1、Designation:E64711 Designation: E647 13 Standard Test Method for Measurement of Fatigue Crack Growth Rates 1 This standard is issued under the xed designation E647; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last
2、revision.Anumber in parentheses indicates the year of last reapproval.A superscript epsilon ( ) indicates an editorial change since the last revision or reapproval. Appendix X4 was corrected, and the year date was changed on January 15, 2013. 1. Scope 1.1 This test method 2 covers the determination
3、of fatigue crack growth rates from near-threshold to K max controlled instability. Results are expressed in terms of the crack-tip stress-intensity factor range ( K), dened by the theory of linear elasticity. 1.2 Several different test procedures are provided, the optimum test procedure being primar
4、ily dependent on the magnitude of the 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 of sufficient thickness to preclude buckling and of sufficient planar size to remain predominantly
5、 elastic during testing. 1.4 A range of specimen sizes with proportional planar dimensions is provided, but size is variable to be adjusted for yield strength and applied force. Specimen thickness may be varied independent of planar size. 1.5 The details of the various specimens and test conguration
6、s are shown in Annex A1-Annex A3. Specimen congurations other than those contained in this method may be used provided that well-established stress-intensity factor calibrations are available and that specimens are of sufficient planar size to remain predominantly elastic during testing. 1.6 Residua
7、l stress/crack closure may signicantly inuence the fatigue crack growth rate data, particularly at low stress-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 give
8、n in parentheses are for information only. 1.8 This test method is divided into two main parts. The rst part gives general information concerning the recommendations and requirements for fatigue crack growth rate testing. The second part is composed of annexes that describe the special requirements
9、for various specimen congurations, special requirements for testing in aqueous environments, and procedures for non-visual crack size determination. In addition, there are appendices that cover techniques for calculating da/dN, determining fatigue crack opening force, and guidelines for measuring th
10、e growth of small fatigue cracks. General information and requirements common to all specimen types are listed as follows: Section Referenced Documents 2 Terminology 3 Summary of Use 4 Signicance and Use 5 Apparatus 6 Specimen Conguration, Size, and Preparation 7 Procedure 8 Calculations and Interpr
11、etation of Results 9 Report 10 Precision and Bias 11 Special Requirements for Testing in Aqueous Environments Annex A4 Guidelines for Use of Compliance to Determine Crack Size Annex A5 Guidelines for Electric Potential Difference Determination of Crack Size Annex A6 Recommended Data Reduction Techni
12、ques Appendix X1 Recommended Practice for Determination of Fatigue Crack Opening Force From Compliance Appendix X2 Guidelines for Measuring the Growth Rates Of Small Fatigue Cracks Appendix X3 Recommended Practice for Determination Of ACR-Based Stress-Intensity Factor Range Appendix X4 1.9 Special r
13、equirements for the various specimen congurations appear in the following order: 1 This test method is under the jurisdiction ofASTM Committee E08 on Fatigue and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack Growth Behavior. Current edition approved May 1, 2011. Published
14、 July 2011. Originally approved in 1978. Last previous approved in 2008 as E64708 1. DOI: 10.1520/E0647-08E01. Current edition approved Jan. 15, 2013. Published January 2013. Originally approved in 1978. Last previous approved in 2012 as E64712. DOI: 10.1520/E0647-13. 2 For additional information on
15、 this test method see RR: E241001. Available from ASTM Headquarters, 100 Barr Harbor Drive, West Conshohocken, PA 19428. 1 This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because it
16、 may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version of the standard as published by ASTM is to be considered the official document. Copyright ASTM International, 100 Barr
17、 Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.The Compact Specimen Annex A1 The Middle Tension Specimen Annex A2 The Eccentrically-Loaded Single Edge Crack Tension Speci- men Annex A3 1.10 This standard does not purport to address all of the safety concerns, if any, ass
