• Journal of Computational Design and Engineering
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• 제3권1호
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• pp.71-90
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• 2016

Steel nitriding is a thermo-chemical process leading to surface hardening and improvement in fatigue properties. The process is strongly influenced by many different variables such as steel composition, nitrogen potential, temperature, time, and quenching media. In the present study, the influence of such parameters affecting physic-chemical and mechanical properties of nitride steels was evaluated. The aim was to streamline the process by numerical-experimental analysis allowing defining the optimal conditions for the success of the process. Input parameters-output results correlations were calculated through the employment of a multi-objective optimization software, modeFRONTIER (Esteco). The mechanical and microstructural results belonging to the nitriding process, performed with different processing conditions for various steels, are presented. The data were employed to obtain the analytical equations describing nitriding behavior as a function of nitriding parameters and steel composition. The obtained model was validated, through control designs, and optimized by taking into account physical and processing conditions.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.207-208
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• 2007

Recently, high performance microelectronic devices are designed in multi-layer structure in order to make dense wiring of metal conductors in compact size. Imprint lithography have received significant attention due to an alternative technology for photolithography on such devices. In this work, we synthesized dielectric composite materials based on epoxy resin, and investigated their thermal stabilities and dynamic mechanical properties for thermal imprint lithography. In order to enhance the mechanical properties and toughness of dielectric material, various modified polyetherimide(PEI) was applied in the resin system. Curing behaviours, thermal stabilities, and dynamic mechanical properties of the dielectric materials cured with various conditions were studied using dynamic differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), and Universal Test Method (INSTRON).

• 대한의용생체공학회:의공학회지
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• 제31권6호
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• pp.472-480
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• 2010

Mechanically deformed cartilage undergoes a temperature dependent phase transformation resulting in reshaping of cartilage. Laser-assisted cartilage reshaping (LCR) is recently introduced to recreate the underlying cartilage framework in structures such as ear, larynx, trachea, and nose. However, this procedure has not been fully supported by confirmed efficacy because of the lack of scientific research and its safety issues. The purpose of this study is to evaluate current laser sources to determine optimal laser wavelength for LCR using mathematical simulations and investigate optical, thermo-mechanical, and backscattering properties of cartilage after laser irradiation. The results showed that 1444 nm wavelength was effective for reshaping of cartilage with minimal thermal damage in the surrounded tissues by monte carlo simulations. Analysis of bend angle changes, thermo-mechanical characteristics, and backscattered properties may be useful to better identify the biophysical transformation responsible for stress relaxation in cartilage and develop an optical feedback control methodologies.

• 터널과지하공간
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• 제1권2호
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• pp.181-203
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• 1991

The effects of geologic structures such as rock joins and bedding planes on the thermal conductivity of a discontinuous rock mass are studied. The expressions for the equivalent thermal conductivities of jointed rock masses are derived and found to be anisotropic. The degree of anisotropy depends primarily on the thermal properties contrast between the joint phase and surrounding intact rock, the joint density expressed as volume fraction and the inclination angle of the joint. Within the context of 2-dimensional finite element heat transfer scheme, the isotherms around a circular hole are analyzed for both the isotropic and anisotropic rock masses in 3 different thermal boundary conditions. i.e. temperature, heat flux and convection boundary conditions. The temperature in the stratified anisotripic rock mass is greatly influenced by the thermal properties of the rock formation in contact with the heat source. Using the excavation-temperature coupled elastic plastic finite element method, analyzed is the thermo-mechanical stability of a circular opening subjected to 10$0^{\circ}C$ at a depth of 527m. It is found that the thermal stress concentration was enough to deteriorate the stability and form a plastic yield zone around the opening, in contrast to the safety factor greater than 2 resulted form the excavation-only analysis.

• 펄프종이기술
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• 제43권2호
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• pp.66-71
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• 2011

Biocomposites were fabricated with biodegradable polymers and natural fibers. Biocomposites have benefits of low cost, low density, and biodegradability over inorganic fiber composite, and give comparable strength properties. Hydrophobic polymer used for sizing in paper industry, AKD (Akenyl Keten Dimer), was applied to natural fibers, red algae fibers (RAF) in this study, to make fiber surfaces more compatible to hydrophobic nature of matrix polymers. Composites with RAF, kenaf, glass fibers, and carbon fibers have been fabricated by a compression molding method and their thermo-mechanical properties have been studied. Also, the thermal dimensional stability test was done from at 30 to $100^{\circ}C$. The storage moduli and the thermo-mechanical stabilities of polypropylene and poly lactic acid based biocomposites were improved by reinforcing with the RAF and much more with AKD treated fibers. Dimensional stability of biocomposite was also markedly improved by AKD pretrement on RAF.

