ASTM E 517 – 00 Plastic Strain Ratio r for Sheet Metal

Introduction 

ASTM E517-00 is a standard test method for determining the plastic strain ratio, otherwise known as the “r-value,” of sheet metal. This measure describes the material’s plastic deformation capability, generally in deep drawing and forming processes. The r-value represents the spread of sheet metal when a tensile force is applied and is one of the critical parameters in various industries related to the metal-forming process.

What is the r-value ( Plastic Strain Ratio)?

The r-value is the ratio of absolute width strain to true thickness strain under uniaxial tensile stress. Formability increases with increased r-values because thinning out is less likely to occur upon stretching or drawing. This is very important in deep drawing operations.

Scope of Plastic Strain Ratio

When sheet metal is exposed to either tensile or compressive stresses in the plane of the sheet, the plastic strain ratio r is a parameter that reflects its capacity to resist thinning or thickening. The r-value is used to determine the drawability of sheet metal. It’s beneficial for assessing materials for parts where a large blank piece must be brought into the die-hole from beneath the blank holder. R-value will find an application in material selection and process design for industries where sheet metal forming is vital, such as the automotive and aerospace sectors.

Significance of Plastic Strain Ratio

The determination of sheet metal r-value of plastic strain (r-value), which is also one of the most important parameters utilized to evaluate formability, is provided based on the ASTM E517-00 standard. High r-values signify resistance to tensile strains and thus result in better suitability for forming processes such as deep drawing. In industries like automotive, aerospace, and appliances manufacturing, there is a need for metals that can be formed in complex shapes without losing strength or facing a reduction in thickness. This test helps material suppliers optimize their choice of materials, enables the development of more efficient production processes, and ensures the quality of products that will not have a high likelihood of becoming defective due to forming and stamping.

Procedure

Specimen Preparation: The test specimen is usually in the form of a flat strip of the sheet metal but with standard dimensions.

Tensile test: The specimen is exposed to a uniaxial tensile test. In this test, the material stretches, and simultaneously, the width and thickness directions are measured for strains.

Specimen Orientation: The r-value is often measured at different orientations from the rolling direction of sheet metal (0°, 45°, and 90°). It enables the evaluation of the material’s anisotropy or directional dependence on mechanical properties.

Result Analysis

The following is the result analysis of ASTM E517-00 plastic strain ratio r for sheet metal:

Specimen:

Each specimen’s measurements must be measured for thickness and breadth uniformity in the gauge section.

Areas Applicable for ASTM E517-00

• Automotive Industry: Sheet metals must be formed into complex shapes with minimal thinning or cracking during the manufacturing of automobile body panels. R-value is significantly important in determining if a material can withstand the deep drawing processes applied in shaping car components.
• Aerospace Industry: The automotive industry, where a large number of sheet metals may be needed in forming complex shapes to provide necessary strength. Higher r-values are sought for the aircraft skins and other structural members.
• Appliance Manufacturing: The manufacturers of appliances, such as refrigerators, washing machines, and ovens, require materials which are good for formability so that the panels and parts produced are strong and also aesthetically pleasing. R-value test ensures that the metal used can withstand forming operations.
• Metal Packaging: In metal canning, manufacturing, etc., capability in formability is critical. Thus, the r-value assures the selection of materials so that the materials do not thin out too much on forming.

Conclusion 

ASTM E517-00 standardizes a test procedure for determining the plastic strain ratio of sheet metals and presents valuable data for industries that use metal-forming processes. Knowledge of the r-value aids in the correct selection of the material. It enhances the manufacturing process toward achieving the desired shape of components without defects like thinning or tearing.

FAQs