GB/T 228.12021 (GB/T228.12021)
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Metallic materials  Tensile testing  Part 1: Method of test at room temperature
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GB/T 228.12021: PDF in English (GBT 228.12021) GB/T 228.12021
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.10
CCS H 22
Replacing GB/T 228.12010
Metallic materials  Tensile testing  Part 1.Method of test at
room temperature
(ISO 68921.2019, MOD)
ISSUED ON. DECEMBER 31, 2021
IMPLEMENTED ON. JULY 01, 2022
Issued by. State Administration for Market Regulation;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword... 4
Introduction... 7
1 Scope... 8
2 Normative references... 8
3 Terms and definitions... 9
4 Symbols and descriptions... 17
5 Principles... 19
6 Specimens... 19
7 Determination of original crosssectional area... 21
8 Original gauge length and extensometer gauge length... 22
9 Accuracy of test equipment... 23
10 Test requirements... 23
11 Determination of upper yield strength... 29
12 Determination of lower yield strength... 29
13 Determination of proof strength, plastic extension... 30
14 Determination of proof strength, total extension... 32
15 Verification and determination of permanent set strength... 32
16 Determination of percentage yield point extension... 32
17 Determination of percentage plastic extension at maximum force... 33
18 Determination of percentage total extension at maximum force... 34
19 Determination of percentage total extension at fracture... 34
20 Determination of percentage elongation after fracture... 34
21 Determination of percentage reduction of area... 35
22 Roundoff of test result values... 36
23 Test report... 36
24 Measurement uncertainty... 37
Annex A (informative) Structural changes between this document and ISO 68921.2019
... 45
Annex B (informative) Technical differences between this document and ISO 6892
1.2019 and their reasons... 46
Annex C (informative) Recommendations for the use of computercontrolled tensile
testing machines... 49
Annex D (normative) Determination of modulus of elasticity of metallic materials by
uniaxial tensile test... 57
Annex E (normative) Specimen types used for sheets and strips with a thickness of
0.1mm ~ < 3mm... 70
Annex F (normative) Types of test specimens used for wires, bars and profiles less than
4mm in diameter or thickness... 73
Annex G (normative) Types of test specimens to be used for plates and flats of thickness
equal to or greater than 3mm and wires, bars and profiles equal to or greater than 4mm
in diameter or thickness... 75
Annex H (normative) Types of specimens used for tubes... 80
Annex I (informative) Estimation of compensating crossbead separation rate
considering the deformation of testing machine system... 84
Annex J (informative) Determination of proof strength, plastic extension (Rp) by step
bystep approximation method... 86
Annex K (informative) Examples for determination of permanent set strength (Rr0.2) by
forceunloading method... 88
Annex L (informative) Method for determination of nonnecked percentage plastic
elongation (Awn) of long products such as bars, wires and strips... 90
Annex M (informative) Method for determination of percentage elongation after
fracture less than 5%... 91
Annex N (informative) Determination of percentage elongation after fracture by
displacement method... 92
Annex O (informative) Evaluation of measurement uncertainty... 94
Annex P (informative) Precision of tensile test Results from interlaboratory testing
protocol... 100
Bibliography... 105
Metallic materials  Tensile testing  Part 1.Method of test at
room temperature
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.
NOTE. Annex C gives additional recommendations for computercontrolled 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 29752018, ISO 377.2017, MOD)
GB/T 8170, Rules of rounding off for numerical values and expression and
judgement of limiting values
GB/T 10623, Metallic material  Mechanical testing  Vocabulary (GB/T 10623
2008, ISO 23718.2007, MOD)
GB/T 12160, Metallic materials  Calibration of extensometers systems used in
uniaxial testing (GB/T 121602019, 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 16825.12008, ISO 75001.2004, 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
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.
8.3 Selection of extensometer gauge length
For determining yield strength and specified strength properties, Le shall cover the
parallel length of the specimen as much as possible. This will ensure that the
extensometer detects all yielding that occurs on the specimen. Ideally Le shall be greater
than 0.5Lo but less than about 0.9Lc. For the performance at or after maximum force, it
is recommended that Le be equal to or approximately equal to Lo. However, Le shall be
equal to Lo when determining the percentage elongation after fracture.
9 Accuracy of test equipment
The force measuring system of the testing machine shall meet the requirements of GB/T
16825.1.Calibrate according to JJG 139, JJG 475 or JJG 1063.Its accuracy shall be
level 1 or better.
