Young Suk Kim

Increased levels of IgG to cytokeratin 19 in sera of patients with toluene diisocyanate-induced asthma

BACKGROUND Inhaled isocyanate binds with cytokeratin (CK) of the epithelial cells, which could induce immune responses. OBJECTIVE To elucidate the possible existence of an isocyanate-induced, asthma-associated autoantigen from the bronchial epithelial cells, which may be associated with toluene diisocyanate (TDI)-induced asthma development. METHODS We cultured bronchial epithelial cells with incubation of TDI-human serum albumin (HSA) conjugate. Gene expression profiles of cultured epithelial cells were analyzed using a microarray technique. CK19 protein expression within the epithelial cells was confirmed by IgG immunoblot using monoclonal antibody to CK19. Serum IgG to CK19 and specific IgG and IgE antibodies to TDI-HSA conjugate were detected by enzyme-linked immunosorbent assay in 68 TDI asthma patients (group 1) and compared with 40 allergic asthma patients (group 2) and 80 unexposed healthy controls (group 3). RESULTS After TDI exposure, increased expression of CK19 and CK14 genes from the culture bronchial epithelial cells was noted using microarray analysis. IgG immunoblot analysis confirmed increased expression of CK19 after the TDI exposure. The levels of serum IgG to CK19 were significantly higher in the TDI asthma group than in groups 2 and 3 (P=.008). The prevalence of IgG to CK19 was significantly higher in group 1 (38.2%) than group 2 (22.5%) or group 3 (1.3%) (P=.008). Significant associations were noted between IgG to CK19 and specific IgG to TDI-HSA conjugate and transglutaminase (P=.02) but not with specific IgE to TDI-HSA conjugate. CONCLUSION We suggest that TDI exposure can augment CK19 expression from the bronchial epithelial cell, which may involve immune responses as an autoantigen to induce airway inflammation in TDI-induced asthma.

Prediction of Formability of Aluminum Alloy 5454 Sheet

Key Words: Formability(성형성), Aluminum Alloy(알루미늄합금), Plastic Instability(소성불안정), FormingLimit Diagram(성형한계도)초록: 자동차산업에서대기오염을줄이고연비를향상시키기위해경량화가중요한과제로여겨지고있다. 이를위해알루미늄소재의적용이증가하고있다. 판재를차체에적용하기위해서는주로프레스가공공정을거치게된다. 이때, 재료, 제품설계및프레스공정의부적절한가공변수의사용으로인하여파단, 주름, 및스프링백등에의한다양한형태의가공불량이발생한다. 따라서이들변수들의적절한조화뿐만아니라엄격한공정관리가요구된다. 이에본연구에서는자동차판재에주로사용되는Al5454 재료에대한이론적으로유도한소성불안정조건을구하고, MATLAB을이용하여성형한계도를도출하였다. 또한, 장출인장실험을통해얻어진실험값과이론적으로도출한성형한계도와의비교를수행하였다.Abstract: In the automobile industry, reducing the weight is the most important objective for reducing airpollution and improving the fuel efficiency. For this reason, the application of aluminum sheets is increasing.When the sheets are applied to the automobile, using inappropriate variables for the material, product design,and press processing can generate tearing, wrinkling, and spring-back problems, which are the main types offailure in the manufacturing process. Therefore, it is necessary to reduce these failures by harmonizing themany variables and strictly managing the processes. In this research, we study the theoretical plasticityinstability of Al5454 and obtain the forming limit diagram (FLD) using MATLAB. Moreover, we comparethe theoretical FLD with an experimental FLD obtained from a stretching test.

Shape Optimization of Multilayer Bellows by Using Sequential Experimental Design

Because of their high flexibility and durability, multilayer bellows are manufactured for use in commercial vehicles, while single-layer bellows are manufactured for use in passenger vehicles. A study based on the finite element method (FEM) and shape optimization for the single-layer bellows has been actively performed; however, until now, a study based on the FEM has rarely been performed for the multilayer bellows with gaps between the layers. This paper presents a finite-element modeling scheme for the multilayer bellows to improve simulation reliability during the evaluation of stress and flexibility. For performing shape optimization for the multilayer bellows, DOE (design of experiment) and the Kriging metamodel followed by the D-optimal method are used.