18、ociated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. Referenced Documents 2.1 ASTM Standards: 3 E4 Practices for Force Verication of Testing Machines
19、 E6 Terminology Relating to Methods of Mechanical Testing E8/E8M Test Methods for Tension Testing of Metallic Materials E337 Test Method for Measuring Humidity with a Psychrometer (the Measurement of Wet- and Dry-Bulb Temperatures) E338 Test Method of Sharp-Notch Tension Testing of High-Strength She
20、et Materials E399 Test Method for Linear-Elastic Plane-Strain Fracture Toughness K Ic of Metallic Materials E467 Practice for Verication of Constant Amplitude Dynamic Forces in an Axial Fatigue Testing System E561 Test Method for K-R Curve Determination E1012 Practice for Verication of Testing Frame
21、 and Specimen Alignment Under Tensile and Compressive Axial Force Application E1820 Test Method for Measurement of Fracture Toughness E1823 Terminology Relating to Fatigue and Fracture Testing 3. Terminology 3.1 The terms used in this test method are given in Terminology E6, and Terminology E1823. W
22、herever these terms are not in agreement with one another, use the denitions given in Terminology E1823 which are applicable to this test method. 3.2 Denitions: 3.2.1 crack size, aL, na linear measure of a principal planar dimension of a crack. This measure is commonly used in the calculation of qua
23、ntities descriptive of the stress and displacement elds 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, the force vari
24、ation from the minimum to the maximum and then to the minimum force. 3.2.2.1 DiscussionIn spectrum loading, the denition 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-growthrate,da/dN,
25、L/cycletherateofcrackextensionunderfatigueloading,expressedintermsofcrack extension per cycle of loading. fatigue. 3.2.4 fatigue cycleSee cycle . 3.2.5 force cycleSee cycle. 3.2.6 forcerange, PFinfatigue,thealgebraicdifferencebetweenthemaximumandminimumforcesinacycleexpressed as: DP 5P max 2P min (1
26、) E0647-13_1 3.2.7 force ratio (also called stress ratio), Rin fatigue, the algebraic ratio of the minimum to maximum force (stress) in a cycle, that is, R=P min /P max . 3.2.8 maximumforce,P max Finfatigue,thehighestalgebraicvalueofappliedforceinacycle.Tensileforcesareconsidered positive and compre
27、ssive forces negative. 3.2.9 maximum stress-intensity factor, K max FL 3/2 in fatigue, the maximum value of the stress-intensity factor in a cycle. This value corresponds to P max . 3.2.10 minimumforce,P min Finfatigue,thelowestalgebraicvalueofappliedforceinacycle.Tensileforcesareconsidered positive
28、 and compressive forces negative. 3.2.11 minimum stress-intensity factor, K min FL 3/2 in fatigue, the minimum value of the stress-intensity factor in a cycle. This value corresponds to P min whenR0andistaken to be zero when R 0. 3.2.12 stress cycleSee cycle in Terminology E1823. 3.2.13 stress-inten
29、sity factor, K, K 1 , K 2 , K 3 FL 3/2 See Terminology E1823. 3.2.13.1 DiscussionIn this test method, mode 1 is assumed and the subscript 1 is everywhere implied. 3 ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatserviceastm.org.ForAnnualBookofASTMStandards
30、volume information, refer to the standards Document Summary page on the ASTM website. E647 13 23.2.14 stress-intensity factor range, K FL 3/2 in fatigue, the variation in the stress-intensity factor in a cycle, that is E0647-13_2 3.2.14.1 DiscussionThe loading variables R, K, and K max are related i
31、n accordance with the following relationships: E0647-13_3 E0647-13_3 3.2.14.2 DiscussionThese operational stress-intensity factor denitions do not include local crack-tip effects; for example, crack closure, residual stress, and blunting. 3.2.14.3 DiscussionWhile the operational denition of K states
32、 that K does not change for a constant value of K max when R 0, increases in fatigue crack growth rates can be observed when R becomes more negative. Excluding the compressive forces in the calculation of K does not inuence the materials response since this response (da/d N) is independent of the op
33、erational denition of K. For predicting crack-growth lives generated under various R conditions, the life prediction methodology must be consistent with the data reporting methodology. 3.2.14.4 DiscussionAn alternative denition for the stress-intensity factor range, which utilizes the full range of
34、R, is K fr = K max K min . (In this case, K min is the minimum value of stress-intensity factor in a cycle, regardless of R.) If using this denition, in addition to the requirements of 10.1.13, the value of R for the test should also be tabulated. If comparing data developed under R 0 conditions wit
