Standards related to:

GB/T 16865-2023**GB/T 16865-2023: PDF in English (GBT 16865-2023) **

GB/T 16865-2023

GB

NATIONAL STANDARD OF THE

PEOPLE’S REPUBLIC OF CHINA

ICS 77.040.10

CCS H 22

Replacing GB/T 16865-2013

Test Pieces and Methods for Tensile Test for Wrought

Aluminum, Magnesium and Their Alloy Products

ISSUED ON: AUGUST 6, 2023

IMPLEMENTED ON: MARCH 1, 2024

Issued by: State Administration for Market Regulation;

Standardization Administration of the People’s Republic of China.

Table of Contents

Foreword ... 3

1 Scope ... 6

2 Normative References ... 6

3 Terms and Definitions ... 7

4 Method Overview ... 7

5 Instruments and Equipment ... 8

6 Specimens ... 13

7 Test Procedures ... 42

8 Result Determination ... 64

9 Test Report ... 65

Appendix A (informative) Estimation Method for Beam Displacement Rate ... 67

Test Pieces and Methods for Tensile Test for Wrought

Aluminum, Magnesium and Their Alloy Products

1 Scope

This document specifies the specimen requirements and test methods for the tensile test of

wrought aluminum, magnesium and their alloy products.

This document is applicable to the room-temperature, high-temperature and low-temperature

tensile test of wrought aluminum, magnesium and their alloy plates, strips, foils, pipes, rods,

profiles, wires, forgings and other processed products.

2 Normative References

The contents of the following documents constitute indispensable clauses of this document

through the normative references in the text. In terms of references with a specified date, only

versions with a specified date are applicable to this document. In terms of references without a

specified date, the latest version (including all the modifications) is applicable to this document.

GB/T 3246 (all parts) Inspection Method for Structure of Wrought Aluminum and Aluminum

Alloy Products

GB/T 8170 Rules of Rounding off for Numerical Values & Expression and Judgement of

Limiting Values

GB/T 10623 Metallic Material - Mechanical Testing - Vocabulary

GB/T 12160-2019 Metallic Materials - Calibration of Extensometers Systems Used in Uniaxial

Testing

GB/T 16825.1-2022 Metallic Materials - Calibration and Verification of Static Uniaxial Testing

Machines - Part 1: Tension / Compression Testing Machines - Calibration and Verification of

the Force-measuring System

GB/T 22638.11 Test Methods for Aluminum and Aluminum Alloy Foils - Part 11:

Determination of Mechanical Properties

GB/T 34104-2017 Metallic Materials - Verification of the Alignment of Testing Machines

JJG 139 Tension, Compression and Universal Testing Machines

JJG 475 Electronic Universal Testing Machine

JJG 762 Extensometer

F---force;

CL---the centerline of the clamping system and the longitudinal axis of the specimen;

1---fixture;

2---specimen;

3---extensometer.

Figure 1 -- Schematic Diagram of Tensile Test

5 Instruments and Equipment

5.1 Testing Machine

5.1.1 The testing machine force measuring system shall be calibrated in accordance with JJG

139, JJG 475 or JJG 1063. The accuracy of the testing machine force measuring system used

for the determination of room-temperature tensile mechanical properties of aluminum foil

products shall reach or be superior to Level 0.5 specified in GB/T 16825.1-2022. The accuracy

of the testing machine force measuring system used for the determination of mechanical

properties of other products shall reach or be superior to Level 1.

5.1.2 The maximum load required for the test should be within the range of 10% ~ 90% of the

maximum load of the testing machine.

5.1.3 Testing machines used for the determination of elastic modulus or mechanical properties

of aviation and aerospace materials shall be inspected for coaxiality in accordance with GB/T

34104-2017. The coaxiality of the testing machines used for the determination of elastic

modulus shall reach or be superior to Level 5. The coaxiality of the testing machines used for

the determination of mechanical properties of aviation and aerospace materials shall reach or

be superior to Level 10.

