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 Copyright Association Europeene des Constructeurs de Materiel Aerospatial Provided by IHS under license with AECMANot for ResaleNo reproduction or networking permitted without license fro
7、m IHS-,-,-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 . . . . Post-test checks Test report . a 9 Annex A (informative) - Use of thermocouples Annex B (informativ
8、e) - 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 Copyright Association Europeene des Constructeurs de Materiel Aerospatial Provided by IHS under license wi
9、th AECMANot for ResaleNo reproduction or networking permitted without license from IHS-,-,- STD-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 organiza
10、tion of this series is described in EN 4258. I Scope This standard applies to constant amplitude 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,
11、 methodology of test and presentation of results. It applies to uniaxially loaded tests carried 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 methodol
12、ogy could well be adopted to provide for such tests. The purpose of this specification is to 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 un
13、dated reference provisions from other publications. These normative references are cited at the 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
14、 incorporated in it by amendment or revision. For undated references the latest edition of the 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 s
15、tandardization - Links between types of EN standards and their use 1) Metallic materials: Tensile 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 Me
16、asurement of Bending in Uniaxial Low Cycle fatigue Testing 3) 1) Published as AECMA Prestandard 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 Laboratori
17、es - Executive Agency of the Depth of Trade the use of an optical measurement method is highly 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 c
18、ross sectional area. Applied stresses shall be calculated based on ambient temperature measurements 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. Copyright Ass
19、ociation Europeene des Constructeurs de Materiel Aerospatial Provided by IHS under license with AECMANot for ResaleNo reproduction or networking permitted without license from IHS-,-,- - STD-AECMA PREN 307i-ENGL 3998 E LU32311 0034488 T7T D Page 14 prEN 3874: 1998 6.4.1 Circular or rectangular secti
20、ons 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 In the case
21、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. Projection measureme
22、nt 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 calculatin
23、g 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 be reported
24、 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 insert the
25、 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 test piece s
26、hall 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 minimum period of
27、 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 during the he
28、ating 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. Copyright Association Europeene des Constructeurs de Materiel Aerospatial
29、Provided by IHS under license with AECMANot for ResaleNo reproduction or networking permitted without license from IHS-,-,- XTD-AECMA PREN 387LI-ENGL li8 I LO123Ll OOLLI489 70b = Page 15 prEN 3874: 1998 7.3 Test commencement 7.3. I Waveform optimisation The same waveform shall be retained throughout
30、 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 temperature rise more than 2 OC in the test piece. Unless the purpose of the test is to assess the effect of this
31、 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 between 95 YO and 100 % of the intended force range. On commencing cycling, the specified force shall not be adjust
32、ed 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 test, the force range or maximum force shall not be reduced. However, in the cases where the specified maximum a
33、nd 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 report. The achieved frequency shall be within f 10 % of the specified frequency. In the case of trapezoidal of trian
34、gular 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, whichever is smaller, and shall not introduce deviations from the specified waveform that exceed the limits defin
35、ed 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, whichever is greater, or 5 % of the intended force or 100 N, whichever is greater, and in the case of trapezoidal wa
36、veforms, 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 smooth and free from discontinuities. 7.3.2 Data recording Monitoring of the indicated test temperature throughout the
37、 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 minima is also kept. This may be achieved in part by the setting of machine force limit trips which indicates if a
38、n 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 exceeded. The criterion for failure is generally complete separation of the test piece. The cycle count attained is t
39、he 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 amplitude. Copyright Association Europeene des Constructeurs de Materiel Aerospatial Provided by IHS under license with
40、 AECMANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-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
41、s rnax., whichever is smaller Figure 5: Waveform optimisation Copyright Association Europeene des Constructeurs de Materiel Aerospatial Provided by IHS under license with AECMANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Page 17 prEN 3874: 1998 8 Post-test check
42、s 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 examined. NOTE: This ma
43、y 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 an invalid result,
44、 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 electron microscope
45、, 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 standard; - test piece id
46、entity, 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 load cycle, frequenc
47、y 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. Copyright Association Europeene des Constructeurs de Materiel Aerospatial Provided
48、 by IHS under license with AECMANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SiD.AECMA PREN 3874-ENGL 1778 1012311 0014492 LiTO m Page 18 prEN 3874: 1998 1 II 9.2 Additional information The following information shall be included in the test report: - material c
49、omposition, heat treatment, microstructure; - complete identification of the part or semi-finished product from which the test pieces are taken; - precise position and orientation 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 ident
