1、BRITISH STANDARD BSENISO 7539-2:1995 Incorporating Amendment No. 1 Corrosion of metals and alloys Stresscorrosion testing Part 2: Preparation and use of bent-beam specimens The European Standard EN ISO 7539-2:1995 has the status of a British StandardBSENISO7539-2:1995 This British Standard, having b
2、een prepared under the directionof the Iron and Steel Standards Policy Committee andthe Non-ferrous Metals Standards Policy Committee, waspublished under the authorityof the Board of BSI andcomes into effect on 31July1990 BSI 03-2000 The following BSI references relate to the work on this standard:
3、Committee reference ISM/NFM/8 Draft for comment 88/36939 DC ISBN 0 580 18792 6 Committees responsible for this BritishStandard The preparation of this British Standard was entrusted by the Iron and Steel Standards Policy Committee (ISM/-) and Non-ferrous Metals Standards Policy Committee (NFM/-) to
4、Technical Committee ISM/NFM/8, upon which the following bodies were represented: Aluminium Federation British Gas plc British Steel Industry Department of Trade and Industry (National Physical Laboratory) Department of Transport (Transport and Road Research Laboratory) Electricity Supply Industry in
5、 England and Wales Institution of Corrosion Science and Technology Institution of Structural Engineers Society of Chemical Industry United Kingdom Atomic Energy Authority Welding Institute Amendments issued since publication Amd. No. Date Comments 8714 October 1995 Indicated by a sideline in the mar
6、ginBSENISO7539-2:1995 BSI 03-2000 i Contents Page Committees responsible Inside front cover National foreword ii Foreword 2 1 Scope 3 2 Normative references 3 3 Definitions 3 4 Principle 3 5 Specimens 3 6 Procedure 8 7 Assessment of results 8 8 Test report 9 Figure 1 Constant strain loading test spe
7、cimens 5 Publications referred to Inside back coverBSENISO7539-2:1995 ii BSI 03-2000 National foreword This Part of BSENISO7539 has been prepared under the direction of the Engineering Sector Board. It is identical with ISO7539-2:1989 Corrosion of metals and alloys Stress corrosion testing Part2: Pr
8、eparation and use of bent-beam specimens, published by the International Organization for Standardization (ISO). BS EN ISO 7539 comprises the following Parts: Part 1: General guidance on testing procedures; Part 2: Preparation and use of bent-beam specimens; Part 3: Preparation and use of U-bend spe
9、cimens; Part 4: Preparation and use of uniaxially loaded tension specimens; Part 5: Preparation and use of C-ring specimens; Part 6: Preparation and use of pre-cracked specimens; Part 7: Slow strain rate testing. A British Standard does not purport to include all the necessary provisions of a contra
10、ct. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard ISO 7539-1:1987 BS EN ISO 7539-1 Corrosion of metals and
11、alloys Stress corrosion testing Part 1:1995 General guidance on testing procedures (Identical) ISO 7539-4:1989 Part 4:1995 Preparation and use of uniaxially loaded tension specimens (Identical) Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, theENISO titl
12、e page, pages2 to10, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 7539-2 May 1995 I
13、CS 77.060 Descriptors: Metals, alloys, tests, corrosion tests, stress corrosion tests, test specimens English version Corrosion of metals and alloys Stress corrosion testing Part2: Preparation and use of bent-beam specimen (ISO 7539-2:1989) Corrosion des mtaux et alliages Essais de corrosion sous co
14、ntrainte Partie2:Prparation et utilisation des prouvettes pour essais en flexion (ISO7539-2:1989) Korrosion der Metalle und Legierungen Prfung der Spannungsrikorrosion Teil2:Vorbereitung und Anwendung von Biegeproben (ISO 7539-2:1989) This European Standard was approved by CEN on 1995-04-08. CEN mem
15、bers are bound to comply with the CEN/CENELEC Internal Regulations which 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 applicat
16、ion to the Central Secretariat or to any CEN member. This European 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 Central Secretariat has the
17、same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardiz
18、ation Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1995 All rights of reproduction and communication in any form and by any means reserved in all countries to CEN and its members. Ref. No. EN ISO 7539-2:1995 EENISO7539-2:1995
