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Suh C.H.,Daegu Mechatronics and Materials Institute | Park M.K.,Korea Advanced Institute of Science and Technology | Park J.K.,Hwashin Co. | Kim Y.S.,Kyungpook National University
Transactions of the Korean Society of Mechanical Engineers, A

Hot forming using boron steel is currently used for manufacturing low-weight automobile body parts, and a high tensile strength of about 1,500 MPa is obtained after hot forming. However, a high fatigue life is a more important factor than high strength when it is used for automobile suspension parts. A tubular torsion beam axle (TTBA) is one of these suspension parts, and this research deals with the fatigue characteristic of TTBA using hot forming. The low cyclic fatigue life of boron steel is investigated according to the cooling method. In addition, a structural and fatigue analysis of TTBA is performed to predict the fatigue life. The stress concentration that occurs in the tubular torsion beam is found, and the longest fatigue life occurs when rapid cooling is utilized in the TTBA fabrication. © 2013 The Korean Society of Mechanical Engineers. Source

Seo H.D.,Kyungpook National University | Ahn S.S.,Daegu Mechatronics and Materials Institute | Yoon J.C.,Kyungpook National University | Lee Y.J.,Kyungpook National University
Applied Mechanics and Materials

This paper introduces a novel spherical robot, KisBot III, with a newly designed wind-driven driving mechanism. The ducted fan for wind propulsion of the robot is installed at the center of the sphere, and according to the direction of the fan, the robot is able to move forwards or backwards. The outer shell is an open framework of spring carbon rods, and also includes two arms that can be folded-out to make the robot stop and partially deform its shape. Plus, for turning and balance control, a pendulum is located under the ducted-fan frame. By adopting wind as the driving mechanism, the robot has enough propulsion to drive over flat and uneven terrain, and negotiate a raised curb and slope. Experiments verify the driving motions and efficiency of the proposed spherical robot. © (2013) Trans Tech Publications, Switzerland. Source

Yoon J.-C.,Kyungpook National University | Ahn S.-S.,Daegu Mechatronics and Materials Institute | Lee Y.-J.,Kyungpook National University
INES 2011 - 15th International Conference on Intelligent Engineering Systems, Proceedings

This paper introduces a spherical robot, called KisBot II, with a new type of two-pendulum driving mechanism. A cross-shape frame is located horizontally in the center of the robot. The main axis of the frame is connected to the outer shell, and each pendulum is connected to the end of the other axis of the frame respectively. The main axis and pendulums can rotate 360 degrees inside the sphere orthogonally without interfering with each other, also the two pendulums can rotate identically or independent of each other. Due to this driving mechanism, KisBot II has various motion generation abilities, including a fast steering ability, turning ability in place and during travelling, and four(forward / backward / left / right) directional driving ability on the ground. Experiments for several motions verify the driving efficiency of the proposed spherical robot. © 2011 IEEE. Source

Oh S.K.,Daegu Mechatronics and Materials Institute | Lee K.K.,Engivice | Na Y.-S.,Korea Institute of Materials Science | Suh C.H.,Daegu Mechatronics and Materials Institute | And 2 more authors.
International Journal of Precision Engineering and Manufacturing

Mg alloy has a hexagonal close-packed(HCP) lattice crystal structure, which has fewer slip systems than other structures, and plastic deformation is difficult to achieve at room temperature. To improve its workability, the non-basal plane slip must be activated by increasing the deformation temperature. In this study, the hot deformation behavior of the AZ80 Mg alloy was examined within the temperature range of 250–400°C and the strain rate range of 0.001–10/s, based on the dynamic materials model. The hot deformation characteristic value was determined using the dynamic materials model (DMM), and was approximated using Kriging meta-model. Based on the results, deformation processing maps were derived, and the entire strains were examined to present the processing maps considering the strain during forming. In addition, the processing maps were established considering the hardness after forming, and the process window was presented considering both the formability and the strength of the parts. © 2015, Korean Society for Precision Engineering and Springer-Verlag Berlin Heidelberg. Source

Suh C.H.,Daegu Mechatronics and Materials Institute | Jang W.S.,Daegu Mechatronics and Materials Institute | Oh S.K.,Daegu Mechatronics and Materials Institute | Lee R.G.,Daegu Mechatronics and Materials Institute | And 2 more authors.
Metals and Materials International

Boron steel is widely used throughout the automobile industry due to its high tensile strength and hardenability. When boron steel is used for body parts, only high strength is required for crashworthiness. However, when boron steel is used for chassis parts, a high fatigue life is needed. The microstructure of boron steel is mainly affected by the cooling rate during hot stamping. Therefore, this study investigated the low cyclic fatigue life according to the cooling rate. The fatigue life increased at a low strain amplitude when the cooling rate was fast. However, at a high strain amplitude, the fatigue life decreased, due to the low ductility and fracture toughness of the martensite formed by rapid cooling. Martensite formed by a fast cooling rate shows excellent fatigue life at a low total strain amplitude; however, a multiphase microstructure formed by a slow cooling rate is recommended if the parts experience high and low total strain amplitudes alternately. In addition, the cooling rate has little effect on the distribution of solute boron and boron precipitations, so it is expected that boron rarely affects low cyclic fatigue. © KIM and Springer. Source

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