Rate and temperature dependences of the yield stress of commercial titanium under conditions of shock-wave loading

摘要

The evolution of elastic-plastic shock waves with the propagation distance has been studied in annealed titanium of commercial purity at temperatures 20 ℃ and 600 ℃. The free surface velocity histories of the shock-loaded samples 0.25-4.0 mm in thickness have been recorded using the Velocity Interferometer System for Any Reflector. The measured decays of the elastic precursor waves have been converted into relationships between the shear stress and the initial plastic strain rate at the Hugoniot elastic limit. It has been found that the temperature practically does not influence on the resistance to high-rate plastic deformation: the plastic strain rate varies with the shear stress as γ = 2.5 × 10~6(τ/τ_0)~(4.8) s~(-1) at 20℃ and γ = 2.9 × 10~6(τ/τ_0)~(4.9) s~(-1) at 600℃. An analysis of the rise times of the plastic shock waves has shown that for the same level of shear stress, the plastic strain rate after small compressive strain is more than by order of magnitude higher than the initial plastic strain rate at the wave's foot. Such acceleration of the plastic deformation seems to be a result of an intense multiplication of the mobile dislocations or twins.