1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58fracture toughness of metallic materials at rates of increase in stress intensity factor greater th
2、an 3.0 MPam0.5sp1ICS 77.040.10Fracture mechanics toughness tests Part 3: Method for determination of BRITISH STANDARDBS 7448-3:2005Incorporating Corrigendum No. 1BS 7448-3:2005Committees responsible BritishThis BritiMtesting, This British Standard was published under the authority of the Standards P
3、olicy and Strategy Committee on 23 March 2005 BSI 2007First published March 2005The following BSI references relate to the work on this British Standard:Committee reference ISE/NFE/4/4Draft for comment 03/303157 DCISBN 978 0 580 59480 9Network RailQinetiQSociety of British Aerospace Companies Ltd.UK
4、 Steel AssociationUnited Kingdom Accreditation ServiceWelding InstituteAmendments issued since publicationAmd. No. Date Comments17334 Corrigendum No. 131 August 2007 In Foreword, added supersession detail.Lloyds RegisterNational Physical Laboratoryfor this Standardsh Standard was entrusted by Techni
5、cal Committee ISE/NFE/4, echanical testing of materials, to Subcommittee ISE/NFE/4/4, Toughness upon which the following bodies were represented:British Non-Ferrous Metals FederationGAMBICA LimitedHSE Health and Safety ExecutiveBS 7448-3:2005 BSI 2007ContentsPageCommittees responsible Inside front c
6、overForeword iii1Scope 12 Normative references 13Terms and definitons 14 Symbols and designations 35 Principle 56 Test specimens 77 Specimen preparation and fatigue precracking 158 Test equipment 179 Test procedure 2110 Analysis of test data 2411 Check lists for qualification of data 3812 Test repor
7、t 38Figure 1 Flow chart for the choice of fracture toughness parameter, specimen design and displacement measurement 6Figure 2 Proportional dimensions and tolerances for the rectangular section bend specimen 7Figure 3 Proportional dimensions and tolerances for the square section bend specimen 8Figur
8、e 4 Proportional dimensions and tolerances for the straight notch compact specimen 9Figure 5 Proportional dimensions and tolerances for the stepped notch compact specimen 10Figure 6 Acceptable fatigue crack starter notches and fatigue crack configurations 12Figure 7 Chevron notch 12Figure 8 Outward
9、pointing knife edges and corresponding notch geometrics 13Figure 9 Outward pointing knife edges and corresponding notch geometrics 14Figure 10 Fixture for three point bend tests 19Figure 11 Typical design of clevis for applying a tensile force to a compact specimen using a circular hole in the clevi
10、s and a pin having a diameter of (0.24 ) W 20Figure 12 Typical design of clevis for applying a tensile force to a compact specimen using a hole with a flat in the clevis, and a pin having a diameter of (0.24 ) W 21Figure 13 Characteristic types of force versus displacement records in fracture tests
11、23Figure 14 Assessment of pop-in behaviour 25Figure 15 Principal types of force versus crack mouth opening gauge displacement records showing the limits of allowable force and displacement variation for KIcdetermination 27Figure 16 Force variation limits for fracture toughness determination 28Figure
12、 17 Limits of crack mouth opening gauge displacement variations for plane strain fracture toughness determination 29Figure 18 Definition of Vp(for determination of CTOD) 30Figure 19 Limits of force and displacement for CTOD and J determination31Figure 20 Force and load point displacement variation f
13、or fracture toughness determination 330.0050.0150.000+0.005iBS 7448-3:2005iiFigure A.1 Resistance strain gauge positions for load measurements from rectangular section bend specimen 41Figure A.2 Limits of loading point displacement variations for CTOD and J determination 42Figure B.1 Schematic repre
14、sentation of the comparator bar 44Figure B.2 Displacements associated with three-point bend specimens 44Figure B.3 Simultaneous determination of extraneous displacements (z2p z1) 45Figure B.4 Location of two notch opening displacement measurements (V1and V2) for the determination of load-line displa
15、cement 45Figure C.1 Basic fracture plane identification Rectangular section 46Figure C.2 Basic fracture plane identification Cylindrical sections 46Figure C.3 Non-basic fracture plane identification 47Figure D.1 Examples of good and unacceptable force records 48Figure D.2 Examples of good and unacce
16、ptable notch opening displacement records 48Figure D.3 Test system for d.c. signal conditioners and amplifiers 49Figure D.4 Example of the amplitude output of an instrument as a function of frequency 49Figure D.5 Test system for a.c. transducers 50Figure E.1 Force versus time record from dynamic ten
