattern of highly oriented electrical sheet under 30.9MPa stress different magnetic field intensity；
Fig. 7 is the domain pattern of highly oriented electrical sheet under 61.9MPa stress different magnetic field intensity；
Fig. 8 is the specific embodiment flow chart based on the stress evaluation method of domain motion threshold field for the present invention；
Fig. 9 is the acquisition flow chart of normalization magnetic domain quantized value；
Figure 10 is to carry out domain pattern pretreatment exemplary plot using wavelet filteration method in the present embodiment；
Figure 11 is to adopt domain pattern binaryzation exemplary plot in the present embodiment；
Figure 12 is SNom- H curve exemplary plot；
Figure 13 is S under different stressNom- H curve and threshold field and stress relation exemplary plot；
Figure 14 is the relation contrast curve chart between different characteristic parameter and stress.
Specific embodiment
Below in conjunction with the accompanying drawings the specific embodiment of the present invention is described, so that those skilled in the art is preferably
Understand the present invention.Requiring particular attention is that, in the following description, when known function and design detailed description perhaps
Can desalinate the present invention main contents when, these descriptions will be ignored here.
In order to technical scheme is better described, first the principle of observation of magnetic domain method is briefly described.
Adopt in the present embodiment and observation of magnetic domain is carried out based on magneto-optical kerr microscope (MOKE) and magneto-optic thin film (MOIF).Fig. 1 is magnetic
Light Ke Er microscope schematic diagram.Fig. 2 is magneto-optic thin film structural representation.As depicted in figs. 1 and 2, a branch of natural light is through being polarized
Device becomes linearly polarized light, and linearly polarized light passes through MOIF, and interacts so that linearly polarized light is inclined with magneto-optic Bi-YIG layer in MOIF
The face that shakes is changed with faraday rotation angle.Light passes through magneto-optic Bi-YIG layer in whole MOIF, occurs anti-after running into Al layer in MOIF
Penetrate.Reflected light occurs after second Faraday effect with magneto-optic Bi-YIG layer again, after compensator and analyzer, faraday
Corner is detected and is imaged, finally by high-speed camera record and preserve.Because MOIF magnetic domain is to vertical magnetic field
Very sensitive, stray field vertical component makes magnetized state in MOIF change.
Fig. 3 is magneto-optic thin film domain pattern illustraton of model under different situations.Wherein, Fig. 3 (a) is that no under magnetic field conditions, magneto-optic is thin
Film domain pattern；Fig. 3 (b) is magneto-optic thin film domain model figure no under magnetic field conditions；Fig. 3 (c) is magneto-optic under magnetic field vertically upward
Thin film magnetic domains variation model figure；Fig. 3 (d) is magneto-optic thin film magnetic domain variation model figure vertically downward.As shown in Fig. 3 (a), no outer
Plus magnetic field conditions, light and shade magnetic domain area equation in MOIF domain pattern, its illustraton of model can be represented with Fig. 3 (b).Certain when applying
Vertically upward behind magnetic field, bright magnetic domain area expansion, dark magnetic domain area reduces, shown in its illustraton of model such as Fig. 3 (c).On the contrary, when applying
Plus necessarily vertically downward behind magnetic field, dark magnetic domain area expansion, bright magnetic domain area reduces, shown in its illustraton of model such as Fig. 3 (d).When
When MOIF is placed on ferrimagnet surface, the magnetic domain on ferrimagnet surface can produce stray field.This stray field vertical component makes
Obtain MOIF magnetized state to change, so that daraf(reciprocal of farad) corner is changed simultaneously.Due to using general view microscope, farad
Signal through analyzer when be averaged.Finally, light and dark image is sample different directions magnetic domain.Magnetic domain is in additional magnetic
Off field, neticdomain wall is moved, its motion speed and pinning strength, internal stress size, anisotropy, dislocation density etc. internal because
Element is closely related, is affected by applied stress, temperature, bigoted magnetic field simultaneously.Fig. 4 is magnetizing assembly block schematic illustration.
