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This standard was drafted according to the rules specified in GB/T 1.1-2009.
GB/T228 consists of the following parts under the general tile “Metallic Materials - Tensile Testing”
- Part 1: Method of Test at Room Temperature
- Part 2: Method of Test at Elevated Temperature
- Part 3: Method of Test at Low Temperature
- Pat 4: Method of Test in Liquid Helium
This Part is the Part 1 of GB/T 228
The modification of this part adopts the international standard ISO 6892-1: 2009 “Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature".
The integral structure, hierarchical division, development, formulation and technical content of this part are consistent with ISO 6892-1 basically.
This part has made modifications and supplements on the international standard in the following aspects, which are marked with perpendicular single line in the margin of relevant clauses in the text.
- In the normative references, this part directly refers to our national standard corresponding to the international standard.
- The following normative references have been added: “Rules of rounding off for numerical values & expression and judgment of limiting values” (GB /T 8170), “Metallic Material - Mechanical Testing - Vocabulary” (GB/T 10623) and “Evaluation for Computerized Data Acquisition Systems for Used in Static Uniaxial Testing Machines”
- The minimum value among three measurements of the original cross-sectional area in Chapter 7 has been changed into average value.
- Basic principles of judgment on the positions of upper and lower yield strength have been added in Chapter 12.
- Chapter 22 "the Numerical Rounding of Test Results" has been added.
The Normative Annex J " Determinations and Specifications of plastic elongation strength Rp) with Successive Approximation Method" has been added.
- The examples of the measurement of permanent set strength (Rro.2) with K Removal of Force have been added.
- The detailed description of proportional sample and non-proportional sample in Annex B, Annex C, Annex D and Annex E has been modified correspondingly.
- The verification method of uncertainty measurement has been modified and was formed into Annex L - the uncertainty evaluation of tensile testing measurement result.
To be convenient for use, the following editing revisions are made in this Part:
a) "This part of the international standard" was changed into "this Part";
b) The decimal ", " has been replaced with the decimal ".".
c) The foreword of the international standard was deleted.
This Part replaces GB/T 228-2002 "Metallic Materials--Tensile Testing at Ambient Temperature", and has made relatively great modification and supplement on the former standard in the following technical content:
- Standard name was modified;
- Normative References;
- The control method of testing rate has been added: Method A Control Method of Strain Rate;
- Numerical Rounding of Test Results
- The verification method of measurement uncertainty in tensile testing;
- Annex A the suggestions when computer controlled tensile testing machine has been added;
- Annex F Crosshead Separation Rate Estimated After the Consideration of the Stiffness (or Flexibility) of Testing Machine.
Annex A, F, G, H, I, K, L and M of this Part are informative and Annex C, D, E and J are Normative.
This Part is proposed by China Iron & Steel Association.
This Part is under the jurisdiction of National Technical Committee on Steel of Standardization Administration of China
The drafting organizations: Iron and Steel Research Institute, Jinan Shijin Group Corporation, China Metallurgical Information and Standardization Institute, Baoshan Iron and Steel Co., Ltd, MTS Systems (China) Co., Ltd., Shougang Group, Shanghai Hualong test Instrument Co., Ltd., Shanghai Entry and Exit Inspection and Quarantine, Dalian hope equipment Co., Ltd., Shanghai Research Institute of Materials and Beijing Non-Ferrous Research Institute.
The major drafting personnel of this Part: Gao Yifei, Liang Xinbagn, Dongli, Sun Shanye, Li Heping, An Jianping, Zhu Linmao, Wang Ping, Lu Changcheng, Yin Jianjun, Wu Yiwen, Wang Bin, Wang Fusheng and Wu Chaohun.
The previous editions of the standard replaced by this Part are as follows:
- GB /T 228-1963, GB /T 228-1976, GB /T 228-1987, GB /T 228-2002;
- GB /T 3076-1982;
- GB /T 6397-1986.
Introduction
In this Part of the standard, there are two methods of testing speeds available. Method A is based on strain rates (including crosshead separation rate) and Method B is based on stress rates. Method A is intended to minimize the variation of the test rates during the moment when strain rate sensitive parameters are determined and to minimize the measurement uncertainty of the test results.
Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature
金屬材料 拉伸試驗 第1部分：室溫試驗方法
1 Scope
This part of GB/T 228 specifies the principle, definition, symbols, explanation, test piece and dimensional measurement, testing equipment, testing requirements, performance determination, the numerical rounding of determination results and testing report of the method for tensile testing of metallic materials.
This Part applies the determination of tensile performance of metallic materials at room temperature.
Note: Annex A indicates complementary recommendations for computer controlled testing machines.
2 Normative References
The following referenced document is indispensable for the application of this document. For dated references, only the edition cited applies. For the undated references, the latest edition of the referenced document (including all the amendments) applies.
GB/T 2975 Steel and Steel Products - Location and Preparation of Samples and Test Piece for mechanical testing (GB/T 2975-1998, eqv ISO 377: 1997)
GB/T 8170 Rules of rounding off for numerical values & expression and judgment of limiting values
GB/T 10623 Metallic material - Mechanical testing - Vocabulary (GB/T 10623-2008, ISO 23718:2007, MOD)
GB/T 12160 Calibration of Extensometers Used in Uniaxial Testing (GB/T 12160-2002, ISO 9513: 1999, IDT)
GB/T 16825 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 17600.1 Steel-Conversion of Elongation Values - Part 1: Carbon and Low Alloy Steels (GB/T 17600.1-1998, eqv ISO 2566-1: 1984)
GB/T 22066 Evaluation for Computerized Data Acquisition Systems for Used in Static Uniaxial Testing Machines
3 Terms and Definitions.
The following terms and definitions as well as those in GB/T 10623 are applicable to this Part.
3.1 Gauge length
L
The length of the circular column or prism part of the sample in measurement of the elongation.
3.1.1 Original gauge length
Lo
Length between gauge length marks on the piece measured at room temperature before the exertion of forces
3.1.2 Final, gauge length after fracture
Lu
Length between gauge length 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.
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.
3.3 Elongation
Increase in the original gauge length at any moment during the test
3 .4 Percentage elongation
Elongation expressed as a percentage of the original gauge length [1].
3.4.1 Percentage of permanent elongation
Increase in the original gauge length Lo of a test piece after removal of a specified stress, expressed as a percentage of the original gauge length.
3.4.2 Percentage elongation after fracture
A
Permanent elongation of the gauge length after fracture (Lu-Lo) expressed as a percentage of the original gauge length (Lo) [1].
Note: For proportional test pieces, if the original gauge length is not equivalent to 5.65 where So is the original cross-sectional area of the parallel length, the symbol A should be supplemented by a subscript indicating the coefficient of proportionality used e.g. A11.3 indicates a percentage elongation of the gauge length, 11.3 . For non-proportional test pieces , the symbol A should be supplemented by a subscript indicating the original gauge length used, expressed in mllimetres, e.g. A80mm indicates a percentage elongation of gauge lenth of 80mm.
3.5 Extensometer gauge Iength
Le
Initial extensometer gauge length used for measurement of extension by means of extensometer.
Note: For measurement of yield and proof strength performances, Le should span as much of the parallel length of the test piece as possible. Ideally, as a minimum, Le should be great than Lo/2 , but less than approximately 0.9Lc. This should ensure that the extensometer detect all yielding events that occur in the test piece. Further, for measurement of parameters at or after reaching maximum force, Le should be approximately equal to Lo.
3.6 Extension
Increase in the extensometer gauge length Le at the moment during the test.
3.6.1 Percentage extension or strain
Extension expressed as a percentage of the extensometer gauge length Le.
3.6.2 Percentage permanent extension
Increase in the extensometer gauge length, after removal of a specified stress from the test piece, expressed as a percentage of the extensometer gauge length, Le.
3.6.3 Percentage yield point extension Ae
In obvious - yielding - displaying (discontinuous yielding) metallic materials, the extension between the start of yielding and the start of uniform work-hardening, expressed as a percentage of the extensometer gauge length, Le .
1)
See Figure 7.
3.6.4 Percentage total extension at maximum force Agt
Total extension (elastic extension plus plastic extension) at maximum force, expressed as a percentage of the extensometer gauge length Le. See Figure 1.