5.2 Extensometer

5.2.1 The extensometer system shall be calibrated in accordance with JJG 762. When

determining the elastic modulus, the accuracy of the extensometer shall reach or be superior to

Level 0.5 specified in GB/T 12160-2019; when determining other mechanical properties, the

accuracy of the extensometer shall reach or be superior to Level 1.

5.2.2 When determining the elastic modulus, the extensometer system shall be able to measure

the average deformation on at least two opposite sides of the specimen. When adopting the

automatic method to determine the plastic strain ratio, the extensometer system shall be able to

measure the deformation in the length direction and the width direction of the rectangular

specimen. The extensometer used to measure the deformation in the width direction of the

specimen should be able to measure the average deformation at both ends of the gauge length

and the three widths in the middle.

7.1.6 For full cross-section specimens with shapes other than circular, rectangular and ring-

shaped, when the original cross-sectional area of the specimens is calculated using the actual

measurement method, the specimen size measurement method shall be agreed upon by both the

supply-side and the demand-side, or a cross-section scanner may be used for automatic

measurement.

7.1.7 When determining the plastic strain ratio of the material, measure the width at both ends

and the middle of the gauge length of the rectangular specimens; the accuracy shall be not

greater than 0.005 mm. Take the average value of the three widths as the average original width

(𝑏0) of the specimens; measure the original thickness (a0) at both ends and the middle of the

gauge length of the rectangular specimens; the accuracy shall be not greater than 0.001 mm.

The range of the three thicknesses should not exceed 0.013 mm. The specimens are allowed to

be machined to comply with the requirements for thickness range. When adopting the artificial

method to determine the plastic strain ratio, the original gauge length (L0) shall also be measured;

the measurement accuracy shall be not greater than 0.01 mm.

7.2 Calculation of Original Cross-sectional Area (S0) of Specimens

7.2.1 Requirements for rounding and error

7.2.1.1 When calculating the area of a circle, the constant must be taken to at least four

significant figures.

7.2.1.2 The calculation results of the original cross-sectional area (S0) of the specimen shall

retain four significant figures, and the numerical rounding shall be carried out in accordance

with the stipulations of GB/T 8170.

7.2.1.3 The determination error of the original cross-sectional area of the specimen shall be not

greater than 1%, and the determination error of the original cross-sectional area of specimens

with a thickness less than 0.3 mm shall be not greater than 2%.

7.2.2 Circular specimens

In accordance with Formula (2), calculate the original cross-sectional area (S0) of circular

specimens, expressed in (mm2).

Where,

d0---the original diameter of the specimen, expressed in (mm).

7.2.3 Rectangular specimens

In accordance with Formula (3), calculate the cross-sectional area of the three locations of the

rectangular specimens, expressed in (mm2). Select the smallest area among the three locations

as the original cross-sectional area (S0) of the specimens.

materials have different sensitivities to tensile rate. The selection of test rate shall be determined

in accordance with the material. When the product standard does not specify the setting method

for the test rate, the test rate recommended in 7.10.2 ~ 7.10.4 shall be used for testing. The

tensile test rate of the arbitration test is determined by the demand-side and the supply-side

through negotiation.

7.10.2 Strain rate2)

7.10.2.1 Room-temperature tensile test

7.10.2.1.1 Aviation materials

Adopt a strain rate ( ) of 0.000083 s1 (with a relative error of 40%) to perform the tensile

test, until the specified non-proportional elongation strength is determined. Afterwards, adopt

a strain rate not exceeding 0.0067 s1 to continue the test.

7.10.2.1.2 Aluminum foil

The selection of the test rate for the room-temperature tensile mechanical properties of

aluminum foil shall be carried out in accordance with the stipulations of GB/T 22638.11.

7.10.2.1.3 Other products

In accordance with different determination items, determine the strain rate:

---When it is necessary to determine the elastic modulus, adopt a strain rate ( ) of

0.000083 s1 (with a relative error of 40%) to perform the tensile test, until the elastic

modulus is measured. Then, adopt a strain rate ( ) of 0.00025 s1 (with a relative error

of 20%) to continue the tensile test, until the specified non-proportional elongation

strength is determined. Afterwards, adopt a strain rate ( ) not exceeding 0.0067 s1 to

continue the test.

