CN110160895A - Plate surface crack growth test method based on mark load - Google Patents
Plate surface crack growth test method based on mark load Download PDFInfo
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- CN110160895A CN110160895A CN201810169773.0A CN201810169773A CN110160895A CN 110160895 A CN110160895 A CN 110160895A CN 201810169773 A CN201810169773 A CN 201810169773A CN 110160895 A CN110160895 A CN 110160895A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/32—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0001—Type of application of the stress
- G01N2203/0005—Repeated or cyclic
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/006—Crack, flaws, fracture or rupture
- G01N2203/0062—Crack or flaws
- G01N2203/0066—Propagation of crack
Abstract
The present invention relates to field of material testing, in particular to the plate surface crack growth test method based on mark load.Loading spectrum parameter is determined by preliminary test, and loading spectrum parameters revision is carried out based on test fracture analysis result, is tested with other test specimens of revised loading spectrum to same type of material, is obtained corresponding data.The complete loading spectrum for crack growth rate test can be established according to this method.This method can completely reproduce surface crack growth overall process information, provide important test method for crack propagation behavioral study and crack growth rate test.The present invention uses based on same type of material parameter and gropes the loading spectrum method for parameter estimation of test and based on the loading spectrum parameter correction method for groping test fracture analysis result, can establish the complete loading spectrum for crack growth rate test.
Description
Technical field
The present invention relates to field of material testing, in particular to the plate surface crack growth test side based on mark load
Method.
Background technique
Using elliptical flaw and 1/4 oval chink line as the partial penetration crackle of representative be in aircaft configuration the most
Extensive crackle form.The extension service life of partial penetration crackle occupies the overwhelming majority of structure fatigue life.Therefore, for
The Crack growth analysis of partial penetration crackle is one of the important process of aircraft structural damage tolerance analysis.Currently, it is used for part
The material characteristic data of penetrated crack extensive diagnostic is usually in laboratory conditions, to use to contain to penetrate according to relevant criterion and split
What the standard specimen of line measured.For the plate with obvious machine direction, such as forging, milled sheet, using increasing material manufacturing or fixed
The metal material manufactured to solidifying process, material can show different CraCk extenslon reslstsnces along different propagation directions.If
Part penetrated crack in this class formation is analyzed using the material crack spreading rate of a direction obtained based on penetrated crack
Expansion process, it may appear that large error.The anisotropy that material crack extended attribute is introduced in analysis helps to improve point
Precision is analysed, guarantees the safety and economy of structure.Therefore, the acquisition of the material crack growth data of different directions is especially heavy
It wants.
For typical aircaft configuration, it is generally concerned with the crack expansion characteristic along surface direction and thickness direction.Surface side
To crack growth rate test often carried out using standard specimen, however the test of the crack growth rate of thickness direction can be by
To the limitation of plate thickness, can not be carried out based on standard specimen.To solve this problem, it is contemplated that use elliptical flaw
Carry out crack growth rate test.It can be completed in same test using elliptical flaw (hereinafter referred to as face crack)
The test of the crack growth rate of surface direction and thickness direction.Because up-front constraint or stress state can expand material crack
Exhibition drag has an impact, and the test specimen containing face crack simulates penetrated crack up-front constraint condition in part in practical structures, institute
With compared to penetrated crack, the crack propagation data that are obtained based on face crack are closer to actual conditions.
Face crack often show as rule half elliptic or semicircle, geometric description often use crack length (2c) and
Two parameters of crack depth (a).In crack expansion test, length surface and crack depth need to be measured simultaneously.Length surface can
It is measured using visual method, and crack depth is difficult to directly measure.In order to measure the depth of face crack, a variety of tests are developed
Method, including DC potential difference method, alternating current potential difference, Alternating current field measurement method, flexibility method, supercritical ultrasonics technology, tempering dyeing
Method, dye-penetrant method, mark load method.All kinds of method advantage and disadvantage are as follows:
Direct current or alternating current potential difference can be realized real-time measurement, and not by environmental restrictions.The disadvantage is that as a kind of indirect
Measurement method, this method needs to establish calibration curve (establishing for calibration curve is extremely complex), and while measure potential difference
Need to measure length surface 2c to combine calibration curve to export a.In addition, this method is more demanding to the susceptibility of potential difference meter,
And the part closure of crackle may result in short circuit, be easy so that measurement result is less than actual size；
Flexibility method have the advantages that it is identical as potential differentiation, the disadvantage is that as a kind of indirect measurement method, this method
Need to establish the relational expression of calibration curve or flexibility and crack size in advance, and to the requirement of the susceptibility of extensometer or strain gauge
It is higher.Generally while measuring flexibility, crack surfaces length is also measured.The measurement accuracy of this method receives extensometer
Or the limitation of the measurement accuracy and calibration curve precision of strain gauge；
Although supercritical ultrasonics technology is not limited by environment, this method is complicated, and ambient noise is separated with coherent signal
It is the difficult point that this method is implemented, and the method can not real-time measurement crack length；
Tempering decoration method and dye-penetrant method are to leave crackle on fracture to reflect its leading edge position
The profile set after test specimen fracture, carries out the crack length under quantitative fractography analysis acquisition different loads recurring number under the microscope
And depth.Both methods can also reflect that crack front evolutionary shapes information, disadvantage are in addition to reflecting crack size information
It is unable to real-time measurement, and the data obtained are less, needs abort when tempering dyeing is with penetration dyeing.Tempering is contaminated
Color method, tempering may change the crack expansion characteristic of material, and for dye-penetrant method, dyeing is possible to pollution fracture, leads
Cause can not obtain valid data.
It is identical as the principle for being tempered decoration method and dye-penetrant method to identify load method, and difference is that identifying load method passes through
Mark load leaves tag line in the form of the crack front for reflecting different moments on fracture, is not necessarily to abort, and will not
The problem of bringing material property change and fracture to pollute.Compared to the above test method, the precision highest of load method is identified.
