ISO/FDIS 7438

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 7438
ISO/TC 164/SC 2
Metallic materials — Bend test
Secretariat: JISC
Voting begins on: Matériaux métalliques — Essai de pliage
2020­05­12
Voting terminates on:
2020­07­07
ISO/CEN PARALLEL PROCESSING
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 7438:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2020
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ISO/FDIS 7438:2020(E)
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© ISO 2020

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Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols, designations and units .......................................................................................................................................................... 1

5 Principle ........................................................................................................................................................................................................................ 2

6 Test equipment....................................................................................................................................................................................................... 2

6.1 General ........................................................................................................................................................................................................... 2

6.2 Bending device with supports and a former ................................................................................................................. 4

6.3 Bending device with a V­block................................................................................................................................................... 4

6.4 Bending device with a clamp ...................................................................................................................................................... 4

7 Test piece ...................................................................................................................................................................................................................... 4

7.1 General ........................................................................................................................................................................................................... 4

7.2 Edges of rectangular test pieces............................................................................................................................................... 4

7.3 Width of the test piece ...................................................................................................................................................................... 5

7.4 Thickness of the test piece ............................................................................................................................................................ 5

7.5 Test pieces from forgings, castings and semi-finished products ................................................................. 5

7.6 Agreement for test pieces of greater thickness and width ............................................................................... 5

7.7 Length of the test piece .................................................................................................................................................................... 5

8 Procedure..................................................................................................................................................................................................................... 6

9 Interpretation of results ............................................................................................................................................................................... 7

10 Test report ................................................................................................................................................................................................................... 7

Annex A (informative) Determination of the bend angle from the measurement of the

displacement of the former ....................................................................................................................................................................... 8

Annex B (normative) Bend test at plane strain conditions ........................................................................................................... 9

Bibliography .............................................................................................................................................................................................................................13

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This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals,

Subcommittee SC 2, Ductility testing, in collaboration with the European Committee for Standardization

(CEN) Technical Committee CEN/TC 459, ECISS – European Committee for Iron and Steel Standardization,

in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

This fourth edition cancels and replaces the third edition (ISO 7438:2016), which has been technically

The main change compared to the previous edition is the addition of new Annex B, describing bending

Any feedback or questions on this document should be directed to the user’s national standards body. A

This document specifies a method for determining the ability of metallic materials to undergo plastic

This document 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

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

Symbols and designations used in the bend test are shown in Figures 1 and 2 and specified in Table 1.

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

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 can be parallel at a specified distance, an insert being used to control this

The bend test shall be carried out in testing machines or presses equipped with the following devices:

6.2.1 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 (see Figure 1). The

6.2.2 Unless otherwise specified, the distance between the supports, l , shall be as given in Formula (1),

NOTE When the distance between the supports, l , is specified as smaller than or equal to D + 2t, it can

The tapered surfaces of the V-block shall form an angle of 180° − α (see Figure 2). The angle α is specified

The edges of the V­block shall have a radius between 1 and 10 times the thickness of the test piece and

The device consists of a clamp and a former of sufficient hardness. It may be equipped with a lever for

Because the position of the left face of the clamp can influence the test results, the left face of the clamp

(as shown in Figure 3) should not reach up to or beyond the vertical line through the centre of the

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 the sampling of

test pieces shall be removed. However, testing a test piece, the affected parts of which have not been