• 한국세라믹학회지
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• 제35권12호
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• pp.1257-1265
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• 1998

Hertzian contact tests were used to investigate the evolution of fracturedamage in the coating layer as functions of contact load and coating thickness by studying crack patterns in porcelain on glass-infiltrated alumina bilayer system conceived to simulate the crown structure of a tooth. Cone cracks initiated at the coating top surface without delamination at interface and crack propagation to substrate. Preferentially the cracks made multi-cracks at the coating top surface rather than proceeding to interface. The cracks were highly stabilized with wide ranges between the loads to initiate first cracking and to cause final failure im-plying damage-tolerant capability. Finite element modelling was used to evaluate the stress distribution. Maximum tensile stress were responsible for the cracking at the coating layer and had a profound influence on the crack pattern and fracture damage in the layered structure materials.

• 한국환경과학회지
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• 제19권6호
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• pp.737-746
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• 2010

Restraint to drying shrinkage is the most common cause of concrete cracking. In many applications, drying shrinkage cracks are inevitable. In this paper, the surface cracks of soil concrete caused by drying shrinkage were considered to become an one of concrete textures. So, laboratory shrinkage tests were conducted and the results were applied to the field applications. The study results were summarized as follows; First, the use of vinyl sheets and concrete polymers helped to control the concrete cracking. Second, crack propagation usually started at the interfaces of soil concrete slabs and the cracks grew to the inner slabs. Third, surface cracks of soil concrete slabs could be an one of good concrete textures

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2020년도 봄 학술논문 발표대회
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• pp.134-135
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• 2020

In this study, optimum time of drilling for injection of repair material was determined through surface stripping and cracking investigation by drilling from the 1 days to the 3 days of the age for the specimens with ∅100 mm. No surface stripping and cracking occurred on the third day of age, and the compressive strength value was above 14 MPa, which resulted in the appropriate time for drilling on the third day of age.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 추계학술발표대회 논문집
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• pp.87-90
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• 2001

In particle or short-fiber reinforced composites, cracking of the reinforcements is a significant damage mode because the broken reinforcements lose load carrying capacity. This paper deals with elastic stress distributions and load carrying capacity of intact and cracked ellipsoidal inhomogeneities. Three dimensional finite element analysis has been carried out on intact and broken ellipsoidal inhomogeneities in an infinite body under pure shear. For the intact inhomogeneity, as well known as Eshelby(1957) solution, the stress distribution is uniform in the inhomogeneity and non-uniform in the surrounding matrix. On the other hand, for the broken inhomogeneity, the stress in the region near crack surface is considerably released and the stress distribution becomes more complex. The average stress in the inhomogeneity represents its load carrying capacity, and the difference of average stresses between the intact and broken inhomogeneities indicates the loss of load carrying capacity due to cracking damage. The load carrying capacity of the broken inhomogeneity is expressed in terms of the average stress of the intact inhomogeneity and some coefficients. It is found that the broken inhomogeneity with higher aspect ratio still maintains higher load carrying capacity.

• Corrosion Science and Technology
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• 제2권4호
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• pp.178-182
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• 2003

Slow Strain Rate Tests (SSRT) were carried out to investigate the effect of environmental factors on the Stress Corrosion Cracking (SCC) susceptibility of 3.5NiCrMoV steels used in discs for Low-Pressure (LP) steam turbines in electric power generating plants. The influences of dissolved oxygen on the stress corrosion cracking of turbine steel were studied, For this purpose, specimens were strained at variously oxygenated conditions at $150^{\circ}C$ in pure water. When the specimen was strained with $1{\times}10^{-7}s^{-1}$ at $150^{\circ}C$ in pure water, increasing concentration of dissolved oxygen decreased the elongation and the UTS. The corrosion potential and the corrosion rare increased as the amounts of dissolved oxygen increased. The increase of the SCC susceptibility of the turbine steel in a highly dissolved oxygen environment is due to the non protectiveness of the oxide layer on the turbine steel surface and the increase of the corrosion current. These results clearly indicate that oxygen concentration increases Stress Corrosion Cracking susceptibility in turbine steel at $150^{\circ}C$.