3.6.5 Percentage plastic extension at maximum force Ag
Plastic extension at maximum force, expressed as a percentage of the extensometer gauge length, Le. See Figure 1.
3.6.6 Percentage total extension at fracture At
Total extension (elastic extension plus plastic extension) at the moment of fracture expressed as a percentage of the extensometer gauge Length, Le.
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 maximum fracture
e -percentage extension
mE - slope of the elastic part of the stress-percentage extension curve
R - stress
Rm - tensile strength
?e - plateau extent (for determination of Ag, see Chapter 17, for determination of Agt
See Chapter 18)
Figure 1: Definitions of Extension
3.7 Testing rate
3.7.1 Strain rate ?
Increase of strain, measured with an extensometer, in extensometer gauge length, Le per time .
3.7.2 Estimated strain rate over the parallel length
?
Value of the increase of strain over the parallel length of the test piece per time based on the crosshead separation rate and the parallel length of the test piece.
3.7.3 Crosshead separation rate
vc
displacement of the crossheads per time.
3.7.4 Stress rate
Increase of stress per time
Note: Stress rate should only be used in the elastic part of the test (Method B)
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
Note: For materials which display discontinuous yielding, but where no workhardening can be established, Fm is not defined in this part (see footnote in Figure 8c).
3.9.1 Maximum force
Fm
As for materials displaying no obvious yielding (discontinuous yielding) highest force during the test.
3.9.2 Maximum force
Fm
As for materials displaying discontinuous yielding, highest force that the test piece withstands during the test after the beginning of workhardening.
See Figure 8a) and 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 Part of GB /T228 are to engineering stress.
Note 2: In what follows, the designation “force” and “stress” or “extension”, “percentage extension” and “strain” respectively, are used on various occasions (as figure axis labels or in explanations for the determination of different properties). However, for a general description of definition of a well-defined point on a curve, the designations “force” and “stress” or “extension”, “percentage extension” and “strain”, respectively, are interchangeable.
3.10.1 Tensile strength
Rm.
Stress corresponding to the maximum force Fm [1] .
3.10.2 Yield strength
When the metallic material exhibits a yield phenomenon, stress corresponding to the point reached during the test at which plastic deformation occurs without an increased. The upper and lower yield strengths should be categorized respectively [1].
3.10.2.1 Upper yield strength
ReH
Maximum value of stress prior to the first decrease in force. See Figure 2.
Key
e - percentage extension
R - stress
ReH - upper yield strength
ReL - lower yield strength
a - Initial transient effect.
Figure 2 Examples of Upper and Lower Yield Strengths for Different Types of Curve
3.10.2.2 Lower yield strength ReL
Lowest value of stress during the yielding, ignoring any initial transient effects. See Figure 2.
3.10.3 Proof strength , plastic extension Rp
Stress at which the plastic extension is equal to a specified percentage of the extensometer gauge length Lo See Figure 3
The used symbols shall be attached with the following footnotes to describe the specified plastic extension percentage, such as Rp0.2, which expresses the specified plastic extension is the stress at 0.2%.
Key
e - percentage extension
ep - specified percentage plastic extension
R - stress
Rp - proof strength, plastic extension
Figure 3 Proof Strength, Plastic Extension, Rp (See 13.1)
3.10.4 Proof strength , total extension R
Stress at which total extension is equal to the specified percentage of the extensometer gauge length, Le. See Figure 4.
The used symbols shall be attached with the following footnotes to describe the specified total extension percentage, such as Rp0.2, which expresses the specified total extension is the stress at 0.5%.
Key
e - percentage extension
et - percentage total extension
R - stress
Rt - proof strength, total extension
Figure 4 Proof Strength, Total Extension, Rt
3.10.5 Permanent set strength Rr
Stress at which, after removal of force, a specified permanent elongation or extension, expressed respectively as a percentage of original gauge length Lo or extensometer gauge length, Le has not been exceeded.
The used symbols shall be attached with the following footnotes to describe the specified percentage permanent extension or elongation, such as Rp0.2, which expresses the specified percentage permanent extension or elongation is the stress at 0.2%.
