AN EXPERIMENTAL STUDY ON ADIABATIC SHEAR BEHAVIOR OF TA2 TITANIUM ALLOY SUBJECT TO DIFFERENT LOADING CONDITION

Adiabatic shear phenomena is generally considered as a material dynamic instability,which comes from the competition among thermal softening and the strain hardening, strain rate hardening. In this paper, the constitutive and dynamic behaviors of TA2 titanium alloy were studied with hat-shaped forced-shear specimens.. The stress states of its shear zone are firstly studied by theoretical analysis and numerical simulation to obtain the pure state of shear stress with the hat-shaped samples. The shear strain in specimen measured directly by the two-dimensional digital image correlation (DIC-2D) method, and the equivalent stress-equivalent strain curves under forced shear loading can be acquired. Furthermore, the dynamic stress-strain behaviors in compression conditions and hat-shaped shear condition are then studied experimentally for TA2 titanium alloy by split Hopkinson pressure bars technique. Its adiabatic shear failure evolution is investigated by microscopic metallurgical observation of ‘freezing’ sample. The dynamic constitutive and failure behavior of TA2 titanium alloy subject to different loading condition are analyzed. The results show that the dynamic constitutive curves obtained by cylindrical compression are in agreement with the curves of shear testing at the initial stage of plastic deformation, but its stress-strain curve appears separation with the plastic damage accumulation and adiabatic shear band (ASB) formation, which suggests that the plastic damage and ASB origination may be with the relevant the state of stress. It is also shown that the softened stress-strain curve gained by shear loading reflected ASBs initiation and evolution in the hat-shaped specimens, by contrast, the apparent equivalent stress-strain curve obtained by compression testing does not appear to be softening characteristic even if the symmetrical bi-conical ASBs and local crack distribution have appeared in the cylindrical specimen.