Effect Of Strain Rate On The Tension-compression Asymmetry Of Two-phase Titanium TC11

Due to their high specific strength, excellent corrosion properties and good formability, two-phase a+(3Titanium alloys are attractive structural materials and are widely used in aerospace and warship components. Such alloys may be subjected to impact loadings such as foreign-object impact and high-speed machining. Therefore, it is necessary to achieve a fundamental understanding of the effect of strain rate on the tension and compression behavior of the alloys.Stress-strain responses of TC11alloy subjected to quasi-static tension and compression loadings (0.001s-1) were investigated using MTS809and MTS810material testing systems. A split Hopkinson bar technique is used to obtain the dynamic stress-strain responses under uniaxial tension (210,450and940s-1) and compression (500,1500and2500s-1) loading conditions. Experimental results indicate that the mechanical responses of the alloy are sensitive to the strain rate and have the tension-compression asymmetry. Both tension yield strength and compression yield strength increase with increasing strain rate. The values of yield strength in compression are much higher than that in tension. The yield strength is more sensitive to change with strain rate in tension than compression. The asymmetry in yield strength increases with the increase of strain rate. The rate of strain hardening in tension decreases at high strain rates when compared with that under quasi-static loading conditions. However, the strain hardening is significant in both quasi-static and dynamic compression loadings and it changes little with strain rate. SEM observations and optical observations show that the tensile specimen is broken in a manner of ductile fracture presenting characteristic dimples, while the compressive specimen fails in a manner of localized shearing failure.Several empirically based and physically based constitutive models are used to formulate the rate-dependent stress-strain relations of TC11in tension and compression. Model results indicate that the modified Johnson-Cook model is capable of capturing the strain-rate effect on the initial yielding and strain hardening over a wide range of strain rates. Furthermore, it can be observed that the tension-compression asymmetry of the flow stress after initial yielding increases with the increase of strain rate.