1、BS 7270:2006Metallic materials Constant amplitude strain controlled axial fatigue Method of testICS 77.040.10NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDPublishing and copyright informationThe BSI copyright notice displayed in this document indicates when th
2、e document was last issued. BSI 2006ISBN 0 580 49023 8The following BSI references relate to the work on this standard:Committee reference ISE/NFE/4/6Draft for comment 01/716136 DCPublication historyFirst edition November 1990This edition December 2006Amendments issued since publicationAmd. no. Date
3、 Text affectedBS 7270:2006 BSI 2006 iBS 7270:2006ContentsForeword ii1 Scope 12 Normative references 13 Terms and definitions 14 Symbols 25 Principle 46 Test equipment and environment 57 Specimen geometry 68 Alignment of test fixtures 99 Test procedure 1010 Test report 12AnnexesAnnex A (informative)
4、Generation of data sets 14Annex B (informative) Test fixtures 14Annex C (normative) Dynamic verification of extensometry 20Annex D (normative) Specimen preparation 20Annex E (normative) Verification of alignment of the load train 21Bibliography 23List of figuresFigure 1 One cycle, defined for sinuso
5、idal and triangular waveform strain histories 3Figure 2 Stressstrain hysteresis loop 4Figure 3 Test section profile for cylindrical specimens 7Figure 4 Alternative test section profile for cylindrical specimens 7Figure 5 Test section profile for plate specimens 8Figure 6 Plot of maximum force agains
6、t cycles for a cyclically softening material 12Figure B.1 Schematic diagram of grips for a button end specimen 16Figure B.2 Schematic diagram of grips for a conical end specimen 17Figure B.3 Schematic diagram of grips for a threaded end specimen 18Figure B.4 Schematic diagram of hydraulically actuat
7、ed grips for flat specimens 19Figure E.1 Strain-gauge locations for a cylindrical specimen 22List of tablesTable 1 Cylindrical specimen geometry 8Table 2 Alternative cylindrical specimen geometry 9Table 3 Plate specimen geometry 9Summary of pagesThis document comprises a front cover, an inside front
8、 cover, pages i and ii, pages 1 to 23 and a back cover.BS 7270:2006ii BSI 2006ForewordPublishing informationThis British Standard was published by BSI and came into effect on 29 December 2006. It was prepared by Subcommittee ISE/NFE/4/6, Fatigue testing of metals and metal matrix composites, under t
9、he authority of Technical Committee ISE/NFE/4, Mechanical testing of metals. A list of organizations represented on this committee can be obtained on request to its secretary.SupersessionThis British Standard supersedes BS 7270:1990, which is withdrawn.Information about this documentThis is a full r
10、evision of the standard, and introduces the following principal changes.a) New Annex on measurement of specimen bending (see Annex E).b) Reference to the use of electromechanical recording systems was deleted and is no longer recommended (see 6.4).c) Recommended ambient temperature range is specifie
11、d (see 6.5).d) New subclause on test commencement (see 9.3).Presentational conventionsThe provisions of this standard are presented in roman (i.e. upright) type. Its requirements are expressed in sentences in which the principal auxiliary verb is “shall”.Commentary, explanation and general informati
12、ve material is presented in smaller italic type, and does not constitute a normative element.Contractual and legal considerationsThis publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standa
13、rd cannot confer immunity from legal obligations. BSI 2006 1BS 7270:20061 ScopeThis British Standard describes a method of cyclically loading a metallic specimen under strain control between set strain limits to determine its fatigue resistance. The fatigue resistance is measured in terms of cycles
14、to failure as a function of the applied strain range and the associated variations in stress range, mean stress and plastic strain range. The method is restricted to uniaxially loaded parallel section specimens tested in air at ambient temperature and to metals where time-dependent deformation can b
15、e ignored. The method is applicable to both high- and low-cycle fatigue tests.NOTE 1 Advice on the generation of data sets from individual specimen results determined using this method is given in Annex A.NOTE 2 Users should assure themselves that the test conditions used and the specimen orientatio
16、n are relevant to their application.2 Normative referencesThe following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments)
17、applies.BS 1134-1, Assessment of surface texture Part 1: Methods and instrumentationBS EN ISO 7500-1:2004, Metallic materials Verification of static uniaxial testing machines Part 1: Tension/compression testing machines Verification and calibration of the force-measuring systemBS EN ISO 9513:2002, M
