Metallic materials — Sheet and strip — Determination of plastic strain ratio
1Key Takeaways
This document specifies a method for determining the plastic strain ratio of flat products (sheet and strip) made of metallic materials.
2Expert Interpretation
In-depth analysis of the determination method of the plastic strain ratio (r-value) of metal sheets in the ISO 10113:2020 standard, including the comparison of three test schemes: manual, semi-automatic and automatic, the principle of anisotropic parameter calculation, and error source analysis technology. It is suitable for material forming performance evaluation in the fields of automotive manufacturing, aerospace, etc.
Analysis of the core content of the standard
This standard specifies the determination method of the plastic strain ratio (r-value) of metal sheets, which is a key indicator for evaluating the forming performance of materials. Through tensile testing machine and different measurement schemes:
| Method type | Measuring equipment | Width measurement accuracy | Applicable scenarios |
|---|---|---|---|
| Manual method (8.2) | Vernier caliper | ±0.005mm | Laboratory basic research |
| Semi-automatic method (8.3) | Length extensometer + manual measurement | ±0.005mm | Process quality control |
| Automatic method (8.4) | Biaxial Extensometer System | ±0.1% | High-precision Forming Simulation |
Evolution of Key Technologies
Main updates of the 2020 version of the standard:
- New semi-automatic method (Chapter 8.3)
- Clearly distinguish the applicable boundaries of the three methods
- Add error source analysis appendix (Appendix A)
- Introduce strain range regression analysis method (8.4.3.3)
Actual Application Case
An automotive sheet manufacturer uses an automatic biaxial extensometer system to measure the r-value of DC04 cold-rolled steel sheet:
- Test direction: 0°, 45°, 90° rolling direction
- Strain range: 8-12% (Ag=22%)
- Obtained parameters: r0=1.85, r45=1.32, r90=2.10
- Calculated: r=1.53, Δr=0.61
Key points for error control
According to the recommendations in Appendix A, special attention should be paid to:
- Transverse bending caused by specimen centering deviation (Figure 2)
- Abnormal plastic strain display in elastic section (Figure A.2-A.3)
- Number of width measurement positions (at least 3 points)
- Influence of Portevin-Le Chatelier effect
Implementation recommendations
1. Method selection: Automatic method is preferred to obtain continuous r-value curve
2. Data processing: Regression analysis is used when PLC effect occurs
3. Equipment verification: Regular calibration of extensometer system (refer to ISO 9513)
4. Report specification: Test method and strain point (e.g. r45/10 or r45/8-12) must be stated