GB/T 228.1-2021Metallic Materials — Tensile Testing — Part 1: Method of Test at Room Temperature

Foreword

This document was drafted in accordance with the rules given in GB/T 1.1-2020 "Directives for standardization - Part 1: Rules for the structure and drafting of standardizing documents".

This document is Part 1 of GB/T 228 "Metallic materials - Tensile testing". The following parts of GB/T 228 have been issued:

- Part 1: Method of test at room temperature;

- Part 2: Method of test at elevated temperature;

- Part 3: Method of test at low temperature;

- Part 4: Method of test in liquid helium.

This document replaces GB/T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". Compared with GB/T 228.1-2010, in addition to structural and editorial changes, the main technical changes in this document are as follows:

b) Add 3 terms and definitions: "modulus of elasticity", "default value" and "coefficient of determination" (see Chapter 3 of this document);

c) Add selection of extensometer gauge length (see Chapter 8 of this document);

d) Add general information about testing rate (see 10.3.1 of this document);

e) Add two different types of strain rate control modes in the testing rate based on strain rate (Method A): Method A1 and Method A2, as well as specific explanations for Method A1 and Method A2 (see 10.3.2 of this document);

f) Add representation of computer-compatible standards (see C.5 of this document);

g) Add the normative annex "Determination of modulus of elasticity for metallic materials by uniaxial tensile test" (see Annex D of this document);

h) Change the longitudinal arc specimen (see Table H.1 of this document, Table i) Change the estimation of the displacement rate of the compensating beam to account for the deformation of the testing machine system (see Annex I of this document, Annex F of Edition 2010);

strength, plastic extension (Rp)" from normative to informative (see Annex J of this document, Annex J of Edition 2010);

k) Change the assessment of measurement uncertainty (see Annex O of this document, Annex L of Edition 2010).

The revision of this document uses ISO 6892-1:2019 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature".

Compared with ISO 6892-1:2019, there are many structural adjustments in this document. See Annex A for a list of structural changes between the two documents.

There are many technical differences between this document and ISO 6892-1: 2019. The outer margins of the clauses involved are marked with a vertical single line (|). See Annex B for a list of these technical differences and their reasons.

The following editorial changes have been made to this document:

- Add the informative annex "Determination of proof strength, plastic extension (Rp) by step-by-step approximation method" (see Annex J of this document);

- Add the informative annex "Examples for determination of permanent set strength (Rr0.2) by force-unloading method" (see Annex K of this document).

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The issuing authority shall not be held responsible for identifying any or all such patent rights.

This document was proposed by China Iron and Steel Association.

This document shall be under the jurisdiction of National Technical Committee on Steel of Standardization Administration of China (SAC/TC 183).

The drafting organizations of this document: Iron and Steel Research Institute, Metallurgical Industry Information Standards Research Institute, Shenzhen Wanshi Testing Equipment Co., Ltd., Jiangyin Xingcheng Special Steel Co., Ltd., China Machinery Testing Equipment Co., Ltd., Shanxi Taigang Stainless Steel Co., Ltd., Nanjing Iron and Steel Co., Ltd., Pabo Testing Technology Service Co., Ltd., Shanghai Shenli Testing Machine Co., Ltd., Lishi (Shanghai) Scientific Instrument Co., Ltd., Nippon Steel Yingkou Medium Plate Co., Ltd., Bengang Plate Co., Ltd., Zhejiang Special Equipment Science Research Institute, Zhongshan Iron and Steel Co., Ltd. Steel Group Zhengzhou Metal Products Research Institute Co., Ltd., Shougang Group Co., Ltd., Baoshan Iron and Steel Co., Ltd., Xuanhua Iron and Steel Group Co., Ltd., Xiwang Metal Technology Co., Ltd., Zhejiang Jinzhou Tubeline Technology Co., Ltd., National Steel and Product Quality Supervision and Inspection Center, Qiqihar Huagong Machine Tool Co., Ltd., Shandong Xindadi Holding Group Co., Ltd., Shanghai Institute of Materials, Changsha Dicastal Technology Co., Ltd., Shandong Juncheng Metal Technology Co., Ltd., Xiamen Special Equipment Inspection and Testing Institute, Beijing Tiger Ruixiang Technology Co., Ltd., Jianlong Xilin Iron and Steel Co., Ltd., Chengde Jianlong Special Steel Co., Ltd., Guohe General Testing, Evaluation and Certification Co., Ltd., Southwest Aluminum (Group) Co., Ltd., Anshan Iron and Steel Co., Ltd., Steel Research Nanogram Testing Technology Co., Ltd.

