• 대한기계학회논문집A
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• 제24권6호
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• pp.1456-1469
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• 2000

Mechanical behaviors of uniaxially fiber-reinforced metal matrix composites under transverse loading conditions were studied at room and elevated temperatures. A mono-filament composite was selecte d as a representative analysis model with perfectly bonded fiber/matrix interface assumption. The elastic-plastic and visco-plastic models were investigated by both theoretical and numerical methods. The product of triaxiality factor and effective strain as well as stress components and strain energy was obtained as a function of location to estimate the failure sites in fiber-reinforced metal matrix composite. Results showed that fiber/ matrix interfacial debond plays a key role for local failure at the room temperature, while void creation and growth in addition to the interfacial debond are major concerns at the elevated temperature. It was also shown that there would be an optimal diameter of fiber for the strong fiber-reinforced metal matrix composite.

• Structural Engineering and Mechanics
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• 제76권5호
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• pp.599-611
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• 2020

A state-space method is developed to investigate the time-dependent behaviors of an angle-ply cylindrical shell in cylindrical bending with surface-bonded piezoelectric layers. Both the interfacial diffusion and sliding are considered to describe the properties of the imperfect interfaces. Particularly, a matrix reduction technique is adopted to establish the transfer relations between the elastic and piezoelectric layers of the laminated shell. Very different from our previous paper, in which an approximate numerical technique, i.e. power series expansion method, is used to deal with the time-dependent problems, the exact solutions are derived in the present analysis based on the piezoelasticity equations without any assumptions. Numerical results are finally obtained and the effects of imperfect interfaces on the electro-mechanical responses of the laminated shell are discussed.

• Composites Research
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• 제17권1호
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• pp.10-17
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• 2004

본 연구에서는 이관능성 에폭시(DGEBA)와 polymethylmethacrylate(PMMA)를 블랜딩하여 열적 특성과 기계적 계면특성을 측정하였다. 열적 특성은 DSC, DMA, 그리고 TGA를 이용하였으며, 블랜드의 기계적 계면특성을 측정하기 위해 contact angle로 표면자유에너지를 조사하였고, 파괴인성은 $K_{IC}$로 측정하고 $K_{IC}$ 실험 후 파괴단면을 SEM을 이용하여 관찰하였다. 실험 결과, 경화 온도와 유리전이 온도는 PMMA의 첨가에 의해 증가하는 것을 확인할 수 있었다. 또한 블랜드의 표면자유에너지는 PMMA의 저함량에서 높은 값을 나타내었고, 이는 비극성 요소의 증가와 극성 요소의 존재에 의한 것으로 판단된다. 블랜드의 파괴인성 측정 결과 5 phr에서 최대값을 나타내었다. 이는 DGEBA/PMMA 간의 상용성 또는 거대분자 사슬에서 물리적 결합의 증가에 기인하는 것으로 판단된다.

• 폴리머
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• 제26권6호
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• pp.767-777
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• 2002

본 실험에서는 4관능성 에폭시 수지 (4EP)와 생분해성 modified aliphatic polyester (MAP) 블렌드의 경화 거동, 열안전성, 유변학적 특성, 그리고 기계적 특성을 살펴보았다. DSC 측정 결과, 경화 활성화 에너지 ( $E_{a}$ )는 4EP에 대한 MAP의 비율이 10 wt%로 증가함에 따라 증가하였다. 이는 4EP와 MAP 사이의 분자상호작용이 증가하였기 때문으로 사료된다. 열안정성과 관련있는 분해 활성화 에너지 ( $E_{t}$ )는 Coats-Redfern 방법을 이용하여 구하였으며 MAP의 함량비가 10에서 30 wt% 내에서 증가하였다. 이는 블렌드 시스템에서의 가교 밀도의 증가 때문으로 사료된다. 유변학적 특성은 레오미터를 이용하여 등온 조건하에서 검토하였고, 겔화 시간과 경화 온도를 이용한 Arrhenius 방정식을 적용하여 가교 활성화 에너지 ( $E_{c}$ )를 검토한 결과, $E_{a}$ 와 유사한 경향을 나타내었다. 기계적 계면특성인 파괴인성 ( $K_{IC}$ )은 시편의 semi-IPN구조 거동으로 고찰하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.663-667
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• 2005

Surface modified carbon nanotubes were applied into the epoxy composites to investigate its tribological property. Carbon nanotubes reinforced epoxy composites were fabricated by casting. Effects to the tribological property of loading concentrations and types of surface modification of carbon nanotubes were investigated under sliding condition using linear reciprocal sliding wear tester. The results show that the small amount of carbon nanotubes into the epoxy exhibited lower weight loss than the pure epoxy. It is concluded that the effect of an enormous aspect ratio of carbon nanotubes surface area which wider than conventional fillers that react as interface for stress transfer. As increased the contents of carbon nanotubes, the weight loss from the wear test was reduced. And the surface modified carbon nanotubes show better tribological property than as produced carbon nanotubes. It is due that a surface modification of carbon nanotubes increases the interfacial bonding between carbon nanotubes and epoxy matrix through chemical bonding. Changes in worn surface morphology are also observed by optical microscope and SEM for investigating wear behaviors. Carbon nanotubes in the epoxy matrix near the surface are exposed, because it becomes the lubricating working film on the worn surface. It reduces the friction and results in the lower surface roughness morphology in the epoxy matrix as increasing the contents of the carbon nanotubes.

