Meaning
Standard testing protocols define the procedure for measuring the plastic strain ratio of metallic sheet materials. The standard known as astm e517 governs the determination of the r-value, which indicates the resistance of a sheet metal to thinning during deep drawing operations. This testing method is essential for selecting steel or aluminum sheets that must undergo complex stamping without tearing.
A higher r-value demonstrates that the material has a greater ability to resist deformation through its thickness.
Testing Method
Mechanical tension testing of a rectangular specimen is performed to extract the necessary dimensional data. The specimen undergoes uniform plastic strain, typically between fifteen and twenty percent, while the length and width are monitored continuously or measured before and after pulling.
Material Behavior
Anisotropic material flow is quantified by comparing the true strain in the width direction to the true strain in the thickness direction. If the ratio differs from unity, the sheet exhibits plastic anisotropy. This directional variation affects how the alloy flows under complex multi-axial stress states in a metal press.
Industrial Utility
Procurement contracts for sheet metals frequently reference this standard to guarantee consistent forming performance in automotive stamping lines. A high strain ratio ensures fewer defects during the manufacturing of structural battery enclosures and outer body panels. Consistency in r-value avoids expensive tooling adjustments.
