CN108956668A - A kind of crack tip ope ning angle degree measurement method based on SEM in situ - Google Patents
A kind of crack tip ope ning angle degree measurement method based on SEM in situ Download PDFInfo
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B15/00—Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
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Abstract
The crack tip ope ning angle degree measurement method based on SEM in situ that the present invention relates to a kind of, comprising the following steps: sample prepares: being machined out to sample, reaches required geometric dimension and surface roughness；Clamping sample, scanning electron microscope imaging: by specimen clamping on the sample table of in-situ test machine, until specimen surface can be obviously observed；Experimental condition is arranged to start to test: the load parameter of setting in-situ test machine, using La-drawing fatigue load precrack；Destructive test and acquisition image, calculate CTOA value and measurement crack lengtha: obtain CTOA- ΔaEvolution trend: the crack propagation increment Delta that the CTOA being calculated and scanning electron microscope are measuredaIt is plotted in the same coordinate system, obtains CTOA- ΔaTendency chart.The present invention realizes the non-cpntact measurement of CTOA, and without carrying out specially treated to specimen surface, in the process without complicated test operation step, post-processing is convenient, and precision is higher.
Description
Technical field
The present invention relates to fracture mechanics researchs, more particularly to a kind of crack tip ope ning angle degree based on SEM in situ
(CTOA) measurement method.
Background technique
Elastic-plastic fracture mechanics and its test method are to assess the important research means of ductile material fracture characteristics.In engineering
In practice, for the thin-walleds such as aircraft skin, petroleum pipeline, thin-slab structure, fracture failure operating condition is close to low constraint condition.It is right
In such issues that, measurement critical crack tip open-angle (Crack Tip Opening Angle, CTOA) is considered a kind of non-
The often fracture assessment criterion suitable for assessment such material and component failure condition, and be widely used.Crack tip
Open-angle reaches critical value in the Crack Stable Growth stage and keeps constant, and the stabilization which can be used for characterizing material is split
Line extends toughness, i.e. fracture toughness.Fracture toughness reflects the resistance to crack extension ability of material, and fracture toughness is bigger, and toughness is higher.
Theoretical Criterion based on CTOA are as follows: CTOA≤CTOAC, when CTOA reaches critical initial value CTOACWhen, crackle starts to stablize extension.
Currently, the testing method of CTOA mainly have direct-reading method, 3D microstructure method,δ 5 The indirect method of measurement.Direct-reading method
The image of Crack Stable Growth process during record test needs the image of measurement acquisition to calculate CTOA after test,
By splitting point and splitting the average value that the anchor point after point calculates crack tip ope ning angle.3D microstructure method passes through the method after test
To the height of separating and measuring break surface, and then the mathematics surface of two discrete definition is obtained, two discrete surfaces are through minimum two
Multiply and fits G-bar and then acquire crack tip ope ning angle.δ 5 Indirect method of measurement technology passes through measurementF-ΔaCurve withF-δ 5
Curve, and then obtainδ 5 -ΔaCurve, CTOA are approximately equal toδ 5 -ΔaSlope of a curve.
Existing testing method generally existing certain deficiency in practical applications, therefore by different degrees of restriction.
In direct-reading method, optical measurement need to accurately identify Crack Tip endpoint, and accuracy of identification is not enough easy to appear data exception discretization；3D is aobvious
Micromorphology method is to measure after experiment to the crack surface of sample, cannot observe and record the change of CTOA in loading procedure in real time
Law；δ 5 The indirect method of measurement need to use standard sample, need to measure displacement using flexibility method and by COD rule during test
Increment, program are more complicated.
SEM experimental technique in situ is a kind of new material Mechanics Performance Testing developed in recent years and research means,
The technology to analyze from micro-scale and characterizing fatigue of materials and fracture failure behavior and provide strong research means, for from
The physical failure process that mechanism level discloses material provides necessary technical support.So-called original position SEM experimental technique, that is, sweep
Retouching electron microscope (SEM) may be implemented under loading environment in situ the surface topography and damage for observing sample in real time in deformation process
Wound develops, and the SEM image recorded in real time can establish in time one-to-one correspondence with macro-stress-strain curve of sample and close
System, is convenient for fracture mechanics correlation analysis.The present invention is developed a kind of based on Matlab's by means of SEM measuring technology in situ
The automatic measurement and read method of crack tip ope ning angle.This method has non-contact, multiple dimensioned, high-precision, easy to operate etc.
