1、BRITISH STANDARD BS 7448-1:1991 Incorporating Amendment No. 1 and Corrigendum No. 1 Fracture mechanics toughness tests Part 1: Method for determination of K Ic , critical CTOD and critical J values of metallic materials ICS 77.040.10 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT
2、 LAWBS 7448-1:1991 This British Standard, having been prepared under the direction of the Iron and Steel and the Non-ferrous Metals Standards Policy Committees, was published under the authority of the Standards Board and comes into effect on 20 December 1991 BSI 27 February 2002 The following BSI r
3、eferences relate to the work on this standard: Committee reference ISM/NFM/4 Draft for comment 90/41825 DC ISBN 0 580 20037 X Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Iron and Steel Standards Policy Committee (ISM/-) and the Non-f
4、errous Metals Standards Policy Committee (NFM/-) to Technical Committee ISM/NFM/4, upon which the following bodies were represented: Aluminium Federation British Gas plc British Non-ferrous Metals Federation British Railways Board British Steel Industry Copper Development Association Department of T
5、rade and Industry (National Engineering Laboratory) Department of Trade and Industry (National Measurement Accreditation Service) Department of Trade and Industry (National Physical Laboratory) ERA Technology Ltd. GAMBICA (BEAMA Ltd.) Ministry of Defence Society of British Aerospace Companies Limite
6、d Welding Institute The following bodies were also represented in the drafting of the standard, through subcommittees and panels: BCIRA BEAMA Ltd. Electricity Supply Industry in United Kingdom Lloyds Register of Shipping Steel Casting Research and Trade Association United Kingdom Atomic Energy Autho
7、rity Amendments issued since publication Amd. No. Date Comments 10543 August 1999 12018 Corrigendum No. 1 27 February 2002 Corrections to Figure 10, Table 2 and 8.2.BS 7448-1:1991 BSI 27 February 2002 i Contents Page Committees responsible Inside front cover Foreword iii 1S c o p e 1 2 Definitions 1
8、 3 Symbols and designations 2 4 Principle 4 5 Test specimens 4 6 Specimen preparation and fatigue precracking 9 7 Test equipment 18 8 Test procedure 22 9 Analysis of test data 25 10 Validity check lists 32 11 Test report 33 Appendix A Bibliography 34 Appendix B Crack plane identification 34 Appendix
9、 C Measurement of load-line displacement (q) in a three point bend test 37 Figure 1 Flow chart for choice of fracture toughness parameter, specimen design and displacement measurement 5 Figure 2 Proportional dimensions and tolerances for a rectangular section bend specimen 6 Figure 3 Proportional di
10、mensions and tolerances for a square section bend specimen 6 Figure 4 Proportional dimensions and tolerances for a straight notch compact specimen 7 Figure 5 Proportional dimensions and tolerances for a stepped notch compact specimen 8 Figure 6 Acceptable fatigue crack starter notches and fatigue cr
11、ack configurations 10 Figure 7 Chevron notch 11 Figure 8 Outward pointing knife edges and corresponding notch geometries 12 Figure 9 Inward pointing knife edges and corresponding notch geometries 13 Figure 10 Fixture for three point bend tests 14 Figure 11 Typical design of clevis for applying a ten
12、sile force to a compact specimen using a circular hole in the clevis, and a pin having a diameter of 0.24W 0.005W, 0.015W 20 Figure 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 diamter of 0.24W +0.000 W, 0.0
13、05W 21 Figure 13 Characteristic type of force versus displacement records in fracture tests 23 Figure 14 Assessment of pop-in behaviour 26 Figure 15 Definition of F Q(for the determination of K Q )2 7 Figure 16 Definition of V p(for the determination of CTOD) 29 Figure 17 Definition of U p(for the d
14、etermination of J)3 1 Figure 18 Basic fracture plane identification: rectangular section 35 Figure 19 Basic fracture plane identification: cylindrical sections 36 Figure 20 Non-basic fracture plane identification 36BS 7448-1:1991 ii BSI 27 February 2002 Page Figure 21 Principle of the “comparator” b
15、ar measurement 37 Figure 22 Displacements associated with three point bend specimens 38 Figure 23 Simultaneous determination of extraneous displacements ( 1 + 2 )3 8 Figure 24 Location of two notch opening displacement measurements (V 1and V 2 ) for the determination of load-line displacement 39 Tab
16、le 1 Dimensions of specimens that may lead to valid K Icvalues 9 Table 2 Values of for three point bend specimens 16 Table 3 Values of for compact specimens 18 Publication(s) referred to 40 f a o W - - f a o W - - BS 7448-1:1991 BSI 27 February 2002 iii Foreword This part of BS 7448 has been publish
