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This document is developed 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 the Part 1 of GB/T 228 Metallic materials—Tensile testing. The following parts under the general title of GB/T 228 have been published:
——Part 1: Method of test at room temperature;
——Part 2: Method of test at high 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. In addition to a number of structural adjustments and editorial changes, the following main technical changes have been made with respect to GB/T 228.1-2010:
a) The normative references JJG 139, JJG 475, JJG 762 and JJG 1063 are added (see Clause 2 hereof);
b) Three terms and definitions of "modulus of elasticity", "default value" and "coefficient of determination" are added (see Clause 3 hereof);
c) The clause “Choice of the extensometer gauge length” is added (see Clause 8 hereof);
d) The subclause “General information regarding testing rates” is added (see 10.3.1 hereof);
e) Two different types of strain rate control modes are added in subclause “Testing rate based on strain rate (method A)”: method A1 and method A2, and specific interpretations of methods A1 and A2 (see 10.3.2 hereof);
f) The subclause “Computer compatible representation of standards” is added (see C.5 hereof);
g) The normative annex “Determination of the modulus of elasticity of metallic materials using a uniaxial tensile test” is added (see Annex D hereof);
h) Longitudinal arc test pieces are modified (see Table H.1 hereof; Table E.1 of Edition 2010);
i) The annex "Estimation of the compensating crosshead separation rate in consideration of the deformation of the testing machine" is modified (see Annex I hereof; Annex F of Edition 2010);
j) The annex "Determination of proof strength at plastic extension (Rp) by successive approximation method" is changed from a normative annex to an informative annex (see Annex J hereof; Annex J of Edition 2010);
k) The annex “Estimation of the uncertainty of measurement” is modified (see Annex O hereof; Annex L of Edition 2010).
This document is modified in relation to ISO 6892-1: 2019 Metallic materials—Tensile testing—Part 1: Method of test at room temperature.
There are many structural adjustments in this document with respect to ISO 6892-1: 2019. See Annex A for the comparison of structure changes between them.
Many technical differences have been made to this document with respect to ISO 6892-1: 2019, which are marked with perpendicular single line (|) in the outside page margin of the provisions concerned. See Annex B for the technical differences and their reasons.
The following editorial changes have been made in this document:
——The informative annex "Determination of proof strength at plastic extension (Rp) by successive approximation method” is added (see Annex J hereof);
——The informative annex "Determination of permanent set strength (Rr0.2) by stress relaxation method” is added (see Annex K hereof).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The issuing body of this document 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 is under the jurisdiction of National Technical Committee on Iron and Steel of Standardization Administration of China (SAC/TC 183).
The previous editions of this document and those replaced by this document are as follows:
——It was firstly issued as GB/T 228-1963 in 1963, firstly revised in 1976, and secondly revised in 1987;
——In the third revision in 2002, 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 were incorporated;
——In the fourth revision in 2010, the document number was changed to GB/T 228.1-2010;
——This edition is the fifth revision.
Introduction
GB/T 228 Metallic materials—Tensile testing is the standard for test method with the widest application and the highest attention in the mechanical test of metallic materials, aiming to standardize the tensile test methods of metallic materials in different temperature ranges.
GB/T 228 consists of 4 parts:
——Part 1: Method of test at room temperature.
——Part 2: Method of test at high temperature.
——Part 3: Method of test at low temperature.
——Part 4: Method of test in liquid helium.
In this document, there are two control methods of testing rate. The first, method A, is based on strain rate (including crosshead separation rate) and the second, method B, is based on stress rate. Method A is intended to minimize the variation of the testing rates during the moment when strain rate sensitive parameters are determined and to minimize the measurement uncertainty of the test results. Therefore, and out of the fact that often the strain rate sensitivity of the materials is not known, the use of method A is strongly recommended.
Note 1: During discussions concerning the testing rate in the revision of this document, it was decided to recommend the use of strain rate control in future revisions of the standard.
Note 2: In what follows, the designations “force” and “stress” or “extension”, “percentage extension”, and “strain”, respectively, are used on various occasions (as figure axis labels or in interpretations for the determination of properties). However, for a general description or point on a curve, the designations “force” and “stress” or “extension”, “percentage extension”, and “strain”, can be interchanged respectively.
Metallic materials—Tensile testing—
Part 1: Method of test at room temperature
1 Scope
This document specifies the definition, symbols and interpretations, principle, test pieces and its dimension measurement, testing equipment, test requirements, property measurement, rounding off of measurement results and test report for tensile testing of metallic materials.
This document is applicable to the determination for tensile properties of metallic materials at room temperature.
Note: Annex C gives further recommendations for computer-controlled testing machines.
