CN108204922A - A kind of method that three-point bending standard sample crack length is determined based on strain measurement technique - Google Patents

A kind of method that three-point bending standard sample crack length is determined based on strain measurement technique Download PDF

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Publication number
CN108204922A
CN108204922A CN201711485649.7A CN201711485649A CN108204922A CN 108204922 A CN108204922 A CN 108204922A CN 201711485649 A CN201711485649 A CN 201711485649A CN 108204922 A CN108204922 A CN 108204922A
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sample
crack length
strain
point bending
measurement
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邢怀念
金立强
李达
孙凯
李书卉
刘增利
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Dalian University of Technology
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Dalian University of Technology
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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
    • G01N3/02—Details
    • G01N3/06—Special adaptations of indicating or recording means
    • G01N3/066—Special adaptations of indicating or recording means with electrical indicating or recording means
    • 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
    • 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
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/06—Indicating or recording means; Sensing means
    • G01N2203/0617—Electrical or magnetic indicating, recording or sensing means
    • 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
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/06—Indicating or recording means; Sensing means
    • G01N2203/067—Parameter measured for estimating the property
    • G01N2203/0682—Spatial dimension, e.g. length, area, angle

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)

Abstract

The present invention relates to fracture mechanics test crack length field of measuring technique, provide a kind of measuring method of the crack length for three-point bending standard sample, including：Propose the method for determination for measuring equation, the arrangement of strain ga(u)ge, crack length of determining crack length.Wherein, the measurement equation can be used prefabricated notched specimen and obtain；The arrangement of the strain ga(u)ge includes arranged direction and position；The measurement of the method for determination of the crack length including force value, the measurement of strain, measurement data processing mode.The present invention provides a kind of measuring method that can determine three-point bending standard sample crack length, the measuring method is simple and practicable reliable, has higher measurement efficiency, and is easy to implement automation collection and monitoring.

