The Effect of Varying Strain Rates and Stress States on the Plasticity, Damage, and Fracture of Aluminum Alloys

Tucker, M.T., Horstemeyer, M., Whittington, W. R., Solanki, K.N., & Gullett, P. (2010). The Effect of Varying Strain Rates and Stress States on the Plasticity, Damage, and Fracture of Aluminum Alloys. In Elsevier (Ed.), Mechanics of Materials. 42(10), 895-907.

In this work we analyze the plasticity, damage, and fracture characteristics of three different processed aluminum alloys (rolled 5083-H13, cast A356-T6, and extruded 6061-T6) under varying stress states (tension, compression, and torsion) and strain rates (0.001/, 1/s., and 1000/s).Typically, compression gave the highest stress levels and torsion gave the lowest stress levels. Variations among three tests were within 3% error, so the stress-state dependence was a definite flow stress phenomenon. At an equivalent effective strain level of 6%, the flow stress difference between compression and tension was 15% for 5083-H131, 16% for A356-T6, and 9% for 6061-T6 at any applied strain rate. Also at 6% equivalent strain for the 5083-H131, A356-T6, and 6061-T6, the flow stress difference between different applied strain rates were 14%, 3%, and 9%, respectively. Hence, the stress state difference had more of a flow stress effect than the applied strain rates for those given in this study (0.001/sec up to 1000/sec). The stress state and strain rate also had a profound effect on the damage evolution of each aluminum alloy. Tension and torsional straining gave much greater damage nucleation rates than compression. Although the damage of all three alloys was found to be void nucleation dominated, the A356-T6 and 5083-H131 aluminum alloys incurred void damage via micron scale particles where the 6061-T6 aluminum alloy incurred void damage from two scales, micron-scale particles and nanoscale precipitates. Having two length scales of particles that participated in the damage evolution made the 6061-T6 incur a strain rate sensitive damage rate that was different than the other two aluminum alloys. Under tension, as the strain rate increased, the 6061-T6 aluminum alloy’s void nucleation rate decreased, but the A356-T6 and 5083-H131 aluminum alloys’ void nucleation rate increased. The Horstemeyer-Gokhale void nucleation model was shown to capture the stress state and strain rate effects on the void nucleation rates.