Study On The Tension-Compression Asymmetric Behavior Of TA7 Titanium Alloy Under Dynamic Loading Conditions

Titanium alloys have excellent material properties in high and low temperature working environments,and they have been widely used in engineering fields such as aerospace,shipbuilding,weapon equipment,biomedical,and rail transit.As a structural component,titanium alloys are highly likely to be subjected to impact loads during production,manufacturing,and service.In addition,titanium alloys often exhibit different mechanical responses under different loading conditions such as tension and compression,loading-unloading-reverse loading,etc.Therefore,it is necessary to study the strain-rate correlation and loading path correlation of tensile and compressive stress-strain responses of titanium alloys.Based on self-developed rotating-disc Hopkinson tension bar system and gas gun Hopkinson compression bar system,uniaxial tensile and compressive experiments were conducted on TA7 titanium alloy,and adiabatic stress-strain curves were obtained.Based on the improved Hopkinson tension bar and compression bar systems,dynamic tensile and dynamic compression loading and unloading experiments were carried out,and the isothermal stress-strain curves at high strain rates were obtained.Experimental results indicate that the mechanical behavior of TA7 titanium alloy exhibits tension-compression asymmetry,and this asymmetry is strain-rate dependent.Based on the crystal plasticity finite element method,the plastic deformation responses of TA7 titanium alloy under tension and compression loadings were simulated.The isothermal stress-strain responses obtained from numerical calculations under quasi-static and dynamic loadings are in good agreement with experimental results.The numerical simulation results can also reflect the tension-compression asymmetry and strain-rate correlation of TA7 titanium alloy.Based on dynamic loading-unloading experimental technique,tension-unloading compression and compression-unloading-tension experiments with at the strain rate of 300s-1 were conducted to investigate the strain-rate correlation and loading path correlation of the Bauschinger effect.Based on the tensile-compression asymmetry characteristics of titanium alloy yielding behavior,the Bauschinger effect stress parameter was proposed to characterize the Bauschinger effect of TA7 titanium alloy under different pre-strain values,loading methods and cycling cycles.Experimental results show that Bauschinger effect of TA7 titanium alloy under high strain-rate loading is smaller than that under quasi-static loading.Bauschinger effect under pre-tension loading is weaker than that under pre-compression loading,but Bauschinger effect under both loading paths decreases with the increase of pre-strain.The cyclic cycles have different effects on the dynamic and quasi-static Bauschinger effect of TA7 titanium alloy.