18、etallic materials Calibration of extensometers used in uniaxial testing 3 Terms and definitionsFor the purposes of this British Standard, the following terms and definitions apply.3.1 stressforce applied to the specimen divided by the original cross-sectional area of its gauge sectionNOTE Stress is
19、considered positive when tensile forces are applied and negative when compressive forces are applied.3.2 cycleshortest complete sequence of strain values that is repeated periodicallyNOTE See Figure 1.3.3 maximumgreatest algebraic value of a variable within one cycle3.4 maximum bending strainlargest
20、 value of the tensile bending strain in the cross-section at which bending is measured BS 7270:20062 BSI 20063.5 minimumsmallest algebraic value of a variable within one cycle3.6 meanone-half of the algebraic sum of the maximum and minimum values of a variable3.7 rangealgebraic difference between th
21、e maximum and minimum values of a variableNOTE See Figure 1 and Figure 2.3.8 amplitudehalf the range of a variable3.9 total strainextension of the specimen gauge length, divided by its original gauge lengthNOTE Total strain is considered positive when the gauge length increases in length and negativ
22、e when it contracts.3.10 total strain rangealgebraic difference between the maximum and minimum strain values within one cycleNOTE See Figure 1 and Figure 2.3.11 plastic strain rangewidth of the hysteresis loop of stress plotted against total strain, determined at the mean stress NOTE See Figure 2.3
23、.12 elastic strain rangedifference between the total strain range and the plastic strain range3.13 frequencynumber of cycles experienced by the specimen in 1 s3.14 half-lifeone-half of fatigue life3.15 fatigue lifenumber of cycles to failure, Nf, in 9.5 and Figure 6 4SymbolsFor the purposes of this
24、British Standard the following symbols apply.%ttotal strain range (see Figure 1 and Figure 2)%eelastic strain range (see 3.12)%pplastic strain range (see Figure 2)%B stress range (see Figure 2)Nfnumber of cycles to failure (see 9.5 and Figure 6)d diameter of gauge section of cylindrical specimen (se
25、e Figure 3 and Figure 4)B width of gauge section of plate specimen (see Figure 5) BSI 2006 3BS 7270:2006t thickness of plate specimen (see Figure 4 and Figure 5)l length of parallel section (see Figure 3, Figure 4 and Figure 5)lgstrain-gauge axial separation (see Figure E.1)R transition radius from
26、parallel section to grip end (see Figure 3, Figure 4 and Figure 5)D diameter of grip end of cylindrical specimen (see Figure 3)L length of grip end of plate specimen (see Figure 4 and Figure 5)W width of grip end of plate specimen (see Figure 4 and Figure 5)1to 4readings of individual strain gauges
27、(see E.2 and Figure E.1)bmaxmaximum bending strain (see E.2)Figure 1 One cycle, defined for sinusoidal and triangular waveform strain historiestSinusoidalwaveformTriangularwaveformOne cycleTotal strainTimeHtHBS 7270:20064 BSI 20065 PrincipleThe method involves the cyclic application of axial strain
28、to a specimen. The specimen has a gauge length of constant cross-section on which an axial extensometer is mounted and the strain is controlled between set limits according to a cycle of chosen waveform. The test is continued until failure occurs. The maxima and minima of strain and stress are monit
29、ored throughout the test. The number of cycles to failure is recorded and additionally the stressstrain hysteresis loops are recorded at intervals during the test. From these loops the stress range, mean stress, total strain range and plastic strain range are determined at half-life.Figure 2 Stresss
30、train hysteresis loopElastic strain range, %e= %tp %pStressTotal strainStress range MeanstressPlastic strain rangeTotal strain rangepHtHs BSI 2006 5BS 7270:20066 Test equipment and environment6.1 Test machine and test fixturesThe test machine shall provide smooth start-up with no backlash.NOTE An in
31、adequately stiff machine (including frame and loading train) might cause specimen buckling during the compressive phase of a test cycle.The test machine shall permit strain-controlled cycling to be carried out between predetermined limits. Its force measurement system shall have a digital output dis
32、play and shall be verified in accordance with BS EN ISO 7500-1:2004, Class 1.0. The verified force measurement system shall also be able to display cyclic force maxima and minima at any time to three significant figures.The test machine control system shall permit transfer from one mode of control t
33、o another without overshoots. In partially or completely reversed loading tests there shall be no backlash in the loading train. The specimen grips shall transmit axial forces to the specimen to accurately and reproducibly locate the specimen. NOTE 1 This to minimize bending.NOTE 2 In the design of