The Effects of Process Parameters of Multi-Stage Forming on Springback for a U-Channel made of Ultra-High-Strength Steel

Ultra-high-strength steels (UHSSs) are widely used for lightweight automobile parts, and the control of springback is very important in sheet-metal forming. The object of this study is to verify the effects of multi-stage forming process parameters for U-channel-type automobile parts made of UHSS. Finite element analysis is carried out to predict the formability and springback. The main parameters considered for the multi-stage forming process are the die angle, die radius, and punch-forming direction. It is shown that multi-stage forming is very effective for reducing springback, and that a small punch-forming angle and die radius reduce springback, whereas the die angle does not have a large effect.

Robust Optimization of the Solenoid Assembly in Electromagnetic Limited Slip Differential by Considering the Uncertainties in Machining Variables

The mechanical limited slip differential (LSD) in vehicles is being replaced by the electromagnetic LSD because of its fast response and better active control characteristics. The coil housing made of STS 304 is one of the most important parts in the solenoid assembly of the electromagnetic LSD. High geometrical accuracy is a prerequisite for the manufacture of such coil housings, but precision machining is difficult because of the use of STS 304 thin plate and the variance in machining variables. The aim of this study is to optimize the mean and variance of the shape accuracy in the coil housing by finding a robust solution for the machining process conditions. The mean and standard deviation of the jaw contact pressure, cutting speed, and feed rate are considered to be the major parameters for minimizing the geometrical mean and variance. The response surface model based on the second-order Taylor series is combined together to minimize the mean and variance of the shape accuracy of the coil housing.

Low-Cycle Fatigue in Quenched Boron Steel Sheet Due to Hot Stamping

Boron steel sheet is suitable for fabricating automobile parts because it is very strong and has low weight. Recently, many car makers are investigating the feasibility of fabricating the chassis part of automobiles using boron steel. In order to use boron steel sheets to fabricate the chassis part of automobiles, much better material property of low cycle fatigue life as well as high formability during hot stamping is required. Therefore, the low-cycle fatigue life of hot-stamped quenched boron steel was investigated in this study. The fatigue life observed at low strain amplitude was longer than that of an as-received boron steel sheet. However, the fatigue life reduced at high strain amplitude because of the low ductility and low fracture toughness of martensite, which was produced as a result of hot stamping.

Study on Fatigue Characteristic of Suspension Part Using Hot Forming

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.

The forming characteristic in the single-point incremental forming of a complex shape

Incremental sheet forming is popularly applied because of its reduced cost, flexibility, and applicability for small batch production. To reduce the manufacturing cost and time consumption, the incremental forming of a complex shape is implemented by combining two forming methods into one process: positive and negative incremental forming. The experiments were done to confirm the applicable ability of the method with the material aluminium Al3004-P. The finite element simulation was done with the ABAQUS explicit finite element code, and its results were compared with the experimental results.

Development of Hole Expansion Test for Sheet Materials Using Pattern-Recognition Technique

Nowadays, one of the most interested area of automobile industry is the production of vehicle which has collision safety and ability to produce less amount of . The achievement of such a dual performance is done by choosing the materials like dual phase steel, ferrite bainite steel, etc. These steels have been used in automotive chassis and body parts, and also used to be formed by hole flanging to meet the goal of strength and design requirement. The formability of sheet material was experimented by hole expansion test and the judgement relies on human eye and his experience. This manual judgement involves many errors and large deviation. This paper develops the automatic crack recognition system which finds a crack based on CCD image to complement the problem of the current method depending on humans sense.

An H∞ Controlller for Active Suspensions and its Robustness Based on a Full-Car Model

Abstract An H ∞ controller is designed for active suspensions of vehicles based on a 7-degree-of-freedom full-car model. Its stability robustness to unmodelled system dynamics and the variations of system parameters such as sprung mass and tire stiffness are assured through μ-framework. Its performance is compared with the performance of a typical LQG controller in computer simulations, where a car is driven on a normal road as well as through a laterally asymmetric bump. It is found that the suspension with the H ∞ controller is more robust in stability and exhibits less acceleration of the sprung mass in the heaving, rolling, and pitching directions with less amount of power consumption.