유전자 알고리즘과 신경회로망을 이용한 적층복합재료의 최적설계에 관한 연구

조석수,장득열 三陟大學校 1997 論文集 Vol.30 No.1

In order to use superior impact properties coupled to low density in laminated composites it is necessary to accommodate the anisotropic nature of resin impregnated fibers. Its stiffness is determined by stacking orientation. Genetic algorithms(GA) is probabilistic optimization technique by principle of natural genetics and natural selection and neural networks(NN) is useful for prediction operation on the basis of learned data. Therefore, in this study minimum stiffness optimization of laminated composites is achieved by GA and required deflection is predicted by NN.

SS41불림재와 M.E.F.복합조직강의 X-선 잔류응력거동에 관한 연구

장득열,조석수,김득진 三陟大學校 1998 論文集 Vol.31 No.1

This study verified the relationship between fracture mechanics parameters ΔK, Kmax and X-ray residual stress σr for normalized SS41 steel with homogeneous crystal structure and M.E.F. dual phase steel(martensite encapsulated islands of ferrite). X-ray stress constant K was determined for the diffraction line of (211) plane using Cr-Kα radiation. K was -340.87 MPa/deg. The fatigue crack propagation test were carried out under stress ratios of 0.1 and 0.5 and X-ray diffraction technique according to crack length direction was applied to fatigue fractured surface Residual stress σr were independent on stress ratio (R=0.1, 0.5) by arrangement of ΔK. The equation of σr-ΔK was established by the experimental data. Therefore, fracture mechanics parameters could be estimated by the measurement of X-ray parameters.

X선 반가폭을 이용한 자동차 압연강의 피로수명평가에 관한 연구

장득열,조석수,김득진 三陟大學校 1998 論文集 Vol.31 No.1

In order to predict the fatigue life using X-ray diffraction techniques, in-plane bending fatigue test was carried out for SPCC steel. The relation between fatigue damage on the specimen surface and half-value breadth of X-ray diffraction lines was investigated in the process of cyclic loading. The change of half-value breadth B consisted of the three sequent except stress amplitude near fatigue limit. On the first stage, half-value breadth B decreased rapidly, on the second stage slightly, and on the third stage rapidly. B/B0-logNf relationship showed linear behavior except the early part of life. The slople of the seemed to take constant value regardless stress amplitude. On the other hand, Nf line was able to be expressed by a straight line on the B/B0-logNf relationship. Therefore, it was possible to prepose a method estimating the fatigue life fraction N/Nf using the gradient of B/B0-logNf relationship and the N? line.

X선 회절을 이용한 Al 2024-T3합금의 피로강도추정에 관한 연구

장득열,조석수,김득진 三陟大學校 1998 論文集 Vol.31 No.1

The fatigue process can be roughly divided into four stages ; cyclic hardening/softening, crack nucleation, crack propagation, and fracture. X-ray diffraction techniques can measure residual stress on the basis of the change of lattice plane spacings and half-value breadth corresponding to nonuiform strain in the constituent grains. The half-value breadth decreased with increase of number of cycles and stress range. The change of half-value breadth in crack nucleation is dependent on applied stress range. The relationship between propagation life ratio(N-Nc)/Nf and crack propagation half-value breadth ratio (Hw-Hwc)/Hwo shows strong linear behavior. Therefore, the remaining life of mechanical components can be predicted using half-value breadth ratio on crack nucleation and in process of crack propagation.

평균기울기법에 의한 Al 2024-T3합금의 X선 반가폭과 피로수명비의 관계

조석수,박승용,김득진,장득렬,주원식 東亞大學校 大學院 1998 大學院論文集 Vol.23 No.-

In order to predict the fatigue life fraction for Al 2024-T3, in-plane bending fatigue test and X-ray diffraction techniques was carried out. The relation between fatigue damage on the specimen surface and half-value breadth of X-ray diffracton lines was investigated in the process of cyclic loading. This paper proposed the estimation of fatigue life using AGM(Average Gradient Method) by the Gradient on the basis of B/Bo and log N/Nf.

