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GB/T 232-2024 PDF in English


GB/T 232-2024 (GB/T232-2024, GBT 232-2024, GBT232-2024)
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GB/T 232-2024: PDF in English (GBT 232-2024)

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.
......
 
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.