Study On Ultrasonic Vibration Stress Relaxation Constitutive Relation Of TC4 Titanium Alloy

Titanium alloy is a widely used lightweight alloy in various fields.Because of its low density,light weight and high strength,it is widely used in aerospace,marine engineering and other fields.TC4 is one of the most commonly used titanium alloys.TC4 has stable microstructure and properties.It is an α + β dual-phase titanium alloy with high specific strength,high temperature resistance and corrosion resistance.However,titanium alloy is a difficult-to-machine material.The problems of low heat transfer rate and low cutting index make the processing of titanium alloy difficult.This paper introduces the introduction of ultrasonic vibration assisted plastic forming technology in TC4 forming process.In the traditional plastic forming process,transverse or axial ultrasonic vibration is applied to the mold,fixture or workpiece.Compared with the traditional plastic forming,ultrasonic can reduce the forming force of the material.On the other hand,the stress relaxation behavior of the material can effectively reduce the residual stress inside the material.Therefore,this paper studies the influence of ultrasonic vibration on the stress reduction phenomenon in the stress relaxation process of TC4 and constructs the stress relaxation constitutive equation of the material under ultrasonic vibration,which is verified by numerical simulation.The main research of the paper is as follows :In this paper,ultrasonic vibration and stress relaxation are combined to improve the processing efficiency by ultrasonic vibration assisted plastic forming.In this paper,the stress relaxation test of TC4 titanium alloy was carried out by combining experimental and theoretical modeling.In the experiment,the ultrasonic vibration experimental device was designed for the high temperature environment and experimental machine of stress relaxation experiment.The conventional stress relaxation test and the stress relaxation test under different ultrasonic vibration conditions were carried out respectively,and the curve of stress changing with time was recorded.It is found that this method can significantly accelerate the stress relaxation process and improve the production efficiency due to the stress superposition and acoustic softening effect.Through the analysis of the experimental results,the strain rate-stress relationship is solved by the cubic delay function fitting processing,and then it is substituted into the sine hyperbolic creep equation.The constitutive relationship of ultrasonic vibration stress relaxation material is established,and the influence of frequency and amplitude on the stress-time relationship is quantitatively described,and the influence of amplitude and frequency on the stress relaxation process is studied respectively.Based on the experimental and theoretical results,the constitutive model is brought into the finite element analysis software Abaqus,and the simulation results are compared with the experimental results to verify the reliability of the theoretical model.Because the vibration only shows the stress superposition effect in the finite element analysis,the acoustic softening effect cannot be reflected.The quantitative description of the ultrasonic vibration constitutive model is brought into the numerical simulation,and the stress relaxation test results can be accurately predicted by the numerical simulation without ultrasonic vibration.The correlation is above 91 %,which provides guidance and prediction for the actual production and processing,and is of great significance for the production and processing of titanium alloys and the reduction of forming time.