19、BSI 03-2000 2 Foreword This European Standard has been taken over by the Technical Committee CEN/TC262, Protection of metallic materials against corrosion, from the work of ISO/TC156, Corrosion of metals and alloys, of the International Organization for Standardization (ISO). This European Standard
20、shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by November 1995, and conflicting national standards shall be withdrawn at the latest by November1995. According to the CEN/CENELEC Internal Regulations, the following countr
21、ies are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, United Kingdom.ENISO7539-2:1995 BSI 03-2000 3 WARNING Bent-beam specimens made from high str
22、ength materials may fracture rapidly; pieces may fly off at high velocity and can be dangerous. Personnel installing and examining specimens must be made aware of this possiblity and be protected against injury. 1 Scope 1.1 This part of ISO 7539 covers procedures for designing, preparing and using b
23、ent-beam test specimens for investigating the susceptibility of a metal to stress corrosion. The term “metal” as used in this part of ISO7539 includes alloys. 1.2 Bent-beam specimens may be used to test a variety of product forms. They are used principally for sheet, plate or flat extruded material,
24、 which conveniently provides flat specimens of rectangular cross-section, but may also be employed for cast material, wire or rod, or for machined specimens of circular cross-section. They can also be used for parts joined by welding. 1.3 Since the preparation of the specimens and the apparatus used
25、 for stressing them are both simple and inexpensive, bent-beam specimens are especially suitable for multiple testing and for atmospheric stress corrosion tests. 1.4 Bent-beam specimens are usually tested under nominally constant strain conditions but nominally constant load conditions may be employ
26、ed. In either case local change of curvature in the specimen when cracking occurs results in changing conditions during crack propagation. The “test stress” is taken as the highest surface tensile stress existing at the start of the test. 2 Normative references The following standards contain provis
27、ions which, through reference in this text, constitute provisions of this part of ISO7539. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO7539 are encouraged to investigate the possibility of ap
28、plying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 7539-1:1987, Corrosion of metals and alloys Stress corrosion testing Part 1: General guidance on testing procedures. ISO 7539-4:1989, Corrosion
29、of metals and alloys Stress corrosion testing Part 4: Preparation and use of uniaxially loaded tension specimens. 3 Definitions For the purposes of this part of ISO7539, the definitions given in ISO7539-1 are applicable. 4 Principle 4.1 The test consists of applying a bending stress to a beam specim
30、en of rectangular or circular section and exposing the stressed specimen to a specified test environment. 4.2 The magnitude of the resultant applied tensile stress in the outer fibres of the bent-beam specimen is calculated from the dimensions and modulus of elasticity of the specimen and the bendin
31、g deflection, as described in5.4. 4.3 Bent-beam specimens are used only for testing at stress levels below the elastic limit since the formulae used for calculating stress in bent beams apply only within the elastic range. 4.4 The time required for cracks to appear after exposure of stressed specime
32、ns to the test environment or the threshold stress below which cracks do not appear can be used as a measure of the stress corrosion resistance of the material in the test environment at the stress level employed. 4.5 Wide variations in test results may be obtained for a given metal and environment
33、even when testing nominally identical specimens and the replication of tests is frequently necessary. 4.6 The possibility of relaxation during the exposure period should be considered especially when specimens are exposed at elevated temperatures. Relaxation can be estimated if creep data are availa
34、ble for a simultaneous effect of the test environment. The difference in thermal expansion should also be considered. 5 Specimens 5.1 General 5.1.1 Identification marks or numbers should be permanently inscribed at each end of the specimen. This is the region of lowest stress and the identification
35、marks will therefore not initiate cracking. 5.1.2 Specimens for determination of mechanical properties shall be taken from the same heat treatment batch, and preferably from the same piece of material, as the stress corrosion specimens. 5.2 Types of specimens 5.2.1 Bent-beam stress corrosion specime
