GB/T 5027-2025Metallic materials - Sheet and strip - Determination of plastic strain ratio (r) (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 5027-2016, Metallic materials - Sheet and strip - Determination of plastic strain ratio. Compared with GB/T 5027-2016, in addition to structural adjustments and editorial changes, the main technical changes of this document are as follows.

-- Modify some symbols and descriptions in Table 1 (see Chapter 4; Chapter 4 of the 2016 edition);

-- Change the test procedure by re-classifying the three methods used for the determination of r (manual, semi-automatic and automatic) (see Chapter 8; Chapter 8 of the 2016 edition);

-- Combine the provisions for the calculation of r into Chapter 8, and the clearly divide data evaluation methods for r into single-point method A (deducting elastic strain), single-point method B (without deducting elastic strain), and interval regression method (see Chapter 8; Chapter 9 of the 2016 edition);

-- Change the terms of weighted average value and anisotropy to additional test results (see Chapter 9; Chapter 9 of the 2016 edition);

This document adopts ISO 10113:2020, Metallic materials - Sheet and strip - Determination of plastic strain ratio (r) by modification.

Compared with ISO 10113:2020, this document makes the following structural adjustments.

-- 8.4.3.4 corresponds to 8.4.3.3 of ISO 10113:2020, and Formula (17) corresponds to Formula (14) of ISO 10113:2020;

-- Appendix B corresponds to Appendix A of ISO 10113:2020.

This document contains many technical differences compared to ISO 10113:2020, which are indicated by a single vertical line (|) in the outer margin of the clauses involved. A list of these technical differences and their reasons is given in Appendix A. This document also makes the following editorial modifications.

-- Delete Note 1 in Table 1 of Chapter 4 of the international standard;

-- Delete the informative Appendix B "Symbol Comparison Table" of the international standard;

-- Add Chinese literatures in the Bibliography.

1 Scope

This document specifies the principle, test apparatus, test samples, test procedures, additional test results and test report for the determination of plastic strain ratio of metal sheet and strip.

This document applies to the determination of plastic strain ratio of metal sheet and strip.

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 228.1-2021, Metallic materials - Tensile testing - Part 1: Method of test at room temperature (ISO 6892-1:2019, 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)

3 Terms and definitions

For the purposes of this document, the following terms and definitions, as well as those given in GB/T 228.1, apply.

4 Symbols and their meanings

The symbols used in this document and their meanings are shown in Table 1.

5 Principle

Plastic strain ratio (r) is usually used to characterize and evaluate materials, and is also used for numerical simulation of forming processes.

Stretch the sample to a specified (engineering) plastic strain level, and calculate r based on the change in sample width and thickness after unloading or after deducting the elastic strain, or calculate r based on the principle of volume invariance, using the changes in sample length and width, see formula (5). Where. epsilon p_a - true plastic strain in the thickness direction, epsilon p_a=ln;

epsilon p_b - true plastic strain in the width direction, epsilon p_b=ln;

epsilon p_l - true plastic strain in the length direction, epsilon p_l=ln.

The volume invariance principle only applies to the situation before the maximum plastic elongation Ag, because after this point the sample will undergo local necking and this principle is no longer valid.

Some materials will show a slight local necking before Ag, which may cause the instantaneous reduction of the sample in the width direction to be too large, resulting in an overestimation of r. This deviation is especially obvious when the transverse extensometer is only clamped in the middle area of the original gauge length of the sample. At this time, the following two processing methods are recommended.

a) The transverse extensometer should be able to measure the instantaneous reduction in the width direction of the sample at multiple locations, and the measurement points should cover the entire (longitudinal) gauge length;

b) The length of the parallel section of the sample should be at least six times the original width bo of the sample gauge length.

The sampling direction of the sample relative to the rolling direction and the (engineering) plastic strain level for determining r are specified by the relevant product standard.

When r >1, the deformation characteristic of the material is that the deformation in the width direction is greater than that in the thickness direction (epsilon p_b >epsilon p_a, as shown in Figure 1); when r< 1, the deformation in the thickness direction is greater than that in the width direction (epsilon p_b< epsilon p_a, as shown in Figure 1); when r=1, the deformation behavior of the material in the thickness direction and the width direction is isotropic (epsilon p_b=epsilon p_a, as shown in Figure 1). Key.

1 - original cross section of the parallel section of the sample;

2 - significant deformation of the material in the width direction;

3 - isotropic material (deformation is uniform across the width and thickness 4 - significant deformation of the material in the thickness direction; a Increase with the plastic extension.

6 Test apparatus

6.1 The tensile testing machine shall meet the requirements of GB/T 228.1 for equipment.

6.2 For the manual measurement method (see 8.2), the device used to measure the original gauge length of the sample and the gauge length after plastic deformation occurs and is unloaded shall have an accuracy of ±0.2% or better. The device used to measure the original width of the sample and the width of the sample after plastic deformation occurs and is unloaded shall have an accuracy of ±0.005 mm or better.

6.3 For the semi-automatic measurement method (see 8.3), the longitudinal extensometer shall meet the accuracy requirements of Class 1 or better in GB/T 12160.

The device used to measure the original width of the sample and the width of the sample after plastic deformation occurs and is unloaded shall have an accuracy of ±0.005 mm or better.

Note: The accuracy of the longitudinal extensometer gauge length Le has a great influence on the determination of the r value.

6.4 For the automatic measurement method (see 8.4), the extensometer shall meet the accuracy requirements of Class 1 or better in GB/T 12160 within the range used, and the device for measuring the original width of the sample shall have an accuracy of ±0.1% or better.

Note: When the gauge length of the extensometer is long and the extension is large, the maximum measurement error of the Class 1 extensometer may exceed ±0.01 mm.

6.5 The clamping method of the sample shall be carried out in accordance with the provisions of GB/T 228.1.

7 Test sample

7.1 Sampling shall be carried out in accordance with the requirements of the relevant product standards. If the product standards do not specify, sampling shall be carried out in accordance with the agreement between the relevant parties.

7.2 The sample type and preparation, including size tolerance, shape tolerance, and marking of the original gauge length, shall comply with the requirements of Appendix E of GB/T 228.1-2021. The two sides of the sample shall be sufficiently parallel within the gauge length to ensure that the difference in width measurements at any two locations is less than 0.1% of the average width measurement.

7.3 In order to ensure that the various types of samples listed in GB/T 228.1-2021 (Appendix E) produce uniform deformation within the gauge length, it shall be ensured that the parallel section length of the sample Lc >= (Lo + 2bo). If Lc >= (Lo + 2bo) cannot be met due to insufficient size of the product, with the agreement of both the supplier and the buyer, a sample with Lc meeting the minimum value specified in Appendix E of GB/T 228.1-2021 can be used. It is recommended to use a transverse extensometer with a multi-line measurement method (see reference [1]), or select a smaller gauge length after consultation and agreement between all parties.

7.4 Unless otherwise specified, the sample thickness shall be the full thickness of the plate being tested.

7.5 There shall be no surface defects (such as scratches) in the parallel section of the sample.

8 Test procedure