17、sile test showing no distinct yield point 52Figure E.2 Force versus time record from dynamic tensile test showing distinct yield point 53Figure E.3 Limits to ram displacement versus time record from dynamic tensile test 53Table 1 Dimensions of specimens that can lead to valid KIcvalues 11Table 2 Val
18、ues of for f three point bend specimens 16Table 3 Values of for f three point bend specimens 17aW-aW-PageFigure 21 Displacement variation limits for CTOD and J determination 34Figure 22 Definition of Up(for determination of J)35 BSI 2007BS 7448-3:2005 BSI 2007adequate for high rate tests.This Britis
19、h Standard supersedes BS 6729:1987 which is withdrawn.This part of BS 7448 is one of a series dealing with fracture mechanics toughness tests, the other parts being: Part 1: Fracture mechanics toughness tests Method for determination of KIccritical CTOD and critical J values of metallic materials. P
20、art 2: Fracture mechanics toughness tests Method for determination of KIc, critical CTOD and critical J values of welds in metallic materials. Part 4: Fracture mechanics toughness tests Method for determination of fracture resistance curves and initiation values for stable crack extension in metalli
21、c materials. It is assumed in the drafting of this standard that the execution of its provisions is entrusted to appropriately qualified and competent people.This British Standard describes methods of test only, and should not be used or quoted as a specification. References to this standard should
22、indicate that the methods of test used are in accordance with BS 7448-3:2005.CAUTION It is important to note that tests of the type described involve the use of large forces, and may involve the rapid movement of machine parts and fractured test specimens. Therefore it is important to consider the s
23、afety of machine operators.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.Summary of pagesThis document comprises a front cover
24、, an inside front cover, pages i to iv, a blank page, pages 1 to 55 and a back cover.The BSI copyright notice displayed in this document indicates when the ForewordThis part of BS 7448 has been prepared by Technical Committee ISE/NFE/4. It is required because the instrumentation and procedures in BS
25、 7448-1 may not be iiidocument was last issued.ivblankBS 7448-3:20051 ScopeThis part of BS 7448 describes a method for determining the opening mode plane strain fracture toughness KIc, the critical crack tip opening displacement (CTOD) fracture toughness and the critical J fracture toughness of meta
26、llic materials. The method uses fatigue precracked specimens tested in displacement control at rates of increase in stress intensity factor greater than 3.0 MPam0.5sp1but less than 3 000 MPam0.5sp11)during the initial elastic deformation. Stress intensity factors greater than 3 000 MPam0.5sp1are cov
27、ered in Annex A. These rates are greater than those permitted in BS 7448-1. The definition of fracture toughness values relevant to particular structural integrity assessments is outside the scope of this British Standard.NOTE This standard does not cover integrity assessments. Such assessments are
28、covered in BS 7910.2 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) applies.BS 7448-4
29、:1997, Fracture mechanics toughness tests Part 4: Method for determination of fracture resistance curves and initiation values for stable crack extension in metallic materials.BS 7935-1, Constant amplitude dynamic force calibration Part 1: Calibration and verification of non-resonant uniaxial dynami
30、c testing systems Method.BS 7935-2, Constant amplitude dynamic force calibration Part 2: Calibration of the calibration device instrumentation to be used for the dynamic calibration of non-resonant uniaxial dynamic testing systems Method.BS EN ISO 7500-1:1999, Metallic materials Verification of stat
31、ic uniaxial testing machines Part 1: Tension/compression testing machines Verification and calibration of the force-measuring system.BS EN ISO 12737, Metallic materials Determination of plane-strain fracture toughness.3 Terms and definitionsFor the purposes of this part of BS 7448 the following term
32、s and definitions apply.3.1 stress intensity factorKmagnitude of the stress field near the crack tip (a stress-field singularity) (see 3.2) in a homogeneous, ideally linear-elastic body NOTE This is a function of applied force, crack length and specimen geometry, and is expressed in units of MPam0.5
33、.3.2 opening modeopening displacement of the crack surfaces in a direction normal to the original (undeformed) crack plane near the crack tip3.3 plane strain fracture toughnessKIcmeasure of a materials resistance to crack extension when the stress state near the crack tip is predominantly plane stra