Wang Hongbin, Mao Shuaishuai , Chen Kai, Huang Fei, Hou Huining, Wang Hongliang, Fu Chongjian, Ba Fahai, Liu Jun, Sun Pu, Xu Huoli, Dong Qiang, Wang Yongbin, Zhang Yajun, Li Ying, Yuan Sheng, Lu Dan, Fang Jian, Li Rongfeng, Wu Yiwen , Yin Jianjun, Liu Sijia, Bai Yun, Zhang Senbao, Jia Yuanwei, Liang Caimeng, Li Jianfeng, Tian Yuwei, Zhang Jun, Shi Li, Jia Jianping, Chen Wenbin, Sun Dayong, Wang Bin, Zhang Hongju, Li Dongyu, Li Hongguang, Zou Zhijian, Gu Feng, Yang You , Ren Yongxiu, Zhang Qingshui, Li Xiaojun.

Versions of standard substituted by this document are:

- GB/T 228-1963 that was issued in 1963 for the first time. The first revision was in 1976. The second revision was in 1987;

- When it was revised for the third time in 2002, it combined the contents of GB/T 3076-1982 "Method for tensile testing of metallic sheet and strip" and GB/T 6397- 1986 "Metallic materials - Test pieces for tensile testing";

- When it was revised in 2010 for the fourth time, the document number was

- This is the fifth revision.

Introduction

GB/T 228 "Metallic materials - Tensile testing" is the most widely used and most concerned test method standard in the mechanical test of metal materials. It aims to specify tensile test methods for metallic materials at different temperature ranges.

- Part 1: Method of test at room temperature;

- Part 2: Method of test at elevated temperature;

- Part 3: Method of test at low temperature;

- Part 4: Method of test in liquid helium.

This document provides two methods for controlling the testing rate. Method A is a control mode based on strain rate (including crossbead separation rate). Method B is the control mode based on the stress rate. Method A is designed to reduce testing rate variation and reduce measurement uncertainty in test results when determining strain rate sensitive parameters. Since the strain rate sensitivity of materials is often unknown, the best method to use is Method A.

decided to recommend the use of strain rate control in future revisions of the standard.

"strain" are used in various contexts, respectively (as a graph axis label or as a description for determining performance). However, for general descriptions or points on a curve, the names "force" and "stress" or "extension", "percent extension" and "strain" can be interchanged, respectively.

1 Scope

This document specifies the definitions, symbols and descriptions, principles, specimens and their dimensional measurements, test equipment, test requirements, performance measurements, numerical rounding of test results, and test reports for tensile tests of metallic materials.

This document applies to the determination of the tensile properties of metallic materials at room temperature.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

GB/T 12160, Metallic materials - Calibration of extensometers systems used in uniaxial testing (GB/T 12160-2019, ISO 9513:2012, IDT) GB/T 22066, Evaluation for computerized data acquisition systems for used in static uniaxial testing machines JJG 139, Verification regulation of Tension, Compression and Universal Testing Machines JJG 475, Verification Regulation of Electronic Universal Testing Machine JJG 762, Verification Regulation for Extensometer JJG 1063, Verification Regulation of Electro-hydraulic Servo Universal Testing Machines

3 Terms and definitions

3.1 gauge length; L

The length of the parallel portion of the specimen on which elongation is measured at any moment during the test.

3.1.1 original gauge length; Lo

The specimen gauge length before applying force at room temperature (3.1).

3.1.2 final gauge length after fracture; Lu

At room temperature, the two parts of the fractured specimen are closely butted together. The axes of the two parts are ensured to be on the same straight line. The gauge length (3.1) after the fracture of the specimen is measured.

