• 한국세라믹학회지
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• 제44권7호
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• pp.343-348
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• 2007

Alumina/silver nanocomposites were fabricated using a soaking method through a sol-gel route to construct an intra-type nanostructure. The pulse electric-current sintering (PECS) technique was used to sinter the nanocomposites. Several specimens were annealed after sintering. The microstructure, mechanical properties, critical frontal process zone (FPZ) size, and thermo-mechanical properties of the nanocomposites were estimated. The relative densities of the specimens sintered at 1350 and $1450^{\circ}C$ were 95% and 99%, respectively. The maximum value of the three-point bending strength was found to be 780 MPa for the $2{\times}2{\times}10 mm$ specimen sintered at $1350^{\circ}C$. The fracture toughness of the specimen sintered at $1350^{\circ}C$ was measured to be $3.60 MPa{\cdot}m^{1/2}$ using the single-edge V-notched beam (SEVNB) technique. The fracture mode of the nanocomposites was transgranular, in contrast to the intergranular mode of monolithic alumina. The fracture morphology suggested that dislocations were generated around the silver nanoparticles dispersed within the alumina matrix. The specimens sintered at $1350^{\circ}C$ were annealed at $800^{\circ}C$ for 5 min, following which the maximum fracture strength became 810 MPa and the fracture toughness improved to $4.21 MPam^{1/2}$. The critical FPZ size was the largest for the specimen annealed at $800^{\circ}C$ for 5 min. Thermal conductivity of the alumina/silver nanocomposites sintered at $1350^{\circ}C$ was 38 W/mK at room temperature, which was higher than the value obtained with the law of mixture.

• 한국산학기술학회논문지
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• 제16권9호
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• pp.5743-5747
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• 2015

본 연구에서는 가스아토마이저로 제조된 Fe계 벌크비정질 합금 분말을 이용하여 제작된 시험편에 레이저 육성용접을 하였고, 인장시험과 경도시험의 실시 및 미세조직을 관찰하여 육성용접 층의 파괴거동을 분석하였다. 인장시험 결과 육성용접층은 탄성변형 후 바로 파괴가 일어났고, 모재는 소성변형 후 파괴가 일어났다. 육성용접층과 모재의 실제 최대인장강도는 각 각 955.9Mpa과 220.4Mpa이다. 육성용접층과 모재의 미소경도는 각 각 $485.5{\pm}21$과 $197.4{\pm}14$ 이었고, 육성용접층은 매우 높은 경도를 갖는다. 모재는 조대한 결정립을 갖는 미세 구조를 나타내었다. 인장시험 후 파단면을 고분해능주사전자현미경으로 관찰한 결과 육성용접층과 모재의 파괴형태는 각각 취성파괴와 연성파괴를 나타내었다.

• 대한기계학회논문집
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• 제3권3호
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• pp.116-123
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• 1979

On the basis of optical microscope and electro microscope observation for the fatigue fracture process of medium corbon martensitic structure produced by rapid heat treatment, mainly the abstracts of the studied results for the morphology of fatigue crack initiation process of high hardened steel are summarized as follows. Fatigue crack initiated from inclusion on the surface or subsurface. Above all the crack which initiated from inclusion exposed on the surface in as follows. (1) fatigue crack initiated from the boundary of the matrix and inclusion. (2) fatigue crack initiated at surrounding of small pit by drop out of inclusion.

• 한국세라믹학회지
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• 제34권11호
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• pp.1107-1112
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• 1997

Mn-Zn ferrite powders prepared by an alcoholic dehydration method. Vacuum casting, a kind of wet forming process was examined with this powders. As binders, polyethylene glycol and polyvinyl alcohol were used. In order to estimate this conditions, fracture morphology, densities of green and sintered bodies and the microstructure were observed. High density and homogeneous microstructure in sintered bodies were obtained in the case of 0.1 wt% PEG or 0.5 wt% PVA.

• KEPCO Journal on Electric Power and Energy
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• 제7권1호
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• pp.125-128
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• 2021

This paper presents the root cause failure analysis of the circulating water pump in the 560 MW thermal power plant. A fractured austenitic stainless-steel shaft operated for 24 years was examined. Fracture morphology was investigated by micro and macro-fractographic analysis. The metallurgical analyses including chemical analysis, metallography and hardness testing were performed. The analysis reveals that the pump shaft was fractured due to the reverse bending load with combination of rotating bending load. Corrective actions for plant operator was recommended based on the analysis.

• 대한치과의사협회지
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• 제53권9호
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• pp.644-655
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• 2015