---When it is not necessary to determine the elastic modulus, adopt a strain rate ( ) of

0.00025 s1 (with a relative error of 20%) to perform the tensile test, until the specified

non-proportional elongation strength is determined. Afterwards, adopt a strain rate ( )

not exceeding 0.0067 s1 to continue the test.

---When neither the elastic modulus nor the specified non-proportional elongation strength

is determined, adopt a strain rate ( ) not exceeding 0.0067 s1 to perform the tensile

test.

7.10.2.2 High-temperature tensile test

Adopt a strain rate ( ) of 0.000083 s1 (with a relative error of 40%) to perform the high-

temperature tensile test, until the specified non-proportional elongation strength is determined.

Afterwards, adopt a strain rate ( ) of 0.00083 s1 (with a relative error of 20%) to continue

2) If the extensometer is removed after determining the specified non-proportional extension strength, the test may

be continued using the beam displacement rate.

the test.

7.10.2.3 Low-temperature tensile test

Adopt a strain rate ( ) of 0.000083 s1 (with a relative error of 40%) to perform the low-

temperature tensile test, until the specified non-proportional elongation strength is determined.

Afterwards, adopt a strain rate ( ) of 0.0067 s1 to continue the test.

7.10.3 Stress rate

Adopt a stress rate ( ) of 2 MPa/s ~ 12 MPa/s to perform the room-temperature tensile test,

until the specified non-proportional elongation strength is determined. Afterwards, adopt a

beam displacement rate (vc) not exceeding 0.48 L0/min to continue the test. A constant beam

displacement rate should be maintained, so that the stress rate in the elastic deformation stage

of the specimen complies with the requirements. When the test rate is controlled in a closed

loop through the force sensor signal, after determining the specified non-proportional

elongation strength, the control mode shall be switched in time, so as to prevent the beam

displacement rate of the testing machine from being too fast or even out of control.

7.10.4 Beam displacement rate

In accordance with the strain rate ( ) specified in 7.10.2, and Formula (7), calculate the beam

displacement rate (vc), expressed in (mm/s). The calculation result shall retain two significant

figures and rounded in accordance with the stipulations of GB/T 8170. Or the beam

displacement rate can also be estimated with reference to Appendix A.

Where,

---the strain rate, expressed in (s1);

Lc---the parallel length, expressed in (mm).

7.11 Determination of Mechanical Properties

7.11.1 Specimen loading

7.11.1.1 Start the testing machine, load the specimen, and when determining the elastic modulus,

the loading of the specimen should be repeatedly performed for at least three times. If it is

necessary to simultaneously determine other mechanical properties, such as: specified non-

proportional elongation strength and tensile strength, loading may be performed only once; it

is also feasible to determine the elastic modulus after three loadings, and then, continuously

apply the load during the last loading, until the other required mechanical properties are

determined.

7.11.1.2 When determining the plastic strain ratio through the artificial method, stretch the

specimen, until it reaches the specified plastic (engineering) strain; when only the elastic

Description of indexes:

R---the stress;

e---the strain;

Rm---the tensile strength;

mE---the slope of the elastic part of the stress-strain curve;

Ag---the plastic elongation at maximum force;

1---the lower limit of the regression interval;

2---the upper limit of the regression interval.

Figure 36 -- Schematic Diagram of Determining the Value Range on the Stress-strain

Curve Based on the Regression Interval

7.11.10.1.2 The value n is related to the specified regression interval. The regression interval

used to determine the value n can be listed in the record or report in a table, or the regression

interval can also be marked with a subscript. For example, n515 represents the value n calculated

in the range of plastic (engineering) strain (ep) of 5% ~ 15%.

7.11.10.1.3 The plastic (engineering) strain range specified in the product standard, or order

sheet (or contract) shall be used as the regression interval. The regression interval shall be no

less than 2%. When the product standard or order sheet (or contract) specifies the value n for

determining a single plastic (engineering) strain level, a 2% strain range with the strain level as

the midpoint shall be selected as the regression interval, for example, the regression interval of

5% strain is 4% ~ 6% strain range. When the plastic (engineering) strain range or a single plastic

(engineering) strain level is not specified in the product standard or order sheet (or contract),

the entire uniform plastic (engineering) strain range should be selected for calculation.

