1、DEUTSCHE NORM December 1997 Axial load fatigue testing of threaded fasteners DIN 969 - ICs 21.060.1 O Supersedes DIN IS0 3800-1, March 1978 edition. Verbindungselemente mit Gewinde - Schwingfestigkeitsversuch bei Axialbelastung - Prfverfahren und Auswertung der Ergebnisse In keeping with current pra
2、ctice in standards published by the International Organization for Standardi- zation (ISO), a comma has been used throughout as the decimal marker. Foreword This standard has been prepared by Technical Committee Festigkeitsklassen Stahl of the Normenaus- schuss Mechanische Verbindungselemente (Faste
3、ners Standards Committee). It conforms in substance to IS0 3800 : 1993, except that the combined test method has not been included and details of the load verification stud for aligning the test Set-up have been changed (cf. sublause 5.5). Amendments This standard differs from DIN IS0 3800-1, March
4、1978 edition, in that details regarding the test Set-up have been amended and recommendations for the evaluation of results have been included (cf. clause 7). Previous edition DIN IS0 3800-1 : 1978-03. 1 Scope This standard specifies the conditions for carrying out axial load fatigue tests on thread
5、ed fasteners and gives recommendations for the evaluation of test results. Since any changes in the test conditions can significantly affect the results, the standard also specifies minimum requirements and calibration and centring control methods for the test equipment. 2 Normative references This
6、standard incorporates, by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text, and the titles of the publications are listed below. For dated references, subsequent amendments to or revisions of any of these publi
7、cations apply to this standard only when incorporated in it by amendment or revision. For undated references, the latest edition of the publication referred to applies. DIN EN 20273 Fasteners - Clearance holes for bolts and screws (IS0 273 : 1979) DIN EN 2401 4 Hexagon head bolts - Product grades A
8、and B (IS0 401 4 : 1988) DIN EN 24032 Hexagon nuts, style 1 - Product grades A and B (IS0 4032 : 1986) DIN EN 24033 Hexagon nuts, style 2 - Product grades A and B (IS0 4033 : 1979) DIN EN 28673 Hexagon nuts, style 1, with metric fine pitch thread- Product grades A and (IS0 8673 : 1988) DIN EN 28674
9、Hexagon nuts, style 2, with metric fine pitch thread- Product grades A and (IS0 8674 : 1988) Continued on pages 2 to Translation by DIN-Sprachendienst. In case of doubt, the German-language original should be consulted as the authoritative text. B B 1 No pari of this translation may be reproduced wi
10、thout the prior permission of V DeutschesInstitut fr Normunge. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany, s the exclusive right of sale for German Standards (DIN-Normen). Ref. No. DIN 969 : 1997-1 Englishpricegroup 08 Sales No. 0108 08.00 COPYRIGHT DIN DEUTSCHES Institut Fur Normung E.V.-
11、 EnglishLicensed by Information Handling ServicesPage 2 DIN 969: 1997-12 3 Quantities and symbols Table 1 Quantity Cross-sectional area at nominal minor diameter Ad3 = nd3A Stress area A, = 4 nd2 ad3P Nominal size of thread of load verification stud Basic minor diameter of thread H Basic pitch diame
12、ter of thread Nominal minor diameter of thread d3 = di - - 6 Diameter at the point of tangency of fillet Nominal thread diameter of the threaded test adaptor Clearance hole diameter Tensile load Tensile load at 0,2 % proof stress, R, Load amplitude (load level) Difference of load amplitudes in the t
13、ransition range Load level at endurance fatigue limit Mean load Height of fundamental triangle of thread Number of stress cycles Number of stress cycles in the transition range Failure probability Failure probability in the finite life range Failure probability in the transition range Thread pitch T
14、ensile strength Constant stress ratio (omin/omax) Width across flats of hexagons Standard deviation of fatigue load Standard deviation of fatigue strength Standard deviation of logarithm of fatigue life Coefficients of regression line for inclined part of S/N curve Stress amplitude Stress amplitude
15、at endurance fatigue limit Axial tensile stress Bending stress Mean stress Minimum stress Maximum stress Minimum stress at endurance fatigue limit Maximum stress at endurance fatigue limit Fatigue strength at N cycles Interval of stress amplitude in the finite life range (inclined part of S/N curve)
16、 Difference in levels of stress amplitude in the transition range l) For calculating mean stress and stress amplitude, the nominal values of either As or, if so agreed between customer and supplier, Ad, shall be used. COPYRIGHT DIN DEUTSCHES Institut Fur Normung E.V.- EnglishLicensed by Information
17、Handling ServicesPage 3 DIN 969 : 1997-1 2 4 Principle Fatigue tests serve to determine the fatigue strength properties of threaded fasteners (e.g. on the basis of a Whler curve (S/N curve). The fasteners to be tested are mounted in a fatigue testing machine and subjected to axial loading for a give
