• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.479-484
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• 2009

Nondestructive evaluation(NDE) of ceramic matrix composites is essential for developing reliable ceramics for industrial applications. In the work, C-Scan image analysis has been used to characterize surface crack of SiC ceramics nondestructively. The possibility of detection of surface crack were carried out experimentally by two types of ultrasonic equipment of SDS-win and $\mu$-SDS, and three types of transducer of 25, 50 and 125 MHz. A surface micro-crack of ceramics was not detected by transducer of 25 MHz and 50 MHz. Though the focus method was detected dimly the crack by transducer of 125 MHz, the defocus method could detect the shape of diamond indenter. As a whole, the focus method and the defocus method came to the conclusion that micro crack have a good possibility for detection.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.377-387
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• 2016

In recent, in case that the underpass is constructed by trenchless method, its stability increases by reinforcing steel pipe with re-bar and mortar after propulsion into the ground to form pipe-roof. Therefore, it can be predicted that the integrated pipe-roof decreases the stress acting on the underpass by sharing load. In this study, to analyze the effect of integrated pipe-roof and behavior of stress around underpass, experimental tests for the rectangular and arch cross section of the underpass are performed using soil chamber. As a result, stress and strain acting on the underpass decrease due to sharing load by integrated pipe-roof. This phenomenon is more pronounced by increasing the stiffness of pipe-roof. Furthermore it can be expected that cross-section of underpass can be economically designed.

• Journal of Korean Association for Spatial Structures
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• v.11 no.3
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• pp.77-83
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• 2011

Laminated composite plates have shown their superiority over metals in applications requiring high specific strength, high specific modulus, and so on. Therefore, they have used in various industry. However, they have poor resistance to impact compared to typical metal materials. To resolve this problem by many researchers for a variety of studies have been attempted. This study investigates characteristic of impact behavior of laminated composite plates due to initial stress. Using finite element program which involved the indentation law, we investigate characteristic of impact behavior of laminated composite plates due to initial stress.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.5
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• pp.199-203
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• 2004

Feasibility of 3Y-TZP for dental implant abutment was evaluated under the Hertzian cyclic fatigue by examining the extent of the indentation damage and strength degradation. Fatigue test was conducted at contact loads of 500 to 3000 N and up to $10^6$ cycles in exact in vitro environments. At 500 N, no strength degradation and crack generation was observed up to $5\times10^5$ contact cycles. As load rose, the dramatic reduction in strength was observed when the damage transition from ring to radial crack occurred. The. extent of strength degradation was more pronounced in vitro environment probably due to chemical corrosion of artificial saliva through cracks introduced during large numbers of contacts.

• Proceedings of the KAIS Fall Conference
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• 2010.05b
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• pp.689-692
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• 2010

일반형 자동차 내장부품은 외부가 플라스틱 사출 성형한 형태로 사용되지만, 고급 차종은 내장재의 미감이나 질감을 위하여 사출물 표면에 엠보싱 무늬가 형성된 표피재가 수지에 추가로 부착되어 제작된다. 부착하는 방법은 한 장비에서 저압 사출 후 플라스틱이 완전 응고 전에 표피재를 넣고 압입하는 저압 사출법과 표피재 수지를 기 사출된 제품위에 놓고 압착시키는 압착법이 있으나 이 두 방법 모두 엠보싱 무늬가 형성된 표피재를 넣고 작업하기 때문에 고온 압착시 기존 무늬가 찌그러지고 코너 부위가 경화되어 기존의 질감을 얻지 못하며, 치수 공차가 변형되어 불량률이 증가하므로 이를 시급히 개선할 새로운 제조 기술의 필요성이 대두된다. 본 연구는 가열 압착기로 지그 및 금형을 새로 개발하여 도어 트림 제조시, 기 사출물을 금형 쪽으로 기 조직을 삽입한 후 엠보싱 무늬가 없는 원소재 표피재로 상부 금형 쪽으로 소재조직을 진공으로 흡입하여 무늬를 성형한 후 하강시켜, 기 사출물에 압착시키는 가열 압착으로 엠보싱무늬의 손상을 방지하는 금형을 제안하였으며 그에 대한 해석, 설계, 실험을 통하여 성능을 평가 분석 하였다.

