Iso 7438-2016 [PDF]

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ISO 7438

INTERNATIONAL STANDARD

Third edition 2016-01-15

Metallic materials — Bend test

Matériaux métalliques — Essai de pliage

Reference number ISO 7438:2016(E) © ISO 2016

ISO 7438:2016(E)

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© ISO 2016 – All rights reserved

ISO 7438:2016(E)

Page

Contents

Foreword ........................................................................................................................................................................................................................................ iv 1 2 3

Scope ................................................................................................................................................................................................................................. 1 Symbols and designations .......................................................................................................................................................................... 1 Principle ........................................................................................................................................................................................................................ 1

4

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

5

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

6

Procedure ..................................................................................................................................................................................................................... 5

7 8

4.1 4.2 4.3 4.4

General ........................................................................................................................................................................................................... 2 Bending device with supports and a former ................................................................................................................. 3 Bending device with a V-block................................................................................................................................................... 3 Bending device with a clamp ...................................................................................................................................................... 4

5.1 5.2 5.3 5.4 5.5 5.6 5.7

General ........................................................................................................................................................................................................... 4 Edges of rectangular test pieces ............................................................................................................................................... 4 Width of the test piece ...................................................................................................................................................................... 4 Thickness of the test piece ............................................................................................................................................................ 4 Test pieces from forgings, castings and semi-finished products ................................................................. 5 Agreement for test pieces of greater thickness and width ............................................................................... 5 Length of the test piece .................................................................................................................................................................... 5

Interpretation of results ............................................................................................................................................................................... 7 Test report................................................................................................................................................................................................................... 7

(informative)

Annex A Determination of the bend angle from the measurement of the displacement of the former ....................................................................................................................................................................... 8

© ISO 2016 – All rights reserved

iii

ISO 7438:2016(E)

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work o f 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 o f electrotechnical standardization. The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the di fferent types o f ISO documents should be noted. This document was dra fted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives). Attention is drawn to the possibility that some o f the elements o f this document may be the subject o f patent rights. ISO shall not be held responsible for identi fying any or all such patent rights. Details o f any patent rights identified during the development o f the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is in formation given for the convenience o f users and does not

constitute an endorsement.

For an explanation on the meaning o f ISO specific terms and expressions related to con formity

assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary in formation The committee responsible for this document is ISO/TC 164, Mechanical testing ofmetals, Subcommittee SC 2, Ductility testing.

This third edition cancels and replaces the second edition (ISO 7438:2005), which has been technically

revised. The following changes have been made: — Figure 3 has been revised; — a note has been added in 4.2.2; — Formula (A.4) and Figure A.1 have been revised.

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© ISO 2016 – All rights reserved

INTERNATIONAL STANDARD

ISO 7438:2016(E)

Metallic materials — Bend test 1 Scope T h i s I nternationa l Standard s p e c i fie s a me tho d

undergo plastic deformation in bending.

for

de term i n i ng the abi l ity o f me ta l l ic materia l s to

T h i s I nternationa l Sta nda rd appl ie s to te s t pie ce s ta ken

from

me ta l l ic pro duc ts , a s s p e ci fie d i n the

relevant product standard. It is not applicable to certain materials or products, for example tubes in full s e c tion or welde d j oi nts ,

for

wh ich o ther s tanda rd s e xi s t.

2 Symbols and designations Symb ol s and de s ignation s u s e d i n the b end te s t a re s hown i n

Symbol a

L l D

α r f c

p

R

and s p e ci fie d i n

Table 1 — Symbols and designations

Designation Thickness or diameter of test piece (or diameter of the inscribed c i rcle

b

Figures 1 and 2

for

p ie ce s o f p ol ygo n a l c ro s s - s e c tion)

Width of the test piece Length of the test piece Distance between supports Diameter of the former Angle of bend Internal radius of bend portion of test piece after bending Displacement of the former Distance between the plane including the horizontal axis of supports and the central axis of the rounded portion of the former before test Distance between the vertical planes including the central axis of each support and the vertical plane including the central axis of the former Radius of the supports

Table 1.