35、h data developed under R 0 conditions, it may be benecial to plot the da/dN data versus K max . 3.3 Denitions of Terms Specic to This Standard: 3.3.1 applied-K curvea curve (a xed-force or xed-displacement crack-extension-force curve) obtained from a fracture mechanics analysis for a specic specimen
36、 conguration. The curve relates the stress-intensity factor to crack size and either applied force or displacement. 3.3.1.1 DiscussionThe resulting analytical expression is sometimes called a K calibration and is frequently available in handbooks for stress-intensity factors. 3.3.2 fatigue crack gro
37、wth threshold, K th FL 3/2 that asymptotic value of K at which da/dN approaches zero. For most materials an operational, though arbitrary, denition of K th is given as that K which corresponds to a fatigue crack growth rate of 10 10 m/cycle. The procedure for determining this operational K th is giv
38、en in 9.4. 3.3.2.1 DiscussionThe intent of this denition is not to dene a true threshold, but rather to provide a practical means of characterizing a materials fatigue crack growth resistance in the near-threshold regime. Caution is required in extending this concept to design (see 5.1.5). 3.3.3 fat
39、igue crack growth rate, da/dN or a/ N, Lin fatigue, the rate of crack extension caused by fatigue loading and expressed in terms of average crack extension per cycle. 3.3.4 normalized K-gradient, C = (1/K). dK/da L 1 the fractional rate of change of K with increasing crack size. 3.3.4.1 DiscussionWh
40、en C is held constant the percentage change in K is constant for equal increments of crack size. The following identity is true for the normalized K-gradient in a constant force ratio test: E0647-13_4 3.3.5 K-decreasing testa test in which the value of C is nominally negative. In this test method K-
41、decreasing tests are conducted by shedding force, either continuously or by a series of decremental steps, as the crack grows. 3.3.6 K-increasing testa test in which the value of C is nominally positive. For the standard specimens in this method the constant-force-amplitude test will result in a K-i
42、ncreasing test where the C value increases but is always positive. 4. Summary of Test Method 4.1 This test method involves cyclic loading of notched specimens which have been acceptably precracked in fatigue. Crack size is measured, either visually or by an equivalent method, as a function of elapse
43、d fatigue cycles and these data are subjected to numerical analysis to establish the rate of crack growth. Crack growth rates are expressed as a function of the stress-intensity factor range, K, which is calculated from expressions based on linear elastic stress analysis. 5. Signicance and Use 5.1 F
44、atigue crack growth rate expressed as a function of crack-tip stress-intensity factor range, d a/dN versus K, characterizes a materials resistance to stable crack extension under cyclic loading. Background information on the ration-ale for employing linear elastic fracture mechanics to analyze fatig
45、ue crack growth rate data is given in Refs (1) 4 and (2). 5.1.1 In innocuous (inert) environments fatigue crack growth rates are primarily a function of K and force ratio, R,orK max andR(Note1).Temperatureandaggressiveenvironmentscansignicantlyaffectda/dNversus K,andinmanycasesaccentuate R-effects a
46、nd introduce effects of other loading variables such as cycle frequency and waveform. Attention needs to be given to the proper selection and control of these variables in research studies and in the generation of design data. NOTE 1 K, K max , and R are not independent of each other. Specication of
47、 any two of these variables is sufficient to dene the loading condition. 4 The boldface numbers in parentheses refer to the list of references at the end of this standard. E647 13 3It is customary to specify one of the stress-intensity parameters ( K or K max ) along with the force ratio, R. 5.1.2 E
48、xpressing da/dN as a function of K provides results that are independent of planar geometry, thus enabling exchange andcomparisonofdataobtainedfromavarietyofspecimencongurationsandloadingconditions.Moreover,thisfeatureenables d a/dN versus K data to be utilized in the design and evaluation of engine
49、ering 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 crack extension per cycle. 5.1.3 Fatigue crack growth rate data are not always geometry-independent in the strict sense since thickness effects sometimes occur. However, data on the inuence of thickness on fatigue crack growth rate are mixed. Fatigue c
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