Description

It is a kind of that three-point bending standard sample crack length is determined based on strain measurement technique Method
Technical field
The present invention relates to fracture mechanics test crack length field of measuring technique more particularly to one kind to be directed to three-point bending mark The measurement of quasi- sample crack length.
Background technology
In fracture mechanics test field, the research for crack Propagation measurement of length never stopped.Mesh Before, the method for the relative maturity that related crack length measures has range estimation direct-reading method, crack opening displacement method, potentiometry, ultrasonic wave Method, acoustic-emission, eddy-current method and magnetic particle method etc..
The present invention herein proposes a kind of one kind for being totally different from above-mentioned measuring method and determines three based on strain measurement technique The method of point bending standard sample crack length.Measuring method mentioned by the present invention is simple and practicable, has higher measurement effect Rate, and it is easy to implement automation collection and monitoring.
Invention content
The present invention provides a kind of method that three-point bending standard sample crack length is determined based on strain measurement technique, packets It includes：Propose the method for determination for measuring equation, the arrangement of strain ga(u)ge, crack length of determining crack length.Wherein, The measurement equation can be used prefabricated notched specimen and obtain；The arrangement of the strain ga(u)ge includes arranged direction and arrangement Position；The measurement of the method for determination of the crack length including force value, the measurement of strain, measurement data processing mode.
The measuring method is directed to the three-point bending standard sample crack length for measuring fracture mechanical property Measurement, be particularly suitable for the real-time measurement of crack length during fatigue crack propagation test.
The measuring method is suitable for the width of three-point bending standard sample, i.e. sampleWFor thicknessB2 times, sample LengthLNot less than specimen widthW4.2 times, and load when be bent spanSFor specimen widthW4 times.
The measuring method is suitable for the isotropic materials such as metal.
The measuring resistance strain gauge is arranged on three-point bending standard sample, and position need to meet following three simultaneously A condition：（1）On the specimen surface for opening up prefabricated notch side；（2）On the central axes of specimen surface length direction；（3） The horizontal distance of the vertical reinforcing action plane of distance is exactly equal to the thickness of sample.
The measurement equation is as follows：
lg[εB 2 E (1–a/W)/(3F)]=K 1+K 2 a/W （1-1）
In formula,EFor the elasticity modulus of sample material, unit N/mm2；FTo apply force value, unit N；WFor specimen width, unit mm；BFor sample thickness, unit mm；εFor microstrain reading；aFor crack length, unit mm；K 1WithK 2For undetermined coefficient, it is and material Expect related constant, can be determined by the sample with prefabricated notch.
Undetermined coefficient in the measurement equationK 1WithK 2Method of determination：It makes and is no less than two standards with prefabricated notch Sample, if specimen configuration size, elasticity modulus, prefabricated notch length andK 1WithK 2It is known that force value is applied by measurementFIt is and corresponding Microstrain readingε, substitute into formula（1-1）It can be obtainedK 1WithK 2Value.
The method of determination of the crack length：To the sample that arbitrary a dimension scale is met the requirements of the standard, if outside it Shape size, elasticity modulus andK 1WithK 2It is known that in Fatigue Cracks Propagation, force value is applied by measurementFAnd it is corresponding it is micro- should Become readingε, substitute into formula（1-1）The crack length value of any time can be obtaineda.It should be noted that applied force when measuring Maximum fatigue load when value is no more than crack propagation.
Beneficial effects of the present invention：This method propose the arrangements for measuring equation, strain ga(u)ge of determining crack length Mode, the method for determination of crack length.Wherein, it measures equation and prefabricated notched specimen acquisition can be used；The arrangement of strain ga(u)ge Mode includes arranged direction and position；The method of determination of crack length includes the measurement of force value, the measurement of strain, measurement number According to processing mode.The measuring method is simple and practicable reliable, has higher measurement efficiency, and be easy to implement automation collection with Monitoring.
Description of the drawings
Fig. 1 is structure diagram provided in an embodiment of the present invention.
The technical characteristic of reference numeral reference is in figure：
1st, three-point bending standard sample, 2, strain ga(u)ge, 3, fatigue growth crack, 4, the bearing of fatigue tester three-point bending platform Roller, 5, fatigue tester loading roller, 6, resistance strain gauge, 7, length direction central axes on sample quit a post and thus leave it vacant discharge surface, 8, data pass Defeated line, 9, prefabricated notch.
Specific embodiment
For make present invention solves the technical problem that, the technical solution that uses and the technique effect that reaches it is clearer, below The present invention is described in further detail in conjunction with the accompanying drawings and embodiments.It is understood that specific implementation described herein Example is used only for explaining the present invention rather than limitation of the invention.It also should be noted that for ease of description, attached drawing In illustrate only part related to the present invention rather than full content.
Fig. 1 is structure diagram provided in an embodiment of the present invention.As shown in Figure 1, provided in an embodiment of the present invention is to be based on Strain measurement technique determines the measuring system of three-point bending standard sample crack length, including：Three-point bending standard sample 1, electricity Hindering strain gauge 2, fatigue growth crack 3, fatigue tester three-point bending platform backing roll 4, fatigue tester loading roller 5, resistance should Become instrument 6, sample open gap length surface direction central axes 7, data line 8, prefabricated notch 9.Wherein, the length of sample 1 isL, width isW, thickness isB, and meetW=2B,L≥4.2W；Before experiment will on the quit a post and thus leave it vacant discharge surface of sample 1 prefabricated notch 9, And fatigue growth crack 3 is generated on this basis；Distance reinforcing action plane distance is on sample upper surface central axes 7B's Respectively one strain ga(u)ge 2 of arrangement, strain ga(u)ge 2 are fixed along the length direction of sample 1 for position；It will be electric with data line 8 Resistance strain gauge 2 is connected with resistance strain gauge 6；Sample 1 is placed on fatigue tester three-point bending platform backing roll 4, is adopted Active force is applied to sample 1 with testing machine loading roller 5F, at this time strain ga(u)ge can show certain microstrain readingε, according to Active forceFWith corresponding microstrain readingεAnd measurement equation noted earlier（1-1）Crack length can be estimateda。
Below for commonly using 45 steel in engineering, it is as follows that specific embodiment is described in detail：
The first step：Prefabricated sample.Specimen size ratio will meetW=2B,L≥4.2W.Notch is preset using mechanical processing mode. Can sample quantities be determined according to test request.But it at least chooses two pieces to be used for determining coefficientK 1WithK 2, and require this two pieces sample Prefabricated notch deptha 1Witha 2It is unequal.
Second step：Arrange strain ga(u)ge.Open up the central axes that length direction is drawn on the surface of notch in sample, and The horizontal distance that the vertical reinforcing action plane of distance is marked on central axes is exactly equal to two positions of sample thickness.It is marking Along specimen length direction adhering resistance strain gauge at position, strain ga(u)ge is connect with resistance strain gauge with data line Get up.
Third walks：It determines to measure equation undetermined coefficientK 1WithK 2.Sample foundation regulation requirement is placed at 3 points of testing machine In bending, sample is loaded using testing machine loading roller, when loading will ensure that sample be in elastic stage, record force value and phase The microstrain reading answered, formula is substituted by measurement result（1-1）If known sample size and elasticity modulus, you can be obtainedK 1、K 2。 The present embodiment（45 steel）It is as follows to obtain measurement equation：
lg[εB 2 E (1–a/W)/(3F)]=5.99201+2.13831a/W （1-2）
4th step：The measurement of crack length.The sample to be tested that will be processed（It may differ from for determining undetermined coefficientK 1WithK 2's Sample）It requires to arrange strain ga(u)ge according to second step, measures its size, be then placed into 3 points of fatigue tester On bending backing roll, start fatigue tester application fatigue load and cause slowly growing crack.In crack propagation process, note The force value of any time and corresponding microstrain reading are recorded, in the case that known to specimen size and elasticity modulus, substitutes into formula （1-2）Crack length can be obtaineda。
Finally it should be noted that：The above embodiments are only used to illustrate the technical solution of the present invention., rather than its limitations；To the greatest extent Pipe is described in detail the present invention with reference to foregoing embodiments, it will be understood by those of ordinary skill in the art that：Its is right Technical solution recorded in foregoing embodiments modifies and either which part or all technical features is equally replaced It changes, the range for various embodiments of the present invention technical solution that it does not separate the essence of the corresponding technical solution.

