SIST EN ISO 7539-6:2003
(Main)Corrosion of metals and alloys - Stress corrosion testing - Part 6: Preparation and use of pre-cracked specimens for tests under constant load or constant displacement (ISO 7539-6:2003)
Corrosion of metals and alloys - Stress corrosion testing - Part 6: Preparation and use of pre-cracked specimens for tests under constant load or constant displacement (ISO 7539-6:2003)
ISO 7539-6:2002 covers procedures for designing, preparing and using pre-cracked specimens for investigating susceptibility to stress corrosion. It gives recommendations for the design, preparation and use of pre-cracked specimens for investigating susceptibility to stress corrosion.
The term "metal" as used in this part of ISO 7539 includes alloys.
Because of the need to confine plasticity at the crack tip, pre-cracked specimens are not suitable for the evaluation of thin products such as sheet or wire and are generally used for thicker products including plate bar and forgings. They can also be used for parts joined by welding.
Korrosion der Metalle und Legierungen - Prüfung der Spannungsrisskorrosion - Teil 6: Vorbereitung und Anwendung von angerissenen Proben für die Prüfung unter konstanter Kraft oder konstanter Verformung (ISO 7539-6:2003)
1.1 Dieser Teil von ISO 7539 behandelt Verfahren für die Gestaltung, Vorberei-tung und Anwendung von ange-ris-senen Proben zur Untersuchung der Beständigkeit von Me-tallen gegen Spannungsrisskorrosion. Empfehlungen für gekerbte Proben werden im Anhang A an-gegeben.
In diesem Teil von ISO 7539 werden mit der Benennung ?Metall" auch Legierungen erfasst.
1.2 Für die Bewertung dünner Erzeugnisse, z. B. Feinblech oder Draht, sind angerisse-ne Proben wegen der Notwendigkeit, die Plastizität auf die Rissspitze zu beschränken, nicht geeignet; sie werden im Allgemeinen für die Bewertung dickerer Erzeugnisse angewendet, zu denen Grobble-che, Stangen und Schmiedestücke gehören. Sie können auch auf miteinander verschweißte Teile angewendet werden.
1.3 Zur Beanspruchung der angerissenen Proben dürfen Prüfeinrichtungen angewendet werden, die eine konstante Kraft aufbringen oder die eine Vorrichtung aufnehmen können, mit der eine konstante Verformung an den Kraftangriffspunkten erzeugt wird. Prüfungen mit konstanter Kraft oder konstanter Verformung sind nach ISO 7539-9 durchzuführen.
1.4 Ein besonderer Vorteil von angerissenen Proben mit bekannter Geometrie, die bekannten Spannungen ausgesetzt werden, ist die Möglichkeit der Ermittlung von Daten zur Abschätzung kritischer Fehlergrößen, bei deren Überschreitung das Auftreten von Spannungsrissen möglich ist. Mit Hilfe von angerissenen Proben ist es ferner möglich, die Ausbreitungsgeschwindigkeit von Spannungskorrosionsrissen zu bestimmen. Diese Daten dürfen für die Überwachung von Teilen herangezogen werden, in denen beim Einsatz Fehler auftreten.
Corrosion des métaux et alliages - Essais de corrosion sous contrainte - Partie 6: Préparation et utilisation des éprouvettes préfissurées pour essais sous charge constante ou sous déplacement constant (ISO 7539-6:2003)
L'ISO 7539-6:2003 couvre les procédures de définition, de préparation et d'utilisation d'éprouvettes préfissurées servant à évaluer la sensibilité d'un métal à la corrosion sous contrainte. Elle donne des recommendations pour la conception, la préparation et l'utilisation d'éprouvettes préfissurées pour évaluer la sensibilité à la corrosion sous contrainte.
Pour les besoins de la présente partie de l'ISO 7539, le terme «métal» inclut également les alliages.
Comme il est nécessaire de confiner la déformation plastique en fond de fissure, les éprouvettes préfissurées ne se prêtent pas à l'évaluation des produits minces tels que les tôles minces et les fils, et sont généralement utilisées pour des produits plus épais tels que les tôles fortes, les barres et les pièces forgées. Elles peuvent aussi être utilisées pour des pièces assemblées par soudage.