The accuracy level of the extensometer shall meet the requirements of GB/T 12160 and
be calibrated according to JJG 762.When determining upper yield strength, lower yield
strength, percentage yield point extension, proof strength, plastic extension, proof
strength, total extension, permanent set strength as well as verification test of permanent
set strength, an extensometer with level 1 or better accuracy shall be used. When
determining other properties with greater percentage extension (extension greater than
5%), such as tensile strength, percentage total extension at maximum force, percentage
plastic extension at maximum force, percentage total extension at fracture as well as
percentage extension after fracture, an extensometer with level 2 or better accuracy
shall be used.
The computercontrolled tensile testing machine shall meet the requirements of GB/T
22066.Recommendations in Annex C are available for reference.
NOTE. The appropriate tensile testing machine is selected according to the calibration range of the
testing machine force value and the size of the specimen.
10 Test requirements
10.1 Setting of force zero point
After the test loading chain is assembled, before both ends of the specimen are gripped,
the zero point of the force measurement system shall be set. Once the force zero point
has been set, the force measurement system shall not change during the test.
NOTE. The above method is to ensure that the weight of the gripping system is compensated during
force measurement on the one hand, and to ensure that the force generated during the gripping
process does not affect the measurement of the force value.
10.2 Specimen gripping method
It shall use suitable grips such as wedge grips, threaded grips, push grips, collar grips
to grip the specimen.
It shall be ensured that the gripped specimen is subjected to axial tension. Minimize
bending (for example, more information is given in ASTM E1012, see Bibliography
[14]). It is particularly important when testing brittle materials or when determining
proof strength, plastic extension, proof strength, total extension, permanent set strength
or yield strength.
To ensure that the specimen is centered on the grip, a pretension may be applied not
exceeding the specified strength or 5% of the expected yield strength. The extension
effect of pretension shall be corrected.
10.3 Testing rate
10.3.1 General information about testing rate
Unless otherwise specified, as long as the requirements of this document are met, the
choice of Method A1, Method A2, or Method B, as well as the testing rate, is decided
by the sample provider or its designated laboratory.
NOTE 1.The difference between Method A and Method B is that the testing rate required by
Method A is defined at the point of interest (for example, Rp0.2), and is also the property to be
measured. The testing rate required by Method B is generally set in the elastic range prior to the
measured property.
Under certain conditions of Method B (for example, for some steels with a stress rate
of approximately 30MPa/s in the elastic range, use a high stiffness gripping system and
P6 specimen in Annex E, Table E.2), the range 2 strain rate of Method A can be
observed.
NOTE 2.Product standards and related test standards (such as aviation standards) or agreements
may specify testing rates that differ from this document.
10.3.2 Testing rate based on strain rate (Method A)
10.3.2.1 General
Method A is intended to reduce testing rate variation and measurement uncertainty in
test results when determining strain rate sensitive parameters (performance).
This document describes two different types of strain rate control modes.
 Method A1 Closed Loop. The strain rate () is based on feedback from the
extensometer.
 Method A2 Open Loop. The strain rate is estimated from the parallel length.
That is, it is realized by controlling the crossbead separation rate obtained by
multiplying the parallel length by the required strain rate [see formula (2)].
NOTE. A more rigorous strain rate estimation procedure for Method A2 is described in Annex I.
If the material exhibits discontinuous yielding or zigzag yielding (as in some steels and
AlMg alloys at the yield stage or as in the PortevinLeChatelier zigzag yielding effect
exhibited by some materials) or when necking occurs, the force value can be kept
nominally constant. The strain rate () and the estimated strain rate () based on
the parallel length are approximately equal. If the material exhibits the ability to deform
uniformly, there will be a difference between the two rates. As the force value increases,
the compliance of the testing machine system may cause the actual strain rate to be
significantly lower than the set value of the strain rate.
The testing rate shall meet the following requirements.
a) Unless otherwise specified, a stress equivalent to half the expected yield strength
may be achieved at any convenient testing rate. Thereafter until the range of ReH,
Rp or Rt is determined, the specified strain rate (), [or the crossbead separation
rate (vc) estimated from the parallel length in Method A2]. This range requires an
extensometer to be gripped on the specimen to measure the maximum specimen
extension and eliminate the influence of the flexibility of the tensile tester, so as
to accurately control the strain rate. Method A2 is also available for testing
machines that are not capable of strain rate control.
b) During discontinuous yielding, an estimated value of the parallel length strain rate
() shall be used, see 3.7.2.In this range it is not possible to control the strain
rate with an extensometer gripped to the specimen, because partial plastic
deformation may occur beyond the extensometer gauge length. Use the constant
crossbead separation rate (vc) calculated from formula (2). In this range it is
possible to keep the estimated value of the required parallel length strain rate
sufficiently accurate.
c) After the determination of RP, Rt or the end of yield range (see 3.7.2), it shall use
area (Z)
After determining yield strength or plastic extension strength, the test rate may be
increased to a strain rate (or equivalent crossbead separation rate) not greater than
0.008s1.