However, the data of conventional mark load method acquisition are few, it is caused to be typically used in other test methods (such as potentiometry, soft
Degree method) calibration curve foundation on, crack growth rate test using less.
Summary of the invention
(1) technical problems to be solved
The object of the present invention is to provide the plate surface crack growth test methods based on mark load, solve existing split
The less problem of line growth data.
(2) technical solution
In order to solve the above technical problem, the present invention provides a kind of plate surface crack propagation surveys based on mark load
Method for testing comprising:
Initial crack is established on the test specimen, determines that the crackle half of the crackle is c long；
Determine the stress ratio R of mark loadmWith the stress ratio R of reference loadb, wherein Rb≤ 0.5, Rm=0.65+0.5Rb；
According to the stress ratio R of mark loadmWith the stress ratio R of reference loadbCarry out the test specimen containing initial crack
Crack Propagation preliminary test obtains reference load recurring number N during the testbWith mark load cycle number Nm；
Apply the N of recurring number containing reference loadbReference load and mark load cycle number NmMark load, until test specimen
Fracture；
Reference load recurring number N is judged according to the fracture tag line of fracture specimenbWith mark load cycle number NmWhether need
It corrects；
If not needing, reference load recurring number N is utilizedbWith mark load cycle number NmTo other test specimens of same material into
Row crack expansion test obtains crack propagation data；
If desired, then it is obtained based on the tag line on fracture along the crack propagation data (c, N) of surface direction and along depth
The crack propagation data (a, N) in direction, are mentioned and being modified according to c-N curve and a-N curve, followed using revised reference load
Number of rings NbWith mark load cycle number NmCrack expansion test is carried out to other test specimens of same material and obtains crack propagation data.
In some embodiments, preferably, described to obtain N during the testbAnd NmInclude:
Applying stress ratio to the test specimen containing initial crack is RmMark load and stress ratio be RbReference load, record
Crack extension Δ caused by reference loadB, cWith make crack propagation ΔB, cThe reference load recurring number N neededb；
According toCalculate Nm, wherein C and n is material constant, f (Rm)
For the stress ratio R for identifying loadmFunction；f(Rb) be benchmark load stress ratio RbFunction, ΔM, cCause for mark load
Propagation of the crackle in surface direction, ΔB, cFor crackle caused by benchmark load surface direction propagation.
In some embodiments, preferably, crack extension ΔB, cPreset range are as follows: 0.1mm~min 0.3mm,
(t-1.8mm)/20}；Then,
The reference load recurring number NbDetermination method include: in preliminary test tracking crack front characteristic point B
Position controls the quantity of reference load so that the crack extension of B point is at 0.1mm~min { 0.3mm, (t-1.8mm)/20 }
Between, reference load recurring number N is determined according to the quantity of the reference loadb。
In some embodiments, preferably, reference load recurring number N is determinedbPreliminary test in, can be used benchmark load
The loading spectrum that lotus recurring number is successively decreased step by step, in the loading spectrum that the reference load recurring number is successively decreased step by step, several pieces continuous
The reference load recurring number of loading spectrum block is constant, and crack extension caused by reference load meets in each loading spectrum block
The preset range.
In some embodiments, preferably, described that reference load recurring number is judged according to the fracture tag line of fracture specimen
NbWith mark load cycle number NmWhether need to correct and includes:
When the fracture tag line of fracture specimen can not recognize, then mark load cycle number N is correctedm；
When the spacing of the fracture tag line of fracture specimen is unsatisfactory for condition, then reference load recurring number N is correctedbAnd mark
Know load cycle number Nm。
In some embodiments, preferably, the amendment reference load recurring number NbMethod include:
Building is big to compose block, includes several in the big spectrum block with same datum load cycle number NbIt is followed with mark load
Number of rings NmSpectrum block；
Tag line spacing is caused to be located at the abnormal spectrum block outside zone of reasonableness in the big spectrum block of analysis；
Determine the reference load circulation sum m of the abnormal spectrum block1Nb；
It is obtained based on the tag line on fracture along the crack propagation data (c, N) of surface direction and splitting along depth direction
Line growth data (a, N), and obtain c-N curve and a-N curve；
Being determined according to c-N curve and a-N curve makes each spectrum block that can generate the crack extension for meeting pitch requirements
Compose block number m1'；
According to N 'b=m1Nb/m′1, obtain revised reference load recurring number Nb’。
In some embodiments, preferably, described to generate each spectrum block according to c-N curve and the determination of a-N curve
Meet the spectrum block number m of the crack extension of pitch requirements1' include:
The m for including by big spectrum block1NbSecondary load is divided into m1+ 1 piece；
Based on c-N curve and a-N curve, reference load recurring number pair is given by three point Lagrange interpolation calculations
The c and a answered, determines whether crack extension Δ c and Δ a caused by each spectrum block divide again after is located at 0.1mm~min
{ 0.3mm, (t-1.8mm)/20 }, if being located at, stops calculating, the m for otherwise including by big spectrum block1NbThe block number of secondary load point adds
1, the calculating and judgement of this step are repeated again.
In some embodiments, preferably, tag line interval is less than the initial position that zone of reasonableness appears in big spectrum block；
Tag line interval is greater than the end position that zone of reasonableness appears in big spectrum block.