34、in, plastic deformation is limited, and opening mode monotonic loading is applied3.4 maximum fatigue stress intensity factor1Kfmaximum value of opening mode stress intensity factor which is applied during the final stages of fatigue crack extension1)1N.mmp1.5= 0.0316 MPam0.5= 0.0316 MNm1.5. BSI 2007
35、BS 7448-3:20053.5 crack tip opening displacementCTODdisplacement of the crack surfaces normal to the original (undeformed) crack plane at the tip of the fatigue precrack, expressed in millimetres3.6 critical CTODvalue of CTOD associated with a particular type of crack extension3.7 J-integralmathemat
36、ical expression, a line or surface integral that encloses the crack front from one crack surface to the other, used to characterize the local stress-strain field around the crack front, expressed in J/mm2NOTE 1 J/mm2= 1 MJ/m2= 1 N/mm.3.8 Jexperimental equivalent of the J-integral3.9 critical Jpartic
37、ular value of J3.10 brittle crack extensionabrupt crack extension which occurs with or without prior stable crack extension (see 3.11)3.11 stable crack extensionslow stable crack extension that includes the stretch zone width (see 3.12)3.12 stretch zone widthSZWlength of crack extension that occurs
38、during crack tip blunting; that is, prior to the onset of brittle crack extension, pop-in (see 3.13) or slow stable crack extension.NOTE The SZW is measured in the same plane as the fatigue precrack.3.13 pop-indiscontinuity in the force versus displacement recordNOTE A pop-in corresponds to a sudden
39、 increase in displacement, and, generally, a sudden decrease in force. Subsequently, the displacement and force increase to above their respective values at pop-in.2 BSI 2007BS 7448-3:20054 Symbols and designationsFor the purposes of this part of BS 7448 the following symbols and designations apply.
40、a crack length or, for the purposes of fatigue precracking (see 7.4.4 and 7.4.5), an assumed value kao, in millimetresaoaverage original crack length (see 9.7.1), in millimetresB specimen thickness, in millimetresBNnet specimen thickness between sidegroove tips, in millimetresC total width of compac
41、t specimen, in millimetresD ram displacement in dynamic tensile test, in millimetresram displacement rate in dynamic tensile test, in millimetres per secondE Youngs modulus of elasticity at the temperature of interest, in GPaf a mathematical function of (a/W) or (ao/W) for bend specimensf a mathemat
42、ical function of (a/W) or (ao/W) for compact specimensf1electrical frequency at which the output signal amplitude is reduced by 10 %, in hertzf2electrical frequency at which the output signal amplitude is reduced by 30 %, in hertzF applied force, in kilonewtonsrate of change of applied force with ti
43、me, in kilonewtons per secondFcapplied force at the onset of brittle crack extension or pop-in when %a is less than 0.2 mm, in kilonewtonsFeapplied force at which permanent plastic deformation is first observed in dynamic tensile test, in kilonewtonsFfmaximum fatigue precracking force during the fin
44、al stages of fatigue crack extension (see 7.4.4 and 7.4.5), in kilonewtonsFmapplied force at the first attainment of a maximum force plateau for fully plastic behaviour, in kilonewtonsFrapplied force at intersection of force versus displacement record in dynamic tensile test with 0.2 % offset line,
45、in kilonewtonsFuapplied force at the onset of brittle crack extension or pop-in when the event is preceded by %a equal to or greater than 0.2 mm, in kilonewtonsFAapplied force (in kilonewtons) at which the nominal stress equals:for a bend specimen; andfor a compact specimenFTSmaximum applied force o
46、bserved after yield or plastic deformation in a dynamic tensile test, in kilonewtonsJ experimental equivalent of the crack tip J-integral, in megajoules per square metreJccritical J at the onset of brittle crack extension or pop-in when %a 0.2 mm, in megajoules per square metreDb) square cross-secti
47、on three point bend (see Figure 3);c) straight notch compact (see Figure 4);d) stepped notch compact (see Figure 5).NOTE Specimens having W/B ratios greater than 2 have an increased tendency to buckle.KeyB specimen thickness (see 6.1)W effective width of the test specimen (W = 2B), or if agreed by t
48、he parties concerned, a width thickness ratio in the range, 1.0 W/B k 4.0a crack length (0.45W k a k 0.55W)Figure 2 Proportional dimensions and tolerances for the rectangular section bend specimenSee figures 6-8and 7.3.7 BSI 2007BS 7448-3:2005KeyB specimen thickness (see 6.1)W effective width of the test specimen (W = B)a crack length (0.45W k a k0.55W)Figure 3 Proportional dimensions and tolerances for the square section bend specimenSee figures 6-8and 7.3.8 BSI 2007BS 7448-3:2005KeyB specimen thicknessW effective width of the te
