X-선 회절을 이용한 피로하중을 받는 일반구조용강의 잔류응력에 관한 연구

장득열,조석수,이성룡 三陟大學校 産業科學技術硏究所 2000 産業科學技術硏究論文集 Vol.5 No.-

The fatigue life of mechanical components and structures has been influenced by mechanical, material and environmental conditions. It is important to search out the load type and size for accurate cause of fracture at the damaged surface of material. The fractographic method by x-ray diffraction can utilize residual stress ??, and half-value breadth B and find out the types and the mechanical conditions of fracture. This study showed the relationship between fracture mechanical parameters ΔK, ?? and X-ray residual stress ?? for normalized SS41 steel with homogeneous crystal structure and M.E.F. dual phase steel(martensite encapsulated islands of ferrite). The fatigue crack propagation tests were carried out under stress ratios 0.1 and 0.5 The X-ray diffraction technique according to crack propagation direction was applied to fatigue fractured surface. Residual stress ?? was independent on stress ratios by arrangement of ΔK. The equation of ?? was established by the experimental data. Therefore, fracture mechanical parameters can be estimated by the measurement of X-ray parameters.

실험계획법과 수리적방법을 이용한 수직형 롤러 분쇄기의 강건 최적화에 관한 연구

장우연,이경영,조석수,장득열 三陟大學校 産業科學技術硏究所 2002 産業科學技術硏究論文集 Vol.7 No.2

A recent research and development has the requirement for the optimization to shorten design time of modified or new product model and to obtain more precise engineering solution. General optimization problem must consider many conflicted objective functions simultaneously. Multi-objective optimization treats the multiple objective functions and constraints with design change. But, real engineering problem doesn't describe accurate constraint and objective function owing to the limit of representation. Therefore this study applies variance analysis on the basis of structure analysis and DOE to the vertical roller mill for portland cement and proposes statistical design model to evaluate the effect of structural modification with design change by performing practical multi-objective optimization considering mass, stress and deflection.

다축하중을 받는 적층복합재료의 강성 및 중량 최적설계에 관한 연구

조석수,주원식,장득열 동아대학교 공과대학부설 생산기술연구소 1997 生産技術硏究所硏究論文集 Vol.2 No.1

The present paper deals with the stiffness and weight optimization of laminated composites under multiaxial loading on the basis of genetic algorithms. Laminated composites are in the form of laminates consisting of multiple laminae oriented in the design directions and bonded together in a structural unit. Design variables used in optimization are layer angle and thickness. In order to prevent GA from premature convergence, subelitism is used instead of elitism. It is shown that GA is applicable to multivariable design as well as single varialbe design.

평면굽힘하중을 받는 Al 2024-T3 합금의 미소균열 분포특성에 관한 연구

조석수,주원식,장득열,장백선,안원기 동아대학교 공과대학부설 생산기술연구소 1997 生産技術硏究所硏究論文集 Vol.2 No.1

Machine structures, aircraft and pressure vessel etc. are designed by fail-safe or safe-fail concept but on the basis of existance of internal defect or crack initiation in early stage of fatigue life. Failure or fracture of machine structures is mainly occured 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 coalescene 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.

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.

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.

Al 2024-T3 합금의 잔존수명평가법에 관한 연구

조석수,주원식,장득열 동아대학교 공과대학부설 생산기술연구소 1997 生産技術硏究所硏究論文集 Vol.2 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 both the distribution of micro-crack length in critical areas and the fatigue damage model.

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.

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.

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.