中高应变率条件下TC18钛合金动态力学行为的实验研究

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

应变和应变率是影响材料力学行为的两个重要因素,分离式霍普金森压杆(SHPB)技术是实现不同应变和应变率加载的有效途径之一。为研究室温下TC18钛合金的塑性变形和破坏行为,采用SHPB,通过调节子弹长度和速度实现对TC18钛合金圆柱试样不同应变和应变率的加载。实验得到了TC18钛合金在不同应变率下的真应力-真应变曲线和同一应变率不同应变下的真应力-真应变曲线,并分别分析了应变硬化和应变率强化效应对TC18钛合金的动态力学性能的影响。实验结果表明:TC18钛合金压缩试样破坏时断口与加载方向(轴线)之间的夹角约为45°,其压缩破坏形式为典型的剪切破坏,与应变和应变率相关;应变率越高,TC18钛合金的流动应力和屈服强度越高,故该材料具有明显的应变率强化效应;绝热剪切带是裂纹形成和试样发生宏观剪切破坏的先兆。

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 3 000 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.