BS 7774-1994 Threaded fasteners - Axial load fatigue testing - Test methods and evaluation of results《螺纹紧固件 轴向负荷疲劳试验 第1部分 试验方法和结果评估》.pdf

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1、BSI BS*7774 94 m 1624667 0425234 LO4 m BRITISH STANDARD Threaded fasteners - Axial load fatigue testing - Test methods and evaluation of results BS 7774 : 1994 IS0 3800 : 1993 BSI BS*7774 94 = Lb2Ybh 0425235 040 = Amd. No. BS 7774 : 1994 Date Text affected This British Standard, having been prepaxed

2、 under the direction of the General Mechanical Engineering Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 August 1994 0 BSI 1994 Committees responsible for this British Standard The preparation of this British Standard was entrusted b

3、y the General Mechanical Engineering Standards Policy Committee (GME/-) to Technical Committee GME/9, upon which the following bodies were represented: BEAMA Ltd. British Constructional Steelwork Association Ltd. British industrial Fasteners Federation British Railways Board British Steel Industry B

4、ritish Steel Industry (Wire Section) Gauge and bol Makers Association Society of Motor Manufacturers and Traders Ltd. Washer Manufacturers Association of Great Britain The following bodies were also represented in the drafting of the standard, through subcommittees and panels: British Turned-parts M

5、anufacturers Association institute of Metal Finishing Metal Finishing Association Stainless Steel Fbricators Association of Great Britain National Centre of Tiibology The following BSI references relate to the work on this standard: Committee reference GME/9 Draft for comment 91/83077 DC ISBN O 5802

6、32433 BSI BS37774 94 W Lb24bb9 O425236 T87 = BS 7774 : 1994 Contents p%e Committees responsible Inside front cover National foreword 11 Specification 1 Scope 1 2 Normative references 1 3 Symbols and their designations 1 4 Principle 2 5 Apparatus 3 6 Test procedure 6 7 Evaluation of results 7 8 kst r

7、eport 16 bles 2 3 1 Symbols and their designations 2 Order system for the statistical evaluation of 8 fatigue tests with a stress amplitude of oa = 150 N/mm2 in the finite life range Example of the evaluation of fatigue tests by the staircase method 8 11 Figures 1 Fxture without insert 2 Fixture wit

8、h insert 3 Load verification stud 3 4 5 4 Stress distribution in the shank of the load verification stud 5 5 Threaded test adapter 6 Rst washer (assembled) 7 Location of test nut 6 6 6 8 Probability of failure pf and number of stress cycles in the finite life range, determined on the basis of 8 fati

9、gue tests with oa = Example of the execution and evaluation of fatigue tests according to 10 Whler curve (S/N cuke) oa = f(N) 13 11 Example of basic pattern of combined test method with 14 specimens 14 12 Example of Whler curve (S/N curve) 17 13 Haigh diagram 17 150 N/mm 9 the boundary method 12 9 1

10、 BSI BS*7774 94 m Lb24bb 0425237 L3 m BS 7774 : 1994 National foreword This British Standard has been prepared under the direction of the General Mechanical Engineering Standards Policy Committee and is identical with IS0 3800 : 1993 Threaded fasteners - Axial load fatigue testing - %t methods and m

11、aluution of results, published by the International Organization for Standardization (ISO). Cross-references Internationai standard IS0 273 : 1979 IS0 885 : 1976 IS0 4032 : 1986 IS0 4033 : 1979 IS0 8673 : 1988 IS0 8674 : 1988 Corresponding British Standard BS EN 20273 : 1992 Fasteners. Clearance hol

12、es for bolts and screws (Identical) BS 4183 1967 Spedfication for machine screws and machine screw nuts. Metric series (Technically equivalent) BS 4190 : 1967 Smation for IS0 metric black -on bolts, scrms and nuts (Technically equivalent) BS 4395 Spec.ification for high strength friction grip bolts

13、and associated nuts and washers for structural engineering part 1 : 1969 General grade (lchnically equivalent) Part 2 : 1969 Higher grade bolts and nuts and geneml (lchnically equivalent) BS EN 24032 ; 1992 Hexagon nuts, style 1. Product grades A and B (Identical) BS EN 24033 : 1992 Hexagon nuts, st

14、yle 2, Product grades A and B (Identical) BS EN 28673 : 1992 Hexagon nuts, style I, with metric fine pitch thread. Product grades A and B (Identical) BS EN 28674 : 1992 Hexagon nuts, style 2, with metric fine pitch thread. Product grades A and B (Identical) gradewashers The Technical Committee has r

15、eviewed the provisions of IS0 554 : 1976 to which normative reference is made in the text, and has decided that they are acceptable for use in conjunction with this standard. Compliance with a British Standard does not of itself confer immunity from legal obligations. BSI BSm7774 94 Lb24bb9 0425238