18、n number of stress cycles or until the test piece fails. The stress induced may be either a constant mean stress, o, or equal to a constant stress ratio, R,. The number of stress cycles is a function of the fastener material or the endurance fatigue strength of the fastener under test. Unless otherw
19、ise specified, failure of the test piece is defined as the complete sepa- ration of the fastener into two parts. The test conditions and evaluation procedures shall be selected with regard to the objective of the test and stated in the test report (cf. clause 8). 5 Apparatus 5.1 Testing machine The
20、testing machine shall be capable of maintaining the load to within I2 YO of the required values throughout the test and be equipped with a device for counting and recording the total number of cycles per test. It shall be calibrated at specified intervals to ensure this accuracy. The test frequency
21、shall not exceed 250 Hz. Loading of the specimen shall be sinusoidal. The machine shall be equipped with a device which prevents its automatic restarting after stopping due to electrical power failure. 5.2 Test fixtures The test fixtures shall be capable of transmitting an axial load to the specimen
22、. Design details of such fixtures are shown in figures 1 and 2. Where self-aligning devices are used, alignment shall be checked carefully. However, use of such devices is not recommended. +O,O7 A I r I Symmetrical 1 08 d- HRC 36 $0 40 -pi O In the above figure, d, is the clearance hole diameter, fi
23、ne series, as in DIN EN 20273; da is the diameter at the point of tangency of the fillet as in DIN EN 24014. Tolerances on perpendicularity and concentricity are in millimetres. Figure 1: Fixture without insert Symmetrical windows (optional) Counterbore (optional) 1, lllo,o251b 1 ,y HRC 36 to 40 a I
24、n the above figure, d, is the clearance hole diameter, fine series, as in DIN EN 20273; da is the diameter at the point of tangency of the fillet as in DIN EN 24014. Tolerances on perpendicularity and concentricity are in millimetres. Figure 2: Fixture with inset+) l) The surface may be case-hardene
25、d to a depth of 0,25 mm to 0,5 mm. The maximum hardness shall be 2) Use of an insert shall not affect the rigidity of the test fixture. 60 HRC, the minimum hardness exceeding that of the specimen by 5 HRC. COPYRIGHT DIN DEUTSCHES Institut Fur Normung E.V.- EnglishLicensed by Information Handling Ser
26、vicesPage 4 DIN 969: 1997-12 5.3 Internally threaded components The internally threaded components used shall be hexagon nuts of appropriate size and property class complying with DIN EN 24032, DIN EN 24033, DIN EN 28673 or DIN EN 28674, or a threaded test adapter as shown in figure 3. 5.4 Test wash
27、ers A test washer with countersunk hole may be used under the bolt head to provide clearance for the head-to- shank fillet, or the fixtures may be countersunk. The maximum diameter of the countersink shall be equal to da, with a + IT12 tolerance. The washer faces shall be parallel to within 0,Ol mm
28、(cf. figure 4). The washer material hardness shall exceed that of the specimen by not less than 5 HRC. Where a test washer is used, this shall be indicated in the test report (cf. subclause 8.4) 5.5 Alignment of test fixtures Alignment of the test fixtures shall be checked at regular intervals using
29、 two load verification studs with diameters equal to the nominal diameters of the largest and smallest fastener to be tested, each stud being provided with four strain gauges located at 90“ intervals on a common centreline around its axis and clamped into the test fixtures with inserts as shown in f
30、igure 5. The length of studs between inserts (when assembled) shall be equal to four times their diameter. When measured at 50 YO of the minimum breaking force required for fasteners of property class 12.9, the difference between the maximum of o, + o, and the nominal value of o, shall not exceed 6
31、YO of the latter (cf. figure 6). 6 Procedure Unless otherwise agreed, testing shall be carried out at ambient temperature, the load being applied centrally in the axial direction, disregarding the influence of any elasticity of the test Set-up on the stress to which the fastener is subjected. The ca
32、pacity of the testing machine shall be selected so that the maximum load on the specimen is equal to or greater than 10 YO of the maximum capacity of the machine. The bearing face of the nut or the face of the threaded adapter shall be located at least four pitches from the unthreaded portion of the
33、 shank and the nut thread shall be engaged, with a bolt length equal to at least 2P protruding beyond the nut (cf. figure 7). Test nuts shall be used only once. Test adapters may be used continually as long as they assemble freely on the externally threaded part and do not exhibit any damage. The sp