17、ed under the direction of the Iron and Steel and the Non-ferrous Metals Standards Policy Committees. It gives a method for determining plane strain fracture toughness (K Ic ), critical crack tip opening displacement (CTOD) 1)and critical J fracture toughness values for metallic materials under displ
18、acement controlled monotonic loading at quasistatic rates. This part of BS 7448 combines and extends the methods for determining K Icvalues, given in BS 5447, and the method for determining crack opening displacement (COD), given in BS 5762:1979, BS 5447:1977 and BS 5762:1979 are withdrawn. Determin
19、ation of K Icfor materials and conditions for which it is appropriate to determine fracture toughness in terms of K Icalone are covered in BS EN ISO 12737. General determinations of fracture toughness, where the fracture behaviour determines the relevant fracture parameters (e.g. K Ic , CTOD or J) a
20、re covered in the procedures in this part of BS 7448, BS 7448-2 and BS 7448-4. The other three parts of BS 7448 are as follows: Part 2: Method for determination of K Ic , critical CTOD or J values of welds in metallic materials; Part 3: Method for determination of dynamic toughness 2) ; Part 4: Meth
21、od for determination of fracture resistance curves and initiation values for stable crack extension in metallic materials. It has been assumed in the drafting of this standard that the execution of its provisions is entrusted to appropriately qualified and experienced people. Safety note. It is impo
22、rtant 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 safety of machine operators. A British Standard does not purport to include all the necessary pr
23、ovisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 40,
24、 an inside back cover and a back cover. The BSI copyright notice displayed throughout this document indicates when the document was last issued. 1) In this British Standard the term CTOD, which refers to crack tip opening displacement, is synonymous with the term COD in BS 5762. 2) In preparation.iv
25、 blankBS 7448-1:1991 BSI 27 February 2002 1 1 Scope This part of BS 7448 specifies a method for determining the opening mode plane strain fracture toughness (K Ic ), the critical crack tip opening displacement (CTOD) fracture toughness, and the critical J fracture toughness of metallic materials. Th
26、e method uses fatigue precracked specimens. These are tested in displacement controlled monotonic loading at a constant rate of increase in stress intensity factor within the range 0.5 MPam 0.5 s 1to 3.0 MPam 0.5 s 1 3)during the initial elastic deformation. The specimens are loaded to fracture or t
27、he maximum force associated with plastic collapse. The method is especially appropriate to materials that exhibit a change from ductile to brittle behaviour with decreasing temperature. No other influences of environment are covered. The definition of fracture toughness values relevant to particular
28、 structural integrity assessments is outside the scope of this British Standard. NOTE 1 The titles of the publications referred to in this standard are listed on the inside back cover. NOTE 2 Numbers in square brackets in the text refer to numbered items in the Bibliography in Appendix A. NOTE 3 Thi
29、s British Standard does not cover the determination of K Icalone. Such determinations are covered in BS EN ISO 12737. 2 Definitions For the purposes of this part of BS 7448 the following definitions apply. 2.1 stress intensity factor (K) the magnitude of the stress field near the crack tip (a stress
30、-field singularity) for a particular mode (see 2.2) in a homogeneous, ideally linear-elastic body NOTE It is a function of applied force, crack length and specimen geometry, and is expressed in units of MPam 0.5 . 2.2 opening mode opening displacement of the surfaces of a crack in a direction normal
31、 to the original (undeformed) crack plane near the crack tip 2.3 plane strain fracture toughness (K Ic ) a measure of a materials resistance to crack extension when the stress state near the crack tip is predominantly plane strain, plastic deformation is limited, and opening mode monotonic loading i
32、s applied 2.4 maximum fatigue stress intensity factor (K f ) the maximum value of opening mode stress intensity factor which is applied during the final stages of fatigue crack extension 2.5 crack tip opening displacement (CTOD) the displacement of the surfaces of a crack normal to the original (und
33、eformed) crack plane at the tip of the fatigue precrack, expressed in mm 2.6 critical CTOD a value of CTOD associated with a particular type of crack extension (see clause 3) 2.7 J-integral a mathematical expression for a line or surface integral that encloses the crack front from one crack surface
