GB/T 5028-2025Metallic materials - Sheet and strip - Determination of tensile strain hardening exponent (n) (English PDF)

Foreword

This document was drafted in accordance with the rules given in GB/T 1.1-2020,

Directives for standardization - Part 1.Rules for the structure and drafting of

standardizing documents.

This document replaces GB/T 5028-2008, Metallic materials - Sheet and strip -

Determination of tensile strain hardening exponent. Compared with GB/T 5028-2008,

in addition to structural adjustments and editorial changes, the main technical Contents

changes of this document are as follows.

-- Change the symbol of true stress from "s" to "sigma", and the symbol of true plastic

strain from "e" to "epsilonp" (see Chapter 4; Chapter 3 of the 2008 edition);

-- Add "Unless otherwise agreed, the method to be used is at the discretion of

the material manufacturer or the laboratory designated by it" (see 8.5; 7.5 of

the 2008 edition);

-- Change the test report by revising item g) to "test results (if necessary, the

strength coefficient C value should be provided)" (see Chapter 9; Chapter 8

of the 2008 edition).

This document adopts ISO 10275.2020 Metallic materials - Sheet and strip -

Determination of tensile strain hardening exponent by modification.

The technical differences between this document and ISO 10275.2020 and their reasons

are as follows.

-- Use the normative reference GB/T 228.1 to replace ISO 6892-1 (see 6.1, 6.3,

7.1, 8.2, 8.3) to conform to national conditions and facilitate use;

-- Use the normative reference GB/T 5027 to replace ISO 10113 (see 6.2, 7.2)

to conform to national conditions and facilitate use;

-- Change the content of 8.5 to adapt to the characteristics of different materials.

It is suggested that the material manufacturer or the laboratory designated by

the material manufacturer decide whether to deduct the elastic strain when

calculating n. Specify Method A. Calculate the true plastic strain using

Formula (4). Add Method B. Approximate the true plastic strain using

Formula (6), to conform to national conditions and facilitate use;

-- Add reference to GB/T 8170 for numerical rounding (see 8.8) to conform to

national conditions and facilitate use;

-- Change item g) of Chapter 9 to "test results (if necessary, the strength

coefficient C value should be provided)" to indicate the importance of the

strength coefficient.

Metallic materials - Sheet and strip - Determination of

tensile strain hardening exponent (n)

1 Scope

This document specifies the principle, test apparatus, test samples, test procedures and

test report for determining the tensile strain hardening exponent (n value) of metal sheet

and strip.

This method is only applicable to the part of the stress-strain curve that shows a

monotonically continuous increase within the plastic deformation range (see 8.4).

If the stress-strain curve of the material during the work hardening stage is saw-toothed

(such as the Portevin-Le Chatelier saw-tooth yield effect exhibited by some AlMg

alloys), in order to make the given results have a certain degree of repeatability, an

automatic measurement method is used (linear regression of the logarithm of the true

stress-true plastic strain, see 8.7).

2 Normative references

The following documents, in whole or in part, are normatively referenced in this

document and are indispensable for its application. 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, Metallic materials - Tensile testing - Part 1.Method of test at room

temperature (GB/T 228.1-2021, ISO 6892-1.2019, MOD)

GB/T 5027, Metallic materials - Sheet and strip - Determination of plastic strain

ratio (r) (GB/T 5027-2025, ISO 10113.2020, MOD)

GB/T 8170, Rules of rounding off for numerical values & expression and judgment

of limiting values

GB/T 12160, Metallic materials - Calibration of extensometers systems used in

uniaxial testing (GB/T 12160-2019, ISO 9513.2012, IDT)

GB/T 16825.1, 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 16825.1-2022, ISO 7500-1.2018,

IDT)

3 Terms and definitions

No terms and definitions need to be defined in this document.

4 Symbols and their meanings

5 Principle

The sample is subjected to axial tensile deformation at a specified constant rate within

the range of uniform plastic deformation. Calculate the tensile strain hardening

exponent (n) using the stress-strain curve over the entire range of uniform plastic

deformation, or using a portion of the stress-strain curve over the range of uniform

plastic deformation.

6 Test apparatus

1 or better in accordance with GB/T 1825.1.The sample clamping method shall comply

with the provisions of GB/T 228.1.

7 Test sample

8 Test procedure