Claims (3)

  1. A kind of 1. method that three-point bending standard sample crack length is determined based on strain measurement technique, which is characterized in that including Following steps：
    a）Prefabricated sample：Notch, the width of the sample are preset using mechanical processing modeWFor thicknessB2 times, the length of sample DegreeLNot less than specimen widthW4.2 times, and load when be bent spanSFor specimen widthW4 times；
    b）Arrange strain ga(u)ge：The central axes that length direction is drawn on the surface of notch are opened up in sample, and on central axes The horizontal distance for marking the vertical reinforcing action plane of distance is exactly equal to two positions of sample thickness；On marked locations edge Specimen length direction adhering resistance strain gauge, is connected strain ga(u)ge and resistance strain gauge with data line, electricity Microstrain reading is read on resistance deformeter to be denoted asε；
    c）It determines to measure equation undetermined coefficientK 1WithK 2：Two pieces is at least chosen to be used for determining coefficientK 1WithK 2, and this two pieces is required to try The prefabricated notch depth of samplea 1Witha 2It is unequal；Sample is placed on the three-point bending platform of testing machine, using testing machine loading roller Sample is loaded, records force value F and corresponding microstrain readingε, measurement result is substituted into formula（1-1）：
    lg[εB 2 E (1–a/W)/(3F)]=K 1+K 2 a/W （1-1）
    In formula,EElasticity modulus for sample material；FTo apply force value；WFor specimen width；BFor sample thickness；εFor microstrain Reading；aFor crack length；K 1WithK 2For undetermined coefficient；
    According to specimen size and elasticity modulus, you can be obtainedK 1、K 2；
    d）The measurement of crack length：By the sample to be tested processed by step b）Requirement arrange strain ga(u)ge, measurement is treated Then sample to be tested is placed on the three-point bending platform backing roll of fatigue tester by test specimens size, start fatigue tester Apply fatigue load and cause slowly growing crack；In crack propagation process, the force value for recording any time is answered with micro- accordingly Become reading, specimen size, elasticity modulus,K 1、K 2In the case of known, force value and corresponding microstrain reading are substituted into formula （1-1）Crack length can be obtaineda。
  2. 2. a kind of side that three-point bending standard sample crack length is determined based on strain measurement technique according to claim 1 Method, which is characterized in that this method is suitable for isotropic material.
  3. 3. a kind of side that three-point bending standard sample crack length is determined based on strain measurement technique according to claim 1 Method, which is characterized in that this method is suitable for metal.
CN201711485649.7A 2017-12-30 2017-12-30 A kind of method that three-point bending standard sample crack length is determined based on strain measurement technique Pending CN108204922A (en)

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KR102083255B1 (en) * 2019-09-02 2020-03-02 주식회사 정진이앤씨 Gauge for measuring crack
CN112067462A (en) * 2020-09-10 2020-12-11 中国建材检验认证集团股份有限公司 Method and device for prefabricating cracks on ultrathin brittle material
CN112161879A (en) * 2020-09-19 2021-01-01 太原理工大学 Device and method for measuring three-point bending fracture toughness of static semicircular disc in warm-pressing environment
CN114441337A (en) * 2022-01-14 2022-05-06 中国石油大学(北京) Detection method for opening displacement of metal fracture toughness crack tip
CN114544351A (en) * 2022-02-25 2022-05-27 广东电网有限责任公司 Method and device for detecting fracture toughness of epoxy material

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR102083255B1 (en) * 2019-09-02 2020-03-02 주식회사 정진이앤씨 Gauge for measuring crack
CN112067462A (en) * 2020-09-10 2020-12-11 中国建材检验认证集团股份有限公司 Method and device for prefabricating cracks on ultrathin brittle material
CN112161879A (en) * 2020-09-19 2021-01-01 太原理工大学 Device and method for measuring three-point bending fracture toughness of static semicircular disc in warm-pressing environment
CN114441337A (en) * 2022-01-14 2022-05-06 中国石油大学(北京) Detection method for opening displacement of metal fracture toughness crack tip
CN114441337B (en) * 2022-01-14 2022-10-18 中国石油大学(北京) Detection method for opening displacement of metal fracture toughness crack tip
CN114544351A (en) * 2022-02-25 2022-05-27 广东电网有限责任公司 Method and device for detecting fracture toughness of epoxy material

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Application publication date: 20180626