1、BSI Standards PublicationBS 8571:2014Method of test fordetermination of fracturetoughness in metallicmaterials using single edgenotched tension (SENT)specimensPublishing and copyright informationThe BSI copyright notice displayed in this document indicates when the documentwas last issued. The Briti
2、sh Standards Institution 2014Published by BSI Standards Limited 2014ISBN 978 0 580 74928 5ICS 25.160.40The following BSI references relate to the work on this document:Committee reference ISE/101Draft for comment 14/30291891 DCPublication historyFirst published December 2014Amendments issued since p
3、ublicationDate Text affectedBS 8571:2014 BRITISH STANDARDContentsForeword ii1 Scope 12 Normative references 13 Terms, definitions and symbols 14 Principle 25 Test sample and test specimen preparation 36 Test procedure 97 Determination of resistance curves a and Ja118 Determination of single point fr
4、acture toughness 189 Test data qualification 19AnnexesAnnex A (informative) Example calculation of J for SENTs 20Bibliography 21List of figuresFigure 1 Flowchart showing how to use the standard 4Figure 2 SENT test specimen configuration 5Figure 3 W/B ratios in SENT test specimens 6Figure 4 Machining
5、 tolerances and surface finish for a SENT specimen 7Figure 5 Crack plane orientation code for fracture toughness specimens ofparent metal and weld metal 8Figure 6 Example knife edges and notch geometries 10Figure 7 Determination of Up, Vpand Ve13Figure 8 Determination of CTOD () from the double clip
6、 gaugearrangement 17Figure 9 Fitting the R-curve to the SENT crack extension data 18List of tablesTable1Values of constants ni,mi,qiand ri14Summary of pagesThis document comprises a front cover, an inside front cover, pages i to ii,pages 1 to 22, an inside back cover and a back cover.BRITISH STANDAR
7、D BS 8571:2014 The British Standards Institution 2014 iForewordPublishing informationThis British Standard is published by BSI Standards Limited, under licence fromThe British Standards Institution, and came into effect on 1 December 2014. Itwas prepared by Subcommittee ISE/101/4, Toughness testing,
8、 under the authorityof Technical Committee ISE/101, Test methods for metals. A list of organizationsrepresented on these committees can be obtained on request to their secretary.Information about this documentThis standard has been developed primarily to meet the needs of the steelpipeline industry
9、where this method has been used to determine the fracturetoughness of girth welds experiencing plastic straining during installation.Hazard warningsWARNING. This British Standard calls for the use of substances and/orprocedures that can be injurious to health if adequate precautions are nottaken. It
10、 refers only to technical suitability and does not absolve the userfrom legal obligations relating to health and safety at any stage.Use of this documentIt has been assumed in the preparation of this British Standard that theexecution of its provisions will be entrusted to appropriately qualified an
11、dexperienced people, for whose use it has been produced.Presentational conventionsThe provisions of this standard are presented in roman (i.e. upright) type. Itsmethods are expressed as a set of instructions, a description, or in sentences inwhich the principal auxiliary verb is “shall”.Commentary,
12、explanation and general informative material is presented insmaller italic type, and does not constitute a normative element.Contractual and legal considerationsThis publication does not purport to include all the necessary provisions of acontract. Users are responsible for its correct application.C
13、ompliance with a British Standard cannot confer immunity from legalobligations.BRITISH STANDARDBS 8571:2014ii The British Standards Institution 20141 ScopeThis British Standard gives methods for determining fracture toughness inmetallic materials in terms of (crack tip opening displacement, CTOD) an
14、d J(experimental equivalent of the J-integral) using single edge notched tension(SENT) specimens.This British Standard gives a method for determining fracture toughness as aresistance to ductile crack extension (R-curve). A method for single pointdetermination of fracture toughness is also given. Th
15、e method uses specimenswhich have been notched and fatigue pre-cracked into parent metal, weld metalor heat affected zone (HAZ). The specimens are loaded in tension, and the forceand crack mouth opening displacement are recorded.NOTE Methods to evaluate the suitability of a weld for notch placement
16、within thetarget area and, where appropriate, to evaluate the effectiveness of the fatiguecrack in sampling these areas are given in BS EN ISO 15653.2 Normative referencesThe following documents, in whole or in part, are normatively referenced in thisdocument and are indispensable for its applicatio
17、n. For dated references, onlythe edition cited applies. For undated references, the latest edition of thereferenced document (including any amendments) applies.BS EN ISO 15653:2010, Metallic materials Method of test for the determinationof quasistatic fracture toughness of weldsISO 12135:2002, Metal