In some embodiments, preferably, the amendment identifies load cycle number NmMethod include:
Judge that tag line can not recognize whether survey derived from mark line width；
If being derived from, load cycle number will be identified by NmIt improves to 2Nm。
In some embodiments, preferably, the amendment identifies load cycle number NmMethod include:
In the case where identifying the measurable situation of line width, mark line width of the measurement tag line in crack front characteristic point B
ΔM, c；
Calculate extension of the mark line width of crack front characteristic point B with crackle under the spectrum block effect of corresponding reference load
The ratios delta of amountM, c/ΔB, c,
It utilizesAmendmentIn
To recalculate Nm。
(3) beneficial effect
Loading spectrum parameter is determined by preliminary test in technical solution provided by the invention, and based on test fracture analysis
As a result loading spectrum parameters revision is carried out, is tested with other test specimens of revised loading spectrum to same type of material, is obtained corresponding
Data.The complete loading spectrum for crack growth rate test can be established according to this method.This method can completely reproduce table
Face crack propagation overall process information provides important test side for crack propagation behavioral study and crack growth rate test
Method.
Detailed description of the invention
Fig. 1 is test load spectrogram of the present invention；
Fig. 2 is the flow chart of loading spectrum parameter confirmation of the present invention before crack growth rate test；
Fig. 3 is the reference load recurring number N to successively decrease step by stepb；
Fig. 4 is the present invention to NbThe flow chart of suitable spectrum block number is determined when amendment；
Fig. 5 is schematic diagram (a) the test specimen figure of Ti-6Al-4V test specimen, (b) semicircle defect；
Fig. 6 is fracture tag line schematic diagram after maiden trial；
Fig. 7 is change curve (a) c-N curve of the obtained crack length of maiden trial with reference load recurring number, (b)
A-N curve；
Fig. 8 is that fracture figure (a) test specimen 1 that official testing obtains is carried out after determining loading spectrum parameter, and test specimen 2 (b) (c) are tried
Part 3；
Fig. 9 is to enter official testing after determining loading spectrum parameter to obtain crack length with the variation of reference load recurring number
(a) c-N curve, (b) a-N curve；
Figure 10 is the cross section of the present invention containing face crack.
Specific embodiment
With reference to the accompanying drawings and examples, specific embodiments of the present invention will be described in further detail.Following instance
For illustrating the present invention, but it is not intended to limit the scope of the invention.
In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, term " installation ",
" connected ", " connection " shall be understood in a broad sense, for example, it may be being fixedly connected, may be a detachable connection, or integrally connect
It connects；It can be mechanical connection, be also possible to be electrically connected；Can be directly connected, can also indirectly connected through an intermediary,
It can be the connection inside two elements." first " " second " " third " " the 4th " does not represent any sequence relation, is only
The differentiation carried out in order to facilitate description.For the ordinary skill in the art, above-mentioned term can be understood with concrete condition
Concrete meaning in the present invention.At the time of " current " is when executing certain movement, occur multiple current in text, is with examination
It is recorded in real time in part passage.
Inaccurate and few data volume problem is acquired based on existing crack propagation data, The present invention gives based on mark
The plate surface crack growth test method of load.
Product, method etc. will be described in detail by basic engineering, extension design and alternative design below.
The present invention provides a kind of plate surface crack growth test method based on mark load, as shown in Fig. 2, it is wrapped
It includes:
Step 01, initial crack is established on test specimen, determines that the crackle half of crackle is c long；
The a length of semicircle of crackle half, can be used the processing method of spark discharge in test specimen table when establishing initial crack
The semicircle defect of face processing pre-set radius.
Step 02, the stress ratio R of mark load is determinedmWith the stress ratio R of reference loadb, wherein Rb≤ 0.5, Rm=
0.65+0.5Rb；
Step 03, according to the stress ratio R of mark loadmWith the stress ratio R of reference loadbOne is carried out containing initial crack
The crack Propagation preliminary test of test specimen obtains reference load recurring number N during the testbWith mark load cycle number
Nm；
This method uses the different test specimens of same material, is tested first using preliminary test one of test specimen
Each loading spectrum parameter is obtained, R is usedbAnd RmIt respectively indicates reference load and identifies the stress ratio of load, NbAnd NmRespectively indicate base
The load cycle number of quasi- spectrum block and mark spectrum block.In this four parameters, Rm、NbAnd NmBe it needs to be determined that.
Step 04, apply the N of recurring number containing reference loadbReference load and mark load cycle number NmMark load,
Until test specimen is broken；
Step 05, reference load recurring number N is judged according to the fracture tag line of fracture specimenbWith mark load cycle number Nm
Whether need to correct；
If not needing, reference load recurring number N is utilizedbWith mark load cycle number NmTo other test specimens of same material into
Row crack expansion test obtains crack propagation data；
If desired, then it is obtained based on the tag line on fracture along the crack propagation data (c, N) of surface direction and along depth
The crack propagation data (a, N) in direction, are modified according to c-N curve and a-N curve, are followed using revised reference load
Number of rings NbWith mark load cycle number NmCrack expansion test is carried out to other test specimens of same material and obtains crack propagation data.
This method belongs to same type of material crack expansion characteristic and gropes the method according to a preliminary estimate of test and based on groping to test
The loading spectrum parameter correction method of fracture analysis result determines loading spectrum parameter by preliminary test, and based on test fracture point
It analyses result and carries out loading spectrum parameters revision, tested with other test specimens of revised loading spectrum to same type of material, obtain phase
Answer data.The complete loading spectrum for crack growth rate test can be established according to this method.This method can completely again
Existing surface crack growth overall process information provides important test for crack propagation behavioral study and crack growth rate test
Method.
Next more specific detail is carried out to this method:
By choosing suitable mark loading spectrum, and quantity and the interval of optimization mark load, it is possible on fracture
Clear readability, the reasonable tag line of spacing are left, so that few this of the crack propagation data of mark load method output be overcome to lack
Point.
