Plastics - Determination of compressive properties (ISO 604:2002)

Kunststoffe - Bestimmung von Druckeigenschaften (ISO 604:2002)

Diese Internationale Norm legt ein Verfahren zur Ermittlung der Druckeigenschaften von Kunststoffen unter definierten Bedingungen fest. Es ist ein genormter Probekörper festgelegt, jedoch kann seine Länge so abgestimmt werden, dass eine Beeinflussung der Ergebnisse durch ein Knicken unter Last vermieden wird. Eine Liste von Prüfgeschwindigkeiten ist mit aufgenommen.
Das Verfahren wird für die Untersuchung des Druckverhaltens der Probekörper und für die Bestimmung der Druckfestigkeit, des Druckmoduls und anderer Gesichtspunkte der Druckspannungs-Stauchungs-Beziehung unter den definierten Bedingungen verwendet.
Das Prüfverfahren ist zur Anwendung auf folgende Werkstoffgruppen geeignet:
¾ steife und halbsteife [1] thermoplastische Spritzguss- und Extrusionswerkstoffe, einschließlich gefüllter und verstärkter Formmassen als Ergänzung zu ungefüllten Typen, z. B. durch Kurzfasern, kleine Stäbchen, Plättchen oder Granulat verstärkte Formmassen; steife und halbsteife thermoplastische Tafeln;
¾ steife und halbsteife duroplastische Werkstoffe, einschließlich gefüllter und verstärkter Formmassen; steife und halbsteife duroplastische Tafeln;
¾ thermotrope flüssigkristalline Polymere.
In Übereinstimmung mit ISO 10350-1 und ISO 10350-2 gilt diese Internationale Norm für faserverstärkte Formmassen mit einer Faserlänge von £ 7,5 mm vor der Verarbeitung.
Das Verfahren ist üblicherweise nicht zur Anwendung bei textilfaserverstärkten Werkstoffen (siehe Verweisungen [2] und [5]), faserverstärkten Kunststoff-Verbundwerkstoffen und Laminaten (siehe [5]) sowie harten Schaumstoffen (siehe [3]) oder Schichtstoff-Verbundwerkstoffen mit Schaumstoffkern oder Gummi (siehe [4]) geeignet.
Das Verfahren ist für Probekörper geeignet, die direkt in den gewählten Maßen geformt werden, aus dem Mittelteil eines Norm-Vielzweckprobekörpers (siehe ISO 3167) ausgearbeitet werden oder aus fertigen oder halbfertigen Produkten wie Formteilen, extrudierten oder gegossenen Tafeln ausgearbeitet werden.

Plastiques - Détermination des propriétés en compression (ISO 604:2002)

Polimerni materiali - Ugotavljanje tlačnih lastnosti (ISO 604:2002)

General Information

Status
Published
Publication Date
29-Jul-2003
Technical Committee
Drafting Committee
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
30-Jul-2003
Completion Date
30-Jul-2003

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Kunststoffe - Bestimmung von Druckeigenschaften (ISO 604:2002)Plastiques - Détermination des propriétés en compression (ISO 604:2002)Plastics - Determination of compressive properties (ISO 604:2002)83.080.01Polimerni materiali na splošnoPlastics in generalICS:Ta slovenski standard je istoveten z:EN ISO 604:2003SIST EN ISO 604:2003en01-december-2003SIST EN ISO 604:2003SLOVENSKI

STANDARDSIST EN ISO 604:20001DGRPHãþD
SIST EN ISO 604:2003

EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN ISO 604July 2003ICS 83.080.01Supersedes EN ISO 604:1996English versionPlastics - Determination of compressive properties (ISO604:2002)Plastiques - Détermination des propriétés en compression(ISO 604:2002)Kunststoffe - Bestimmung von Druckeigenschaften (ISO604:2002)This European Standard was approved by CEN on 26 June 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, Slovakia, Spain, Sweden, Switzerland and UnitedKingdom.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 604:2003 ESIST EN ISO 604:2003

