BS 3518-1-1993 Methods of fatigue testing - Methods of fatigue testing - Guide to general principles《疲劳试验方法 第1部分 一般原理指南》.pdf

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1、BRITISH STANDARD BS3518-1: 1993 Methods of Fatigue testing Part1: Guide to general principlesBS3518-1:1993 This British Standard, having been prepared under the directionof the Iron and Steel andthe Non-ferrous Metals Standards Policy Committees, waspublished under the authorityof the Standards Boar

2、dand comes intoeffect on 15 July 1993 BSI 03-1999 First published July1962 Second edition July1993 The following BSI references relate to the work on this standard: Committee reference ISM/NFM/4 Draft for comment 91/41694 DC ISBN 0 580 21901 1 Committees responsible for this British Standard The pre

3、paration 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 Committee ISM/NFM/4, upon which the following bodies were represented: Aluminium Federation British Gas plc British Non-ferr

4、ous Metals Federation British Railways Board British Steel Industry Copper Development Association 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 Defenc

5、e Society of British Aerospace Companies Limited University College London Welding Institute The following bodies were also represented in the drafting of the standard, through subcommittees and panels: AEA Technology BCIRA Electricity Association University of Birmingham University of Portsmouth Am

6、endments issued since publication Amd. No. Date CommentsBS3518-1:1993 BSI 03-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 References 1 3 Symbols, terms and definitions 1 4 Preparing a test programme 8 5 Presentation of results 15 Figure 1 Fatigue stress cycl

7、e 2 Figure 2 Types of stress cycle with algebraic notation 3 Figure 3 Stress-strain hysteresis loop 6 Figure 4 Determination of fatigue crack growth rates by the three-point secant method 7 Figure 5 A portion of the standard sequence “COLOS” 15 Figure 6 S/N curve (linear stress scale) 17 Figure 7 S/

8、N curves (logarithmic stress scale) 17 Figure 8 S/N curves corresponding to particular mean stresses (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 amplitud

9、e resulting in a given life 20 Figure 11 Experimentally determined relationships between the level of mean stress and the cyclic stress amplitude resulting in given fatigue lives 21 Figure 12 Strain amplitude versus number of cycles to failure 23 Figure 13 Strain amplitude versus reversals to failur

10、e 23 Figure 14 Relationship betweenand cycles to failure 24 Figure 15 Definition of the cyclic curve 25 Figure 16 Determination of the cyclic hardening coefficient and the cyclic hardening exponent 26 Figure 17 Illustration of Masings hypothesis 27 Figure 18 Schematic da/dN versus DK curve for fatig

11、ue crack propagation at a fixed value of stress ratio 28 Table 1 Symbols, terms and definitions relating to stress controlled fatigue testing 4 Table 2 Symbols, terms and definitions relating to strain controlled fatigue testing 5 Table 3 Symbols, terms and definitions relating to fatigue crack grow

12、th rate testing 8 Table 4 Guidelines for the selection of the minimum number of test pieces and the minimum degree of replication 9 List of references Inside back coverBS3518-1:1993 ii BSI 03-1999 Foreword This Part of BS3518 has been prepared under the direction of the Iron and Steel and the Non-fe

13、rrous Metals Standards Policy Committees. It is a revision of BS3518-1:1962, 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

14、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

15、 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.

16、 Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to28, 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 theinside f

17、ront cover.BS3518-1:1993 BSI 03-1999 1 1 Scope This Part of BS3518 recommends the general principles to be followed in conducting fatigue tests on metallic materials. It gives definitions of recommended terms, guidance on the planning of the tests, and describes effective methods for the graphical p

18、resentation 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 the latter under stress control and within the limits imposed by linear elastic fracture mechanics. The general pr

19、inciples 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 principles are extended to include additional concepts and recommendations associated with the testing of notched test

20、 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 references This Part of BS3518 incorporates, by reference, provisions from specific editions of other publications. These

21、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 publications apply to this Part of BS3518 only when incorporated in it by updating or revision. 2.2 Informative refer

22、ences This Part of BS3518 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 the inside back cover, but reference should be made to the latest editions. 3 Symbols, terms and definitions 3.1 Gen

23、eral 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 associated changes in mechanical properties. The term stress control is used to describe tests in which the force ac

24、ting 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 fatigue failure may result from a repeated axial, bending or torsional loading, applied separately or in any combinat

25、ion. 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 nomenclature used to describe this simple form of loading is equally applicable to other stress systems. 3.2 Constant amplitu

26、de 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 nominal stresses calculated from the measured loads and with reference to the net section under consideration. Conventiona

27、l 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 function which is repeated periodically is the stress cycle. This is shown for a sinusoidal cycle in Figure 1. Figure 1

