1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS EN 3873:2010Aerospace series Testmethods for metallic materials Determination of fatiguecrack growth rates usingCorner-Cracked (CC) test piecesBS EN 3873:2010 BRITISH STANDARD
2、National forewordThis British Standard is the UK implementation of EN 3873:2010.The UK participation in its preparation was entrusted to TechnicalCommittee ACE/61/-/6, Mechanical Testing of Metallic Materials forAerospace Purposes.A list of organizations represented on this committee can beobtained
3、on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2011ISBN 978 0 580 53262 7ICS 49.025.05; 49.025.15Compliance with a British Standard cannot confer immunity fromlegal obligations.
4、This British Standard was published under the authority of theStandards Policy and Strategy Committee on 28 February 2011.Amendments issued since publicationDate Text affectedBS EN 3873:2010EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 3873 November 2010 ICS 49.025.05; 49.025.15 English Versi
5、on Aerospace series - Test methods for metallic materials - Determination of fatigue crack growth rates using Corner-Cracked (CC) test pieces Srie arospatiale - Mthodes dessais applicables aux matriaux mtalliques - Dtermination de la vitesse de propagation de fissure en fatigue laide dprouvettes ave
6、c fissure en coin Luft- und Raumfahrt - Prfverfahren fr metallische Werkstoffe - Ermittlung der Rifortschritts- Geschwindigkeit an Cornercrackproben (Eckanris) This European Standard was approved by CEN on 30 July 2010. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which
7、stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member. This Europ
8、ean Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions. CEN members are
9、 the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden
10、, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels 2010 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Re
11、f. No. EN 3873:2010: EBS EN 3873:2010EN 3873:2010 (E) 2 Contents Page Foreword 3Introduction . 41 Scope 52 Normative references 53 Symbols and abbreviations 54 General 75 Resources. 86 Test pieces . 97 Procedures . 118 Health and safety . 149 Evaluation of results . 1410 Test record . 16Annex A (nor
12、mative) Information on measuring crack depths in corner-crack test pieces with the direct-current Potential-drop method 18Annex B (normative) Stress-intensity function for corner-crack test pieces 22Annex C (normative) Guidelines on test piece handling and degreasing 24BS EN 3873:2010 EN 3873:2010 (
13、E) 3 Foreword This document (EN 3873:2010) has been prepared by the Aerospace and Defence Industries Association of Europe - Standardization (ASD-STAN). After enquiries and votes carried out in accordance with the rules of this Association, this Standard has received the approval of the National Ass
14、ociations and the Official Services of the member countries of ASD, prior to its presentation to CEN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by May 2011, and conflicting national standards s
15、hall be withdrawn at the latest by May 2011. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. According to the CEN/CENELEC Internal Reg
16、ulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, M
17、alta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. BS EN 3873:2010 EN 3873:2010 (E) 4 Introduction This standard and its parts belong to the general organization of the ASD collection of metallic material standards for aerospa
18、ce applications BS EN 3873:2010 EN 3873:2010 (E) 5 1 Scope This standard specifies the requirements for determining fatigue crack growth rates using the corner-crack (CC) test piece. Crack development is measured using a potential-drop system, and the calculated crack depths can be corrected via mar
19、ker bands created on the fracture surface during the test. Results are expressed in terms of the crack-tip stress-intensity range (K), with crack depths and test stress level noted. 2 Normative references The following referenced documents are indispensable for the application of this document. For
20、dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 2002-002, Aerospace series Metallic materials Test methods Part 002: Tensile testing at elevated temperature EN ISO 7500-1, Metallic material
21、s Verification of static uniaxial testing machines Part 1: Tension/compression testing machines Verification and calibration of the force-measuring system (ISO 7500-1:2004) EN ISO 3785, Metallic materials Designation of test specimen axes in relation to product texture (ISO 3785:2006) ASTM E 647-200
22、8, Standard test method for measurement of fatigue crack growth rates 1)ASTM E 1012-2005, Verification of test frame and specimen alignment under tensile and compressive axial force application 1)3 Symbols and abbreviations a Crack depth. The crack depth a is the distance from the extrapolated origi
23、nal corner containing the notch to the centre of the crack front (45 position). For the calculation of stress-intensity factor, the crack length must be given in metres aeFinal crack depth (in millimetres) aiInitial crack depth (in millimetres) amMeasured crack depth (optical, post-test fracture sur
24、face micrography or with SEM) avCalculated (Potential) crack depth is the average crack depth due to the averaging nature of the potential measurement method. Calculation involving average lengths measured at several positions along the crack front are best for correlation with the potential measure
25、ments (in millimetres) a Crack growth increment (in millimetres) da/dN Fatigue crack growth rate (FCGR) (in metres per cycle) W Test piece width (in millimetres) 1) Published by: American Society for Testing and Materials (ASTM), http:/www.astm.org/. BS EN 3873:2010 EN 3873:2010 (E) 6 a/W Normalized
26、 crack depth (in millimetres/millimetres) f Frequency (in Hertz) E Youngs modulus (in gigapascals) K Stress-intensity factor (general) The stress-intensity factor K is a load parameter which characterises the stress field at the crack tip. It is a function of load, crack depth and test piece geometr
27、y (in MPa m) Kmax.Maximum value of K during a loading cycle, corresponding to the maximum tensile force applied (in MPa m) Kmin.Minimum value of K during a loading cycle (in MPa m) K Range of K during a loading cycle = Kmax. Kmin.= (1 R)*Kmax. (in MPa m) KeffEffective range of K, due to crack closur
28、e-induced reduction applied K (in MPa m) KthFatigue crack growth threshold The asymptotic value of K for which da/dN approaches zero. For most materials the operational threshold is defined as the K corresponding to 10-7m/cycle. When reporting Kth, the corresponding lowest decade of near threshold d