EN ISO 604:2003 (E)2ForewordThe text of ISO 604:2002 has been prepared by Technical Committee ISO/TC 6 "Plastics” of theInternational Organization for Standardization (ISO) and has been taken over as EN ISO604:2003 by Technical Committee CEN/TC 249 "Plastics", the secretariat of which is held byIBN.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 January 2004, and conflicting nationalstandards shall be withdrawn at the latest by January 2004.This document supersedes EN ISO 604:1996.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, Slovakia, Spain, Sweden, Switzerland andthe United Kingdom.Endorsement noticeThe text of ISO 604:2002 has been approved by CEN as EN ISO 604:2003 without anymodifications.NOTE

Normative references to International Standards are listed in Annex ZA (normative).SIST EN ISO 604:2003

EN ISO 604:2003 (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 2911997Plastics - Standard atmospheres forconditioning and testingEN ISO 2911997ISO 294-11996Plastics - Injection moulding of testspecimens of thermoplastic materials- Part 1: General principles, andmoulding of multipurpose and bar testspecimensEN ISO 294-11998ISO 2951991Plastics - Compression moulding oftest specimens of thermosettingmaterialsEN ISO 2951998ISO 28181994Plastics - Preparation of testspecimens by machiningEN ISO 28181996ISO 31671993Plastics - Multipurpose-testspecimensEN ISO 31671996ISO 10724-11998Plastics - Injection moulding of testspecimens o f thermosetting powdermoulding compounds (PMCs) -

Part1: General principles and mouldingof multi purpose test specimensEN ISO 10724-12001SIST EN ISO 604:2003

SIST EN ISO 604:2003
Reference numberISO 604:2002(E)© ISO 2002

INTERNATIONAL STANDARD ISO604Third edition2002-03-01Plastics — Determination of compressive properties Plastiques — Détermination des propriétés en compression

SIST EN ISO 604:2003

ISO 604:2002(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

ISO 2002 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester. ISO copyright office Case postale 56 • CH-1211 Geneva 20 Tel.

+ 41 22 749 01 11 Fax
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copyright@iso.ch Web
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ii © ISO 2002 – All rights reserved
SIST EN ISO 604:2003

ISO 604:2002(E) © ISO 2002 – All rights reserved iii Contents Foreword.....................................................................................................................................................................iv 1 Scope..............................................................................................................................................................1 2 Normative references....................................................................................................................................2 3 Terms and definitions...................................................................................................................................2 4 Principle..........................................................................................................................................................4 5 Apparatus.......................................................................................................................................................5 6 Test specimens..............................................................................................................................................6 7 Number of test specimens............................................................................................................................8 8 Conditioning of test specimens...................................................................................................................8 9 Test procedure...............................................................................................................................................9 10 Calculation and expression of results.......................................................................................................11 11 Precision.......................................................................................................................................................13 12 Test report....................................................................................................................................................13 Annex A (normative)

Small test specimens...........................................................................................................14 Annex B (informative)

Limits of buckling...............................................................................................................15 Annex C (normative)

Compliance correction.........................................................................................................17 Bibliography..............................................................................................................................................................18

SIST EN ISO 604:2003
ISO 604:2002(E) iv © ISO 2002 – 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 3. 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 International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 604 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical properties. This third edition cancels and replaces the second edition (ISO 604:1993), which has been technically revised.  a method of correcting for curvature at the beginning of the stress/strain curve is given (see 10.2.2);  a method of correcting for the compliance of the test machine is given (see annex C). Annexes A and C form a normative part of this International Standard. Annex B is for information only.

