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Standard ID | GB/T 232-2024 (GB/T232-2024) | Description (Translated English) | Metallic materials -- Bend testing method | Sector / Industry | National Standard (Recommended) | Classification of Chinese Standard | H23 | Classification of International Standard | 77.040.10 | Word Count Estimation | 15,162 | Date of Issue | 2024-03-15 | Date of Implementation | 2024-10-01 | Older Standard (superseded by this standard) | GB/T 232-2010 | Administrative Organization | National Steel Standardization Technical Committee (SAC/TC 183) | Proposing organization | China Iron and Steel Industry Association | Issuing agency(ies) | State Administration for Market Regulation, National Standardization Administration | Standard ID | GB/T 232-2010 (GB/T232-2010) | Description (Translated English) | Metallic materials. Bend test | Sector / Industry | National Standard (Recommended) | Classification of Chinese Standard | H23 | Classification of International Standard | 77.040.10 | Word Count Estimation | 12,172 | Date of Issue | 2010-09-02 | Date of Implementation | 2011-06-01 | Older Standard (superseded by this standard) | GB/T 232-1999 | Quoted Standard | GB/T 2975 | Adopted Standard | ISO 7438-2005, MOD | Drafting Organization | Shougang Corporation | Administrative Organization | National Steel Standardization Technical Committee | Regulation (derived from) | National Standard Approval Announcement 2010 No.4 (Total No.159) | Proposing organization | China Iron and Steel Association | Issuing agency(ies) | Administration of Quality Supervision, Inspection and Quarantine of People's Republic of China; Standardization Administration of China | Summary | This standard specifies test methods for metallic materials side given plastic deformation ability to withstand bending. This standard applies to metallic materials relevant product standard bend test specimen. But not for metal tubing and metal bending tests of welded joints. Metal pipes and metal welded joints bending test prescribed by other criteria. | Standard ID | GB/T 232-1999 (GB/T232-1999) | Description (Translated English) | Metallic materials--Bend test | Sector / Industry | National Standard (Recommended) | Classification of Chinese Standard | H23 | Classification of International Standard | 77.040.10 | Word Count Estimation | 8,878 | Date of Issue | 1999/11/1 | Date of Implementation | 2000/8/1 | Older Standard (superseded by this standard) | GB/T 232-1988 | Quoted Standard | GB/T 2975-1998 | Adopted Standard | ISO 7438-1985, MOD | Regulation (derived from) | Announcement of Newly Approved National Standards 2010 No. 4 (No. 159 overall) | Proposing organization | State Bureau of Metallurgical Industry | Issuing agency(ies) | State Quality and Technical Supervision |
GB/T 232-2024
GB
NATIONAL STANDARD OF THE
PEOPLE'S REPUBLIC OF CHINA
ICS 77.040.10
CCS H 23
Replacing GB/T 232-2010
Metallic materials - Bend testing method
(ISO 7438:2020, Metallic materials - Bend test, MOD)
ISSUED ON: MARCH 15, 2024
IMPLEMENTED ON: OCTOBER 1, 2024
Issued by: State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 5
4 Symbols and descriptions ... 5
5 Principles ... 6
6 Test equipment ... 6
6.1 General requirements ... 6
6.2 Bending device with two supports ... 8
6.3 Bending device with a V-block ... 8
6.4 Bending device with a clamp ... 8
6.5 Other bending devices... 8
7 Test pieces ... 9
7.1 General requirements ... 9
7.2 Edges of test pieces ... 9
7.3 Width of the test piece... 9
7.4 Thickness of the test piece ... 10
7.5 Test pieces from forged materials, cast materials and semi-finished products ... 10
7.6 Test pieces with greater thickness and width ... 10
7.7 Length of the test piece ... 11
8 Test procedures ... 11
9 Evaluation of test results ... 13
10 Test report ... 13
Appendix A (Normative) Bending test under plane strain conditions ... 14
A.1 Overview ... 14
A.2 General requirements ... 15
A.3 Test piece ... 16
A.4 Result evaluation ... 16
A.5 Test report ... 17
Appendix B (Informative) Determination method of bending angle by measuring the
displacement of the bending former ... 18
References ... 19
-- The "inner radius" is changed to "diameter of the former" (see 9.2) for better
operability;
-- The "square root of η" is changed to "η value" (see A.2) to keep it consistent with
the previous sentence.
