• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.79-80
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• 2013

The purpose of this study was to investigate $2^{nd} $nanotube formed surface observation of the Ti-25Ta-xZr alloys using ATO(anodic titanium oxide) technique. Ti-25Ta-xZr alloy was anodized in 1M $H_3PO_4$ electrolytes containing 0.8 Wt. % NaF at room temperature. After formation of nanotube was achieved out, nanotube was eliminated, and then anodization was carried out repeatedly. The microstructures, phase transformation, and morphology of nanotubular Ti-25Ta-xZr alloys and process of nanotube growth by using ATO method was examined by optical microscopy (OM), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). The ${\alpha}$ phase and ${\beta}$ phases were affected to form the second nanotube morphology of Ti-25Ta-xZr alloys.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.427-733
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• 2003

Adiabatic shear bands have been observed in the serrated chip during high strain rate metal cutting process of medium carbon steel and titanium alloy. The recent microscopic observations have shown that dynamic recrystallization occurs in the narrow adiabatic shear bands. However the conventional flow stress models such as the Zerilli-Armstrong model and the Johnson-Cook model, in general, do not predict the occurrence of dynamic recrystallization (DRX) in the shear bands and the thermal softening effects accompanied by DRX. In the present study, a strain hardening and thermal softening model is proposed to predict the adiabatic shear localized chip formation. The finite element analysis (FEA) with this proposed flow stress model shows that the temperature of the shear band during cutting process rises above 0.5T$\sub$m/. The simulation shows that temperature rises to initiate dynamic recrystallization, dynamic recrystallization lowers the flow stress, and that adiabatic shear localized band and the serrated chip are formed. FEA is also used to predict and compare chip formations of two flow stress models in orthogonal metal cutting with AISI 1045. The predictions of the FEA agreed well with the experimental measurements.

• Journal of Korean Neurosurgical Society
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• v.57 no.1
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• pp.61-64
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• 2015

A number of dynamic stabilization systems have been used to overcome the problems associated with spinal fusion with rigid fixation recently and the demand for an ideal dynamic stabilization system is greater for younger patients with multisegment disc degeneration. Nitinol, a shape memory alloy of nickel and titanium, is flexible at low temperatures and regains its original shape when heated, and the Nitinol shape memory loop (SML) implant has been used as a posterior tension band mostly in decompressive laminectomy cases because the Nitinol implant has various characteristics such as high elasticity and a tensile force, flexibility, and biological compatibility. The reported short-term outcomes of the application of SMLs as posterior column supporters in cervical and lumbar decompressive laminectomies seem to be positive, and complications are minimal except for the rare occurrence of pullout and fracture of the SML. However, there was no report of neurological complications related to neural compression in spite of the use of the loop of SML in the epidural space. The authors report a case of delayed development of radiating pain caused by subsidence of the SML resulting epidural compression.

• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.647-653
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• 2020

Stainless steel is used commonly in nuclear applications for shielding radiation, so in this study, three different types of new stainless steel samples were designed and developed. New stainless steel compound ratios were determined by using Monte Carlo Simulation program Geant 4 code. In the sample production, iron (Fe), nickel (Ni), chromium (Cr), silicium (Si), sulphur (S), carbon (C), molybdenum (Mo), manganese (Mn), wolfram (W), rhenium (Re), titanium (Ti) and vanadium (V), powder materials were used with powder metallurgy method. Total macroscopic cross sections, mean free path and transmission number were calculated for the fast neutron radiation shielding by using (Geant 4) code. In addition to neutron shielding, the gamma absorption parameters such as mass attenuation coefficients (MACs) and half value layer (HVL) were calculated using Win-XCOM software. Sulfuric acid abrasion and compressive strength tests were carried out and all samples showed good resistance to acid wear and pressure force. The neutron equivalent dose was measured using an average 4.5 MeV energy fast neutron source. Results were compared to 316LN type stainless steel, which commonly used in shielding radiation. New stainless steel samples were found to absorb neutron better than 316LN stainless steel at both low and high temperatures.

• International Journal of Fluid Machinery and Systems
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• v.5 no.2
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• pp.91-99
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• 2012

The Fighter aircraft transmission system consists of a light weight, High Speed Flexible Coupling (HSFC) known as Power Take-Off shaft (PTO) for connecting Engine gearbox (EGB) with Accessory Gear Box (AGB). The HSFC transmits the power through series of specially contoured metallic annular thin flexible plates whose planes are normal to the torque axis. The HSFC operates at high speed ranging from 10,000 to 18,000 rpm. The HSFC is also catered for accommodating larger lateral and axial misalignment resulting from differential thermal expansion of the aircraft engine and mounting arrangement. The contoured titanium alloy flexible plates are designed with a thin cross sectional profile to accommodate axial and parallel misalignment by the elastic material flexure. This paper investigates the effect of misalignment on the transmission characteristics of the HSFC couplings. A mathematical model for the HSFC coupling with misalignment has been developed for analyzing the torque transmission and force interaction characteristics. An extensive testing has been conducted for validating characteristics of the designed coupling under various misalignment conditions. With this the suitability of the model adapted for the design iteration of HSFC development is validated. This method will reduce the design iteration cycles of HSFC and can be extended for the similar development of flexible couplings.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.3 no.1
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• pp.72-78
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• 2004