If only the tensile strength of the material is to be determined, a single testing rate of
not more than 0.008s1 may be selected throughout the test.
10.3.4 Representation of test conditions
To report the test control mode and testing rate in simple form, the following
abbreviated representations can be used.
GB/T 228.1 Annn or GB/T 228.1 Bn
Here "A" is defined as to use Method A (the control mode based on strain rate). "B" is
defined as to use Method B (the control mode based on stress rate). The symbol "nnn"
in Method A refers to the rate used in each test phase, as defined in Figure 9.The symbol
"n" in Method B refers to the chosen stress rate during the elastic phase.
Example 1.GB/T 228.1 A224 defines the test as a control mode based on strain rate.
The range of test rates for different stages is 2, 2 and 4, respectively.
Example 2.GB/T 228.1 B30 defines the test as a control mode based on stress rate. The
nominal stress rate of the test is 30MPa·s1.
Example 3.GB/T 228.1 B defines the test as a control mode based on stress rate. The
nominal stress rate of the test is in accordance with Table 3.
11 Determination of upper yield strength
Upper yield strength (ReH) can be measured from the forceextension curve or a peak
force display. It is defined as the stress corresponding to the maximum force value
before the first drop in force. ReH is calculated by dividing this force by the original
crosssectional area of the specimen (see Figure 2).
12 Determination of lower yield strength
Lower yield strength (ReL) can be measured from the forceextension curve. It is defined
as the stress corresponding to the minimum force in the yield phase, ignoring initial
transient effects. ReL is calculated by dividing this force by the original crosssectional
area of the specimen (see Figure 2).
The basic principles for determining the upper and lower yield strength positions are as
follows.
a) The first peak stress before yielding (the first maximum stress) is judged as the
upper yield strength, regardless of whether the subsequent peak stress is larger or
smaller than it.
b) If there are two or more valley stresses in the yield stage, the first valley stress
(the first minimum stress) shall be discarded, and the smallest of the remaining
valley stresses shall be taken as the lower yield strength. If there is only one drop
valley, the valley stress is judged as the lower yield strength.
c) The yield plateau appears in the yield stage, and the plateau stress is judged as the
lower yield strength. If there are multiple yield plateaus and the latter is higher
than the former, the stress of the first plateau is judged as the lower yield strength.
d) The correct judgment result is that the lower yield strength is lower than the upper
yield strength.
In cases where the material exhibits significant yield and no determination of the
percentage yield point extension is required. To improve test efficiency, the lowest
stress within 0.25% extension after the upper yield strength can be reported as the lower
yield strength, regardless of any initial transient effects. After the lower yield strength
has been determined by this method, the testing rate may be increased in accordance
with 10.3.2.4 or 10.3.3.3.The test report shall indicate that this shortcut method is used.
13 Determination of proof strength, plastic extension
13.1 Determine the proof strength, plastic extension (Rp) from the forceextension curve.
On the curve, draw a line parallel to the elastic straight segment of the curve. The
distance between the elastic straight line segment and the straight line segment on the
extension axis is equal to the specified percentage plastic extension, for example, 0.2%.
The intersection of this parallel line with the curve gives the force corresponding to the
desired proof strength, plastic extension. This force is divided by the original cross
sectional area (So) of the specimen to obtain the proof strength, plastic extension (see
Figure 3).
If the elastic straight portion of the forceextension curve cannot be determined so
clearly that this parallel line cannot be drawn with sufficient accuracy, the following
method is recommended (see Figure 6).
an automatic test system (see Annex C).
13.3 The proof strength, plastic extension may be determined using the stepbystep
approximation method provided in Annex J.
14 Determination of proof strength, total extension
14.1 On the forceextension curve, draw a parallel line parallel to the force axis and at
a distance from this axis equivalent to the specified percentage total extension. The
intersection of this parallel line with the curve gives the force corresponding to the proof
strength, total extension. This force is divided by the original crosssectional area (So)
of the specimen to obtain the proof strength, total extension Rt (see Figure 4).
14.2 The proof strength, total extension can be determined using automatic processing
devices (such as microprocessors) or automatic testing systems. The forceextension
curve may not be drawn (see Annex C).
15 Verification and determination of permanent set strength
The specimen is subjected to a force corresponding to the permanent set strength.
Maintain the force for 10s~12s. Verify that the percentage permanent extension does
not exceed the specified percentage after the force is removed (see Figure 5).
