1、DEUTSCHE NORM Auaust 1995 Stress corrosion testing Preparation and use of bent beam specimens DIN - euth Verlag GmbH, Berlin. has the exclusive right of sale for German Standards (DIN-Normen). 03.96 DIN EN IS0 7539-2 Engl. Price group Sales NO. i i 07 IEN IS0 7539-2 (IS0 7539-2 : 1989) English versi
2、on of DIN EN IS0 7539-2 This standard incorporates the English version of I so 7539-2. ICs 77.060 Descriptors: Metals, corrosion test, testing, stress corrosion. Korrosion der Metalle und Legierungen; Prfung der Spannungsrikorrosion. Teil 2: Vorbereitung und Anwendung von Biegeproben (IS0 7539-2 : 1
3、989) European Standard EN IS0 7539-2: 1995 has the status of a DIN Standard. A comma is used as the decimal marker. National foreword This standard has been published in accordance with a decision taken by CEN/TC 262 to adopt, without alteration, International Standard IS0 7539-2 as a European Stand
4、ard. The responsible German body involved in its preparation was Technical Committee Korrosion und Korrosionsschutz of the Normenausschu Materialprfung (Materials Testing Standards Committee). EN comprises 7 pages. EUROPEAN STANDARD NORME EUROPENNE EUROPAISCHE NORM EN IS0 7539-2 May 1995 ICs 77.060
5、Descriptors: Metals, corrosion test, testing, stress corrosion. English version Corrosion of metals and alloys Stress corrosion testing Part 2: Preparation and use of bent beam specimens (IS0 7539-2 : 1989) Corrosion des mtaux et alliages; essais de corrosion sous contrainte. Partie 2: Prparation et
6、 utilisation des prouvettes pour essais en flexion (IS0 7539-2: 1989) Korrosion der Metalle und Legierungen; Prfung der Spannungsrikorrosion. Teil 2: Vorbereitung und Anwendung von Biege- proben (IS0 7539-2:1989) This European Standard was approved by CEN on 1995-04-08 and is identical to the IS0 St
7、andard as referred to. CEN members are bound to comply with the CENKENELEC 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 standard
8、s may be obtained on application 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
9、 Central Secretariat has the 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 Euro
10、pean Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, 6-1 050 Brussels O 1995. Copyright reserved to all CEN members. Ref. No. EN IS0 7539-2 : 1995 E Page 2 EN IS0 7539-2 : 1995 Foreword International Standard IS0 75
11、39-2 : 1989 Corrosion of metals and alloys; stress corrosion testing; preparation and use of bent beam specimens, which was prepared by ISOTTC 156 Corrosion of metals and alloys of the International Organization for Standardization, has been adopted by Technical Committee CEN/TC 262 Protection of me
12、tallic materials against corrosion as a European Standard. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, and conflicting national standards withdrawn, by November 1995 at the latest. In accordance with the CENKE
13、NELEC Internal Regulations, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. Endorsement notice The te
14、xt of the International Standard IS0 7539-2:1989 was approved by CEN as a European Standard without any modi- fication. WARNING - Bent-beam specimens made from high strength materials may fracture rapidly: pieces may fly off at high velocity and can be dangerous. Personnel installing and examining s
15、pecimens must be made aware of this possibllty and be protected against injury. 1 Scope 1.1 This part of IS0 7539 covers procedures for designing, preparing and using bent-beam test specimens for investigating the susceptibility of a metal to stress corrosion. The term “metal” as used in this part o
16、f IS0 7539 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, which conveniently provides flat specimens of rectangular cross-section, but may also be employed for cast material, wire or rod,
17、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 for stressing them are both simple and in- expensive, bent-beam specimens are especially suitable for multiple testing and for atm
18、ospheric stress corrosion tests. 1.4 Bent-beam specimens are usually tested under nominally constant strain conditions but nominally constant load con- ditions may be employed. In either case local change of curvature in the specimen when cracking occurs results in changing conditions during crack p
19、ropagation. The “test stiess” is taken as the highest surface tensile stress existing at the start of the test. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this part of IS0 7539. At the time of publication, the edi
20、tions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of IS0 7539 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently vali
21、d International Standards. IS0 7539-1 : 1987, Corrosion of metals and alloys - Stress cor- rosion testing - Part 1 : General guidance on testing pro- cedures. IS0 7539-4 : 1989. Corrosion of metals and alloys - Stress corrosion testing - Part 4: Preparation and use of uniaxially loaded tension speci
22、mens. 3 Definitions For the purposes of this part of IS0 7539, the definitions given in IS0 7539-1 are applicable. 4 Principie 4.1 The test consists of applying a bending stress to a beam specimen of rectangular or circular section and exposing the stressed specimen to a specified test environment.