Advantage, can obtain crack tip deformation pattern and crack tip ope ning angle in real time, high degree of automation, and measurement result is accurate, can
It leans on, there is application potential in material property research.
Summary of the invention
Main contents of the present invention are the SEM image obtained under sample loads in situ by means of SEM measuring technology in situ, so
It utilizes " CTOA calculation method " model based on Matlab language to calculate afterwards and obtains corresponding crack tip ope ning angle degree on image.
During load in situ, the crack length in image can be measured using scanning electron microscopea, scanning electron microscope can be according to certain
Load time or crack growth amount ΔaSuccessively acquire multiple series of images.Finally, being calculated according to " CTOA calculation method " model
CTOA value and the crack length gone out by sweep electron microscopic measurea, can be obtained CTOA- ΔaEvolution trend.
This method is easy to operate, intuitively, can be widely applied to the CTOA measurement of material, can significantly improve efficiency.Meanwhile
While so that researcher is observed material failure process in situ, obtain can quantitatively characterizing its fracture toughness parameter, widened original
The application range of bit test technology.
The measurement method of crack tip ope ning angle degree based on SEM experimental technique in situ specifically comprises the following steps:
Step (1) sample prepares: being machined out to sample, reaches required geometric dimension and surface roughness.
Step (2) clamping sample, scanning electron microscope imaging: by specimen clamping on the sample table of in-situ test machine, adjustment is swept
The multiplying power and contrast of Electronic Speculum are retouched, until specimen surface can be obviously observed；
Step (3) setting experimental condition starts to test: the load parameter of setting in-situ test machine, pre- using La-drawing fatigue load
Crackle processed.
Step (4) destructive test and acquisition image: after precrack, fracture examination is carried out using simple tension load
It tests, at the same time, scanning electron microscope carries out Image Acquisition to crack tip every certain load time.
Step (5) calculates CTOA value and measurement crack lengtha: after test, successively measured in image with scanning electron microscope
Crack lengtha, and image is sequentially inputted to calculate corresponding CTOA value in " CTOA calculation method " model.
Step (6) obtains CTOA- ΔaEvolution trend: the crackle that the CTOA being calculated and scanning electron microscope are measured expands
Open up increment DeltaaIt is plotted in the same coordinate system, obtains CTOA- ΔaTendency chart.
In step (1), sample uses unilateral gap tensile sample (Single Edge Notch Tensile), i.e.,
SENT sample, notch use in wire linear cutter.It is successively polished using the sand paper of 1000# and 2000# sample, is then used
The diamond polishing liquid that diameter is 3 μm and 0.5 μm polishes, cleaning, not observe sample table under optical microscopy (about 400X)
Face scratch is standard.
In step (2), the degree of getting a clear view of scanning electron microscope is adjusted, specimen surface can be observed under 1000X clearly as mark
It is quasi-.Observation area need to comprising splitting point, and include after splitting point distance split the region that point is not less than 1.5mm.
In step (5), " CTOA calculation method " model is the program code write based on Matlab language, by right
Gray value in image carries out analysis comparison, finds out the position of several discrete points on two Crack lines, on two Crack lines
Point carry out least square fitting respectively, it is believed that the size of angle is CTOA value between two fitting a straight lines.
Compared with prior art, the present invention having the following advantages and outstanding effects:
(1) a kind of research technique of home position observation crack propagation behavior is provided.SEM test skill in situ involved in the present invention
Art can observe deformational behavior and the crack propagation behavior of material in real time under meso-scale.Facilitate the microcosmic of research material
Deformational behavior and fracture mechanism.
(2) the SEM imaging system involved in the present invention, relative to optical microscopy with higher resolution ratio and clearly
Degree.
(3) has the advantages that non-cpntact measurement, without carrying out specially treated to specimen surface, in the process without complicated test
Operating procedure, post-processing is convenient, and precision is higher.During test, it can synchronize and carry out crack growth rate research and crackle expansion
Open up other research work such as path analysis.
Detailed description of the invention
Fig. 1 is the principle flow chart of " CTOA calculation method ".
Fig. 2 is the schematic illustration of " CTOA calculation method ".
Fig. 3 is SENT specimen size schematic diagram in example.
Fig. 4 is a wherein image for scanning electron microscope acquisition in example.
Fig. 5 is the output figure of " CTOA calculation method " in example.
Fig. 6 is the partial enlarged view of the output figure of " CTOA calculation method " in example.