, obtain its magnetic domain figure under different additional tensions and different magnetic field intensity respectively taking highly oriented electrical sheet as a example
Picture.Fig. 5 is the domain pattern of highly oriented electrical sheet under 0MPa stress different magnetic field intensity.Fig. 6 is 30.9MPa stress different magnetic field
The domain pattern of highly oriented electrical sheet under intensity.Fig. 7 is the magnetic domain of highly oriented electrical sheet under 61.9MPa stress different magnetic field intensity
Image.As shown in Figures 5 to 7, gray scale dark for 180 degree magnetic domain, gray scale brighter for -180 degree magnetic domain.As Fig. 5 (a) and 6
Shown in (a), when magnetic field intensity is for 177A/m, under 0MPa and 30.9MPa effect, electrical sheet all magnetic domains orientation both facing to
180 degree direction；However, under 61.9MPa, having a lot -180 degree magnetic domain to occur, such as shown in Fig. 7 (a).When magnetic field intensity drops to
25A/m, magnetic domain orientation there occurs change, and when stress is 61.9MPa, -180 degree magnetic domain there occurs expansion, and 180 degree domain width contracts
Little, such as shown in Fig. 7 (b)；Under 30.9MPa stress, a large amount of -180 degree magnetic domain occurs, such as shown in Fig. 6 (b)；However, in stress being
In the case of zero, still both facing to 180 degree direction, such as Fig. 5 (b) is shown for all of magnetic domain.When magnetic field drops to 0A/m situation,
When stress is 0, a large amount of -180 degree magnetic domain occurs, such as shown in Fig. 5 (c)；In the case of 30.9MPa and 61.9MPa, -180 degree magnetic domain
All there occurs expansion, 180 degree domain width reduces；This phenomenon shows, hardware internal stress increases, and makes magnetic in magnetic history
Magnetic field intensity required for farmland all occurs to overturn increases.
It can be seen that, there is corresponding relation between magnetic domain dynamic behaviour and application, the present invention is exactly this right by extracting
Characteristic value in should being related to, sets up the relational model between characteristic value and stress, thus qualitative assessment stress.Fig. 8 is the present invention
The specific embodiment flow chart of the stress evaluation method based on domain motion threshold field.As shown in figure 8, the present invention is based on magnetic
The stress evaluation method in farmland movement threshold magnetic field comprises the following steps：
S801：Initialization application parameter value and change of magnetic field strength scope：
Determine the stress parameters collection φ={ σ of the required simulation of feeromagnetic metal component according to actual needs1,σ2…,σKAnd magnetic
Field intensity excursion [- Hmax,Hmax], wherein K represents stress parameters quantity, HmaxRepresent maximum field strength.
S802：Setting stress parameters sequence number k=1.
S803：Obtain and under different magnetic field intensity, normalize magnetic domain quantized value：
By magnetic field intensity H from-HmaxIt is gradually increased to Hmax, more progressively it is decreased to-Hmax, obtain stress parameters σkDescend each
Magnetic field intensity H corresponding normalization magnetic domain quantized value SNom.Fig. 9 is the acquisition flow chart of normalization magnetic domain quantized value.As Fig. 9 institute
Show, each magnetic field intensity H corresponding normalization magnetic domain quantized value SNomAcquisition methods comprise the following steps：
S901：Obtain domain pattern：
Obtain stress parameters σkWith the domain pattern under magnetic field intensity H.
S902：Domain pattern denoising：
Denoising is carried out to the domain pattern obtaining in step S901.Image denoising algorithm is the normal of image processing field
With technological means, specific Image denoising algorithm can be selected as needed, to be entered using wavelet filteration method in the present embodiment
Row denoising.Figure 10 is to carry out domain pattern pretreatment exemplary plot using wavelet filteration method in the present embodiment.
