1、Designation: E647 13a1E647 15Standard Test Method forMeasurement of Fatigue Crack Growth Rates1This standard is issued under the fixed designation E647; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1 NOTEX4.3.6 and Eq X4.3 were editorially corrected in July 2014.1. Scope1.1 This test method2 covers the determination of fatigue crack growth rate
3、s from near-threshold to Kmax controlled instability.Results are expressed in terms of the crack-tip stress-intensity factor range (K), defined by the theory of linear elasticity.1.2 Several different test procedures are provided, the optimum test procedure being primarily dependent on the magnitude
4、 ofthe fatigue crack growth rate to be measured.1.3 Materials that can be tested by this test method are not limited by thickness or by strength so long as specimens are ofsufficient thickness to preclude buckling and of sufficient planar size to remain predominantly elastic during testing.1.4 A ran
5、ge of specimen sizes with proportional planar dimensions is provided, but size is variable to be adjusted for yieldstrength and applied force. Specimen thickness may be varied independent of planar size.1.5 The details of the various specimens and test configurations are shown in Annex A1 Annex A3.
6、Specimen configurationsother than those contained in this method may be used provided that well-established stress-intensity factor calibrations areavailable and that specimens are of sufficient planar size to remain predominantly elastic during testing.1.6 Residual stress/crack closure may signific
7、antly influence the fatigue crack growth rate data, particularly at lowstress-intensity factors and low stress ratios, although such variables are not incorporated into the computation of K.1.7 Values stated in SI units are to be regarded as the standard. Values given in parentheses are for informat
8、ion only.1.8 This test method is divided into two main parts. The first part gives general information concerning the recommendationsand requirements for fatigue crack growth rate testing. The second part is composed of annexes that describe the specialrequirements for various specimen configuration
9、s, special requirements for testing in aqueous environments, and procedures fornon-visual crack size determination. In addition, there are appendices that cover techniques for calculating da/dN, determiningfatigue crack opening force, and guidelines for measuring the growth of small fatigue cracks.
10、General information andrequirements common to all specimen types are listed as follows:SectionReferenced Documents 2Terminology 3Summary of Use 4Significance and Use 5Apparatus 6Specimen Configuration, Size, and Preparation 7Procedure 8Calculations and Interpretation of Results 9Report 10Precision a
11、nd Bias 11Special Requirements for Testing in Aqueous Environments Annex A4Guidelines for Use of Compliance to Determine Crack Size Annex A5Guidelines for Electric Potential Difference Determination ofCrack SizeAnnex A6Recommended Data Reduction Techniques Appendix X1Recommended Practice for Determi
12、nation of Fatigue CrackOpening Force From ComplianceAppendix X21 This test method is under the jurisdiction of ASTM Committee E08 on Fatigue and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack GrowthBehavior.Current edition approved Oct. 15, 2013May 1, 2015. Published Febru
13、ary 2014July 2015. Originally approved in 1978. Last previous approved in 2013 asE647 13.E647 13a1. DOI: 10.1520/E0647-13A.10.1520/E0647-15.2 For additional information on this test method see RR: E24 1001. Available from ASTM Headquarters, 100 Barr Harbor Drive, West Conshohocken, PA 19428.This doc
14、ument is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as
15、 appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1Guidelines for Measuring the Growth Rates Of Small Fatig
16、ueCracksAppendix X3Recommended Practice for Determination Of ACR-BasedStress-Intensity Factor RangeAppendix X41.9 Special requirements for the various specimen configurations appear in the following order:The Compact Specimen Annex A1The Middle Tension Specimen Annex A2The Eccentrically-Loaded Singl
17、e Edge Crack TensionSpecimenAnnex A31.10 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimit
18、ations prior to use.2. Referenced Documents2.1 ASTM Standards:3E4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE8/E8M Test Methods for Tension Testing of Metallic MaterialsE338 Test Method of Sharp-Notch Tension Testing of High-Strength
