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GB/T 39152-2020 English PDF (GBT39152-2020)

GB/T 39152-2020 English PDF (GBT39152-2020)

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GB/T 39152-2020: Test method of the bending stress relaxation for copper and copper alloy

This Standard specifies the method principles, instruments and apparatuses, samples, test conditions, determination of various parameters before the test, test procedures, test data processing, and test reports for the test method of the bending stress relaxation for copper and copper alloy materials. This Standard applies to the determination of the bending stress relaxation properties for copper and copper alloy plates and strips whose thickness is 0.1 mm ~ 1.0 mm under constant strain conditions.
GB/T 39152-2020
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 77.040.10
H 22
Test method of the bending stress relaxation for
copper and copper alloy
ISSUED ON: OCTOBER 11, 2020
IMPLEMENTED ON: SEPTEMBER 01, 2021
Issued by: State Administration for Market Regulation;
Standardization Administration of the PEOPLE Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 Principle of the method ... 5
5 Instruments and apparatuses ... 6
6 Sample ... 7
7 Test conditions ... 8
8 Determination of various parameters before the test ... 8
9 Test procedure ... 9
10 Test data processing ... 9
11 Test report ... 10
Test method of the bending stress relaxation for
copper and copper alloy
1 Scope
This Standard specifies the method principles, instruments and apparatuses, samples, test conditions, determination of various parameters before the test, test procedures, test data processing, and test reports for the test method of the bending stress relaxation for copper and copper alloy materials.
This Standard applies to the determination of the bending stress relaxation properties for copper and copper alloy plates and strips whose thickness is 0.1 mm ~ 1.0 mm under constant strain conditions.
2 Normative references
The following documents are indispensable for the application of this document. For dated references, only the dated version applies to this document. For undated references, the latest edition (including all amendments) applies to this document.
GB/T 8170, Rules of rounding off for numerical values and expression and
judgment of limiting values
GB/T 10623-2008, Metallic material - Mechanical testing - Vocabulary
GB/T 22315, Metallic materials - Determination of modulus of elasticity and poisson's ratio
GB/T 26303.3, Measuring methods for dimensions and shapes of wrought
copper and copper alloys - Part 3: Sheets and strips
GB/T 34505, Copper and copper alloy materials - Tensile testing at room temperature
3 Terms and definitions
Terms and definitions determined by GB/T 10623-2008 and the following ones are applicable to this document.
3.1 Bending stress
The normal stress that is generated by the sample in the single-ended bending state.
3.2 Initial stress
At the beginning of the stress relaxation test, the maximum bending stress that is generated by the sample at the moment of the specified bending deformation. Note: Rewrite GB/T 10623-2008, definition 3.27.
3.3 Initial deformation
The artificially set elastic bending deformation that is generated by the sample at room temperature.
3.4 Initial reference height
Give initial deformation at room temperature; after unloading, the height of the load point of the sample to the reference surface.
3.5 Relaxed stress
The reduced bending stress on the sample at any time in the stress relaxation test.
Note: Rewrite GB/T 10623-2008, definition 3.29.
3.6 Permanent deformation
The plastic bending deformation that is caused by stress relaxation.
3.7 Stress relaxation ratio
The percentage of relaxed stress and initial stress, which is expressed as the ratio of permanent deformation and initial deformation.
4 Principle of the method
Copper and copper alloys maintain a certain bending deformation under the action of long-term stress and a certain temperature. With the extension of time, their internal elastic strain will gradually transform into plastic strain, which will cause stress relaxation, which is an important form of failure of metal components. Heat the sample to a specified temperature; maintain a constant bending deformation at this temperature; remove the sample load after the specified time; measure the permanent deformation of the sample.
The initial deformation (??0) shall not be greater than 1/2 of the length of the bending section (ls). The initial deformation is recommended to be 4 mm; other negotiated values can also be used. Only when the initial deformation is the same, the stress relaxation ratio can be compared with each other.
8.5 Measurement of the initial reference height
Clamp the sample on the fixture; give the initial deformation at the specified position of the free end of the sample; unload it after standing at room temperature for 30 s ~ 35 s; measure the height from the load point of the free end of the sample to the reference surface, which is the initial reference height (Hi).
9 Test procedure
9.1 The test temperature is 125?? C or 150 ??C; the time is 24 h, 48 h, 96 h, 192 h. After negotiation, the temperature and time can also be other values. The time accuracy shall be within 3%.
9.2 Use a fixture to fix the sample; place it in the heating equipment. When the temperature reaches 95% of the specified temperature, start timing.
9.3 After reaching the specified test time, remove the fixture from the heating equipment and place it at room temperature. After the sample is cooled to room temperature, remove the sample load; measure the distance from the sample load point to the reference surface, which is the height after stress relaxation (Ht).
10 Test data processing
10.1 Permanent deformation
For samples which are tested under different test conditions (temperature and time), after removing the device, calculate the occurred permanent deformation (??t) according to Formula (2):
Where:
??t -- permanent deformation, in millimeters (mm);
Ht -- height after stress relaxation, in millimeters (mm);
Hi -- initial reference height, in millimeters (mm).

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