The following editorial changes are made to this document:
-- The name of the standard is changed to "Metallic materials - Bend testing
method";
-- The reference to Figure 5 is added [see 8.2 a)].
Please note that some content in this document may be subject to patents. The publisher
of this document assumes no responsibility for identifying patents.
This document was proposed by the China Iron and Steel Association.
This document is under the jurisdiction of the National Technical Committee on Steel
of Standardization Administration of China (SAC/TC183).
Drafting organizations of this document: Shougang Group Co., Ltd., Zhejiang Kingland
Pipe Industry Co., Ltd., Rizhao Quality Inspection and Testing Institute [National
Carbon Structural Steel Product Quality Inspection and Testing Center (Shandong)],
Tongling Fuxin Iron and Steel Co., Ltd., Hunan Valin Xiangtan Iron and Steel Co., Ltd.,
Jiangsu Chengxin Inspection, Testing and Certification Co., Ltd., Ningxia Jianlong
Special Steel Co., Ltd., Inner Mongolia Baotou Steel Union Co., Ltd., Jianlong Xilin
Iron and Steel Co., Ltd., Shandong Xindadi Holding Group Co., Ltd., Zhejiang
Academy of Special Equipment Science, Shenzhen SUNS Technology Stock Co., Ltd.,
Jilin Jianlong Steel Co., Ltd., Shandong Special Equipment Inspection Institute Group
Co., Ltd., China Metallurgical Information and Standardization Institute, Wuhan
Fanzhou Chuetsu Metal Co., Ltd.
Main drafters of this document: Qiu Yu, Yang Weifang, Lu Xianbao, Ding Gang, Kuang
Yonghai, Zou Fanqiu, Gan Meilu, Wang Shifeng, Ma Yue, Xu Weili, Fu Chongjian,
Cheng Dongyue, Liu Jie, Zhao Junqing, Yao Xiaojing, Dong Li, Yao Lian, Zhang
Qingshui, Ni Guoliang, Cui Lei, Hou Huining, Zhang Xing, Su Zan, Wang Shuqiang,
Wang Bin, Wang Shangkun, Sun Dayong, Liu Zhongqiang, Zhang Haihua, Wang
Chunmao, Li Qiuhan, Zhang Qi, Mou Xueping, Zhang Qiang, Zhou Zhichao, Wu
Chaohui, Wang Wei.
This document was first published in 1963, revised for the first time in 1982, for the
second time in 1988, for the third time in 1999, and for the fourth time in 2010. This is
the fifth revision.
6.2 Bending device with two supports
6.2.1 The length of support and the width of the bending former shall be greater than
the width or diameter of the test piece (see Figure 1). The diameter of the bending
former is specified by the product standard. The supports and bending former shall have
sufficient hardness.
6.2.2 Unless otherwise specified, the distance l between the supports shall be
determined according to formula (1). This distance shall remain constant during the test.
NOTE: If the distance l between the supports is specified to be no greater than D+2a, the test piece may
be clamped during the test and may be deformed by bending.
6.3 Bending device with a V-block
The angle of the tapered surface of the V-block shall be 180°-α (see Figure 2), and the
bending angle α shall be specified in the relevant product standards.
The supporting edges of the block shall be rounded, and the rounding radius shall be 1
to 10 times the thickness of the test piece. The width of the block and the bending former
shall be greater than the width or diameter of the test piece and shall have sufficient
hardness.
6.4 Bending device with a clamp
The device consists of a clamp and a bending former with sufficient hardness (see
Figure 3), and can be equipped with a force lever.