34、the test fixture, attention should be paid to maintaining axial alignment of the specimen in order to comply with Clause 8. Guidance notes on the design of fixtures are given in Annex B.6.2 Extensometry The extensometry system shall incorporate a digital output display able to show cyclic extension
35、maxima and minima at any time to, at least, three significant figures. An axial extensometer shall be used to measure and control the extension of the specimen gauge length. For gauge lengths below 20 mm, the extensometer shall have a certificate of compliance with BS EN ISO 9513:2002, Class 0.5, is
36、sued within the previous 12 months. For gauge lengths equal to or greater than 20 mm, the extensometer shall have a certificate of compliance with BS EN ISO 9513:2002, Class 1, as a minimum, issued within the previous 12 months. If the extensometer is to be used for measuring both positive and negat
37、ive displacements, the grade of the extensometer shall be assessed using the same calibration factor for both positive and negative displacements. In addition, the procedure given in Annex C shall be followed to verify that the characteristics of the extensometer and its associated signal conditioni
38、ng and recording equipment (see 6.4) are acceptable.Extensometry shall not be used above the frequency at which conformity with Annex C has been demonstrated.Cognizance shall be taken of the manufacturers recommended operating limits and procedures in both selecting and using the extensometer (see 9
39、.2).6.3 Cycle countingThe number of cycles shall be recorded such that for tests lasting less than 10 000 cycles, individual cycles can be resolved. For longer tests the resolution shall be better than 0.1% of the indicated life.BS 7270:20066 BSI 20066.4 Recording of hysteresis loopsStressstrain hys
40、teresis loops shall be recorded at intervals without changing the test frequency.Where discrete pairs of values of force and extension (or stress and strain) are recorded, the sampling frequency shall be sufficient to ensure correct definition of the hysteresis loops especially in the regions of str
41、ain reversal.NOTE Different data collection strategies give different numbers of data points per loop. Typically, 200 points per loop are required.6.5 Test environmentA recording or maximum-minimum thermometer shall be used for recording ambient temperature and throughout the test. If required, a hy
42、grometer shall be used for recording the relative humidity during the test. Tests shall be performed within the ambient temperature range 10 C to 35 C in a non-condensing atmosphere. In the case of a dispute the test shall be performed at an ambient temperature of 23 C 5 C.NOTE In the case of a disp
43、ute it is advisable to monitor the specimen temperature throughout the test. 7 Specimen geometry7.1 Unless otherwise specified in the product standard, the specimen shall be in accordance with Figure 3, Figure 4 or Figure 5 and Table 1, Table 2 or Table 3. The design shall ensure that:a) buckling do
44、es not occur at the highest compressive forces in the test programme; andb) premature failure (cracking) does not occur at the transition with the parallel length or within the transition radii.NOTE 1 The use of specimens in accordance with Figure 3 is recommended.NOTE 2 In selecting a specimen geom
45、etry, the test material microstructure should be taken into account.Specimens shall only be machined in accordance with Figure 4 and Table 2 if the original stock is less than 8 mm thick or if it is necessary to retain the original plate surface.NOTE 3 Fatigue test results determined on plate specim
46、ens are not always comparable to those determined on cylindrical specimens because of the difficulty in obtaining an adequate surface finish on plate specimens and because fatigue cracks initiate preferentially at specimen corners.The parallel length, l, of all specimens shall be greater than the ga
47、uge length of the extensometer (=e). NOTE 4 It is recommended that 0.7= k= ek0.9= BSI 2006 7BS 7270:20067.2 Unless otherwise specified in the product standard, the parallel length and the transition radii of the specimen shall be machined and finished in accordance with Annex D. Specimens that can c
48、orrode under ambient conditions shall be protected until they are tested.NOTE Take care not to damage the surface of the specimen when checking its dimensions.Figure 3 Test section profile for cylindrical specimensNOTE See Table 1.d 0.01Dimensions in millimetresFigure 4 Alternative test section prof
49、ile for cylindrical specimensNOTE 1 It is essential that the specimen be symmetrical about the gauge length centre line. NOTE 2 See Table 2.d 0.01W 0.02t 0.02Dimensions in millimetres0.020.020.02drlDSmooth blend with no undercutAAA0.040.040.02drl0.02LtWSmooth blend withno undercutAAABBBS 7270:20068 BSI 2006Figure 5 Test section profile for plate specimensNOTE 1 It is essential that the specimen be symmetrical about the gaug
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