Inelastic deformation of an aluminum alloy under combined stress at elevated temperature

Abstract

Biaxial stress tests were performed on thin-wall tubes of polycrystalline 2024-T81 aluminum at temperatures of 150°C and 250°C. The nominal metallurgical stabilization temperature for this alloy is 190°C. Transient and steady-state creep strain rates exhibited a considerable dependence on load path history. For a prescribed history it is possible to determine unique surfaces of constant creep strain rate. For the zero history, involving a single loading from the origin to a prescribed point in stress space, surfaces of constant steady-state strain rate, at elevated temperature, have the same shape as room temperature yield surfaces of moderate offset. In the temperature and small strain regions considered here, room-temperature yield surfaces were found to be unaffected by elevated temperature deformation. The changes in shape of room-temperature yield surfaces, due to room-temperature plastic deformation caused corresponding changes in the elevated temperature surfaces of constant steady-state creep rate. At a given stress point, an outward local motion of the yield surface resulted in a corresponding outward local motion of the steady-state creep rate surfaces. The experimental determination of surfaces of constant flow potential was also attempted.