극치통계해석을 이용한 잔존수명평가법에 관한 연구

조석수,장득열 三陟大學校 1997 論文集 Vol.30 No.1

The fracture of a structure, machine, machine part comes of surface micro-crack initiated and propagated at the root of notch, where the stress is high. Irregular distribution characteristics of micro-crack on the basis of elastic-plastic fracture mechanics doesn't predict exactly remaining life of them. It is thought that maximum micro-crack length represents the total fatigue damage because fatigue can be characterized as a progressive failure phenomenon that proceeds by the propagation and coalescence of micro-cracks to an unstable size. The maximum micro-crack length in an area larger than the sample area can be estimated by statistics of extremes. Therefore, the remaining life of components can be accurately predicted using the distribution of micro-crack length in critical areas and the fatigue damage model.

Surface plasmon-enhanced light-emitting diodes using silver nanoparticles embedded in p-GaN

Cho, Chu-Young,Kwon, Min-Ki,Lee, Sang-Jun,Han, Sang-Heon,Kang, Jang-Won,Kang, Se-Eun,Lee, Dong-Yul,Park, Seong-Ju IOP Pub 2010 Nanotechnology Vol.21 No.20

<P>We demonstrate the surface plasmon-enhanced blue light-emitting diodes (LEDs) using Ag nanoparticles embedded in p-GaN. A large increase in optical output power of 38% is achieved at an injection current of 20 mA due to an improved internal quantum efficiency of the LEDs. The enhancement of optical output power is dependent on the density of the Ag nanoparticles. This improvement can be attributed to an increase in the spontaneous emission rate through resonance coupling between the excitons in multiple quantum wells and localized surface plasmons in Ag nanoparticles embedded in p-GaN. </P>

2024-T3 A1합금의 표면미소균열의 통계적 분포특성에 관한 연구

조석수,장득열 三陟大學校 1997 論文集 Vol.30 No.1

Machine structures, aircraft and pressure vessel etc. are designed by fail-safe or safe-fail concept but on the basis of existence of internal defect or crack initiation in early stage of fatigue life. Failure or fracture of machine structures is mainly occurred by fatigue and relation between stress intensity factor range and crack growth rate can predict remaining life in components containing through-the-thickness crack but fatigue life of smooth specimen is dependent of initiation, growth and colescence of micro crack. Therefore, this paper presents relation between statistical properties of micro crack and fatigue life ratio in age-hardened Al 2024-T3 tested in plane bending.

평면굽힘하중을 받는 표면미소균열의 프랙탈 특성에 관한 연구

장득열,조석수,김득진 三陟大學校 1998 論文集 Vol.31 No.1

Irregular shapes and growth behavior of surface nicro-crack showed very complex and nonlinear properties and many investigators have performed theoretical analyses and experiments on them to characterize fatigue strength. They had difficulties in estimating fatigue life due to random distribution, growth and coalescence of surface micro-cracks. The straightness of crack growth along intergranular and transgranular was prevented from irregular microstructure and precipitates. Euclid geometry can't quantify shape of surface micro-crack but fractal geometry can. Therefore, it is suggested that average fractal dimension of surface micro-cracks is able to estimate fatigue life but fractal dimension of maximum surface micro0crack is not in Al 2.24-T3 alloy.

충격을 받는 적층복합재료의 최적설계에 관한 연구

조석수,장득열 三陟大學校 1997 論文集 Vol.30 No.1

Impact loads may be expected in many of the engineering applications of composites. The suitability of composites for such applications is determined not only by the usual parameters, but its impact or energy-absorbing properties. Frequently, an attempt to improve tensile properties results in a deterioration of impact properties. Therefore, it is necessary to have a good understanding for both safe and efficient design of structures and to develop new composites suitable to service conditions. This study presents optimization techniques on the basis of genetic algorithms minimum stiffness design of laminated composites.