Papers by Author: Seong Jin Kim

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Authors: Seong Jin Kim, Sang Jin Park, Rena H. Basch, James W. Fash, Ho Jang
Abstract: The role of transfer film on high temperature wear properties of a multiphase composite for a brake friction material was investigated using a pad-on-disk type tribometer. A novolac resin-bonded composite based on a simple formulation with 6 ingredients (aramid pulp, cashew dust, Cu fiber, graphite, potassium titanate, and zirconium silicate) was used in this study. Results showed that the wear properties of the composite were significantly affected by the temperature at the frictioninterface when the transfer film was present on the counter face during sliding. In particular, the transfer film on the disk surface was well developed at approximately 200°C, resulting in theimproved wear resistance. It suggested that the transfer film on the disk surface effectively prevented direct contacts of the composite onto the counterface. On the other hand, no apparent relationship between transfer film thickness and friction coefficient was found in this experiment.
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Authors: Jang Hyuk Yoon, Seong Jin Kim, Ho Jang
Abstract: Molecular dynamics (MD) simulation was performed to study the stress induced grain boundary migration caused by the interaction of dislocations with a grain boundary. The simulation was carried out in a Ni block (295020 atoms) with a Σ = 5 (210) grain boundary and an embedded atom potential for Ni was used for the MD calculation. Stress was provided by indenting a diamond indenter and the interaction between Ni surface and diamond indenter was assumed to have a fully repulsive force to emulate a traction free surface. Results showed that the indentation nucleated perfect dislocations and the dislocations produced stacking faults in the form of a parallelepiped tube. The parallelepiped tube was comprised of four {111} slip planes and it contained two pairs of parallel dislocations with Shockley partials. The dislocations propagated along the parallelepiped slip planes and fully merged onto the Σ = 5 (210) grain boundary without emitting a dislocation on the other grain. The interaction of the dislocations with the grain boundary induced the migration of the grain boundary plane in the direction normal to the boundary plane and the migration continued as long as the successive dislocations merged onto the grain boundary plane. The detailed mechanism of the conservative motion of atoms at the grain boundary was associated with the geometric feature of the Σ = 5 (210) grain boundary.
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