Unit mm mm mm mm mm degrees mm mm mm mm mm

3 Principle T he b end te s t con s i s ts o f s ubm itti ng a te s t pie ce o f rou nd , s quare, re c tangu lar or p olygona l cro s s s e c tion to pla s tic de formation b y b end i ng , without changi ng the d i re c tion o f lo ad i ng , u nti l a s p e c i fie d

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 18 0 ° bend, the two lateral s ur faces may, dep ending on the requirements o f the pro duc t s tandard, lie flat agai ns t each other or may b e p aral lel at a s peci fied dis tance, an i nsert b ei ng us ed to control this di s tance.

© ISO 2016 – All rights reserved

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ISO 7438:2016(E)

4 Test equipment 4.1

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 — Bending device with two supports and a former

Figure 2 — Bending device with a V-block and a former

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© ISO 2016 – All rights reserved

ISO 7438:2016(E)

Key

1 clamp 2 former Figure 3 — Bending device with a clamp

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 f f f f Figure 1).

diameter o f the tes t p iece. The diameter o f the p iece s up p o rts and the

4.2.2 l

o rmer s hall b e o

o rmer is determined by the p ro duct s tandard. The tes t

s u ficient hardnes s (s ee

, shall be:

Unles s o therwis e s p ecified, the dis tance b etween the s up p o rts , l

= ( D + 3a ) ±

(1)

a

2

and shall not change during the bend test.

NOTE When the distance between the supports ( in clamping during the test and stretch forming of the test piece.

l ) i s s p e c i fie d s m a l ler th a n or e qu a l to D + 2 a, it c a n re s u lt

4.3

Bending device with a V-block

T he tap ere d s u r face s o f the V-blo ck s ha l l

in the relevant standard.

© ISO 2016 – All rights reserved

form

an angle o f 1 8 0 °−

α (see Figure 2). The angle α i s s p e ci fie d

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ISO 7438:2016(E)

The edges of the V-block shall have a radius between 1 to 10 times the thickness of the test piece and

shall be o f su fficient hardness.

4.4 Bending device with a clamp

The device consists o f a clamp and a former o f su fficient hardness; it may be equipped with a lever for applying force to the test piece (see Figure 3). Because the position o f the le ft face o f the clamp could influence the test results, the le ft face o f the

clamp (as shown in Figure 3 ) should not reach up to or beyond the vertical line through the centre of the circular former shape. 5

Test piece

5.1

General

Round, square, rectangular, or polygonal cross-section test pieces shall be used in the test. Any areas o f the material a ffected by shearing or flame cutting and similar operations during sampling o f 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 satis factory. 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 a ffect the test results. However, testing a test piece, the edges o f which have not been rounded, is acceptable, provided that the result is satis factory. 5.3

Width of the test piece

Unless otherwise specified in the relevant standard, the width o f 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: 1) (20 ± 5) mm for products of thickness less than 3 mm, 2) between 20 mm and 50 mm for products of thickness equal to or greater than 3 mm. 5.4 Thickness of the test piece

The thickness of test pieces from sheets, strips and sections shall be equal to the thickness of 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. 5.4.1

the product to be tested. I f the thickness o f the product is greater than 25 mm, it may be reduced by

Test pieces o f round or polygonal cross-section shall have a cross-section equal to that o f the product, i f the diameter (for a round cross-section) or inscribed circle diameter (for a polygonal cross-

5.4.2

section) does not exceed 30 mm. When the diameter, or the inscribed circle diameter, of the test piece 4

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ISO 7438:2016(E)

exceeds 3 0 mm up to and including 5 0 mm, it may b e reduced to no t les s than 2 5 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.

Dimensions in millimetres

Figure 4 — Diameter and the inscribed circle diameter of the test piece

5.5 Test pieces from forgings, castings and semi- finished products I n the c as e o f

forgi ngs ,

c as ti ngs

and s em i-fi n i s he d pro duc ts ,

the d i men s ion s

o f the te s t pie ce a nd

s ampl i ng s ha l l b e a s defi ne d i n the genera l del iver y re qu i rements , or b y agre ement.

5.6 Agreement for test pieces of greater thickness and width B y agre ement, te s t pie ce s o f a gre ater width and th ickne s s th an tho s e s p e ci fie d i n

5.3 and 5.4

may b e

s ubj e c te d to the b end te s t.

