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1、BRITISH STANDARD BS 3518-1: 1993 Methods of Fatigue testing Part 1: Guide to general principles Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 05:27:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3518-1:1993 This British Standard, having been prepared under the direction of the Iron and St
2、eel and the Non-ferrous Metals Standards Policy Committees, was published under the authority of the Standards Board and comes into effect on 15 July 1993 BSI 03-1999 First published July 1962 Second edition July 1993 The following BSI references relate to the work on this standard: Committee refere
3、nce ISM/NFM/4 Draft for comment 91/41694 DC ISBN 0 580 21901 1 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Iron and Steel Standards Policy Committee (ISM/-) and Non-ferrous Metals Standards Policy Committee (NFM/-) to Technical Commi
4、ttee 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 Trade and Industry (National Measurement Accreditation Service) Depa
5、rtment of Trade and Industry (National Physical Laboratory) ERA Technology Ltd. GAMBICA (BEAMA Ltd.) Ministry of Defence Society of British Aerospace Companies Limited University College London Welding Institute The following bodies were also represented in the drafting of the standard, through subc
6、ommittees and panels: AEA Technology BCIRA Electricity Association University of Birmingham University of Portsmouth Amendments issued since publication Amd. No.DateComments Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 05:27:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3518-1:1993 BSI
7、03-1999i Contents Page Committees responsibleInside front cover Forewordii 1Scope1 2References1 3Symbols, terms and definitions1 4Preparing a test programme8 5Presentation of results15 Figure 1 Fatigue stress cycle2 Figure 2 Types of stress cycle with algebraic notation3 Figure 3 Stress-strain hyste
8、resis loop6 Figure 4 Determination of fatigue crack growth rates by the three-point secant method7 Figure 5 A portion of the standard sequence “COLOS”15 Figure 6 S/N curve (linear stress scale)17 Figure 7 S/N curves (logarithmic stress scale)17 Figure 8 S/N curves corresponding to particular mean st
9、resses (linear stress scale)18 Figure 9 S/N curves corresponding to particular stress ratios (logarithmic stress scale)19 Figure 10 Two proposed relationships between the level of mean stress and amplitude resulting in a given life20 Figure 11 Experimentally determined relationships between the leve
10、l of mean stress and the cyclic stress amplitude resulting in given fatigue lives21 Figure 12 Strain amplitude versus number of cycles to failure23 Figure 13 Strain amplitude versus reversals to failure23 Figure 14 Relationship betweenand cycles to failure24 Figure 15 Definition of the cyclic curve2
11、5 Figure 16 Determination of the cyclic hardening coefficient and the cyclic hardening exponent26 Figure 17 Illustration of Masings hypothesis27 Figure 18 Schematic da/dN versus K curve for fatigue crack propagation at a fixed value of stress ratio28 Table 1 Symbols, terms and definitions relating t
12、o stress controlled fatigue testing4 Table 2 Symbols, terms and definitions relating to strain controlled fatigue testing5 Table 3 Symbols, terms and definitions relating to fatigue crack growth rate testing8 Table 4 Guidelines for the selection of the minimum number of test pieces and the minimum d
13、egree of replication9 List of referencesInside back cover Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 05:27:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3518-1:1993 ii BSI 03-1999 Foreword This Part of BS 3518 has been prepared under the direction of the Iron and Steel and the Non-fer
14、rous Metals Standards Policy Committees. It is a revision of BS 3518-1:1962, which is withdrawn. In the interim new methods of predicting fatigue life have been developed and, in parallel with them, new methods of test. Thus whilst as in the previous edition the determination of stress range-life re
15、lationships is covered, in addition strain-life tests are considered and also methods of determining the rate of growth of fatigue cracks. Guidance on the selection of test conditions and numbers of specimens is provided, but detailed test procedures are not described. For these the user is referred
16、 to the relevant British Standard method. A British Standard does not purport to include all the necessary provisions 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.