The crack growth rate test of material carries out under constant amplitude load.It is such as high-strength for common aircraft metal material
Steel, titanium alloy, aluminium alloy are spent, applicable mark load includes lesser overload, load, and load mean value is constant, amplitude reduces
Constant amplitude spectrum block and load peaks are constant, stress ratio improves constant amplitude compose block.One suitable mark loading spectrum should be able to be disconnected
Clearly tag line is left on mouthful, and minimizes influence of the mark loading spectrum to overall crack propagation.In addition, on fracture
Tag line can allow for carrying out fracture quantity analysis using instrument simple as far as possible, such as optical microscopy.Below based on this two
A principle carries out the comparison of four classes mark loading spectrum:
The small overload of usual negligible amounts can leave tag line high-visible under SEM on fracture, but overload meeting
The validity for influencing reference load immediately after, generates a degree of overload retardation effect.
The advantages of load, is identical as small overload, but load can introduce a degree of acceleration effect, and it is applied
The limitation of test specimen, the i.e. test specimen to not pressure-bearing are received, buckling may be caused by applying load.
The constant amplitude that the constant amplitude spectrum block and load peaks that load mean value is constant, amplitude reduces are constant, stress ratio improves composes block shape
It is identical at the principle of tag line, be raising stress ratio, change the extension plane of crackle, formed with caused by reference load
The different angles of reflection of the plane of disruption, so that visible tag line be presented under light source.Theoretically, identify the stress ratio of load with
The difference of reference load is more obvious, and tag line is more clear.But it with the raising of stress ratio, is formed needed for visible tag line
The load cycle number wanted is more.Under conditions of equally mark load cycle number, load peaks are constant, stress ratio improves
The constant amplitude spectrum block that constant amplitude spectrum block weight/HP ratio mean value is constant, amplitude reduces is more prone to produce clearly tag line, because of load peaks
The stress ratio for the constant amplitude spectrum block that constant, stress ratio improves and the difference of big spectrum block become apparent from.Compared with overloading with low carry, this two
Kind mark load will not generate reciprocation with reference load, and the tag line formed can identify under an optical microscope.
It based on the above analysis, keeps load peaks identical as reference load, improves stress ratio, this kind of mark load is more
Meet selection principle, the potential crack growth rate for face crack is tested.In order to using the mark load of this form
The spreading rate test of face crack is carried out, application considers the crack propagation equation of crack closure herein, in conjunction with groping to test,
It is few to solve the problems, such as that mark load method obtains crack propagation data for the construction method for establishing mark loading spectrum.
The loading spectrum for being typically used for the load containing mark of crack growth rate test is as shown in Figure 1, Figure 10 shows.Each load
It includes one piece of reference load spectrum and a block identification loading spectrum that lotus, which composes block, constitutes a second level spectrum block.Reference load expands crackle
Exhibition, mark load record shape and the position of crack front.The two peak value having the same, different stress ratios.Use RbWith
RmIt respectively indicates reference load and identifies the stress ratio of load, NbAnd NmRespectively indicate the load of baseline spectrum block and mark spectrum block
Recurring number.In this four parameters, Rm、NbAnd NmBe it needs to be determined that.In order to estimate Rm、NbAnd NmThese three parameters, propose
Based on same type of material crack expansion characteristic and grope the method according to a preliminary estimate of test and based on groping to test fracture analysis result
Loading spectrum parameter correction method:
Step 110, a collection of test specimen with material is prepared；
Step 112, the manufacturing deficiency on test specimen；
Manufacturing deficiency be establish initial crack for convenience, so, need to process in surface of test piece before preliminary test pre-
If the semicircle defect of radius.
Step 114, the stress ratio R of mark load is determinedmWith the stress ratio R of reference loadb
The difference of the stress ratio and reference load that identify load is more obvious, and the tag line on fracture is more clear.But with
It is more to form load cycle number required for visible tag line for the raising of stress ratio.As reference load stress ratio Rb≤
When 0.5, using Rm=0.65+0.5RbConstant amplitude load as mark load, such constant amplitude load can stay on fracture
Under clearly tag line, while the problem acceptable, and that load will not be brought difficult of recurring number for identifying loading spectrum block.
Step 116, reference load recurring number N is determinedbWith mark load cycle number Nm
Step 116-1 determines reference load recurring number Nb
Under conditions of reaching measurement accuracy requirement, crack propagation data are usually The more the better, but use face crack
The quantity of the crack propagation data obtained with mark load method receives the limitation of plate thickness and fracture legibility.It is given in plate thickness
In the case where, excessive tag line certainty spacing very little is difficult to differentiate between under the microscope.In view of disconnected under optical microscopy
Mouth interpretation precision to meet requirement of engineering precision, while guaranteeing the robustness of data generally in 0.01mm or so, tag line
Interval should at least 10 times of interpretation precisions, that is, the spacing of tag line will at least reach 0.1mm.It is initially split in view of establishing
When line, crack extension is not less than 1.3mm, and Initial Flaw Size can reach 0.5mm, therefore, at the end of crackle is prefabricated, split
Line depth may reach 1.8mm.And be to meet analysis needs, crack propagation data will typically at least reach 20 pairs, also
It is that (t-1.8mm)/20 (t indicates plate thickness) is not to be exceeded in tag line spacing.When larger in view of thickness, (t-1.8mm)/20 meeting
It is excessive, the upper bound of tag line spacing is taken as the smaller value in 0.3mm and (t-1.8mm)/20, is expressed as min { 0.3mm, (t-
1.8mm)/20}。
In order to estimate the N for meeting pitch requirementsb, can be located in groping test using headshape microscope tracking and be split
The position of line leading edge characteristic point B, control the quantity of reference load so that B point propagation 0.1mm~min 0.3mm,
(t-1.8mm)/20 between }, to obtain Nb.Given crack extension Δb, required reference load recurring number NbIt is with splitting
Line extension is successively decreased, and as shown by the dotted line in fig. 3, dotted line is curve, and curve is the constant corresponding N of crack extensionbWith
The c long variation of crackle half.And it is difficult to make crack extension exactly equal to Δ by control load recurring number in testingb.It examines
Consider this point, loading spectrum that reference load recurring number is successively decreased step by step can be used to carry out test, as shown in solid in Fig. 3.?
