• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1349-1354
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• 2003

Ultrasonic Machining process is an efficient and economical means of precision machining on glass and ceramic materials. However, the mechanics of the process with respect to crack initiation and propagation, and stress development in the ceramic workpiece subsurface are still not well understood. In this research, we investigate the basic mechanism of chemical assisted ultrasonic machining(CUSM) of glass through the experimental approach. For the purpose of this study, we designed and fabricated the desktop micro ultrasonic machine. The feed is controlled precisely by using the constant load control system. During the machining experiment, the effects of HF(hydrofluoric acid) characteristics and machining condition on the surface roughness and the material removal rate are measured and compared.

• 소성∙가공
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• 제11권7호
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• pp.608-613
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• 2002

An ultrasonic machining process is efficient and economical means for precision machining of glass and ceramic materials. However, the mechanism of the process with respect to the crack initiation and propagation and the stress development in the ceramic workpiece subsurface arc still not well understood. In this research, we have investigated the basic mechanism of ultrasonic machining of ultrasonic machining of glass by the experimental approach. For this purpose, we designed and fabricated the desktop micro ultrasonic machine. The feed is controlled precisely by using the constant load control system. During machining experiments, the effects of abrasive characteristics and machining conditions on the surface roughness and the material removal rate are measured and compared.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
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• pp.458-461
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• 2006

Early age cracking of concrete is a widespread and complicated problem, and diverse applications in practical engineering have focused on this issue. Since massive concrete base slab composes the infrastructure of other concrete structures such as pier, concrete dam, and high rise buildings, early age cracking of that is considered as a crucial problem. In this study, finite element analysis (FEA) implemented with the age-dependent microplane model was performed. For a massive concrete base slab, cracking initiation and propagation, and deformation variation were investigated with concrete age. In massive concrete slab, autogenous shrinkage increases the risk of early age cracking and it reduces reinforcement effect on control of early age cracking. Gradual crack occurrence is experienced from exterior surface towards interior of the slab in case of combined hydration heat and autogenous shrinkage. FEA implemented with enhanced microplane model successfully simulates the typical cracking patterns due to edge restraint in concrete base slab.

• 열처리공학회지
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• 제6권3호
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• pp.127-137
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• 1993

The changes of lamellar(${\alpha}_2+{\gamma}$) structure of TiAl intermetallic compound which is a high potential, high temperature aerospace material was investigated by heat treatment. The lamellar structure was short and made subgrain in prior a grains after homogenizing at 1523 K. It became longer and finer, and the subgrain went out during subsequent isothermal heatteating at 1273 K. The yield, fracture strength and strain to fracture if the heat treated specimens was increased and the hardness of them was decreased a little in the finer lamellar structure, because fine lamellar interface, sugrain boundary and grain boundary may block initiation and propagation of crack.

• Corrosion Science and Technology
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• 제18권2호
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• pp.49-54
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• 2019

The purpose of this paper is to present failure analysis, of the heat exchanger tube in a district heating system. SS304 stainless steel is used, as material for the heat exchanger tube. The heat exchanger operates in a soft water environment containing a small amount of chloride ions, and regularly repeats operation and standstill period. This causes concentration of chloride ions on the outer surface of the tube, as well as repeat of thermal expansion, and shrinkage of the tube. As a result of microscopic examination, cracks showed transgranular as well as branched propagation, and many pits were present, at the initiation point of each crack. Energy disperstive spectroscopy analysis showed Fe and O peak, as well as Cl peak, meaning that cracks were affected by Cl ion. Failure of the tube was caused by chloride-induced stress corrosion cracking by thermal stress, high temperature, and localized enrichment of chloride ions.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
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• pp.519-524
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• 1998

The shear behavior and reinforcement effects of simply supported reinforced concrete deep beams with web opening subject to concentrated loads have been scrutinized experimentally to verify the effects of structural parameters such as size, location and reinforcements of web opening. A total of 14 specimens were tested at the laboratory under two-point top loading. The shear span ratio was taken constantly 0.8, and various types of reinforcements based on truss models were adopted. In the tests, the effects of loction, reinforcements of web openings on the shear behavior, and crack initiation and propagation have been carefully checked and analyzed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 가을 학술발표회 논문집
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• pp.273-278
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• 1994

The shear behavior of simply supported reinforced concrete deep beams subject to concentrated loads has been scrutinized experimentally to verify the influence of the structural parameters such as shear span ratio, and the horizontal and vertical web reinforcements. A total of 27 specimens has been tested at the laboratory. In the tests all specimens have failed in shear causing inclined cracks from the load application points to the supports. The load bearing capacities have changed significantly depending on the shear span ratio. The effects of the vertical and horizontal reinforcements on the shear strength and crack initiation and propagation have been carefully checked and analyzed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.131-134
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• 2005

Until recently tensile stresses in concrete have not been considered, since it does not affect the ultimate strength of reinforced concrete flexural members significantly. However, to verify the load-deflection relationship, the effect of tensile stresses between reinforcing bars and concrete, so-called tension stiffening effect must be taken into account. Main parameters of the tension stiffening behavior are known as concrete strength, and bond between concrete and reinforcing bars. In this study a total of twenty specimen subject to bending was tested with different concrete strength, coverage, and de-bonding length of longitudinal bars. The effects of these parameters on the flexural rigidity, crack initiation and propagation were carefully checked and analyzed.

• 한국군사과학기술학회지
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• 제8권1호
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• pp.5-13
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• 2005

In order to evaluate the credibility of the welded joint design for combat vehicle using A12519, the numerical analysis for the joint model has been studied and the results are compared with the experimental works by the impact projectiles. The numerical approach using LS-DYNA involves the process of the crack initiation and propagation as well as the applications of the failure criteria for both the ductile and brittle failures. The good agreement between the numerical and experimental works are proved.

• 한국정밀공학회지
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• 제21권2호
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• pp.138-144
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• 2004

The initiation and the propagation of solder joint crack depend on its environmental conditions, such as high temperature creep and thermal fatigue. Creep is known to be the most important factor for the mechanical failure of solder joints in micro-electronic components and micro-systems. This is mainly caused by the different thermal expansion coefficients of the materials used in the micro-electronic packages. To determine the reliability of solder joints and consequently the electronic components, the characterization of the creep behavior of this group of materials is crucial. This paper is to apply the theory of creep into solder joints and to provide related technical information needed for evaluation of reliability of solder joint to failure. 63Sn-37Pb solder was used in this study. This paper experimentally shows a way to enhance the reliability of solder joints.