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 2975 Steel and steel products—Location and preparation of samples and test pieces for mechanical testing (GB/T 2975-2018, ISO 377: 2017, MOD)
GB/T 8170 Rules of rounding off for numerical values & expression and judgment of limiting values
GB/T 10623 Metallic materials—Test pieces for tensile testing (GB/T 10623-2008, ISO 23718: 2007, MOD)
GB/T 12160 Metallic materials—Calibration of extensometers systems used in uniaxial testing (GB/T 12160-2019, ISO 9513: 2012, IDT)
GB/T 16825.1 Verification of static uniaxial testing machines—Part 1: Tension/ compression testing machines—Verification and calibration of the force measuring system (GB/T 16825.1-2008, ISO 7500-1: 2004, IDT)
GB/T 22066 Evaluation for computerized data acquisition systems for used in static uniaxial testing machines
JJG 139 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
For the purposes of this document, the terms and definitions given in GB/T 10623 as well as the following apply.
3.1
gauge length
L
length of the parallel portion of the test piece on which elongation is measured at any moment during the test
Note: See reference [6] in the Bibliography.
3.1.1
original gauge length
Lo
length between gauge length (3.1) marks on the test piece measured at room temperature before the test
Note: See reference [6] in the Bibliography.
3.1.2
final gauge length after fracture
Lu
length between gauge length (3.1) marks on the test piece measured after rupture, at room temperature, the two pieces having been carefully fitted back together so that their axes lie in a straight line
Note: See reference [6] in the Bibliography.
3.2
parallel length
Lc
length of the parallel reduced section of the test piece
Note: The concept of parallel length is replaced by the concept of distance between grips for unmachined test pieces. See No. [6] in Bibliography.
3.3
elongation
increase in the original gauge length (3.1.1) at any moment during the test
Note: See reference [6] in the Bibliography.
3.4
percentage elongation
elongation (3.3) expressed as a percentage (%) of the original gauge length(Lo) (3.1.1)
Note: See reference [6] in the Bibliography.
3.4.1
percentage permanent elongation
increase in the original gauge length (Lo) (3.1.1) of a test piece after removal of a specified stress, expressed as a percentage (%) of the original gauge length
Note: See reference [6] in the Bibliography.
3.4.2
percentage elongation after fracture
A
permanent elongation (3.3) of the gauge length after fracture (Lu–Lo), expressed as a percentage (%) of the original gauge length (Lo) (3.1.1)
Note: For further information, see 8.1 and reference [6] in the Bibliography.
3.5
extensometer gauge length
Le
initial gauge length of the extensometer used for measurement of extension (3.6)
Note 1: For the determination of several properties which are based (partly or complete) on extension, e.g. Rp, Ae or Ag, the use of an extensometer is mandatory.
Note 2: For further information, see 8.3 and reference [6] in the Bibliography.
3.6
extension
increase in the extensometer gauge length (Le) (3.5), at any moment during the test
Note: See reference [6] in the Bibliography.
3.6.1
percentage extension
strain
e
extension (3.6) expressed as a percentage of the extensometer gauge length (Le) (3.5)
Note: e is commonly called engineering strain.
3.6.2
percentage permanent extension
increase in the extensometer gauge length (3.5), after removal of a specified stress (3.10) from the test piece, expressed as a percentage (%) of the extensometer gauge length (Le)
Note: See reference [6] in the Bibliography.
3.6.3
percentage yield point extension
Ae
< discontinuous yielding materials > extension (3.6) between the start of yielding and the start of uniform work-hardening, expressed as a percentage (%) of the extensometer gauge length Le (3.5)
Note: See Figure 7 and reference [6] in the Bibliography.
3.6.4
percentage total extension at maximum force
Agt
total extension (3.6) (elastic extension plus plastic extension) at maximum force, expressed as a percentage (%) of the extensometer gauge length (Le) (3.5)
Note: see Figure 1.
3.6.5
percentage plastic extension at maximum force
Ag
plastic extension (3.6) at maximum force, expressed as a percentage (%) of the extensometer gauge length (Le) (3.5)
Note: see Figure 1.
Key:
A——percentage elongation after fracture (determined from the extensometer signal or directly from the test piece, see 20.1);
Ag——percentage plastic extension at maximum force;
Agt——percentage total extension at maximum force;
At——percentage total extension at fracture;
e——percentage extension;
mE——slope of the elastic part of the stress-percentage extension curve;
R——stress;
Rm——tensile strength;
Δe——plateau extent (for determination of Ag, see Clause 17, for determination of Agt, see Clause 18).
Figure 1 Definition of extension
3.6.6
percentage total extension at fracture
At
total extension (3.6) (elastic extension plus plastic extension) at the moment of fracture, expressed as a percentage (%) of the extensometer gauge length (Le) (3.5)
Note: see Figure 1.