N in this loading spectrum, in continuous several pieces of loading spectrumsbConstant number, and wherein in every piece of loading spectrum reference load spectrum
Caused crack extension is all between 0.1mm~min { 0.3mm, (t-1.8mm)/20 }.
Step 116-2 determines mark load cycle number Nm
Mark load cycle number N in one piece of loading spectrummIt should not only make tag line clear, but also tag line will not be made wide
And influence whole crack propagation.It means that meet tag line clarity require under conditions of, mark line width with it is right
1/10 should be no more than by answering the ratio of crack extension caused by reference load.Experiments have shown that when the width Delta of tag linem?
When between 0.01mm~0.02mm, tag line can meet above-mentioned requirements simultaneously.In the following, being used with reference to the parameter of same type of material
Consider the crack propagation equation N according to a preliminary estimate of crack closurem.For crack front characteristic point B, crack propagation law be can be used
Following equation indicates:
Dc/dN=C (Δ KC, eff)n (1)
Wherein: C and n is material constant, Δ KC, effIt is the effective stress intensity factor change journey of B point, Δ KC, effWith stress
Intensity factor becomes journey Δ KcRelational expression it is as follows:
ΔKC, eff=U Δ Kc (2)
Wherein, U is that effective stress becomes journey ratio (effective stress range ratio).In given experimental condition
In the case where, U can be considered the function of stress ratio R, i.e. U=f (R).Introduce Δ KC, effIt is contemplated that stress ratio Crack Propagation Rate
Influence, correspondingly, the crack propagation under reference load can use formula (3) and formula (4) to describe respectively:
[dc/dN]b=C [fRb)·(1-Rb)KC, max]n (3)
[dc/dN]m=C [f (Rm)·(1-Rm)KC, max]n (4)
Assuming that starting to apply one containing NbThe reference load and N of circulationmWhen the spectrum block of the mark load of circulation, face crack
Length be 2c, depth a, then this spectrum block in reference load with identify load caused by B point propagation estimate respectively
Are as follows:
Assuming that flaw size is from (2c a) becomes (2c+2 Δ by the effect that reference load is composedB, c, a+ ΔB, a).So
Afterwards by identifying the effect of loading spectrum, flaw size is from (2c+2 ΔB, c, a+ ΔB, a) become (2c+2 ΔB, c+2ΔM, c, a+
ΔB, a+ΔM, a).Using the mid-point formula in numerical integration, can obtain
Thus it obtains:
Crack extension Δ caused by the mark load of characteristic point A can be obtained in same methodM, aCause with reference load
Crack extension ΔB, aRatio:
Width of the tag line in characteristic point B and A should all be met the requirements.But since characteristic point A is under reference load
Propagation ΔB, aIt can not obtain in real time, formula (10) can not be used to just estimate Nm.Therefore, N is estimated using formula (9)m.In view of test
Crack depth is unknown in the process, and the stress intensity factor of characteristic point B can not calculate.In order to estimate Nm, it is approximately consideredThus it obtains
By ΔM, c, the propagation Δ of B point that arrives of test observationB, cAnd corresponding load cycle number substitutes into NbBelt
(11), the n and f (R) for then substituting into respective material can obtain the mark load cycle number N in a spectrum blockm.For common
Metal material, n between 3~4, n can approximation be taken as 3.5.In addition, listing the f of common airframe material in table 1
(R)。ΔM, cFor propagation of the crackle in surface direction caused by mark load, ΔB, cIt is crackle caused by benchmark load in table
The propagation in face direction.
With NbIt is similar, in test, in continuous several pieces of loading spectrums, NmQuantity can keep constant, as long as according to formula
(10) the mark line width estimated is between 0.01mm~0.02mm.
Table 1 often uses the f (R) of aerial metal
Step 118, apply the N of recurring number containing reference loadbReference load and mark load cycle number NmMark load,
Until test specimen is broken；
Step 120, reference load recurring number N is judged according to the fracture tag line of fracture specimenbWith mark load cycle number Nm
Whether need to correct；
Due to the crack expansion characteristic of real material and same type of material difference that may be present and estimation method itself
Similar properties, fruit with the parameter obtained according to a preliminary estimate may result in fracture tag line do not know or tag line spacing it is too small or
Excessive problem.There may be aiming at the problem that, before formal test, based on grope test fracture modified result benchmark carry
Lotus recurring number NbWith mark load cycle number Nm。
Step 120-1, reference load recurring number NbAmendment
When tag line spacing is too small or excessive, need to NbIt is modified.Modification method is as follows:
(1) interpretation is carried out to the fracture for groping test acquisition, based on visible tag line on fracture, obtained along surface side
To crack propagation data (c, N) and along the crack propagation data (a, N) of depth direction.According to the pitch requirements of tag line, really
Surely lead to the baseline spectrum block that tag line spacing is too small or excessive.