Korozija kovin in zlitin - Preskušanje napetostne korozije - 6. del: Priprava in uporaba preskušancev z umetno razpoko za preskuse pri konstantni obremenitvi ali konstantni deformaciji (ISO 7539-6:2003)
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Korozija kovin in zlitin - Preskušanje napetostne korozije - 6. del: Priprava in uporaba preskušancev z umetno razpoko za preskuse pri konstantni obremenitvi ali konstantni deformaciji (ISO 7539-6:2003)Korrosion der Metalle und Legierungen - Prüfung der Spannungsrisskorrosion - Teil 6: Vorbereitung und Anwendung von angerissenen Proben für die Prüfung unter konstanter Kraft oder konstanter Verformung (ISO 7539-6:2003)Corrosion des métaux et alliages - Essais de corrosion sous contrainte - Partie 6: Préparation et utilisation des éprouvettes préfissurées pour essais sous charge constante ou sous déplacement constant (ISO 7539-6:2003)Corrosion of metals and alloys - Stress corrosion testing - Part 6: Preparation and use of pre-cracked specimens for tests under constant load or constant displacement (ISO 7539-6:2003)77.060Korozija kovinCorrosion of metalsICS:Ta slovenski standard je istoveten z:EN ISO 7539-6:2003SIST EN ISO 7539-6:2003en01-december-2003SIST EN ISO 7539-6:2003SLOVENSKI
STANDARDSIST EN ISO 7539-6:19991DGRPHãþD
SIST EN ISO 7539-6:2003
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN ISO 7539-6February 2003ICS 77.060Supersedes EN ISO 7539-6:1995English versionCorrosion of metals and alloys - Stress corrosion testing - Part6: Preparation and use of pre-cracked specimens for tests underconstant load or constant displacement (ISO 7539-6:2003)Corrosion des métaux et alliages - Essais de corrosionsous contrainte - Partie 6: Préparation et utilisation deséprouvettes préfissurées pour essais sous chargeconstante ou sous déplacement constant (ISO 7539-6:2003)Korrosion der Metalle und Legierungen - Pru¨fung derSpannungsrisskorrosion - Teil 6: Vorbereitung undAnwendung von angerissenen Proben für die Prüfung unterkonstanter Kraft oder konstanter Verformung (ISO 7539-6:2003)This European Standard was approved by CEN on 7 February 2003.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovak Republic, Spain, Sweden, Switzerland andUnited Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2003 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN ISO 7539-6:2003 ESIST EN ISO 7539-6:2003
EN ISO 7539-6:2003 (E)2CORRECTED
2003-03-12ForewordThis document (EN ISO 7539-6:2003) has been prepared by Technical Committee ISO/TC 156"Corrosion of metals and alloys" in collaboration with Technical Committee CEN/TC 262"Metallic and other inorganic coatings", the secretariat of which is held by BSI.This European Standard shall be given the status of a national standard, either by publication ofan identical text or by endorsement, at the latest by August 2003, and conflicting nationalstandards shall be withdrawn at the latest by August 2003.This document supersedes EN ISO 7539-6:1995.According to the CEN/CENELEC Internal Regulations, the national standards organizations ofthe following countries are bound to implement this European Standard: Austria, Belgium, CzechRepublic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,Luxembourg, Malta, Netherlands, Norway, Portugal, Slovak Republic, Spain, Sweden,Switzerland and the United Kingdom.Endorsement noticeThe text of ISO 7539-6:2003 has been approved by CEN as EN ISO 7539-6:2003 without anymodifications.NOTE
Normative references to International Standards are listed in Annex ZA (normative).SIST EN ISO 7539-6:2003
EN ISO 7539-6:2003 (E)3Annex ZA(normative)Normative references to international publicationswith their relevant European publicationsThis European Standard incorporates by dated or undated reference, provisions from otherpublications. These normative references are cited at the appropriate places in the text and thepublications are listed hereafter. For dated references, subsequent amendments to or revisions ofany of these publications apply to this European Standard only when incorporated in it byamendment or revision. For undated references the latest edition of the publication referred toapplies (including amendments).NOTE Where an International Publication has been modified by common modifications, indicatedby (mod.), the relevant EN/HD applies.PublicationYearTitleENYearISO 7539-11987Corrosion of metals and alloys -Stress corrosion testing - Part 1:General guidance on testingproceduresEN ISO 7539-11995SIST EN ISO 7539-6:2003
Reference numberISO 7539-6:2003(E)© ISO 2003
INTERNATIONAL STANDARD ISO7539-6Second edition2003-02-15Corrosion of metals and alloys — Stress corrosion testing — Part 6: Preparation and use of pre-cracked specimens for tests under constant load or constant displacement Corrosion des métaux et alliages — Essais de corrosion sous contrainte — Partie 6: Préparation et utilisation des éprouvettes préfissurées pour essais sous charge constante ou sous déplacement constant