Since the position of the left end face of the clamp will affect the test results, the left
end face of the clamp (see Figure 3) cannot reach or exceed the vertical center line of
the circular former.
6.5 Other bending devices
Other bending devices that comply with the bending test principle (such as a turning-
plate bending device) can also be used.
7 Test pieces
7.1 General requirements
The test shall use circular, square, rectangular or polygonal cross-section test pieces,
and the surface of the test piece shall not be scratched or damaged that would affect the
test results. The cutting position and direction of the sample blank shall comply with
the provisions of relevant product standards. If not specified, for steel products, the
requirements of GB/T 2975 shall be followed. The test pieces shall be free of portions
that would affect the material properties due to shearing, flame cutting, or similar
operations. If the test results are not affected, the affected part of the test piece may not
be removed.
7.2 Edges of test pieces
Edges of rectangular and polygonal cross-section test pieces shall be rounded, and the
rounding radius shall not exceed the following values:
-- 1 mm, when the test piece thickness is less than 10 mm;
-- 1.5 mm, when the test piece thickness is greater than or equal to 10 mm and less
than 50 mm;
-- 3 mm, when the test piece thickness is greater than or equal to 50 mm.
When the edges are rounded, no transverse burrs, scratches or marks that may affect the
test results shall be formed. If the test results are not affected, the edges of the test piece
may not be rounded.
7.3 Width of the test piece
The width of the test piece shall comply with the provisions of the relevant product
standards. If no specific provisions are given, the following requirements shall apply:
a) When the product width is not greater than 20 mm, the test piece width is the
product width;
b) When the product width is greater than 20 mm:
1) When the product thickness is less than 3 mm, the test piece width is (20±5)
mm;
2) When the product thickness is greater than or equal to 3 mm, the test piece
8.4 During the test that the test piece is bent until the two arms are parallel to each other,
first bend the test piece (see Figure 5), then place the test piece between two parallel
pressing plates, and continuously apply force to both ends to further bend it until the
two arms are parallel (see Figure 6). The test can be performed with or without spacers.
The thickness of the spacer shall be in accordance with the provisions specified in
relevant standards or agreements.
8.5 During the bending test requiring two arms of the test piece in direct contact, the
test piece is first pre-bent, and then the test piece is placed between two parallel pressing
plates, and the force is continuously applied to both ends of the test piece to further
bend it until the two arms are in direct contact (See Figure 7).
9 Evaluation of test results
9.1 The bending test results shall be evaluated in accordance with the requirements of
the relevant product standards. If the product standards do not specify, the test piece
after bending shall be observed without using magnifying auxiliary equipment. If there
are no visible cracks on the outer surface of the bend, it shall be evaluated as qualified.
9.2 If the relevant product standard specifies the bending angle, this value is the
minimum test value; if the diameter of the former is specified, this value is the
maximum test value.
NOTE: The presence of an oxide layer on the unmachined surface of the bending test piece on the tension
side will affect the assessment of the test results. This is generally specified by the product standard or
relevant parties.
10 Test report
The test report shall at least include the following contents:
a) This document number;
b) Identification of the test piece (material grade, heat number, sampling
direction, etc.);
c) Shape and dimensions of the test piece;
d) Test conditions (diameter of the bending former and the bending angle);
e) Deviations from this document;
f) Test results.
Bend testing that is suitable for all applications and product sizes can determine product
bending performance in the most extreme state. When the test piece is in a plane strain
state, it will reach an extreme state of bending. When the width-to-thickness ratio (b/a)
is not less than 10, the test piece will be in a plane strain state. But if the width of the
test piece is too small, this critical state (plane strain) will not be reached[1-5].
The provisions given in this appendix will still lead to the following effects:
-- Compared with the test piece with the width specified in 7.3, the effective
bending angle α is reduced;
-- The test piece may be unqualified;
-- Loading test force will increase;
-- The weight of the test piece will increase;
-- The bending performance requirements in product standards may not be met.
For some applications, the results measured according to this appendix will be more
realistic.
