• 한국해양공학회지
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• 제7권2호
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• pp.19-29
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• 1993

The static tensile tests of GFRP, ID300, CFRID300 and CFRPEEK were made on the plain and notched specimens at room temperature. The results were discussed based on linear notch mechanics which was proposed by H.Nistani. The fracture of notched GFRP, ID300, CFRID300 and CFRPEEK specimens is controlled by the elastic maximum stress, $({\sigma}_max)$, and the notch root racius,$\rho$, alone, independently of the other geometrical conditions. The relation between fracture nominal stress,$({\sigma}_max)$, and stress concentration factor, $K_t$ and a part where $({\sigma}_c)$ is nearly constant independent of $K_t$. A similar phenomenon can be seen in the fatigue tests of notched specimes under rotating bending or push-pull. The almost constant $({\sigma}_c)$ values correspond to the nearly constant apparent stress intensity factor, $K_{1pc}$ values, obtained by assuming ,$\rho$=0. This can be attributed to the existence of the stable crack. Linear notch mechanics is very useful for analyzing the static tensile fracture behavior of notched GFRP, ID300, CFRPEEK specimens.

• 한국정밀공학회지
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• 제19권9호
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• pp.98-105
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• 2002

Some materials exhibit a rising K-R curve, while the K-R curve for other materials is flat. The shape of the K-R curve depends on material behavior and, to a lesser extent, on the configuration of the cracked structure. The K-R curve for an ideally brittle material is flat because the surface energy is an invariant material property. However, the K-R curve can take on a variety of shapes when nonlinear material behavior accompanies fracture. Five different hot-rolled thin plates are tested to investigate K-R curve behavior. A special experimental apparatus is used to prevent specimens from buckling.

• 대한자원환경지질학회:학술대회논문집
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• 대한자원환경지질학회 1999년도 춘계 공동학술발표회
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• pp.90-93
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• 1999

We present a high frequency electromagnetic (EM) inversion scheme for detecting and characterizing a fracture using single-hole data. At high frequencies, say above tens of mega-hertz, since displacement currents cannot be ignored, electrical permittivity as well as electrical conductivity is to be considered together for analyzing the EM scattering data. In this paper, we have developed a three-step inversion scheme to map the fracture and to evaluate its electrical conductivity and permittivity. We performed EM profiling along the z-axis using three-component receivers for each source. The model was excited by a vertical magnetic dipole and the resistant magnetic fields were inverted using the non-linear least-squares method. Background resistivity and permittivity were easily obtained using vertical magnetic fields below 1 MHz and above 10 MHz, respectively. Both the vertical and dipping sheets were successfully mapped using the phase difference between 40 and 41 MHz. The electrical property of the sheet was well resolved using the information obtained in the previous two steps and secondary magnetic fields. Our study shows the potential of imaging the fracture in single-hole survey environment using the high frequency EM method.

• 한국구조물진단유지관리공학회 논문집
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• 제11권1호
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• pp.113-120
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• 2007

새로운 재료의 적용 실험을 통하여, 탄소섬유 분말 혼입 모르타르 복합 구조체의 파괴예측 자가진단 적용 특성에 대해 검토하였다. 본 연구에서는 자가진단 성능을 부여하기 위해 코크스와 탄소섬유분말(미분쇄 탄소섬유)이 혼입된 전도성 모르타르의 개발 및 자가진단 재료로서의 사용이 제안되었다. 각 하중재하단계에서의 균열발생 전후의 전기저항값과 AE특성치의 변화특성 시험을 통해, 이들 각 인자의 상호 연관성을 검토하였다. 그 결과, 코크스와 탄소섬유분말(미분쇄 탄소섬유)을 사용하여 새롭게 제안된 복합재료는 모르타르 시험체의 파괴 자가진단에 사용이 가능함을 알 수 있었다.

• 한국세라믹학회지
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• 제46권5호
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• pp.484-487
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• 2009

$SiC_f$/SiC composites with whiskers and pyrolytic carbon (PyC) coated whiskers in the matrix were fabricated for enhancement of the fracture behaviors by the whisker growing assisted chemical vapor infiltration (WA-CVI) process, respectively. $SiC_f$/SiC composites were also prepared by the conventional CVI process as reference material. The mechanical properties and fracture behaviors were analyzed by comparison of the two types of composites prepared by WA-CVI and conventional CVI. The densities of $SiC_f$/SiC composites were in the range of $2.6{\sim}2.65g/cm^3$. The flexural strengths of composite with whiskers and with those coated by PyC were 650 MPa and 600 MPa, respectively. The tensile strength of composites with whiskers was ${\sim}285$ MPa.

