Papers by Author: Yo Sep Yang

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.

Abstract: Effects of microstructural parameters on fatigue resistance (σFL) of the steel tire cords have been investigated experimentally from microscopic points of view. At first, microstructural parameters depending on carbon content have been identified by using transmission electron microscopy (TEM). The fatigue resistance of the steel tire cords depending on carbon content has been measured by using the Hunter rotating beam tester under the bending stress of 900 to 1500 MPa. The fatigue resistance was improved with increasing the carbon content from 0.7, 0.8 to 0.9 wt. % C, due to variations of microstructural parameters, such as lamellar spacing (λp), cementite thickness (tc), and volume fraction (Vc) of cementite. As the carbon content increased, the lamellar spacing and the cementite thickness decreased, while the volume fraction of cementites increased. The effects of microstructure on fatigue resistance have been discussed in terms of the microstructural parameters mentioned above.