BRITISH STANDARD
Metallic materials — Bend test
The European Standard EN ISO 7438:2005 has the status of a British Standard
ICS 77.040.10
BS EN ISO 7438:2005
BS EN ISO 7438:2005
National foreword This British Standard is the official English language version of EN ISO 7438:2005. It is identical with ISO 7438:2005. It supersedes BS EN ISO 7438:2000 which is withdrawn. The UK participation in its preparation was entrusted by T echnical Committee ISE/NFE/4, Mechanical testing of metals, to Subcommittee ISE/NFE/4/2, Ductility testing, which has the responsibility to: —
aid enquirers to understand the text;
—
present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep UK interests informed;
—
monitor related international and European developments and promulgate them in the UK.
A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations.
Summary of pages This document comprises a front cover, an inside front cover, the EN ISO title page, the EN ISO foreword page, the ISO title page, pages ii t o iv, pages 1 to 8, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued.
Amendments issued since publication This British Standard was published under the authority of the Standards Policy and Strategy Committee on 21 October 2005 © BSI 21 October 2005
ISBN 0 580 46375 3
Amd. No.
Date
Comments
EUROPEAN STANDARD
EN ISO 7438
NORME EUROPÉENNE EUROPÄISCHE NORM
June 2005
ICS 77.040.10
Supersedes EN ISO 7438:2000
English version
Metallic materials - Bend test (ISO 7438:2005) Matériaux métalliques - Essai de pliage (ISO 7438:2005)
Metallische Werkstoffe - Biegeversuch (ISO 7438:2005)
This European Standard was approved by CEN on 13 June 2005. CEN members 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 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 Central Secretariat has the sam e status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36
© 2005 CEN
All rights of exploitation in any form and by any means reserved worldwide for CEN national Members.
B-1050 Brussels
Ref. No. EN ISO 7438:2005: E
EN ISO 7438:2005
Foreword
This document (EN ISO 7438:2005) has been prepared by Technical Committee ISO/TC 164 "Mechanical testing of metals" in collaboration with Technical Committee ECISS/TC 1 "Steel Mechanical testing", the secretariat of which is held by AFNOR. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by December 2005, and conflicting national standards shall be withdrawn at the latest by December 2005. This document supersedes EN ISO 7438:2000. According to the CEN/CENELEC Internal Regulations, the national standar ds organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
Endorsement notice
The text of ISO 7438:2005 has been approved by CEN as EN ISO 7438:2005 without any modifications.
EN ISO 7438:2005
INTERNATIONAL STANDARD
ISO 7438 Second edition 2005-06-15
Metallic materials — Bend test Matériaux métalliques — Essai de pliage
Reference number ISO 7438:2005(E)
ii
EN ISO 7438:2005
Contents
Page
Foreword............................................................................................................................................................ iv 1
Scope ..................................................................................................................................................... 1
2
Symbols and designations .................................................................................................................. 1
3
Principle ................................................................................................................................................. 1
4
Test equipment ..................................................................................................................................... 2
5
Test piece .............................................................................................................................................. 4
6
Procedure .............................................................................................................................................. 5
7
Interpretation of results........................................................................................................................ 7
8
Test report ............................................................................................................................................. 7
Annex A (informative) Determination of the bend angle from the measurement of the displacement of the former.................................................................................................................. 8
iii
EN ISO 7438:2005
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 7438 was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Subcommittee SC 2, Ductility testing . This second edition cancels and replaces the first edition (ISO 7438:1985), which has been technically revised.
iv
EN ISO 7438:2005
Metallic materials — Bend test
1
Scope
This International Standard specifies a method for determining the ability of metallic materials to undergo plastic deformation in bending. This International Standard applies to test pieces taken from metallic products, as specified in the relevant product standard. It is not applicable to certain materials or products, for example tubes in full section or welded joints, for which other standards exist.