28、 also shows that any stress varying periodically over a given range (D) between limits maxand mincan also be regarded as the sum of a static stress (the mean stress, m ) and a cyclic stress of zero mean varying between two values opposite in sign, but equal in magnitude (the stress amplitude, a ). T

29、he stress cycles may take any of the forms shown inFigure 2. The stress ratio, that is the algebraic ratio of the minimum stress to the maximum stress in one cycle, has a value which is greater than unity for cycles of fluctuating compression, less than zero for reversed cycles, and between zero and

30、 unity for cycles of fluctuating tension. The recommended symbols, terms and definitions relating to stress controlled fatigue testing are summarized inTable 1. Terms related to stress are also exemplified inFigure 1 andFigure 2.BS3518-1:1993 2 BSI 03-1999 3.3 Constant amplitude strain controlled te

31、sting When strain cycles are applied to a test piece such that a macroscopic 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 repe

32、atedly develops. Typically the fatigue life is less than100000 cycles 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 i

33、n response to the processes of cyclic hardening or softening of the material. The initial changes are the greatest, but they progressively decline so that by20% to40% 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

34、 hysteresis loop can be divided into the plastic strain range and 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 rec

35、ommended. Table 2 summarizes the recommended symbols, terms and definitions 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, ha

36、s shown that the rate is primarily related to the range of stress 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

37、tip itself. For the opening mode of crack surface displacement, in which the crack surfaces move directly apart, the stress intensity factor (K) is defined by the relationship: where Figure 1 Fatigue stress cycle (1) P is the applied force; B is the test piece thickness; W is the test piece width; Y

38、 is the stress intensity factor function (obtained from Table2 to Table5 of BS6835:1988).BS3518-1:1993 BSI 03-1999 3 Figure 2 Types of stress cycle with algebraic notationBS3518-1:1993 4 BSI 03-1999 Table 1 Symbols, terms and definitions relating to stress controlled fatigue testing Symbol Term Defi

39、nition orS Stress The force applied divided by the original cross-sectional area; tensile stress is considered positive and compressive stress negative. max Maximum stress The highest algebraic value of stress in the stress cycle. min Minimum stress The lowest algebraic value of stress in the stress

40、 cycle. m Mean stress Half of the algebraic sum of the maximum and minimum stresses. a Stress amplitude Half of the algebraic difference between the maximum and minimum stresses. D Range of stress The algebraic difference between the maximum and minimum stresses. R Stress ratio The algebraic ratio o

41、f the minimum stress to the maximum stress in one cycle. n Number of stress cycles The number of cycles applied. f Frequency of cycles The number of cycles applied per second. N or N f Endurance or fatigue life The number of stress cycles to failure. NOTEThis is generally stated as decimal fractions

42、 or multiples of10 6 . N Fatigue 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 leastN cycles with a stated probability. NOTEIf no probability is stated50 % is implied. If no stress ratio is stated a value of 1 is im

43、plied. D Fatigue limit The 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. NOTECertain materials do not show a fatigue limit. Others only show a fatigue limit in certain environments. K t Theoretical

44、stress concentration factor The ratio of the notch tip stress, calculated in accordance with elastic theory, to the net section stress. K f Fatigue strength reduction factor The ratio of the fatigue strength at a specified life for a plain polished test piece to that of a test piece with a stress co

45、ncentration, expressed in terms of net section stress. NOTEThe values of K fcommonly quoted usually refer to the fatigue limit. FLF Fatigue life factor The ratio of the mean fatigue life at a specified stress amplitude of samples of treated test pieces to that of untreated test pieces. NOTETreated t

46、est 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.BS3518-1:1993 BSI 03-1999 5 Table 2 Symbols, terms and definitions relating to strain controlled fatigue Symbol Term Definition Strain The extension of th

47、e 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. max Maximum strain The highest algebraic value of strain in the strain cycle. min Minimum strain The lowest algebraic value of strain in the strai

48、n cycle. m Mean strain One-half the algebraic sum of the maximum and minimum strain. D t Total strain range The algebraic difference between the maximum and minimum strain in one strain cycle. D p Plastic strain range The width of the hysteresis loop of stress plotted against strain, determined at t

49、he mean stress. D e Elastic strain range The difference between the total strain range and the plastic strain range. aor D t /2 Strain amplitude Half the total strain range. D p /2 Plastic strain amplitude Half the plastic strain range. D e /2 Elastic strain amplitude Half the elastic strain range. 2N f Fatigue life in reversals The number of reversals, or half cycles, to failure (see5.2). b Fatigue strength exponent The slope of the “elastic” line obtained by plotting the loga