34、ecimen shall be assembled in the fixture without constraint, with no torsional stress being induced in the assembly by fitting the nut, .e. the load shall be induced by the testing machine only. The test frequency shall be selected so that the temperature of the specimen does not exceed 50 “C during
35、 testing. Suitable measures shall be taken to ensure that the loading conditions do not change during testing. i Not convex Tolerances on flatness, perpendicularity and con- centricity are in millimetres. Figure 3: Threaded test adapter (example) Figure 4: Test washer (assembled) 3) The tolerance cl
36、ass for the screw thread shall be 6H. COPYRIGHT DIN DEUTSCHES Institut Fur Normung E.V.- EnglishLicensed by Information Handling ServicesPage 5 DIN 969 : 1997-1 2 I I ! I h6/H6 fit I Not convex Key fo figure 1 Test fixture 2 Insert 3 Load verification stud Figure 5: Alignment of test fixtures Tensil
37、e load (F) 4F nd oax = 7 ob - 5 0,06 oax Cylindrical section of load verification stud Figure 6: Stress distribution in the load verification stud Figure 7: Location of test nut 7 Evaluation of results 7.1 General Fatigue strength values can be determined in the finite life range (failure of all spe
38、cimens before a prede- termined number of stress cycles has been achieved), in the transition range where, up to the predetermined number of stress cycles (in general 5 x 1 O6 to 5 x 1 O7), failures as well as non-failures will occur, or in the infinite life range with non-failures only (cf. figure
39、1 O). Depending on the objective of testing, the fatigue tests are to be carried out and evaluated according to two methods: a) A minimum number of stress cycles is achieved at a predetermined stress level in the finite life and transition ranges. b) The scatter and position of the finite life and t
40、ransition ranges are determined using statistical evalu- ation methods. Reproducibility of results is only ensured when testing and evaluation of results are carried out in the same manner. 7.2 Testing in the finite life range 7.2.1 A minimum of six specimens shall be tested, with each test being te
41、rminated once the specified number of stress cycles has been achieved. 7.2.2 Determining scatter and position of finite life range (cf. subclause 7.1 b) The scatter for a given number of stress cycles in the finite life range can economically only be approximated using statistical methods. For asses
42、sing the finite life range, fatigue testing shall be carried out at not less than two stress levels, one corresponding to 1,6 times and the other to 2,4 times the assumed fatigue strength. To enable a reliable assessment to be made of the 1 O YO, 50 YO and 90 YO probabilities of failure, a minimum o
43、f eight specimens shall be tested per stress level. Tests involving a minimum number of stress cycles (cf. subclause 7.la) COPYRIGHT DIN DEUTSCHES Institut Fur Normung E.V.- EnglishLicensed by Information Handling ServicesPage 6 DIN 969: 1997-12 No. of specimen (i) Number of stress cycles, N x 1 O3
44、(in ascending order) Probability of failure, pf, as a percentage (cf. equation (1) The scatter in the finite life range at one stress level can be determined on distribution in the Gaussian probability net using the following equation: 1 2 3 4 5 6 7 8 178 271 280 305 405 11 5 129 169 8 20 32 44 56 6
45、8 80 92 - 1 O0 pf=- 3i - 1 3n + 1 the basis of the normal Gaussian (1 1 where pf is the estimated failure probability in the finite life range; i is the ordinal number of a specimen assigned to a stress level; y1 is the number of specimens tested per stress level. EXAMPLE: y1 = 8 bolts are tested wi
46、th a constant stress level, o, of 150 N/mm2. The stress cycles reached until failure are, in chronological order: N = (169, 178, 271, 129, 405, 11 5, 280, 305). 1 O3 First, the numbers of stress cycles are arranged according to size, and the specimen number i assigned to them. The specimen with the
47、lowest y1 value shall be given no. 1 and the nth specimen (with the highest number of stress cycles), no. 8. This results in the order or evaluation system given in table 2. Following this, the numbers of stress cycles belonging to the respective probabilities of failure, pf, are plotted in a Gaussi
48、an probability net (cf. figure 8) and a regression line is drawn from which stress cycles N, N, and N, can be derived. EXAMPLE : N, = 11 O x 103, N, = 21 3 x 103, and N, = 41 5 x 1 O3 (.e. 1 O % of all specimens are expected to fail within 11 O x 1 O3 stress cycles, 50 % within 213 x 1 O3 stress cyc
49、les, and 90 % within 415 x 1 O3 stress cycles). The scatter in the finite life range can then be determined on the basis of the numbers of stress cycles achieved for the second stress level. 7.3 Tests in the transition range or infinite life range 7.3.1 For checking whether the requirement for a minimum number of stress cycles is satisfied, not less than six specimens shall be tested at the specified stress level, with each test being terminated once the specified number of stress cycles has been achieved (generally, 5 x 1 O6 to 5 x 107). Achieving a given numbe