2
Symbols and designations
Symbols and designations used in the bend test are shown in Figures 1 and 2 and specified in Table 1. Table 1 — Symbols and designations Symbol
Unit
a
Thickness or diameter of test piece (or d iameter of the inscribed circle for pieces of polygonal cross-section)
mm
b
Width of the test piece
mm
L
Length of the test piece
mm
Distance between supports
mm
Diameter of the former
mm
l D α
3
Designation
Angle of bend
degrees
r
Internal radius of bend portion of test piece after bending
mm
f
Displacement of the former
mm
c
Distance between the plane including the horizontal axis of supports and the central axis of the rounded portion of the former before test
mm
p
Distance between the vertical planes including the central axis and the vertical axis of each support and the vertical plane including the horizontal central axis of the former after test
mm
Principle
The bend test consists of submitting a test piece of round, square, rectangular or polygonal cross-section to plastic deformation by bending, without changing the direction of loading, until a specified angle of bend is reached. The axes of two legs of the test piece remain in a plane perpendicular to the axis of bending. In the case of a 180° bend, the two lateral surfaces may, depending on the requirements of the product standard, lie flat against each other or may be parallel at a specified distance, an insert being used to control this distance.
1
EN ISO 7438:2005
4 4.1
Test equipment General
The bend test shall be carried out in testing machines or presses equipped with the following devices: a)
bending device with two supports and a former as shown in Figure 1;
b)
bending device with a V-block and a former as shown in Figure 2;
c)
bending device with a clamp as shown in Figure 3.
Figure 1
Figure 2
2
EN ISO 7438:2005
Key 1
clamp
2
former
Figure 3
4.2
Bending device with supports and a former
4.2.1 The length of the supports and the width of the former shall be greater than the width or diameter of the test piece. The diameter of the former is determined by the product standard. The test piece supports and the former shall be of sufficient hardness (see Figure 1). 4.2.2 l
Unless otherwise specified, the distance between the supports, l , shall be: =
( D + 3a ) ±
a
2
(1)
and shall not change during the bend test.
4.3
Bending device with a V-block
The tapered surfaces of the V-block shall form an angle of 180° − the relevant standard.
(see Figure 2). The angle α is specified in
α
The edges of the V-block shall have a radius between 1 to 10 times the thickness of the test piece and shall be of sufficient hardness.
4.4
Bending device with a clamp
The device consists of a clamp and a former of sufficient hardness; it may be equipped with a lever for applying force to the test piece (see Figure 3). Because the position of the left face of the clamp could influence the test results, the left face of t he clamp (as shown in Figure 3) should not reach up to or beyond the vertical line through the centre of the circular former shape.
3
EN ISO 7438:2005
5 5.1
Test piece General
Round, square, rectangular, or polygonal cross-section test pieces shall be used in the test. Any areas of the material affected by shearing or flame cutting and similar operations during sampling of test pieces shall be removed. However, testing a test piece, the affected parts of which have not been removed, is acceptable, provided the result is satisfactory.
5.2
Edges of rectangular test pieces
The edges of rectangular test pieces shall be rounded to a radius not exceeding the following values:
3 mm, when the thickness of the test pieces is 50 mm or greater;
1,5 mm, when the thickness of the test pieces is less than 50 mm and more than or equal to 10 mm (inclusive);
1 mm when the thickness is less than 10 mm.
The rounding shall be made so that no transverse burrs, scratches or marks are formed which might adversely affect the test results. However, testing a test piece, the edges of which have not been rounded, is acceptable, provided that the result is satisfactory.
5.3
Width of the test piece
Unless otherwise specified in the relevant standard, the width of the test piece shall be as follows: a)
the same as the product width, if the latter is equal to or less than 20 mm;
b)
when the width of a product is more than 20 mm:
5.4
(20 ± 5) mm for products of thickness less than 3 mm,
between 20 mm and 50 mm for products of thickness equal to or greater than 3 mm.
Thickness of the test piece
5.4.1 The thickness of test pieces from sheets, strips and sections shall be equal to the thickness of the product to be tested. If the thickness of the product is greater than 25 mm, it may be reduced by machining one surface to attain a thickness not less than 25 mm. During bending, the unmachined side shall be on the tension-side surface of the test piece. 5.4.2 Test pieces of round or polygonal cross-section shall have a cross-section equal to that of the product, if the diameter (for a round cross-section) or inscribed circle diameter (for a polygonal cross-section) does not exceed 30 mm. When the diameter, or the inscribed circle diameter, of the test piece exceeds 30 mm up to and including 50 mm, it may be reduced to not less than 25 mm. When the diameter, or inscribed circle diameter, exceeds 50 mm it shall be reduced to not less than 25 mm (see Figure 4). During bending, the unmachined side shall be on the tension-side surface of the test piece.
