Papers by Author: Jong Gu Bae

Abstract: The residual stress in axial direction of the steel wires has been measured by using a method based on the combination of the focused ion beam (FIB) milling and digital image correlation (DIC) program. The residual stress is calculated from the measured displacement field before and after the introduction of a slot along the steel wires. The displacement is obtained by the digital correlation analysis of high-resolution scanning electron micrographs, while the slot is introduced by FIB milling with low energy beam. The experimental procedures are described and the feasibilities are demonstrated in steel wires fabricated with different conditions.

Abstract: In this study, the effects of drawing strain and annealing at low temperature on the mechanical properties have been investigated. The mechanical properties, such as hardness and strength and fatigue, were performed. The fatigue tests of hyper eutectoid steel wires were performed by the Hunter-type tester, specially designed for ultra thin wires (<0.2mmφ), under the bending stress. The mechanical properties of the steel wires increased with increase of annealing temperature, and the increase was more significant with higher drawing strain. Also, as annealing temperature increased, the hardness and tensile strength gradually increased up to 200 °C and then dramatically decreased at above temperature. However, bending fatigue limit, including fatigue life, showed the some different phenomena with increase of annealing temperature. These different behaviors depending on annealing temperature were discussed in terms of microstructural parameter changes such as pearlite morphology, rearrangement and coalescence of the dislocations.