Since most test pieces with circular or regular hexagonal cross-sections (bar) will not
reach a critical state (plane strain), the content of this appendix is not involved.
A.2 General requirements
The bending performance of a thin plate or strip (rectangular test pieces) depends
largely on the width of the test piece. Different test piece widths will show different
strain states. The test piece with a too-small width can promote the possibility of the
bending test results being judged as qualified, see Figure A.2. The same bending former
is used for the test, but the results vary greatly due to the different test piece widths.
The width-to-thickness ratio (b/a) of the test piece on the left is 4, which does not meet
the critical stress triaxiality condition (η [̅=0] = +1/√3≈0.58) required by plane strain
(tension)[6]. The critical stress triaxiality condition value can be obtained based on the
relationship between stress triaxiality η and the Lode angle parameter ̅ [7-9] [see
formula (A.1)]; let θ=0 (representing the plane strain path) and calculate the η value.
Figure A.2 shows the estimated values of stress triaxiality (using finite element
simulations), confirming that there is a good correlation between the area causing the
failure and reaching the stress triaxiality above the critical plane strain condition.
......
GB/T 232-2010
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.10
H 23
Replacing GB/T 232-1999
Metallic Materials - Bend Test
(ISO 7438:2005, MOD)
ISSUED ON: SEPTEMBER 2, 2010
IMPLEMENTED ON: JUNE 1, 2011
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative References ... 5
3 Symbols and Instructions ... 5
4 Principle ... 6
5 Test Equipment ... 7
6 Test Pieces ... 8
7 Test Procedure ... 10
8 Evaluation of Test Result ... 12
9 Test Report ... 12
Appendix A (Informative) A Comparison List of Chapter No. in this Standard and
ISO 7438:2005 ... 14
Appendix B (Informative) Determination Method of Bending Angle through
Measurement of Displacement of Bent Indenter ... 16
Foreword
The modification of this Standard adopts international standard ISO 7438:2005
Metallic Materials - Bend Test (English version) as a reference.
This Standard was re-drafted in accordance with ISO 7438:2005. In order to make it
convenient for comparison, Appendix A provides a comparison list between the chapter
No. in this national standard and the Chapter No. in the international standard.
The main technical differences between this Standard and the international standard
are as follows:
---Chapter 2 “Normative References” is added;
---Figure 3 and Figure B.1 are added to Chapter 3;
---5.5 “other bending devices (for example, flap-type bending device) that comply
with the principle of bend test may also be adopted” is added;
---“The cutting location and direction of test piece shall comply with the
requirements of relevant product standards. If it is not specifically stipulated,
steel products shall comply with the requirements in GB/T 2975.” is added to
6.1.
In order to make it convenient to be used, this Standard makes the following editorial
modifications:
---The phrase “this International Standard” is modified into “this Standard”;
---Decimal point “.” is used to replace comma “,”, which serves as decimal point;
---The foreword in the international standard is deleted.
This Standard serves as a replacement of GB/T 232-1999 Metallic Materials - Bend
Test.
This amendment of this Standard makes the following modifications in technical
content based on GB/T 232-1999:
---The term “flexural center” is deleted;
---The formula that determines test piece’s length is deleted;
---The stipulations of test piece’s thickness are modified;
---The stipulations of fillet radius value of rectangular test piece are added;
Metallic Materials - Bend Test
1 Scope
This Standard stipulates the test method for the determination of metallic materials’
ability of withstanding plastic deformation in bending.
This Standard is applicable to bend test of test pieces of metallic materials stipulated
in relevant product standards. However, it is not applicable to bend test of metal pipes
and metal welded joints. The bend test of metal tubes and metal welded joints shall be
stipulated by other standards.
2 Normative References
Through the reference in this Standard, clauses of the following documents become
clauses of this Standard. In terms of references with a specific date, all the subsequent
modification sheets (excluding the corrected content) or the revised editions are not
applicable to this Standard. However, all parties that reach an agreement in
accordance with this Standard are encouraged to explore the possibility of adopting
the latest version of these documents. In terms of references without a specific date,
the latest version is applicable to this Standard.
