Dynamic Mechanical Properties And Deformation Behavior In Machining Of Ti-6Al-4V Alloy

Titanium alloy Ti-6Al-4V,as one of the mainly aeronautical structural materials,has the characteristics of small elastic modulus and low thermal conductivity,making it a typical difficult-to-machine material.The machinability and machining surface quality of Ti-6A1-4V alloy are affected by many factors.The deformation behavior of Ti-6A1-4V alloy in machining presents unique characteristics.Dynamic mechanical properties and deformation behavior in machining of Ti-6A1-4V alloy are related to strain,strain rate and cutting temperature.Establishing prediction model of dynamic mechanical properties and deformation behavior in machining of Ti-6AI-4V alloy is an important part of the research on dynamic machining performance.Iin this thesis,the dynamic mechanical properties and deformation behavior in machining of Ti-6A1-4V alloy are studied.A high strain rate and high temperature dynamic impact test platform and a non-contact measuring platform for machining Ti-6Al-4V alloy are built.The dynamic mechanical properties and deformation behavior of Ti-6Al-4V alloy under high strain rate and high temperature loading are studied by means of dynamic impact tests at room temperature and high temperature,orthogonal cutting tests of Ti-6Al-4V alloy,one-dimensional stress wave theory,digital image correlation technology and finite element simulation.Firstly,the dynamic mechanical properties of Ti-6Al-4V alloy under high strain rate and high temperature as well as the coupling effect between thermodynamic parameters of Ti-6A1-4V alloy are studied.The dynamic impact tests of Ti-6A1-4V alloy in the strain rate range of 4000 s-1-12000 s-1 and the temperature range of 25?-600? show that the plastic deformation stage of Ti-6A1-4V alloy is affected by strain rate hardening and thermal softening.The flow stresses of Ti-6A1-4V alloy at different temperatures show that the strain-temperature coupling effect occurs in the plastic deformation stage of Ti-6A1-4V alloy.The strain hardening rate of Ti-6Al-4V alloy decreases with the increase of temperature.Secondly,based on the strain-temperature coupling effect of titanium alloy Ti-6A1-4V,a modified Johnson-Cook(JC)constitutive model of titanium alloy Ti-6A1-4V is constructed.The strain-temperature sensitivity coefficient was proposed according to the dynamic mechanical properties of Ti-6A1-4V alloy under high strain rate and high temperature.The JC constitutive model is modified by the quantitative expression of strain-temperature coupling effect.The maximum relative errors between the flow stress calculated by the modified JC constitutive model based on the strain-temperature coupling effect and the original JC constitutive model are 4.19%and 10.43%,respectively,which proves the modified JC constitutive model can more accurately reflect the dynamic mechanical properties of Ti-6Al-4V alloy under high strain rate and high temperature.The modified JC constitutive model is applied to the finite element simulation for machining of Ti-6A1-4V alloy by the Abaqus VUMAT subroutine.Finally,a non-contact measuring platform for machining of Ti-6A1-4V alloy based on digital image correlation technology is built to verify the accuracy of the modified JC constitutive model for machining of Ti-6A1-4V alloy.The chip morphology,strain rate field and cutting force of Ti-6AI-4V alloy are measured without interfering with the machining process.Based on the non-contact measuring platform for machining of Ti-6Al-4V alloy,the chip morphology,strain rate and cutting force of the finite element model based on the original JC constitutive model and the modified JC constitutive model are compared.It is verified that the accuracy of the deformation behavior of Ti-6A1-4V alloy predicted by the finite element model based on the modified JC constitutive model is higher than that based on the original JC constitutive model.