STRAIN AND STRAIN-RATE HARDENING EFFECTS IN PUNCH STRETCHING OF 5182-0 ALUMINUM AT ELEVATED-TEMPERATURES

The influences of material properties on stretch forming are often studied by testing a wide variety of materials. However, differences in texture, fracture strain, and crystal structure are not taken into account. These material differences are eliminated in the present study by performing tests on a single material (5182-0 aluminum alloy) in which strain hardening, strain-rate hardening, and limit strain vary in a precise manner with temperature and strain-rate. This allows a comparison to be made between experimental results and analytical calculations to separate the contributions of these two types of hardening in distributing strain during elevated temperature forming. Furthermore, the influence of a change in limit strain to overall formability can be assessed since the hardening phenomenon is better understood. The strain distributions developed during forming over a spherical punch are calculated using the finite element method and material properties obtained from tensile tests at 25, 130, and 200°C at varying strain rates. These are compared to experimental strain distributions over the same temperature range. Measurements of limit strains are taken from forming limit diagrams. This research demonstrates that formability is improved at elevated temperatures through increases in both strain-rate hardening and limit strains. © 1979 American Society for Metals and the Metallurgical Society of AIME.