Key
e - percentage elongation or percentage extension
er - percentage permanent set extension or elongation
R - stress
Rr - specified permanent set strength
Figure 5 Permanent Set Strength, Rr
3.11 Racture
phenomenon which is deemed to occur when total separation of the test piece occurs
Note: criteria for fracture which may be used for computer controlled testing machines are given in Figure A.2.
4 Terms and Symbols
The symbols used in this Part of GB /T 228 and corresponding designations are given in Table 1.
Table 1 Symbols and Designations
Symbol Unit Designation
Test piece
ao, T a mm original thickness of a flat test piece or wall thickness of a tube
bo
mm original width of the parallel length of a flat test piece or average width of the longitudinal strip taken from a tube or width of flat wire
do mm
original diameter of the parallel length of a circular test piece, or 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 initial gauge length for determination of Awn (see Annex I)
Lc mm parallel length
Le mm extensometer gauge length
Lt mm total length of test piece
Lu mm final gauge length after fracture
L′u mm final gauge length after fracture for determination of Awn (see Annex I)
So mm2 original cross-sectional area of the parallel length
Su mm2 minimum cross-sectional area after fracture
k — coefficient of proportionality (see 6.1.1)
Z % percentage reduction of area
Elongation
A % percentage elongation after fracture (see 3.4.2)
Awn % percentage plastic elongation without necking (see Annex I)
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
?Lm mm extension at maximum force
?Lf mm extension at fracture
Rates
?
s?1 strain rate
?
s?1 estimated strain rate over the parallel length
MPa s?1 stress rate
vc mm s?1 crosshead separation rate
Force
Fm N maximum force
Yield strength — Proof strength — Tensile strength
E MPa b modulus of elasticity
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 c
ReH MPa upper yield strength
ReL MPa lower yield strength
Rm MPa tensile strength
Rp MPa proof strength, plastic extension
Rr MPa specified permanent set strength
Rt MPa proof strength, total extension
a Symbol used in steel tube product standards.
b 1MPa = 1 N mm?2.
c 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 can closely agree with the value of the modulus of elasticity if optimal conditions (high resolution, double sided, averaging extensometers, perfect alignment of the test piece, etc.) are used.
5 Principle
The test involves straining a test piece by tensile force, generally go fracture, for the determination of one or more of the mechanical properties defined in Chapter 3.
The test is carried out at room temperature between 10 ℃~35℃, unless otherwise specified. Tests carried out under controlled conditions shall be made at a temperature 23℃±5℃.
6 Test Piece
6.1 Shape and dimensions
6.1.1 General
The shape and dimension of the test pieces may be constrained by the shape and dimensions of the metallic product from which the test pieces are taken.
The test piece is usually obtained by machining a sample from the product or a pressed blank or casting. However, products of uniform cross-section (sections, bars, wires, etc.) and as-cast test piece (i.e. for cast iron and non-ferrous alloys) may be tested without being machined.
The cross-section of the test pieces many be circular, square, rectangular, annular or, in special cases, some other uniform cross-section.
Preferred test piece have a direct relationship between the original gauge length Lo and the original cross sectional area, So, expressed by the equation Lo= The internationally adopted value for k is 5.65. The original gauge length shall be not less than 15mm. When the cross-sectional area of the test piece is too small for this requirement to be met with, k=5.65, a higher value (preferably 11.3) or a non-proportional test piece may be used.
Note: By using an original gauge length smaller than 20mm, the measurement uncertainty is increased.
For non-proportional test pieces, the original gauge length, Lo is independent of the original cross-sectional area, So.
The dimensional tolerances of the test pieces shall be in accordance with the Annexes b to E (see 6.2)
6.1.2 Machined Test Pieces
Machined test pieces shall incorporate a transition radius between the gripped ends and the parallel length if these have different dimensions. The dimensions of the transition radius are important and it is recommended that they be defined in product specification if they are not given in the appropriate annex (see 6.2)
The gripped ends may be of any shape to suit the grips of the testing machine. The axis of the test piece shall coincide with the axis of application of the force.
The parallel length Lc or in the case where the test piece has no transition radii, the free length between the grips, shall always be greater than the original gauge length, Lo.
