Molecular dynamics study on surface effect in ultrasonic vibration assisted upsetting of monocrystalline copper
YH Zhao and YJ Guan and FJ Chen and HQ Chu and JQ Zhai and J Lin and L Chen, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, 322, 118189 (2023).
DOI: 10.1016/j.jmatprotec.2023.118189
Ultrasonic vibration assisted plastic forming is a promising technology. However, the microscopic mechanism of ultrasonic vibration on interface friction behavior during the metal plastic forming process has not been fully understood yet. In this paper, based on the molecular dynamics method, the model for ultrasonic vibration assisted upsetting of monocrystalline copper was established, and the microscopic mechanism behind the surface effect of ultrasonic vibration was studied. The results show that the related data of interface friction can be directly extracted by the molecular dynamics method, and the plastic deformation behavior and interface friction behavior in the ultrasonic vibration assisted upsetting can be well reflected in the established model. The interface friction behavior of specimen is improved under the surface effect of ultrasonic vibration. On the one hand, ultrasonic vibration changes the relative position of the interface configurations, reduces the energy barrier Delta U, and helps the surface atoms to complete the potential well transitions on the periodic interface configuration, thereby reducing the energy dissipation in the sliding friction process. On the other hand, ul-trasonic vibration induces the surface lattice mismatch or misalignment between the upper surface and the indenter plate, which avoids the structural interlocking phenomenon between different atomic interfaces, thereby promoting the change of interface friction from commensurability to incommensurability. With the increase of ultrasonic amplitude and ultrasonic frequency, the surface effect of ultrasonic vibration shows a trend of first decreasing and then flattening out. These findings play an essential role in revealing the microscopic mechanism of surface effect in ultrasonic vibration assisted plastic forming.
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