3.2 parallel length; Lc

The length of the parallel reduced portion of the specimen.

gripping portions of the unmachined specimen. See Bibliography [6].

3.3 elongation

The increase in the original gauge length (3.1.1) at any moment during the test.

3.4 percentage elongation

3.4.1 percentage permanent elongation

The ratio of the elongation to the original gauge length (Lo) (3.1.1), expressed in %, after the specified stress has been removed.

The ratio of residual elongation of gauge length after fracture (3.3) (Lu−Lo) to original gauge length (Lo) (3.1.1), expressed in %.

4 Symbols and descriptions

The symbols used in this document and their corresponding descriptions are shown in Table 1. L’o mm Original gauge length to determine Awn (see Annex N) Lc mm Parallel length Le mm Extensometer gauge length Lt mm Specimen total length du mm Minimum diameter at the neck of the circular cross-section specimen after fracture Lu mm Gauge length after fracture L’u mm Gauge length after fracture to determine Awn (see Annex N) So mm2 Original cross-sectional area Su mm2 Minimum cross-sectional area after fracture k - Proportionality coefficient (see 6.1.1) Percentage elongation A % Percentage elongation after fracture (see 3.4. […]

5 Principles

Unless otherwise specified, the test shall be carried out at room temperature between 10°C~35°C. For laboratories whose room temperature does not meet the above requirements, the laboratory shall evaluate the impact of testing machines operating under such environmental conditions on test results and/or calibration data. When testing and calibration activities exceed the requirements of 10°C~35°C, the temperature shall be recorded and reported. If there is a large temperature gradient during testing and/or calibration, the measurement uncertainty may increase, and outof-tolerance conditions may occur.

For tests with strict temperature requirements, the test temperature shall be 23°C ± 5°C.

6 Specimens

6.1 Shape and size

6.1.2 Machined specimens

If the dimensions of the gripping end of the specimen and the parallel length are not the same, they shall be connected by a transition arc. If the transition radius is not specified in the corresponding appendix (see 6.2), it is recommended to specify it in the relevant product standard.

The shape of the gripping end of the specimen shall be suitable for the grip of the testing machine. The axis of the specimen shall coincide with the action line of the force.

The parallel length Lc of the specimen or the free length between the grips when the specimen does not have a transition arc shall be greater than the original gauge length (Lo).

6.1.3 Unmachined specimens

If the specimen is a length or test bar of unmachined product, the length between the two grips shall be sufficient, so as to make the original gauge mark and the collet have a reasonable distance (see Annex E ~ Annex H). […]

7 Determination of original cross-sectional area

The relevant dimensions of the specimen shall be measured at a sufficient number of points in the area of the parallel length of the specimen.

It is recommended that when measuring the cross-sectional area of the specimen, measurements shall be made at a minimum of three different locations along the parallel length of the specimen.

The original cross-sectional area (So) is the average value of the calculated crosssectional area based on the measured actual dimensions.

The calculation accuracy of the original cross-sectional area depends on the specimen type. Annex E ~ Annex H give the evaluation methods of the original crosssectional area So of different types of specimens. A detailed description of the measurement accuracy is also provided.

All measuring devices used to measure the original cross-sectional area shall be calibrated according to appropriate reference standards that can be traceable to national measurement system.

8 Original gauge length and extensometer gauge length

8.2 Marks of original gauge length

For manual determination of percentage elongation after fracture A, both ends of the original gauge length Lo shall be marked with thin dots or lines. However, marks that cause premature fracture cannot be used. The original gauge length shall be marked with an accuracy of ±1%.

For proportional specimens, if the difference between the calculated value of the original gauge length and its marked value is less than 10% Lo, the calculated value of the original gauge length can be rounded to the nearest multiple of 5mm according to GB/T 8170.

If the parallel length (Lc) is much longer than the original gauge length, for example for unmachined specimens, a series of nested original gauge lengths can be marked. Sometimes, a line parallel to the longitudinal axis of the specimen can be drawn on the surface of the specimen. And mark the original gauge length on this line.