It (2) will be by several N having the samebAnd NmSpectrum block (by one piece of reference load spectrum and a block identification loading spectrum
Constituting) the spectrum block that constitutes is known as one big spectrum block.Tag line interval too small would generally occur in the initial position of spectrum block greatly, and
Tag line interval is excessive to be occurred in the end position of spectrum block greatly.Assuming that the preceding m of one big spectrum block1The spacing of block is too small,
It is m that then these side crops industries, which compose included reference load circulation sum,1Nb.Using a-N curve and c-N curve, such one is found
A spectrum block number m '1, so that every piece of baseline spectrum can generate the crack extension for meeting pitch requirements.In this way, benchmark adjusted
Load cycle number N 'b=m1Nb/m′1.Equally, for rear m2The excessive spectrum block of the spacing of block, using a-N curve and c-N curve,
Find such a spectrum block number m '2, so that every piece of baseline spectrum can generate the crack extension for meeting pitch requirements.After adjustment
Reference load recurring number N 'b=m2Nb/m′2。
Below by taking the first situation as an example, the method for finding suitable spectrum block number using a-N curve and c-N curve is introduced.Side
Method flow chart is as shown in figure 4, be summarized as follows:
(1) horizontal axis be load cycle number, the longitudinal axis be crack size linear coordinate system in make respectively (c, N) with (a,
N) curve marks the beginning and end position for the baseline spectrum for causing spacing too small on curve；
(2) if investigating the m for including by this section of baseline spectrum1NbSecondary load is divided into m1Can+1 piece meet the requirements.Based on (c,
N) and (a, N) curve, given reference load recurring number corresponding c and a is calculated by the method for three point Lagrange interpolation, from
And (load cycle number is m to first piece of baseline spectrum of calculating1Nb/(m1+ 1) crack extension Δ c caused by) and Δ a, investigate Δ c and
Whether Δ a falls in allowed limits.
(3) if by m1NbSecondary load is divided into m1+ 1 piece, can Δ c and Δ a caused by first piece of baseline spectrum, which meet, wants
It asks, then stops calculating；Otherwise, the spectrum block number of equal part adds 1, second step is repeated, until meeting pitch requirements.
Step 120-2 identifies load cycle number NmAmendment
Utilize R according to a preliminary estimatemAnd NmIt is tested, it is possible that tag line is not known or wide situation.For
The first situation, if reference load stress ratio RmNo more than 0.5, the stress ratio R of load is identifiedmIt is taken as 0.65+0.5RbUsual energy
Guarantee the identification of tag line, and tag line does not know to may be caused by tag line is narrow.If identifying line width immeasurability,
It is contemplated that by NmIt improves to 2Nm.It can measure the tag line of width, width Delta of the measurement tag line in characteristic point B if it existsM, c,
Calculate the ratios delta of propagation of the mark line width of B point with crackle under the spectrum block effect of corresponding reference loadM, c/ΔB, c, into
And it obtainsN according to a preliminary estimate is corrected with thismIt usesIt is revisedIt will be used to recalculate Nm.For second case, when tag line is wide, using with mark
It is narrow to know line, and the identical method of the measurable situation of width corrects Nm。
Step 122, reference load recurring number N is utilizedbWith mark load cycle number NmOther test specimens of same material are carried out
Crack expansion test obtains crack propagation data.
Next, having carried out the building of mark load by taking Ti-6Al-4V (Ti64) titanium alloy plate as an example, having been split based on surface
The processing for the crack propagation data that line obtains:
(1) test specimen is made to be process shown in test specimen such as Fig. 5 (a) by the Ti64 milled sheet of 8mm thickness.At the heat of plate
Science and engineering skill is the 1h that anneals at 800 DEG C, is then air-cooled to room temperature.Test specimen sample direction be L-T to.The material component of Ti64 and
Basic mechanical performance is respectively as shown in table 2, table 3.Initial crack is established for convenience, before test, using spark discharge
Processing method surface of test piece radius of machining R=0.5mm semicircle defect, as shown in Fig. 5 (b).
The material component of 2 Ti64 of table
Table 3Basic mechanical property of Ti64plate
(2) loading spectrum
The stress ratio R of reference loadbIt is 0.1, identifies the stress ratio R of loadmAccordingly it is taken as 0.7.One piece of loading spectrum is wrapped
The reference load recurring number N containedbIt will be carried out according to a preliminary estimate according to the face crack for groping test along the propagation of surface direction,
And identify load cycle number NmThen according to corresponding reference load recurring number Nb, estimated using formula (10).Grope the fracture of test
Analysis result will be used to correct the N obtained according to a preliminary estimatebAnd Nm.The determination of loading spectrum will be introduced together with test process.
(3) process is tested
A. initial crack is established.According to the requirement of crack growth rate testing standard, established using the method for load shedding step by step
The load of initial crack, use is as shown in table 4.After crackle is prefabricated, the crackle half that surface direct-reading measures is c=1.8mm long.
B. loading spectrum parameter is according to a preliminary estimate.Apply peak stress σmaxThe benchmark of=230MPa, stress ratio R=0.1 carry
Lotus controls the recurring number of reference load, makes the crack extension Δ of surface directionB, cIn 0.2mm or so, record causes crackle to expand
Exhibition amount ΔB, cReference load recurring number Nb.Using f (R) expression formula for the Ti64 that table 1 is listed, R=0.1 and R=0.7 are obtained
Effective stress to become journey ratio U be respectively 0.812 and 1, substitute into formula (10), obtain Nm≈ΔM, cNb/(0.0443ΔB, c), then
By ΔM, c=0.015mm, actual measurement ΔB, cWith corresponding NbSubstitute into the formula, estimation mark load cycle number Nm.Next, applying
NmThe mark load of circulation.
Above procedure repeats, until test specimen is broken.The loading spectrum parameter obtained according to a preliminary estimate is shown in Table 5, gropes to test
Fracture figure see Fig. 6.Fracture shows clearly tag line, this shows NmEstimation it is relatively reasonable.