SIST EN ISO 7539-6:2003
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SIST EN ISO 7539-6:2003
ISO 7539-6:2003(E) © ISO 2003 — All rights reserved iii Contents Page Foreword.iv 1 Scope.1 2 Normative references.1 3 Terms and definitions.2 4 Principle.4 5 Specimens.5 6 Initiation and propagation of fatigue cracks.23 7 Procedure.25 8 Test report.33 Annex A (normative)
Use of notched specimens for stress corrosion tests.35 Annex B (normative)
Determination of crack growth velocity.38
SIST EN ISO 7539-6:2003
ISO 7539-6:2003(E) iv © ISO 2003 — All rights reserved Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 7539-6 was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys, in collaboration with the National Physical Laboratory (United Kingdom). This second edition cancels and replaces the first edition (ISO 7539-6:1989), Clauses 1, 2, 3, 4 and 7; subclause 5.2.5 d); Figures 1, 2 d), 5 b), 8, 9, and 10; Annexs A and B of which have been technically revised. ISO 7539 consists of the following parts, under the general title Corrosion of metals and alloys — Stress corrosion testing: =Part 1: General guidance on testing procedures =Part 2: Preparation and use of bent-beam specimens =Part 3: Preparation and use of U-bend specimens =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 for tests under constant load or constant displacement =Part 7: Slow strain rate testing =Part 8: Preparation and use of specimens to evaluate weldments =Part 9: Preparation and use of pre-cracked specimens for tests under rising load or rising displacement
SIST EN ISO 7539-6:2003
INTERNATIONAL STANDARD ISO 7539-6:2003(E) © ISO 2003 — All rights reserved 1 Corrosion of metals and alloys — Stress corrosion testing — Part 6: Preparation and use of pre-cracked specimens for tests under constant load or constant displacement 1 Scope 1.1 This part of ISO 7539 covers procedures for designing, preparing and using pre-cracked specimens for investigating susceptibility to stress corrosion. It gives recommendations for the design, preparation and use of pre-cracked specimens for investigating susceptibility to stress corrosion. Recommendations concerning notched specimens are given in Annex A. The term “metal” as used in this part of ISO 7539 includes alloys. 1.2 Because of the need to confine plasticity at the crack tip, pre-cracked specimens are not suitable for the evaluation of thin products such as sheet or wire and are generally used for thicker products including plate bar and forgings. They can also be used for parts joined by welding. 1.3 Pre-cracked specimens may be loaded with equipment for application of a constant load or can incorporate a device to produce a constant displacement at the loading points. Tests conducted under increasing displacement or increasing load are dealt with in ISO 7539-9. 1.4 A particular advantage of pre-cracked specimens is that they allow data to be acquired from which critical defect sizes, above which stress corrosion cracking may occur, can be estimated for components of known geometry subjected to known stresses. They also enable rates of stress corrosion crack propagation to be determined. The latter data may be taken into account when monitoring parts containing defects during service. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 7539-1, Corrosion of metals and alloys — Stress corrosion testing — Part 1: General guidance on testing procedures ISO 11782-2, Corrosion of metals and alloys — Corrosion fatigue testing — Part 2: Crack propagation testing using precracked specimens SIST EN ISO 7539-6:2003
ISO 7539-6:2003(E) 2 © ISO 2003 — All rights reserved 3 Terms and definitions For the purposes of this part of ISO 7539, the definitions given in ISO 7539-1 and the following apply. 3.1 crack length a effective crack length measured from the crack tip to either the mouth of the notch or the loading point axis depending on the specimen geometry 3.2 specimen width W effective width of the specimen measured from the back face to either the face containing the notch or the loading plane depending on the specimen geometry 3.3 specimen thickness B side-to-side dimension of the specimen being tested 3.4 reduced thickness at side grooves Bn minimum side-to-side dimension between the notches in side-grooved specimens 3.5 specimen half-height H 50 % of the specimen height measured parallel to the direction of load application for compact tension, double cantilever beam and modified wedge opening loaded test pieces 3.6 load P that load which, when applied to the specimen, is considered positive if its direction is such as to cause the crack faces to move apart 3.7 deflection at loading point axis VLL crack opening displacement produced at the loading line during the application of load to a constant displacement specimen 3.8 deflection away from the loading line V0 crack opening displacement produced at a location remote from the loading plane, e.g. at knife edges located at the notch mouth, during the application of load to a constant displacement specimen 3.9 modulus of elasticity E elastic modulus (i.e. stress/strain) in tension SIST EN ISO 7539-6:2003
