• Journal of the Korea Concrete Institute
• /
• v.25 no.6
• /
• pp.621-630
• /
• 2013

Several techniques for steel corrosion detection are proposed and HCP (half cell potential) technique is widely adopted for field investigation. If concrete has cracks on surface, steel corrosion is rapidly accelerated due to additional intrusion of chloride and carbon dioxide ions. This study is for an evaluation of HCP in cracked concrete exposed chloride attack. For this work, RC (reinforced concrete) beams are prepared considering 3 w/c ratios (0.35, 0.55, and 0.70) and several cover depths (10~60 mm) and various crack widths of 0.0~1.0 mm are induced. For 35 days, SST (salt spraying test) is performed for corrosion acceleration, and HCP and corrosion length of rebar are evaluated. With increasing crack width, w/c ratios, and decreasing cover depth, HCP measurements increase. HCP evaluation technique is proposed considering the effects of w/c ratios, crack width, and cover depth. Furthermore anti-corrosive cover depths are obtained through Life365 program and the results are compared with those from this study. The results shows relatively big difference in cracked concrete, however provide similar anti-corrosive conditions in sound concrete.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2010.06a
• /
• pp.68-68
• /
• 2010

To reduce PV manufacturing costs, the thickness of solar cell is getting thinner. Bow is shown after cooling down the temperature of solder cell. It happens because of different thermal expansion coefficients of different metals. Bowed cell can make micro crack while module processing and it can drop off efficiency of PV module. As thinner solar cell is produced, the thickness of ribbon should be concerned to prevent extra bow. In this paper we investigate the contrast of deflection when we solder different thickness of ribbons on same solar cell. This approach would help to find out the optical thickness of ribbon for particular thickness of solar cell later on.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.10 no.4
• /
• pp.79-86
• /
• 2006

This study was investigated to corrosion resistance of Cr-bearing rebars to macrocell corrosion caused by concrete with crack. Ten types of steel bars having different Cr contents were embedded in concretes with imitation crack. The corrosion resistance of the Cr-bearing rebar was examined by measuring half-cell potential, macrocell corrosion current, corrosion area and weight loss up to 105 cycles of salt spray testing. The results revealed that the Cr content required for corrosion resistance in a macrocell corrosion environment caused by chloride ion gap of $3kg/m^3$ was 9% or more. The corrosion-resisting performance of Cr-bearing rebar was particularly noticeable with a Cr content of 11% or more.

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

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.595-595
• /
• 2012

현재 대부분의 태양전지는 약 90% 이상이 si을 기판으로 제작되고 있다. Solar cell의 효율을 감소시키는 원인은 여러 가지가 있다. bulk life time 감소, 수분침투, 우박, 바람에 의한 영향들이 태양전지 효율을 감소시킨다. 모듈에 눈이 쌓이거나 바람이 불어 외부적 힘이 가해져 micro crack 가게 된다면 전체 모듈은 과부하와 발열 현상이 일어나고 interconnection 감소로 인하여 효율도 떨어지게 된다. 본 연구에서는 평균적인 효율이 17.5%, 크기가 6인치 단결정 태양전지에 일정 간격으로 힘을 가하여 파라미터 변화를 측정하였다. 두께가 $250{\mu}m$인 cell에 0.8lb에 힘을 가했을 때 cell이 파괴 되는 것을 알 수 있었다. 힘을 가해줄 수록 Voc와 Isc가 감소하는 경향성을 보였고 결국에 효율도 감소하였다. 또한 ANSYS 시뮬레이션을 사용하여 셀에 힘이 가해졌을 때 어떤 변화가 생기는 지 확인하였다. 시뮬레이션을 통하여 셀에 힘이 가해졌을 때 힘의 분포도, bowing 현상을 3D 그래프로 나타내었다. 힘이 세기가 강해질수록 bowing 현상은 심해졌고 힘의 분포도도 달라졌다.

• Korean Chemical Engineering Research
• /
• v.50 no.1
• /
• pp.118-127
• /
• 2012

TiN or Ti/TiN was coated on stainless steel as bipolar plate in polymer electrolyte membrane fuel cells (PEMFCs) to improve their corrosion resistance and electric conductivity, and their properties were examined under fuel cell operating condition. After 200 hours operation, the behaviors for the corrosion, crack and dissolution of coating layer were investigated by various techniques. The corrosion and exfoliation of coating layer were considerably generated except for SUS316L-Ti/TiN after fuel cell operation even if the electric conductivity and corrosion resistance of coated stainless steel bipolar plates were improved. The adoption of Ti layer between TiN layer and the surface of stainless steel enhanced the adhesion of TiN layer and decreased the possibility of corrosion by the increase of coating layer.