17、 Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 28, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the ins
18、ide front cover. Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 05:27:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3518-1:1993 BSI 03-19991 1 Scope This Part of BS 3518 recommends the general principles to be followed in conducting fatigue tests on metallic materials. It gives definition
19、s of recommended terms, guidance on the planning of the tests, and describes effective methods for the graphical presentation of the results. The forms of fatigue testing considered encompass both the use of uncracked and precracked test pieces; the former under either stress or strain control, and
20、the latter under stress control and within the limits imposed by linear elastic fracture mechanics. The general principles are presented initially in terms of the fatigue testing of plain test pieces under a constant amplitude loading in a normal laboratory environment. Subsequently the general prin
21、ciples are extended to include additional concepts and recommendations associated with the testing of notched test pieces or structural components, testing in different environments and testing under variable amplitude loadings. Welded test pieces are not covered. 2 References 2.1 Normative referenc
22、es This Part of BS 3518 incorporates, by reference, provisions from specific editions of other publications. These normative references are cited at the appropriate points in the text and the publications are listed on the inside back cover. Subsequent amendments to, or revisions of, any of these pu
23、blications apply to this Part of BS 3518 only when incorporated in it by updating or revision. 2.2 Informative references This Part of BS 3518 refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on
24、 the inside back cover, but reference should be made to the latest editions. 3 Symbols, terms and definitions 3.1 General In this standard the term “fatigue” relates to the initiation and growth of cracks in metallic materials due to the repeated application of mechanical stresses or strains and any
25、 associated changes in mechanical properties. The term stress control is used to describe tests in which the force acting on a known specimen cross-sectional area is controlled, whilst strain control refers to tests in which the displacement of an extensometer of known gauge length is controlled. A
26、fatigue failure may result from a repeated axial, bending or torsional loading, applied separately or in any combination. For reasons of simplicity, the loadings considered in this standard are assumed to be axial with tension taken as positive and compression taken as negative. However the nomencla
27、ture used to describe this simple form of loading is equally applicable to other stress systems. 3.2 Constant amplitude stress controlled testing The stresses observed in service or used in testing may be of a simple repetitive form. In general the stresses considered in a fatigue test will be nomin
28、al stresses calculated from the measured loads and with reference to the net section under consideration. Conventional elastic formulae will be used. However sometimes they may be calculated from measured strains provided these are within the elastic limit. The smallest section of the stress-time fu
29、nction which is repeated periodically is the stress cycle. This is shown for a sinusoidal cycle in Figure 1. Figure 1 also shows that any stress varying periodically over a given range () between limits max and min can also be regarded as the sum of a static stress (the mean stress, m) and a cyclic
30、stress of zero mean varying between two values opposite in sign, but equal in magnitude (the stress amplitude, a). The stress cycles may take any of the forms shown in Figure 2. The stress ratio, that is the algebraic ratio of the minimum stress to the maximum stress in one cycle, has a value which
31、is greater than unity for cycles of fluctuating compression, less than zero for reversed cycles, and between zero and unity for cycles of fluctuating tension. The recommended symbols, terms and definitions relating to stress controlled fatigue testing are summarized in Table 1. Terms related to stre
32、ss are also exemplified in Figure 1 and Figure 2. Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 05:27:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3518-1:1993 2 BSI 03-1999 3.3 Constant amplitude strain controlled testing When strain cycles are applied to a test piece such that a macros
33、copic plastic strain is repeatedly developed within the test piece, this has two significant effects. First, the observed fatigue life is greatly reduced compared to that achieved if no significant macroscopic plastic strain repeatedly develops. Typically the fatigue life is less than 100 000 cycles