36、ns are usually flat strips of metal of uniform rectangular cross-section and uniform thickness. They may alternatively be lengths of wire or rod of uniform circular cross-section.ENISO7539-2:1995 4 BSI 03-2000 5.2.2 Bent-beam stress corrosion tests may also be carried out on specimens having a gauge
37、 length of uniform rectangular or circular cross-section with threaded ends of larger cross-section as described in ISO 7539-4. 5.3 Surface finish 5.3.1 Wire or rod specimens and flat specimens cut from sheet, plate and extruded sections may be tested with the original surface retained. This is ofte
38、n desirable as the structure of the original surface may be different from that of the layers of metal beneath. 5.3.2 If it is desired to exclude the effects of variations in the original surface conditions for a comparison of different alloys, the specimens should be finished by grinding or machini
39、ng to a depth of at least0,25mm. This is usually sufficient to eliminate original surface imperfections without completely removing any outer recrystallized layer. The maximum depth of machining or grinding of the surface should be decided after studying the structure of the material as shown in an
40、etched metallographic section. It is desirable to remove the required amount of metal in several steps by alternatively machining or grinding opposite surfaces. This practice minimizes warping due to unequal residual stresses introduced by machining. All edges should be similarly ground or machined
41、to remove any cold worked material remaining from shearing. 5.3.3 Chemical or electrochemical treatments are generally inappropriate for flat rectangular section specimens as attack at the edges tends to be greater and less easy to control than on the faces. 5.3.4 If chemical or electrochemical trea
42、tments are employed, care must be taken to ensure that the conditions used do not result in selective phase attack on the metal or leave a deposit of undesirable residues on the surface. 5.3.5 Chemical or electrochemical treatments that generate hydrogen on the specimen surface must not be used on m
43、aterials that are susceptible to hydrogen-induced damage. 5.3.6 Before testing, the specimens should be degreased to remove surface contamination; they should then be tested immediately, or stored in such a way as to avoid contamination or deterioration until they can be tested. 5.4 Methods of stres
44、sing 5.4.1 Constant strain methods 5.4.1.1 Modes of loading Figure 1 shows six methods of stressing specimens under nominally constant strain conditions. The two-point loaded, three-point loaded and four-point loaded specimens represent the three basic modes ofloading used for bent-beam specimens. T
45、he double-beam specimen, fully supported specimen and lever-loaded specimen may be regarded as special cases of four-point loading. 5.4.1.2 Two-point loading 5.4.1.2.1 The maximum stress in a two-point loaded specimen occurs at the mid-point of its convex surface and decreases to zero at the specime
46、n ends. 5.4.1.2.2 Flat two-point loaded specimens should be approximately 15mm to25mm wide by110mm to255mm long as shown inFigure 1 a). The specimen thickness, t, exact length, L, and holder span, H, are selected to give the required stress calculated according to5.4.1.2.4 and to give a value for (L
47、 H)/H between0,01and0,50to keep the error in calculating stress within acceptable limits. A specimen of thickness0,8mm to1,8mm with a holder span of175mm to215mm has proved convenient when working with very high strength steels and with aluminium alloys, with test stresses ranging from about200MN/m
48、2for aluminium to1500 MN/m 2for steel. 5.4.1.2.3 Care should be taken when fitting specimens into their holders to avoid overstressing, distortion or misalignment.ENISO7539-2:1995 BSI 03-2000 5 Figure 1 Constant strain loading test specimensENISO7539-2:1995 6 BSI 03-2000 5.4.1.2.4 The approximate el
49、astic stress at the mid-point of the convex surface is calculated from the relationship L = (ktE/ ) sin 1(H /ktE) where The equation should be used only with H /ktE =1,0 This equation can be solved by computer, by trial and error, or by using a series expansion of the sine function. 5.4.1.2.5 A more rigorous calculation of stress may be based on a theoretically exact large deflection analysis. Calculation of stresses above the limit of elasticity may be carried out on the basis of an elastic-plastic analysis. 5
