High strain rate tensile testing of automotive aluminum alloy sheet

The desire for more fuel efficient vehicles has resulted in a renewed interest in aluminum alloy sheet as a replacement for mild steel in automobile bodies due to its higher strength-to-weight ratio. When considering the crashworthiness of vehicles, the dynamic behavior of the materials used must be considered when simulating crash events, although traditionally, the strain rate sensitivity of aluminum alloys has been considered to be low. Room temperature and elevated temperature experiments were conducted on a tensile split Hopkinson bar apparatus to identify the constitutive response and damage evolution in AA5754 and AA5182 aluminum alloy sheet at high strain rates. Modifications were made to the apparatus in order to minimize wave distortions at the interface between the specimen and the bar, and to the specimen design to minimize specimen geometry effects. The rate dependency of flow stress was shown to be low; however, a marked increase in elongation was measured with increases in strain rate. The data was shown to be amenable to fits using the Johnson-Cook constitutive model.