Mechanical behavior and microstructure of low-carbon steel undergoing low-frequency vibration-assisted tensile deformati
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Zhao School of Engineering Technology, Purdue University, West Lafayette, Indiana 47906, USA
Jingxiang Lia) School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China; and Xi’an Jiaotong University Suzhou Academy, Suzhou, Jiangsu 215123, People’s Republic of China
Shengdun Zhao School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China
Qingyou Han School of Engineering Technology, Purdue University, West Lafayette, Indiana 47906, USA (Received 4 May 2017; accepted 17 August 2017)
Ultrasonic vibration can lead to significant load reduction in metal forming, and this concept has been widely applied in microforming. Recently, we discovered that low-frequency mechanical vibration (less than 100 Hz) with micro-amplitudes also features the same effects. In this study, low-frequency vibration-assisted tensile deformation experiments were conducted on commercially low-carbon steel. Effects of vibration softening and residual softening were obtained during experiments. Both these softening effects became prominent at high vibration amplitudes. Detailed microstructural analyses reveal that a low-frequency vibration treatment altered the interior characteristics of the metal. Electron backscatter diffraction results showed low-angle grain boundaries, and the interior misorientation angle increased greatly with the application of a low-frequency vibration. Changes in the microstructure became more pronounced with the rise of vibration amplitudes. Instantaneous stress reduction results from the additional energy applied in the form of vibration, which lowers the barrier energy for the dislocation motion. The residual softening effect can be interpreted via a dislocation density decrease as a result of vibration markedly improving the opportunity for dislocation annihilation or stacking.
I. INTRODUCTION
Simultaneous ultrasonic vibration can lead to a significant reduction in forming stress during metal plastic deformation.1,2 Over the past 60 years, considerable research has been devoted in investigating this phenomenon in micro-forming, which includes extrusion, drawing, and casting.3–5 Numerous researchers observed that acoustic softening occurs over a wide frequency range,6,7 and the softening effect becomes more effective with increase in the ultrasonic power density.8–11 Although the ultrasonic frequency can reach 45 kHz or higher, it still difficult to be applied in the practical industrial field due to its poor exciting force. In recent years, with the development of servo presses12,13 and hydraulic vibration technology,14,15 low-frequency vibration can now be Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.359
superimposed during plastic forming, thereby markedly benefiting force reduction and surface quality improvement. Compared with ultrasonic vibration, low-frequency vibration can generate a higher exciting force, which is more appropriate to
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