19、Sheet Materials (Withdrawn 2010)4E399 Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic MaterialsE467 Practice for Verification of Constant Amplitude Dynamic Forces in an Axial Fatigue Testing SystemE561 Test Method forK-R Curve DeterminationE1012 Practice for Verificati
20、on of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial ForceApplicationE1820 Test Method for Measurement of Fracture ToughnessE1823 Terminology Relating to Fatigue and Fracture Testing3. Terminology3.1 The terms used in this test method are given in Terminology E6, and Termin
21、ology E1823. Wherever these terms are not inagreement with one another, use the definitions given in Terminology E1823 which are applicable to this test method.3.2 Definitions:3.2.1 crack size, aL,na linear measure of a principal planar dimension of a crack. This measure is commonly used in thecalcu
22、lation of quantities descriptive of the stress and displacement fields and is often also termed crack length or depth.3.2.1.1 DiscussionIn fatigue testing, crack length is the physical crack size. See physical crack size in Terminology E1823.3.2.2 cyclein fatigue, under constant amplitude loading, t
23、he force variation from the minimum to the maximum and then tothe minimum force.3.2.2.1 DiscussionIn spectrum loading, the definition of cycle varies with the counting method used.3.2.2.2 DiscussionIn this test method, the symbol N is used to represent the number of cycles.3.2.3 fatigue-crack-growth
24、 rate, da/dN, L/cyclethe rate of crack extension under fatigue loading, expressed in terms of crackextension per cycle .3.2.4 fatigue cycleSee cycle.3.2.5 force cycleSee cycle.3.2.6 force range, P Fin fatigue, the algebraic difference between the maximum and minimum forces in a cycle expressedas:3 F
25、or referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.4 The last approved version of this historical standard is refer
26、enced on www.astm.org.E647 152P 5Pmax2Pmin (1)3.2.7 force ratio (also called stress ratio), Rin fatigue, the algebraic ratio of the minimum to maximum force (stress) in acycle, that is, R = Pmin/Pmax.3.2.8 maximum force, Pmax Fin fatigue, the highest algebraic value of applied force in a cycle. Tens
27、ile forces are consideredpositive and compressive forces negative.3.2.9 maximum stress-intensity factor, Kmax FL3/2in fatigue, the maximum value of the stress-intensity factor in a cycle.This value corresponds to Pmax.3.2.10 minimum force, Pmin Fin fatigue, the lowest algebraic value of applied forc
28、e in a cycle. Tensile forces are consideredpositive and compressive forces negative.3.2.11 minimum stress-intensity factor, Kmin FL3/2in fatigue, the minimum value of the stress-intensity factor in a cycle.This value corresponds to Pmin when R 0 and is taken to be zero when R 0.3.2.12 stress cycleSe
29、e cycle in Terminology E1823.3.2.13 stress-intensity factor, K, K1, K2, K3 FL3/2 See Terminology E1823.3.2.13.1 DiscussionIn this test method, mode 1 is assumed and the subscript 1 is everywhere implied.3.2.14 stress-intensity factor range, K FL3/2in fatigue, the variation in the stress-intensity fa
30、ctor in a cycle, that isK 5Kmax2Kmin (2)3.2.14.1 DiscussionThe loading variables R, K, and Kmax are related in accordance with the following relationships:K 512R!Kmax for R$0,and (3)K 5Kmax for R#0.3.2.14.2 DiscussionThese operational stress-intensity factor definitions do not include local crack-ti
31、p effects; for example, crack closure, residualstress, and blunting.3.2.14.3 DiscussionWhile the operational definition of K states that K does not change for a constant value of Kmax when R 0, increases in fatiguecrack growth rates can be observed when R becomes more negative. Excluding the compres
32、sive forces in the calculation of Kdoes not influence the materials response since this response (da/dN) is independent of the operational definition of K. Forpredicting crack-growth lives generated under various R conditions, the life prediction methodology must be consistent with thedata reporting
33、 methodology.3.2.14.4 DiscussionAn alternative definition for the stress-intensity factor range, which utilizes the full range of R, is Kfr = Kmax Kmin. (In this case,Kmin is the minimum value of stress-intensity factor in a cycle, regardless of R.) If using this definition, in addition to therequir
34、ements of 10.1.13, the value of R for the test should also be tabulated. If comparing data developed under R 0 conditionswith data developed under R 0 conditions, it may be beneficial to plot the da/dN data versus Kmax.3.3 Definitions of Terms Specific to This Standard:3.3.1 applied-K curvea curve (
