Loading and Unloading Split Hopkinson Tension Bar Technique for Studying Dynamic Microstructure Evolution of Materials

In order to investigate the microstructure evolution of materials, loading and unloading experiments with specimens deformed at different strains are required. In this paper, momentum traps were introduced for rendering the conventional Split Hopkinson Tension Bar suitable for loading-unloading experiment. The new technique allows a specimen to be loaded to a preset strain for post-test characterization. This technique was applied to study the dynamic mechanical properties of pure titanium. The results show that: 1) the twinning density of titanium increases rapidly as the strain increases. 2) The strength and ductility of titanium exhibited on the adiabatic curve are much smaller then those exhibited on the isothermal curve, which may be caused by the adiabatic heat generated during the transient deformation process.

Photofragmentation of Cl2 at 308 nm

The velocity distributions for the Cl(2P3/2) and Cl(2P1/2) photofragments produced by the photolysis of Cl2 at 308 nm are measured using ion imaging. The angular distributions yield anisotropy parameters of β(2P3/2)=−1.00±0.05,β(2P1/2)=−0.95±0.05, suggesting that Cl(2P3/2) and Cl(2P1/2) is essentially produced via non-adiabatic curve crossing between the lu and the 0u+ excited electronic states.