Lack of Hardening in Drawn Bars of Copper and Aluminum in Tension Tests

Oxygen-free copper, 6061 aluminum, and 1100 aluminum bars were drawn from various initial diameters in the annealed state to bars of 11.8 mm (0.464 in.) at maximum reductions in area up to 79.5 percent. It was found that an apparent lack of hardening existed at the higher strains up to the maximum investigated as was determined in tension tests of the drawn bars. The lack of hardening observed was thought to be due, at least in part, to the development of microcracks at the larger strains, a theory proposed by Shaw. It was also found that the oxygen-free copper of the two different heats had appreciable variations in ductility at fracture in tension tests. The reason for this behavior was not determined.