• 한국결정성장학회지
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• 제26권2호
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• pp.67-73
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• 2016

The degradation behaviors of TiN coating layers under thermo-mechanical stress were investigated in terms of comparison of finite element analysis (FEA) and experimental data. The coating specimen was designed to quarter cylinder model, and the pulsed laser ablation was assumed as heat flux condition. The FEA results showed that heat accumulation at the center of the laser-ablated spot occurred and principle stress was concentrated at the lower region of the coating layer. The microstructural observation revealed that surface melting and decrease of the coating thickness occurred in the TiN/Inconel 617 and the interfacial cracks formed in the TiN/Si. The delamination was caused by the mechanical stress from the center to the outside of the ablated spot as the FEA results expected. It was considered that the improvement of the thermal shock resistance was attributed to higher thermal conductivity of Si wafer than that of Inconel 617.

• 대한기계학회논문집
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• 제11권2호
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• pp.304-313
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• 1987

본 논문에서는 하부가열식 실험용 태양연못을 제작하여 열유속과 초기의 소금 농도구배를 변화시켜 가면서 실험을 수행하였다.실험을 통하여 측정한 각 층안의 온도와 소금농도구배 및 하부혼합층의 성장율 등을 바탕으로 지배방정식과 가정을 세 운뒤 이들 방정식을 풀어 실험테이터와 비교하였다.

• Geomechanics and Engineering
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• 제32권4호
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• pp.361-373
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• 2023

This study aimed to investigate the engineering properties and mechanical behaviors of polymer-fibers treated sand. Para rubber (PR), natural fiber (NF), and geosynthetic fiber (GF) were used to reinforce poorly graded sand. A series of unconfined compressive and splitting tensile strength tests were performed to analyze the engineering behaviors and strength enhancement mechanism. The experiment results indicated that the PR-fibers mixture could firmly enhance the strength properties of sand. The stress-strain characteristics and failure patterns have been changed due to the increase of PR and fibers content. The presence of PR and fibers strengthened the sand and enhanced the stiffness and ductility behavior of the mixture. The stiffness of reinforced sand reaches an optimum state when both NF and GF are 0.5%, while the optimum PR contents are 20% and 22.5% for the mixture with NF and GF, respectively. An addition of PR and fiber into sand contributed to increasing interlocking zone and bonding of PR-sand interfacial.

• 접착 및 계면
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• 제5권1호
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• pp.3-11
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• 2004

본 연구에서는 DSC와 DMA를 이용하여 잠재성 양이온 개시제인 BPH에 의해 개시된 DGEBA/PMR-15 블렌드계의 경화거동에 대해 연구하였다. 본 블렌드계의 열안정성과 기계적 계면 특성은 TGA 분석과 임계 응력 세기 인자($K_{IC}$) 측정을 통하여 고찰하였다. 본 실험 결과, DSC 측정을 통하여 Ozawa 방정식으로부터 구한 경화 활성화 에너지($E_a$)와 DMA 측정을 통하여 구한 relaxation 활성화 에너지($E_r$)는 PMR-15의 함량이 증가함에 따라 증가하는 것을 알 수 있었다. 적분 열분해 온도(IPDT)와 유리전이온도($T_g$)로 알아본 열안정성은 PMR-15의 우수한 내열성으로 인해 PMR-15의 함량이 증가함에 따라 크게 증가하였다. 기계적 계면 특성인 $K_{IC}$ 또한 경화 활성화 에너지와 같은 경향을 나타내는 것을 알 수 있었는데, 이는 블렌드계의 분자들간의 수소 결합 또는 계면 결합력이 증가되었기 때문인 것으로 사료된다.

• 대한금속재료학회지
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• 제50권12호
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• pp.939-948
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• 2012

A 3-ply clad metal consisting of aluminum and copper was fabricated by roll bonding process and the microstructures and mechanical properties of the roll-bonded and post-roll-bonding heat treated Cu/Al/Cu clad metal were investigated. A brittle interfacial reaction layer formed at the Cu/Al interfaces at and above $400^{\circ}C$. The thickness of the reaction layer increased from $12{\mu}m$ at $400^{\circ}C$ to $28{\mu}m$ at $500^{\circ}C$. The stress-strain curves demonstrated that the strength decreased and the ductility increased with heat treatment up to $400^{\circ}C$. The clad metal heat treated at $300^{\circ}C$ with no indication of a reaction layer exhibited an excellent combination of the strength and ductility and no delamination of layers up to final fracture in the tensile testing. Above $400^{\circ}C$, the ductility decreased rasxpidly with little change of strength, reflecting the brittle nature of the intermetallic interlayers. In Cu/Al/Cu clad heat treated above $400^{\circ}C$, periodic parallel cracks perpendicular to the stress axis were observed at the interfacial reaction layer. In-situ optical microscopic observation revealed that cracks were formed in the Cu layer due to the strain concentration in the vicinity of horizontal cracks in the intermetallic layer, promoting the premature fracture of Cu layer. Vertical cracks parallel to the stress axis were also formed at 15% strain at $500^{\circ}C$, leading to the delamination of the Cu and Al layers.