4
EN ISO 7438:2005
Dimensions in millimetres
Figure 4
5.5
Test pieces from forgings, castings and semi-finished products
In the case of forgings, castings and semi-finished products, the dimensions of the test piece and sampling shall be as defined in the general delivery requirements, or by agreement.
5.6
Agreement for test pieces of greater thickness and width
By agreement, test pieces of a greater width and thickness than those specified in 5.3 and 5.4 may be subjected to the bend test.
5.7
Length of the test piece
The length of the test piece depends on the thickness of the test piece and the test equipment used.
6
Procedure
WARNING — During the test, adequate safety measures and guarding equipment shall be provided. 6.1 In general, tests are carried out at ambient temperature between 10 °C and 35 °C. Tests carried out under controlled conditions, where required, shall be made at a temperature of (23 ± 5) °C. 6.2 The bend test shall be carried out using one of the following methods as specified in the relevant standard: a)
a specified angle of bend is achieved under an appropriate force and for the given conditions (see Figures 1, 2 and 3);
b)
the legs of the test piece are parallel to each other at a specified distance apart while under an appropriate force (see Figure 6);
c)
the legs of the test piece are in direct contact while under an appropriate force (see Figure 7).
5
EN ISO 7438:2005
Figure 5
Figure 6
Figure 7
6.3 In the bend test to a specified angle of bend, the test piece shall be placed on the supports (see Figure 1) or on the V-block (see Figure 2) and bent in the middle between supports by the action of a force. The angle of bend, α, can be calculated from the measurement of the displacement of the former as given in Annex A. For the three methods (Figures 1, 2 and 3), the bending force shall be applied slowly so as to permit free plastic flow of the material. In case of dispute, a testing rate of (1 ± 0,2) mm/s shall be used. If it is not possible to bend the test piece directly to the specified angle in the manner described above, the bend shall be completed by pressing directly on the ends of the legs of the test piece (see Figure 5). In a bend test requiring parallel legs, the test piece may be bent first, as indicated in Figure 5, and then placed between the parallel plates of the press (see Figure 6), where it is further formed by application of a force to obtain parallelism of the legs. The test may be carried out with or without an insert. The thickness of the insert shall be as defined in the relevant standard or by agreement. An alternate method of test is that of bending over a f ormer (see 4.4).
6
EN ISO 7438:2005
6.4 If specified, the test piece, after its preliminary bending, shall be further bent between the parallel plates of the press, by application of a force, to obtain direct contact between the legs of the test piece (see Figure 7).
7
Interpretation of results
7.1 The interpretation of the bend test shall be carried out according to the requirements of the product standard. When these requirements are not specified, absence of cracks visible without the use of magnifying aids is considered as evidence that the test piece withstood the bend test. 7.2 The angle of bend, specified in product standards, is always considered as a minimum. If the internal radius of a bend is specified, it is considered as a maximum.
8
Test report
The test report shall include the following information: a)
a reference to this International Standard;
b)
identification of the test piece (type of material, cast number, direction of the test piece axis relative to a product, etc.);
c)
shape and dimensions of the test piece;
d)
test method;
e)
any deviation from this International Standard;
f)
test result.
7
EN ISO 7438:2005
Annex A (informative) Determination of the bend angle from the measurement of the displacement of the former
This International Standard specifies the determination of the bend angle, α , of a test piece under force. The direct measurement of this angle is complicated. For this reason, the method of calculation of this angle from the measurement of the displacement, f , of the former is proposed. The bend angle, α , of the test piece under force can be determined from the displacement of the former and the values given in Figure A.1, as follows:
sin
α
2
cos
α
2
=
p × c + W × ( f p
=
W
2
×
+
(f
−
c)
p −c×( f
p 2
+
(f
−
−
c)
2
−
c)
c) 2
(A.1)
(A.2)
where W
c
=
=
p2
+(
25 + a +
f
D
2
− c)
2
−c
2
(A.3)
(A.4)
Dimensions in millimetres
Figure A.1 — Values for the calculation of the bend angle ,
8
α
blank
BS EN ISO 7438:2005
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