• Journal of Advanced Marine Engineering and Technology
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• 제9권4호
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• pp.328-338
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• 1985

When the low temperature service steels are used as materials for welded structure, some problems-brittleness and weld cracking, etc.-occur in welded part due to the change of mechanical and metallurgical characteristics resulted from the thermal cycle during the welding procedure. In this study, the experiments were conducted to investigate the change of mechanical and metallurgical characteristics of the welded part for the low temperature and high pressure service steels. Moreover, the Static and Dynamic Implant Test Method was introduced to this study in order to find out the mechnism of weld cracking. In addition, the fracture toughnesses of welded bond were inspected under the various low temperature environments. Main results obtained are as follows; 1) The effect of the hydrogen on the fatigue characteristics of the weld bond can be estimated by the new self-contrived Dynamic Implant Test equipment. 2) The fine micro-structure and low hardness in the heat affected zone can be obtained by the small heat input multi-pass welding. 3) The susceptibility of the delayed cracking is largely affected by the condition of used electrode. 4) The transition temperature of the fracture surface in weld bond appears to be higher 20 .deg. C than that in base metal.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.362-367
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• 2008

In the present work, we address electric fatigue behavior in bending piezoelectric actuators using an acoustic emission technique. Electric cyclic fatigue tests have been performed up to ten million cycles on the fabricated specimens. To confirm the fatigue damage onset and its pathway, the source location and distributions of the AE behavior in terms of count rate are analyzed over the fatigue range. It is concluded that electric cyclic loading leads to fatigue damages such as transgranular damages and intergranular cracking in the surface of the PZT ceramic layer, and intergranular cracking even develops into the PZT inner layer, thereby degrading the displacement performance. The electric-induced fatigue behavior seems to show not a continuous process but a step-by-step process because of the brittleness of PZT ceramic. Nevertheless, this fatigue damage and cracking do not cause the final failure of the bending piezoelectric actuator loaded up to 107 cycles. Investigations of the AE behavior and the linear AE source location reveal that the onset time of the fatigue damage varies considerably depending on the existence of a glass-epoxy protecting layer.

• 한국재료학회지
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• 제4권3호
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• pp.334-338
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• 1994

Pb-Sn eutectic bulk specimens을 thermal cycling동안 electronic package의 땜납이 격게되는 변형 조건 즉 $10^{-3}-10^{-5}$/s정도의 낮은 frequency와 0.2-1%정도의 적당한 strain range에서 피로파괴 실험을 했을때, grain boundary sliding과 관련하여 임계면을 따라 일어나는 균열이 5단계에 의해 묘사될 수 있다는 것을 보였음.

• Journal of Mechanical Science and Technology
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• 제15권6호
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• pp.709-719
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• 2001

In particle or short-fiber reinforced composites, cracking of reinforcements is a significant damage mode because the cracked reinforcements lose carrying capacity. This paper deals with elastic stress distributions and load carrying capacity of intact and cracked ellipsoidal inhomogeneities. Three dimensional finite element analysis has been carried out on intact and cracked ellipsoidal inhomogeneities in an infinite body under uniaxial tension and pure shear. For the intact inhomogeneity, as well known as Eshelbys solution, the stress distribution is uniform in the inhomogeneity and nonuniform in the surrounding matrix. On the other hand, for the cracked inhomogeneity, the stress in the region near the crack surface is considerably released and the stress distribution becomes more complex. The average stress in the inhomogeneity represents its load carrying capacity, and the difference between the average stresses of the intact and cracked inhomogeneities indicates the loss of load carrying capacity due to cracking damage. The load carrying capacity of the cracked inhomogeneity is expressed in to cracking damage. The load carrying capacity of the cracked inhomogeneity is expressed in terms of the average stress of the intact inhomogeneity and some coefficients. It is found that a cracked inhomogeneity with high aspect ratio still maintains higher load carrying capacity.

• Advances in concrete construction
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• 제16권2호
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• pp.107-117
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• 2023

Textile-reinforced concrete composite (TRC) is a new alternative material that can satisfy sustainable development needs in the civil engineering field. Its mechanical behaviour and properties have been identified from the experimental works. However, it is necessary for a numerical approach to consider the effect of the parameters on TRC's behaviour with lower analysis duration and cost related to the experiment. This paper presents obtained results of the numerical modelling for TRC composite using the cracking model for the cementitious matrix in TRC. As a result, the TRC composite exhibited a strain-hardening behaviour with the cracking phase characterized by the drops in tensile stress on the stress-strain curve. This model also showed the failure mode by multi-cracking on the TRC specimen surface. Furthermore, the parametric studies showed the effect of several parameters on the TRC tensile behaviour, as the reinforcement ratio, the length and position of the deformation measurement zone, and elevated temperatures. These numerical results were compared with the experiment and showed a remarkable agreement for all cases of this study.