GB/T 2975 Steel and Steel Products - Location and Preparation of Test Pieces for
Mechanical Testing (GB/T 2975-1998, eqv ISO 377: 1997)
3 Symbols and Instructions
The symbols adopted in this Standard, and the instructions of the symbols are shown
in Table 1, Figure 1, Figure 2, Figure 3 and Figure B.1.
Table 1 -- Symbols and Instructions
Symbols Instructions Unit
Test piece’s thickness or diameter (or inscribed circle diameter of
polygonal cross section) mm
b Test piece’s width mm
L Test piece’s length mm
l Distance between rollers mm
D Diameter of bent indenter mm
a Bending angle ()
r Bending radius of test piece after bending mm
f Displacement distance of bent indenter mm
c Before test, the distance between the horizontal plane where the roller’s mm
5.3 V-shaped Mold Bending Device
The angle of V-shaped groove of the mold shall be (180 - a) (see Figure 2). Bending
angle (a) shall be stipulated in relevant product standards.
The supporting edges of the mold shall be rounded; the rounding radius shall be (1 ~
10) times of the test piece’s thickness. The width of the mold and bent indenter shall
be more than the width or diameter of the test piece. In addition, the mold and bent
indenter shall have sufficient hardness.
5.4 Clamp-type Bending Device
The device is constituted of clamp and bent indenter, which has sufficient hardness
(see Figure 3). A lever of force application may be allocated. The diameter of bent
indenter shall comply with the requirements of relevant product standards; the width of
bent indenter shall be more than the width or diameter of test pieces.
Sine the position of the left end face of the clamp will affect the test result, the left end
face (see Figure 3) of the clamp cannot reach or exceed the bent indenter’s central
vertical line.
5.5 Other bending devices (for example, flap-type bending device) that comply with
the principle of bend test may also be adopted.
6 Test Pieces
6.1 General Requirements
Test pieces of circular, square, rectangular or polygonal cross section shall be used in
test. The cutting location and direction of test piece shall comply with the requirements
of relevant product standards. If it is not specifically stipulated, steel products shall
comply with the requirements in GB/T 2975. Parts where material performance is
affected by shearing or flame cutting, or similar operations, shall be removed. If the
test result is not affected, it is allowed to retain the affected parts.
6.2 Edges of Rectangular Test Pieces
The surface of test pieces shall not manifest any scratch or damage. The edges of
square, rectangular and polygonal cross section test pieces shall be rounded; the
rounding radius cannot exceed the following numerical values:
---1 mm, when test piece’s thickness is less than 10 mm;
---1.5 mm, when test piece’s thickness is more than or equals to 10 mm, and less
than 50 mm;
---3 mm, when test piece’s thickness is not less than 50 mm.
7.3 In the test that bends test piece to the stipulated bending angle, the test piece shall
be placed on the two rollers (see Figure 1) or the V-shaped mold (see Figure 2); test
piece’s axes shall be vertical to the bent indenter’s axes. In the midpoint between the
two supports, the bent indenter continuously applies force on the test piece to make it
bent, till the stipulated bending angle is reached. Bending angle (a) may be calculated
through the measurement of the displacement of the bent indenter, as it is shown in
Appendix B.
The method shown in Figure 3 may be adopted to conduct the bend test. Fixate one
end of the test piece; bend it around the bent indenter. It may be bent across the bent
indenter, till it reaches the stipulated bending angle (see 5.4 for details).
In bend test, slowly apply the bending force, so that materials can freely conduct plastic
deformation.
When there is a dispute, test rate shall be (1 ± 0.2) mm/s.
If it is impossible to directly reach the stipulated bending angle through the above-
mentioned methods, place the test piece between two parallel pressing plates (see
Figure 5); continuously apply force onto both ends, so that the test piece would further
bend, till it reaches the stipulated bending angle.
