Measurement of Axial and Circumferential <i>r</i>-values of Tube

In recent years, the application of tubular materials has been expanding, especially in the automotive industry, but a method of measuring the r-value, an important property for the secondary processing of tubular materials, had not been established. Therefore, we investigated a method of accurately measuring the axial and circumferential r-values of tube materials by both FEM and experiments. The axial r-value was calculated from the circumferential and thickness direction strains after a tensile test with an arc-shaped specimen to obtain a highly accurate r-value. A highly accurate r-value can also be calculated from the average of the strains obtained from tensile tests with strain gauges attached to the inside and outside surfaces of the arc-shaped tensile specimen. However, a correction factor must be applied. The circumferential r-value can also be calculated from the average of the strains obtained from tensile tests with strain gauges attached to the inside and outside surfaces of a ring tensile specimen. However, a correction factor must again be applied.