C. loading spectrum parameter NbAnd NmAmendment.Quantitative analysis is carried out to groping the obtained fracture of test first.Fracture point
It analyses and is carried out under the optical microscopy with grating scale, the measurement accuracy of grating scale is 0.005mm.Origin is arranged in semiellipse
The center of crackle, as shown in Figure 6.Since surface of test piece is in plane stress state, crackle is in the position close to surface of test piece
The place of setting can be bent, this causes on crack front from origin along the farthest point of surface direction not in the friendship of leading edge and surface of test piece
Point, but in some position close to surface of test piece.In fracture interpretation, have recorded along the surface direction point farthest from y-axis
X coordinate obtains the length of crackle with this, and crack depth is then obtained by being located at y-coordinate of the leading edge away from x-axis farthest point, such as Fig. 6
It is shown.Based on fracture analysis as a result, having made c-N and a-N curve, as shown in Figure 7.On c-N and a-N curve, mark out
The data point of pitch requirements is not met.As it can be seen that these data points all concentrate on the end position of one big spectrum block.According to this
A little data points and c-N and a-N curve, the method provided using 3.2 sections, to the N obtained according to a preliminary estimatebIt is modified, it is corresponding
NmAlso it changes correspondingly.Loading spectrum parameter adjusted is as shown in table 6.
D. crack growth rate is tested.In the prefabricated initial crack ruler for reaching first test specimen of the crackle of second test specimen
After very little, the crack expansion test of second test specimen is carried out using revised loading spectrum.No longer monitoring crack during test
Along the extension of surface direction.Shown in the fracture figure such as Fig. 8 (a) obtained after test specimen fracture.Compared with the fracture of first test specimen,
Tag line is denser.Fracture analysis shows other than the spacing of last three tag lines is wide, between other tag lines
Away from all meeting the requirements.Consider that the corresponding crack growth rate of last three tag lines is higher, and is primarily upon splitting for stage II
Line propagation law, therefore further amendment no longer is done to loading spectrum parameter.Using the loading spectrum of foundation, 3 test specimens have been carried out altogether
Crack expansion test, test specimen fracture is as shown in figure 8, obtained crack propagation data are as shown in Figure 9.
Table 4 establishes load used in initial crack
The loading spectrum parameter of table 5 according to a preliminary estimate
The revised loading spectrum parameter of table 6
This technology gives the mark load constructing technology for surface crack growth behavioral study, with Ti64 plate
The application of method is illustrated for crack growth rate test.The conclusion of acquirement is as follows:
(1) in test method, using consider the Paris formula of crack closure establish based on same type of material parameter and
Grope the loading spectrum method for parameter estimation of test and based on the loading spectrum parameter correction method for groping test fracture analysis result.
According to this method, the complete loading spectrum for crack growth rate test can be established.This method passes through Ti64 titanium alloy plate
Crack growth rate test to have obtained good verifying.
(2) this method can completely reproduce surface crack growth overall process information, be crack propagation behavioral study and crackle
Spreading rate test provides important tests method.
The foregoing is merely illustrative of the preferred embodiments of the present invention, is not intended to limit the invention, all in essence of the invention
Within mind and principle, any modification, equivalent replacement, improvement and so on be should all be included in the protection scope of the present invention.
Claims (10)
1. a kind of plate surface crack growth test method based on mark load characterized by comprising
Initial crack is established on the test specimen, determines that the crackle half of the crackle is c long；
Determine the stress ratio R of mark loadmWith the stress ratio R of reference loadb, wherein Rb≤ 0.5, Rm=0.65+0.5Rb；
According to the stress ratio R of mark loadmWith the stress ratio R of reference loadbThe fatigue for carrying out a test specimen containing initial crack is split
Line extends preliminary test, obtains reference load recurring number N during the testbWith mark load cycle number Nm；
Apply the N of recurring number containing reference loadbReference load and mark load cycle number NmMark load, until test specimen be broken；
Reference load recurring number N is judged according to the fracture tag line of fracture specimenbWith mark load cycle number NmWhether need to repair
Just；
If not needing, reference load recurring number N is utilizedbWith mark load cycle number NmOther test specimens of same material are split
Line expanding test obtains crack propagation data；
If desired, then it is obtained based on the tag line on fracture along the crack propagation data (c, N) of surface direction and along depth direction
Crack propagation data (a, N), be modified according to c-N curve and a-N curve, utilize revised reference load recurring number Nb
With mark load cycle number NmCrack expansion test is carried out to other test specimens of same material and obtains crack propagation data.
2. the plate surface crack growth test method as described in claim 1 based on mark load, which is characterized in that described
N is obtained during the testbAnd NmInclude:
Applying stress ratio to the test specimen containing initial crack is RmMark load and stress ratio be RbReference load, record benchmark
Crack extension Δ caused by loadB, cWith make crack propagation ΔB, cThe reference load recurring number N neededb；
According toCalculate Nm, wherein C and n is material constant, f (Rm) it is mark
The stress ratio R of loadmFunction；f(Rb) be benchmark load stress ratio RbFunction, ΔM, cFor crackle caused by mark load
In the propagation of surface direction, ΔB, cFor crackle caused by benchmark load surface direction propagation.
3. the plate surface crack growth test method as claimed in claim 2 based on mark load, which is characterized in that crackle
Propagation ΔB, cPreset range are as follows: 0.1mm~min { 0.3mm, (t-1.8mm)/20 }；Then,
The reference load recurring number NbDetermination method include: in preliminary test track crack front characteristic point B position,
Control reference load quantity so that the crack extension of B point between 0.1mm~min { 0.3mm, (t-1.8mm)/20 },
Reference load recurring number N is determined according to the quantity of the reference loadb。
4. the plate surface crack growth test method as claimed in claim 3 based on mark load, which is characterized in that determine
Reference load recurring number NbPreliminary test in, the loading spectrum that reference load recurring number is successively decreased step by step can be used, in the benchmark
The reference load recurring number of several pieces of continuous loading spectrum blocks is constant in the loading spectrum that load cycle number successively decreases step by step, and each load
Crack extension caused by reference load all meets the preset range in lotus spectrum block.