7.4 In test that test piece is bent till its two arms are mutually parallel, firstly,
preliminarily bend the test piece; then, place the test piece between two parallel
pressing plates (see Figure 5); continuously apply force onto both ends, so that the
test piece would further bend, till the two arms become parallel (see Figure 6). In the
test, an internal insert may, or, may not be added. The thickness of the insert equals
to the stipulated diameter of bent indenter, unless it is otherwise stipulated in product
standards.
7.5 In test that test piece is bent till its two arms directly contact with each other, firstly,
preliminarily bend the test piece; then, place the test piece between two parallel
pressing plates; continuously apply force onto both ends, so that the test piece would
further bend, till the two arms directly contact with each other (see Figure 7).
Figure 5
......
GB/T 232-1999
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.10
H 23
eqv ISO 7438:1985
Replacing GB/T 232-1988
Metallic Materials – Bend Test
ISSUED ON: NOVEMBER 01, 1999
IMPLEMENTED ON: AUGUST 01, 2000
Issued by: State Bureau of Quality and Technical Supervision
Replaced
Table of Contents
Foreword ... 3
ISO Foreword ... 4
1 Scope ... 5
2 Normative References ... 5
3 Principle ... 5
4 Symbols ... 6
5 Test Device ... 7
6 Specimen ... 9
7 Test Procedures ... 11
8 Test Results ... 13
9 Test Report ... 13
Metallic Materials - Bend Test
1 Scope
This Standard specifies the principle for bend test method, symbols, test devices,
specimen, test procedures, assessment of test results, and test report.
This Standard is applicable to the bend test for specimen that is specified by the
relevant product standards of the metallic materials; and determine its bending plastic
deformation. However, it is not applicable to the bend tests for metallic tubes and
metallic welded joints.
2 Normative References1)
The following standards contain provisions which, through reference in this Standard,
constitute provisions of this Standard. At the time of publication, the editions indicated
are valid. All standards are subject to revision. The parties who are using this Standard
shall explore the possibility of using the latest version of the following standards.
GB/T 2975-1998 Steel and Steel Products - Location and Preparation of Test
Pieces for Mechanical Testing
3 Principle
The bend test consists of submitting a specimen 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.
During the bend test, the axes of two arms of the specimen remain in a plane
perpendicular to the axis of bending. In the case of a 180° bend test, according to the
requirements of relevant product standard, the specimen shall be bent till the two arms
are at a specified distance, parallel to each other; or the two arms come into contact
directly.
1) The contents of this Clause are not specified in ISO 7438:1985. The quoted national standard GB/T
2975-1998 is equivalent to the international standard ISO 377:1997 Steel and Steel Products - Location
and Preparation of Test Pieces for Mechanical Testing.
one of the following bending devices:
a) Bending device with roller as shown in Figure 1;
b) Bending device with a V-block as shown in Figure 2;
c) Bending device with a clamp as shown in Figure 3;
d) Bending device with turning plate as shown in Figure 4.
5.1 Bending device with roller
5.1.1 The length of the roller shall be greater than the width or diameter of the specimen.
The radius of the roller shall be 1~10 times thickness of the specimen. The roller shall
be of sufficient hardness.
5.1.2 Unless otherwise specified, the distance between the rollers (see Figure 1) shall
be determined as per the Formula (1):
Such distance shall remain unchanged during the test.
5.1.3 The diameter of the bending head shall be specified in the relevant product
standard. The width of the bending head shall be greater than the width or diameter of
the specimen. The bending head shall be of sufficient hardness.
5.2 Bending device with a V-block
The angle of the V-block shall be 180°- α (see Figure 2). The bending angle shall be
specified in the relevant product standard. The corner radius of the bending head is
d/2.
The supporting edges of the V-block shall be rounded; and its rounding radius shall be
1 ~ 10 times thickness of the specimen. The width of the mold and bending head shall
be greater than the width or diameter of the specimen. The bending head shall be of
sufficient hardness.
