Compensation of elastic strains in the determination of plastic strain ratio (R) in sheet metals

Plastic strain ratios of AA8011 aluminum alloy and commercially pure titanium sheet with, respectively, low and high elastic spring-back were determined by digital imaging of marked tensile specimens with and without considering elastic strains. To calculate the actual R-values, a new method was proposed for the compensation of elastic strains. The essential feature in the approach proposed consists of defining elastic strains with respect to gage length before unloading. Comparison with experimental data shows that the new method is generally more accurate than the existing ones, especially in the cases where materials with very high elastic spring-back, such as titanium, are concerned. The results were discussed on the basis of elastic and yield behavior of the materials.