16、85T INTERNATIONAL STANDARD IS0 3800:1993(E) Threaded fasteners - Axial load fatigue testing - Test methods and evaluation of results 1 Scope This International Standard specifies the conditions for carrying out axial load fatigue tests on threaded fasteners, as well as recommendations for the evalu-

17、 ation of the results. Unless otherwise agreed, the tests are of the fluctu- ating tension type and are carried out at room tem- perature, the loading applied being centric along the longitudinal axis of the fastener. The influence of the compliance of clamped parts on the strain of the fastener is

18、not taken into account. This method allows determination of the fatigue strength of threaded fasteners. The test results can be influenced by the test condi- tions. For this reason, minimum requirements are specified to reduce this effect. In addition, calibration and centring control methods for th

19、e testing appar- atus are included. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publi- cation, the editions indicated were valid. All standards are subject to revision, a

20、nd parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most re- cent editions of the standards indicated below. Members of IEC and IS0 maintain registers of cur- rent ly valid l nternationa l Standard s. IS0 273: 1979, Fasteners -

21、Clearance holes for bolts and screws. IS0 554: 1976, Standard atmospheres for conditioning and/or testing - Specifications. IS0 885:1976, General purpose bolts and screws - Metric series - Radii under the head. IS0 4032:1986, Hexagon nuts, style 1 - Product grades A and B. IS0 4033:1979, Hexagon nut

22、s, style 2 - Product grades A and B. IS0 8673:1988, Hexagon nuts, style 1, with metric fine pitch thread - Product grades A and B. IS0 8674: 1988, Hexagon nuts, style 2, with metric fine pitch thread - Product grades A and B. 3 Symbols and their designations See table 1 1 I l I BSI BS*7774 94 m Lb24

23、bb 0425239 796 m IS0 3800:1993(E) I Table 1 - Symbols and their designations Symbol Ad3 4 d dl 4 4 4 4 4 D F F0,2 Fa Ma, FA Fm H N NG P Pf Pt P Rm,min Designation Area at nominal minor diameter, AQ E n$/4 Stress area A. = JL - 4 (“:“) Area to be used in clculations of mean stress and stress amplitud

24、e. By agreement between the user and supplier, AQ may be used. Nominal size of the thread of the load verification stud Basic minor diameter of the thread Basic pitch diameter of the thread Nominal minor diameter of the thread, Diameter at the point of tangency of the fillet Clearance hole diameter

25、Shank diameter of the load verification stud Nominal thread diameter of the threaded test adaptor Tensile load Tensile load at proof stress RpO, Load amplitude Difference of load amplitudes in the transition range Load amplitude at endurance fatigue limit Mean load 4=d -E 6 Height of the fundamental

26、 triangle of the thread Number of stress cycles The number of stress cycles in the case where the test has discontinued without failure Failure probability Failure probability in the finite life range Failure probability in the transition range Pitch of the thread Minimum tensile strength 4 Principl

27、e Test are made on threaded fasteners to determine fatigue properties such as those shown by the Whler curve (S/N curve). Threaded fasteners to be tested are mounted in an axial load fatigue testing machine and subjected to fluctuating tension type loading. Symbol 4 VA) S(QA) a, S S( log N Qa =A Qax

28、 Ob Qm Qmin Qmax =Milin QMax =AN =ition range NOTES 1 The symbol A is used in the case of estimated val- ues. For example, the estimated value GA, of the fatigue strength at the number of cycles N. 2 The symbol - is used in the case of q, or log N val- ues which are derived from the regression line;

29、 e.g. 0,3 C2 (See explanations of symbols in table3.1 Table 3 shows an example of the evaluation of fatigue tests by the staircase method. 7.2.3.2 Boundary method The procedure for the boundary method is explained on the basis of figure9. As the position of the transi- tion range is not known prior

30、to the test and can in general only be approximated, first test a test piece on a first load amplitude. In this case, this load ampli- tude Fa = 2 500 N. If this first test piece shows no failure up to the predetermined number of stress Cy- cles NG, the load amplitude is subsequently increased until

31、 the first test piece fails. In the example, this is the load amplitude Fa, = 4 O00 N. Carry out several tests on the level on which there is now for the first time an event (failure or non-failure) deviating from the previous tests. Thereby the number of test pieces depends on the required accuracy

32、 of the result. In this example, the number of test pieces is eight. For the selection of the second load amplitude, it is advan- tageous to know the width of the transition range; this allows the second level to be chosen, in a math- ematically useful way, at its limit where the expected result bec

33、omes more exact. The following applies to the determination of the second level: Fa2 =Fei + with Ma, = (1 - x)BFal for r , 0,5n Quantity B takes account of the width of the transition range. For B, a value between 0,15 and 0,2 is rec- ommended. On the second load amplitude, found in the example in f

34、igure9, again eight test pieces are tested and the probabilities of failure, p, are plotted in the Gaussian probability net according to the estimator: 3r- 1 fi=m figure 9, b where r is the number of failures; n is the number of test pieces tested. Using the normal Gaussian distribution, the two poi

