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GB/T 228.1-2021 English PDF (GBT228.1-2021)

GB/T 228.1-2021 English PDF (GBT228.1-2021)

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GB/T 228.1-2021: Metallic materials -- Tensile testing -- Part 1: Method of test at room temperature

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 extensio...

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