29、ata used in its determination must be given C Normalized K-gradient C = (1/K dK/da). For load-shedding to attain a desired initial K, C defines the fractional rate of change of K with increasing crack depth a. C = 1/K dK/da = 1/Kmax. dKmax./da = 1/Kmin. dKmin./da = 1/K dK /da, (in mm-1) N Number of
30、loading cycles Stress cycle (fatigue cycle, load cycle) is the smallest segment of the loading waveform spectrum which is repeated periodically N Number of stress cycles between two marker cycles NmNumber of stress cycles in a marker cycle N Stress cycle difference r Notch radius (expressed in milli
31、metres) FmMean force (expressed in kilonewtons) Fmax.Maximum tensile force applied to the test piece during a cycle (expressed in kilonewtons) Fmin.Minimum tensile force (in kilonewtons) F Force range (in kilonewtons), F = Fmax. Fmin.q Resolution of crack depth measuring system (expressed in millime
32、tres) R Force ratio (= Fmin./Fmax.= Kmin./Kmax.) R*mRatio Fmin./Fmax.during a marker cycle Rp0,2 % offset yield strength (Proof Stress Rp0,2) at test temperature (expressed in megapascals) BS EN 3873:2010 EN 3873:2010 (E) 7 RmTensile strength at test temperature (expressed in megapascals) f Flow str
33、ess here defined as the arithmetic mean of Rpand Rm(expressed in megapascals) Z Axial distance from crack plane to each wire used for potential measurement (expressed in millimetres) (2Z = wire separation distance) 4 General 4.1 The corner-crack (CC) test piece is useful in determining da/dN for com
34、ponents where the cracks usually appear at a corner, such as in holes in turbine disks. The determination involves the use of an axially-loaded test piece of square or rectangular cross-section. It may be loaded in tension and compression for positive and negative stress ratio testing if suitable en
35、d designs permit backlash-free loading. A carefully defined and produced notch or a small arc strike enables cracking to be initiated at the centre of the reduced section. A fatigue crack is induced at the root of the notch by cyclic loading, and its growth is monitored by a suitable method, e.g. po
36、tential drop techniques. As the crack grows, the force range applied to the test piece is maintained or reduced in a controlled manner until the cracks are of sufficient depth for the influence of the notch and the crack initiation method to be negligible, and the K has reached the lowest level of i
37、nterest. The test is then carried out. The force range is maintained constant and the crack depth recorded as a function of elapsed cycles. These data are then subjected to numerical analysis, enabling da/dN to be determined as a function of K. 4.2 The majority of metallic materials can be tested us
38、ing the method described here, provided that the force applied is such as to ensure that the plastic zone in front of the crack tip is small in relation to the remaining cross section (linear-elastic criterion). 4.3 The test piece used here is a corner-crack (CC) test piece. See Figure C.1. 4.4 In t
39、he standard crack-growth test the load amplitude is assumed to be constant throughout the test, after the required K level and R-ratio is reached. Another load range can be added if certain transient effects are to be investigated. 4.5 The range of the stress-intensity factor K is: K = Kmax. Kmin.(1
40、) where the ratio R R = min.max.KK (2) applies. From Equations (1) and (2) it follows that, for R 0, K = (1 R) Kmax.(3) 4.6 The reference point for measuring the crack depth with CC test pieces is the original corner of the test piece, determined by the projections of the sides of the test piece on
41、the fracture surface adjacent to the notch. Possible rounding of the corner during test piece manufacture will result in this reference point being no longer on the fracture surface. This rounding must be determined to obtain a “Zero-point offset” between the reference point and the rounded corner w
42、here the measurement wire is welded, which is used in the calibration of the potential-drop measurements. BS EN 3873:2010 EN 3873:2010 (E) 8 4.7 The purpose of the crack propagation measurements is to allocate the relevant load cycles N to the crack depth a. The measurements (a-N points, see Figure
43、C.2) are normally evaluated in the form of a da/dN versus K curve (see Figure C.3). It is not always the case that the crack propagation can be described by the range of stress-intensity factor K. If it cannot be so described, other laws can be applied, e.g. crack growth rate as a function of Kmax.
44、4.8 The crack growth behaviour depends on a number of parameters. The framework within which the test is to be carried out needs to be precisely defined in order to avoid undesired effects on the results. The most important factors affecting the results are: a) temperature and environment; b) load s
45、pectrum. The test parameters R, dwell time and loading frequency must be defined and recorded before testing commences. The results can also be affected by the loading history, including interruption times, e.g. stop and restart of cycling to check surface crack length or other parameters, work stop
46、page at weekends, etc. These should be recorded. c) Residual stresses Residual stresses are usually ignored, as they are difficult to determine, and a duplication of the residual stresses in a component is very difficult to obtain in a test piece. Their presence in a component will affect the life o
47、f the component, and should be regarded in the use of the crack growth data. The presence of unexpected residual stresses in the test piece may be witnessed in an asymmetry of the crack front. 4.9 Applicability of results The crack-growth measurements are generally used for: a) investigating the inf
48、luence of fatigue-crack growth on the predicted life of a component, or for evaluating the crack-growth resistance of a material or heat-treat condition; b) defining the requirements of NDT testing; and c) macroscopic quantitative determination of various factors (e.g. load, microstructure, manufact
49、ure, etc.). 5 Resources 5.1 Test machine 5.1.1 General Tests shall be performed with a feed-back load-controlled servohydraulic or electromechanical test system designed for smooth loading from first load cycle without exceeding the desired Fmax. The system should be capable of halting the cycling at desired intervals of cycles or crack depth, at a desired potential level, or at will, to enable measurements of the optical crack depth, potential or thermal potential,