18、lic materials Unified method of test for thedetermination of quasistatic fracture toughness3 Terms, definitions and symbolsFor the purposes of this British Standard, the following terms, definitions andsymbols apply.3.1 Terms and definitions3.1.1 bluntingapparent crack extension not associated with
19、the creation of new fracturesurface prior to the onset of unstable crack extension, pop-in or slow stablecrack extension and occurring within the same plane as the fatigue pre-crack3.1.2 target areaintended fatigue pre-crack tip position within the parent metal, weld metal orheat affected zone (HAZ)
20、3.1.3 pop-inabrupt discontinuity in the force versus displacement record, indicated by asudden increase in displacement and, generally, a sudden decrease in force,subsequent to which displacement and force increase to above their previousvalues3.1.4 sampleun-notched blank cut from the source materia
21、l3.1.5 specimenmachined and notched sample ready for testingBRITISH STANDARD BS 8571:2014 The British Standards Institution 2014 13.2 SymbolsFor the purposes of this British Standard, the symbols given inBS EN ISO 15653 and ISO 12135 apply, together with the following:a crack length, in millimetres
22、(mm);a0initial crack length, in millimetres (mm);B specimen thickness, perpendicular to the width, inmillimetres (mm);BNspecimen thickness after side-grooving, inmillimetres (mm);E modulus of elasticity, in megapascals (MPa);H distance between clamped grips, in millimetres (mm);JJ-integral fracture
23、toughness, in kilojoules per metre squared ornewtons per millimetre (kJ/m2or N/mm);Lcgauge length in a pin-loaded SENT specimen, in millimetres (mm);P nominal force in a SENT specimen, in newtons (N);Rp0.2b0.2% offset yield strength of the parent metal at thetemperature of the fracture toughness tes
24、t, inmegapascals (MPa);Rp0.2w0.2% offset yield strength of the weld metal at the temperatureof the fracture toughness test, in megapascals (MPa);V0crack mouth opening displacement (CMOD), in millimetres (mm);V1, V2clip gauge displacements, in millimetres (mm);Ve1, Ve2elastic components of clip gauge
25、 displacement, inmillimetres (mm);Vp1, Vp2plastic components of clip gauge displacement, inmillimetres (mm);W specimen width, measured in the direction of the notch, inmillimetres (mm); crack tip opening displacement (CTOD), in millimetres (mm); Poissons ratio; nominal stress in a pin-loaded SENT sp
26、ecimen, innewtons per millimetre (N/mm2);a sum of stable crack extension and crack tip blunting, inmillimetres (mm).4 PrincipleA test sample is cut from the source material. The sample is machined andnotched to provide a test specimen with the tip of the notch located in eitherthe parent metal, the
27、weld metal or the HAZ.A fatigue crack is extended from the notch tip into the target area by applyinga controlled alternating force to the specimen in bending. The specimen is thentested in tension by clamping or by pin-loading the specimen in the grips of atensile test machine.BRITISH STANDARDBS 85
28、71:20142 The British Standards Institution 2014The force and clip gauge displacement are continuously recorded during thetest. To construct a resistance curve a number of identical specimens are testedto different displacements and then unloaded. These data, together withmeasurements of specimen and
29、 crack dimensions, are used to determine fracturetoughness and crack extension for the resistance curve. Alternatively, it ispossible to test a single specimen to obtain a value of fracture toughness.If specified by the customer, post-test metallography is performed to confirmthat the crack tip was
30、located in the target weld feature and/or microstructureand to determine the microstructure through which crack extension has takenplace.NOTE A flowchart illustrating how to use this British Standard is given in Figure 1.5 Test sample and test specimen preparation5.1 Test sampleA blank sample shall
31、be cut from the test source material.NOTE The choice of specimen design should take into consideration the likelyoutcome of the test, any preference for J or CTOD fracture toughness values, thecrack plane orientation of interest and the quantity and condition of the materialavailable.5.2 Test specim
32、enA test specimen shall be prepared from the sample. The SENT test specimenconfiguration shall be as shown in Figure 2a) or Figure 2b). The cross-sectiondimensions shall be expressed as the specimen thickness (B) width (W). TheW/B ratio of the test specimen shall be between 0.5 and 2, as illustrated
33、 inFigure 3.BRITISH STANDARD BS 8571:2014 The British Standards Institution 2014 3Figure 1 Flowchart showing how to use the standardBRITISH STANDARDBS 8571:20144 The British Standards Institution 2014Figure 2 SENT test specimen configurationa) Clamped single edge notched tension specimen b) Directly
