Research Of Ultrasonic Vibration Assisted Pure Titanium Plastic Deformation Behavior

In recent years,titanium and titanium alloy have been widely used in aviation,spaceflight,medical,ocean engineering and other fields,because of its good corrosion resistance and high specific strength.However,the plastic forming ability of titanium is low and the processing and manufacturing of titanium alloy products are difficult,which limits the development and application of titanium and titanium alloy products.As we all know,ultrasonic vibration assisted plastic forming technology can reduce the deformation resistance and friction,and improve the forming property of materials,so it has been widely used in plastic forming processing,such as wire drawing,tension,extrusion,forming of powder and so on.Therefore,the application of ultrasonic vibration assisted plastic forming technology to titanium and titanium alloy can improve its forming ability,which will further promote the development and application of titanium and its alloy products.But the theoretical research of ultrasonic vibration assisted plastic forming technology in titanium and titanium alloy are relatively few.The mechanism of deformation of ultrasonic vibration in titanium and titanium alloy are still unclear.In quantitative analysis of the influence of ultrasonic vibration on the deformation behavior of materials and predicting the stress-strain distribution during ultrasonic vibration assisted deformation,there is a lack of reliable,accurate and applicable constitutive model for ultrasonic vibration assisted plastic deformation.In addition,there are no studies on surface friction coefficient and friction model during the process of ultrasonic vibration assisted plastic deformation of titanium and titanium alloy.In this paper,TA1 pure titanium was selected as the research material.Aiming at the above problems,the ultrasonic vibration assisted compression test of TA1 pure titanium column is firstly carried out to study the influence of the ultrasonic vibration on flow stress and deformation mechanism.In the compression process,the change of temperature of specimen was detected and the microstructure was observed.Then,inorder to construct a constitutive model suitable for ultrasonic vibration assisted compression of TA1 pure titanium,based on the Johnson-Cook model(J-C model for short),the effect of ultrasonic amplitude on various parameters in J-C model and J-C improved model was studied through the test of ultrasonic vibration assisted compression at different strain rates and amplitudes.Finally,in order to study the change of friction coefficient in the process of ultrasonic vibration assisted compression,friction model of ultrasonic vibration assisted compression was established,and friction coefficient was calculated by the experimental data of ultrasonic vibration assisted compression.The numerical simulation of ultrasonic vibration assisted compression process was carried out by using the software of ABAQUS.The friction model was verified by the experiment and the method of iteration finite element.The results show that ultrasonic vibration can reduce the yield strength and flow stress of materials,and the amount of reduction increases with the increase of energy density of ultrasonic vibration.Compared with conventional compression,the yield stress of materials with amplitudes of 4.6 ?m and 6 ?m decreased by 21 MPa and 31 MPa respectively,and the flow stress at strain of 0.59 decreased by 35.6 MPa and 46.7 MPa respectively.In the process of ultrasonic vibration assisted compression,there are ultrasonic softening,stress superposition and strain hardening mechanisms.When the vibration stopped,the material shows the effect of residual softening.Ultrasonic vibration can promote the generation of deformation twins in the pure titanium material which refining the grain,thus reducing the number of twins.The less the number of twins in the material,the more obvious effect of residual softening.Constitutive model established in this paper based on the J-C model can accurately predict the stress-strain curve,which the relative error between the prediction result and the experimental value is 4.48%.The constitutive model established in this paper predicts a wider strain range of 0?0.65.while the strain range predicted by the J-C model and the modified J-C model of Lin et al is 0-0.2 and 0-0.4,respectively.The friction coefficient calculated by the established friction model is relatively accurate,which is verified by experiment and iterative finite-element simulation.The maximum relative error between the simulated and experimental values is 2.7%.The surface friction coefficient of the material and the tool is reduced from 0.32 to 0.28 and 0.26 respectively in the state of 4.6 ?m and 6 ?m amplitude,indicating that ultrasonic vibration can reduce the surface friction of the material,and the anti-friction effect is proportional to the amplitude.