• 대한기계학회논문집
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• 제14권5호
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• pp.1166-1180
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• 1990

본 연구에서는 열간 반경단조를 해석하는데 있어서 재료의 변형 해석은 강-점 소성해석법으로 해석하고 온도분포도 유한 요소법으로 해석한다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.437-440
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• 2010

이 논문은 발사체 노즐에 사용되는 내열성 재료인 C/SiC에 대한 이방성 물성을 예측하는 방법으로, 평면 방향의 실험 데이터를 이용해서 9개의 엔지니어링 물성을 간단하고 효과적으로 계산하는 준 이론적 접근에 대해 설명하였다. 이 방법은 C/SiC 복합재료를 직조 보강재의 굴곡율에 따라 세 층으로 이상화 하여, 고전 적층 평판이론으로 계산한다. 평면 방향으로 실행된 실험 데이터와 직조 구조물의 굴곡율을 초기 데이터로 이용하며, 측정이 어려운 두께 방향의 물성을 효과적으로 얻을 수 있었다. 예제를 통하여 이 방법의 유용성을 증명하였다.

• 한국재료학회지
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• 제23권9호
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• pp.525-530
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• 2013

This study investigated the continuous cooling transformation, microstructure, and mechanical properties of highstrength low-alloy steels containing B and Cu. Continuous cooling transformation diagrams under non-deformed and deformed conditions were constructed by means of dilatometry, metallographic methods, and hardness data. Based on the continuous cooling transformation behaviors, six kinds of steel specimens with different B and Cu contents were fabricated by a thermomechanical control process comprising controlled rolling and accelerated cooling. Then, tensile and Charpy impact tests were conducted to examine the correlation of the microstructure with mechanical properties. Deformation in the austenite region promoted the formation of quasi-polygonal ferrite and granular bainite with a significant increase in transformation start temperatures. The mechanical test results indicate that the B-added steel specimens had higher strength and lower upper-shelf energy than the B-free steel specimens without deterioration in low-temperature toughness because their microstructures were mostly composed of lower bainite and lath martensite with a small amount of degenerate upper bainite. On the other hand, the increase of Cu content from 0.5 wt.% to 1.5 wt.% noticeably increased yield and tensile strengths by 100 MPa without loss of ductility, which may be attributed to the enhanced solid solution hardening and precipitation hardening resulting from veryfine Cu precipitates formed during accelerated cooling.

• Structural Engineering and Mechanics
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• 제53권4호
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• pp.703-723
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• 2015

In this paper optimization of volume fraction distribution in a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) and subjected to steady state thermal and mechanical loadings is considered. The finite element method with graded material properties within each element (graded finite elements) is used to model the structure. Volume fractions of constituent materials on a finite number of design points are taken as design variables and the volume fractions at any arbitrary point in the cylinder are obtained via cubic spline interpolation functions. The objective function selected as having the normalized effective stress equal to one at all points that leads to a uniform stress distribution in the structure. Genetic Algorithm jointed with interior penalty-function method for implementing constraints is effectively employed to find the global solution of the optimization problem. Obtained results indicates that by using the uniform distribution of normalized effective stress as objective function, considerably more efficient usage of materials can be achieved compared with the power law volume fraction distribution. Also considering uniform distribution of safety factor as design criteria instead of minimizing peak effective stress affects remarkably the optimum volume fractions.

• 열처리공학회지
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• 제10권1호
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• pp.20-29
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• 1997

Pure copper is widely used for base material for electrical and electronic parts because of its good electrical conductivity. However, it has such a low strength that various alloying elements are added to copper to increase its strength. Nevertheless, alloying elements which exist as solid solution elements in copper matrix severely reduce the electrical conductivity. The reduction of electrical conductivity can be minimized and the strengthening can be maximized by TMT(Thermo-Mechanical Treatment) in copper alloys. In this research, the effects of TMT on mechanical and electrical properties of Cu-Ni-Al-Si-P, Cu-Ni-Al-Si-P-Zr and Cu-Ni-Si-P-Ti alloys aged at various temperatures were investigated. The Cu alloy with Ti showed the hardness of Hv 225, electrical conductivity of 59.8%IACS, tensile strength of 572MPa and elongation of 6.4%.