ISO 7539-6:2003(E) © ISO 2003 — All rights reserved 3 3.10 stress intensity factor KI function of applied load, crack length and specimen geometry having dimensions of stress × length which uniquely define the elastic stress field intensification at the tip of a crack subjected to opening mode displacements (mode I) NOTE It has been found that stress intensity factors, calculated assuming that specimens respond purely elastically, correlate the behaviour of real cracked bodies provided that the size of the zone of plasticity at the crack tip is small compared to the crack length and the length of the uncracked ligament. In this part of ISO 7539, mode I is assumed and the subscript I is implied everywhere. 3.11 initial stress intensity factor KIi stress intensity applied at the commencement of the stress corrosion test 3.12 plane strain fracture toughness KIc critical value of KI at which the first significant environmentally independent extension of the crack occurs under the influence of rising stress intensity under conditions of high resistance to plastic deformation 3.13 provisional value of KIc, KQ KQ = KIc when the validity criteria for plane strain predominance are satisfied 3.14 threshold stress intensity factor for susceptibility to stress corrosion cracking KISCC that stress intensity factor above which stress corrosion cracking will initiate and grow for the specified test conditions under conditions of high resistance to plastic deformation, i.e. under plane strain predominant conditions 3.15 provisional value of KISCC, KQSCC KQSCC = KISCC when the validity criteria for plane strain predominance are satisfied 3.16 maximum stress intensity factor Kmax in fatigue highest algebraic value of the stress intensity factor in a cycle, corresponding to the maximum load 3.17 0,2 % proof stress Rp0,2 stress which must be applied to produce a plastic strain of 0,2 % during a tensile test 3.18 applied stress σ stress resulting from the application of load to the specimen 3.19 stress intensity factor coefficient Y factor derived from the stress analysis for a particular specimen geometry which relates the stress intensity factor for a given crack length to the load and specimen dimensions SIST EN ISO 7539-6:2003
ISO 7539-6:2003(E) 4 © ISO 2003 — All rights reserved 3.20 load ratio R in fatigue loading algebraic ratio of minimum to maximum load in a cycle: minminmaxmaxPKRPK== 3.21 crack velocity instantaneous rate of stress corrosion crack propagation measured by a continuous crack monitoring technique 3.22 average crack velocity average rate of crack propagation calculated by dividing the change in crack length due to stress corrosion by the test duration 3.23 specimen orientation fracture plane of the specimen identified in terms of firstly the direction of stressing and secondly the direction of crack growth expressed with respect to three reference axes identified by the letters X, Y and Z where Z is coincident with the main working force used during manufacture of the material (short-transverse axis); X is coincident with the direction of grain flow (longitudinal axis); Y is normal to the X and Z axes 4 Principle 4.1 The use of pre-cracked specimens acknowledges the difficulty of ensuring that crack-like defects introduced during either manufacture or subsequent service are totally absent from structures. Furthermore, the presence of such defects can cause a susceptibility to stress corrosion cracking which in some materials (e.g. titanium) may not be evident from tests under constant load on smooth specimens. The principles of linear elastic fracture mechanics can be used to quantify the stress situation existing at the crack tip in a pre-cracked specimen or structure in terms of the plane strain-stress intensity. 4.2 The test involves subjecting a specimen in which a crack has been developed by fatigue, from a machined notch, to either a constant load or displacement at the loading points during exposure to a chemically aggressive environment. The objective is to quantify the conditions under which environmentally-assisted crack extension can occur in terms of the threshold stress intensity for stress corrosion cracking, KISCC, and the kinetics of crack propagation. 4.3 The empirical data can be used for design or life prediction purposes in order to ensure either that the stresses within large structures are insufficient to promote the initiation of environmentally-assisted cracking at whatever pre-existing defects may be present or that the amount of crack growth which would occur within the design life or inspection periods can be tolerated without the risk of unstable failure. 4.4 Stress corrosion cracking is influenced by both mechanical and electrochemical driving forces. The latter can vary with crack depth, opening or shape because of variations in crack-tip chemistry and electrode potential and may not be uniquely described by the fracture mechanics stress intensity factor. 4.5 The mechanical driving force includes both applied and residual stresses. The possible influence of the latter shall be considered in both laboratory testing and the application to more complex geometries. Gradients in residual stress in a specimen may result in non-uniform crack growth along the crack front. SIST EN ISO 7539-6:2003