23、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 bending deflection, as described in 5.4. 4.3 Bent-beam specimens are used only for testing at stress levels belo
24、w the elastic limit since the formulae used for calculating stress in bent beams apply only within the elastic range. Page 3 EN IS0 7539-2: 1995 4.4 The time required for cracks to appear after exposure of stressed specimens to the test environment or the threshold stress below which cracks do not a
25、ppear 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 even when testing nominally identical specimens and the replication of tests i
26、s frequently necessary. 4.6 The possiblity 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 available for a simultaneous effect of the test environ- ment. The difference in ther
27、mal expansion should also be con- sidered. 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 marks will therefore not initiate cracking. 5.1.2 Specimens for determinati
28、on of mechanical properties shall be taken from the same heat treatment batch, and preferably from the same piece of material, as the stress cor- rosion specimens. 5.2 Types of specimens 5.2.1 Bent-beam stress corrosion specimens are usually flat strips of metal of uniform rectangular cross-section
29、and uniform thickness. They may alternatively be lengths of wire or rod of uniform circular cross-section. 5.2.2 Bent-beam stress corrosion tests may also be carrried out on specimens having a gauge length of uniform rectangular or circular cross-section with threaded ends of larger cross- section a
30、s described in IS0 7W-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 often desirable as the structure of the original surface may be different from that of the layers of metal
31、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 machining to a depth of at least 0,25 mm. This is usually sufficient to eliminate original surface imperfectio
32、ns without completely removing any outer recrystallized layer. The maximum depth of machin- ing or grinding of the surface should be decided after studying the structure of the material as shown in an etched metallographic section. It is desirable to remove the required amount of metal in several st
33、eps 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 to remove any cold worked material remaining from shearing. 5.3.3 Chemical or electrochemical treat
34、ments 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 treatments are employed, care must be taken to ensure that the conditions used do not result in selecti
35、ve 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 materials that are susceptible to hydrogen-induced damage. 5.3.6 Before testing, the specimens shoul
36、d be degreased to remove surface contamination; they should thenbe tested im mediately, or stored in such a way as to avoid contamination or deterioration until they can be tested. 5.4 Methods of stressing 5.4.1 Constant strain methods 5.4.1.1 Modes of loading Figure 1 shows six methods of stressing
37、 specimens under nominally constant strain conditions. The two-point loaded, three-point loaded and four-point loaded specimens represent the three basic modes of loading used for bent-beam speci- mens. The doublebeam specimen, fully supported specimen and lever-loaded specimen may be regarded as sp
38、ecial 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 specimen ends. 5.4.1.2.2 Flat two-point loaded specimens should be approxi- mately 15 mm to 25 mm wide b
39、y 110 mm to 255 mm long as shown in figure 1 a). The specimen thickness, t, exact length, L, and holder span, H, are selected to give the required stress calculated according to 5.4.1.2.4 and to give a value for (L - H)/H between 0,Ol and 0,50 to keep the error in calculating stress within acceptabl
40、e limits. A specimen of thickness 0,8 mm to 1,8 mm with a holder span of 175 mm to 215 mm has proved convenient when working with very high strength steels and with aluminium alloys, with test stresses ranging from about Mo MNImzfor aluminium to 1 500 MN/m2 for steel. 5.4.1.2.3 Care should be taken
41、when fitting specimens into their holders to avoid overstressing, distortion or misalignment. Page 4 EN IS0 7539-2 : 1995 - L - L H a -0 O a) Two-point loaded specimen I b) Three-point loaded specimen cv c) Four-point loaded specimen I Weld Weld d) Double-beam specimen r h e) Fully supported specime
42、n Specimen Dimensions in millimetres P li) Specimen L2 L-. U I- I L 37,s A I = -1 II Il (i) Lever f) Lever-loaded specimen Figure 1 - Constant strain loading test specimens Page 5 EN IS0 7539-2 : 1995 5.4.1.2.4 The approximate elastic stress at the mid-point of the convex surface is calculated from
43、the relationship L = k?E/oi sin- (HulktE) where L is the specimen length in metres; 17 is the maximum stress in newtons per square metre: E is the modulus of elasticity in newtons per square metre; H is the holder span in metres: t is the thickness of specimen in metres; k = 1,280. an empirical cons
44、tant. The equation should be used only with HulktE = 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 s
45、tresses above the limit of elasticity may be carried out on the basis of an elastic-plastic analysis. 5.4.1.3 Threepoint loading 5.4.1.3.1 The maximum tensile stress in a three-point loaded specimen occurs at the mid-point of its convex surface and decreases linearly to zero at the outer supports. A
46、 disadvantage of three-point loaded specimens is the possiblity of crevice cor- rosion occurring at the central support close to the region of maximum tensile stress. The pressure of the central support also introduces unknown bi-axial stresses in the region of maxi- mum calculated longitudinal tens
47、ile stress. 5.4.1.3.2 Three-point loaded specimens are usually flat strips 15 mm to 50 mm wide and 110 mrn to 250 mm long. The thick- ness of the specimen is usually dictated by the mechanical pro- perties of the material and the product form available. Speci- men dimensions can be modified to suit
48、specific needs but the approximate dimensional proportions should be preserved. 5.4.1.3.3 The specimen is supported near the ends and bent by forcing a ball-ended screw against it at its mid-point as shown in figure 1 b). 5.4.1.3.4 The elastic stress at the mid-point of the convex sur- face is calcu
49、lated from the relationship O = GEtylH2 where Q metre: E metre: is the maximum tensile stress in newtons per square is the modulus of elasticity in newtons per square I is the thickness of specimen in metres; y is the maximum deflection in metres; H is the distance between outer supports in metres. 5.4.1.4 Four-point loading 5.4.1.4.1 Four-point loading gives a uniform longitudinal tensile stress in the convex surface of the part of the specimen between the inner supports. The stress decreases linearly to zero from the inner supports to the outer supports. The re