SIST EN ISO 604:2003

INTERNATIONAL STANDARD ISO 604:2002(E) © ISO 2002 – All rights reserved 1 Plastics — Determination of compressive properties 1 Scope This International Standard specifies a method for determining the compressive properties of plastics under defined conditions. A standard test specimen is defined but its length may be adjusted to prevent buckling under load from affecting the results. A range of test speeds is included. The method is used to investigate the compressive behaviour of the test specimens and for determining the compressive strength, compressive modulus and other aspects of the compressive stress/strain relationship under the conditions defined. The method applies to the following range of materials:  rigid and semi-rigid [1] thermoplastic moulding and extrusion materials, including compounds filled and reinforced by e.g. short fibres, small rods, plates or granules in addition to unfilled types; rigid and semi-rigid thermoplastic sheet;  rigid and semi-rigid thermoset moulding materials, including filled and reinforced compounds; rigid and semi-rigid thermoset sheet;  thermotropic liquid-crystal polymers. In agreement with ISO 10350-1 and ISO 10350-2, this International Standard applies to fibre-reinforced compounds with fibre lengths u 7,5 mm prior to processing. The method is not normally suitable for use with materials reinforced by textile fibres (see references [2] and [5]), fibre-reinforced plastic composites and laminates (see [5]), rigid cellular materials (see [3]) or sandwich structures containing cellular material or rubber (see [4]). The method is performed using specimens which may be moulded to the chosen dimensions, machined from the central portion of a standard multipurpose test specimen (see ISO 3167) or machined from finished or semi-finished products such as mouldings or extruded or cast sheet. The method specifies preferred dimensions for the test specimen. Tests which are carried out on specimens of different dimensions, or on specimens which are prepared under different conditions, may produce results which are not comparable. Other factors, such as the test speed and the conditioning of the specimens, can also influence the results. Consequently, when comparable data are required, these factors must be carefully controlled and recorded. SIST EN ISO 604:2003

ISO 604:2002(E) 2 © ISO 2002 – All rights reserved

2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 291:1997, Plastics — Standard atmospheres for conditioning and testing ISO 293:1986, Plastics — Compression moulding test specimens of thermoplastic materials ISO 294-1:1996, Plastics — Injection moulding of test specimens of thermoplastic materials — Part 1: General principles, and moulding of multipurpose and bar test specimens ISO 295:—1), Plastics — Compression moulding of test specimens of thermosetting materials ISO 2602:1980, Statistical interpretation of test results — Estimation of the mean — Confidence interval ISO 2818:1994, Plastics — Preparation of test specimens by machining ISO 3167:—2), Plastics — Multipurpose test specimens ISO 5893:—3), Rubber and plastics test equipment — Tensile, flexural and compression types (constant rate of traverse) — Specification ISO 10724-1:1998, Plastics — Injection moulding of test specimens of thermosetting powder moulding compounds (PMCs) — Part 1: General principles and moulding of multipurpose test specimens 3 Terms and definitions For the purposes of this International Standard, the following terms and definitions apply (see also Figure 1). 3.1 gauge length L0 initial distance between the gauge marks on the central part of the test specimen NOTE It is expressed in millimetres (mm). 3.2 test speed v rate of approach of the plates of the test machine during the test NOTE It is expressed in millimetres per minute (mm/min). 3.3 compressive stress s compressive load, per unit area of original cross-section, carried by the test specimen NOTE 1 It is expressed in megapascals (MPa).

1) To be published. (Revision of ISO 295:1991) 2) To be published. (Revision of ISO 3167:1993) 3) To be published. (Revision of ISO 5893:1993) SIST EN ISO 604:2003