S903：Domain pattern binaryzation：
According to the explanation to domain pattern before, in domain pattern, gray scale dark for 180 degree magnetic domain, gray scale
It is brighter that and the width of 180 degree magnetic domain and -180 degree magnetic domain can change with the change in stress and magnetic field for -180 degree magnetic domain,
Therefore the present invention magnetic domain is quantified using the area of 180 degree magnetic domain and -180 degree magnetic domain.For the ease of quantifying, first to magnetic
Farmland image carries out binaryzation, and with 0 representative -180 degree magnetic domain, 1 represents 180 degree magnetic domain.Image binaryzation is also image processing field
Common technology means, specific algorithm can be selected as needed.Due to the even property of uneven illumination, domain pattern brightness irregularities,
Through comparing, the Image binarizing algorithm being preferably based on local auto-adaptive threshold value in the present embodiment to carry out two-value to domain pattern
Change.Figure 11 is to adopt domain pattern binaryzation exemplary plot in the present embodiment.
S904：Calculate magnetic domain quantized value：
Also rest on magnetic domain qualitative description aspect to magnetic domain description in the industry at present.Also rare research is quantified to magnetic domain.Base
In ferromagnetic material 180 degree to -180 degree magnetic domain wall moving, the present invention quantifies its moving characteristic using below equation：
Wherein, Δ S represents magnetic domain quantized value,WithRepresent all 180 degrees and -180 degree magnetic domain area respectively.?
Under demagnetized state, 180 degree and -180 degree magnetic domain area equation, Δ S be equal to zero.After applying externally-applied magnetic field, neticdomain wall moves
Dynamic, corresponding magnetic domain area changes, and the value of Δ S changes therewith.
It can be seen that, when calculating magnetic domain quantized value Δ S, need to obtain all 180 degrees and -180 degree magnetic domain area first
WithIts computational methods is：The binaryzation domain pattern that step S806 is obtained, 0 and 1 in statistics binaryzation domain pattern
Pixel quantity, is designated as n respectively-180°And n180°, then 180 degree magnetic domain area- 180 degree magnetic domain areaS represents the area of single pixel point in domain pattern.Obviously s is to be determined by the resolution ratio of domain pattern
's.
S905：Magnetic domain score normalization：
For the ease of subsequent treatment, using below equation, magnetic domain quantized value is normalized, obtains normalizing magnetic domain amount
Change value SNom：
After normalization, SNomValue between -1 to+1.Work as SNomWhen being worth for -1, represent all magnetic domains all towards -180 degree side
To；Work as SNomWhen being worth for+1, represent all magnetic domains all towards 180 degree direction.
S804：Matching SNom- H curve：
According to step S803, because ferromagnetic material magnetization is a magnetic hysteresis process, the therefore magnetic field intensity of the present invention
First from-HmaxChange to Hmax, then change back-H againmax, remember in unidirectional change procedure there is N number of magnetic field intensity, 2N magnetic altogether
Field intensity value, each magnetic field intensity can obtain a normalization magnetic domain quantized value, thus obtain 2N normalization magnetic domain quantifying
Value.So according to this 2N to field strength values and normalization magnetic domain quantized value it is possible to matching obtains current stress parameters σkUnder
Normalization magnetic domain quantized value is with the S of magnetic field intensity value changesNom- H curve.
Figure 12 is SNom- H curve exemplary plot.As shown in figure 12, in SNomIn-H curve, there are 4 and make SNomFor 1 or -1
Threshold limit value magnetic field Hth1、Hth2、Hth3、Hth4, wherein Hth1And Hth4Positioned at 1st quadrant, Hth2And Hth3Positioned at third quadrant.Under
Fall, along (during magnetic field intensity diminishes), works as Hth2＜ H ＜ Hth1When, neticdomain wall is moved, H ＞ Hth1(H ＜ Hth2) when, own
Neticdomain wall is both facing to 180 degree (- 180 degree direction).Rising edge (during magnetic field intensity becomes big), work as Hth3＜ H ＜ Hth4When, magnetic
Domain wall is moved, H ＞ Hth4(H ＜ Hth3) when, all neticdomain walls are both facing to 180 degree (- 180 degree direction).Understand, this 4 are faced
Boundary threshold field Hth1、Hth2、Hth3、Hth4It is exactly corresponding threshold field under current stress parameters.Therefore according to SNom- H curve obtains
To current stress parameters σkLower 4 order normalization magnetic domain quantized value SNomThreshold limit value magnetic field H for 1 or -1th1(k)、Hth2(k)、
Hth3(k)、Hth4(k).