NOTE. This verification test is a test that checks for pass or fail. Usually, it is not part of a standard
tensile test. Apply stress to the specimen. The allowable permanent extension is specified by the
relevant product standard (or the test client). For example, reporting "Rr0.5 = 750MPa pass" means
that a stress of 750MPa is applied to the specimen, resulting in a permanent extension of less than
or equal to 0.5%.
To obtain the specific value of the permanent set strength, the determination shall be
carried out. Annex K provides examples of determining the permanent set strength.
16 Determination of percentage yield point extension
For materials that exhibit discontinuous yielding, the percentage yield point extension
(Ae) is determined from the forceextension curve by subtracting the extension at the
upper yield strength (ReH) from the extension at the start of uniform workhardening.
The extension at the start of uniform workhardening is defined by the intersection of a
horizontal line through the last local minimum point, or a regression line through the
range of yielding, prior to uniform workhardening and a line corresponding to the
highest slope of the curve occurring at the start of uniform workhardening (see Figure
7). It is expressed as a percentage of the extensometer gauge length (Le).
For some materials, the percentage plastic extension at maximum force is not equal to
the nonnecked percentage plastic extension. For long products such as bars, wires and
strips, the method in Annex L may be used to determine the percentage plastic extension
without necking (Awn).
18 Determination of percentage total extension at maximum
force
The percentage total extension at maximum force is determined on the forceextension
curve obtained with an extensometer. The percentage total extension at maximum force
(Agt) is calculated according to formula (4).
NOTE. Some materials exhibit a plateau at maximum force. When this occurs, take the percentage
total extension corresponding to the midpoint of the maximum force plateau (see Figure 1).
19 Determination of percentage total extension at fracture
The percentage total extension at fracture is determined on the forceextension curve
obtained with an extensometer. The percentage total extension at fracture (At) is
calculated according to formula (5).
20 Determination of percentage elongation after fracture
20.1 The percentage elongation after fracture shall be determined as defined in 3.4.2.
To determine the percentage elongation after fracture, the fractured parts of the
specimen shall be carefully fitted together so that their axes are on the same straight
line. Take special measures to ensure proper contact of the fractured portion of the
specimen. Measure the gauge length after fracture of the specimen. This is especially
important for small crosssection specimens and low percentage elongation specimens.
Calculate the percentage elongation after fracture (A) according to formula (6).
The percentage elongation after fracture (Lu  Lo) shall be determined with a measuring
tool or measuring device with sufficient resolution. The result shall be accurate to ±
0.25mm.
If the specified minimum percentage elongation after fracture is less than 5%, it is
recommended to adopt a special method for determination (see Annex M). In principle,
it is valid only if the distance between the fracture and the nearest gauge mark is not
less than onethird of the original gauge length. However, the percentage elongation
after fracture is greater than or equal to the specified value. The measurement is valid
no matter where the fracture position is. If the distance between the fracture and the
nearest gauge length mark is less than half of the original gauge length, the
displacement method specified in Annex N may be used to measure the percentage
elongation after fracture.
20.2 For the testing machine capable of measuring extension at fracture with an
extensometer, the extensometer gauge length shall be equal to the original gauge length
of the specimen. There is no need to mark the original gauge length of the specimen.
When the total extension at fracture is used as the elongation measurement, to obtain
the percentage elongation after fracture, the elastic extension shall be deducted from
the total extension. There are some additional requirements (such as high dynamic
response and frequency bandwidth of the extensometer, see C.2.2) in order to obtain
results comparable to manual methods.
In principle, the fracture is valid if it occurs within the extensometer gauge length (Le).
However, the percentage elongation after fracture is equal to or greater than the
specified value. The measurement is valid regardless of where the fracture location is.
If the product standard specifies that a fixed gauge length is used to measure the
percentage elongation after fracture, the extensometer gauge length shall be equal to
this gauge length.
20.3 By agreement before the test, the percentage elongation after fracture can be
determined at a fixed gauge length. Then use the conversion formula or conversion
table to convert it into the percentage elongation after fracture of the proportional gauge
length (for example, the conversion methods of GB/T 17600.1 and GB/T 17600.2 can
be used).
NOTE. Only when the gauge length or extensometer gauge length, the shape, and crosssectional
area are the same or when the proportionality coefficient (k) is the same, the percentage elongation
after fracture is comparable.
21 Determination of percentage reduction of area
The percentage reduction of area shall be determined according to the definition of the
term. 3.8 "percentage reduction of area".
If necessary, the fractured parts of the specimen shall be carefully fitted together so that
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