34、 pin-loaded single edge notchedtension specimenKey1 Region of the specimen within the clampsH Length between the gripsBRITISH STANDARD BS 8571:2014 The British Standards Institution 2014 5Figure 3 W/B ratios in SENT test specimensa) W/B=2 b) W/B=1 c) W/B=0.5KeyMachined notchFatigue pre-crackLigament
35、NOTE Specimen type a) is suitable for through-thickness (NP) notching; b) can be used for surface (NQ) orthrough-thickness (NP) notching; c) is intended for surface notching (NQ). Crack plane orientations for fracturetoughness specimens are given in Figure 5.NOTE 1 For pin-loaded specimens J and CTO
36、D equations are only provided forspecimens with W/B ratios between 0.5 and 1.The smaller dimension of the test specimen after machining shall be as close aspossible to the full thickness of the source material. When preparing specimensfrom pipe sections, the machining along the specimen length shall
37、 be theminimum necessary to remove pipe curvature so that a square or rectangularcross-section is obtained.NOTE 2 The test specimen thickness should be at least 85% of the thickness of thesource material for pipeline applications.NOTE 3 The pin-loaded ends of the specimens should be sufficiently lar
38、ge to avoidthe specimen yielding at the sides of the pin-holes. It might not be necessary for thegripped portions to be the same width or for them to be fully machined in the sameway as the portion between the grips. The surface finish of the gripped region canbe rougher than the central portion of
39、the specimen, to aid gripping.Testing of sub-size specimens where the specimen thickness is less than 85% ofthe material wall thickness shall be permitted. However, in such cases theoriginal thickness and final specimen dimensions and position through thicknessshall be given in the test report.If sa
40、mples cut from welds are not straight along their length because ofdistortions arising from the welding process (due to misalignment and/orangular distortion at the weld), distortions shall be removed by machining toobtain a straight specimen, noting restrictions regarding specimen thickness.The por
41、tions of the reduced section on a test specimen and/or the sectionbetween the grips shall be fully machined within the tolerances, and with asurface finish as given in Figure 4.BRITISH STANDARDBS 8571:20146 The British Standards Institution 2014Figure 4 Machining tolerances and surface finish for a
42、SENT specimenSurface finish is in micrometresKey1 Machined notcha Crack length, including machined notch and fatigue pre-crackFor clamped test specimens tested between rigid grips, the distance, H, shallbe 10 times the test specimen width, W.The total length of the SENT specimen shall allow sufficie
43、nt material to bewithin the grips for effective clamping.NOTE 4 A length of 100 mm within each grip is usually sufficient for clampedspecimens, although this depends on size of specimen, test machine, etc.For pin-loaded specimens an increase in the clamping distance does notinfluence the results. Pi
44、n-loading means that there is no restraining bendingmoment from the testing machine on the SENT specimens in the plane of thefatigue crack. The specimen geometry as shown in Figure 2b) restricts its use tonotch orientations of YX and XY for parent metals, and NP and PN for welds(see Figure 5 and 5.3
45、). The parallel length (Lc) of a pin-loaded specimen shallhave a minimum length given by Lc= 5.65(B W).NOTE 5 Due to material restrictions it might be difficult, in practice, to obtain idealpin-loading. However, the expressions in 7.4.3 are acceptable (if slightly conservative)if the specimen is gri
46、pped; e.g. in test machine wedge grips, or by other pin clevisesconnected to the testing machine with a bolt (pin) bearing. In this situation there isno restriction on the notch orientation.NOTE 6 For both test specimen configurations it is permissible to weld extensionpieces to the specimen, for ex
47、ample, using electron beam welding or frictionwelding, to produce sufficient length provided the distance between the welds, andthe associated HAZs, and the notched tip is at least equal to the test specimenwidth, W.5.3 NotchingSpecimens shall be notched from the surface specified by the customer. T
48、hespecimen and crack plane orientation relative to the weld direction and theparent metal rolling direction shall be as given in Figure 5.NOTE 1 The orientation of the notch determines which dimension is taken to bethe thickness, B, and which is taken to be the width, W.NOTE 2 W is the same directio
49、n as the notch (so that the crack depth may beexpressed as the a/W ratio) and B is the dimension perpendicular to this.BRITISH STANDARD BS 8571:2014 The British Standards Institution 2014 7Figure5Crackplaneorientationcodeforfracturetoughnessspecimensofparentmetalandweldmetala)Parentmetalb)WeldmetalKey 1Primaryworking/rollingdirectionPParalleltowelddirectionNNormaltowelddirectionQWeldthicknessdirectionWeldmetalFirstletterdesignation:thenormaltothecrackplane.Secondletterdesignation:theexpecteddirectionofcrackpropagation.Spe