S805：Judging whether k ＜ K, if it is, entering step S806, otherwise entering step S807.
S806：Make k=k+1, return to step S803.
S807：Feature extraction：
According to step S802 to step S806, for each stress parameters σk, S can be obtainedNom- H curve,
It is exactly that each stress parameters has 4 threshold fields.Figure 13 is S under different stressNom- H curve and threshold field are closed with stress
It is exemplary plot.It has been investigated that, 4 threshold fields and stress value all have the linear dependence of height, and Figure 13 (b) illustrates
SNom- H curve trailing edge first quartile threshold field (Hth1) linear relationship and stress between.Therefore can be according to K stress
Parameter σkCorresponding threshold field carries out linear fit and obtains threshold field expression formula：
Hth1=a1σ+b1
Hth2=a2σ+b2
Hth3=a3σ+b3
Hth4=a4σ+b4
Wherein, am、bmIt is the linear dimensions in threshold field expression formula respectively, m=1,2,3,4.
S808：Stress evaluation：
When stress evaluation is carried out to feeromagnetic metal component, obtain S initially with step S803 identical modeNom-H
Curve, obtains 4 threshold fields, substitutes in the threshold field expression formula that the matching of step S807 obtains, and can be calculated 4 should
Force value σ (1), σ (2), σ (3) and σ (4), 4 stress value σ (1), σ (2), σ (3) and σ (4) are carried out averagely, you can obtain final
Stress value σ：
Embodiment
In order to the technique effect of the present invention is better described, using the stress based on domain motion threshold field in the present invention
Appraisal procedure carries out Experimental comparison with the Evaluated effect of the stress evaluation method based on traditional macro magnetic characteristic characteristic parameter.Tradition
Macroscopical magnetic characteristic characteristic parameter includes remanent magnetism, magnetic hystersis loss, coercivity.In the present embodiment, sample is the highly oriented silicon steel of Baosteel, chi
Very little：300mm × 30mm × 0.27mm (length × width × height), experiment parameter is：Excitation waveform：Triangular wave；Driving frequency：
0.01Hz；Magnetic field amplitude：1000A/m.It is respectively using the threshold field expression formula obtained by the present invention：
Hth1=3.93* σ+19.18
Hth2=-3.93* σ -78.25
Hth3=-3.93* σ -21.50
Hth4=3.93* σ+77.40
Because the unit of characteristic parameter is different, need first to be normalized, normalization process can be expressed as：No
With the value under stress divided by maximum.Figure 14 is the relation contrast curve chart between different characteristic parameter and stress.As Figure 14 institute
Show, be not linear relationship between traditional macro magnetic characteristic characteristic parameter and stress, and threshold field of the present invention (with
Threshold field Hth1As a example) there is linear relationship and stress between.Hereinafter the threshold field that analysis in terms of three proposes is corresponded to
Power detects advantage：The different ranges of stress, each magnetic characteristic parameter is with rate of stressing, stress mornitoring effect, minimal stress change
Evaluated effect discuss.
Table 1 is the speed (unit that different stage of stress stress change with parameter of magnetic characteristic：Percentage/MPa).
Table 1
From table 1 it is known that threshold field is more uniform in different stage of stress change ratio with STRESS VARIATION, all 1.44%
Every MPa, sensitivity is higher；Coercivity all changes relatively slowly in 0-61.9MPa scope, and sensitivity is very poor；Remanent magnetism is in 0-
In the range of 12.3MPa, quickly, sensitivity is very high for rate of change, reaches 5% every MPa, in the range of 12.3MPa-24.7MPa
Change rate of change reduces soon, and sensitivity is general, and in the 24.7MPa-61.9MPa stage, rate of change becomes slowly, sensitive
Difference；Magnetic hystersis loss is all relatively slow in whole stage of stress rate of change, sensitive relatively low.
