1、AECMA STANDARD NORME AECMA AECMA NORM Edition approved for publication prEN 3874 Edition P 1 April 1998 C5 Chairman Comments should be sent within six months after the date of Dublication to PUBLISHED BY THE EUROPEAN ASSOCIATION OF AEROSPACE INDUSTRIES (AECMA) Gulledelle 94 - 6-1 200 BRUXELLES - Tel
2、. (+32i 2 775 81 1 O - Fax. (+32) 2 775 81 11 ICs: Descriptors: ENGLISH VERSION Aerospace series Test methods for metallic materials Constant amplitude force-controlled low cycle fatigue testing Srie arospatiale Mthodes dessais applicables aux matriaux mtalliques Essais de fatigue oligocyclique en c
3、ontrainte impose Luft- und Raumfahrt Prfverfahren fr metallische Werkstoffe Niedriglactwechselermdung (LCF) im kraftgesteuerten Versuch This “Aerospace Series“ Prestandard has been drawn up under the responsibility of AECMA The European Association of Aerospace lndustriesl. It is published on green
4、paper for the needs of AECMA-Members. It has been technically approved by the experts of the concerned Technical Committee following comment by the Member countries. Subsequent to the publication of this Prestandard, the technical content shall not be changed to an extent that interchangeability is
5、affected, physically or functionally, without re-identification of the standard. After examination and signature of the AECMA Standard Checking Centre (NPSI and formal agreement of the Official Services of the Member countries it will be submitted as a draft European Standard to CEN (European Commit
6、tee for Standardization) for formal vote. I 998-04-30 Mr Evetts AECMA Gulledelle 94 B-1200 BRUXELLES aecrna 1998 Page 2 prEN 3874: 1998 Contents list Page Introduction O Scope . . 1 . Normative refer . 2 Principle 3 . . 4 Definitions and symbols . 5 Test equipment . . 6 Test piece 7 Test method . .
7、. . Post-test checks Test report . a 9 Annex A (informative) - Use of thermocouples Annex B (informative) - Test piece preparation . Annex C (informative) - Guidelines on test piece handling and degreasing Annex D (informative) - Guidelines on producing an S-N curve 3 3 6 10 14 17 17 19 20 22 23 - S
8、TD-AECMA PREN 3874-ENGL 1998 = 1012313 OU34477 194 Page 3 prEN 3874: 1998 O Introduction This standard is part of the series of EN metallic material standards for aerospace applications. The general organization of this series is described in EN 4258. I Scope This standard applies to constant amplit
9、ude force-controlled low cycle fatigue (LCF) testing of metallic materials governed by EN Aerospace standards. It defines the mechanical properties that may need to be determined, the equipment, test pieces, methodology of test and presentation of results. It applies to uniaxially loaded tests carri
10、ed out on plain or notched test pieces under ambient and elevated temperatures. It is not intended to cover the testing of more complex test pieces, full scale components or structures, although the methodology could well be adopted to provide for such tests. The purpose of this specification is to
11、ensure the comparability and reproduceability of the test results. It does not cover the evaluation or interpretation of the results. 2 Normative references This European Standard incorporates by dated or undated reference provisions from other publications. These normative references are cited at t
12、he appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of th
13、e publication referred to applies. IS0 3785 EN 4258 EN 10002-2 ASTM E 1 O1 2A: 1993 NPL MMS 001 : 1995 Steel - Designation of test piece axes Aerospace series - Metallic materials - General organization of standardization - Links between types of EN standards and their use 1) Metallic materials: Ten
14、sile testing - Part 2: Verification of the force measuring systems of the tensile testing machine Standard Practice for Verification of Specimen Alignment Under Tensile Loading 2) Code of Practice for the Measurement of Bending in Uniaxial Low Cycle fatigue Testing 3) 1) Published as AECMA Prestanda
15、rd at the date of publication of this standard 2) This standard is published by American Society for Testing and Materials (ASTM), i916 Race Street - Philadelphia PA 19103 USA 3) National Physical Laboratories - Executive Agency of the Depth of Trade the use of an optical measurement method is highl
16、y recommended. The dimensions (outer diameter and possibly inner diameter) of the test section shall be measured at three positions along the gauge length. The average of these values are used to calculate cross sectional area. Applied stresses shall be calculated based on ambient temperature measur
17、ements and no compensation is to be made for the change in section and effective stress due to heating for elevated temperature tests, or due to deformation of the test section during the test. - - STD-AECMA PREN 307i-ENGL 3998 E LU32311 0034488 T7T D Page 14 prEN 3874: 1998 6.4.1 Circular or rectan
