Byoung Ho Choi

Traction injury of the recurrent laryngeal nerve: Results of continuous intraoperative neuromonitoring in a swine model

Recurrent laryngeal nerve (RLN) palsy is the most serious complication after thyroidectomy. However, little is known about the degree of traction injury that causes loss of signal. The purpose of this study was to evaluate traction injuries in the swine RLN using continuous intraoperative neuromonitoring (IONM) and determine the traction power that results in loss of signal.

Characterization of Al2O3 and ZnO multilayer thin films deposited by low temperature thermal atomic layer deposition on transparent polyimide

Recently, flexible and stretchable displays with organic light emitting diodes are one of hottest technical issues in electronic industries. Therefore, the application of polymer substrates is required because current glass-based materials cannot meet the required properties of flexible and stretchable displays. But there are some limitations for using polymers in display substrate such as inferior surface characteristics such as low scratch resistance, low hardness, and so on. Polymers have many additional technical issues like low stiffness, low heat resistance, low barrier properties, and high sensitivity to degradation compared with glass material. The low temperature atomic layer deposition (ALD) can be a good solution as a functional coating on the polymer substrate to resolve such surface characteristic issues. In this study, two oxide thin films, i.e., Al2O3 and ZnO, are deposited on a transparent polyimide (TPI) film substrate using a low temperature thermal ALD technique. To fabricate a reliable...

Characterization of an injection-moulded car audio chassis made of polycarbonate–(acrylonitrile–butadiene–styrene)-based composite using metal-coated carbon fibre:

Engineering plastics are widely used as a substitute for stainless steel in the automobile industry to reduce weight and to improve fuel efficiency. In this paper, a polycarbonate–(acrylonitrile–butadiene–styrene)-based composite with nickel-coated carbon fibre was developed, and the application of the composite to a lightweight car audio chassis was examined. The mechanical and electrical properties of the composite were evaluated through various physical tests, i.e. tensile, impact, flexural and electromagnetic interference shielding effectiveness tests. In addition, the characteristics of this material were compared with those of a material previously developed by the present authors, i.e. a polycarbonate–(acrylonitrile–butadiene–styrene)-based composite with metal fibre and glass fibre. Finally, the actual car audio chassis was made by injection moulding under various moulding conditions pertaining to the injection speed and the tool temperature to find the optimum injection-moulding conditions. Two required key tests, i.e. a full-scale electromagnetic interference shielding effectiveness test and vibration analysis, were conducted to confirm the applicability of the polycarbonate–(acrylonitrile–butadiene–styrene)-based composite with nickel-coated carbon fibre as a material for a car audio chassis.

Modeling of the Elasto-plastic Deformation Behavior of Two-Dimensional Anisotropic Foam under Compressive Loads using Voronoi Cells

Foam structure is usually hard to model due to the complexity of the geometry of cells. So, many simplified models to represent complicated foam structures have been proposed, but most of them are not actually describe the random feature of the cell structure well. So, in this study, two dimensional isotropic and anisotropic closed cell structures of the foam were modeled using the concept of Voronoi cells. The elasto-plastic deformation behavior under compressive loads was investigated by finitie element analysis, and the results were compared with ideal honeycomb structure. In addition, the effect of anisotropy of Voronoi cell structures of the foam on Young`s modulus and yield stress under compressive loads was studied.

Modeling the compressive fracture behavior of foams for energy absorption

Polymeric foams and foams in general have a wide variety of applications ranging from energy absorption, noise and vibration absorption, and thermal insulation. In some segments of transportation applications, foams are used specifically for energy absorption during a vehicle crash. These foams are designed for one-time use to protect vehicle occupants where recoverability of the foam is not prescribed. Recently, it has been identified that a ‘square-wave’ load versus displacement response is desired for these applications. Observations of foam crushing during compression have demonstrated the need for an appropriate phenomenological model for foam failure. Current foam—structure—property models do not go all the way to final failure and can predict the early stage of load—displacement relationship. But, in terms of energy absorption, the model which covers the extensive load—displacement relationship is very important. This article will detail the development of a structure—property model used throughout the development of a new family of lightweight, space efficient, energy absorbing foams.