For the Detection results to stress and minimal stress change for the contrast different characteristic parameter, definition is when rate of change is more than 1%
Every MPa is that detection effect is fine；It is general for detection effect when rate of change is more than 0.5% and is less than 1% every MPa；
It is that detection effect is poor when rate of change is less than 0.5%.Table 2 is characterized parameter stress and the detection effect pair of minimal stress change
Compare result.Learn from table 2, when stress is less, remanent magnetism and threshold field are to the detection of stress and minimal stress change all
There is very high sensitivity, remanent magnetism and magnetic hystersis loss Detection results are poor；After stress becomes big, threshold field Detection results are still
Very well, but coercivity, remanent magnetism, magnetic hystersis loss Detection results are all poor.
Table 2
To sum up analyze, compared to coercivity, remanent magnetism, magnetic hystersis loss tradition parameter of magnetic characteristic, the present invention proposes threshold field
To stress and minimal stress detection, there are good Detection results.
Although to the present invention, illustrative specific embodiment is described above, in order to the technology of the art
Personnel understand the present invention, the common skill it should be apparent that the invention is not restricted to the scope of specific embodiment, to the art
For art personnel, as long as various change is in the spirit and scope of the present invention of appended claim restriction and determination, these
Change is it will be apparent that all utilize the innovation and creation of present inventive concept all in the row of protection.
Claims (2)
1. a kind of stress evaluation method based on domain motion threshold field is it is characterised in that comprise the following steps：
S1：Determine the stress parameters collection φ={ σ of the required simulation of feeromagnetic metal component according to actual needs1,σ2…,σKAnd magnetic
Field intensity excursion [- Hmax,Hmax], wherein K represents stress parameters quantity, HmaxRepresent maximum field strength；
S2：Setting stress parameters sequence number k=1；
S3：By magnetic field intensity H from-HmaxIt is gradually increased to Hmax, more progressively it is decreased to-Hmax, obtain stress parameters σkEach magnetic lower
Field intensity H corresponding normalization magnetic domain quantized value SNom, each magnetic field intensity H corresponding normalization magnetic domain quantized value SNomAcquisition
Method comprises the following steps：
S3.1：Obtain feeromagnetic metal component in stress parameters σkWith the domain pattern under magnetic field intensity H；
S3.2：Denoising is carried out to domain pattern；
S3.3：Binaryzation is carried out to domain pattern, with 0 representative -180 degree magnetic domain, 1 represents 180 degree magnetic domain；
S3.4：To binaryzation domain pattern, count in binaryzation domain pattern 0 and 1 pixel quantity, be designated as n respectively-180°With
n180°, calculate 180 degree magnetic domain areaWith -180 degree magnetic domain areaS represents magnetic domain figure
The area of single pixel point in picture；Then magnetic domain quantized value Δ S is calculated according to below equation：
S3.5：Using below equation, magnetic domain quantized value is normalized, obtains normalizing magnetic domain quantized value SNom：
S4：According to the corresponding normalization magnetic domain quantized value S of each magnetic field intensity H in step S3Nom, matching obtains current stress ginseng
Number σkLower normalization magnetic domain quantized value is with the S of magnetic field intensity value changesNom- H curve；According to SNom- H curve obtains 4 makes normalizing
Change magnetic domain quantized value SNomThreshold limit value magnetic field threshold limit value magnetic field H for 1 or -1th1(k)、Hth2(k)、Hth3(k)、Hth4(k)；
S5：If k is ＜ K, makes k=k+1, return to step S3, otherwise enter step S6；
S6：According to K stress parameters σkCorresponding 4 threshold fields carry out linear fit and obtain threshold field expression formula：
Hth1=a1σ+b1
Hth2=a2σ+b2
Hth3=a3σ+b3
Hth4=a4σ+b4
S7：When stress evaluation is carried out to feeromagnetic metal component, obtain S initially with the same way in step S3Nom- H is bent
Line, obtains 4 threshold fields, then substitutes in the threshold field expression formula of step S6, is calculated 4 stress value σ (1), σ
(2), σ (3) and σ (4), 4 stress value σ (1), σ (2), σ (3) and σ (4) are averagely obtained final stress value σ.
2. stress evaluation method according to claim 1 is it is characterised in that in described step S3.2, enter to domain pattern
Row binaryzation is using the Image binarizing algorithm based on local auto-adaptive threshold value.
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