34、 to failure and therefore the test regime is said to be that of low cycle fatigue. Second, a stress-strain hysteresis loop is developed. Frequently it is observed that the shape of the hysteresis loop changes under cyclic loading in response to the processes of cyclic hardening or softening of the m
35、aterial. The initial changes are the greatest, but they progressively decline so that by 20 % to 40 % of the fatigue life of a test piece a stable hysteresis loop is generally established. Figure 3 shows how the total strain range of a hysteresis loop can be divided into the plastic strain range and
36、 elastic strain range components by means of simple working definitions. The maximum, minimum and mean strains are defined in an analogous manner to that used previously for defining stress cycles, the same algebraic notation being recommended. Table 2 summarizes the recommended symbols, terms and d
37、efinitions which relate to strain controlled fatigue testing. 3.4 Fatigue crack growth rate testing Direct measurement of fatigue crack growth rates in engineering materials, under conditions where they remain predominantly elastic, has shown that the rate is primarily related to the range of stress
38、 intensity factor and not the stress amplitude. The stress intensity factor characterizes the elastic stress field in the vicinity of the crack tip, and also indicates the magnitude of the monotonic plastic zone developed at the crack tip itself. For the opening mode of crack surface displacement, i
39、n which the crack surfaces move directly apart, the stress intensity factor (K) is defined by the relationship: where Figure 1 Fatigue stress cycle (1) Pis the applied force; Bis the test piece thickness; Wis the test piece width; Yis the stress intensity factor function (obtained from Table 2 to Ta
40、ble 5 of BS 6835:1988). Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 05:27:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3518-1:1993 BSI 03-19993 Figure 2 Types of stress cycle with algebraic notation Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 05:27:57 GMT+00:00 2006, Uncont
41、rolled Copy, (c) BSI BS 3518-1:1993 4 BSI 03-1999 Table 1 Symbols, terms and definitions relating to stress controlled fatigue testing SymbolTermDefinition orSStressThe force applied divided by the original cross-sectional area; tensile stress is considered positive and compressive stress negative.
42、maxMaximum stressThe highest algebraic value of stress in the stress cycle. minMinimum stressThe lowest algebraic value of stress in the stress cycle. mMean stressHalf of the algebraic sum of the maximum and minimum stresses. aStress amplitudeHalf of the algebraic difference between the maximum and
43、minimum stresses. Range of stressThe algebraic difference between the maximum and minimum stresses. RStress ratioThe algebraic ratio of the minimum stress to the maximum stress in one cycle. nNumber of stress cyclesThe number of cycles applied. fFrequency of cyclesThe number of cycles applied per se
44、cond. N or NfEndurance or fatigue life The number of stress cycles to failure. NOTEThis is generally stated as decimal fractions or multiples of 106. NFatigue strength at N cycles The value of the stress amplitude at a stated stress ratio under which the test piece would have a life of at least N cy
45、cles with a stated probability. NOTEIf no probability is stated 50 % is implied. If no stress ratio is stated a value of 1 is implied. DFatigue limitThe value of the stress amplitude below which the test piece would be expected to endure an infinite number of stress cycles with a stated probability.
46、 NOTECertain materials do not show a fatigue limit. Others only show a fatigue limit in certain environments. KtTheoretical stress concentration factor The ratio of the notch tip stress, calculated in accordance with elastic theory, to the net section stress. KfFatigue strength reduction factor The
47、ratio of the fatigue strength at a specified life for a plain polished test piece to that of a test piece with a stress concentration, expressed in terms of net section stress. NOTEThe values of Kf commonly quoted usually refer to the fatigue limit. FLFFatigue life factorThe ratio of the mean fatigu
48、e life at a specified stress amplitude of samples of treated test pieces to that of untreated test pieces. NOTETreated test pieces are those to which a thermal or mechanical process has been applied in order to assess the effect of that process on fatigue behaviour. Licensed Copy: sheffieldun sheffi
49、eldun, na, Wed Nov 29 05:27:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3518-1:1993 BSI 03-19995 Table 2 Symbols, terms and definitions relating to strain controlled fatigue SymbolTermDefinition StrainThe extension of the gauge length divided by the original gauge length. It is taken to be positive when the gauge length increases in length and negative when it contracts. maxMaximum strainThe highest algebraic value of strain in the strain cycle. minMinimum strainThe lowest algebraic value of