The effects of microstructural evolution on the spall response of 1100 aluminum

In order to develop a better understanding of the spall response of aluminum and aluminum alloys, spall plate impact experiments in conjunction with shock recovery plate impact experiments were conducted using 1100 aluminum. The objectives of this thesis are to first study the effects of peak shock stress, pulse duration, strain rate, and shock induced microstructural evolution on the spall response of 1100-O aluminum. Then the 1100-O aluminum was cold rolled to various percent reductions and shock loaded to different peak shock stresses so that the effects of cold rolling on the spall response of 1100-O aluminum can be studied. These objectives may lead to a better understanding of the substructure evolution and spall failure process of aluminum and aluminum alloys under shock loading conditions and consequently lead to improved hydrocode models and the design of superior armors.;Plate impact experiments were conducted to study the effects of peak shock stress and pulse duration on the spall response of fully annealed 1100 aluminum. The spall strength was observed to decrease as the pulse duration was increased from approximately 0.58 μs to 1.17 μs. Also, an increase in tensile unloading strain rate increases the spall strength. However, our results also show an increase in spall strength with increase in peak shock stress up to approximately 8.3 GPa, followed by a decrease in spall strength for higher shock stresses.;Next, shock and spall plate impact recovery experiments were conducted to probe the microstructural evolution of fully annealed 1100 aluminum. It was found that as the shock stress is increased from 4.0 to approximately 8.3 GPa, the material shock hardened due to increase in the net dislocation density. Ductile transgranular fracture was identified as the fracture mode for this shock stress range. The decrease in spall strength beyond 8.3 GPa appears to be due to grain refinement induced by dynamic recovery. Brittle intergranular fracture with isolated pockets of nanovoids was identified as the fracture mode in this domain. The contributions of nanovoids to the dynamic recovery process (if any) were unresolved. Microhardness measurements show an increase in residual hardness throughout the shock stress range. This suggests that thermal softening was not operative throughout the shock stress range.;Finally, the as received 1100-O aluminum was cold rolled (CR) to 30, 70, and 80 percent reduction respectively to study the effects of deformation-induced microstructural evolution on the spall response using plate impact experiments. The maximum in spall strength as a function of shock stress was not observed for the 30% CR, which showed only an increase in pullback velocity over the shock stress range of 4 to 12 GPa. As the rolling increased up to 70% CR, no change was observed in the pullback velocity over the range tested, probably due to saturation in dislocation density. Similar observations were made for the 80% CR, that is, no change was observed in the spall response between 4 GPa and 11.5 GPa. However, variations were observed in the spall response for the 80% CR; these variations are attributed to material inhomogeneity possibly caused by increased cold rolling beyond saturation. The results also show a significant increase in Hugoniot Elastic Limit (HEL) with increase in percent cold rolling.