7.11.10.1.4 The upper limit of the plastic (engineering) strain range used to calculate the value

n shall not be greater than the plastic elongation at maximum force (Ag). When the Ag of the

specimen is less than the upper limit of the strain range specified in the product standard or

order sheet (or contract), it cannot be used for the calculation of the value n. However, when

the demand-side and the supply-side agree and indicate it in the product standard or order sheet

(or contract), the Ag of the specimen can be used as the upper limit of the plastic (engineering)

strain range to calculate the value n.

7.11.10.2 Calculation of strain hardening index (value n)

7.11.10.2.1 On the stress-strain curve, determine the lower limit (e1) and upper limit (e2) of the

engineering strain corresponding to the upper and lower limits of the plastic (engineering) strain

of the regression interval.

7.11.10.2.2 In the range of e1 ~ e2 on the stress-strain curve, select at least 5 data points at equal

passing through the origin of the regression interval, and the numerical value is

dimensionless; then, in accordance with Formula (30), calculate the value r, and

numerical value is dimensionless. The calculation results shall retain two decimal

places and rounded to the nearest multiple of 0.05 in accordance with the

stipulations of GB/T 8170.

From the test record, select the specified plastic (engineering) strain interval.

When the elastic strain in the length direction of all points in the interval is less

than 10% of the engineering strain, the total true strain (L) in the length direction

of the specimen can be calculated in accordance with Formula (10), and the

numerical value is dimensionless; in accordance with Formula (27), calculate the

total true strain (b) in the width direction of the specimen, and the numerical value

is dimensionless; in accordance with Formula (31), calculate the slope mr of the

best-fit straight line passing through the origin in the regression interval, and the

numerical value is dimensionless; then, in accordance with Formula (30), calculate

the value r, and the numerical value is dimensionless. The calculation results shall

retain two decimal places and rounded to the nearest multiple of 0.05 in accordance

with the stipulations of GB/T 8170.

7.11.11.3 Result expression

7.11.11.3.1 Expression of plastic strain ratio (value r)

The value r is related to the sampling direction of the specimen, and the specific plastic

(engineering) strain value (or interval). When recording or reporting, the specimen direction

and the specified plastic (engineering) strain value (or interval) can be listed in the table, or a

subscript can be used to identify the specimen direction and the specified plastic (engineering)

strain value (or interval).

EXAMPLE:

For example, r0/10 signifies the value r determined when the specimen direction is parallel to the rolling

direction, and the plastic (engineering) strain (ep) is 10%; r90/8-12 signifies the value r when the specimen

direction is perpendicular to the rolling direction, and the plastic (engineering) strain (ep) is in the range

of 8% ~ 12%.

7.11.11.3.2 Weighted average of plastic strain ratio (𝒓) and plastic strain ratio anisotropy

(r)

Under the same plastic (engineering) strain value (or interval), determine the value r of the

specimen in the three directions of 0, 45 and 90 (r0, r45 and r90 respectively). In accordance

with Formula (32), calculate the weighted average of the plastic strain ratio (𝑟 ), and the

numerical value is dimensionless. The calculation results shall retain two decimal places and

rounded to the nearest multiple of 0.05 in accordance with the stipulations of GB/T 8170. In

accordance with Formula (33), calculate the plastic strain ratio anisotropy (r), and the

numerical value is dimensionless. The calculation results shall retain two decimal places and

rounded to the nearest multiple of 0.05 in accordance with the stipulations of GB/T 8170.

NOTE: the value r in the three directions is determined at the same plastic (engineering) strain

value (or interval), and the symbol indicating the plastic (engineering) strain value (or

interval) in the subscript is omitted from the Formula.