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.

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.

6.1

6.2

The

bend

te s t s h al l

relevant standard:

be

carri e d

o ut using o ne

o f th e

fo l l o wi n g

s p e ci fi e d

in

th e

a s p e ci fie d angle o f b end i s ach ieve d u nder an appropri ate

b)

the legs o f the te s t pie ce are p a ra l lel to e ach o ther at a s p e c i fie d d i s tance ap ar t wh i le u nder an

and

for

as

a)

Figures 1, 2 and 3);

force

m e th o d s

the given cond ition s (s e e

appropriate force (see Figure 6); c) the legs of the test piece are in direct contact while under an appropriate force (see Figure 7).

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5

ISO 7438:2016(E)

Figure 5 — Bending the legs of the test piece

Figure 6 — Legs of the test piece parallel to each other

Figure 7 — Legs of the test piece in direct contact 6.3

I n the b end tes t to a s p ecified angle o f b end, the tes t p iece s hall b e p laced o n the s up p o rts (s ee

Figure 1) or on the V-block (see Figure 2 f 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 f f ) and b ent in the middle b etween s up p o rts by the actio n o

) , the b end i ng

orce s ha l l b e appl ie d slowly s o as to p erm it

a

re e

p las tic flow o f the materi a l .

In case of dispute, a testing rate of (1 ± 0,2) mm/s shall be used. I f it i s no t p o s s ible to b end the te s t pie ce d i re c tly to the s p e ci fie d angle i n the man ner de s crib e d ab ove,

Figure 5). Figure 5, and then

the b end sha l l b e comple te d b y pre s s i ng d i re c tly on the end s o f the legs o f the te s t pie ce (s e e

I n a b end te s t re qu i ri ng p aral lel le gs , the te s t pie ce may b e b ent fi rs t, a s i nd ic ate d i n

placed between the parallel plates of the press (see Figure 6

of a

force

) , where it i s

fu r ther forme d

by appl ic ation

to ob tai n p a ra l lel i s m o f the legs . T he te s t may b e c arrie d out with or without an i n s er t. T he

th ickne s s o f the i n s er t s ha l l b e a s defi ne d i n the releva nt s tandard or b y agre ement.

An alternate method of test is that of bending over a former (see 4.4). 6

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ISO 7438:2016(E)

6.4

I f s p ecified, the tes t p iece, a fter its p reliminary b ending, s hall b e

p lates o f the p res s , by ap p licatio n o f a

(see Figure 7).

fo rce,

further b ent b etween

the p arallel

to o b tain direct co ntact b etween the legs o f the tes t p iece

7 Interpretation of results 7.1

The interpretation of the bend test shall be carried out according to the requirements of the

p ro duct s tandard. When thes e requirements are no t s p ecified, ab s ence o f cracks vis ib le witho ut the us e o f magni fying aids is co ns idered as evidence that the tes t p iece withs to o d the b end tes t.

7.2

The angle o f b end, s p ecified in p ro duct s tandards , is always co ns idered as a minimum. I f the

internal radius o f a b end is s p ecified, it is co ns idered as a maximum.

8 Test report

The test report shall include the following information: a) a reference to this International Standard, i.e. ISO 7438; b)

identi fic ation o f the te s t pie ce (typ e o f materi a l , c a s t nu mb er, d i re c tion o f the te s t pie ce a xi s relative

e)

a ny deviation

to a product, etc.) ; c) shape and dimensions of the test piece; d) test method; from

th i s I nternationa l Standard;

f) test result.

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7

ISO 7438:2016(E)

Annex A

(informative) Determination of the bend angle from the measurement of the displacement of the former 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: T h i s I nternationa l Sta nda rd s p e c i fie s the de term i nation o f the b end angle,

sin

cos

α 2

α 2

= =

p × c + W × ( f − c)

(A.1)

p 2 + ( f − c)2

(A.2)

W × p − c × ( f − c) p 2 + ( f − c) 2

where W = p 2 + ( f − c)2 − c 2

(A.3)

D

(A.4)

c =R+a+

2

Figure A.1 — Values for the calculation of the bend angle, α

8

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ISO 743 8: 2 01 6(E)

I CS  

7 7 . 0 40 . 1 0

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