Superplastic behaviour of AA5083 sheets in the presence of an oscillating load

Abstract

The superplastic flow behaviour of AA5083 sheets was investigated at 450°C in the presence of a minor oscillating load. Uniaxial tensile specimens were tested to fracture at constant strain rates with a minor oscillating load superimposed onto the monotonically increasing tensile load. In each test, the oscillating load was applied as a sine wave having a constant amplitude of 0.5 N and a constant frequency. A series of tests was conducted in which the strain rate ranged from 0.001 to 0.4 s-1 and the frequency of the oscillating load ranged from 10 to 40 Hz. And other tensile specimens were subject to a constant mean load with a superimposed oscillating load until a predetermined elongation was reached. The flow behaviour of AA5083 showed a significant sensitivity to the oscillations although the tensile strengths remained practically unchanged. The addition of a minor oscillating load resulted in a 20% - 50% relative increase in fracture strain for the strain rates considered compared to the same tensile tests without oscillation. Finite element simulation of the tensile tests conducted at constant mean load with superimposed oscillations were carried out with LS-Dyna using material data obtained from the experiments. The numerical simulation results were compared with experimental results obtained under the same loading conditions to confirm their validity. The addition of a minor oscillating load led to greater uniformity in thickness in the specimen gauge. It can be concluded that superimposing a minor oscillating load during superplastic forming results in significantly greater deformation prior to fracture.