8 Result Determination

8.1 When one of the following circumstances occurs in the test, the test results are invalid, and

the same quantity of specimens shall be taken from the same batch of materials for a re-test:

---The specimen has a poor machined surface, and the size does not comply with the

requirements, or its performance changes due to poor modes of machining;

---The test method is incorrect or the test equipment fails;

---When determining the elastic modulus, multiple different evaluation areas were selected,

but none of them could satisfy the determination coefficient r2 0.9995;

---When determining the value n, the Ag of the specimen is less than the upper limit of the

plastic (engineering) strain range specified in the product standard or order sheet (or

contract);

---When determining the value r, the Ag of the specimen is less than the plastic (engineering)

strain value (or upper limit of the interval) for the determination of the value r specified

in the product standard or order sheet (or contract);

---When determining the value r, the specimen laterally bends during the test (that is, the

middle part of the width of the parallel part of the rectangular specimens bulges in the

direction perpendicular to the specimen plane, and the cross section is similar to an arc-

shaped specimen);

---The fracture of the specimen is not within the middle area shown in Figure 37, and the

elongation after break is lower than the value specified in the product standard. In

addition, the tensile fracture is inspected in accordance with GB/T 3246.1 and (or)

e) Test rate method;

f) One or several of tensile strength, specified non-proportional elongation strength,

elongation after break, elongation at yield point, total elongation at maximum force,

plastic elongation at maximum force, reduction of area, elastic modulus, strain

hardening index, and plastic strain ratio;

g) Test equipment;

h) Test temperature;

i) Extensometer clamping and gauge length correction methods for high-temperature

tensile test or low-temperature tensile test;

j) Type of extensometer system when determining elastic modulus;

k) The number of loadings when determining the elastic modulus, and the elastic

modulus value determined for each loading;

l) The minimum stress value, maximum stress value and the number of stress-strain data

pairs in the evaluation range when determining the elastic modulus,

m) Coefficient of determination when determining the elastic modulus,

n) Plastic (engineering) strain range when determining the strain hardening index;

o) The number of data points for calculating the strain hardening index (which can be

omitted when using all data points in the regression interval) and the calculation

method (using the true plastic strain or total true strain for calculation);

p) The plastic (engineering) strain value or plastic (engineering) strain range when

determining the plastic strain ratio;

q) The determination method when determining the plastic strain ratio (artificial method

or automatic method);

r) The calculation method when determining the plastic strain ratio by the automatic

method (using the true plastic strain or total true strain for calculation);

s) Reasons for supplementary test;

t) Reasons for re-performed test;

u) Serial No. of this document;

v) Test personnel and test time.

Appendix A

(informative)

Estimation Method for Beam Displacement Rate

A.1 Estimation through Preliminary Tests

In accordance with the estimated beam displacement rate, carry out a preliminary test. Then, in

accordance with Formula (A.1), calculate the beam displacement rate (vc) corresponding to the

specified strain rate, expressed in (mm/s). The calculation results shall retain two significant

figures and rounded in accordance with the stipulations of GB/T 8170.

Where,

vc_p---the beam displacement rate of the preliminary test, expressed in (mm/s);

---the specified strain rate when determining the specified non-proportional elongation

strength, expressed in (s1);

---the actual strain rate of the preliminary test when determining the specified non-

proportional elongation strength, expressed in (s1).

A.2 Estimation through Testing Stiffness and Material Properties

A.2.1 When the stiffness of the testing machine (CM) is known, and the slope (m) at the specified

non-proportional elongation strength on the stress-strain curve of the specimen can be roughly

determined, the beam displacement rate (vc) can be calculated in accordance with Formula (A.2),

expressed in (mm/s). The calculation results shall retain two significant figures and rounded in

accordance with the stipulations of GB/T 8170. The values of m and CM within the elastic range

on the stress-strain curve shall not be used, especially when the stiffness of the test equipment

is non-linear (for example, when a wedge-shaped fixture is used), m and CM shall take a value

within the range around the specified non-proportional elongation strength.

Where,

m---the slope at the specified non-proportional elongation strength on the stress-strain curve,

expressed in (MPa);

CM---the stiffness of the test equipment, expressed in (N/mm).

A.2.2 After conducting the tensile test at a slow and constant beam displacement rate, determine

the slope (m) and strain rate ( ) at the specified non-proportional elongation strength on the

stress-strain curve of the specimen. Then, in accordance with Formula (A.3), calculate the

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