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
GB/T 228.4-2019 The following standards are cited：