Fig. 7 is the CTOA- Δ obtained in example by data processingaEvolution trend figure.
Specific embodiment
The SEM image under sample loads in situ is obtained the present invention is based on SEM measuring technology in situ, then using being based on
It is corresponding on " CTOA calculation method " the model calculating acquisition image of Matlab language to split tip opening angle.Use scanning electron microscope
Measure the crack extension Δ in imagea, in conjunction with the CTOA value being calculated by " CTOA calculation method " model, can obtain
Take CTOA- ΔaEvolution trend.
Fig. 1 is " CTOA calculation method " principle flow chart of the invention, presses program to " CTOA calculation method " in flow chart
The sequencing of processing is summarized.
Fig. 2 is " CTOA calculation method " schematic illustration of the invention.The principle of " CTOA calculation method ": Crack Tip is imported
Hold image；The im2bw function in Matlab is called, with the threshold value of setting by image binaryzation, so that the pixel in image is only
There are two types of tonal gradation, the pixel that gray value is greater than threshold value is 1, and the pixel that gray value is less than threshold value is 0；Cusp is split in selection
A and point B at 1.5mm is split after point,yIn axis direction, A → B area is the region for participating in calculating；L is using A as starting pointyAxis side
To line segment, it is corresponding that terminal is located at point BxIt is uniformly distributed on line segment L on axial linenA pointl i ,i=1~n；Withl i For starting point, edgexAxis
Positive direction scans pixel one by one, when scanning to some pixel tonal gradation andl i Tonal gradation difference when,
The pixel is the pixel being present on fault line, records this pixel；Then froml i+1 Start to scan at point, and so on,
Untili=n；Similarly, withl i For starting point, edgexThe scanning of axis negative direction, untili=n；So far, have recorded with split point for starting point, every
On fault linenA pixel.The pixel on every Crack line is subjected to straight line fitting by least square method respectively, calculates two
Angle between straight line, i.e., corresponding CTOA value.
For a better understanding of the present invention, below with reference to example, the present invention is described in further detail.The present invention with
For unilateral gap tensile sample, fatigue load is loaded to it with precrack, then carry out tension failure test.Destructive test
In the process, scanning electron microscope observation specimen surface crack tip region and the image of crack tip region is acquired.Then using being based on
It is corresponding on " CTOA calculation method " the model calculating acquisition image of Matlab language to split tip opening angle, in conjunction with scanning electricity
The crack length that mirror is measureda, obtain CTOA- ΔaEvolution trend figure.Specific embodiment is as follows:
Sample prepares.This example the selection of material is that common 316L stainless steel, the material have good intensity and extension in engineering
Property.316L stainless steel is machined out, sample is length 50mm, width 10mm, thickness 1mm, and the unilateral of notch length 1mm lacks
Mouth tensile sample, specimen size schematic diagram are shown in Fig. 3.The sample processed the sand paper of 1000# and 2000# is polished, then will
Sample is placed on polishing machine and is polished, and successively uses 3 μm and 0.5 μm of diameter of diamond polishing liquid, grinding and polishing is later with ultrasound
Wave cleaning machine washed samples, are then dried.
Clamping sample, adjusting scanning electron microscope makes blur-free imaging.By on the specimen clamping in situ collet of testing machine, by sample
It is placed in scanning electron microscope vacuum tank together with chuck as a whole, so that test process is in the observation visual field of scanning electron microscope.Adjustment is swept
Focal length, contrast, the astigmatism of Electronic Speculum are retouched, until specimen surface can be obviously observed at 1000X.
Setting experimental condition starts to test.Using La-drawing fatigue load to sample carry out precrack, stress ratio R=0.1,σ max=0.6σ y (σ maxFor maximum nominal stress,σ y For yield strength), final precrack length is 2mm, at this point, crackle overall length
Degree is 3mm.
Destructive test and Image Acquisition.After precracks, axial tensile loads are applied to sample and carry out destructive test,
Test uses Bit andits control, strain rate 10-4/s.Every 40s pause test, scanning electron microscope acquire the clear figure of crack tip region
Picture, multiplying power 14X-100X, until rupture failure occurs for sample.
