Dynamic shear testing of 2024 T351 aluminium at elevated temperature

Abstract

2024-T351 aluminium hat-shaped specimens have been used to experimentally investigate the effect of different initial test temperatures on the strain at which a thermo-plastic instability occurs. A universal testing machine and split Hopkinson pressure bar (SHPB) were used to determine resolved shear stress—nominal plastic shear strain for specimens tested at room temperature, 125 °C and 250 °C, respectively. The shear strain rates was 2 × 10−3 for quasi-static tests and ranged between 5 × 103 to 17.8 × 103 s−1 for dynamic tests. Microstructural observations using optical, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were presented to explain the observed mechanical properties. The flow stress of the 125 °C specimens tested at intermediate and high strain rate (γ˙ > 10 × 103 s−1) was higher than the flow stress of the room temperature specimens at the same rates. This is believed to be due to different precipitate types, leading to variable strain rate sensitivity as a function of temperature. No quantifiable effect of initial temperature on the strain at which the thermo-plastic instability occurs was identified.