Purpose: This study was conducted to evaluate the effect of the fixture abutment connection type and diameter on the screw joint stability in external butt joint for 2nd surgery and internal cone connected type implant system for 1st and 2nd surgery using ultimate fracture strength. Materials and Methods: USII system, SSII system and GSII system of Osstem Implant were used. Each system used the fixture with two different diameters and cement-retained abutments, and tungsten carbide / carbon coated abutment screws were used. Disc shaped stainless steel metal tube was attached using resin-based temporary cement. The experimental group was divided into seven subgroups, including the platform switching shaped specimen that uses a regular abutment in the fixture with a wide diameter in USII system. A static load was increased to the metal tube at 5mm deviated point from the implant central axis until it reached the compression bending strength at a rate of 1mm/min. Then the deformations and patterns of fracture in threaded connection were compared. Results and Conclusion: 1. In the comparison between the Regular diameter, compression bending strength of SSII system was higher than USII system and GSII system. There was no significant difference between USII system and GSII system. 2. In the comparison between wide diameter, compression bending strength was increased in the order of GSII system, USII system, and SSII system. 3. In comparison between the implant diameter, compression bending strength of the wide diameter was greater than the regular diameter in any system(P<0.05). 4. There was no significant difference between the platform switching (III group) and the regular diameter (I group) in USII system. 5. In USII system, fracture of abutment screw and deformation of both fixture and abutment were observed in I, II and III subgroups. 6. Failure pattern of SSII system, which was the fracture of abutment screw and deformation of the abutment and fixture, was observed in both IV and V subgroups. Fracture of some fixtures was observed in subgroup V. 7. Failure pattern of GSII system, which was the fracture of the abutment screw and deformation of the fixture and the abutment, was observed in both VI and VII subgroups. Apart from other subgroups, subgroup VII demonstrated no bending neither the fracture at the top of the fixture. The compressive deformation of internal slope in the fixture was the only thing observed in subgroup VII.

• 한국주조공학회지
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• 제38권1호
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• pp.1-8
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• 2018

In this study, we focused on the correlation between the solidification structure, heat treatment and mechanical properties of the A356 alloy according to the conditions of Sr modification. The microstructural evolution of the eutectic Si and ${\alpha}-Al$ phase in the A356 alloy castings depending on the amount of Sr were investigated during solid solution heat treatment using an optical microscope, a scanning electron microscope and an image analyzer. In addition, tensile tests on the heat treated materials examined the relationship between the microstructure and the fracture surface. The as-cast A356 alloys under 40 ppm Sr showed an undermodified microstructure, but that of the added 60-80 ppm Sr had well modified structure of fine fibrous silicon. After solid solution treatment, the microstructure of the undermodified A356 alloy exhibited a partially spheroidized morphology, but the remainder showed the fragmentation of fibrous shaped silicon. The spheroidization of the eutectic silicon in the modified A356 alloys was completed during heat treatment, which was very effective in increasing the elongation. This is supported by the fracture surface in the tensile test.

• The Korean Journal of Ceramics
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• 제6권1호
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• pp.27-31
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• 2000

A series experiments were performed to evaluate mechanical behavior of non-oxide boride type ceramics formed on the AISI 1040 plain carbon steel. Boronizing was performed in a slurry salt bath consisting of borax, boric acid, and ferro-silicon at $950^{\circ}C$ for 2-6h. The AISI 1040 steel used as substrate material was containing 0.4%C, 0.13%Si, 0.65%Mn, 0.02%P, 0.014%S. The presence of non-oxide boride type ceramics $Fe_2B $ and FeB formed on the surface of steel was confirmed by metallographic technique and X-ray diffraction (XRD) analysis. The hardness of borides measured via Vickers indenter with a load of 2N reached a microhardness of up to 1800 DPN. The hardness of unborided steel was 185 DPN. The fracture toughness of borides measured by means of Vickers indenter with a load of 10N was about 2.30 MPa.$m^{1/2}$. The thickness of boride layers ranged from 72$\mu\textrm{m}$ to 145$\mu\textrm{m}$. Boride layers have a columnar morphology.

• 대한기계학회논문집A
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• 제25권11호
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• pp.1887-1894
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• 2001

The effects of carbon black on the material properties and the fatigue life of the carbon-black filled natural rubbers were investigated. Different kinds of carbon blacks resulted in different fatigue lives, hysteresis, and critical J-values. It was noticed that the hysteresis was inversely proportional to the difference between DBPA and CTAB, and the critical J-value was almost the same regardless of the length of a precrack. In addition, different kinds of carbon blacks resulted in different fracture morphologies, and micro-scale and macro-scale roughnesses. The critical J-value was proportional to the micro-scale roughness. and it seemed relate to the size distribution of carbon black particles. By reviewing all the experimental data. it was finally noticed that the logarithmic value of the fatigue life could be linearly expressed by a multiplication of the critical J-value and the logarithmic value of the hysteresis.

• 공업화학
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• 제1권2호
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• pp.124-132
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• 1990

최근 개발된 사관능성 에폭시 수지인 EPON HPT 1071과 diaminodiphenyl sulfone (DDS) 경화제를 이용하여, 이 HPT 1071/DDS계의 기계적 성질을 개선할 목적으로 열가소성 고분자인 Poly(aryl etherimide) (PEI)를 도입하여 그 영향을 고찰하였다. HPT 1071/DDS계의 경우, 에폭시/DDS계의 농도를 각각 0.54, 0.71, 1.0으로 달리한 조성들의 강인성과 굴곡강도는 큰 변화가 없었다. HPT 1071/DDS/PEI 계에서는 PEI 농도가 증가할수록 에폭시 경화물의 강인성 및 굴곡강도는 증가하였으며, 수지와 PEI의 상용성으로 인하여 심한 상분리가 관찰되지 않았다. 경화된 에폭시 수지의 기계적 물성과 형태학에 대한 상관관계도 함께 고찰하였다.