3.7
testing rate
rate used during the test
3.7.1
strain rate
e ̇_Le
increase of strain, measured with an extensometer, in extensometer gauge length (Le) (3.5), per time
3.7.2
estimated strain rate over the parallel length
e ̇_Lc
value of the increase of strain over the parallel length Lc (3.2) of the test piece per time based on the crosshead separation rate (3.7.3) and the parallel length of the test piece
3.7.3
crosshead separation rate
vc
increase of the crosshead separation per time
3.7.4
stress rate
R ̇
increase of stress (3.10) per time
Note: Stress rate is only used in the elastic part of the test (method B) (see 10.3.3).
3.8
percentage reduction of area
Z
maximum change in cross-sectional area which has occurred during the test (So–Su), expressed as a percentage (%) of the original cross-sectional area (So)
3.9
maximum force
Fm
< materials displaying no discontinuous yielding > highest force that the test piece withstands during the test
< materials displaying discontinuous yielding > highest force that the test piece withstands during the test after the beginning of work-hardening
Note 1: For materials which display discontinuous yielding, but where no work-hardening can be established, Fm is not defined in this document [see footnote to Figure 8c)].
Note 2: See Figure 8 a) and Figure 8 b).
3.10
stress
R
at any moment during the test, force divided by the original cross-sectional area, So, of the test piece
Note 1: All references to stress in this document are to engineering stress.
Note 2: See reference [6] in the Bibliography.
3.10.1
tensile strength
Rm
stress (3.10) corresponding to the maximum force (Fm) (3.9.2)
Note: See reference [6] in the Bibliography.
3.10.2
yield strength
when the metallic material exhibits a yield phenomenon, stress (3.10) corresponding to the point reached during the test at which plastic deformation occurs without any increase in the force
Note: Yield strength is divided into upper yield strength and lower yield strength. See No. [6] in Bibliography.
3.10.2.1
upper yield strength
ReH
maximum stress (3.10) prior to the first decrease in force
Note: See Figure 2 and reference [6] in the Bibliography.
3.10.2.2
lower yield strength
ReL
lowest value of stress (3.10) during plastic yielding, ignoring any initial transient effects
Note: See Figure 2 and reference [6] in the Bibliography.
Key:
e——percentage extension;
R——stress;
ReH——upper yield strength;
ReH——lower yield strength.
a Initial transient effect.
Figure 2 Examples of upper and lower yield strengths for different types of curve
3.10.3
proof strength at plastic extension
Rp
stress (3.10) at which the plastic extension (3.6) is equal to a specified percentage of the extensometer gauge length (Le) (3.5)
Note 1: Adapted from GB/T 24182-2009 “proof strength at plastic extension”.
Note 2: The symbol used shall be accompanied by a subscript to indicate the proof percentage plastic extension, for example, Rp0.2 refers to the stress when the proof percentage plastic extension is 0.2%.
Note 3: See Figure 3 and reference [6] in the Bibliography.
Key:
e——percentage extension;
ep——proof percentage at plastic extension;
R——stress;
Rp——proof strength at plastic extension.
Figure 3 Proof strength at plastic extension (Rp) (See 13.1)
3.10.4
proof strength at total extension
Rt
stress (3.10) at which total extension (3.6) (elastic extension plus plastic extension) is equal to a specified percentage of the extensometer gauge length (Le) (3.5)
Note 1: The symbol used shall be accompanied by a subscript to indicate the proof percentage total extension, for example, Rt0.5 refers to the stress when the proof percentage total extension is 0.5%.
Note 2: See Figure 4 and reference [6] in the Bibliography.
Key:
e——percentage extension;
et——proof percentage total extension;
R——stress;
Rt——proof strength at total extension.
Figure 4 Proof strength at total extension (Rt)
3.10.5
permanent set strength
Rr
stress (3.10) at which, after removal of force, a specified permanent elongation (3.3) or extension (3.6), expressed respectively as a percentage of original gauge length (Lo) (3.1.1), or extensometer gauge length (Le) (3.5), has not been exceeded
Note 1: The symbol used shall be accompanied by a subscript to indicate the proof percentage permanent extension. For example, Rt0.2 refers to the stress when the proof percentage permanent extension is 0.2%.
Note 2: See Figure 5 and reference [6] in the Bibliography.
Key:
e——percentage extension;
et——proof percentage permanent extension;
R——stress;
Rr——permanent set strength.
Figure 5 Permanent set strength (Rr)
3.11
fracture
phenomenon which is deemed to occur when total separation of the test piece occurs
Note: Criteria for fracture for computer-controlled testing machine are given in Figure C.2.
