Standards related to:

GB/T 228.1-2021**GB/T 228.1-2021: PDF in English (GBT 228.1-2021) **

GB/T 228.1-2021

NATIONAL STANDARD OF THE

PEOPLE’S REPUBLIC OF CHINA

ICS 77.040.10

CCS H 22

Replacing GB/T 228.1-2010

Metallic materials - Tensile testing - Part 1.Method of test at

room temperature

(ISO 6892-1.2019, 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 cross-sectional 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 Round-off of test result values... 36

23 Test report... 36

24 Measurement uncertainty... 37

Annex A (informative) Structural changes between this document and ISO 6892-1.2019

... 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 computer-controlled 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-

by-step approximation method... 86

Annex K (informative) Examples for determination of permanent set strength (Rr0.2) by

force-unloading method... 88

Annex L (informative) Method for determination of non-necked 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 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 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 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, 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 computer-controlled 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 Portevin-LeChatelier 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

0.008s-1.

If only the tensile strength of the material is to be determined, a single testing rate of

not more than 0.008s-1 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·s-1.

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 force-extension 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

cross-sectional area of the specimen (see Figure 2).

12 Determination of lower yield strength

Lower yield strength (ReL) can be measured from the force-extension 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 cross-sectional

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 short-cut method is used.

13 Determination of proof strength, plastic extension

13.1 Determine the proof strength, plastic extension (Rp) from the force-extension 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 force-extension 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 step-by-step

approximation method provided in Annex J.

14 Determination of proof strength, total extension

14.1 On the force-extension 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 cross-sectional 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 force-extension

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 force-extension curve by subtracting the extension at the

upper yield strength (ReH) from the extension at the start of uniform work-hardening.

The extension at the start of uniform work-hardening 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 work-hardening and a line corresponding to the

highest slope of the curve occurring at the start of uniform work-hardening (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 non-necked 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 force-extension

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 force-extension 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 cross-section 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 one-third 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 cross-sectional

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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