In this paper, mechanical behaviors of developed pedicle screw system, made of bio-mechanical materials(Ti-6Al-4V, Grade 5), ale predicted using FEM analysis. As a first step, morphologic construction of normal Korean spines and surgical operation convenience are considered to design optimum pedicle screw system. In this step, various design variables are considered as design parameters to develop optimized models. As a next step, tension and bending tests are performed to improve the structural performance of the developed system using finite element method. In this step, required Static compression and bending test specifications by ASTM F-04 25 04 01 are applied to understand the bio-mechanical behaviors of the designed spinal implant system under various load types. As the results of this research, it is possible to develop efficient pedicle screw system, having enough rigidity and fixation to stand any spinal damage under allowable stress conditions.

• Steel and Composite Structures
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• v.21 no.3
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• pp.573-588
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• 2016

Carbon Fiber Reinforced Plastic (CFRP) and Titanium Alloy (Ti6Al4V) stack, extensively used in aerospace structural components are assembled by fasteners and the holes are made using drilling process. Drilling of stack in one shot is a complicated process due to dissimilarity in the material properties. It is vital to have optimal machining condition and tool geometry for better hole quality and tool life. In this study the tool wear and hole quality were analysed by experimental analysis using three modified twist drills and online tool condition monitoring using Acoustics Emission (AE) sensor. Helix angle and point angle influence tool performance and cutting force. It was found that a tool geometry (TG1) with high helix angle of $35^{\circ}$ with low point angle $130^{\circ}$ results in reduction in thrust force of 150-500 N range but the TG2 also perform almost similar to TG1, but when compared with the AErms voltage generated during drilling it was found that progressive rise in voltage in TG1 is less with respect to TG2 which can be attributed to tool life. In process wear monitoring was done using crest factor as monitoring index. AErms voltage were measured and correlated with the performance of the drills.

• Journal of Korea Foundry Society
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• v.21 no.1
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• pp.15-23
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• 2001

The changes in the microstructures and $D0_3{\leftrightarrow}B2$ transition temperature were investigated for Fe-30at.%AI-5at.%Cr alloy with the ordered $D0_3$, structure when Ti, Hf and Zr were added respectively. The addition of Cr has no effect on the microstructure. However, as the amount of Ti addition increased, the grain size became smaller. Addition of Ti+Hf, Ti+Zr and Ti+Hf+Zr also showed the similar effect. When 20at.% of Ti was added, the second phase precipitates on the substrate. The addition of Cr, Hf and Zr alone has no effect on $D0_3{\leftrightarrow}B2$ transition temperature. However, as the amount of Ti addition increased by 5, 10, 15 and 20at.%, the transition temperatures showed 929, 930, 960 and $930^{\circ}C$ respectively.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.3
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• pp.425-432
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• 2012

This paper investigates shape design processes of two implant systems for bone fracture treatment ; Bone plate and Interlocking nail system. These systems can directly fix fractured human bones by surgical operations. The bone plates consist of various shaped plates and implant screws for fixation of fractured human bones with various manual instruments allowing to handle them. The material corresponds to titanium alloy Ti6Al4V because it is harmless material for human body as well as significantly rigid. This system has to be suitably rigid as well as manually bended in orthopedic surgery operations. The Interlocking nail system is a kind of nail implanted inside fractured human bones. The shapes of these systems have to be suitably designed in order to endure various loads as well as avoid any damages. If various shaped prototypes would be fabricated and tested to design the optimal shapes, optimal shapes could be obtained but very long time and expensive costs must be required. In this paper finite element method was applied into these systems. Under various boundary conditions a series of structural analysis was conducted by using ANSYS. Finally important shape factors could be determined on the basis of the analysis results.

• Corrosion Science and Technology
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• v.17 no.4
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• pp.166-175
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• 2018

In this study, the electrochemical properties of CP-Ti (commercially pure titanium) and Ti-64 (Ti-6Al-4V) were evaluated and the effect of hydrofluoric acid on corrosion resistance and electrochemical properties was elucidated. Additive manufactured materials were made by DMT (Directed Metal Tooling) method. Samples were heat-treated for 1 hour at $760^{\circ}C$ and then air cooled. Surface morphologies were studied by optical microscope and SEM. Electrochemical properties were evaluated by anodic polarization method and AC-impedance measurement. The oxide film formed on the surface was analyzed using an XPS. The addition of HF led to an increase in the passive current density and critical current density and decreased the polarization resistance regardless of the alloys employed. Based on the composition of the oxide film, the compositional difference observed by the addition of HF was little, regardless of the nature of alloys. The Warburg impedance obtained by AC-impedance measurement indicates the dissolution of the constituents of CP-Ti and Ti-64 through a porous oxide film.