ISO 604:2002(E) © ISO 2002 – All rights reserved 3 NOTE 2 In compression tests, the stresses σ and strains ε are negative. The negative sign, however, is generally omitted. If this generates confusion, e.g. in comparing tensile and compressive properties, the negative sign may be added for the latter. This is unnecessary for the nominal compressive strain εc. 3.3.1 compressive stress at yield σy first stress at which an increase in strain (see 3.4) occurs without an increase in stress (see Figure 1, curve a, and note 2 to 3.3) NOTE 1 It is expressed in megapascals (MPa). NOTE 2 It may be less than the maximum attainable stress. 3.3.2 compressive strength σM maximum compressive stress sustained by the test specimen during a compressive test (see Figure 1 and note 2 to 3.3) NOTE It is expressed in megapascals (MPa). 3.3.3 compressive stress at break (rupture) σB compressive stress at break of the test specimen (see Figure 1 and note 2 to 3.3) NOTE It is expressed in megapascals (MPa). 3.3.4 compressive stress at x % strain σx stress at which the strain reaches a specified value x % (see 3.5) NOTE 1 It is expressed in megapascals (MPa). NOTE 2 The compressive stress at x % strain may be measured, e.g., if the stress/strain curve does not exhibit a yield point (see Figure 1, curve b, and note 2 to 3.3). In this case, x is taken from the relevant product standard or agreed upon by the interested parties. In any case, x will have to be lower than the strain at compressive strength. 3.4 compressive strain ε decrease in length per unit original gauge length L0 [see 10.2, equation (6), and note 2 to 3.3] NOTE It is expressed as a dimensionless ratio or percentage (%). 3.5 nominal compressive strain εc decrease in length per unit original length L of the test specimen [see 10.2, equation (8)] NOTE It is expressed as a dimensionless ratio or percentage (%). 3.5.1 nominal compressive yield strain εcy strain corresponding to the compressive stress at yield σy (see 3.3.1) NOTE It is expressed as a dimensionless ratio or percentage (%). SIST EN ISO 604:2003

ISO 604:2002(E) 4 © ISO 2002 – All rights reserved

3.5.2 nominal compressive strain at compressive strength εcM strain corresponding to the compressive strength σM (see 3.3.2) NOTE It is expressed as a dimensionless ratio or percentage (%). 3.5.3 nominal compressive strain at break εcB strain at break of the test specimen NOTE It is expressed as a dimensionless ratio or percentage (%). 3.6 compressive modulus Ec ratio of the stress difference (σ2 – σ1) to the corresponding strain difference values (ε2 = 0,002 5 minus ε1 = 0,000 5) [see 10.3, equation (9)] NOTE 1 It is expressed in megapascals (MPa). NOTE 2 The compression modulus is calculated on the basis of the compressive strain ε only (see 3.4). NOTE 3 With computer-aided equipment, the determination of the modulus Ec using two distinct stress/strain points may be replaced by a linear regression procedure applied to the part of the curve between these points. 4 Principle The test specimen is compressed along its major axis at constant speed until the specimen fractures or until the load or the decrease in length reaches a predetermined value. The load sustained by the specimen is measured during this procedure.

Figure 1 — Typical stress/strain curves SIST EN ISO 604:2003

ISO 604:2002(E) © ISO 2002 – All rights reserved 5 5 Apparatus 5.1 Test machine 5.1.1 General The test machine shall comply with ISO 5893, and meet the specifications given in 5.1.2 to 5.1.5, as follows. 5.1.2 Test speeds The machine shall be capable of maintaining the test speeds as specified in Table 1. If other speeds are used, the machine shall be capable of maintaining the speed to a tolerance of ± 20 % for speeds less than 20 mm/min and ± 10 % for speeds greater than 20 mm/min. Table 1 — Recommended test speeds Test speed v mm/min Tolerance % 1 ± 20 2 ± 20 5 ± 20 10 ± 20 20 ± 10 a

