The Effects of Specimen Geometry on the Plastic Deformation of AA 2219-T8 Aluminum Alloy Under Dynamic Impact Loading

Abstract

The effects of specimen geometry on shear strain localization in AA 2219-T8 aluminum alloy under dynamic impact loading were investigated. The alloy was machined into cylindrical, cuboidal and conical (frustum) test specimens. Both deformed and transformed adiabatic shear bands developed in the alloy during the impact loading. The critical strain rate for formation of the deformed band was determined to be 2500 s−1 irrespective of the specimen geometry. The critical strain rate required for formation of transformed band is higher than 3000 s−1 depending on the specimen geometry. The critical strain rate for formation of transformed bands is lowest (3000 s−1) in the O5 mm × 5 mm cylindrical specimens and highest (> 6000 s−1) in the conical specimens. The cylindrical specimens showed the greatest tendency to form transformed bands, whereas the conical specimen showed the least tendency. The shape of the shear bands on the impacted plane was also observed to be dependent on the specimen geometry. Whereas the shear bands on the compression plane of the conical specimens formed elongated cycles, two elliptical shaped shear bands facing each other were observed on the cylindrical specimens. Two parallel shear bands were observed on the compression planes of the cuboidal specimens. The dynamic stress–strain curves vary slightly with the specimen geometry. The cuboidal specimens exhibit higher tendency for strain hardening and higher maximum flow stress than the other specimens. The microstructure evolution leading to the formation of transformed bands is also discussed in this paper.