• Advanced Composite Materials
• /
• v.18 no.1
• /
• pp.77-93
• /
• 2009

This paper investigated the damage transition mechanism between the fiber-breaking mode and the fiber-avoiding crack mode when the fiber-length is reduced in the unidirectional discontinuous carbon fiber-reinforced-plastics (CFRP) composites. The critical fiber-length for the transition is a key parameter for the manufacturing of flexible and high-strength CFRP composites with thermoset resin, because below this limit, we cannot take full advantage of the superior strength properties of fibers. For this discussion, we presented a numerical model for the microscopic damage and fracture of unidirectional discontinuous fiber-reinforced plastics. The model addressed the microscopic damage generated in these composites; the matrix crack with continuum damage mechanics model and the fiber breakage with the Weibull model for fiber strengths. With this numerical model, the damage transition behavior was discussed when the fiber length was varied. The comparison revealed that the length of discontinuous fibers in composites influences the formation and growth of the cluster of fiber-end damage, which causes the damage mode transition. Since the composite strength is significantly reduced below the critical fiber-length for the transition to fiber-avoiding crack mode, we should understand the damage mode transition appropriately with the analysis on the cluster growth of fiber-end damage.

• 한국태양에너지학회:학술대회논문집
• /
• 2011.04a
• /
• pp.25-30
• /
• 2011

In this paper, we analyzed the electrical characteristics with Micro-cracks in Photovoltaic module. Micro cracks are increasing the breakage risk over the whole value chine from the wafer to the finished module, because the wafer or cell is exposed to mechanical stress. And The solar cells have to with stand the stress under out door operation in the finished module. Here the mechanical stress is induced by temperature changes and mechanical loads from wind and snow. So, we experimentally analyze the direct impact of micro-cracks on the module power and the consequences after artificial aging. The first step, we made micro-cracks in PV module by mechanical load test according to IEC 61215. Next, PV modules applied the thermal cycling test, because micro-cracks accelerated aging by thermal cycling test, according to IEC61215. Before every test, we checked output and EL image of PV module. As the result of first step, we detected little power loss(0.9%). But after thermal cycling test increased power loss about 3.2%.

• Coupled systems mechanics
• /
• v.9 no.2
• /
• pp.125-145
• /
• 2020

In this paper, we present a 3D thermo-hydro-mechanical coupled discrete beam lattice model of structure built of the nonisothermal saturated poro-plastic medium subjected to mechanical loads and nonstationary heat transfer conditions. The proposed model is based on Voronoi cell representation of the domain with cohesive links represented as inelastic Timoshenko beam finite elements enhanced with additional kinematics in terms of embedded strong discontinuities in axial and both transverse directions. The enhanced Timoshenko beam finite element is capable of modeling crack formation in mode I, mode II and mode III. Mode I relates to crack opening, mode II relates to in-plane crack sliding, and mode III relates to the out-of-plane shear sliding. The pore fluid flow and heat flow in the proposed model are governed by Darcy's law and Fourier's law for heat conduction, respectively. The pore pressure field and temperature field are approximated with linear tetrahedral finite elements. By exploiting nodal point quadrature rule for numerical integration on tetrahedral finite elements and duality property between Voronoi diagram and Delaunay tetrahedralization, the numerical implementation of the coupling results with additional pore pressure and temperature degrees of freedom placed at each node of a Timoshenko beam finite element. The results of several numerical simulations are presented and discussed.

• Proceedings of the KIEE Conference
• /
• 2011.07a
• /
• pp.1318-1319
• /
• 2011

In this paper, we analyzed of growth and electrical characteristics of micro-cracks with thermal effect in PV module. The micro-cracks are increasing the breakage risk over the whole value chine from the wafer to the finished module, because the wafer or cell is exposed to mechanical stress. we experimentally analyze the direct impact of micro-cracks on the module power and the consequences after artificial aging. The first step, we made micro-cracks in PV module by mechanical load test according to IEC 61215. Next, PV modules applied the thermal cycling test, because microcracks accelerated aging by thermal cycling test. according to IEC61215. Before every test, we checked output and EL image of PV module.