5. the plate surface crack growth test method as described in claim 1 based on mark load, which is characterized in that described
Reference load recurring number N is judged according to the fracture tag line of fracture specimenbWith mark load cycle number NmWhether need to correct packet
It includes:
When the fracture tag line of fracture specimen can not recognize, then mark load cycle number N is correctedm；
When the spacing of the fracture tag line of fracture specimen is unsatisfactory for condition, then reference load recurring number N is correctedbWith mark load
Recurring number Nm。
6. the plate surface crack growth test method as claimed in claim 5 based on mark load, which is characterized in that described
Correct reference load recurring number NbMethod include:
Building is big to compose block, includes several in the big spectrum block with same datum load cycle number NbWith mark load cycle number Nm
Spectrum block；
Tag line spacing is caused to be located at the abnormal spectrum block outside zone of reasonableness in the big spectrum block of analysis；
Determine the reference load circulation sum m of the abnormal spectrum block1Nb；
It is obtained based on the tag line on fracture along the crack propagation data (c, N) of surface direction and along the crack propagation of depth direction
Data (a, N), and obtain c-N curve and a-N curve；
Being determined according to c-N curve and a-N curve makes each spectrum block that can generate the spectrum block for meeting the crack extension of pitch requirements
Number m1'；
According to N 'b=m1Nb/m′1, obtain revised reference load recurring number Nb’。
7. the plate surface crack growth test method as claimed in claim 6 based on mark load, which is characterized in that described
Being determined according to c-N curve and a-N curve makes each spectrum block that can generate the spectrum block number m for meeting the crack extension of pitch requirements1’
Include:
The m for including by big spectrum block1NbSecondary load is divided into m1+ 1 piece；
Based on c-N curve and a-N curve, the corresponding c of reference load recurring number is given by three point Lagrange interpolation calculations
And a, determine whether crack extension Δ c and Δ a caused by each spectrum block divide again after is located at 0.1mm~min { 0.3mm, (t-
1.8mm)/20 }, if being located at, stop calculating, the m for otherwise including by big spectrum block1NbThe block number of secondary load point adds 1, repeats again
The calculating and judgement of this step.
8. the plate surface crack growth test method as claimed in claim 6 based on mark load, which is characterized in that mark
Line interval is less than the initial position that zone of reasonableness appears in big spectrum block；Tag line interval is greater than zone of reasonableness and appears in big spectrum block
End position.
9. the plate surface crack growth test method as claimed in claim 5 based on mark load, which is characterized in that described
Amendment mark load cycle number NmMethod include:
Judge that tag line can not recognize whether survey derived from mark line width；
If being derived from, load cycle number will be identified by NmIt improves to 2Nm。
10. the plate surface crack growth test method as claimed in claim 5 based on mark load, which is characterized in that institute
State amendment mark load cycle number NmMethod include:
In the case where identifying the measurable situation of line width, tag line width Delta of the measurement tag line in crack front characteristic point BM, c；
Calculate the ratio of propagation of the mark line width of crack front characteristic point B with crackle under the spectrum block effect of corresponding reference load
It is worth ΔM, c/ΔB, c,
It utilizesAmendmentIn
To recalculate Nm。
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111678819A (en) * | 2020-06-01 | 2020-09-18 | 中国航空工业集团公司沈阳飞机设计研究所 | Identification method for fatigue cracks under multi-working-condition load |
| CN112485107A (en) * | 2020-10-30 | 2021-03-12 | 中国直升机设计研究所 | Method for verifying crack propagation endurance time of girder of metal blade |
| CN117191371A (en) * | 2023-09-07 | 2023-12-08 | 北京航空航天大学 | Durability test method for combining high loads under random load |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3638230A (en) * | 1969-06-27 | 1972-01-25 | Japan Synthetic Rubber Co Ltd | Apparatus for measuring dynamic loss angle |
| US20130305833A1 (en) * | 2012-05-17 | 2013-11-21 | Department Of The Navy, Office Of Counsel - Nawcad | Method for Measuring Fatigue |
| CN105371769A (en) * | 2015-11-04 | 2016-03-02 | 西北工业大学 | Method and device of measuring dynamic crack lengths |
| CN106568662A (en) * | 2016-11-08 | 2017-04-19 | 北京航空航天大学 | Bidirectional fatigue crack expansion rate testing method and testing system |
-
2018
- 2018-02-15 CN CN201810169773.0A patent/CN110160895A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3638230A (en) * | 1969-06-27 | 1972-01-25 | Japan Synthetic Rubber Co Ltd | Apparatus for measuring dynamic loss angle |
| US20130305833A1 (en) * | 2012-05-17 | 2013-11-21 | Department Of The Navy, Office Of Counsel - Nawcad | Method for Measuring Fatigue |
| CN105371769A (en) * | 2015-11-04 | 2016-03-02 | 西北工业大学 | Method and device of measuring dynamic crack lengths |
| CN106568662A (en) * | 2016-11-08 | 2017-04-19 | 北京航空航天大学 | Bidirectional fatigue crack expansion rate testing method and testing system |
Non-Patent Citations (1)
| Title |
|---|
| YINGHAO DONG 等: "Marker load-aided bidirectional fatigue crack growth rate measurement via a semi-elliptical surface crack", 《INTERNATIONAL JOURNAL OF FATIGUE》 * |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111678819A (en) * | 2020-06-01 | 2020-09-18 | 中国航空工业集团公司沈阳飞机设计研究所 | Identification method for fatigue cracks under multi-working-condition load |
| CN112485107A (en) * | 2020-10-30 | 2021-03-12 | 中国直升机设计研究所 | Method for verifying crack propagation endurance time of girder of metal blade |
| CN112485107B (en) * | 2020-10-30 | 2022-08-02 | 中国直升机设计研究所 | Method for verifying crack propagation endurance time of girder of metal blade |
| CN117191371A (en) * | 2023-09-07 | 2023-12-08 | 北京航空航天大学 | Durability test method for combining high loads under random load |
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