34、to the other, used to characterize the local stress-strain field around the crack front 1, expressed in J/mm 2 4) 3) 0.031 6 MPa m 0.5 =1N mm 1.5 = 0.031 6 MN m 1.5 . 4) 1 J/mm 2= 1 MJ/m 2 .BS 7448-1:1991 2 BSI 27 February 2002 2.8 J an experimental equivalent of the J-integral 2.9 critical J a valu
35、e of J associated with a particular type of crack extension (see clause 3) 2.10 brittle crack extension an abrupt crack extension which occurs with or without prior stable crack extension (see 2.11) 2.11 stable crack extension slow stable crack extension that includes the stretch zone width (see 2.1
36、2) NOTE In true displacement control the crack extension usually stops when the applied displacement is held constant. 2.12 stretch zone width (SZW) the length of crack extension that occurs during crack tip blunting; that is, prior to the onset of brittle crack extension, pop-in (see 2.13) or slow
37、stable crack extension, and which occurs in the same plane as the fatigue precrack 2.13 pop-in a discontinuity in the force versus displacement record NOTE The pop-in corresponds to a sudden increase in displacement, and, generally, a sudden decrease in force. Subsequently, the displacement and forc
38、e increase relatively slowly to above their respective values at pop-in (see 9.1). 3 Symbols and designations For the purposes of this part of BS 7448 the following symbols and designations apply. a nominal crack length (see Figure 2 to Figure 6) or, for the purposes of fatigue precracking (see 6.4.
39、5 and 6.4.6), an assumed value a o a o average original crack length (see 8.7.2) B specimen thickness C total width of compact specimen E Youngs modulus of elasticity at the temperature of interest f a mathematical function of or for bend specimens f a mathematical function of or for compact specime
40、ns F applied force F d particular value of F, as shown in Figure 15 F c applied force at the onset of brittle crack extension or pop-in when a is less than 0.2 mm F f maximum fatigue precracking force during the final stages of fatigue crack extension (see 6.4.5 and 6.4.6) F m applied force at the f
41、irst attainment of a maximum force plateau for fully plastic behaviour F max maximum force in a K Icdetermination (see Figure 15) F Q particular value of F, as shown in Figure 15 F u applied force at the onset of a brittle crack extension or pop-in when the event is preceded by a equal to or greater
42、 than 0.2 mm J experimental equivalent of the crack tip J-integral a W - - a o W - - a W - - a o W - - BS 7448-1:1991 BSI 27 February 2002 3 J c critical J at the onset of brittle crack extension or pop-in when a is less than 0.2 mm J m value of J at the first attainment of a maximum force plateau f
43、or fully plastic behaviour J u critical J 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 K stress intensity factor rate of change of K with time K Ic plane strain fracture toughness K f maximum fatigue stress intensity factor applied
44、 during the final stages of fatigue crack extension K Q provisional value of K Ic q displacement of bend specimen or stepped notch compact specimen along the load-line q c value of q at the onset of brittle crack extension or pop-in when a is less than 0.2 mm q m value of q at the first attainment o
45、f a maximum force plateau for fully plastic behaviour q p plastic component of q corresponding to F c , F uand F m q u value of q 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 R fatigue force ratio, i.e. the algebraic ratio of minim
46、um to maximum fatigue precracking force during any single cycle of fatigue operation S span between outer loading points in three point bend test T test temperature U p plastic component of area under plot of force (F) versus specimen displacement along the load-line (see Figure 17) V notch opening
47、displacement at or near to notch mouth NOTE In a stepped notch compact specimen V = q. V c value of V at the onset of brittle crack extension or pop-in when a is less than 0.2 mm V m value of V at the first attainment of a maximum force plateau for fully plastic behaviour V p plastic component of V
48、corresponding to F c , F uand F m(see Figure 16) V u value of V at the onset of brittle crack extension or pop-in when this is preceded by a equal to or greater than 0.2 mm W effective width of test specimen y half the distance between knife edge fixing points, as shown in Figure 8 and Figure 9 z di
49、stance of the notch opening gauge location above the surface of the specimen see Figure 8(b) crack tip opening displacement (CTOD) c critical CTOD at the onset of brittle crack extension or pop-in when a is less than 0.2 mm m value of CTOD at the first attainment of a maximum force plateau for fully plastic behaviour u critical CTOD at the onset of brittle crack extension or pop-in when the event is precede
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