35、nts determined can be connected to form a straight line which then allows determination of the median FA50 and of the limiting values, such as FA10 and FAW, etc. 10 BSI BS*7774 94 m 1624669 0425248 T9 m TestpieceNo. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Sum of columns 3, 4, 6, 7, 8 8 7 - 757 CAE IS0 3

36、800:1993(E) Table 3 - Example of the evaluation of fatigue tests by the staircase method S(FA) = 1 ,62AFa, Column 1: load amplitude Cdumn 2: Column 3: Column 4: Column 5: indication of event (failure x, non-failure o) number of failures per load amplitude number of non-failures per load amplitude or

37、dinal z, starting with O at the lowest load amplitude It is assigned to the event with the lower frequency in columns 3 and 4 respectively. In the example in table3, it is column 4 with only 7 non-failures as compared to column 3 with 9 failures. frequency, repetition of values from column 3 or 4 wi

38、th the lower sum (here column 4). product of columns 5 and 6 (i$ product of columns 5 and 7 z% sum of columns 6, 7 and 8 lowest load amplitude in columns 3 or 4 with the lower number of events (here column 4. median, load amplitude with 50 % probability of survival + 0,5 when column 6 = column 4 - 0

39、.5 when column 6 = column 3 step (here Ma, = 400 N) Column 6: Column 7: Column 8: C, A, E: Fa, Fa, = 3 500 N) : i X: Mati S standard deviation 11 BSI BS*?374 94 9 Lb24bb9 O425249 b35 9 IS0 3800:1993(E) 4 500 4000 z tL O +i U al 3500 a f o 5 u 3000 o 2 2 500 2468 Number of test piece- . Failure o Non

40、-failure - ai Load amplitude * Fa. N - b) - Figure 9 - Example of the execution and evaluation of fatigue tests according to the boundary method 7.2.3.3 Arc sine method The procedure for the arc sine method is similar to that for the boundary method. Carry out fatigue tests on several equidistant al

41、ternating load levels with the same number of test pieces per level. For each of these levels, calculate the corres onding probabilities of survival using the arcsin P p transformation, for example, = arcsin J- + arcsin J- Determine the transition range either graphically in a corresponding probabil

42、ity net or mathematically by determining a regression line after the corresponding transformation of the calculated values. 7.3 Development of complete Whler curve (SIN curve) For the development of a complete Whler curve, the results of the test according to 7.1.2 and 7.2.2 are represented graphica

43、lly in figure 1 O. 7.4 Combined test method 7.4.1 Number of test specimens At least 14 specimens are required for the test, that is 2 specimens for each of four stress amplitude lev- els (8 pieces in total) in order to determine the inclined part of the S/N curve, and 6 specimens in order to determi

44、ne the horizontal part because the staircase method requires a small number of specimens. Since the test does not always proceed, in practice, as shown in figure11 and there are some cases where more than 14 specimens are required, reserve some extra specimens. 12 BSI ElSS7774 94 m Lb24bb9 0425250 3

45、57 m IS0 3800:1993(E) 10 NG Number of stress cycles, N Figure 10 - Whler curve (S/N curve) o, =f(N) 13 BSI BS*7774 74 M 162Ybb7 0425251 293 IS0 3800.1993(E) 180 160 N g 140 z a” 6 120 3 E e 100 a c - Y L 4- ul ao 60 - - - - - - - - - - - - - - Failure o Non-failure at 5 x IO6 Horizontal part, 6 piec

46、es Staircase method I (53) (s5) Q 1 I 1 IlIlII I 1 I 111111 I I I IlilII 10 sxiob 105 5 x 105 io6 5 x 106 Number of stress cycles, N NOTE - The numbers in the figure show the order of test. Figure 11 - Example of basic pattern of combined test method with 14 specimens 7.4.2 Test in the finite life r

47、ange Test the first specimen at the stress amplitude level (1) = UM - AuaI. Test one specimen at a time in the order The test method for the finite life range (inclined part a(2) = ua(1) - AUaI, g(3) = ua(2) - AuaI, *a of the S/N curve) is as follows. , Predict the finite life strength uM and uAB of

48、 the specimen at N = 5 x lo4 and N = 1 x lo6 by referring to existing data on materials of the same class, specimens of the same shape and stress cycles of the same type. Obtain Au, = (uAA - uAB)/3. (Round off the numerical values.) Take this value of Aua as the initial set value for intervals of th

49、e test stress amplitude in the in- clined part, and take uAA + haaI (k = f 1, f 2, ) as the initial set valuefor the test stress amplitude level. by lowering the stress amplitude levels by Aua, each time until the first unbroken specimen is obtained”. In this case, check the value of AU, as the test pro- gresses, correct it and reset AuaI for subsequent lev- els, if necessary.) Test one specimen at each of the stress amplitude levels at which no specimen has been broken, among the four higher levels adjacent to the level2) at which t