Calculate CTOA value and measurement crack extension Δa.After test, successively measured in image with scanning electron microscope
Crack extension Δa, image is sequentially inputted to calculate corresponding CTOA value in " CTOA calculation method " model.It is chosen in this example
A wherein image, is shown in Fig. 4, and the treatment process of this figure is shown.Fig. 5 is the output figure of " CTOA calculation method ", the figure
As corresponding CTOA value is 23.91 °.Fig. 6 is the partial enlarged view for exporting Fig. 5, it can be seen that passes through the crack surface of procedure identification
On several discrete points, and the straight line being fitted to by these discrete points.The corresponding crack propagation of each image is obtained as a result,
Measure ΔaWith crack tip ope ning angle CTOA.And then obtain crack extension Δ during Stable Crack GrowthaWith corresponding Crack Tip
Hold open-angle CTOA relationship, and CTOA tend towards stability state when lower limit value be considered as the critical of crack tip ope ning angle
Value CTOAC。
Obtain CTOA- ΔaEvolution trend.The crack propagation increment Delta that the CTOA being calculated and scanning electron microscope are measuredaIt is plotted in the same coordinate system, available CTOA- ΔaTendency chart, as shown in Figure 7.It critical is split by Fig. 7 is available
Line tip open-angle CTOAC, critical value CTOACCan be used as a kind of fracture toughness of the material (316L stainless steel), for its
Fracture failure assessment under low constraint operating condition.
The present invention provides a kind of research techniques of home position observation crack propagation behavior, can see in real time under meso-scale
Measure and monitor the growth of standing timber material deformational behavior and crack propagation behavior.Facilitate microdeformation behavior and the fracture mechanism of research material.
The crack tip image acquired in the present invention by SEM imaging system has high resolution ratio and clarity.
The present invention realizes the non-cpntact measurement of CTOA, without carrying out specially treated to specimen surface, in the process without complexity
Test operation step, post-processing is convenient, and precision is higher.During test, can synchronize carry out crack growth rate research and
Other research work such as crack propagation path analysis.
Claims (8)
1. a kind of crack tip ope ning angle degree measurement method based on SEM in situ, which comprises the following steps:
(1) sample prepares: being machined out to sample, reaches required geometric dimension and surface roughness；
(2) scanning electron microscope imaging: clamping sample by specimen clamping on the sample table of in-situ test machine, adjusts scanning electron microscope
Multiplying power and contrast, until specimen surface can be obviously observed；
(3) setting experimental condition starts to test: the load parameter of setting in-situ test machine, using La-, drawing fatigue load is prefabricated splits
Line；
(4) destructive test and acquisition image: after precrack, carrying out destructive test using simple tension load, same with this
When, scanning electron microscope carries out Image Acquisition to crack tip every certain load time；
(5) CTOA value and measurement crack length are calculateda: after test, the crackle successively measured in image with scanning electron microscope is long
Degreea, and image is sequentially inputted to calculate corresponding CTOA value in " CTOA calculation method " model；
(6) CTOA- Δ is obtainedaEvolution trend: the crack propagation increment Delta that the CTOA being calculated and scanning electron microscope are measuredaIt is plotted in the same coordinate system, obtains CTOA- ΔaTendency chart.
2. crack tip ope ning angle degree measurement method as described in claim 1, which is characterized in that in step (1), will process
Good sample is polished with the sand paper of 1000# and 2000#, and then sample is placed on polishing machine and is polished, and successively uses diameter 3
μm and 0.5 μm of diamond polishing liquid, grinding and polishing use supersonic wave cleaning machine washed samples later, then dry.
3. crack tip ope ning angle degree measurement method as described in claim 1, which is characterized in that in step (2), by sample
On the collet of testing machine, sample is placed in scanning electron microscope vacuum tank together with chuck as a whole in situ for clamping, so that test process
In observation visual field in scanning electron microscope, focal length, contrast, the astigmatism of scanning electron microscope are adjusted, until can clearly see at 1000X
Observe specimen surface.
4. crack tip ope ning angle degree measurement method as described in claim 1, which is characterized in that described in step (5)
" CTOA calculation method " model is the program code write based on Matlab language, by analyzing the gray value in image
Compare, find out the position of several discrete points on two Crack lines, it is quasi- to carry out least square respectively to the point on two Crack lines
It closes, the size of angle is CTOA value between two fitting a straight lines.
5. crack tip ope ning angle degree measurement method as described in claim 1, which is characterized in that in step (7) a metallic, split
Line stablizes crack extension Δ in expansion processaWith the relationship of corresponding crack tip ope ning angle CTOA.