35、a fixed-force or fixed-displacement crack-extension-force curve) obtained from a fracturemechanics analysis for a specific specimen configuration. The curve relates the stress-intensity factor to crack size and eitherapplied force or displacement.3.3.1.1 DiscussionE647 153The resulting analytical ex
36、pression is sometimes called a K calibration and is frequently available in handbooks for stress-intensityfactors.3.3.2 fatigue crack growth threshold, Kth FL3/2that asymptotic value of K at which da/dN approaches zero. For mostmaterials an operational, though arbitrary, definition of Kth is given a
37、s that K which corresponds to a fatigue crack growth rateof 1010 m/cycle. The procedure for determining this operationalKth is given in 9.4.3.3.2.1 DiscussionThe intent of this definition is not to define a true threshold, but rather to provide a practical means of characterizing a materialsfatigue
38、crack growth resistance in the near-threshold regime. Caution is required in extending this concept to design (see 5.1.5).3.3.3 fatigue crack growth rate, da/dN or a/N, Lin fatigue, the rate of crack extension caused by fatigue loading andexpressed in terms of average crack extension per cycle.3.3.4
39、 normalized K-gradient, C = (1/K). dK/daL1the fractional rate of change of K with increasing crack size.3.3.4.1 DiscussionWhen C is held constant the percentage change in K is constant for equal increments of crack size. The following identity is truefor the normalized K-gradient in a constant force
40、 ratio test:1KdKda 51KmaxdKmaxda 51KmindKminda 51KdKda (4)3.3.5 K-decreasing testa test in which the value of C is nominally negative. In this test method K-decreasing tests areconducted by shedding force, either continuously or by a series of decremental steps, as the crack grows.3.3.6 K-increasing
41、 testa test in which the value of C is nominally positive. For the standard specimens in this method theconstant-force-amplitude test will result in a K-increasing test where the C value increases but is always positive.4. Summary of Test Method4.1 This test method involves cyclic loading of notched
42、 specimens which have been acceptably precracked in fatigue. Cracksize is measured, either visually or by an equivalent method, as a function of elapsed fatigue cycles and these data are subjectedto numerical analysis to establish the rate of crack growth. Crack growth rates are expressed as a funct
43、ion of the stress-intensityfactor range, K, which is calculated from expressions based on linear elastic stress analysis.5. Significance and Use5.1 Fatigue crack growth rate expressed as a function of crack-tip stress-intensity factor range, d a/dN versus K, characterizesa materials resistance to st
44、able crack extension under cyclic loading. Background information on the ration-ale for employinglinear elastic fracture mechanics to analyze fatigue crack growth rate data is given in Refs (1)5 and (2).5.1.1 In innocuous (inert) environments fatigue crack growth rates are primarily a function of K
45、and force ratio, R, or Kmaxand R (Note 1). Temperature and aggressive environments can significantly affect da/ dN versus K, and in many cases accentuateR-effects and introduce effects of other loading variables such as cycle frequency and waveform. Attention needs to be given tothe proper selection
46、 and control of these variables in research studies and in the generation of design data.NOTE 1K,Kmax, and R are not independent of each other. Specification of any two of these variables is sufficient to define the loading condition.It is customary to specify one of the stress-intensity parameters
47、(K or Kmax) along with the force ratio, R.5.1.2 Expressing da/dN as a function of K provides results that are independent of planar geometry, thus enabling exchangeand comparison of data obtained from a variety of specimen configurations and loading conditions. Moreover, this feature enablesd a/dN v
48、ersus K data to be utilized in the design and evaluation of engineering structures. The concept of similitude is assumed,which implies that cracks of differing lengths subjected to the same nominal K will advance by equal increments of crackextension per cycle.5.1.3 Fatigue crack growth rate data ar
49、e not always geometry-independent in the strict sense since thickness effects sometimesoccur. However, data on the influence of thickness on fatigue crack growth rate are mixed. Fatigue crack growth rates over a widerange of K have been reported to either increase, decrease, or remain unaffected as specimen thickness is increased. Thicknesseffects can also interact with other variables such as environment and heat treatment. For example, materials may exhib
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