ISO 7539-6:2003(E) © ISO 2003 — All rights reserved 5 5 Specimens 5.1 General 5.1.1 A wide range of standard specimen geometries of the type used in fracture toughness tests may be applied. The particular type of specimen used will be dependent upon the form, the strength and the susceptibility to stress corrosion cracking of the material to be tested and also on the objective of the test. 5.1.2 A basic requirement is that the dimensions be sufficient to maintain predominantly triaxial (plane strain) conditions in which plastic deformation is limited in the vicinity of the crack tip. Experience with fracture toughness testing has shown that for a valid KIc measurement, both the crack length, a, and the thickness, B, shall not be less than 2Icp0,22,5KR and that, where possible, larger specimens where both a and B are at least 2Icp0,24KR shall be used to ensure adequate constraint. From the view of fracture mechanics, a minimum thickness from which an invariant value of KISCC is obtained cannot be specified at this time. The presence of an aggressive environment during stress corrosion may reduce the extent of plasticity associated with fracture and hence the specimen dimensions needed to limit plastic deformation. However, in order to minimize the risk of inadequate constraint, it is recommended that similar criteria to those used during fracture toughness testing should also be used regarding specimen dimensions, i.e. both a and B shall be not less than 2Ip0,22,5KR and preferably should be not less than 2Ip0,24KR where KI is the stress intensity to be applied during testing. The threshold stress intensity value eventually determined should be substituted for KI in the first of these expressions as a test for its validity. 5.1.3 If the specimens are to be used for the determination of KISCC, the initial specimen size should be based on an estimate of the KISCC of the material (in the first instance, it being better to over-estimate the KISCC value and therefore use a larger specimen than may eventually be found necessary). Where the service application involves the use of material of insufficient thickness to satisfy the conditions for validity, it is permissible to test specimens of similar thickness, provided that it is clearly stated that the threshold intensity value obtained, KQSCC, is of relevance only to that specific application. Where determining stress corrosion crack growth behaviour as a function of stress intensity is required, the specimen size shall be based on an estimate of the highest stress intensity at which crack growth rates are to be measured. SIST EN ISO 7539-6:2003
ISO 7539-6:2003(E) 6 © ISO 2003 — All rights reserved 5.1.4 Two basic types of specimen can be used a) those intended for testing under constant displacement, which are invariably self-loaded by means of built-in loading bolts; b) those intended for testing under constant load, for which an external means of load application is required. 5.1.5 Constant displacement specimens, being self-loaded, have the advantage of economy in use since no external stressing equipment is required. Their compact dimensions also facilitate exposure to operating service environments. They can be used for the determination of KISCC by the initiation of stress corrosion cracks from the fatigue pre-crack, in which case a series of specimens must be used to pin-point the threshold value, or by the arrest of a propagating crack since under constant displacement testing conditions the stress intensity decreases progressively as crack propagation occurs. In this case a single specimen will suffice in principle, but in practice the use of several specimens (not less than 3) is often recommended, taking into account the disadvantages described in 5.1.6. 5.1.6 The disadvantages of constant displacement specimens are a) applied loads can only be measured indirectly by displacement changes; b) oxide formation or corrosion products can either wedge open the crack surfaces, thus changing the applied displacement and load, or can block the crack mouth, thus preventing the ingress of corrodent and impairing the accuracy of crack length measurements by electrical resistance methods; c) crack branching, blunting or growth out of plane can invalidate crack arrest data; d) crack arrest must be defined by crack growth below some arbitrary rate which can be difficult to measure accurately; e) elastic relaxation of the loading system during crack growth can cause increased displacement and higher loads than expected; f) plastic relaxation due to time-dependent processes within the specimen can cause lower loads than expected; g) it is sometimes impossible to introduce the test environment prior to application of the load, which can retard crack initiation during subsequent testing. 