18、gular sections The diameter or width and thickness of the test section shall be measured at three positions on the gauge length. The average of these values are used to calculate cross sectional area. For continuous radius test sections the minimum diameter shall be used. 6.4.2 Notched test pieces I
19、n the case of rectangular sections, the average thickness of the test piece measured at three equidistant positions in the plane of the notch root, and the average value of the notch root separation measured at each side of the test piece, shall be used in calculating cross-sectional area. Projectio
20、n measurement equipment shall be used in determining the notch separation. In the case of circular notched sections, the minimum diameter shall be determined by a projection measurement method from at least two directions with an angular separation of 90. The average of these values is to be used in
21、 calculating the cross-sectional area. For both geometries the average notch root radius shall be similarly measured. The Kt value quoted may be affected to varying degrees by variations in the notch dimensions, depending on the method used to calculate it. The accuracy of the value of the Kt shall
22、be reported if the tolerance on machining the notch geometry affects the average Kt value by more than f 5 %. If the variability of the Kt value exceeds rt 5 % then the notch geometry shall be measured and reported with each test piece. , 7 Test method 7.1 Test piece insertion The method employed to
23、 insert the test piece into the test fixture shall not jeopardise the alignment mechanisms, surface finish integrity or material properties. Excessive twisting shall be avoided and compressive forces within the test section limited to a maximum of 50 % of yield strength. 7.2 Test piece heating The t
24、est piece shall be heated to the specified temperature at a rate not exceeding 50 OCmin and shall be maintained at that temperature for a sufficient period to ensure that the temperature has fully stabilized. In general a period of 30 s per mm2 of cross-sectional area shall be allowed, with a minimu
25、m period of 15 min. If the total time to reach and stabilize at the test temperature exceeds 12 h, then the actual soak time shall be reported. During the heating process, the temperature of the test piece shall not exceed the specified temperature within the tolerances outlined in 5.6. Expansion du
26、ring the heating process shall not result in compressive forces being applied to the test piece. The force applied to the test piece shall therefore be controlled throughout the heating process and shall not exceed 10 % of yield stress. XTD-AECMA PREN 387LI-ENGL li8 I LO123Ll OOLLI489 70b = Page 15
27、prEN 3874: 1998 7.3 Test commencement 7.3. I Waveform optimisation The same waveform shall be retained throughout the whole test programme unless the aim of this programme is to study the effect of the waveform on the behaviour of the material. The frequency shall be such that it does not cause any
28、temperature rise more than 2 OC in the test piece. Unless the purpose of the test is to assess the effect of this parameter, the initial loading shall be in the tensile direction. Prior to commencing cycling the waveform generator shall be set such that the achieved maximum and minimum forces are be
29、tween 95 YO and 100 % of the intended force range. On commencing cycling, the specified force shall not be adjusted in order to achieve the precise intended force cycle. Actual forces and R ratios shall be recalculated based on measured values. If the test piece is overloaded during the start of the
30、 test, the force range or maximum force shall not be reduced. However, in the cases where the specified maximum and minimum forces are mandatory, the specified force shall be adjusted so that the correct maxima and minima are achieved within the first 10 cycles. This shall be stated in the test repo
31、rt. The achieved frequency shall be within f 10 % of the specified frequency. In the case of trapezoidal of triangular waveforms, the discontinuities at the nodes shall be well defined and angular. Any adjustment to the waveform shape shall be complete within 100 cycles or 1 % of the expected life,
32、whichever is smaller, and shall not introduce deviations from the specified waveform that exceed the limits defined below. Thereafter it shall remain unadjusted throughout the duration of the test. Oscillation and rounding features at the nodes shall not exceed 1 % of the intended force or 20 N, whi
33、chever is greater, or 5 % of the intended force or 100 N, whichever is greater, and in the case of trapezoidal waveforms, shall not constitute more than 20 YO of the hold time or a maximum of 0,2 s, whichever is smaller (see figure 5). In the case of sinusoidal waveforms, the waveform shall be smoot