3.12
computer-controlled tensile testing machine
machine for which the control and monitoring of the test, the measurements, and the data processing are undertaken by computer
3.13
modulus of elasticity
E
quotient of change of stress ΔR and change of percentage extension Δe in the range of evaluation, multiplied by 100%
Note: It is recommended to report the value in GPa rounded to the nearest 0.1 GPa and according to GB/T 8170.
3.14
default value
lower or upper value for stress (3.10), strain (3.6.1) respectively, which is used for the description of the range where the modulus of elasticity (3.13) is calculated
3.15
coefficient of determination
R2
additional result of the linear regression which describes the quality of the stress-strain curve in the evaluation range
Note: The used symbol R2 is a mathematical representation of regression and is no expression for a squared stress value.
4 Symbols and interpretations
See Table 1 for symbols used in this document and their corresponding interpretations.
Table 1 Symbols and interpretations
Symbols Unit Interpretations
Test piece
ao, Tan mm original thickness of a test piece of rectangular cross-section or original wall thickness of a tube
bo mm original width of the parallel length of a rectangular cross-section test piece or width of the longitudinal strip taken from a tube or original width of flat wire
do mm original internal diameter of the parallel length of a circular cross-section test piece, or original diameter of round wire or internal diameter of a tube
Do mm original external diameter of a tube
Lo mm original gauge length
L′o mm original gauge length for determination of Awn (see Annex N)
Lc mm parallel length
Le mm extensometer gauge length
Lt mm total length of test piece
du mm minimum diameter of necking after fracture of circular test piece
Lu mm final gauge length after fracture
L′u mm final gauge length after fracture for determination of Awn (see Annex N)
So mm2 original cross-sectional area
Su mm2 minimum cross-sectional area after fracture
k — coefficient of proportionality (see 6.1.1)
Z % percentage reduction of area
Percentage elongation
A % percentage elongation after fracture (see 3.4.2)
Awn % percentage plastic elongation without necking (see Annex N)
Percentage extension
Ae % percentage yield point extension
Ag % percentage plastic extension at maximum force (Fm)
Agt % percentage total extension at maximum force (Fm)
At % percentage total extension at fracture
ΔL mm extension
ΔLm mm total extension at maximum force
ΔLf mm total extension at fracture
Rates
e ̇_Le s–1 strain rate
e ̇_Lc s–1 estimated strain rate over the parallel length
R ̇ MPa s–1 stress rate
vc mm s–1 crosshead separation rate
Force
Fm N maximum force
Yield strength, proof strength, tensile strength
R MPab stress
ReH MPab upper yield strength
ReL MPa lower yield strength
Rm MPa tensile strength
Rp MPa proof strength at plastic extension
Rr MPa permanent set strength
Rt MPa proof strength at total extension
Modulus of elasticity , slope of the stress-percentage extension curve
E GPa modulus of elasticity c
m MPa slope of the stress-percentage extension curve at a given moment of the test
mE MPa slope of the elastic part of the stress-percentage extension curve d
R1 MPa lower stress value
R2 MPa higher stress value
e1 % lower strain value
e2 % higher strain value
R2 — coefficient of determination
Sm MPa standard deviation of slope e
Sm(rel) % relative standard deviation of slope f
a Symbol used in steel tube product standards.
b 1 MPa = 1 N·mm–2.
c The calculation of the modulus of elasticity is described in Annex D. It is not required to use Annex D to determine the slope of the elastic part of the stress-extension curve for the determination of proof strength at plastic extension.
d In the elastic part of the stress-percentage extension curve, the value of the slope may not necessarily represent the modulus of elasticity. This value of the slope is s very close to that of the modulus of elasticity under the optimal conditions (see Annex D).
e The additional result of the linear regression, which describes the difference between the stress value and the best fit line for a given extension value in the evaluation range.
f Quotient of standard deviation of slope and the slope in the evaluation range, multiplied by 100%.
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols and descriptions
5 Principle
6 Specimens
7 Determination of the original cross-sectional area
8 Original and extensometer spacing
9 Accuracy of test equipment
10 Test requirements
11 Determination of the upper yield strength
12 Determination of lower yield strength
13 Determination of the specified plastic elongation strength
14 Determination of the specified total elongation strength
15 Verification and determination of the specified residual elongation strength
16 Determination of elongation at yield point
Appendix A (informative) List of structural changes in this document compared to ISO 6892-1:
Appendix B (informative) List of technical differences between this document and ISO 6892-1:2019 and their causes
Appendix C (informative) Recommendations for the use of computer-controlled tensile testing machines
Appendix D (normative) Determination of the modulus of elasticity of metallic materials by uniaxial tensile testing
Appendix E (prescriptive) Types of specimens used for thin plates and strips 0.l mm to <3 mm thick
Appendix F (normative) Types of specimens for use with bars and sections of wire less than 4 mm in diameter or thickness