5.1.7 Constant load specimens have the advantage that stress parameters can be quantified with confidence. Since crack growth results in increasing crack opening, there is less likelihood that oxide films will either block the crack or wedge it open. Crack length measurements can be readily made via a number of continuous monitoring methods. A wide choice of constant load specimen geometries is available to suit the form of the test material, the experimental facilities available and the objectives of the test. This means that crack growth can be studied under either bend or tension loading conditions. The specimens can be used for either the determination of KISCC by the initiation of a stress corrosion crack from a pre-existing fatigue crack using a series of specimens, or for measurements of crack growth rates. Constant load specimens can be loaded during exposure to the test environment in order to avoid the risk of unnecessary incubation periods. 5.1.8 The principal disadvantage of constant load specimens is the expense and bulk associated with the need for an external loading system. Bend specimens can be tested in relatively simple cantilever beam equipment, but specimens subjected to tension loading require constant load creep rupture or similar testing machines. In this case, the expense can be minimized by testing chains of specimens connected by loading links which are designed to prevent unloading on the failure of specimens. The size of these loading systems means that it is difficult to test constant load specimens under operating conditions, but they can be tested in environments bled off from operating systems. 5.2 Specimen design 5.2.1 Figure 1 shows some of the pre-cracked specimen geometries which are used for stress corrosion testing. SIST EN ISO 7539-6:2003
ISO 7539-6:2003(E) © ISO 2003 — All rights reserved 7
NOTE Stress intensity factor coefficients for the specimens shown above are available in the published literature. Figure 1 — Pre-cracked specimen geometries for stress corrosion testing SIST EN ISO 7539-6:2003
ISO 7539-6:2003(E) 8 © ISO 2003 — All rights reserved 5.2.2 Constant load specimens can be of two distinct types: a) those in which the stress intensity increases with increasing crack length; b) those in which the stress intensity is effectively independent of crack length. Type a) is suitable for KISCC determinations and studies of crack propagation rates as a function of KI, while type b) is useful for fundamental studies of stress corrosion mechanisms. 5.2.3 Increasing K constant load specimens can be subjected to either tension or bend loading. Depending on the design, tension loaded specimens can experience stresses at the crack tip which are predominantly tensile (as in remote tension types such as the centre-cracked plate) or contain a significant bend component (as in crackline loaded types such as compact tension specimens). The presence of significant bending stress at the crack tip can adversely affect the crack path stability during stress corrosion testing and can facilitate crack branching in certain materials. Bend specimens can be loaded in 3-point, 4-point or cantilever bend fixtures. 5.2.4 Constant K constant load specimens can be subjected to either torsion loading as in the case of the double torsion single edge cracked plate specimen, or tension loading as in the case of contoured double cantilever beam specimens. Although loaded in tension, the design of the latter specimens produces crackline bending with an associated tendency for crack growth out of plane, which can be curbed by the use of side grooves. 5.2.5 Constant displacement specimens are usually self-loaded by means of a loading bolt in one arm which impinges on either an anvil or a second loading bolt in the opposite arm. Two types are available: a) those which are (W-a) dominated such as the modified wedge opening loaded (modified WOL) specimen in which the proximity of the back face to the crack tip influences the crack tip stress field; b) those which are (W-a) indifferent, such as the double cantilever beam (DCB) specimen in which the back face is sufficiently remote from the crack tip to ensure that its position has a negligible effect on the crack tip stress field. 5.2.6 A number of the specimen geometries described above have specific advantages which have caused them to be frequently used for stress corrosion testing. These include: a) cantilever bend specimens, which are easy to machine and inexpensive to test under cons
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