6.1.3 Unmachined test pieces.
If the test piece consists of an unmachined length of the product or of an unmachined test bar, the free length between the grips shall be sufficient for gauge marks to be at a reasonable distance from the grips (see Annexes B to E).
As-cast test pieces shall incorporate a transition radius between the gripped ends and the parallel length. The dimensions of this transition radius are important and it is recommended that they be defined in the product standard. The gripped ends may be of any shape to suit the grips of the testing machine. The parallel length, Lc shall always be greater than the original gauge length Lo.
6.2 Types of test pieces
The main types of test pieces are defined in Annexes B to E according to the shape and type of product, as shown in Table 2. Other types of test pieces can be specified in relevant product standard.
Table 2 Main Types of Test Piece According to Product Type Dimensions
In millimetres
Types of product Corresponding
Annex
Sheets-Plates- Flats
Thickness a Wire – Bars – Sections
Diameter or side
0.1≤a<3 - B
- <4 C
a≥3 ≥4 D
Tubes E
6.3 Preparation of test pieces
The test pieces shall be taken (cut)and prepared in accordance with the requirements of the relevant product standard or GB/T 2975.
7 Determination of Original Cross-sectional Area
The relevant dimensions of the test piece should be measured at sufficient cross-sections around the longitudinal axis in the central region of the parallel length of the test piece with sufficient points.
The original cross-sectional area So is the average cross-sectional area and shall be calculated from the measurements of the appropriate dimensions.
The accuracy of this calculation depends on the nature and type of the test piece. Annexes B to E describe methods for the evaluation of So for different types of test pieces and contain specifications for the accuracy of measurement.
Foreword I
Introduction III
1 Scope
2 Normative References
3 Terms and Definitions.
4 Terms and Symbols
6 Test Piece
7 Determination of Original Cross-sectional Area
8 Marking the Original Gauge Length
9 Accuracy of Testing Apparatus
10 Conditions of Testing
11 Determination of the Upper Yield Strength
12 Determination of the Lower Yield Strength
13 Determination of Proof Strength, Plastic Extension
14 Determination of Proof Strength, Total Extension
15 Method of Verification of Permanent Set Strength
16 Determination of the Percentage Yield Point Extension
17 Determination of the Percentage Plastic Extension at Maximum Force
18 Determination of the Percentage Total Extension at Maximum Force
19 Determination of the Percentage Total Extension at Fracture
20 Determination of Percentage Elongation After Fracture
21 Determination of Percentage Reduction of Area
22 Rounding of Numerical Values of Testing Results
23 Test Report
24 Measurement Uncertainty
Annex A (Informative) Recommendations Concerning the Use of Computer-controlled Tensile Testing Machines
Annex B (Normative) Types of Test Pieces to Be Used for Thin Products: Sheets, Strips and Flats Between 0.1mm and 3mm Thick
Annex C (Normative) Types of Test Pieces to Be Used for Wire, Bars and Sections with a Diameter or Thickness of Less Than 4mm
Annex D (Normative) Types of Test Pieces to Be Used for Sheets and Flats of Thickness Equal to or Greater than 3mm, and Wire, Bars and Sections of Diameter or Thickness Equal to or Greater Than 4mm
Annex E (Normative) Types of Test Pieces to Be Used for Tubes
Annex F (Informative) Estimation of the Crosshead Separation Rate in Consideration of the Stiffness (or Compliance) of the Testing Machine
Annex G (Informative) Measuring the Percentage Elongation after Fracture If the Specified Value Is Less Than 5%
Annex H (Informative) Measurement of Percentage Elongation after Fracture Based on Displacement Method
Annex I (Informative) Determination of the Percentage Plastic Elongation Without Necking, Awn, for Long Products Such as Bars, Wire and Rods
Appendix J (Normative) Determination for Proof Strength of Plastic Extension (Rp) under Successive Approximation Method
Appendix K (Informative) Examples for Measurement of Permanent Set Strength (Rr0.2) under Force Removing Method
Appendix L (Informative) Assessment for the Uncertainty of Measuring Result of Tension Test
Appendix M (Informative) Precision of Tension Test-According to Results of Interlaboratory Tests
Bibliography