• Composites Research
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• v.16 no.1
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• pp.50-57
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• 2003

Usually many researchers have used the modified Hertzian contact law or experimental static indentation law to analyze impact response of composite laminates subjected to the low-velocity impact. In this study, physical meaning of the method using the laws was investigated and the difference between the analytical results obtained using the laws was also investigated. Furthermore parametric study on contact constant and exponent in the contact law was performed. Finally it was shown that a linearized contact law can be well applied to low-velocity impact response analysis of composite laminates. If this concept is used, commercial finite element software can be used to solve impact problem without making any auxiliary code.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.4
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• pp.394-400
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• 2007

The properties and weldability of lap joints by PFSW with 1050 Al sheet was investigated according to tool shape. dimension and welding condition. Tensile shear test was carried out for lap jointed specimen, and the hardness in the joint regions was examined. Moreover interfacial joining length, metallograph and failure location of the lap-jointed cross section were discussed. Two tool types were a simple cylindrical type and a notched cylindrical type. Under joining conditions such as plunging depth of 2.2mm. rotating speed of 1600rpm and dwelling time of 3s, the tensile shear strength of lap-jointed specimen by the notched type tool was superior to that by simple cylindrical type tool. The maximum tensile shear load of lap jointed specimen was 5807N. Optimal dimensions of the notched type tool were as follows : diameters of the shoulder and pin were $18{\phi}mm$ and $10{\phi}mm$, and pin length was 2.2mm.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.383-399
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• 2020

Optimizing the spacing of the disc cutter is a key element in the design of the TBM cutter head, which determines the drilling performance of the TBM. The full-scale linear cutting test is known as the most reliable and accurate test for calculating the spacing of the disc cutter, but it has the disadvantage of costly and time-consuming for the full-scale experiment. In this study, through the numerical analysis study based on the discrete element method, the tendency between Specific Energy-S/P ratio according to uniaxial compression strength and penetration depth of rock was analyzed, and the optimum spacing of 17-inch disc cutter was derived. To examine the appropriateness of the numerical analysis model, the rolling force acting on the disc cutter was compared and reviewed with the CSM model. As a result of numerical analysis for the linear cutting test, the rolling force acting on the disc cutter was analyzed to be similar to the rolling force derived from the theoretical formula of the CSM model. From the numerical analysis on 5 UCS cases (50 MPa, 70 MPa, 100 MPa, 150 MPa, 200 MPa), it is found that the range of the optimum spacing of the disc cutter decreases as the rock strength increases. And it can be concluded that 80~100 mm of disc cutter spacing is the optimum range having minimum specific energy regardless of rock strength. This tends to coincide with the optimal spacing of previously reported disk cutters, which underpins the disk cutter spacing calculated through this study.

• Journal of the Korean Vacuum Society
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• v.18 no.5
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• pp.372-376
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• 2009

In the modern semiconductor industry, lithography process is used to construct specific patterns. However, due to the decreasing of line width, these days, more and more researchers are interested in PMMA(Poly Methyl Methacrylate) lithography by using e-beam instead of the prior method, PR(Photoresist) lithography by using UV(Ultra-Violet). Additionally, the patterns constructed by lithography are collapsed during the process of cleansing remnants and the resistance against the breakdown of the patterns is known to be proportional to the elastic modulus of pattern-constructing materials. In this research, we measured the change of hardness and elastic modulus of PMMA film surface according to the change of time spent to soft-bake the PMMA film. During the measurement, we controlled the tip pressure from $25{\mu}N$ to $8,500{\mu}N$ having intervals that are $134.52{\mu}N$. For these measurements, we used the Triboindenter from Hysitron to gauge the hardness and elastic modulus and the tip we used was Berkovich diamond Tip.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.12
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• pp.6060-6065
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• 2013

Minimizing the height of the die roll is very important for maximizing the size of effective shear planes. In this study, the die roll change was investigated for the change in the amounts and clearance of the V-ring indentation. Shear analysis and experiments were conducted with the V-ring distance fixed to 2mm. Fine blanking die was applied to the die insert with different clearances. Several specimens were analyzed about the height of the die roll. As a result, the pressure of V-ring effectively inhibited the flow of materials. And the height of the die roll was lowest when the clearance between the die and punch was 1% of the material thickness.