34、h and free from discontinuities. 7.3.2 Data recording Monitoring of the indicated test temperature throughout the test shall be employed in order to ensure that the test temperature has remained within the limits specified in 5.6. NOTE: It is recommended that a monitor of achieved force maxima and m
35、inima is also kept. This may be achieved in part by the setting of machine force limit trips which indicates if an overload or underload has occurred. 7.4 Test termination Tests shall be continued without interruption until the test piece fails or until a predetermined number of cycles has been exce
36、eded. The criterion for failure is generally complete separation of the test piece. The cycle count attained is the fatigue life. It cannot be assumed that tested but unbroken test pieces have not suffered fatigue damage. Those test pieces therefore shall not be retested at a different stress amplit
37、ude. Page 16 prEN 3874: 1998 1 Specified hold time y I 1 % of the intended force or 20 N, whichever is greater y I 5 % of the intended force or 1 O0 N, whichever is greater x I 20 % of the specified hold time or 0,2 s rnax., whichever is smaller Figure 5: Waveform optimisation Page 17 prEN 3874: 199
38、8 8 Post-test checks 8.1 Accuracy of control parameters In order to validate the test, the test temperature record shall be examined to ensure that there were no deviations outside the limits specified in 5.6. If a record of achieved force maxima and minima has been kept then this shall also be exam
39、ined. NOTE: This may be achieved by checking that the set force trips have not been exceeded. 8.2 Examination of fracture surface The failure position along the length of the test section shall be noted. Failure of the test piece at a transition radius or outside the test section shall be considered
40、 an invalid result, as failure caused by initiation at the corner of a rectangular section test piece. Examination of the fracture surface shall also be made to establish whether the crack initiated from a surface blemish or other obvious feature. NOTE: A more thorough examination, using a scanning
41、electron microscope, may be necessary to see if the crack initiates from surface scratches generated by poor machining or handling procedures, or thermocouple interference and to identify the initiation site (inclusion, porosity, .). 9 Test report 9.1 Essential information - reference to this standa
42、rd; - test piece identity, drawing number, dimensions and reference to a documented method of preparation; - stress concentration factor plus method and source of its determination for notched test pieces; - temperature of the test plus any deviation from the specified limits; - waveform, shape of l
43、oad cycle, frequency of application and R ratio; - total stress range, noting any initial adjustments made; - cycles to failure and position of failure; - any other occurrences that may affect the test result e.g. test suspensions, etc. SiD.AECMA PREN 3874-ENGL 1778 1012311 0014492 LiTO m Page 18 pr
44、EN 3874: 1998 1 II 9.2 Additional information The following information shall be included in the test report: - material composition, heat treatment, microstructure; - complete identification of the part or semi-finished product from which the test pieces are taken; - precise position and orientatio
45、n of each test piece; - predominant material orientations due to the manufacturing process, such as rolling direction or casting direction; - testing machine, heating device; - fractographic examination of the two fracture surfaces to identify the initiation site and to determine any unusual causes
46、of failure that might invalidate the test result. 9.3 Presentation of results The most popular presentation of results for a series of related tests is via a graphical S-N diagram. Its construction involves plotting the number of cycles to failure as the abscissa and the stress range for a given for
47、ce ratio as the ordinate. A logarithmic scale is commonly used for the number of cycles and a linear scale for the stress axis (see figure 6). 850 800 II 750 h lu a g 700 $ 650 i! G L z S 600 550 1 O0 1 O00 1 O000 Cycles To failure 100000 1000000 Figure 6: Typical S-N diagram STD-AECMA PREN 3874-*EN
48、GL 191d II lUL231L 001LiLi73 337 Page 19 prEN 3874: 1998 Annex A (informative) Use of thermocouples A. 1 Calibration Thermocouples shall be made from batches of wire that have been calibrated over the whole working range against the recognised fixed points for thermocouples calibration or by compari
49、son with a similarly calibrated and carefully maintained secondary standard reference thermocouple. A.2 Use For short test sections ( 25 mm), two thermocouples equally spaced along the test section are generally sufficient to guarantee uniformity of the temperature of the test piece unless prior verification has been performed according to 5.6.1. For longer test sections at least three thermocouples shall be used. The thermocouple junctions shall be maintained in close thermal contact with the surface of the test piece and be suitably screened