5.3 Bending device with a clamp
The device consists of a clamp and a bending center of sufficient hardness (see Figure
3). It may be equipped with a lever for applying force. The diameter of the bending
center shall be as specified in relevant product standard; the width of the bending
center shall be greater than the width or diameter of the specimen.
a) When the width of product is no greater than 20mm, the width of the specimen
shall be that of the original product;
b) When the width of a product is greater than 20 mm, and the thickness is less
than 3mm, the width of the specimen shall be (20 ± 5) mm. When the thickness
is no less than 3mm, the width of the specimen shall be 20~50mm.
6.4 The thickness or diameter of the specimen shall meet the requirements of relevant
product standard. If not specified, it shall be as follows:
6.4.1 For the sheets, strips and sections, when the thickness of the product is no
greater than 25mm, the thickness of the specimen shall be that of the original product.
When the thickness of the product is greater than 25mm, the thickness of the specimen
may be reduced by machining to no less than 25mm, and one-side shall be retained
unmachined. The unmachined side of the specimen during the bend test shall be on
the tension-side.
5.4.2 For products with a diameter or polygonal cross-section whose inscribed circle
diameter is no greater than 50mm, the cross-section of the specimen shall be that of
the product. If the capacity of the test equipment is insufficient, for products with a
diameter or polygonal cross-section whose inscribed circle diameter exceeds 30~50
mm, it may be machined into a specimen with a cross-section whose inscribed circle
diameter is no less than 25 mm according to Figure 5. For products with a diameter or
a polygonal cross section whose inscribed circle diameter is greater than 50 mm, it
may be machined into a specimen with a cross-section whose inscribed circle diameter
is no less than 25 mm according to Figure 5. During the test, the unmachined original
surface of the specimen shall be on the tensile deformation side. Unless otherwise
specified, steel-reinforced products are tested by their total cross-section.
6.5 In the case of forgings, castings and semi-finished products, the dimensions of the
specimen shall be as defined in the general delivery requirements, or by agreement.
6.6 For non-arbitration test, the test may be carried out by specimens with width and
thickness larger than that specified in 6.3 and 6.4.
6.7 The length of the specimen depends on the thickness of the specimen and the
used test equipment. When the method in Figures 1 and 4 are used, it may be
determined by Formula (3):
Where:
π is circumference ratio, taking the value of 3.1.
Figure 5 – Shape and Dimension of Cross-Section of Thinning Specimen
7 Test Procedures
7.1 In general, the test shall be carried out at ambient temperature between 10 °C and
35 °C. For the test with strict requirements for the temperature, the test temperature
shall be at (23 ± 5) °C.
7.2 As specified by the relevant product standard, the test shall be finished by one of
the following methods.
a) The specimen is bent to a specified angle of bend under the conditions and force
g given in Figures 1, 2, 3 or 4;
b) The specimen is bent under the force till a specified distance between the two
arms and parallel to each other [see Figure 4c) and Figure 7];
c) The specimen is bent under force till the two arms are in direct contact (see Figure
8).
7.3 For the test when the specimen is bent to the specified bending angle, the
specimen shall be placed on two rollers [see Figure 1a] or V-block (see Figure 2) or
two horizontal turning plates [see Figure 4a)]; the axis of the specimen shall be
perpendicular to the axis of the bending head; and the bending head shall continuously
apply force to the specimen at the midpoint between the two supports to bend it until it
reaches the specified bending angle.
If the specified bending angle cannot be reached directly, the specimen shall be placed
between two parallel pressing plates (see Figure 6); and apply continuous pressure to
both ends to further bend it until the specified bending angle is reached.
7.4 When the specimen is bent to a 180° angle, the two arms are spaced apart at a
specified distance and are parallel to each other, and the method shown in Figure 1 is
adopted, the specimen is bent initially (the bending angle shall be as large as possible);
and then place the specimen between two parallel pressing plates (see Figure 6) to
apply continuous pressure to both ends to further bend it till the two arms are parallel
(see Figure 7). The cushion block may or may not be added. Unless otherwise
specified in the product standard, the thickness of the cushion block is equal to the
(Min.) (Min.)
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