a This tolerance is smaller than that indicated in ISO 5893. Acceleration, seating and machine compliance may contribute to a curved region at the start of the stress/strain curve. This can be avoided as explained in 9.4 and 9.6. 5.1.3 Compression tool Hardened-steel compression plates shall be used to apply the deformation load to the test specimen, so constructed that the load sustained by the specimen is axial to within 1:1 000 and is transmitted through polished surfaces which are flat to within 0,025 mm, parallel to each other and perpendicular to the loading axis. NOTE A self-aligning device may be used where required. 5.1.4 Load indicator The load indicator shall incorporate a mechanism capable of showing the total compressive force sustained by the test specimen. The mechanism shall be essentially free of inertia lag at the specified test speed and shall indicate the value of the load with an accuracy of ± 1 %, or better, of the relevant value. NOTE Systems have become commercially available that use ring-shaped strain gauges, and thus any lateral forces which may be generated by misalignment of the test set-up are compensated for (see 9.3). 5.1.5 Extensometer The extensometer shall incorporate a mechanism suitable for determining the relative change in length of the appropriate part of the test specimen. If compressive strain ε is to be measured (the preferred approach), then this length is the gauge length; otherwise, for nominal compressive strain εc, it is the distance between the contact surfaces of the compression tool. It is desirable, but not essential, that this instrument automatically records this distance. SIST EN ISO 604:2003

ISO 604:2002(E) 6 © ISO 2002 – All rights reserved

The instrument shall be essentially free of inertia lag at the specified test speed. For modulus determination using a type A specimen, it shall be accurate to ± 1 %, or better, of the strain interval used. This corresponds to ± 1 µm for the measurement of the compressive modulus, based on a gauge length of 50 mm and a strain interval of 0,2 %. When the extensometer is attached to the test specimen, care shall be taken to ensure that any distortion of or damage to the test specimen is minimal. It is also essential that there is no slippage between the extensometer and the test specimen. The specimens may also be instrumented with longitudinal strain gauges, the accuracy of which shall be 1 %, or better, of the strain interval used. This corresponds to a strain accuracy of 2,0 ¥ 10–5 for the measurement of the modulus. The gauges, the specimen surface preparation method and the bonding agents used shall be chosen to ensure adequate performance with the material under test. NOTE Slight misalignment and initial warpage of the test specimen may generate differences in strain between the opposite surfaces of the specimen, resulting in errors at low strains. In these cases, the use of strain-measuring methods that average the strain on the two opposite sides of the specimen may be used. However, the use of strain gauges on either side of the specimen, with independent data collection, will detect buckling and bending much more rapidly than will devices that average the strain on the opposite surfaces. 5.2 Devices for measuring the dimensions of the test specimens 5.2.1 Rigid materials Use a micrometer, or equivalent, reading to 0,01 mm or better, to measure the thickness, width and length. The dimensions and shape of the anvils shall be suitable for the specimens being tested and shall not exert a force on the specimen such as to detectably alter the dimension being measured. 5.2.2 Semi-rigid materials Micrometer, or equivalent, reading to 0,01 mm or better and provided with a flat circular foot which applies a pressure of 20 kPa ± 3 kPa, to measure the thickness. 6 Test specimens 6.1 Shape and dimensions 6.1.1 General Test specimens shall be in the shape of a right prism, cylinder or tube. The dimensions of the test specimens shall be such that the following inequality is satisfied (see also annex B): εc* u 0,422xl (1) where εc* is the maximum nominal compressive strain, expressed as a dimensionless ratio, which occurs during the test; l is the length of the specimen, measured parallel to the axis of the compressive force; x is the diameter of the cylinder, the outer diameter of the tube or the thickness (the shortest side of the cross-section) of the prism, depending on the shape of the test specimen. SIST EN ISO 604:2003

ISO 604:2002(E) © ISO 2002 – All rights reserved 7 NOTE 1 For measurement of the compressive modulus Ec as defined in 3.6, a value of the dimensionless ratio x/l of > 0,08 is recommended. NOTE 2 When carrying out compression tests in general, a value of the dimensionless ratio x/l of W 0,4 is recommended. This corresponds to a maximum compressive strain of about 6 %. Equation (1) is based upon the linear stress/strain behaviour of the material under test. Values of ε*c two to three times higher than the maximum strain used in the test shall be chosen with increasing compressive strain and ductility of the material. 6.1.2 Preferred test specimens The preferred dimensions for test specimens are given in Table 2. Table 2 — Dimensions of preferred specimen types

