Study On Dynamic And Static Tensile Properties Of TC4 Alloy Based On In-situ X-ray Imaging

(?+?)titanium alloys have been widely used in military and civil fields due to their low weight and high strength.In engineering applications,these titanium alloys maybe subjected to extreme environment and extreme conditions.Therefore,it is necessary to investigate the accurate measurement and reliable characterization for mechanical responses of(?+?)titanium alloys.In this paper,dynamic and quasi-static tensile experiments are conducted on TC4 alloy with a mini material testing system and a mini split Hopkinson tension bar,respectively.The in-situ X-ray phase contrast imaging,scanning electron microscopy,electron back scattering diffraction technology,X-ray digital image correlation(XDIC)implemented to characterize the quasi-static and dynamic deformation and fracture process of TC4 alloys.The results are as follows:(1)XDIC is implemented to map strain fields of TC4 alloy under quasi-static and dynamic tension.The size distribution of X-ray speckles are quantified via a morphological analysis,with a mean of ?20 ?m.Systematic error analyses of displacement and strain field measurements are firstly conducted for XDIC,and demonstrate that the displacement and strain errors can be controlled below 0.01 pixel and 0.1%,respectively.(2)The stress-strain curves demonstrate an obvious strain-rate effect for TC4 alloy.The dynamic yield and tensile strengths(815 MPa and 1010 MPa,respectively)are obviously higher than those under quasi-static loading(624 MPa and 725 MPa).TC4 alloy exhibits little strain hardening under quasi-static tension,but pronounced hardening under dynamic tension.(3)Under dynamic tension,a sharp transition to bulk strain exceeds about 0.04,which leads to a lower dynamic fracture strain(8.72%)than the quasi-static one(9.88%).The corresponding strain fled mapping demonstrates that shear deformation localizations grow and coalesce rapidly into a narrow shear deformation band under dynamic loading,while tensile deformation and necking progresses gradually under quasi-static loading.(4)The void nucleation occurs mainly at the interface of ?/? phases for both quasi-static and dynamic tension.However,microvoids coalesce preferentially along colony boundaries or the boundary ? phase under quasi-static tension,but along the maximum shear stress direction(across colonies)under dynamic tension.