Observation and Characterization of Squeak Noises of Polymeric Materials for Automotive Interior Parts Under Field-Degradation

In this work, the effect of field-degradation of automotive polymeric interior parts on the squeak characteristics was studied for a number of used vehicles with various mileages and years of service. The purpose of this study was to characterize the squeak noise related with long-term degradation in service life. The characteristics of field-degraded polymeric samples are analyzed using Fourier transform infrared(FT-IR) spectroscopy and scanning electron microscopy(SEM). Complicated carbonyl spectra from FT-IR were deconvoluted into various carbonyls to trace field-degradation phenomenon. In addition, various mechanical tests, i.e. tensile test, hardness test as well as coefficient of friction test, were performed to analyze the variation in mechanical properties due to field-degradation. Squeak noise was measured and analyzed by frequency analysis. It was shown that the changes in the chemical structures of polymer due to field-degradation influenced the variation in mechanical properties, and squeak noise may worsen by increasing the squeak noise level in the wide frequency range. The results indicated that customer complaints regarding the squeak noise coming from used vehicles might be one of the important reliability issues because the increase in sound pressure level especially in the high frequency range could annoy drivers and passengers.

PWSCC Initiation of Alloy 600: Effect of Long-Term Thermal Aging and Triaxial Stress

Thermally aged nickel based Alloy 600 was investigated to evaluate the effects of long-term thermal aging and triaxial stress on primary water stress corrosion crack initiation behavior. Long-term thermal aging was simulated by heat treatment at 400 °C, a temperature that does not cause excessive formation of second phases that cannot form in nuclear power plant service conditions. Triaxial stress was applied by a round notch in the gauge length of some test specimen; other specimens were smooth. Slow strain rate tests (SSRT) monitored by the direct current potential drop method were conducted to evaluate stress corrosion crack initiation susceptibility of the thermally aged specimens in the primary water environment. For smooth specimens (which experience uniaxial stress), the susceptibility of those thermally aged for the equivalent of 10-years was the highest, while the susceptibility of the as-received specimens was the lowest. However, for the notched specimens (which experience triaxial stress), the specimens thermally aged for the equivalent of 20-years showed the highest susceptibility, while the as-received specimens showed the lowest.

Inelastic stress analysis and failure prediction of the turbine housing in engine motoring tests

In order to predict the thermomechanical failure of the turbine housing, it is essential to consider temperature-dependent inelastic materials undergoing thermal cyclic loads and to obtain the transient temperature distributions. This paper presents the analysis methods to calculate the thermal stresses and the plastic strain ranges for prediction of the fatigue life. The presented work is based on the engine motoring mode test that is commonly used for accelerated engine endurance tests. The results showed that the localized critical regions coincided well with the crack locations identified on the basis of a thermal shock test. The plastic strain values were predicted to lie within the range 0.216–0.396% corresponding to a range of 628–1450 cycles for 1600 target cycles.

Parametric study of the hydrogen diffusion in carbon steels under fatigue loading conditions using Green’s function

Hydrogen diffusion is one of critical mechanisms of stress corrosion cracking (SCC) of engineering materials such as carbon steels. Especially, it is known that the degradation of pipe grade carbon steels under fatigue loading conditions is accelerated by hydrogen diffusion steels, but the classical diffusion equation cannot address this specific issue. So, in this paper, the conventional diffusion equation, i.e. Fick’s second law, is modified by applying new boundary conditions considering fatigue loading conditions, and the solution is given analytically using Green’s function. In addition, some parametric studies are provided by applying some key parameters of the solution, and the results are discussed to understand physical meanings of the final solution.

Environmental stress cracking behavior of high crystalline polypropylene in different surface active agents using modified notched constant load test

Environmental stress cracking (ESC) of polymeric materials is induced by the penetration and diffusion of surface agents in the stressed polymers, which lubricates the mobility of polymer chains. In this paper, ESCR tests of high crystalline polypropylene (HCPP) were conducted by use of modified notched constant load test in contact with two different scent oils. The relationship between the lifetime and the loading condition were observed for two types scent oil. Swelling tests were also conducted to compare the diffusivity of two scent oils. The higher diffusivity of limonene oil results in shorter lifetime than in case of lavender oil.