• Multiscale and Multiphysics Mechanics
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• 제1권1호
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• pp.53-64
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• 2016

Amyloid fibrils have recently been considered as an interesting material, since they exhibit the excellent mechanical properties such as elastic modulus in the order of 10 GPa, which is larger than that of other protein materials. Despite recent findings of these excellent mechanical properties for amyloid fibrils, it has not been fully understood how these excellent mechanical properties are achieved. In this work, we have studied the nanomechanical deformation behaviors and properties of amyloid fibrils such as their elastic modulus as well as fracture strength, by using atomistic simulations, particularly steered molecular dynamics simulations. Our simulation results suggest the important role of the length of amyloid fibrils in their mechanical properties such that the fracture force of amyloid fibril is increased when the fibril length decreases. This length scale effect is attributed to the rupture mechanisms of hydrogen bonds that sustain the fibril structure. Moreover, we have investigated the effect of boundary condition on the nanomechanical deformation mechanisms of amyloid fibrils. It is found that the fracture force is critically affected by boundary condition. Our study highlights the crucial role of both fibril length and boundary condition in the nanomechanical properties of amyloid fibrils.

• 한국분말재료학회지
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• 제19권6호
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• pp.416-423
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• 2012

This paper introduces an effect of a preparing $ZrO_2$-Ag composite on its mechanical properties and microstructure. In present study, $ZrO_2$-Ag was prepared by reduction-deposition route and wetting dispersive milling method, respectively. Two type of Ag powders (nano Ag and micron Ag size, respectively) were dispersed into $ZrO_2$ powder during wetting dispersive milling in D.I. water. Each sample was sintered at $1450^{\circ}C$ for 2hr in atmosphere, and then several mechanical tests and analysis of microstructure were carried out by bending test, hardness, fracture toughness and fracture surface microstructure. As for microstructure, the Ag coated $ZrO_2$ showed homogeneously dispersed Ag in $ZrO_2$ in where pore defect did not appear. However, $ZrO_2$-nano Ag and $ZrO_2$-micro Ag composite appeared Ag aggregation and its pore defect, which carried out low mechanical property and wide error function value.

• 한국안전학회지
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• 제21권4호
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• pp.33-41
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• 2006

Material degradation should be considered to assess integrity and residual life of high temperature equipments. However, the property data reflecting degradation are not sufficient for practical use. In this study measuring properties for 1Cr-1Mo-0.25V forging steel generally used for turbine rotor was carried out. Degradation was simulated by isothermal ageing. heat treatment and variation of microstructure was observed. Mechanical properties such as tensile strength, impact energy, hardness and fracture toughness were measured. Assuming a semi-elliptical surface crack at the bore hole in a turbine rotor, material risk was estimated by using the aged material property data obtained in this study. Safety margin was decreased and life of the rotor was exhausted. This procedure can be used in assessing the residual life of a turbine rotor due to material degradation.

• 한국전기전자재료학회논문지
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• 제14권12호
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• pp.979-986
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• 2001

This paper was researched the effect of slurry stability on the mechanical and electrical property of the porcelain insulator with various raw materials such as feldspar, quartz, clay and l7wt% alumina. The slurry was fabricated after ball milling the mixed raw materials. Green compacts were made by the extrusion and were sintered at 1300$\^{C}$ for 60min in the tunnel kiln. All of the specimens were densified 96% of the theoretical density. The 3-point flexural strength($\sigma$$\_$B/) of the specimen stabilized slurry pH 7.8 was 1650 k9/㎠ and the vickers hardness(Hv) and the fracture toughness(K$\_$IC/) were 27.5 GPa and 2.2 MPa$.$m$\^$$\sfrac{1}{2}$/, respectively. The mechanical properties of the specimen stabilized slurry PH 9.3 were 1716 kg/㎠($\sigma$$\_$B/), 27.6 GPa(Hv) and 3.0 MPa$.$m$\^$$\sfrac{1}{2}$/(K$\_$IC/), respectively. The dielectric strength was increased from 8.3kV/mm to 13.2kV/mm as the increase of the slurry pH from 7.8 to 9.3. Therefore the physical properties of the specimen stabilized slurry pH 9.3 were improved.

• 소성∙가공
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• 제26권6호
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• pp.356-364
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• 2017

In this study, submerged arc cladded Fe-Cr-Ni-Mo-CuWNbV-C stainless steels containing various Cr contents between 11.2 wt.% and 16.7 wt.% were prepared with fixed C content at about 0.14 wt.%. Using these alloys, changes in microstructure, tensile property, and thermal fatigue property were investigated. Phase fraction of delta-ferrite was increased gradually with increasing Cr content. However, tensile strength, hardness, and thermal fatigue resistance appeared to be decreased. When the microstructure of delta-ferrite was observed, it was revealed that the mesh structure retained up to about 15% Cr content. Although thermal fatigue resistance was almost the same for Cr contents between 11.0 and 14.5 wt.%, it was significantly decreased at higher Cr contents. This was evident from mean value of crack lengths of 10 largest ones. Evaluation of thermal fatigue resistance on alloys with various Cr contents revealed the following important results. First, the reproducibility of ranking test was excellent regardless of the number of cycles. Second, thermal fatigue resistance was increased in proportion to true tensile fracture strength values of overlay materials. Finally, the number of thermal fatigue cracks per unit length was increased with increasing true tensile fracture strength.