Experimental Research on Dynamic Mechanical Behavior of TC18 Titanium Alloy under Medium and High Strain Rates

Strain and strain rate are two important factors that affect the mechanical behavior of materials, and the split Hopkinson pressure bar (SHPB) technique is one of the effective ways to realize different strain and strain rate loading conditions. To study the plastic deformation and fracture behavior of TC18 titanium alloy under dynamic loading (ranging from 300 to 3000 s^-1), a series of dynamic compression tests on TC18 titanium alloy have been performed by means of SHPB technique at room temperature. The different strain and strain rate loading conditions are realized by changing the length and velocity of the striker. Macro true stress-true strain curves are obtained under different strain rate loading, so are the true stress-true strain curves under the same strain rate with different strain loading conditions. The effects of strain hardening and strain rate hardening on the dynamic mechanical properties of TC18 titanium alloy are discussed. Results indicate that the collapse of specimen occurs along a plane inclined at an angle of about 45° to the compression axis, namely, shear failure is the main failure mechanism for TC18 titanium alloy under compression loading at room temperature, and it is dependent on strain and strain rate; the higher the strain rate is, the larger the flow stress (or yield stress) of TC18 titanium alloy is, therefore, the material shows clearly evident strain rate hardening effect; and the analyses of microstructure and fracture morphology show that adiabatic shear bands are the precursor to the crack formation and fracture.