6. crack tip ope ning angle degree measurement method as claimed in claim 5, which is characterized in that in step (7) a metallic, CTOA
The lower limit value when state that tends towards stability is considered the critical value CTOA of crack tip ope ning angleC。
7. crack tip ope ning angle degree measurement method as described in claim 1, which is characterized in that " the CTOA calculation method "
Model is the im2bw function called in Matlab.
8. crack tip ope ning angle degree measurement method as described in claim 1, which is characterized in that " the CTOA calculation method "
Model is with the threshold value that sets by image binaryzation, so that the pixel in image is only there are two types of tonal gradation, gray value is greater than threshold
The pixel of value is 1, and the pixel that gray value is less than threshold value is 0.
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Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109781517A (en) * | 2019-01-11 | 2019-05-21 | 东南大学 | Asphalt mastic and aggregate Interface breaking mechanics parameter obtain test fixture and its test method under a kind of meso-scale |
| CN110376226A (en) * | 2019-07-03 | 2019-10-25 | 浙江大学 | A kind of turbine engine rotor crack propagation feature determines method |
| CN110967254A (en) * | 2019-12-25 | 2020-04-07 | 哈尔滨工业大学 | SEM (scanning electron microscope) in-situ tensile test method for researching fracture behavior of interface of metal matrix and ceramic membrane layer |
| CN111597740A (en) * | 2020-04-14 | 2020-08-28 | 扬州大学 | Harvester health monitoring method based on mesoscale ultrasonic teratocardio-band |
| CN111859616A (en) * | 2020-06-12 | 2020-10-30 | 中国石油天然气集团有限公司 | High-pressure natural gas pipeline fracture critical dimension and service life assessment method |
| CN113411515A (en) * | 2021-06-18 | 2021-09-17 | 吉林大学 | Camera-based TIP (time-of-flight) head auxiliary positioning system and positioning and information acquisition processing method thereof |
| CN114152616A (en) * | 2021-10-14 | 2022-03-08 | 盐城工学院 | Crack image recognition system and use method thereof |
| CN114441336A (en) * | 2022-01-14 | 2022-05-06 | 中国石油大学(北京) | Method for testing CTOD-delta a resistance curve of metal |
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| CN109781517B (en) * | 2019-01-11 | 2021-07-20 | 东南大学 | Test fixture and test method for acquiring fracture mechanical parameters of asphalt cement and aggregate interface under microscopic scale |
| CN110376226B (en) * | 2019-07-03 | 2021-01-08 | 浙江大学 | Method for determining crack propagation characteristics of turbine engine rotor |
| CN110376226A (en) * | 2019-07-03 | 2019-10-25 | 浙江大学 | A kind of turbine engine rotor crack propagation feature determines method |
| CN110967254A (en) * | 2019-12-25 | 2020-04-07 | 哈尔滨工业大学 | SEM (scanning electron microscope) in-situ tensile test method for researching fracture behavior of interface of metal matrix and ceramic membrane layer |
| CN110967254B (en) * | 2019-12-25 | 2021-01-08 | 哈尔滨工业大学 | SEM (scanning electron microscope) in-situ tensile test method for researching fracture behavior of interface of metal matrix and ceramic membrane layer |
| CN111597740A (en) * | 2020-04-14 | 2020-08-28 | 扬州大学 | Harvester health monitoring method based on mesoscale ultrasonic teratocardio-band |
| CN111597740B (en) * | 2020-04-14 | 2023-04-25 | 扬州大学 | Harvester health monitoring method based on mesoscale ultrasonic abnormal narrow band |
| CN111859616A (en) * | 2020-06-12 | 2020-10-30 | 中国石油天然气集团有限公司 | High-pressure natural gas pipeline fracture critical dimension and service life assessment method |
| CN113411515A (en) * | 2021-06-18 | 2021-09-17 | 吉林大学 | Camera-based TIP (time-of-flight) head auxiliary positioning system and positioning and information acquisition processing method thereof |
| CN114152616A (en) * | 2021-10-14 | 2022-03-08 | 盐城工学院 | Crack image recognition system and use method thereof |
| CN114441336A (en) * | 2022-01-14 | 2022-05-06 | 中国石油大学(北京) | Method for testing CTOD-delta a resistance curve of metal |
| CN117491142A (en) * | 2024-01-02 | 2024-02-02 | 西南科技大学 | Method for rapidly detecting surface crushing characteristics of granite particles |
| CN117491142B (en) * | 2024-01-02 | 2024-03-12 | 西南科技大学 | Method for rapidly detecting surface crushing characteristics of granite particles |
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Application publication date: 20181207 |