Representing the effect of crystallographic texture on the anisotropic performance behavior of rolled aluminum plate

Rolled aluminum alloys are known to be anisotropic due to their processing histories. This paper focuses on measuring and modeling monotonic and cycli c strength anisotropies as well as the associated anisotropy of the elastic /elastic-plastic transition of a commercially-available rolled plate produc t. Monotonic tension tests were conducted on specimens in the rolling plane of 25.4 mm thick AA 7075-T6 plate taken at various angles to the rolling d irection (RD). Fully-reversed tension/compression cyclic experiments were a lso conducted As expected, we found significant anisotropy in the back-extr apolated yield strength. We also found that the character of the elastic/el astic-plastic transition (knee of the curve) to be dependent on the orienta tion of the loading mis. The rests performed in RD and TD (transverse direc tion) had relatively sharp transitions compared to the test data from other orientations. We found the cyclic response of the material to reflect the monotonic anisotropy. The material response reached cyclic stability in 10 cycles or less with very little cyclic hardening or softening observed For this reason, we focussed our modeling effort on predicting the monotonic re sponse. Reckoning that the primary source of anisotropy in the rolled plate is the processing-induced crystallographic texture, we employed the experi mentally-measured texture of the undeformed plate material in continuum sli p polycrystal plasticity model simulations of the monotonic experiments. Th ree types of simulations were conducted upper and lower bound analyses and a finite element calculation that associates an element with each crystal i n the aggregate. We found drat all three analyses predicted anisotropy of t he back-extrapolated yield strength and post-yield behavior with varying de grees of success in correlating the experimental data. In general the upper and lower bound models predicted larger and smaller differences in the bac k-extrapolated yield strength respectively than was observed in the data. T he finite element results resembled those of the upper bound when initially cubic elements were employed. We found that by employing an element shape that was more consistent with typical rolling microstructure, we were able to improve the finite element prediction significantly. The anisotropy of t he elastic/elastic-plastic transition predicted by each model was also diff erent in character. The lower bound predicted sharper transitions than the upper bound model capturing the shape of the knee for the RD and TD data bu t failing to capture the other orientations. In contrast the upper bound mo del predicted relatively long transitions for all orientations As with the upper bound the FEM calculation predicted gentle transitions with less tran sition anisotropy predicted than that of the upper bound.