Dimensions in millimetres Type Measurement Length, l Width, b Thickness, h A Modulus 50 ± 2 B Strength 10 ± 0,2 10 ± 0,2 4 ± 0,2

The specimens should preferably be cut from a multipurpose test specimen (see ISO 3167). NOTE Annex A details two types of small test specimen for use when, owing to lack of material or because of geometric constraints on a product, the preferred specimen types cannot be used. 6.2 Preparation 6.2.1 Moulding and extrusion compounds Specimens shall be prepared in accordance with the relevant material specification. When none exists, and unless otherwise agreed by the interested parties, specimens shall be either directly compression moulded or directly injection moulded from the material in accordance with ISO 293, ISO 294-1, ISO 295 or ISO 10724-1, as appropriate. 6.2.2 Sheets Specimens shall be machined from sheets in accordance with ISO 2818. 6.2.3 Machining All machining operations shall be carried out carefully so that smooth surfaces result. Great care shall be taken in machining the ends so that smooth, flat, parallel surfaces and sharp, clean edges, perpendicular to the longest axis of the specimen to within 0,025 mm, result. It is recommended that the end surfaces of the test specimen be machined with a lathe or a milling machine. 6.2.4 Gauge marks If optical equipment is used to measure the change in length, it is necessary to put gauge marks on the specimen to define the gauge length. These shall be approximately equidistant from the midpoint of the test specimen, and the distance between the marks shall be measured to an accuracy of 1 % or better. SIST EN ISO 604:2003

ISO 604:2002(E) 8 © ISO 2002 – All rights reserved

Gauge marks shall not be scratched, punched or impressed upon the test specimen in any way which causes damage to the material being tested. It shall be ensured that the marking medium has no detrimental effect on the material being tested and that they are as narrow as possible. 6.3 Specimen inspection The specimens shall be free of twist. The surfaces and edges shall be free from scratches, pits, sink marks, flash and other visible imperfections that are likely to influence the results. The surfaces facing the compression plates shall be parallel and at right angles to the longitudinal direction. The specimens shall be checked for conformity with these requirements by visual observation against straight edges, squares and flat plates, and by measuring with micrometer calipers. Specimens showing measurable or observable departure from one or more of these requirements shall be rejected or machined to proper size and shape before testing. NOTE Injection-moulded test specimens usually have draft angles of between 1° and 2° to facilitate demoulding. Therefore side faces of moulded test specimens will generally not be parallel. 6.4 Anisotropic materials 6.4.1 In the case of anisotropic materials, the test specimens shall be chosen so that the compressive stress will be applied in the test procedure in the same or a similar direction to that experienced by the products (moulded articles, sheet, tubes, etc.) during service in the intended application, if known. 6.4.2 The relationship between the dimensions of the test specimen and the size of the product will determine the possibility of using preferred test specimens. If the use of one of the preferred test specimens is impossible, the size of the product will govern the choice of the dimensions of the test specimens as well as 6.1. It should be noted that the orientation and dimensions of the test specimens sometimes have a very significant influence on the test results. 6.4.3 When the material shows a significant difference in compressive properties in two principal directions, it shall be tested in these two directions. If, because of its intended application, the material will be subjected to compressive stress at some specific orientation other than one of the principal directions, it is desirable to test the material in that orientation. The orientation of the test specimens relative to the principal directions shall be recorded. 7 Number of test specimens 7.1 Test at least five specimens for each sample in the case of isotropic materials. 7.2 Test at least ten specimens, five normal to and five parallel to the principal axis of anisotropy, for each sample in the case of anisotropic materials. 7.3 Specimens that break at some obvious flaw shall be discarded and replacement specimens tested. 8 Conditioning of test specimens The test specimens shall be conditioned in accordance with the requirements of the International Standard for the material. In the absence of such requirements, use the most appropriate conditions given in ISO 291, unless otherwise agreed between the interested parties. The preferred set of conditions is atmosphere 23/5

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