Theoretical And Experimental Research Of Constitutive Model Of Ultrasonic Vibration Assisted Forming

As one of the most effective metal plastic forming assisted technologies, ultrasonic vibration has been wildly used in various areas of forming process. It is well known that ultrasonic vibration has these advantages, including reducing stress and forming stress, improving friction condition between workpiece and tool, obtaining better surface quality and higher dimensional accuracy. But the existing research results are mostly focused on the analysis of the phenomena of the experiment instead of the internal mechanism of the forming. Besides, the transmission mechanism of ultrasonic vibration in plastic deformation and its influence on the inside and surface of the processed material is very complex. So the theory of this technology is seriously lagging behind the application. Aimed at solving these problems, the study on the mechanism of ultrasonic vibration assisted forming is completed. The main research content is summarized as follows:Based on the superposition effect and the softening effect of the forming process, the constitutive relation of metal under uniaxial ultrasonic vibration was established by theoretical derivation, and the mechanism of constitutive model of ultrasonic vibration assisted forming was quantitatively analyzed.The uniaxial tension properties of 6061 aluminum alloy under ultrasonic vibration conditions were studied. Then the relevant parameter of the constitutive model of ultrasonic vibration assisted forming was determined and reliability of the model was verified. Results showed that the constitutive model could well describe the stress-strain relationship in ultrasonic vibration assisted forming and accurate reveal the constitutive relation of linear strengthening material under ultrasonic vibration.Uniaxial tensile experiment of 6061 under static, whole vibration and interval vibration condition was carried out, and the stress-strain curve was analyzed. It was found that the elastic deformation under static and whole vibration was the same, so the ultrasonic vibration had no influence on the elastic deformation. As the increase of the load, the yield strength of material under whole vibration was significantly declined. When applying ultrasonic vibration, the stress and hardening coefficient of 6061 dropped rapidly.Ultrasonic vibration rate-dependent experiment was carried out, and the influence of ultrasonic vibration to the rate-dependent material under different strain rates was studied. It was found that when the amplitude was the same, the stress state would rise with the increase of the strain rate for rate-dependent material.Combined with the finite element numerical simulation technology, the interval vibration tensile experiment of 6061 aluminum alloy was simulated by using ABAQUS. The change of the stress and strain state and the characteristics after applying vibration were analyzed. The the influence of strain rate and ultrasonic vibration on the stress-strain curve was analyzed by finite element model.