• 한국세라믹학회지
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• 제51권5호
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• pp.399-405
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• 2014

Porous alumina with different porosities, 5.2 - 47.5%, were coated with cover-glass having a thickness of $160{\mu}m$, using epoxy adhesive. We investigated the effect of the porosity of the substrate layer on the crack initiation load, and the size of cracks propagated in the coating layer. Hertzian indentations were used to evaluate the damage behavior under a constrained loading condition. Typically, two types of cracks, ring cracks and radial cracks, were observed on the surface of the glass/porous alumina structure. Indentation stress-strain curves, crack initiation loads, crack propagation sizes, and flexural strengths were investigated as a function of porosities. The results indicated that a porosity of less than 30% and a higher substrate elastic modulus were beneficial at suppressing cracks occurrence and propagation. We expect lightweight mechanical components with high strength can be successfully fabricated by coating and controlling porosities in the substrate layer.

• 한국철도학회논문집
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• 제12권3호
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• pp.396-404
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• 2009

고속열차의 개발과 함께 구름접촉피로에 의한 레일의 피로균열 및 피로파괴에 대한 연구를 통해 주행안정성을 확보할 수 있는 방안 마련이 필요하다. 따라서 본 연구에서는 Eisenmann의 근사계산식(실용식)을 이용하여 속도, 차륜반경, 궤도지지강성, 침목간격, 축중, 궤도품질에 따른 레일내부 발생응력을 검토하였다. 또한, 유한요소해석을 통해 초기균열의 길이 및 각도, 온도에 따라 레일두부에서 발생하는 전단응력을 검토하여 모드별 응력확대계수를 도출하였다. 이로써 고속철도 레일의 피로수명에 영향을 미치는 주요인자들을 확인하였다.

• International Journal of Railway
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• 제1권3호
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• pp.106-112
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• 2008

Rolling-sliding, cyclic contact of wheel and rail progressively alters the microstructure of the contacting steels, eventually leading to micro-scale crack initiation, wear and macro-scale crack growth in the railhead. Relating the microstructural changes to subsequent wear and cracking is being accomplished through modelling at three spatial scales: (i) bulk material (ii) multi-grain and (iii) sub-grain. The models incorporate detailed information from metallurgical examinations of used rails and tested rail material. The initial 2-dimensional models representing the rail material are being further developed into 3-dimensional models. Modelling is taking account of thermal effects, and traffic patterns to which the rails are exposed.

• 한국항공우주학회지
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• 제30권4호
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• pp.1-9
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• 2002

항공기 동체에 널리 사용되고 있는 기계적 체결은 응력집중 및 접촉압력 등으로 인해 체결부로부터의 균열발생 가능성이 상대적으로 높다. 본 연구에서는 가중함수법을 적용하여 기계적 체결부에 존재하는 경사진 타원형 모서리균열의 표면점과 최심점에서의 혼합모드 응력확대계수 해석을 수행하였다. 가중함수에 포함된 미정계수들은 기준하중에 대한 유한 요소해석으로부터 구하였다. 경사각에 따른 응력확대계수의 변화를 해석하여 모드 I 응력 확대계수가 최대가 되는 임계 경사각을 결정하였고, 간극의 크기와 균열깊이가 임계 경사각에 미치는 영향을 조사하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.727-730
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• 2001

In many structures a common method of construction is to make use of bolted or riveted joints. With this type of joint the load is transmitted through a pin from one section of the structure to another. Fatigue cracks often start from the edges of holes, due to local stress concentration. In order to predict the fatigue crack growth, the stress intensity factor K for hole-edge cracks should be available. In this paper the stress intensity factors are computed for cracks in bolt-joint region considering the contact condition.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.874-882
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• 2008

In a domestic, HSR-350x which has the maximum speed 350km/h was developed and then next, the next generation high speed train which has the maximum speed 400km/h has still been developing. With developing the next generation high speed railway, there need to be a general plan to make sure of dynamic safety though the a study on the crack and failure of rail by rolling contact fatigue. Therefore, this study investigated occurring stress of rail according to the track quality, train velocity, wheel radius, track stiffness, distance between sleepers, axial force using Eisenmann's equations. For the more, via the finite element method, it investigated shear force on the rail head which could be changed by the early crack length, angle and temperature. As a result, this study confirmed the main elements which effect on the fatigue life cycle of rail.

• 한국세라믹학회지
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• 제40권7호
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• pp.662-666
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• 2003

인공치관용 알루미나-유리 복합체를 유사 구강분위기인 인공타액 하에서 200-1000 N의 하중 조건으로 $10^{6}$ 횟수까지 헤르찌안 반복하중 피로특성을 조사하였다. 200 N의 하중에서 $10^{6}$까지 반복피로 실험결과, 강도 저하 및 균열 현상은 관찰되지 않았다. 하중이 1000 N으로 증가함에 따라 링 균열에서 방사상 균열로 전이되었을 때 급격한 강도 저하 현상이 발생하였다. 강도 저하 현상은 유사 구강 분위기하에서 반복 하중 접촉 시 발생한 방사상 균열을 통해 침투한 인공타액과 유리상의 화학적 반응으로 더욱 가속화 되었다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.950-953
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• 2002

Trepan prevents wear of an inside part of a bearing when the initial shaft rotates. It continuously contacts with the eccentric part of the shaft in rotation and is loaded repeatedly. Therefore, even if an early crack of a trepan part is small, a crack progresses by a repeated load. If a crack progresses, very small chips come out. This is pill in the rotor and prevents rotation of the compressor. There can be leaks in a microgroove and extreme wear can occur due to lack of oil on the surface contact pan. Therefore, this study was carried out to compare and investigate trepan strength and deflection characteristics between trepan locations and dimension changes using a finite element method and search a motor bearing for a model with bigger stiffness of a trepan part and the same deflection. And then. five different types of the oil groove model were chosen to prevent small crack and considered also machining ability and the analysis was carried out on oil feeding flow.

• 한국정밀공학회지
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• 제18권5호
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• pp.34-41
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• 2001

More accurate and fast inspection method for mechanical parts and structure is required to guarantee the safety. Conventional methods using compliance method, eddy current method, ultrasonic wave, acoustic emission for non-destructive testing in mechanical parts and structure have been performed as the method of contact with objects to be inspected. With this reason these methods have been taken relatively much time, money, and manpower. In this study, in order to overcome these shortcomings, we used In-plane Electronic Speckle pattern Interferometry(In-plane ESPI) that was full-field measurement and noncontact method. We detected the cracks of the specimen at a real time and measured the length of the crack by using In-place ESPI system. Finally, we compared this results with conventional microscope method.

• Structural Engineering and Mechanics
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• 제23권1호
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• pp.1-13
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• 2006

Structural cracks may cause variations in structural stiffness and thus produce bilinear vibrations to structures. This study examines the dynamic behavior of structures with breathing cracks. A generalized algorithm based on the finite element method and bilinear theory was developed to study the influence of a breathing crack on the vibration characteristic. All the formulae derived in the time domain were applied to estimate the period of the overall bilinear motion cycle, and the contact effect was considered in the calculations by introducing the penetration of the crack surface. Changes in the dynamic characteristics of cracked structures are investigated by assessing the variation of natural frequencies under different crack status in either the open or closed modes. Results in estimation with vibrational behavior variation are significant compared with the experimental results available in the literature as well as other numerical calculations.