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GB/T 228 consists of the following parts, under the general title 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;
— Part 4: Method of Test in Liquid Helium.
This is Part 4 of GB/T 228.
This standard is drafted in accordance with the rules given in the GB/T 1.1-2009.
This part replaces GB/T 24584-2009 Metallic Materials — Tensile Testing — Method of Test in Liquid Helium in whole. The following technical deviations have been made with respect to the GB/T 24584-2009 (the previous edition):
— addition of the control method of (see Introduction);
— addition of the note of scope (see Clause 1);
— modification of the designation of austenitic stainless steel to the Chinese designation (see Clause 6; Clause 6 of GB/T 24584-2009);
— addition of the note of extensometer (see Clause 6);
— addition of the note of round bar test piece (see Clause 7);
— addition of the size requirements of non-standard test piece (see Clause 7);
— modification of the rate range of testing (see Clause 8; Clause 8 of GB/T 24584-2009);
— addition of the measurement uncertainty (see Clause 11).
This part has been redrafted and modified adoption of International Standard ISO 6892-4:2015 Metallic Materials — Tensile Testing — Part 4: Method of Test in Liquid Helium.
The technical deviations between this part and ISO 6892-4:2015, together with their justifications, are as follows:
— The normative references in this part are adjusted based on technical deviations so as to adapt to the technical conditions of China. The adjustment is mainly reflected in Clause 2 "Normative References" with the specific adjustments as follows:
● IEC 6892-1:2009 is replaced by GB/T 228.1-2010, which has been redrafted and modified adoption of the international standard (see Clause 3, 6.1.2, 7.3 and Clause 11);
● IEC 6892-3 is replaced by GB/T 228.3, which has been redrafted and modified adoption of the international standard (see Clause 3);
● ISO 7500-1 is replaced by GB/T 16825.1, which is identical with the international standard (see 6.1.1);
● ISO 9513 is replaced by GB/T 12160, which is identical with the international standard (see 6.4.1);
● addition of GB/T 34104 for reference (see 6.1.5);
— modification of the test pieces of Annex, and addition of the bar or plate test pieces with diameter or width of 3 mm (see Tables A.1 and A.2).
This part was proposed by China Iron and Steel Industry Association.
This part is under the jurisdiction of SAC/TC 183 (National Technical Committee on Iron and Steel of Standardization Administration of China).
The previous editions of the standard replaced by this part are as follows:
— GB/T 24584-2009.
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Introduction
The force-time and force-extension records for alloys tested in liquid helium using displacement control are serrated. Serrations are formed by repeated bursts of unstable plastic flow and arrests. The unstable plastic flow (discontinuous yielding) is a free-running process occurring in localized regions of the parallel length at higher rates than nominal strain rates with internal test piece heating. Examples of serrated stress-strain curves for a typical austenitic stainless steel with discontinuous yielding are shown in Figure 1.
Key:
X — strain;
Y — stress, N/mm2;
Z — temperature, K.
Figure 1 Example of typical stress-strain curves and test piece temperature histories at four different nominal strain rates, for 022Cr19Ni10 (304L) stainless steel tested in liquid helium
A constant test piece temperature cannot be maintained at all times during testing in liquid helium. Due to adiabatic heating, the test piece temperature at local regions in the parallel length rises temporarily above 4 K during each discontinuous yielding event (see Figure 1). The number of events and the magnitude of the associated force drops are a function of the material composition and other factors such as test piece size and test speed. Typically, altering the mechanical test variables can change the type of serration but not eliminate the discontinuous yielding. Therefore, tensile property measurements of alloys in liquid helium (especially tensile strength, elongation, and reduction of area) may lack the usual significance of property measurements at room temperature where deformation is more nearly isothermal and discontinuous yielding typically does not occur. Strain control is the preferred control mode (see Method A of GB/T 228.1) and displacement control is the secondary method, according to Method B of GB/T 228.1.
Metallic Materials — Tensile Testing — Part 4: Method of Test in Liquid Helium
1 Scope
This part of GB/T 228 specifies the principles, definitions, symbols and designations, test piece and determination of its size, apparatus, test conditions, determination of the properties and test report of tensile testing of metallic materials in liquid helium (the boiling point is -269 °C or 4.2 K, designated as 4 K).
This part is applicable to the determination of tensile properties of metal materials in liquid helium. This part may apply also to tensile testing at cryogenic temperatures (less than -196 °C or 77 K), which requires special apparatus, smaller test pieces, and concern for serrated yielding, adiabatic heating, and strain-rate effects.
Note: The boiling point of the rare 3He isotope is 3.2 K. Usually, the tests are performed in 4He or a mixture of 3He and 4He with a high concentration of 4He. Therefore, the temperature is, as designated before, 4 K.
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 228.1-2010 Metallic Materials — Tensile Testing — Part 1: Method of Test at Room Temperature (ISO 6892-1:2009, MOD)
GB/T 228.3 Metallic Materials — Tensile Testing — Part 3: Method of Test at Low Temperature (GB/T 228.3-2019, ISO 6892-3:2015, MOD)
GB/T 12160 Calibration of Extensometer Systems Used in Uniaxial Testing (GB/T 12160-2002, ISO 9513:1999, 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 34104 Metallic Materials — Verification of the Alignment of Testing Machines (GB/T 34104-2017, ISO 23788:2012, MOD)
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in GB/T 228.1, GB/T 228.3 and the following apply.
3.1
adiabatic heating
internal heating of a test piece resulting from deformation under conditions such that the heat generated by plastic work cannot be quickly dissipated to the surrounding cryogen
3.2
axial strain
longitudinal strains measured at opposite or equally spaced surface locations on the sides of the longitudinal axis of symmetry of the test piece
Note: The longitudinal strains are measured using two or more strain-sensing transducers located at the mid-length of the parallel length.
3.3
bending strain
difference between the strain at the surface of the test piece and the axial strain
Note: The bending strain varies around the circumference and along the parallel length of the test piece.
3.4
dewar
vacuum-insulated container for cryogenic fluids
3.5
discontinuous yielding strength
Ri
peak stress at the initiation of the first measurable serration on the stress-strain curves
3.6
tensile cryostat
test apparatus for applying tensile forces to test pieces in cryogenic environments
Foreword II
Introduction IV
1 Scope
2 Normative References
3 Terms and Definitions
4 Symbols and Designations
5 Principle
6 Apparatus
7 Test Piece
8 Testing Conditions
9 Determination
10 Test Report
11 Measurement Uncertainty
Annex A (Informative) Examples of Test Pieces for Tensile Testing in Liquid Helium
